genesis of gemstone bearing pegmatites of great mica belt, jharkhand

1

GENESIS OF GEMSTONE BEARING

PEGMATITES OF GREAT MICA BELT,

JHARKHAND

THESIS

SUBMITTED TO THE UNIVERSITY OF JAMMU

FOR THE AWARD OF THE DEGREE OF

DOCTOR OF PHILOSOPHY

IN

GEOLOGY

(FACULTY OF SCIENCE)

BY

SURJEET SINGH

POST GRADUATE DEPARTMENT OF GEOLOGY

UNIVERSITY OF JAMMU

JAMMU-180 006

2014

2

CERTIFICATE

This is to certify that:

1) This thesis entitled “Genesis of Gemstone bearing Pegmatites of Great

Mica Belt, Jharkhand” embodies the work of Mr. Surjeet Singh.

2) The candidate worked under my supervision for the period required under the

statutes of the University of Jammu, Jammu.

3) It is further certified that Mr Surjeet Singh has put in the required attendance

in the Department during the period.

4) The conduct of the candidate remained satisfactory during the period of his

research work.

5) The candidate has fulfilled the statutory conditions as laid down in Statutes

(Section 18).

Sd/=

Prof. Pankaj K. Srivastava

Supervisor

Countersigned

Sd/=

Prof. R.K. Ganjoo

Head of the Department

Post Graduate Department of Geology

University of Jammu

Jammu-180006

3

This dissertation is dedicated to the

loving memory of my dear father

Sh. Mir Chand Shan.

He was a man of impeccable ethos. He was very proud of my development as a person and my scientific and professional progress. Unfortunately, he is not here with us to see the whole thing finished. However, his unexpected and tragic death opened my eyes to life and helped me re-estimate and re-value my own life. I am sure he is somewhere out there always watching us closely.……………

LOVE YOU PAPA

4

ACKNOWLEDGEMENTS

This PhD thesis is the culmination of a few years of fervent learning and research experience.

Throughout these years, I have received a lot of support from many people who have contributed

to its completion in many ways: spiritual, psychological, scientific, financial and technical for

making it an unforgettable experience for me. At the end of my thesis, it is a pleasant task to

express my thanks here.

With great pride, I have the privilege to acknowledge deep sense of gratitude, indebtness and

heartfelt thanks for my revered guide Prof. Pankaj K. Srivastava, Post Graduate Department of

Geology, University of Jammu, who has spared no pains in imparting his scholarly and inspiring

guidance, enlightening discussion, valuable suggestions and perfect guidance in completing this

work.

I am highly thankful to Prof. R K Ganjoo, Head of the Department of Geology, University of

Jammu for providing the necessary facilities required during the completion of this work. Thanks

are due to all the teaching staff, Prof. C S Sudan, Prof. M A Malik, Prof. G M Bhat, Prof. A S

Jasrotia, Prof. S K Pandita, Dr. Varun Parmar, Dr. S N Kundal, Dr. Yudhbir Singh, and Dr.

Rajwant, of the Department for their cooperation and time to time suggestions as and when

needed.

Most of the results described in this thesis would not have been obtained without a close

collaboration with few laboratories. I am greatly indebted to Sh. K T Ramchandran (Executive

Secretary), Dr. M D Sastry (Head of Research and Development), Mrs. Silvia Scqueire (Senior

Gemmologist), Mr. Mahesh Gaoankar, Mrs. Seema Athavale, Mr. Sandesh Mane (Research

Felllows) of Gemmological Institute of India, Mumbai for providing analytical facilities. I am

also thankful to Prof. Rajnikant, Department of Physics, University of Jammu for XRD facility.

I owe a great deal of appreciation and gratitude to Dr. Rajesh Sharma, Dr. P. P. Khanna, and Dr.

N. K. Saina, and at Wadia Institute of Himalayan Geology, Dehradun for Raman Probe and

geochemistry of the rock .

I record to my admiration for the help extended by my seniors and colleagues, particularly

Dr. Sukh Chain Sharma, Dr. Ravinder Singh Manhas, Miss Rajni Magotra, Mr. Vipen Katoch,

Mr. Stanzin Namga, and Mrs. Neha Arora, Research Scholar’s of the Economic Geology Research

Group (EGRG), Department of Geology for their valuable help and providing a stimulating and

fun filled environment during my submission days.

Help received from the non teaching staff of this Department is also acknowledged. In particular,

I am highly thankful to Dr. A K Sahni, Smt. Radha Bharti, Dr. B A Lone, Sh. Sudesh Sharma.

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Sh, Sham Sunder, Sh. Janak Raj, Sh. Ashok Sharma, Sh. Harvinder, Sh. Mukash, Sh. Madan Lal,

Sh. Yogesh, Sh. Joginder, and Sh. Latief for their help and cooperation.

I am indebted to many Research Scholars and colleagues of the department for their support and

encouragement, My thanks go in particular to Dr. Naveen , Dr. Ajay K., Mr. Mateen, Mr.

Rahul, Mr. Deepak , Mr. Shiv, Miss. Meera, Mrs. Monika, Miss. Shewata, Miss. Neha, Mr.

Sandeep, Mr. Gyan, Mr, T. Jigmet, Mr. Arjun, Mr. Waquar, Mr. Rigzin, Mr. Gulzar.

It’s my fortune to gratefully acknowledge the support of a special individual, Dr. G. A. Mukhtar

(Chief Geologist, JKSPDC). Words fail me to express my appreciation to my colleagues Mr. Vishal

Atray and Mr. Rajnesh Kundal for their constant moral support. My appreciation also goes to the

whole staff of the Geological Wing, JKSPDC.

Words are short to express my deep sense of gratitude towards my following friends, Mr.

Parshotam, Mr, Rajdeep, Mr. Sanjeev, Mr. Vijay, Mr. Varun Vara, Mr. Davinder, Mr. Brahm

Singh.

I am also very much grateful to all my family members and relatives for their constant inspiration

and encouragement. I sincerely acknowledge the constant support and love I received from my

sisters and their spouses & kids all throughout my life. I am thankful to the family of my Parent-

in- laws, who have been continuous support to me in the form of prayers and best wishes. Besides

this, several people have knowingly and unknowingly helped me in the successful completion of

this thesis.

Last but not least, I would like to pay high regards to my mother Smt. Shankri Devi for her

sincere encouragement and inspiration throughout my life. My special acknowledgement goes to

my wife Mrs. Ishya Shan. Her support, encouragement, quiet patience and unwavering love were

undeniably the bedrock upon which the past 3 years of my life have been built. Being the part of

EGRG, she was with me as a researcher, besides executing the management of our household

activities. My last affectionate words goes for “YESHU”, my baby boy, who has been the light of

my life for the last nine months and who has given me the extra strength and motivation to get

things done. I owe everything to them.

For any errors or inadequacies that may remain in this work, of thesis, the responsibility is entirely

my own.

At the end, I thank the Almighty for giving me moral strength and courage to carry out my work.

Surjeet Singh Shan

Jammu. 25/09/2014

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CONTENTS PAGE

CHAPTER-1 : INTRODUCTION

17-32

1.1 Historical Background 17

1.2 The Great Mica Belt 18

1.2.1 Mining History of Great Mica Belt 21

1.2.2 Gemstone Potential of Great Mica Belt 22

1.3 Previous Work 24

1.4 Study Area 26

1.4.1 Accessibility 26

1.4.2 Climate 27

1.4.3 Physiography 27

1.4.4 Drainage 27

1.5 Objectives 29

1.6 Methodology 29

1.6.1 Field Studies 29

1.6.2 Laboratory Investigations 30

1.7 Organization of the Thesis 31

CHAPTER-2 : GREAT MICA BELT-GEOLOGICAL

PERSPECTIVE

34-48

2.1 Regional Framework 34

2.2 Geological formations of GMB 37

2.2.1 Metasediments 39

2.2.2 Granitic Rocks 41

2.2.3 Pegmatites 42

2.3 Structural Evolution 43

2.4 Geology of Lokai-Indarwa 44

2.4.1 Conglomerate 45

2.4.2 Metasediments 45

2.4.3 Pegmatites 45

CHAPTER-3 : GEM CHARACTERIZATION

50-73

3.1 Introduction 50

3.2 Gemmological Instruments 51

3.3 Gemmological Properties of Gemstone from Area 55

3.3.1 Moonstone 55

3.3.2 Apatite 59

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3.4 X-ray analysis of Moonstone 64

3.4.1 X-ray Diffraction studies 65

3.4.2 Energy Dispersion X-ray Fluorescence 66

3.5 Raman Spectroscopic of the Moonstone of Lokai-

Indarwa Area 68

CHAPTER-4 : PETROGRAPHY

75-92

4.1 Introduction 75

4.2 Petrographic Study of Different Rocks 76

4.2.1 Amphibolites 76

4.2.2 Mica-Schist 80

4.2.3 Pegmatites 84

CHAPTER-5 : GEOCHEMISTRY

94-125

5.1 Introduction 94

5.2 Sampling and Analytical Method 95

5.3 Major Oxides 96

5.3.1 Pegmatites 96

5.3.1 Amphibolite 98

5.4 Trace elements 108

5.4.1 Pegmatites 110


5.5 Rare earth geochemistry 119

5.5.1 Pegmatites 122


CHAPTER-6 : FLUID INCLUSION AND

MICROTHERMETRY

127-154

6.1 Sample Preparation and Instrumentation 128

6.2 Fluid Inclusion Petrography 128

6.2.2 Classification and Petrographic Characteristics of

Fluid Inclusions 129

6.3 Microthermometry 134

6.3.1 Freezing Study 134

6.3.2 Heating Studies 145

6.4 Raman Spectroscopy 151

6.4.1 Sample Preparation and Instruments used 151

6.4.2 Micro-Raman Spectroscopy of Fluid Inclusion 152

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CHAPTER-7 : DISCUSSION

156-184

7.1 Modals for the genesis of Pegmatite 157

7.1.1 The early models 159

7.1.2 The recent models 159

7.2 Classification of Pegmatites 162

7.3 Moonstone in the Pegmatite of Lokai-Indarwa 165

7.4 Physico-chemical conditions of Moonstone formation 168

7.4.1 Fluid composition 168

7.4.2 Salinity and density 170

7.4.3 Trapping conditions 171

7.5 Genesis of Pegmatite 176

REFERENCES

186-211

APPENDIX

213-215

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LIST OF TABLES

Table Description

2.1 Classification of Chotanagpur Granitic Complex.

2.2 Geological succession of Great Mica Belt (after

Ramachandran et al, 1998).

3.1 Traditional and advanced nondestructive instruments and

methods used for gem identification.

3.2 (a-e) Gemmological properties of gemstone.

3.3 Unit Cell parameters of moonstone and apatite.

3.4 Composition of moonstone by EDXRF.

3.5 Raman spectral peaks data of the analysed moonstone samples

4.1 Modal analysis of the Lokai-Indarwa pegmatites.

5.1 Major oxides analysis of pegmatites.

5.2 Major oxides analysis of amphibolite.

5.3 Trace elements analysis of pegmatites.

5.4 Trace elements analysis of amphibolites.

5.5 Rare earth analysis of pegmatites and amphibolites.

5.6 Chondrite normalized data for REEs in Pegmatites and

amphibolites.

6.1 Classification of the fluid inclusion from the area and their

characteristics.

6.2 Freezing studies of the Type-I inclusions.

6.3 Freezing studies of the Type-II inclusions.

6.4 Freezing studies of the Type-III inclusions.

6.5 Freezing studies of the Type-IV inclusions.

6.6 Freezing studies of the Type-V inclusions.

6.7 Heating studies of the Type-I inclusions.

6.8 Heating studies of the Type-II inclusions.

6.9 Heating studies of the Type-III inclusions.

6.10 Heating studies of the Type-IV inclusions.

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7.1 The pegmatite classification scheme of Cerny (1991).

7.2 The pegmatite classification scheme of Cerny and Erict

(2005).

7.3 Total thermometric data of the fluid inclusion studied

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LIST OF FIGURES

Fig.1.1 Map showing gemstone distribution in India.

Fig.1.2 Artisanal mining for the exploration of gemstones in the study area.

Fig.1.3 The location map of the area.

Fig.2.1 Geological map of the Chotanagpur Gneiss Complex (CGC) and

Singhbhum craton (SC) (after Achary, 2003) NSO-North Singhbhum

Orogen. EGMB-Eastern Ghats Mobile Belt.

Fig. 2.2 The geological map of parts of Great Mica Belt (after Ramchandran

et al., (1994).

Fig.2.3 Study area covered with alluvium and forest.

Fig.2.4 Outcrop exposed due to artisan mining in the area.

Fig.2.5 Development of migmatic veins within metasediments.

Fig.2.6 Sketch of Pegmatite veins.

Fig.3.1 Moonstone exhibting blue sheen of colour.

Fig.3.2 Zoning within Moonstone.

Fig. 3.3 Sample under gemmological microscope.

Fig.3.4 Inclusions observed within Moonstone.

Fig.3.5 Lamellas seen in transparent Moonstone crystal.

Fig.3.6 Tarten twinning within Moonstone.

Fig.3.7 Numerous Moonstones, in which blue colour is seen in particular

directions.

Fig.3.8 Crystals of Apatite.

Fig.3.9 Apatite seen under microscope.

Fig.3.10 Raman Spectral peaks of the analysed moonstone.

Fig.4.1. Granofelsic metamarphic rock showing weak gnessic texture.

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Fig.4.2 Amphibolite field according to SCMR definition.

Fig.4.3 Hornblende showing light green cores and darker green margin.

Fig.4.4 Biotite and Hornblende in same direction.

Fig.4.5 Augite crystal associated with mica schist.

Fig.4. 6 Mica flakes alligned along the foliation.

Fig.4.7 Quartzo-feldspathic layers within mica schist showing folded pattern.

Fig.4.8 Intersertial texture in biotite

Fig.4.9 Biotite lath penetrating the crystallized granular quartz.

Fig.4.10 Sillamanite with biotite.

Fig.4.11 Percentage of minerals present in the pegmatites.

Fig4.12 Poikilitic texture in plagioclase.

Fig.4.13 Myrkmitic texture within quartz and plagioclase.

Fig.4.14 Parthitic texture with in plagioclase and microcline.

Fig.4.15 Two generation plagioclase.

Fig.4.16 Alteration within plagioclase showing formation of sericite.

Fig.4.17 Undulatory contact between plagioclase and biotite.

Fig.4.18 Two generation of quartz.

Fig.4.19 Granophyric texture between quartz and alkali feldspar.

Fig.4.20 Microcline showing Cross hatched twinning .

Fig.4.21 Orthoclase showing Carlsbad twinning.

Fig.4.22. Sanidine showing Carlsberg twinning.

Fig.4.23. Alteration of muscovite into chlorite.

Fig.4.24. Zircon mineral making halos within biotite.

Fig.4.25. Zonning within tourmaline.

Fig.4.26. Idioblastic crystal of sphene.

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Fig.4.27 Epidote associated with biotite.

Fig.4.28 Crystal of allanite (epidote).

Fig.5.1 Harkar variation diagram of oxides with SiO2 for pegmatites.

Fig.5.2 Total alkalis vs Silica (TAS) diagram for pegmatites.

Fig.5.3 Silica-alkalis (SiO2 vs K2O+Na2O) diagram for pegmatites.

Fig.5.4 Harkar variation diagram of oxides with SiO2 for amphibolites.

Fig.5.5 Classification of the host rock from the area.

Fig.5.6 Alumina saturation (Shand index) diagram for studied amphibolites.

Fig.5.7 The discrimination of theolitic from calc-alkaline series shown in

AFM (Na2O+K2O-FeO-MgO) diagram.

Fig.5.8 Plot for TiO2 vs Fe2O3.

Fig.5.9 The Harker variation diagram for trace elements of Pegmatites.

Fig.5.10 Primitive mantle normalized plot of trace elements in Pegmatites.

Fig.5.11 The Harker variation diagram for trace elements of amphibolites.

Fig.5.12 Primitive mantle normalized plot of trace elements in amphibolites.

Fig.5.13. The chondrite normalized REE data profile for the pegmatite.

Fig.5.14. The chondrite normalized REE data profile for the amphibolites.

Fig.6.1 Multiphase aqueous inclusions.

Fig.6.2 Multiphase aqueous-carbonic inclusions.

Fig.6.3 Biphase aqueous inclusions.

Fig. 6.4 Biphase aqueous-carbonic inclusions.

Fig. 6.5 Monophase nitrogen inclusions.

Fig.6.6 Trail of monophase carbonic inclusions.

Fig.6.7 Histogram showing temperature of first melting of ice of Type I

Fig.6.8 Histogram showing temperature of first melting of Type I

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Fig. 6.9 Histogram showing temperature of first melting of CO2 of Type I

Fig.6.10 Histogram showing temperature of first melting of clathrate of Type

II.

Fig.6.11 Histogram showing temperature of homogenization of CO2 of Type

II.

Fig.6.12. Histogram showing temperature of final melting of ice of Type III.

Fig.6.13 Histogram showing temperature of first melting of ice of type III.

Fig.6.14. Histogram showing temperature of first melting of clathrate of Type

IV.

Fig.6.15 Histogram showing temperature of first melting of CO2 of Type IV.

Fig.6.16 Histogram showing temperature of homogenization of CO2 of Type

IV.

Fig.6.17 Histogram showing temperature of melting of CO2 of Type V.

Fig.6.18. Histogram showing temperature of dissolution of halite of Type I.

Fig.6.19. Histogram showing temperature of homogenization of Type I.

Fig.6.20. Histogram showing temperature of dissolution of halite of Type II.

Fig.6.21 Histogram showing temperature of homogenization of Type II.

Fig.6.22. Histogram showing temperature of homogenization of Type III.

Fig.6.23. Histogram showing temperature of homogenization of Type IV.

Fig.6.24. Raman spectral peaks of Type IIIb.

Fig.6.25 Raman spectral peaks of Type N2.

Fig.6.26. Raman spectral peaks of Type H2O.

Fig.7.1 Temperature of homogenization vs salinity plot

Fig.7.2. Isochores corresponding to densities of H2O, CO2 fluid

Fig.7.3. Continental crust normalized pattern for pegmatites.

Fig.7.4. Plot for Rb-Sr.

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Fig.7.5. Plot for Sr-Ba.

Fig.7.6. Distribution of Pegmatites data on Cr-Y diagram.

Fig.7.7 Tectonic discrimination diagram (Rb-Y+Nb) for Lokai Indarwa

pegmatites.

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CHAPTER-1

INTRODUCTION

17

INTRODUCTION

1.1 HISTORICAL BACKGROUND

References to gemstones appear in many ancient writings. Crystals, stones and

talismans have provided an irresistible attraction to all human beings from the time

immemorial. They were considered as a means of barter, a symbol of wealth, the

source of power and magic or the objects of adoration. Using gemstones as attractive

jewellery by men and women can be traced back to prehistoric times (Rao, 1986).

Several archaeological excavations in India have yielded ornamental beads made out

of terra-cotta and silica (Mackay, 1937; Rao, 1973). Besides being beautiful, gems are

an important part of our cultural heritage on this planet. A review of the ancient

Sanskrit texts indicates that Arthashastra by Kautilya (4th

century BC) was one of the

earliest treatises on gemstones. Several other ancient Indian texts like Varahamihira’s

Bhrihat Samhita, 5th

century AD. Garuda Mahapuranam 10th

century AD. Skanda

Puranam, 13th

-14th

century AD have described a number of varieties of gemstones

(Murthy, 1990, 1993). Probably in ancient days gemstones were used to cater to one’s

aesthetic taste. Later, however, gemstones appear to have been used as talisman to

bring in better luck and to remove the bad effects of planets positioned in the

horoscope. One of the oldest known Talisman Jewel is the Navratna, in Hindu

astrology. Possibly the sight of celestial objects as seen from the earth prompted the

ancient Indians to assign certain stones to certain planets. Gemstone is also often

mentioned in the Sutra of Buddhism.

There are over 4000 known mineral species. However, very few of these are

gemstones. A gemstone can be defined as a mineral, or in the case of coral or pearl, an

organic substance, which looks attractive when fashioned into an ornamental object

such as a bead, carving, box, cabochon or faceted stone. A gemstone’s value is based

on its beauty, rarity, durability and history behind that particular stone. Well known

gemstones such as diamond, emerald, ruby and sapphire have all four of these

qualities, which make them more valuable than others, for example, quartz, which is

beautiful, attractive and durable, but not rare. The most important physical properties

18

of gemstones are habit, weak planes, hardness, colour, clarity, diaphaneity, size and

lusture.

The physicochemical controls on gem formation were first time described by

the philosopher Theophrastus in his “De Mineralibus”. But some of the best and most

useful work on the genesis of gemstone deposits is based on the careful, detailed and

precise descriptions of the geology, mineralogy and geochemical nature of the

deposit. But very little work is available regarding the fluid inclusion and stable

isotopic work in order to understand the genesis of such deposits. Some of the best

gem deposits on our planet, such as the ruby deposits of Myanmar or the sapphire

deposits of Jammu and Kashmir, India are not even worked out specifically to

understand their genesis. Therefore, one has to rely on descriptive geology done many

years ago until modern scientific arsenal to decode how and why these fabulous gems

were formed, are unleash.

India is a homeland of many fabulous diamond and coloured gemstones (Fig

1.1). Despite the country being inhabited by various civilizations for over 500 years,

many parts of India are potentially rich in gemstones. There are still many tribal areas

which are inaccessible and unexplored. At many of such places artisanal mining is

going on (Fig 1.2). The gemstone mineralization associated with the mica belt of

Jharkhand is one such region where a number of coloured precious and semi-precious

stones have been reported. But no detailed work regarding their characterization and

genesis is available in the literature. In the present research work an endeavour is

done to characterize the available gemstones and also to understand the genesis of the

gemstones bearing pegmatites of the area in the Koderma district.

1.2 THE GREAT MICA BELT

India is one of the largest producers of block mica in the world, producing

between 70% and 80% of the total block mica global output. In India, mica is found

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Fig. 1.1. Map showing gemstone distribution in India

20

Fig. 1.2. Artisanal mining for gemstones in the study area.

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mainly from the three major mica belts namely Great Mica Belt (GMB) of Jharkhand

and Bihar, Bhilwara Mica Belt of Rajasthan and Nellore Mica Belt of Andhra

Pradesh. About 60% of country,s total yield for mica is produced in Jharkhand. Till

date, commercial scale of mica production in India has defied almost all attempts at

mechanization, and most of the ‘splitting’ of mica is done by hand, with India leading

the world in the mica ‘splitting’ trade (Singh et al., 2001).

The Great Mica Belt, previously known as Bihar Mica Belt, extends to a

distance of 160 km having an average width of 25 kms. It extends from Gurpa in

Gaya district in the west through Nawada, Koderma, Hazaribag, Giridih in Jharkhand

and Jamui as well as Bhagalpur district of the Bihar state in the east. Its maximum

width is about 40 km at Koderma-Hazaribagh-Nawada area. The whole belt

encompasses roughly around 4,000 sq. km. area. It runs in an east-northeast to west-

southwest direction. The major part of the Great Mica Belt is located in Jharkhand

state. The Koderma area is the biggest mica track in the country and occupies an area

of about 145.74 square kilometers. Jharkhand’s other sizable mica deposits are found

around the towns of Dharokhola, Manodih, Dhab, Gawan, and Tisri. With the advent

of built-up mica or micanite (laminated insulating material manufactured by manual

or mechanical pasting of mica with glyptal, silicone, gluing varnish and other

materials), Jharkhand confirmed its position as the national and global leader in the

manufacturing and export of mica. The mica from the Great Mica Belt is also famous

for its thermal properties (highly infusible and extremely heat resistant, and even at

red heat temperatures doesn’t undergo any typical or chemical changes) and perfect

dielectric property.

1.2.1 Mining history of Great Mica Belt

During ancient times mica sheets have been extensively used for decorative,

ornamental purposes or as a base plate for painting. Powdered biotite mica had been

used in Ayurveda. With the dawn of the electrical age in 1878, Indian mica has

22

dominated the world market with contributing about 80% towards the world’s

requirement of sheet mica.

The artisanal mica mining was started by local aboriginal tribes known as

Labanas and Mahajins from the Koderma area in Jharkhand about 150 years ago.

They extracted mica by breaking pegmatites containing mica books by heating and

sudden cooling with water. They started extracting mica from narrow cylindrical

shafts, hardly exceeding 10 m. in depth. However systematic mining of mica started

in this mica belt sometime 1880. Prospecting for mica was usually done by “surface

scratching” locally known as upperchella working; the pegmatites which are exposed

on the surface and showing indications of mica are dug up. The local people,

experienced in exploration have carried out the “upperchella working ” for all

companies. In recent years, prospecting has been carried out by trial pits and trenches

followed by open-cast or underground mining. Underground mining is further carried

out by “Pillar and Stall” method for flat pegmatites and “Drifts” method for steeply

dipping pegmatites. Depending on the dip of the vein, either a vertical ‘shaft’ or an

‘incline’ is sunk, and levels are then driven at suitable intervals. The levels are

connected either by rise or winze foe blocking out pillars or stopes and for facilitating

ventilation. The different levels are connected by wooden ladders.

According to the Indian Bureau of Mines, 50 years back there were more than

350 workable active mine in the Bihar state. But now gradually excavation of low

quality of mica ore and high cost of production results in the closure of mica mines

and related industries.

1.2.2 Gemstone potential of Great Mica Belt

Beside the high quality mica production, Great Mica Belt also hosts a wide

variety of gemstones and also some rare metals. Some of the reported semiprecious

gemstones from the area are moonstone, tourmaline, garnet, amazonite, citrine,

garnet, cat’s eye, bytownite and apatite.

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Moonstone is the best known gem variety of the feldspar group. Its importance

as a gemstone arises because of adularescence, a floating light effect and sheen,

compared to the light of the moon. This phenomena generally results from alternating

layers of albite and orthoclase feldspars, which cause light to scatter. In the GMB,

export quality of moonstone is found to be concentrated in Koderma area.

Tourmaline is one on the most complex gemstones of the silicate group and

there are 10 different varieties with a full range of colours due to presence of different

trace elements. Transparent pink-red, blue, green, yellow-brown and uncoloured

varieties are used as gemstones. Black opaque stones are also often cut and worn as

jewellery. Tourmaline is found in pegmatites with cavities and rarely in schists. In

Great Mica Belt three varieties of tourmaline are found in the Koderma area. They are

green tourmaline, black tourmaline and blue tourmaline (Indicolite).

Garnets are nesosilicates. They do not show cleavage so when they fracture

under stress, sharp irregular pieces are formed. Because the chemical composition of

garnet varies, the atomic bonds in some species are stronger than in others. The harder

species are often used for abrasive purposes. The dominant varieties present in the

GMB are hessonite or cinnamon stone and almandine. Hessonite is mainly

concentrated in Chatra district while almandine in the Koderma and Hazaribagh

districts of Jharkhand.

Amazonite (sometimes called "Amazon stone") is a green variety of

microcline feldspar. Because of its bright green colour when polished, amazonite is

sometimes cut and used as a gemstone, although it is easily fractured. It displays a

schiller of light which is caused by inclusions. Schiller is a lustrous reflection from

planes in a mineral grain and is similar to what is more commonly known as

iridescence. The schiller is caused by a feature of the stone's crystal structure.

Orthoclase feldspar and albite are present in close association, arranged in layers. This

causes an interference effect of light. This mineral is also found in the Koderma area

of Jharkhand.

Citrine is transparent, coarse-grained variety of the silica mineral quartz with

ferric iron impurities. Citrine is a semiprecious gem that is valued for its yellow to

24

brownish colour and its resemblance to the rarer topaz. The yellow colour is from the

presence of iron, the darker the colour - the higher the grade. Natural citrine is rare

compared to amethyst or smoky quartz, both of which are often heated to turn their

natural colour into that of citrine. In Indian market citrine is being sold by the name of

golden topaz or quartz topaz. Citrine is also present in some of the pegmatite veins

from the Koderma area.

Chrysoberyl (Cat’s eye) is really something special with its narrow, bright

band of light on a shimmering golden background, which seems to glide magically

across the surface when the stone is moved. From the mineralogical point of view,

chrysoberyls are aluminium oxide containing beryllium, and thus actually have little

in common with the beryl, which belong to the silicate family. Indeed, with their

excellent hardness of 8.5 on the Mohs scale, they are clearly superior to the beryls.

Singhbhum in Jharkhand state is known for the deposits of cat’s eye.

Bytownite is a rare form of feldspar, more commonly seen as a faceted

gemstone than as a collectors mineral. It is usually translucent without a crystal form.

Bytownite belongs to the plagioclase group in which exsolution takes place, it leads to

physical optical effects of iridescence and chatoyancy. This has a bulk composition of

An67 to An90 and shows huttenlocher intergrowth.

Apatite is part of the phosphate mineral group. It is frequently used as

gemstones. Transparent stone of clean colour have been faceted, and chatoyant

specimen have been cabochon. The origin of its name is from Greek apate meaning

deceit alluding to its similarity to other more valuable minerals such as olivine,

peridot and beryl. Apatite is found in the mica pegmatites. It is mostly found in the

shape of needles.

1.3 PREVIOUS WORK

The earliest published work on the geology of the Great Mica Belt (then

known as Bihar Mica Belt) is by Mallet (1874). Later Holland (1902) published a

memoir on the mica deposits of India, where he discussed, very minutely, the mode of

25

occurrences of mica pegmatite veins of the area. In this first exhaustive account of the

geology of mica pegmatitic areas in India, Holland concluded that the mica pegmatite

veins have formed by “hydatopyrogenetic” magma which themselves resulted as

residual portion of granitic magmas. Iyer (1939 & 1944) and other workers first

mapped the mica pegmatite veins from the Bihar and Jharkhand area. Some of the

pegamtites from the Great Mica Belt have been reported to contain many rare metals

and radioactive minerals like pitchblende, triplite, illmenite, zircon, columbite,

tourbernite and graftonite (Tipper, 1919; Burton, 1913; Mukherjee and Parsad, 1958).

Detailed work on the geology of area was given by Iyer (1939-1944), Vemban

(1951), Mahadevan (1957), and Thiagarajan (1960,1961). The petrographic features

of the rocks of the GMB were described by Sharma (1940) and Mahadevan (1957).

Mahadevan and Maithani (1967) have exhaustively worked on the classification of

mica bearing pegmatite veins and their origin. Mahadevan (2002) has compiled all

these work in his text book on Geology of Bihar and Jharkhand.

Deformation features in quartz, feldspars and beryl in pegmatite have been

described by Sen and Saha (1961). Zoned nature of the mica pegmatite veins was

recognised by Roy et al., (1939). A general description of mica pegmatite veins of the

GMB with special reference to the problem of mining is given by Kalia (1961).

Structure of the area has been worked out by Ramachandran et al. (1994).

The other significant contribution on the geology, petrology, geochemistry and

structure of the pegmatite and related granites of the mica belt (GMB) is made by a

number of workers (Dunn,1942; Sen and Saha,1961; Anand and Mahadevan, 1969;

Bhola,1968; Chattopadhyay,1974; Bhattacharaya,1986; Ghosh,1983; and

Sarkar,1988).

A number of theories on the origin of these pegmatite veins have been

suggested by different workers. Vredenberg (1910) postulates that an anhydrous

solvent was produced at great depth with high fluidity due to its fluorine content.

Biswas (1929) considers that the mica pegmatite veins have formed from a residual

magma which assimilated large amounts of schists at depth and precipitated

muscovite after its final emplacement. Magmatic origin for the pegmatite veins were

26

suggested by Dunn (1942), Roy et al. (1939) and Rode (1947). However some other

workers like Fox (1930) suggested that the mica pegmatite veins are products of

recrystallisation of mica-schist under the influence of hot water. Holmes (1949), and

Mahadevan and Aswathanarayane (1955) suggested 955 ± 40 my age by radioactive

age determination of the monazite from the Pichhli Pegmatites of the area.

Role of barium in geochemical exploration of mica pegmatite veins was

studied by Bhattacharyya and Seshadri (1983). The characteristics of the fluid

inclusions present in two of the mica pegmatite were reported by Santosh (1986).

1.4 STUDY AREA

The studied area is a part of Great Mica Belt (GMB), in the Koderma district of

Jharkhand. Out of the hundreds of pegmatite veins present in whole of the GMB, the

Koderma district contains some of the major gem-bearing pegmatites. The pegmatite

veins exposed in the Lokai-Indarwa areas are selected for the present study. Some of

the reasons behind selection of this area for study are;

1. There are plenty of mineralization of moonstone.

2. As the artisanal mining of gemstones is going on at different places so samples

from underground mines can be extracted.

3. There is no existing scientific literature regarding these deposits, so the study

will fullfill this gap in scientific knowledge.

1.4.1 Accessibility

Koderma District town is situated 155 km north of Ranchi on National

Highway (NH 31) and is well connected with railway on eastern railways grand cord

sections at Jhumri Tilaiya. Lokai-Indarwa area is 5 km east of the Koderma on the

Koderma-Domchanch metalled road. The mine can be approached by fair weathered

road which is 0.5 to 1 km from the main Koderma-Domchanch road. The area lies in

the latitudes 24° 28´53˝ and longitude 85° 37´ 43˝ and is covered under toposheet no

27

72 H/11 of Survey of India. The area is present in the dense reserve forest. The

location map of the area is shown in Fig. 1.3).

1.4.2 Climate:

The Koderma district experiences three climatic seasons, hot season (March to

May), rainy season (June to October) and a cold season (November to February). The

average rainfall (10 years) of the district is 1125.1mm.The temperature of the district

varies between mean minimum temperature of 10°C in winter and mean maxmium

temperature of 40°C in summer. Temperature varies between 4°C to 46°C.

1.4.3 Physiography

The study area is a part of Chhotanagpur plateau. It exhibits undulating

topography comprising hills, hillocks, plains and mounds. Altitude of the area varies

between 392 to 592 m above m.s.l with the highest peak of 667m at Debour Ghati.

The area is characterised by plantation surfaces, intense dissection along the

plantation margins, separation by deep valley incision and formation of valley fills.

The level of plantation is at 330m above m.s.l marked by flat hill tops.

1.4.4 Drainage

The area is characterized by radial drainage system. Koderma district lies in

the Barakar sub-basin. The Barakar river flows from west to east in the southern part

of the district. Rivers flowing from west to east are Ponchkhara, Keso, Akto, Gurio

and Gukhana nadi and these are the tributaries of the Barakar River. Sakri River is the

main river in the northern part of the district which flows from south east to north

west.

28

N

SCALE

10 K.M.K.M. 5 0 5

NH 31

KODERMA

Jhumri Tilaiya

DomchanchIndarwa

Lokai

Towar

ds R

anch

i

Tow

a rds P

at n

a

Towards Kolkata

Towards Jam

mu

Study Area

Town/Village

Railway Line

Road

LEGEND

I I

I

85° 30´ 85° 45´

I85° 45´I85° 30´

24°

15´

I24°

30´

I24°15´

I24°

30´

CH

A

T

T

I

S

G

A

R

H

W E S T B E N G A L

O R I S S A

U

TT

AR

P

AR

DE

S

H

BIHAR

J H A R K H A N DI N D I A

Fig. 1.3 Location map of the area

29

1.5 OBJECTIVES

The GMB has a number of zoned and unzoned pegmatite veins which are

famous for the production of ruby mica. Many of these pegmatite veins contain

number of semi precious coloured stones which are largely ignored for their genesis

in the exiting geological literature. In view of these lacunas in the existing knowledge

about GMB, a humble beginning is made by taking one major gemstone bearing

pegmatite veins. The study is carried out with following objectives:

Mineralogical and Gemmological characterization of the gemstone bearing

pegmatites.

Characterization of different types of fluid inclusions present in the

pegmatites.

Fluid evolution responsible for the formation of Gemstones.

Genesis of the gemstone bearing pegmatites.

1.6 METHODOLOGY

In order to achieve the proposed objectives, a detailed field study for

understanding the mode of occurrence, nature and control of mineralization is

required. Further the laboratory data regarding gemstone characterization, fluid

inclusion study along with Raman probe, host rock petrography, and mineralogical

and chemical characteristics of host rock and gem minerals are required. The

methodology to be adopted is divided into two major components:

A. Field Studies

B. Laboratory Studies

1.6.1 FIELD STUDIES

Extensive fieldworks were done in the southern part of Great Mica Belt in and

around Koderma District to identify the gemstone bearing pegmatites. Mineralization

pattern and control of localization for the gemstone mineralization in the area was

established. Systematic sampling of the host rock, pegmatites and gemstones for the

30

laboratory work including mineralogical, petrographical, geochemical and fluid

inclusion studies was done.

1.6.2 LABORATORY INVESTIGATION

1. Gemstone Characterization

The systematically collected gemstones are studied for their mineralogical

properties and gemmological characterization using specially designed modern

gemmological instruments, EDXRF and Raman Spectroscopy at Gemmological

Institute of India (Mumbai). The unit cell dimensions of the gemstone were studied by

Single Crystal X-Ray Diffractometer at Department of Physics, University of Jammu.

2. Petrography

In order to understand the genesis of the pegmatites, petrography is of the

paramount use. Therefore the host rock and pegmatite petrography is studied using

high definition microscope. Replacement, wall rock alteration and other depositional

features are studied in order to understand the environment of deposition.

3. Geochemistry

Major, trace and rare earth elements analysis is carried out on the pegmatite

and host rock in order to understand the genesis of pegmatites. Analytical facilities

(XRF and ICPMS) present at WIHG Dehradun are used for this analysis.

4. Fluid Inclusion Microthermometry

Fluid inclusion studies are one of the very important tools in order to

understand the nature of mineralizing fluid and physicochemical conditions for the

deposition of gemstones. Thin wafers of the pegmatites were utilized to study the

fluid inclusion characteristics. The microthermometric studies are carried out on

selected fluid inclusions. The data generated is further interpreted to know the

temperature of formation, salinity, density and composition of the gemstone bearing

31

fluid. The microthermometric measurement is carried out on the existing LINKAM

heating freezing stage (THMSG 600) mounted on the Nikon microscope. The

composition of the fluid is analysed with the help of Raman Probe at Wadia Institute

of Himalayan Geology (WIHG) Dehradun.

1.7 ORGANIZATION OF THE THESIS

The research work carried out is detailed and organized into 7 Chapters. The

first chapter encompasses the historical prospective of gemstones, background

information about area in particular mining history and gemstones potential and

Great Mica Belt in general. It also includes the previous work, objectives, and

methods of investigations.

The second chapter is divided into two sections. The first section deals with

detailed description of the regional geology of the Great Mica Belt. This section is

followed by local geology of the study area. The regional structures, various

lithological units are discussed in details based upon published literature and field

works carried out in the area.

The gemstone characterization is the title form the chapter three of the thesis.

In this chapter a brief description is given regarding the instruments used for the

identification and characterization of gemstones. The Gemmological properties

(mineralogical and optical) are elaborated in the next section of the chapter, which

also includes the analyzed properties of the gemstones. The last part of the chapter

includes the Raman spectroscopy and EDXRF data.

Fourth chapter includes the detailed petrographic studies of the rocks exposed

in the area. The mineralogical and textural characteristics of the representative

samples of the area are discussed in detailed.

In the Chapter fifth of the thesis the geochemistry of the host rock and

pegmatite of the area is discussed. The representative samples were subjected to

32

geochemical treatment in the laboratories for the major oxides, trace elements and

REE analysis. The geochemical data has been studied in detailed to know the

geochemical characteristics and to understand the origin of the gemstones.

Realizing the importance of fluid inclusions in mineral genetic studies, the

fluid inclusion study of pegmatites from the present area of study have been carried

out. It is discussed in the Chapter sixth of the thesis. This chapter comprises the

petrography of the various fluid inclusion assemblages present in the pegmatites and

their heating and freezing studies. The data of the fluid inclusions has been interpreted

to know the physicochemical conditions responsible for the formation of moonstone

mineralization in the GMB. The identification of the fluids within the inclusion is

done by Raman Spectroscopy.

The final part of the thesis, marked as seventh chapter, deals with the

interpretations and discussions of the available data in terms of the genesis of the

moonstone and pegmatites of GMB.

33

CHAPTER-2

GREAT MICA BELT GEOLOGICAL

PERSPECTIVE

34

GREAT MICA BELT - GEOLOGICAL PERSPECTIVE

2.1 REGIONAL FRAMEWORK

The Singhbhum crustal province and Chotanagpur Gneissic Complex (CGC)

are the two major crustal provinces of the eastern Indian shield (Ghosh et al., 2005).

The Singhbhum Proterozoic basin has a tectonic boundary with the northern high-

grade metamorphic-migmatite belt of the CGC, trending parallel to the basinal axis

(Bose, 1990). Great Mica Belt (GMB) is a major distinctive geological unit in the

Chotanagpur Gneissic Complex (CGC), occurring north of Singhbhum mobile belt.

The CGC is slightly arcuate east-west trending linear belt which has a strike

extension of 500 km and a width of 200 km (approximately). The entire

Chhotanagpur Plateau north of Tamar-Porapahar Khatra Fault is classified as CGC

and major part of it is exposed in south Bihar and Jharkhand. The Chotanagpur Gneiss

Complex is bounded by Tamar-Porapahar Khatra Fault (TPKF) zone towards

southern side and Quaternary Gangetic Alluvium toward north, Bengal Basin in east

and by Mahanadi-Gondwana Basin in west (Fig. 2.1). CGC is characterized by

complex assemblages of diversified rocks of gneiss-grannulite-granite association

with several periods of magmatic, metamorphic, tectonic and sedimentation. The

East-West trending rift zone represented by the Gondwana Sediments divides the

CGC into two parts. The southern part of CGC is characterized by the dominant

gneissic rocks with number of pockets of granulites and high grade supracrustal rocks

while the northern part is mostly having presence of younger meta-sediments and

Rajmahal volcanic rocks.

Reviews of this terrain are found in Banerji (1991), Ghose (1992), Mazumder

(1988, 1996), Singh (1998), Ghose and Mukherjee (2000), Acharyya (2001, 2003)

and Mahadevan (2002).

The CGC is classified into a number of lithostratigraphic units by Ghose (1983) and

Banerjee (1991) as given in table 2.1

35

EGMB

D

MGB

SNSFSNNF

RAJGIR

MUNGER

INDEX

IIIII

II

II

II

I

CPG

RSB

NPSZ

TPSZDV

D

B

G CCHDGB

D

H

B

OM

BMB

HDGB

D

D

SC

SSZ

NSO

IIIIII

II

0 50 Km

Fig. 2.1. Geological map of the Chotanagpur Gneiss Complex (CGC) and Singhbhum craton (SC)

(after Acharya, 2003) . .

TECTONIC DIVISIONS:

TPSZ=Tamar-Poropahar shear zone,GPG=Gumla-Purulia granulite belt,

RSB=Ranchi Supracrustal belt,NPSZ=North Purulia shear zone,

HDGB=Hazaribagh-Dumka granulite belt,G=Garwa, H=Hesatu, B=Belbathan belt

BMB=Bihar Mica belt,MGB-Makrohar granulite belt,

SNSF=Son Narmada South Fault,SNNF=Son Narmada North Fault,

SSZ=Singhbhum Shear zone,D=Daltonganj

NSO=North Singhbhum OrogenEGMB- Eastern Ghats Mobile Belt

36

Table 2.1: Classification of Chottanagpur Granitic Complex.

Late

Intrusive

Rajmahal Basalt, dolerites, hornblende, quartz-apatite rock,

alkali-syenite porphyry emplaced between 100-435 Ma.

Biotite-granodiorite, tonalite, biotite-gneiss, orthamphibolite

etc. emplaced between 635-765 Ma.

Satpura

Orogeny

Metamorphism of pre-existing rocks up to granulite facies and

emplaced of anorthosite, gabbro, granite, granodiorite, tonalite

and pegmatite (ca. 900±200 Ma).

Older

Metasediments

Pelitic schists, gneisses, migmatites, calc-silicates, calcitic and

dolomitic marble (probably equivalent to Singhbhum Group

(2000-2600 Ma)

Crystalline

Basement

Tonalitic gneiss, charnokite, khondalite, granulite, and

leptynite (Probably equivalent to Eastern Ghat Group-first

phase of metamorphism ca. 2600 Ma).

Geological Survey of India in its miscellaneous publication (2009) on geology

and mineral resources of Bihar and Jharkhand has suggested six major distinctive

lithotectonic domain of CGC, out of which BMB (popularly known as GMB) is one

of the major lithotectonic unit of CGC.

A number of shallow metasedimentary basin have been recorded all along the

northen flank of CGC, namely GMB, Gaya-Rajgir Belt and Munger Belt, from west

to east. These basins are running mostly in concordance with the regional trend i.e

satpura trend. Ghose (1992) suggested that these metasedimentary basin do not belong

to same phase of sedimentation.

In GMB there are numerous pegmatite veins which are intruded into the

metasediments as well as within the granitic rocks. Some of these veins contain

gemstones which have already been discussed in the previous chapter. In order to

understand the characteristics of the fluid responsible for forming the gem bearing

37

pegmatites in this belt, it is necessary to understand entire geological background of

GMB.

2.2 GEOLOGICAL FORMATIONS OF GMB

The Great Mica Belt (GMB) covers a larger area, about 160 km long and 25

km wide. Mallet (1874) and Holland (1902) described the geology of the mica belt for

the first time and gave the mode of occurrences of mica-pegmatites. However, the

first detailed map of the belt was generated by Iyer (1939-1944). Mahadevan (1957)

and Ramchandran et al., (1994) have given a detailed structural map of the area.

The GMB has a geological setting distinct from extensive migmatitic granite-

gneiss belts of the Chotanagpur Granitic Gneissic Complex. It is characterized by

large phaccoliths, often domical, plutons emplaced into relatively more open-folded

schistose formations, “supracrustals”, metamorphosed to upper amphibolite to lower

granulite facies conditions. The belt trends roughly ENE-WSW. Geographically this

belt rises with a discrete bold topography, separated from the Hazaribagh plateau in

the south by the low-lying paniplained Barakar river valley and bounded by the vast

Gangetic alluvial plains in the north.

A sequence of arenaceous and pelitic rocks interbanded with horenblende-

schists, amphibolite and subordinate calcareous units characterize the major

geological formations of the belt. Large bodies of granitic rocks are emplaced in this

formation. A few anorthosite lenses, dolerite dykes, gabbro etc constitute the other

minor rock types. The stratigraphic sequence of the formations is presented in Table

2.2 and the geological map of the area by Ramchandran et al., (1994) is given in Fig

2.2. GMB metasedimentary assemblages have been referred as Koderma Group

which includes Phulwari Formation, Dhab Formation and Kakolat Formation (Singh

1998). The reported occurrence of matrix-dominated Indarwa Conglomerate at NW of

Neropahar and north of Jaganathpur college, Koderma at the contact between GMB

metasedimentary and gneisses belonging to CGC signifies a stratigraphic hiatus

38

KODERMA05 Km

AR

CH

EA

N

Fig. 2.2. Geological map of parts of Great Mica Belt (after Ramachandran et al 1994)

5Km

I I II I I I I III

N

I N D I A

39

(Ghosh. 1992). Thus GMB represents a sub-basin showing basement-cover

relationship with CGC.

The main lithounits exposed in the belt dominantly are the muscovite-biotite

schist, which are at places garnetiferous. They are interbedded with prominent bands

of hornblende-schists, micaceous quartzites and relatively minor calc-silicate

granulites and local conglomerates. The quartzites become more prominent in the

east. The primary sedimentary structures like bedding and cross bedding are preserved

in the schistose rocks and quartzites very often. The granitic bodies emplaced into the

schistose formations are the next dominant geological formation which covers around

30-40% of the area. These granites are rimmed by various migmatitic zones. A

number of mica pegmatite veins of different generations have intruded these rocks.

The detailed description of the different lithounits exposed in the belt is given

in the following paragraph.

2.2.1 Metasediments

The metasedimentary rocks constitute about 67% of the area. The

metasediments on the mica belt are dominantly represented by mica-schist and garnet-

sillimanite mica schist with some quartzitic bands. At places calc-silicate, granulites

and amphibolites are also exposed. The mica schist shows a wide range of

mineralogical variations. The gradations of mica schists are noticed from muscovite

biotite schists to types rich in quartz, biotite, sillimanite, and garnet. The most

dominant is sillimanite bearing biotite muscovite schist, which has been described by

Mahadevan and Maithani (1967) as the fibrolite muscovite-biotite schist. The mineral

assemblage associated with the GMB has witnessed metamorphic conditions

equivalent to an upper amphibolite facies.

40

Table 2.2: Geological succession of Great Mica Belt (after Ramachandran et. al, 1998)

AGE ROCK TYPE

Recent Alluvium

Permo-Carboniferous Gondwana sediments

--------------------------------Unconformity---------------------------------------------

Dolerite dykes

Rapakivi granite and pegmatites

Biotite augen series, coarse porphyritic

granite gneisses and pegmatites

Medium grained massive granites and

Pegmatites

Amphibolites and anorthosites

Proterozoic Massive quartzite with phyllitic and slaty

Intercalations

Sillimanite-muscovite schist, calc-silicate

and hornblende schists

Schistose quartzite and quartz-mica-schist

Hornblende schist, garnetiferous biotite-

Schist

Migmatites and composite gneisses

-----------------------------Unconformity-----------------------------------------

Achaean Chotanagpur Granite Gneiss

41

Five mineral assemblage groups have been identified by Bhattacharya (1986)

in the metapelites of the area. These include assemblages with and without sillimanite

± staurolite, sillimanite-bearing assemblages without staurolite, staurolite-bearing

assemblages without sillimanite and staurolite-kyanite assemblages.

Mahadevan and Maithani (1967) and Mahadevan (2002) suggested that the

GMB has witnessed upper amphibolites facies of metamorphism. However even the

metamorphic conditions up to Amphibolite-Granulite facies have also been reported

from some of the areas Bhattacharya (1986).

The main structural trends in the mica belt are controlled by the folding in the

meta-sedimentary rocks of the area. The schist of the mica field present a grooved

appearance on the weathered outcrop due to alternating quartz-rich and mica-rich

bands the former being more resistant to weathering. In the arenaceous members of

the metasedimentaries, conglomeratic beds are present at a few places. The foliation

of the schistose rocks is ranging from ENE-WSW to NE-SW and the dip varies from

30-60° in either directions. The foliation is poorly developed where bedding is well

preserved and also along the nose of folds. The lineations of the schistose rocks are

well-lineated except where bedding is well preserved. The lineation is mainly due to

the elongation of minerals crenulations in micas and “rodding” in quartz. The

schistose rocks of the area are traversed by numerous slip-planes along which there

appears to have been varying degrees of movement. Such slip-planes may be parallel

or sub parallel to the axis of folds and, therefore, to the foliation in the schist are in

some cases at an angle to both foliation and bedding.

2.2.2 Granitic Rocks

The Granitic rocks of the belt were designated as “Dome Gneiss” by Holland

(1902), because of their characteristic physiographic expression. On the basis of

structural features they are classified into two broad types as (a) strongly to mildly

foliated and lineated gneisses generally medium to coarse grained but often grading

into porphyritic types and occurring as phaccolithic sheets along the noses and limbs

of folds and (b) massive equigranular types forming sub-elliptical boss–like bodies

foliated along their margins with the country rocks. The former is the most extensive.

42

The petrographic features of the two types seem more or less alike, except that they

differ in their texture. These granitic rocks show sharp contact with the country rocks.

At places they are bordered by the bands of hornblende-schists. Enclaves of tonolitic

rocks, amphibolite, mica-schists and diopside granulites are commonly present

(Sarkar et al., 1988). Saha et al., (1987) and Sarkar et al., (1988) have modeled the

source of the melt responsible for the formation of these granitic rocks.

According to Mahadevan (1981) the granite and gneisses of Great Mica Belt

indicate three different ages as (i) 3200-3000 Ma. (ii) 2250-2050 Ma. and (iii) 900-

350 Ma.

2.2.3 Pegmatites

Pegmatite veins of varying dimension and shapes are emplaced in the

metasediments and granites of the belt. They vary in their length from few cm to

about 500 m and a width from a few cm to 30 m. For mining purpose the common

dimensions of the pegmatites are ranging from 50 to 300 m in length and 1 to 5 m in

width. They have been worked to a maximum vertical depth of about 213 mt. The

shape of the pegmatites varies from one pegmatite to other, more commonly they

form long narrow bodies thinning out at either end and also at depth. Some of the

veins are lenticular in shape having a maximum thickness at central portion. Some of

the pegmatites have arcuate to sinuous shapes. The crescent shaped pegmatites are

also observed along the nose of the fold and are seen in road cuttings between

Koderma and Rajauli.

The pegmatites are both zoned and unzoned in nature. In zoned pegmatites the

massive white quartz and occasionally microcline perthite forms the core which is

surrounded by intermediated zone of blocky perthite. The wall zone generally consists

of an intergrowth of quartz, microcline, plagioclase, and muscovite. The border zone

is normally very thin in such pegmatites. The zoned pegmatites are mostly economic

in nature and contain variety of minerals including gem stones and rare metals.

Mahadevan (2002), identified four different types of the pegmatites in GMB based

upon the spatial relation. According to him the interior pegmatites occur within the

granitic rocks as ‘nests’ and segregated masses. Early pegmatites emplaced into the

43

schistose rocks are generally potassic. They are pre- to syn-kinematic and are

involved in deformation. Later pegmatites in the schist belts are of perthite acid

plagioclase types (K-Na). They are late to post deformation and are the sources of

commercial mica. The book mica is predominantly of ruby variety while the green

variety is also rarely present. A variety of other minerals besides quartz, feldspar and

mica are present in these pegmatites. These minerals include the gem variety of

feldspar (moonstone and bytownite), apatite, garnet (hossenite) and tourmaline

(indicolite), and some rare metals like columbite-tantelite and cassiterite.

Ramachandran et al. (1994) suggested different age for the pegmatites of the

belt. According to him the age of mica pegmatite is 1392-1200 Ma. The ages of

different minerals like uraninite, monazite, allanite and lapidolite from different

pegmatites of the belt vary from 1050 Ma -950 Ma. (Ramachandran et al., 1994).

Mahadevan (1967), based on the studies in the underground mines, suggested

that most of the pegmatites trends E-W with some of the NW-SE and N-S. They are

sub parallel to the bedding and foliation in folded schistose rocks. They normally dip

steeply from 60 to 70 in variable directions.

The formation of mica pegmatites has been suggested to be controlled by

lithology as well as structure (Mahadevan and Maithani, 1967). They are mostly

confined to mica schist and less confined to micaceous quartzites and hornblende-

schist. Further they are also structurally controlled and are mostly present along the

bedding and foliation planes, noses and limbs of folds, tension joints and slip or

fracture planes in schists.

2.3 STRUCTURAL EVOLUTION

Saha et. al (1987), Bhattacharaya (1988) and Ramchandran et. al (1994) have

discussed the structural evolution of the Mica Belt. According to these workers three

phases of deformation are observed in the GMB. In the first phase two interfering

folds, F1a and F1b produced hook shaped pattern of folds. The second phase of folding

44

is more open and has an E-W trending axial plane and plunge to the east at steep

angles. This resulted in the development of a prominent axial plane schistosity S2.

This period is marks the synkinaematic anorthosite and granitic rocks (Ramchandran

et al, 1994). The third and final phase of deformation (F3), which is relatively weak

and less extensive, has produced NNE-SSW to NNW-SSE axial trends in some of the

area (Mahadevan, 2002). Bhattacharya (1988) relates three successive phases of

metamorphism in the GMB with the three deformation phases. The metamorphism of

the area has gone up to almandine-amphibolite facies (Bhola, 1968). In the area three

to five sets joints are also noted in the intrusive granite.

2.4 GEOLOGY OF LOKAI-INDARWA

Lokai - Indarwa area forms the southern part of the Great mica belt in

Koderma district. The area is covered with dense forest and alluvium (Fig.2.3) with a

few outcrops. The artisan mining going on in the area has helped to expose the rocks

(Fig. 2.4). The rock types exposed in the area are mostly metasediments represented

by hornblende mica schist, mica schist belonging to the Koderma Group.

Amphibolite, and anorthosite are also commonly present. All these rocks have been

intruded by a number of pegmattitc veins. Apart from these rocks a rare conglomerate

bed is also seen near Indarwa area.

The general geological succession of the area can be given as below:

Pegmatites and quartz veins

Granite Gneiss

Metasediments : Hornblende schists, mica schist

Amphibolites and Anorthosite

Conglomerates

CGC

The rocks have been dissected by a number of crossfolds with antiforms and

synforms. The metasedimentary rocks are mostly trending ESE-WNW but at places

changes to NNE-SSW. Description of different sequences exposed in the area is

given below.

45

2.4.1 CONGLOMERATE

A matrix dominated conglomerate bed has been seen near Indarwa from NW

of Neropahar at the contact between Great Mica Belt metasedimetaries and gneisses

belonging to CGC. It has been named as Indarwa Conglomerate by Ghosh (1992).

This signifies a stratigraphic hitus. Ramakrishnan and Vaidyanathan (2008) have

suggested the Indarwa Conglomerates might have formed at the base but are now

dismembered by deformation.

2.4.2 METASEDIMENTS

The area is dominated by hornblende-mica schist with few bands of

amphibolites. The mica schist is also present in the peripheral areas. The development

of migmatitic zones are also locally observed (Fig. 2.5) The hornblende-mica schist

present a grooved appearance on the weathering outcrops due to quartz rich and mica

rich bands. Mahadevan and Maithani suggested that the plane separating these bands

are the bedding planes. However this is very poorly preserved particularly along the

nose of the fold. The foliations of the schistose rocks strikes about ENE to SWS to

NE-SW. The dip are variable from 55° to 65° in the northly or some time southerly

directions depending on the folded nature of schist. At places the schistose rock are

showing lineations due to the elongation of minerals. Some small fault marked in the

area by silcification, brecciation.

Schists contains varing proportion of plagioclase, feldspar, biotite. The schist rock are

intensively intruded by pegmatites which contains significant amount of feldspar with

biotite. The content of biotite is less than 4%.

2.4.3 PEGMATITES

Pegmatites in the area are introduded within country rocks (schist) showing

sharp contact. These are unzoned pegmatites and consists mostly of quartz and

perthitic microcline with plagioclase and small amount of biotite, muscovite.

Pegmatites veins show pinching and swelling structures (Fig. 2.6). where nodules of

moonstone are seen engulfed within the fine flakes of biotite

46

Fig. 2.3. Study area covered with alluvium and forest.

Fig. 2.4. Outcrops exposed due to artisan mining in the area.

Fig. 2.5. Development of migmatitic veins within metasediments.

47

Mostly pegmatites veins are seen oriented parallel to sub parallel to the

foliation plain. These pegmatites dips in NE direction with an amount of 50° to 65°

with an average of 55° with E-W strike.

The majority of the pegmatites are controlled by schistosity and foliation.

These pegmatites are ribbon like bands. They are however traceable for considerable

lengths and the pinch and swell depending upon the strike of the bedding plane of the

country rock.

It has been suspected that these pegmatites are emplaced possibly along

originally sheared planes parallel to schoistosity/foliation. Relationship of pegmatites

to country rocks is that thin layers of the schist are enclosed within the pegmatites

near their margin and are separated from main schist wall by pegmatites which are a

few cm thick.

The two prominent pegmatitic units which are centrally placed are;

Plagioclase-quartz±Muscovite±Biotite-Pegmatite and Plagioclase-

Perthite±Muscovite±Biotite-Pegmatite intruded within host rock. With in this zone

some of the plagioclase shows nodular occurrences bounded by fine mica schist. It

shows blue adularescence (sheen) which is a gem variety of plagioclase called

Moonstone. Books of the biotite are commonly observed in the border zone at the

contact with schist rock. There are number of parallel pegmatites veins separated by

bands of schist. Some of these pegmatites also contain apatite in the form of small

needles like crystals.

48

10 cm

N

Pegmatite Vein

Moonstone pockets in biotite.

Host Rock

Dip & Strike

LEGEND

Fig. 2.6 Sketch of Pegmatite veins

49

CHAPTER-3 GEM

CHARACTERIZATION

50

GEM CHARACTERIZATION

3.1 INTRODUCTION

Gems include a wide range of materials (natural, synthetic, treated,

imitation diamonds, coloured stones, and organic). Various processes (such as

irradiation, heating, filling of open fractures or cavities, and coating) are also

used to treat low quality gem materials to improve their colour, appearance, or

durability (Nassau, 1983; Johnson et al., 1999; Reinitz et al., 2000). The physical

and compositional differences between natural, synthetic, and treated gem

materials can range from significant to minor. Thus, it is necessary to check for

potentially small differences through advanced analytical methods which have

sufficiently high resolution and sensitivity. This requires gathering observations

and measurements to determine distinctive characteristics of gem materials. Such

characteristics are summarized in standard reference books (Webster, 1994;

Liddicoat, 1981). Although effective in many cases, traditional gem testing

instruments and methods cannot always distinguish synthetic and laboratory

treated gem materials from their natural counterparts. Advanced nondestructive

characterization techniques are used to find diagnostic properties to distinguish

these materials. Visual characteristics such as colour, luster, growth features, and

inclusions are examined with a 10x magnifier (loupe) and a binocular microscope

with bright and dark field illumination and polarizing functions. Refractive index

and birefringence (double refraction) are determined by a refractometer.

Pleochroism (dichroism) is examined with a dichroscope. Strains and optical

character are observed using a polariscope. Visible absorption spectrum is

examined with a hand spectroscope. Specific gravity, electric conductivity, and

thermal conductivity are measured by a hydrostatic balance, conductivity meter,

and thermal conductivity tester respectively. Inclusions are one of the primary

visual means of separating natural from synthetic, imitation, and treated gems

(Gubelin and Koivula, 1986).

51

3.2 GEMMOLOGICAL INSTRUMENTS

For a gemmologist nothing is more important than the gemological testing

equipment. Depending upon the utility of these instruments, the rank as well as

cost of these instruments varies. For some this may mean a lot of expensive and

cumbersome equipment. For others it may mean only a few instruments carried in

a shirt pocket. Table 3.1 lists the traditional and advanced methods and

instruments that are now in relatively widespread use in gemological laboratories

for gem identification. Some of the most often used gemological testing

equipments are discussed in following paragraphs.

Loupes

Loupes, also known as Jewelers’ Loupe or Eye Loupe, are the most

important basic instrument used for evaluating gemstone. It is a compact portable

hand lens (Convex lens).The recommended and standard magnification for a

jewelers loop is 10X magnification. It is used to give basic information on the

external conditions like surface cracks, flaws, scratches, polishing standard, worn

facet edges and quality of cutting. Some internal features of the gemstone like

characteristic inclusions, internal cracks, flaws, clarity and uniformity of the

colour of the gemstone can also be detected using loupe.

Gemmological Microscope

The microscope is probably one of the most important and widely used

gem testing instrument. The microscopes used in gemmology are modern

binocular microscopes with dark and light field illumination that are specially

made for the gemstone and diamond industry. Some of the characteristics of a

good gemological microscope include its zoom capability which ranges from

10X to 90X magnification, overhead illumination, adjustable iris and an

integrated stone holder. In a gemological microscope different types of

illumination are used for different purpose.

52

Refractometer

The refractometer is specially designed to measure the refractive indices

for gems and is one of the important gem testing instruments. It has some

limitations like; it cannot be used for rough gemstones. Most of the

refractometers available are the critical angle refractometers. Gemstones with a

refractive index of more than 1.8 cannot be tested on a refractometer. However a

new generation refractometer, called as Brewster Angle Refractometer, can

measure a much wider range of R.I. from 1.4 to 3.5. An added advantage of this

model is that it does not require contact liquid. Gemstones can be either singly

refractive (Isotropic) or double refractive (Anisotropic). The Optic Character of a

gemstone (Uniaxial or Biaxial), the direction of the optic axis, optic sign

(Positive or negative) and the approximate refractive index on curved surfaces

can also be determined using a refractometer.

Spectroscope

A spectroscope is another important, easily portable instrument used for

the identification of gemstones. A spectroscope splits light into its component

colours after it passes through the material that is to be tested. The visible

spectrum ranges from 4000Å to 7000Å. If the gemstone absorbs certain type of

light, it will reveal a characteristic appearance. The wavelengths that are absorbed

by the stone are seen in the spectroscope as vertical black lines in the spectrum.

The spectroscope is one of the few instruments that can be used to test gemstones

deeply set in jewellery. Both rough and cut gemstones can be examined using a

spectroscope.

Diffraction Grating Spectroscope is the most commonly used

spectroscope in the gem and jewellery trade. This spectroscope is based on the

principle of diffraction. Here light is diffracted by a thin film of diffraction

grating material after it enters through a narrow slit.

53

Table 3.1: Traditional and advanced nondestructive instruments and methods

used for gem identification

Instruments and methods Observation Measurement

Traditional

Loupe Colour, appearance,

morphology, inclusions,

growth features, surface

features

Binocular microscope Colour, appearance,

morphology, surface features,

internal features (inclusions,

twins, strain, growth zonings,

etc.), cut proportion

Polariscope Strain, twinning, optical

character

Refractometer Refractive index,

birefringence

Dichroscope Pleochroism (dichroism)

Hand spectroscope Visible absorption spectrum

Colour filter Colour appearance

Hydrostatic balance Specific gravity, weight

Thermal conductivity meter Thermal conductivity

Electric conductivity meter Electric conductivity

Ultraviolet lamp Fluorescence

Advanced

X-ray radiography Differences in X-ray

transparency

X-ray diffraction Crystal structure, crystallinity

X-ray topography Lattice imperfections

(dislocations, twins)

X-ray fluorescence Chemical composition

(major, minor, and trace

elements)

UV imaging system Fluorescence image

UV-VIS, infrared

spectrophotometers

Absorption spectra from UV to

mid infrared range

Micro raman spectroscopy Raman spectrum of

host materials and inclusions

Luminescence spectroscopy Excitation and emission spectra

Cathodoluminesence Luminescence related

to impurities and defects

Scanning electron

microscope

High magnification

of surface microstructures

Electron probe X-ray

microanalysis

Chemical composition

(major, minor, and trace

elements)

Colour measurement Colour appearance and

colour change

54

Polariscope

A polariscope is a simple instrument used to make quick determination of

single refraction (SR) or double refraction (DR).The light source from the bottom

of the instrument has to pass through two crossed polaroid discs, oriented at right

angles to each other. The gemstone should be placed between the two discs, on

the stage of the polariscope. The lower polaroid disc is fixed and it is known as

the polarizer while the upper one is rotatable and is known as the analyzer. A

polariscope can also be used to determine the pleochroism and optic figure

(Uniaxial/biaxial) of a gemstone.

Dichroscope

Dichroscope is critical in identifying many synthetic and imitation

gemstones. Dichroscopes can be used for both rough and cut gemstones.

However colourless gemstones cannot be tested by a dichroscope. Dichroscopes

work on the principal of pleochroism to detect some natural gemstones from their

artificial counterparts. It is used to differentiate singly refractive gemstones (e.g

alamandine garnet & blue spinel) from double refractive gemstones with similar

colour (such as ruby and blue sapphire respectively).

Chelsea Colour Filter

It is also known as emerald filter or colour filter. A chelsea colour filter

absorbs visible light except deep red (long red wavelength) and yellow green.

This filter is very useful to identify emerald simulants.

Other smaller instruments used for identification of gemstones are

Ultraviolet lamps, hardness pencils, heavy liquids etc. Apart from these handy

instruments, some major analytical instruments/ equipments are used to

chemically analyze the gemstones. These are XRD, XRF, Raman Spectroscope

etc.

55

3.3 GEMMOLOGICAL PROPERTIES OF GEMSTONES

FROM AREA

Out of the many minerals found from the area, feldspar and apatite are the

two minerals which are present as crystals and show some properties which

classify them as semiprecious gemstone. Gemmological properties were obtained

on 15 samples using standard gemmological instruments mostly at Gemmological

Institute of India, Mumbai. The internal features were examined with a

gemmological microscope and absorption spectra were observed with a GIA

spectroscope. The refractive index and birefringence is measured using the

Gemled Refractometer. To calculate the specific gravity of the gemstones

weighing scales model Metteler Toledo CB603, (Monobloc inside weighting

technology) using the hydrostatic weighing method is used. The hydrostatic

method uses the formula that is based on the Archimedes principle. The weight of

the gemstone in air and the weight of the gemstone in water should be known.

The quantitative chemical analysis of 10 samples is done using the

EDXRF at GII, Mumbai. While the crystallographic parameters were determined

by using X-Ray Diffractometer. In order to understand the composition and

identify the gemstones, Raman Spectra of the gemstones were obtained with a

Renishaw inVia micro Raman System at Gemmological Institute of India,

Mumbai. The working conditions of these instruments are discussed in other

sections of this chapter.

The detailed gemmological properties of the feldspar and apatite minerals

from the area is discussed in following paragraphs.

3.3.1 Moonstone

The feldspar minerals from Lokai- Indarwa have been collected from

different parts of the area from different pegmatites. Some of the feldspar from

the area shows brilliant play of colour, by a milky white to sky blue shimmering

56

sheen effect. These feldspar with blue shimmering sheen effects are known as

Moonstone. For studying the gemmological properties of this gemstone, 15

samples were selected from different locations of artisian workings with in an

area of 2km (approx). The size of the crystals is upto 5 cm which shows prismatic

habit. Most of these are translucent but some transparent varieties are also found.

Most of these samples show bluish sheen and play of colours from white to light

blue(Fig. 3.1). Some of the stones show bluish grey patches. In addition, some of

the stones rarely present with whitish-blue alternate zoning giving a very

characteristic gemmological feature (Fig. 3.2). The optical effect which produces

these brilliant colours is mostly due to interference of light, the fine lamella of the

repeated twinning and attributed to lamellar microperthitic or crypto-perthitic

intergrowth. The cleavages are commonly observed and some of the samples

have broken cleavage surfaces. Most of the common features of feldspars are

observed in all the samples.

The gemmological properties are summarized in table 3.2 a-e. The size of

the crystals is upto 5 cm which shows prismatic habit. The specific gravity of the

samples approximates 2.68, two samples shows 2.65 and 2.77 respectively. The

greatest and least refractive index are 1.551 to 1.550, other two shows 1.541-

1.540 and 1.561-1.560 with birefringence 0.008. No characteristic absorption

spectrum is observed in these samples nor do they exhibit any luminescence. The

samples fluoresced weak inert under UV radiation.

Microscopic examination revealed that most of the samples shows

transparent blue sheen colour (Fig. 3.3) few needle like inclusions are observed

under high magnification (Fig. 3.4). In few samples the lamellae are alternatively

thick and thin (Fig. 3.5). Under optical microscope, in thin sections, the mineral

shows characteristic very fine albite-pericline tartan twinning (Fig. 3.6). A few

stones also contained partially healed fractures that had no surface expression in

reflected light. The optical effect which produces these brilliant colours is mostly

due to interference of light, the fine lamella of the repeated twinning, that’s why

when we observe the gemstones, the colour is observed on a particular direction

only as in Fig. 3.7, only few stones shows blue sheen which are in the particular

direction to the light.

57

Fig. 3.1 Moonstone exhibting blue sheen of colour.

Fig. 3.2 Zoning with in moonstne.

Fig. 3.3 Sample under gemmological microscope.

58

Fig. 3.4 Inclusion observed with in

moonstone.

Fig. 3.5 Lamellas seen in transparent

moonstone crystal

Fig. 3.6 Tarten twinning with in

moonstone

Fig. 3.7 Numerous moonstones, in which

blue colour is seen in particular

directions.

Fig. 3.8 Crystals of Apatite. Fig. 3.9 Apatite under thin section.

50X 20X

μm

59

3.2 Apatite

Apatite is a mineral of calcium phosphate with chlorine and fluorine. The

size of non-gem quality crystals of apatite reaches enormous sizes but clean

crystals are not found in large sizes. Despite of all other properties of gemstones

like colour and transparency, apatite are not usually count into gemstones

category this is due to lack of hardness.

Table. 3.2 a. Gemmological properties of gemstones.

Properties F 1 F 2 F 3

Crystal System Triclinic Triclinic Triclinic

Habit Prismatic Prismatic Prismatic

Colour Exhibiting blue sheen and play of colours.

Transparency Transparent Opaque Transparent

Lusture Vitreous Pearly Vitreous

Hardness 6.0 6.5 6.0

Specific gravity 2.68 2.68 2.68

Cleavage Perfect Perfect Perfect

Fracture Splintery Splintery Splintery

SR/DR DR DR DR

Pleochroism Strong Strong Strong

Optic sign B+ve B+ve B+ve

Optic character Biaxial Biaxial Biaxial

RI range 1.554-1.555 1.558-1.559 1.558-1.559

Birefringence 0.001 0.001 0.001

Spectrum None None None

Dispersion 0.012 0.012 0.012

Inclusion Not observed Small needle like fractured

observed

UV light Inert weak Inert weak Inert weak

Simulants Beryl, Quartz, Fibrolite, Kyanite

Treatment Heat, Irradiation

Mineral variety Labradorite Labradorite Labradorite

Mineral species Feldspar Feldspar Feldspar

60

Table. 3.2 b. Gemmological properties of gemstones.





Transparency Transparent Transparent Transparent

Lusture Vitreous Vitreous Vitreous





SR/DR DR DR DR




RI range 1.558-1.559 1.555-1.556 1.555-1.556



Dispersion 0.012 0.012 0.012

Inclusion Not observed Small needle like inclusions






61

Table. 3.2 c. Gemmological properties of gemstones.





Transparency Opaque Transparent Transparent

Lusture Pearly Vitreous Vitreous





SR/DR DR DR DR




RI range 1.558-1.559 1.556-1.557 1.554-1.555



Dispersion 0.012 0.012 0.012

Inclusion Not observed






62

Table. 3.2 d. Gemmological properties of gemstones.



Habit Prismatic Aggregate Prismatic

Colour Transparent Translucent Yellowish

Transparency Transparent Transparent Opaque





Fracture Splintery Splintery Conchoidal

SR/DR DR DR DR

Pleochroism Strong Weak Strong

Optic sign B+ve B-ve B-ve


RI range 1.555-1.556 1.540-1.541 1.560-1.561



Dispersion 0.012 0.012 0.012

Inclusion Not observed Not observed

UV light Inert weak Weak Inert weak

Simulants Beryl, Gold Stone

Treatment Irradiation Heat, Irradiation

Mineral variety Labradorite Oligoclase Bytownite


63

Table. 3.2 e. Gemmological properties of gemstones.

Properties A 1 A 2 A 3

Crystal System Hexagonal Hexagonal Hexagonal

Habit Columnar Columnar Columnar

Colour Sky blue Sky blue Sky blue

Transparency Transparent Transparent Transparent


Hardness 5 5 5


Cleavage Imperfect Imperfect Imperfect

Fracture Uneven Uneven Uneven

SR/DR DR DR DR

Pleochroism Weak Weak Weak

Optic sign U –ve U -ve U -ve

Optic character Uniaxial Uniaxial Uniaxial

RI range 1.634-1.635 1.634-1.635 1.636-1.367


Spectrum Blue & yellow

Dispersion 0.013 0.013 0.013

Inclusion Not observed

UV light SW & LW Bright blue

Simulants Topaz, Beryl, Sappphire, Quartz, Andalusite


Mineral variety Apatite Apatite Apatite

Mineral species Apatite Apatite Apatite

Apart from the mineralization of moonstone within pegmatites from the

study area, presence of apatite is also observed which are associated with fine

flakes of biotite in pegmatites (Fig. 3.8). They are present in the form of

crisscross needles. The crystals belong to the hexagonal system and their habitat

is usually stumpy prismatic. The specific gravity of apatite falls in the range 3.12-

3.21. Refractive Index are in the range of 1.634-1.635 uniaxial negative with

64

birefringence low at 0.001. The samples respond variously to Ultra violet rays,

long wave as well as short wave shows bright blue.

Microscope examination of thin sections shows hexagonal or elongated

(Fig. 3.9) crystals with high relief, low birefringence, straight extinction and

absence of good cleavage.

3.4 X RAY ANALYSIS OF THE MOONSTONE

X-rays discovery helped the scientists to probe and understand crystalline

structures of the solids at the atomic level. It has been further used by the

geochemists to analyse the mineral and rocks for their chemical composition. X-

rays are produced by bombarding a metal target (Cu, Mo, Rh usually) with a

beam of electrons emitted from a hot filament (often tungsten). The incident

beam will ionize electrons from the K-shell (1s) of the target atom and X-rays are

emitted as the resultant vacancies are filled by electrons dropping down from the

L (2P) or M (3p) levels. This gives rise to X-ray spectra. When the geometry of

the incedent X-rays impinging the sample satisfy the Bragg equation,

constructive interference occurs and a peak in intensity occurs. A detector record

and process this X-ray signal and converts the signal to a count rate which is then

output to a device to show the peaks. This ultimately helps to understand the

structure by using X-Ray Difractometer (XRD) and elemental concentration in

the minerals by X-Ray Fluorescence (XRF) methods.

All minerals and compounds have unique crystallographic structures so

XRD can be used to precisely identify a mineral or compound by comparing its

diffraction data against a database of known minerals and compounds. X-ray

fluorescence analysis provides information on elemental composition of the

particular mineral.

The semi-precious moonstone from the Kodarma area have been

subjected to X-ray analysis for identification/characterization of the mineral and

understanding its unit cell dimensions by using the XRD method. The major

65

element oxides have been analyzed by using EDXRF method. The details are

given in the following paragraphs.

3.4.1 X-Ray Diffraction Studies

The XRD has been very much helpful in two main areas: (a) to fingerprint

characterization of minerals and gemstones and (b) to determine of the structures

of minerals/gemstones. Each crystalline solid has its unique characteristic X-ray

powder pattern which may be used as a fingerprint for its identification. Once the

material is identified, X-ray crystallography may be used to determine its

structure, i.e. how the atoms pack together in the crystalline state and what the

inter-atomic distance and angle are etc. X-ray diffraction is one of the most

important characterization tools used in mineralogy and gemology. The size and

the shape of the unit cell for any gemstone can also be determined most easily

using X-ray diffraction (Jenkin and Snyder, 1996). Crystallographic structure can

be calculated using Bragg’s Law (nλ = 2d sinθ) where n is 1, λ is the known

wavelength of the incident X-ray beam, d is the interatomic spacing (in

ångstroms), θ is the angle between the incident X-ray beam and the lattice plane.

The identification of the material is made by matching its d spaces with the ICDD

(International Centre for Diffraction Data) database.

In order to exactly identify and understand the cell dimensions of the gem

minerals present in the present area of study, the carefully separated minerals

were subjected to X-Ray Diffraction studies. The crystal data was collected

using OXFORD DIFFRACTION X-Calibur Single Crystal X-Ray Diffractometer

using monochromatore Mo Kα radiations (λ=0.71073Å) at Department of

Physics, University of Jammu. The single crystal XRD was equipped with CCD

camera and Keppa geometry, 4-circle diffractometer, CCD area detector with

water chiller (type KMW200CCD). The accelerating voltage was maintained at

50 Kv and the tube current at 30mA. For analyzing the sample 15 number of

frames was used within 3 runs. The diffraction % was 54%. The Target resolution

was 0.74°.

66

From the diffraction data obtained, the crystallographic parameters viz

unit cell dimensions (a, b, c and α, β, Ƴ) and unit cell volume (V) of the important

gem minerals present in the area were determined. The unit cell parameters for

Moonstone and apatite are given in Table. 3.3. The crystal with calculated unit

cell dimension, a=8.187 Å, b=8.698 Å, c=9.364 Å and α=89.81, β=84.53,

λ=82.76 with v=658.42 Å3 was identified as moonstone. While the calculated

unit cell dimensions for apatite are, a=9.334Å, b=9.371 Å, c=6.890 Å and

α=90.12, β=89.80, Ƴ=119.81 with v=522.9 Å3.

Table. 3.3 Unit Cell parameters of moonstone and apatite.

Mineral UNIT CELL DIMENSIONS

a b c α β λ V

Moonstone 8.187Å 8.698

Å

9.364

Å

89.81 84.53 82.76 658.4 Å3

Apatite 9.334Å 9.371

Å

6.890

Å

90.12 89.80 119.81 522.9 Å3

3.4.2 Energy Dispersion X-ray Fluorescence

Gemstones have been known to undergo various manipulations to

enhance their perceived quality. As technology advances, confirming the

authenticity of gemstones becomes more and more difficult, creating a large

demand for a non-destructive, time-efficient method of determining the

composition of gemstones and precious metals. One such method is X-ray

spectroscopy, a technique that enables a user to quickly and easily differentiate

between a true stone and a fraud or determine if any chemical enhancement have

been made. This method allows for non-destructive analysis of gemstones to

avoid the purchase of fraudulent stones.

Two common methods of X-ray spectroscopy namely wave length

dispersive X-ray Fluorescence (WD-XRF) and energy dispersive X-ray

Fluorescence (ED-XRF). The main difference between two methods is how the

67

emitted x rays are measured. WD-XRF uses an analyzing crystals to diffract the

different X-ray wave lengths and various detectors placed at different angles

measure the number of X-ray diffracted at each angle. In case of the energy

dispersive X-ray Fluorescence (ED-XRF). The detectors collects x rays of all

energies and sorts out each X-ray energy by the amount of electrons each x ray

knocks free in detector lattics. The number of electrons knocked free depends

upon the incoming X-ray energy and the particular interactions that x ray has

with crystal lattices.

The energy dispersive X-ray fluorescence analysis (ED-XRF) is a well-

established tool for multi-elements composition analysis in different fields. It

works non-conducting and it is non-destructive. No particular sample preparation

is necessary if the specimens have an almost planar and smooth surface. For the

characterization of precious gemstone material it is also important that the

deposited X-ray radiation dose is definitely too weak for inducing colour

alterations, in contrast to WD-XRF.

Elemental measurement is important in gemology for identification,

classification and characterization of both natural and synthetic gemstones. Minor

and trace levels of metals, especially the transition metals, as well as alkali

elements and alkaline earth elements (such as Mg, K, Ca, Sr and Rb) help to

establish the geographic region and environmental conditions during the

formation of a gemstone. Other elements like Au and Pb can be used to indicate

processing requirements of synthetics

In order to analyze the elemental concentration of the gemstones of the

area i.e. moonstone, ED-XRF is used at Gemological Institute of India, Mumbai.

For this application a Horiba scientific XGT-7200 X-ray Analytical Microscope

was used. This is a completely new generation of XRF microscope. It offers a

seamless merge between optical observation and elemental analysis functions.

The analysis is done single point as well as multiple point. Element peaks are

automatically located and labeled, and quantitative analysis down to ppm level is

carried out. Rhodium target was used with SDD (Silicon drift detector ) peltier

68

cooled. The accelerating voltage was maintained at 50 Kv and the tube current at

1mA. The analysis is done using XGT ( X Ray guided tube) 1.2mm.

10 samples of the moonstone were analysed using ED-XRF. The major

element oxides analysed for moonstone is given in detail in Table 3.4.

The analysis shows higher SiO2 concentration varying from 65.53 to

66.95 wt % with an average of 66.26 wt % with Al2O3 varying from 24.71 to

26.04 with an average of 25.38 wt % and CaO from 7.47 to 8.30 wt % averaging

7.82 wt % with minor percentage of K2O, MnO2 Fe2O3 and SrO.

Table. 3.4 : Composition of moonstone by EDXRF

Sample no. Al2O3 SiO2 K2O CaO MnO2 Fe2O3 SrO Total

MS 1 25.53 66.127 0.345 7.775 0.006 0.116 0.1 100

MS 2 25.606 66.022 0.299 7.893 0.002 0.091 0.087 100

MS 3 25.33 66.347 0.341 7.793 0 0.08 0.109 100

MS 4 26.047 65.537 0.329 7.879 0.003 0.11 0.096 100

MS 5 25.406 66.605 0.335 7.498 0 0.066 0.09 100

MS 6 24.815 66.363 0.301 8.308 0.007 0.109 0.098 100

MS 7 25.769 65.721 0.278 8.027 0 0.108 0.096 100

MS 8 25.473 66.217 0.297 7.827 0.005 0.09 0.092 100

MS 9 24.717 66.95 0.358 7.757 0.011 0.118 0.089 100

MS 10 25.154 66.736 0.302 7.519 0.005 0.198 0.085 100

3.5 RAMAN SPECTROSCOPIC OF THE MOONSTONE OF

LOKAI-INDARWA AREA.

Raman spectroscopy is considered as confirmatory methodology for the

identification of unknown polyatomic species occurring in any phase viz. solid,

liquid or gas. It has wide application, not only in Geosciences but in many other

areas such as Archeology, Nanosciences, Semiconductors, and Pharmaceuticals

etc. Raman spectroscopy has a fundamental relevance in the study of the

gemstones as;

69

Certify gem authenticity and determine whether natural, synthetic or

treated

Determine whether gem fissures have been disguised with fillers

Identify solids, liquids, and gaseous inclusions

Identify mineral crystal types

Study crystal defects, vacancies and substitutions

Analyse inclusions, even when they are deep inside the gem

In addition, Raman spectroscopy is a non-destructive technique, so your gems

and minerals are not damaged.

3.5.1 Sample and Methods

New problems in the identification of different gemstones can be solved

by using advanced non invasive spectroscopic techniques. In fact, all the solid

state spectroscopy methods are invaluable in material testing and

characterization. The laser based micro Raman Spectroscopy (Renishaw inVia

Raman Microscope) being used in Gemmological Institute of India is fitted with

three lasers operating at 325nm, 514.5nm Ar ion laser (VIS) and 785 nm Laser

(IR). Raman microscope enclosure RE 02 is used to focus the laser on the

samples, using objectives lenses of 20X and 50X magnification. The microscope

is equipped with colour video camera, allowing to position the sample and to

select a specific region for investigation. The backscattered light is dispersed by

using a 2400line/mm and 1200 lines/mm grating and is detected on a Peltier-

cooled CCD-detector. This configuration allows a record spectra with a spectral

resolution of 1 datapoint/cm-1

.

Spectra were obtained from a 0.1-mm diameter area of finely powdered

sample and were referenced to a blank window. These spectra closely resemble

those obtained with the use of KBr pellets, but are considerably more convenient

to obtain.

70

3.5.2 Result

The Raman spectra of a large number of gemstones of moonstone were

obtained to determine the compositional information for the identification of

these minerals.

Feldspar group of minerals belong to tectosilicates. Tectosilicates

structure with fully linked tetra hedra produces a Raman spectral pattern which is

totally different from those of ortho, chain, ring and layer silicate, (Deer et al

1991). The strongest Raman peak in the tectosilicates spectrum is located below

600 cm-1

which is the identification feature of tectosilicates. From the position of

strongest Raman peak in the spectrum, further species of a mineral group can be

identified. Within the group of tectosilicates the Raman spectral features of the

feldspar are distinctly different from those of others, such as quartz and zeolite

(Sharma et al 1983, Matson et al. 1986). Raman spectra of the feldspar are readily

recognized by the presence of two or three Raman peaks lying between 450 and

515 cm-1

the strongest of which falls within the narrow region of 505 to 515 cm-1

.

We put the analyzed data in the group of spectral range given by Freeman et al.

(2008), where they have given different groups for different spectral ranges.

Group-I: In this group the peaks occurs in the spectral range of 450 to 520 cm-1

.

Group-II: Spectral range of 200-400 cm-1

.

Group-III: Peaks below 200 cm-1

.

Within the Group-I very strong peaks are seen which are marked as Ia, Ib and Ic

on the basis of intensity of height respectively. In Group-II the stronge peak is

defined as IImax and IIImax in Group III.

The result of Raman spectra’s of analyzed feldspar (moonstone) samples

is shown in table 3.5

The assignments (based on McKeown,s 2005) show that the two region

(Group I) belong to the ring-breathing modes of the four-membered rings of

71

tetrahedral. The Raman peaks in Group II and III corresponds to rotation-

translation modes of the four-membered rings and cage-shear mode, respectively.

From our present study ten samples were analyzed the data shows that

most samples belong to intermediate plagioclase composition: two andesine

samples (An 33.6 46.3) and five labradorite samples (An 51.5-63.5). Other three

samples belong to ternary feldsfar.

Table. 3.5. Raman spectral peaks data of the analyzed moonstone samples.

Sample

no.

Raman Band Frequency (cm-1

) Feldspar Phase.

Group-I Group-

II

Group-

III

Ia Ib Ic IImax IIImax

MS 1 509.8 481.2 468.5 287.7 186.0 Labradorite

MS 2 508.9 481.2 460.6 283.7 176.6 Labradorite

MS 3 510.6 480.4 455.0 286.8 175.8 Andesine

MS 4 511.4 478.0 451.8 286.9 179.0 Ternary feldspar

MS 5 509.7 480.4 447.0 286.9 179.8 Labradorite

MS 6 510.6 482.0 455.0 286.9 179.8 Andesine


MS 8 509.7 480.4 443.1 287.6 182.1 Labradorite


MS 10 509.1 480.5 455.0 286.1 162.4 Labradorite

The spectral peaks are shown in Fig.3.10. They all have similar Raman

spectral patterns. More importantly, these mid-An plagioclase samples have

distinct Ia peak positions ranging from 508.9 to 510.6 cm-1

.These plagioclase

samples also have a fairly prominent Ib band near 481 cm-1.

The Ic band is noticed

as weak spectra adjacent to Ib band.

72

Three feldspar samples have composition which falls in ternary feldspars

systems. In these samples the raman spectral peaks do not match exactly with the

known peaks of plagioclase group. However the bands shows resemblance

associated with high temperature plagioclase. The Ia peak positions of these

samples comes around 511 cm-1

, similar to high temperature plagioclase. The

variations in the Ib and II peaks positions are relatively larger, which may reflect

changes in the composition.

73

478.0

511.3

455

.0

286.

8

177.

4

481.2

509.

8

46

8.5

287.7

186

.0

481.

2

50

8.9

460.6

283.

7

176

.6

48

0.4

510.

6

455.0

286

.8

175.

8

478.0

511

.4

451

.8286

.9

179

.0

150 200 250 300 350 400 450 500 550

Raman Sh ift (cm )- 1

480.4

509

.7

447

.0

286.

9

179.

8

150 200 250 300 350 400 450 500 550


482.

0

510.6

455.0

286.9

179.8

479.

6

511.4

455

.8

28

3.7

163.9

48

0.4

509

.4

443.1

28

7.6

182.1

480.

5

509.1

455.0

28

6.1

162.

4

{

{ {

Group I

Group IIGroup III

{Group I

{Group II

{Group III

M S-1

M S-2

M S-3

M S-4

M S-5

M S-6

M S-7

M S-8

M S-9

M S-10

Fig. 3.10. Raman spectral peaks of the analysed moonstone.

150 200 250 300 350 400 450 500 550


150 200 250 300 350 400 450 500 550


150 200 250 300 350 400 450 500 550


150 200 250 300 350 400 450 500 550


150 200 250 300 350 400 450 500 550


150 200 250 300 350 400 450 500 550


150 200 250 300 350 400 450 500 550


150 200 250 300 350 400 450 500 550


74

CHAPTER-4

PETROGRAPHY

75

PETROGRAPHY

4.1 Introduction

Petrographic studies can be useful do decipher the mineralogical

composition, textural relationship, alteration, and deformation present in the rock.

It is also important to classify the rocks and can be used to correlate the

mineralogical composition with the whole rock chemical analysis. In order to do

the petrographic studies, systematic sampling of the pegmatites and country rock

(amphibolites and mica schist) was carried out during the different field seasons.

Due to the artesian mining, mines present in the area, most of the samples

collected were fresh in nature. Apart from collecting samples systematically from

different part of the pegmatites and country rock, they have also been carried out

from different depth levels from various mines. Detailed megascopic and

microscopic examinations of the representative samples, systematically collected

from the study area were carried out for petrographic studies. 100 thin sections of

different rock type were prepared by using standard techniques using Logitech

Thin Section Preparation Unit (CL 40 lapping/polishing machine & IU 30) at

University of Jammu. The thin sections were studied using Leica (DM750P) and

Nikon (ECLIPSE LV100POL) Microscopes. Various minerals were identified

properly.

The modal percentages of the minerals present in different types of rocks

have been calculated using Automatic Point Counter using point count technique.

To conduct the point count a grid is imposed over the sample to be counted, and

the composition of the grain under each grid point is recorded using a

petrographic microscope. In order to choose the increment for the point count

precautions to is taken so that it could cover as much of the slide as possible to

minimize potential bias due to inhomogeneities in the thin section. This interval

was between 1.0 mm and 1.67 mm.

76

4.2 Petrographic study of different rocks

4.2.1 Amphibolites

Good exposure of the amphibolites rocks are observed all around the area

particularly near Indarwa village. It is a massive medium to coarse grained dark

coloured rock with high amount of amphiboles. The other important mineral

present is white to grey coloured feldspar. In field, most of the places it is soil

covered but in few exposures, it shows sharp contact with mica-schist. The rock

is mostly unfoliated but at places week foliations have been developed. At places

they show development of migmatite with highly folded quartzo-feldspathic

veins.

The rock is mostly granofelsic metamorphic rock showing week gneissic

texture at places (Fig. 4.1). Megascopically, it consists of black/greenish black

amphibole and white to grayish white plagioclase. These two minerals together

form 80% of the rock. The other minerals (clinopyroxene, biotite, chlorite,

epidote and quartz etc.), however, were identified under microscope. The

nomenclature of the rock as amphibolites is consistent with the definition

suggested by IUGS Sub-commission on the Systematics of Metamorphic Rocks

(Countinoh et al, 2007). which defines the petrographical boundaries of

amphibolites also includes the rock from this area (Fig.4.2) .

The study of the thin sections of the amphibolite of the present area of

study suggests that they are characterized by the presence of more than 60%

amphiboles along with plagioclase and clinopyroxenes. The other minerals like

biotite, quartz, cholorite, epidote, sphene, microcline and opaque minerals are

present as accessory minerals. The various varieties of amphibole identified in

the rocks are hornblende, anthophyllite & tremolite-actinolite in order of their

abundance. Hornblende is the most common amphibole present in these rocks.

Under microscope it shows pleochroic colour from dark green to greenish brown.

In some samples it is zoned with light green cores and darker green margins

77

Fig. 4.1: Granofelsic metamorphic rock showing weak gneissic texture.

78

Remaining constituents

Plagioclase Amphibole

75%

30% 95%

Fig. 4.2. Amphibolite field according to the SCMR defination

79

(Fig. 4.3). It occurs mostly as elongated grains with ragged terminations. There is

usually an obvious preferred orientation of grains which defines lineation. It

makes sharp contact with clinopyroxenes suggesting its simultaneous origin.

Anthophyllite shows moderate to high positive relief in thin section. It is

colourless to pale brown in thin section. It shows weak pleochroism.

Anthophyllite is distinguished from hornblende by the parallel extinction.

Tremolite-Actinolite shows high relief, colourless to pale green in thin

section. Tremolite is distinguished from anthophyllite by the inclined extinction

and from hornblende by larger degree of inclined extinction.

The next common mineral plagioclase forms about 18% of the rock.

Under thin sections the plagioclase are identified by their lamellar twinning and

extinction. Composition of the plagioclase generally ranges from (An10 to An40 )

albite to andesine. Mostly the grains are xenoblastic in nature. In some sections,

two generations of plagioclase are seen at a place. The next abundant mineral

biotite are present as prismatic brown coloured prismatic flaks. In some of the

sections, the biotite shows alignment in same direction as of hornblende (Fig.

4.4). Under microscope it shows pleochroic colours from dark brown to light

brown and parallel extinction. Pleochroic halloes are not common in the biotites.

Clinopyroxene forms the next abundant mineral. In thin section they are

augite and diopside. Augite is usually pale to grey coloured in thin section, with

grayish pleochroism (Fig. 4.5). It is distinguished from orthopyroxene by inclined

extinction and higher birefringence. Diopside is brownish green in thin section.

The mineral, at places, shows the alteration into chlorite.

Amphiboles forms slender prisms and needles, with marked parallel

orientation. In some cases hornblende also forms porphyroblasts. Iron oxide is

typically in platy subhedra. Sphene occurs in grains and overgrowths on ilmenite.

Quartz and feldspar are anhedral, in aggregates or interstitial grains.

80

4.2.2 Mica Schist

Mica-schist is an important rock unit in the area for emplacement of

pegmatite. The rock shows sharp contact with the Amphiboles. It shows well-

developed schistosity with three sets of joints at few out outcrops. At places, the

schist is interbedded with thinly quartz and feldspar bands, due to this the

grooved appearance on the weathered outcrops is noticeable.

Mica schist from the study area is medium to coarse grained with foliation

plane defined by alignment of micas flaks (Fig. 4.6). It consists of biotite,

muscovite and quartz as essential minerals with minor amount of sodic

plagioclase and rare K feldspar.

The mica schist of the area shows marked variation in their texture and

mineral content. Mineralogically the mica schist is composed of varying amount

of plagioclase, quartz, biotite, muscovite and chlorite. Some of the rocks in the

area consist of less foliated rock which is rich in feldspar and is hard. However

the other group of rocks are highly foliated and rich in micas.

Petrographic analysis indicates that these schists are the amphibolites

grade of metamorphism and have undergone intense deformation. This is

apparent from the presence of highly folded and sheared mineral grains

producing a well aligned foliations. In some of the mica schist there are quartzo-

feldspathic layers along the foliation planes. At places these layers are highly

folded (Fig. 4.7). This supports the possibility of anatexis taking place prior to the

second stage of deformation.

Biotite from the area is typically brown, or reddish brown, and distinctly

pleochroic. Perfect cleavage on easily seen in thin section, and controls fragment

orientation and shape. Extinction is parallel. Birefringence is strong and yields

maximum interference colors. It shows pebbly or finely mottled “birds eye”

extinction that is characteristic of the micas. Impressive decussate/intersertal

biotite texture is seen which is an important mica schist texture (Fig. 4.8). Here

81

Fig.4.3. Hornblende showing light green

core and darker green margin.Fig. 4.4. Biotite and hornblende aligned

in the same direction.

Fig. 4.5. Augite crystal associated with

mica schist.

.

Fig. 4.6. Mica flaks alligned along the

foliation.

Fig. 4.8.Intersertial texture in biotite . Fig. 4.9. Laths of biotite penetrating within

crystallized quartz.

82

the vectorial nature of the lath interpenetration in observed. Often the long axis

penetrates into the short axis of the same mineral. At places biotite laths

penetrating the crystallized granular quartz was also observed (Fig. 4.9).

Muscovite is colorless in thin section, rarely very pale pink or green

(peacock colour). Perfect cleavage on is well displayed in thin section and

controls fragment orientation. Extinction is parallel to cleavage in all orientations.

Birefringence is high. Some times intersertal muscovite/biotite associated with

prismatic plagioclase and quartz, which though might be later recrystallization

occupying the spaces between prismatic muscovite.

Quartz is colourless in thin section. It is recognized by its low relief, low

birefringence, and lack of cleavage or twinning. Mostly it is fine to medium

grained. Some grains that has been deformed shows undulatory extinction.

Intergrowth of quartz with plagioclase showing myrmekitic texture is commonly

noticed.

Plagioclase is colorless in thin section. It shows perfect cleavage,

extinction is inclined in almost all orientation, and polysynthetic twinning which

are the distinguish features in plagioclase. The plagioclase is present as laths as

well as interstitial between mica as well as quartz grains. Within the plagioclase

megablast some secondary plagioclase is seen intruded which is recognized by its

twinning. Myrmekitised plagioclase is commonly noticed. Replacement with in

plagioclase is seen at some places.

Mostly microcline and rarely orthoclase varieties of K feldspar are

noticed with in the schists from the area. They are colourless in thin section, and

clouding (especially in orthoclase) is common. Twinning is common. Extinction

angle is large and birefringence is low. They are distinguished from from each

other on the basis of its twinning. Orthoclase shows Carlsberg twinning where as

microcline shows cross hatched twinning.

Sillimanite is also seen associated with mica schist. In thin section, mats

of fibrous sillimanite (fibrolite) are seen (Fig. 4.10). It is characterized by colour

83

Fig. 4.7. Quartzo-feldspathic layers within mica schist showing folded

pattern.

84

less, has high relief than mica (muscovite), birefringence higher then kyanite and

andalusite.

4.2.3 Pegmatites

On the basis of marked variation in mineralogy and texture, petrological

types of the pegmatites can be classified as (a) Plagioclase-Quartz± Biotite±

Muscovite and (b) Plagioclase-Perthite± Biotite± Muscovite. Many pegmatites of

the studied area exhibit more or less uniform texture and mineralogy. They are

medium to coarse grained rocks and mainly composed of plagioclase feldspar,

quartz, K- feldspar, biotite, muscovite and with variable accessory minerals such

as apatite, tourmaline etc.

The depth wise sampling of the pegmatites have been carried out from the

underground artition mines since the pegmatites are not well exposed on surface,

It is noticed that plagioclase-quartz± biotite± muscovite unit makes the wall of

the pegmatites which encloses plagioclase-perthite± biotite± muscovite unit. This

unit is rich in biotite and contains only small amount of muscovite. The

moonstone mineralization is seen in this type of pegmatite only. At places the

pockets of moonstone are surrounded by the fine biotite flakes.

In the major part of the pegmatite the plagioclase predominate over the

quartz. The large irregular shaped patches of quartz also occur at places.

Occasionally microcline is found in small quantity. Microcline is seen mostly as

small replacement patches contain the plagioclase particularly in the border zone.

There are different varieties of plagioclase present in the pegmatite. However,

oligoclase is predominant over other varieties. The average modal percentage of

the pegmatites is given in the Tables 4.1, which are also presented in the form of

pie chart in Fig. 4.11. Mineral wise description of the pegmatite is given below;

85

Table 4.2: MODEL ANALYSIS OF THE LOKAI-INDARWA PEGMATITE (in %age)

Mineral

Slide no

Quartz Plagioclase Microcline Orthoclase Muscovite Biotite Apatite Other Total

LI-Ap 2.8 83.22 - 0.50 1.2 7.9 3.3 1.08 100.00

LI-Ms 1.95 86.93 3.56 - 2.18 2.51 - 2.87 100.00

LI-1 4.13 78.15 1.2 2.0 3.60 5.70 - 5.22 100.00

LI-2 3.6 90.0 1.3 - 1.60 2.0 - 1.5 100.00

LI-3 45.71 45.68 1.68 1.82 0.57 2.17 0.96 1.41 100.00

LI-4 19.33 68.09 - 2.5 3.15 1.25 2.18 3.5 100.00

LI-5 25.30 41.21 6.10 - 1.79 20.01 4.46 1.13 100.00

LI-6 25.13 44.67 10.32 17.21 1.6 - - 1.07 100.00

LI-7 44.67 38.35 - 1.99 3.06 7.71 2.73 1.92 100.00

LI-8 19.27 61.73 1.87 1.9 4.91 0.70 4.7 4.92 100.00

LI-9 80.25 5.10 2.13 4.1 - 5.93 - 2.49 100.00

LI-10 13.32 76.08 2.0 - 1.98 5.9 - 0.72 100.00

Average% 23.79 59.93 2.51 2.66 2.13 5.19 1.53 2.32

86

Plagioclase

Plagioclase is the most dominant mineral in the area (59.93 %). It occurs

generally as coarse subhedral aggregates or also as the phenocryst in the granular

aggregates of quartz.

It is generally colourless. Blocky varieties are commonly present along

with platy and sugary variety. The plagioclase is present along with quartz,

muscovite and biotite. The plagioclase shows poikilitic texture in which oikocryst

of plagioclase and chadocrysts of quartz are present (Fig. 4.12). Further in some

samples intergrowth of plagioclase and quartz is observed in form of myrkmitic

texture (Fig. 4.13). Exolution of plagioclase lamella making parthitic texture is

also observed (Fig. 4.14) The relationship between plagioclase and quartz in the

pegmatites suggests that plagioclase has crystallized after the bulk of the quartz

was crystallized. Some amount of quartz, however, crystallized simultaneously

with the plagioclase in places resulting in the intergrowth. Petrographically two

generations of plagioclase have been identified (Fig. 4.15).

Occasionally the plagioclase laths shows alteration into sericite (Fig.

4.16). In some samples sericitization effect is more. As a result of this plagioclase

laths are distorted and masked. These altered laths contain inclusions of

secondary quartz and are cloudy in appearance. At some places lath of

plagioclase is bounded by biotite showing an undulatory boundary between the

two (4.17). The composition of plagioclase is calculated based on the optical

properties and is found to be falling between oligoclase to bytownite. Gem

variety of plagioclase i.e, moonstones is also present. It display on particular

surfaces a sheen or iridescence, attributed to lamellar microperthitic or

cryptoperthitic intergrowth. Detailed nature of this variety is described in

previous chapter.

Quartz

It is the second most dominant minerals present in the both areas. Three

types of quartz are commonly seen. They are milky quartz, smoky quartz and

87

Fig. 4.10. Sillamanite with biotite. Fig. 4.12. Poikilitic texture in plagioclase.

Fig. 4.13. Myrkmitic texture within Quartz

and plagioclase.

Fig. 4.14. Parthitic texture with in plagioclase

and microcline.

Fig. 4.15. Two generation plagioclase. Fig. 4.16. Alteration within plagioclase

showing formation of sericite.

88

rosy quartz. Mostly the massive quartz core is made up of milky and rosy quartz,

while in some cases muscovite books are associated with translucent colourless

quartz. The size of quartz grains is quite variable. Quartz is also present as

inclusions within the plagioclase. At many places replacement of quartz

aggregates by plagioclase is observed. Muscovite shows a very close association

with quartz. Few sections two generation of quartz is seen. One is coarse grained

and another one is fine grained (Fig. 4.18). Granophyric textures of quartz with

alkali feldspar are also seen (Fig. 4.19).

Alkali Feldspar

The alkali feldspar is mainly represented by microcline with occasionally

orthoclase and few grains of sanidine. Mostly the microcline is fresh and occurs

as subhedral to anhedral in shape. It is characterized by well developed Cross

hatched twinning (Fig. 4.20). Some samples show alternation of microcline, and

in some samples flakes of mica are intruded within it. Orthoclase is present in

fewer amounts and it coexists with plagioclase and microcline. The grains of

orthoclase are euhedral to subhedral in shape, and are characterized by carlsbad

twinning (Fig. 4.21), Sanidine also shows the same twinning but differs by the

orientation of the optic plane (Fig. 4.22).

The perthitic feldspar is very commonly present. They occur either as

large pockets set in a matrix of aggregates of quartz and plagioclase or also at the

contact of plagioclase and quartz. Graphic intergrowth with quartz is also

observed. Grains and blebs of quartz and plagioclase are also present in some of

the perthites.

Muscovite

The muscovite occurs embedded mostly in aggregates of quartz or along

the contact of quartz and plagioclase as big books or small crystals. They are

rarely enclosed by the plagioclase itself. Such close association of muscovite

books and quartz is a characteristic feature in these pegmatites. Generally the

muscovite seems to be more with the quartz and less with the perthite content.

89

Fig. 4.17. Undulatory contact between

plagioclase and biotite.

Fig. 4.18. Two generation of quartz.

Fig. 4.19. Granophyric texture between

quartz and alkali feldspar.Fig. 4.20. Microcline showing cross

Hatched twinning.

Fig. 4.21. Orthoclase showing carlsberg

twinning.

Fig. 4.22. Sanidine showing carlsberg

twinning.

90

Muscovite flakes are fresh and are characterized by peacock colour. The average

content of the muscovite from the area is 2.51% by volume.

The muscovite is seen mostly enclosed by the quartz. The thin flakes of

muscovite, however, are often intergrown with plates of quartz. Such intergrowth

is commonly seen among the smaller books. Where the quartz and feldspar both

are present the muscovite is partially enclosed by both the minerals. These

suggest that the muscovite started crystallization earlier than the feldspar.

Alteration of muscovite is commonly noticed resulting formation of secondary

minerals like chlorite (Fig. 4.23).

Biotite

Biotite is mostly more than the muscovite in the areas. The average

percentage by volume is 5.19%. The books of biotite occur ingrown within

certain portions of the pegmatites. Sometimes they assume large size of book (30-

40 cm in length). In the zone where nest of plagioclase are present biotite is

grown into small to large aggregates and are enclosed within the plagioclase.

Otherwise generally the biotite is confined to quartz or at the quartz -feldspar

boundary. Generally the biotite is brown in colour and occurring as anhedral to

subhedral flakes. It is strongly pleochroic mostly from yellow to reddish brown.

Prominent pleochroic halos are observed in some biotite flakes. Biotite halos are

present, which are formed due to the presence of zircon mineral (4.24).

Apatite

Apatite is the abundant accessory mineral and the most widely distributed.

Usually show pale grayish colour in thin section. Cleavage is poor and does not

have a strong influence on fragment orientation. Distinguished by its moderate to

high relief, low birefringence, and uniaxial character.

91

Tourmaline

Tourmaline occur mostly as euhedral crystals in shape and commonly a

decimeter across in size. Discrete or aggregate of crystals of varying sizes are

concentrated either within the quartz, feldspar or muscovite or along the foliation

of recrystallized schist. Tourmaline is black in colour and shows variation in

composition. It is evidenced by variations in pleochroism in different parts of

even the same crystals. In such crystals the core is pleochroic from pale yellow to

greenish brown, while along the borders the mineral is pleochroic from green to

shades of blue. Under microscope tourmaline of present area shows blue colour

with strongly pleochroic and high relief. In some of the samples euhedral

prismatic zoned tourmaline is also seen (Fig. 4.25).

Accessory Minerals

Other than these common minerals, some other accessory minerals are

also noticed with in pegmatites, these are, Sphene which is characterized by its

high relief and extreme birefringence, Fig. 4.26 shows idioblastic crystal of

sphene crystallized within quartz. Epidote is also seen in some of the samples

(Fig. 4.27), Allanite a cerium bearing variety of epidote having high relief,

strong pleochorism and brown colour are distinctive feature from epidote (Fig.

4.28). Chlorite, is formed where the alteration in muscovite is present.

92

Fig. 4.23. Alteration of muscovite into

chlorite.

Fig. 4.24. Zircon mineral making halos

within biotite.

Fig. 4.25. Zonning within tourmaline. Fig. 4.26. Idioblastic crystal of sphene.

Fig. 4.27. Epidote associated with biotite. Fig. 4.28. Crystal of allanite (epidote).

93

CHAPTER-5

GEOCHEMISTRY

94

GEOCHEMISTRY

5.1 INTRODUCTION

Geochemistry is an important field in the study of mineral deposits

because mineralization involves several processes, of which chemical processes

are the ones that finally result in the precipitation of metals or formation of

minerals. Studying the geochemical characteristics of mineral deposits is,

therefore, important in: (a) understanding ore genesis (the usage of term ‘ore’

here does not necessarily mean a mineral deposit that can be exploited at an

economic profit); (b) mineral deposit classification; (c) mineral exploration; (d)

extractive metallurgy or mineral processing; and (e) geo-environmental studies.

Understanding the genesis and classification of mineral deposits have

traditionally been carried out together (Westra and Keith 1981; Hitzman et al.

2003; Dill 2010). Knowledge of various geological processes relevant to the

mineral deposit formation provides a conceptual framework for the application of

geo-computational technique for generating mineral exploration targets

(Bonham-Carter 1994; Porwal and Kreuzer 2010; Carranza 2011a). Knowledge

of ore genesis is important in developing geo-environmental models for mineral

deposits (Seal and Foley 2002). Some workers (Cabri, 1988 and Clout, 2003)

have demonstrated the relevance of understanding of the genesis of ore deposits

in providing guidance for mineral processing and metal extraction. Thus, out of

the different fields of application of geochemical characterization of mineral

deposits, understanding ore genesis is the most important because it provides

information that is essential to the other applications.

To understand the genesis of gemstone deposits and gem bearing

pegmatites, rock samples from host rock and pegmatites were analyzed for major

oxides, trace and rare earth elements.

95

5.2 SAMPLING AND ANALYTICAL METHODS

15 representative samples (10 pegmatite, and 5 amphibolite) were

selected for the geochemical studies. These samples were collected from the

underground artisan mines at different locations and at different depths. The

detail analysis of these samples was done in the laboratories of Wadia Institute of

Himalayan Geology, Dehradun using standard procedures.

For the preparation of samples for XRF (major and trace elements)

analysis, the samples were powdered (-200 mesh). In order to overcome the

moisture problem the LOI % of the powdered sample was calculated. About 10

gm of sample is thoroughly mixed with polyvinyl alcohol for the preparation of

pellets in Automatic Hydraulic Press. These pellets are used for the XRF

analysis.

For doing the analysis of samples in XRF, an advanced system S8 Tiger

from Bruker-AXS, Germany, with a high power X-ray Rh anode tube of 4kW

capacity (60 kV, 170 mA) with three optimized coarse and fine collimators is

used. Elements routinely determined as weight % oxide in geological materials

with a repetitive value in the range of less than 1%. Trace elements routinely

determined in geological samples at the > 5 ppm ( 2 ppm for some elements) with

a repetitive value of 5 ppm.

Method used for analysis of rare earth elements including sample

preparation is described here briefly. The solution of the 100 mg rock powdered

(-200 mesh) is digested with 10 ml of HF-HNO3 mixture (2:1) in open Teflon

crucible on hot plate. Processes are repeated 3-4 times with evaporation to

incipient dryness to ensure complete digestion. It is followed by two treatments

of HClO4 ( 2 ml each) and contents are evaporated to complete dryness. Finally

the dried mass is dissolved in 10 ml of 20% nitric acid and final volume is made

upto 100 ml with the help of distilled water (Khanna, et al. 2009). Solution

obtained; after this the solution was ready for the analysis.

From the prepared solution the rare earth elements (REE) were analyzed

using PerkinElmer SCIEX quadrupole type Inductively Coupled Plasma Mass

96

Spectrometer ELAN DRC-e. Sample solution was introduced into argon plasma

using a peristaltic pump and a cross flow nebulizer. The analysis is done by

running the instrument with 10 W RF power; plasma gas flow of 15.00 L/min,

auxiliary gas flow of 1.20 L/min, nebulizer gas flow of 0.89 L/min, and with Ni

sampling cone.

5.3 MAJOR OXIDES

The major oxide data plays an important role for the nomenclature,

classification and petrogenesis of various rock-suits. The analysis of the

pegmatites and ambhibolite is done in order to understand their genetic relations,

if any. The samples used for the analysis were carefully selected after the

petrography. The analyzed data is discussed in following paragraphs.

5.3.1 Pegmatite

Ten representative samples of pegmatite from different veins were

selected for their geochemical treatments. Care has been taken that the samples

are without any alteration. The analyzed major oxide geochemistry data of the

representative samples is summarized in Table 5.1. The pegmatites of the area

have SiO2 content ranging from 63.92 to 73.62% with an average of 68.40%. The

pegmatite veins are also characterized with higher Al2O3 which ranges from

12.97 to 15.83% with an average of 14.67%. Total alkali percentage (Na2O+K2O)

varies from 5.65 to 10.28% with K2O/Na2O always more than 2. Some of the

samples show a very high content of K2O which goes upto 8% in some cases.

These samples also show presence of higher percentage of anorthite and

orthoclase during petrography. Na2O in the pegmatite from area shows value

ranging from 1.03 to 1.85% with an average of 1.49%. CaO also varies from 1.63

to 3.96% with an average of 2.72%. This is consistent with the presence of

plagioclase in the samples.

97

Table. 5.1. Major oxide analysis of pegmatites from Lokai Indarwa (in wt %).

Oxides

Sample no. SiO2 Al2O3 CaO Fe2O3 MgO Na2O K2O MnO TiO2 P2O5 SUM LOI

SP2 71.15 14.19 2.42 2.22 1.36 1.57 6.24 0.04 0.33 0.17 99.69 0.41

SP3 70.93 14.39 2.38 1.63 0.73 1.43 8.10 0.03 0.22 0.61 100.45 0.35

SP4 65.15 14.20 3.00 5.12 4.58 1.41 4.94 0.09 0.79 0.31 99.59 0.64

SP6 69.41 15.83 2.57 1.48 0.52 1.85 8.43 0.03 0.19 0.18 100.49 0.43

SP7 73.62 12.97 2.91 2.54 1.33 1.56 4.45 0.04 0.41 0.19 100.02 0.55

SP10 68.24 14.50 1.63 2.92 2.12 1.12 8.66 0.06 0.45 0.26 99.96 0.46

SP11 67.95 15.80 2.36 2.52 1.41 1.63 8.23 0.05 0.39 0.20 100.54 0.43

SP12 66.99 15.55 2.36 2.96 1.71 1.56 8.16 0.05 0.47 0.26 100.07 0.47

SP13 66.66 14.68 3.56 4.44 4.08 1.03 4.89 0.08 0.54 0.18 100.14 0.57

SP15 63.92 14.54 3.96 4.64 3.90 1.71 3.94 0.10 0.66 0.37 97.74 0.59

Average 68.40 14.66 2.71 3.04 2.17 1.48 6.60 0.05 0.44 0.27

98

MgO and Fe2O3 in most of the samples are from 0.52 to 2.14% and 1.48

to 2.96% respectively, however, two of the samples show higher percentage of

MgO of approximately more than 4% and also higher Fe2O3 i.e. more than 5%.

This is because of higher percentage of biotite in these samples. The

FeO/(FeO+MgO) values vary from 0.5 to 0.7. P2O5 in the samples ranges from

0.17 to 0.61% with an average of 0.27%, while TiO2 varies from 0.22 to 0.79%.

The MnO is less than 0.1 %. The leucocratic nature of the pegmatites is evident

by the fact that the normative quartz and feldspar content of the pegmatite is

always higher than 90%.

The variation of different oxides with SiO2 is shown in Fig. 5.1. From

these diagrams for pegmatites, it is interpreted that with increasing SiO2 content,

Fe2O3, MgO, TiO2 and MnO decreases. These oxides show negative trends with

SiO2.. Other oxides, however do not show any significant differentiation trends

for pegmatites. The pegmatites are showing enrichment Al2O3. K2O varies from

4.45 to 8.66% and averages at 6.60% while Na2O ranges from 1.03 to 1.85% with

an average of 1.48%.

There are several diagrams used to classify rocks based on the major

elements composition. The total alkalis verses silica diagram (TAS) is used to

classify igneous rocks. The whole rock geochemistry of pegmatites are plotted in

the TAS diagram given by Middlemost (1994). The samples of the pegmatites

fall in the category of quartz monzonite to granite (Fig. 5.2). On the basis of

silica–alkalis (SiO2 vs. K2O+Na2O) discrimination diagram (Figure 5.3), (Irvine

and Baragar, 1971), the pegmatites of the area may be classified alkaline in

nature. One sample, however, falls on the boarder of alkaline and subalkaline.

5.3.2 Amphibolite

Amphibolite rocks present in the area and in very close vicinity have been

selected for their geochemical studies of major oxides. The analyzed major oxide

geochemistry data of the 5 representative samples is summarized in Table 5.2

99

Table. 5.2. Major oxide analysis of amphibolites from Lokai Indarwa (in wt %).

Oxide

Sample no. SiO2 Al2O3 CaO Fe2O3 MgO Na2O K2O MnO TiO2 P2O5 SUM LOI

SHR1 55.17 12.39 7.27 8.11 10.98 0.66 3.45 0.19 0.89 0.40 99.51 0.68

SHR2 53.21 13.33 5.68 9.41 11.39 0.47 4.93 0.25 1.09 0.39 100.15 0.77

SHR3 53.60 14.20 3.54 8.88 11.01 0.42 5.92 0.17 1.18 0.41 99.33 1.28

SHR4 43.58 13.42 6.09 12.5 14.41 0.47 6.00 0.33 1.82 0.56 99.18 1.57

SHR5 55.27 13.37 3.59 8.39 10.31 0.42 5.55 0.15 1.10 0.38 98.53 1.37

Average% 52.16 13.34 5.23 9.45 11.62 0.48 5.17 0.21 1.21 0.42

100

0.00

0.50

1.00

1.50

2.00

60.00 65.00 70.00 75.00N

a2O

(w

t %

)SiO2 (wt %)

0.00

1.00

2.00

3.00

4.00

5.00

60.00 65.00 70.00 75.00

Mg

O(w

t %

)

SiO2 (wt %)

8.00

9.00

10.00

11.00

12.00

13.00

14.00

15.00

16.00

60.00 65.00 70.00 75.00

Al 2

O3

(w

t %

)

SiO2 (wt %)

0.00

2.00

4.00

6.00

8.00

10.00

60.00 65.00 70.00 75.00

K2O

(w

t %

)

SiO2 (wt %)

0.00

1.00

2.00

3.00

4.00

5.00

60.00 65.00 70.00 75.00

Ca

O(w

t %

)

SiO2 (wt %)

0.00

0.20

0.40

0.60

0.80

1.00

60.00 65.00 70.00 75.00

TiO

2 (w

t %

)

SiO2 (wt %)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

60.00 65.00 70.00 75.00

Mn

O(w

t %

)

SiO2 (wt %)

0

1

2

3

4

5

6

60.00 65.00 70.00 75.00Fe 2

O3

(w

t %

)

SiO2 (wt %)

Fig. 5.1. Harker variation diagram of oxides with silica for Pegmatites

101

35 40 45 50 55 60 65 70 75 80

0

2

4

6

8

10

12

14

Granodiorite

Granite

Syenite

QuartzMonzoniteMonzonite

Monzo-diorite

Monzo-gabro

GabroGabrodiorite Diorite

Fig. 5.2 Total alkalis vs silica diagram for Pegmatites (after Midddlemost, 1994)

Na

O

+ K

O

(w

t. %

)2

2

SiO (wt. %)2

102

35 40 45 50 55 60 65 70 75 80

SiO (wt %)2

0

2

4

6

8

10

12

14

Na

O+

KO

(w

t %

) 2

2

ALKALINE

SUBALKALINE

Fig. 5.3 SiO vs K O + Na O plot for pegmatites (after Irvine and Barager 1971).

2 2 2

103

The amphibolites of the area have SiO2 content ranging from 43.58 to 55.27%

with an average of 52.17%. A higher concentration of Al2O3 is also present

within these amphibolites, showing a range of 12.39 to 14.20%, with an average

of 13.34 %.

Total alkali percentage (Na2O+K2O) varies from 4.11 to 6.47% with very

low percentage of Na2O. Na2O in the amphibolite from area shows value ranging

from 0.42 to 0.66% with an average of 0.49%. CaO also varies from 3.54 to

7.27% with an average of 5.23%. MgO and Fe2O3 in most of the samples are

from 10.31 to 14.41% and 8.11 to 12.5% respectively. The Fe2O3/(Fe2O3+MgO)

values vary from 0.42 to 0.46. P2O5 in the samples range from 0.38 to 0.56% with

an average of 0.43%, while TiO2 varies from 0.89 to 1.82%. The MnO is less

than 0.3 %. Major element data and their variability with SiO2 is shown in Fig.

5.4. The ambhibolites of the area show negative trend for many of the oxides,

MgO, Fe2O3, TiO2, & MnO with SiO2, while Na2O show positive trends with

SiO2. However other oxides do not show any specific trends.

In, total alkalis versus silica (TAS) diagram (Figure 5.5), the

amphibolites of the Lokai-Indarwa area plot within the alkaline magma series and

fall predominantly in the trachyandesite field, with a few samples plotting in

tephriphonolite field. Alumina saturation (Shand index) diagram for studied

amphibolites is given in Fig. 5.6 and it is showing that the rocks fall in the

metaluminous field.

To distinguish among tholeiitic and calc-alkaline affinities, and thereby

place some broad tectonic constraints on protolith, the amphibolites were plotted

on an AFM (alkalis + FeO oxides + MgO) diagram (Fig. 5.7) of Irvine and

Baragar (1971). Most of the amphibolites cluster in the calc-alkaline field.

104

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.00 20.00 40.00 60.00

Na

2O

(w

t %

)

SiO2 (wt %)

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

0.00 20.00 40.00 60.00

MgO

(wt

%)

SiO2 (wt %)

12.00

12.50

13.00

13.50

14.00

14.50

0.00 20.00 40.00 60.00

Al 2

O3

(w

t %

)

SiO2

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

0.00 20.00 40.00 60.00

K2O

(w

t %

)

SiO2 (wt %)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

0.00 20.00 40.00 60.00C

aO

(wt

%)

SiO2

0.00

0.50

1.00

1.50

2.00

0.00 20.00 40.00 60.00

TiO

2 (w

t %

)

SiO2 (wt %)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.00 20.00 40.00 60.00

Mn

O(w

t %

)

SiO2 (wt %)

0

2

4

6

8

10

12

14

0.00 20.00 40.00 60.00

Fe 2

O3

(w

t %

)

SiO2 (wt %)

Fig. 5.4. Harker variation diagram of oxides with silica for Amphibolites

105

35 40 45 50 55 60 65 70 75 80

SiO (wt %)2 .

0

2

4

6

8

10

12

14

Na

O+

K

O (

wt

%)

2

2

Dacite

Rhyolite

Andesite

Basalticandesite

BasaltPicro- basalt

Basanite

Basaltictrachyandesite

Trachy-basalt

Tephrite

Phonotephrite

Trachyandesite

Tephriphonolite

Phonolite

Foidite

ULTRABASIC BASIC INTERMEDIATE ACID

Trachyte

Trachydacite ALKALINE

SUBALKALINE

Fig. 5.5. Classification of host rock from area. The shaded portion represents the composition of amphibolite from the area.

( after Le Bas et al., 1986, Irvine and Barager 1971).)

106

Mola

r A

l O

/(N

a O

+K

O

)2

32

2

Molar Al O /(CaO+Na O+K O)2 3 2 2

1.0 2.0

1.0

3.0

2.0

Fig. 5.6 Alumina saturation (Shand index) diagram for discrimination

metaluminous, peraluminous and peralkaline compositions.

(Shand 1943).

Peralkaline

Metaluminous Peraluminous

107

FeO

MgONa O + K O2 2

Tholeiitic

Calc-Alkaline

Fig. 5.7. The discrimination of tholeiitic from calc-alkaline series is shown in the AFM diagram (after Kuno,1968)

108

Figure 5.8 is plot of TiO2 versus Fe2O3 examining the concentration of fairly

incompatible element as a function of mafic differentiation in the amphibolites.

The amphibolites show typical low Ti/Fe ratios

5.4 TRACE ELEMENTS

After emerging the plate tectonics theory in 1960s, the emphasis on the

geochemistry has been increased. Various sophisticated analytical techniques

have been devised to improve the quality data and as a result various

discrimination diagrams have been constructed to constrain and discriminate the

rock suits belonging to different tectonic setting.

Geochemically, all the elements of the periodic table have been classified

into major, minor, trace and rare earth elements and each of these groups have

their own importance for the classification, nomenclature, and petrogenesis of

rocks. In addition to these broad divisions, the major, minor, and trace elements

have also been geochemically divided as mobile and immobile elements and

elements and these elements play an important role in the various geological

processes. Majority of these elements are more or less mobile as is suggested by

Cann (1969), Hart et.al., (1970) and Hatori et. al., (1972). Therefore many

workers have used mainly immobile and compatible elements to constrain the

petrogenesis, because mobile elements are not suitable for the petrogenesis.

Trace element spider diagrams are often used to view a lot of trace-

elements on the same plot in order to maximize the information content. The

measured trace-element concentration of pegmatite sample is normalized by

primitive mantle as a reference composition. The normalization is required for

two purposes. It turns out that the abundances of trace element masses is such

that even masses are much higher than odd masses. This is a primordial feature of

the solar system (or galaxy for that matter), which results from the

nucleosynthetic processes that create the elements. Thus, if one simply plots

concentrations of various trace-elements on the same diagram, a very jagged

diagram would appear. Normalization to any other rock reference eliminates this

109

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0 2 4 6 8 10 12 14

TiO

2 (w

t %

)

Fe2O3 (wt %)

Fig. 5.8 Plot for TiO2 (wt %) vs Fe2O3 (wt %)

110

jaggedness. The second reason for normalization is that one can learn something

about geologic processes that fractionate (i.e. change the relative proportions of

trace-elements) trace-element relative abundances from their original relative

abundances. It is common to normalize to a hypothetical “primitive mantle”

composition or a chondritic meteoritic composition. For lithophile elements, both

references are believed to approximate the primordial relative abundances of

elements in the silicate part of the Earth. In the case of primitive mantle, the

absolute abundances are believed to represent the primordial silicate Earth, that

is, an estimate of the starting composition.

Keeping in mind the importance of trace elements in the genesis and to

know the tectonic environment of the pegmatites, 10 samples of the pegmatites

and 5 samples of the amphibolites from the Lokai-Indarwa area are analyzed for

Ni, Cu, Co, Sc, Cr, V, Pb, Zn, Ga, Rb, Sr, Y, Zr, Nb, Ba, Th and U by XRF. The

result of the analyzed samples is represented in next section.

5.4.1 Pegmatite

10 representative samples were carefully selected for the determination of

their trace element contents. The result of the trace elements analysis of the

pegmatites samples is given in table 5.3. The pegmatites are characterized by

very high content of barium, robidium, zirconium and lead. The Ba concentration

is varying from 727 to 940 ppm with an average of 800 ppm. The Sr content vary

from 261 to 355 ppm), with an average of 311 ppm. While Rb value range from

147 ppm to 266 ppm with an average of 220 ppm. The Sr is always higher than

Rubidium. Rb/Sr value for the pegmatites is 0.4 to 0.9. Cr in the rock vary

between 97 to 421 ppm, with an average of 190 ppm. Cr/Ni ratio for the

pegmatites is always more then 1, and remains between 1.29 to 5.61. The Y

value for pegmatites of Lokai-Indarwa varies from 20-29 ppm without much

variation, while Nb ratio for such rock varies from 3-24 ppm. Ga varies from 10-

19. Th and U are also on higher side.

111

Table. 5.3. Trace element analysis of pegmatites from Lokai-Indarwa area.

Sc

ppm

Co

ppm

Ni

Ppm

Cu

ppm

Zn

ppm

Ga

ppm

Pb

ppm

Th

ppm

Rb

ppm

U

ppm

Sr

ppm

Y

ppm

Zr

ppm

Nb

ppm

Ba

ppm

Cr

ppm

V

ppm

SP2 6.1 11.8 78 6 37 15 77 39 190 11.3 314 21 174 13 727 116 29

SP3 5.8 12.1 75 5 31 10 126 33 218 1.1 312 26 60 5 780 97 20

SP4 12.3 15.2 133 7 99 18 50 95 245 15.7 261 26 433 24 785 281 78

SP6 5.7 10.7 64 5 31 13 138 50 216 3.2 355 23 68 3 777 67 16

SP7 7.4 10.8 75 116 46 15 53 56 147 7.2 336 20 259 18 940 421 33

SP10 7.9 17.5 87 7 52 13 118 109 266 14.1 292 29 157 11 783 144 41

SP11 6.2 15.5 83 8 57 14 130 55 242 5.9 342 23 146 10 840 117 40

SP12 8.1 18.6 106 11 51 14 103 54 257 6.7 322 24 208 13 782 140 46

SP13 10.6 18.2 140 10 72 18 51 49 217 11.3 306 23 232 23 754 260 60

SP15 10.3 14.4 133 12 104 19 58 128 203 18.7 271 26 417 15 837 260 72

112

The Harker variation diagram for trace elements of Pegmatites are shown

in Fig. 5.9. From the plot, it is observed that some decreases with the increase of

SiO2 (V, Zn, Ga, Sc, Ni, and Y) and showing negative relation with SiO2. A

positive correlation is observed between Cu, and Sr with SiO2.

In order to see the variation of trace elements within pegmatites with

respect to primitive mantle the trace element data is normalized by the primitive

mantle (data taken from McDonough and Sun 1995). The spider diagram of the

normalized trace elements is presented in figure 5.10. The pegmatites are

characterized by enrichment in Rb, Ba, Th, U, Sr, Zr, Pb, and Ga and are depleted

in Nb, Ni, Co, Sc, and Cr.

5.4.2 Amphibolite

For determination of trace elements in amphibolites 5 representative

samples were selected. The result of the trace elements analysis of the

amphibolite samples is shown in table 5.4. The amphibolite are characterized by

very high content of Chromium, Barium, Strontium, and Zirconium. The Cr

concentration is varying from 1028 to 1147 ppm with an average of 1091.9 ppm.

Cr/Ni ratio for the amphibolite remains between 3.09 to 3.95. The Ba. content

vary from 735 to 986 ppm with 824 ppm as an average. The Sr is always higher

than Rubidium. Rb/Sr value for the amphibolite is 0.51 to 1.96. Zr in also present

in higher concentration, which ranges from 416 to 500 ppm. The Y value for

pegmatites of Lokai-Indarwa varies from 35 to 49 ppm without much variation,

while Nb ratio for such rock varies from 18 to 32 ppm. Ga varies from 17 to 24

ppm. Concentration of V is also towards higher side with ranging from 161 to

264 ppm. The Sc/Ni ratios of the amphibolites vary from 0.051 to 0.119 ppm.

The Harker variation diagram for trace elements of amphibolites are

shown in Fig. 5.11. From the plot, it is observed that most of these elements

decreases with the increase of SiO2 (V, Zn, Ga, Sc, Co, Ni, Th, Rb, U, and Y )

and showing negative relation with SiO2. A positive correlation is observed

between Pb, Cu, and Sr with SiO2.

113

0

100

200

300

400

500

60.00 65.00 70.00 75.00

Cr

(pp

m)

SiO2 (wt %)

0

20

40

60

80

100

60.00 65.00 70.00 75.00

V (

pp

m)

SiO2 (wt %)

0

20

40

60

80

100

120

60.00 65.00 70.00 75.00

Zn

(p

pm

)

SiO2 (wt %)

0

100

200

300

400

500

60.00 65.00 70.00 75.00

Zr

(pp

m)

SiO2 (wt %)

0

200

400

600

800

1000

60.00 65.00 70.00 75.00

Ba

(p

pm

)

SiO2 (wt %)

0

50

100

150

200

250

300

350

400

60.00 65.00 70.00 75.00

Sr

(pp

m)

SiO2 (wt %)

0

5

10

15

20

60.00 65.00 70.00 75.00

Ga (p

pm

)

SiO2 (wt %)

0

2

4

6

8

10

12

14

60.00 65.00 70.00 75.00

Sc

(pp

m)

SiO2 (wt %)

Fig. 5.9 a. Harker variation diagram for trace elements in Pegmatites

114

0

5

10

15

20

60.00 65.00 70.00 75.00

Co (

pp

m)

SiO2 (wt %)

0

20

40

60

80

100

120

140

160

60.00 65.00 70.00 75.00

Ni

(pp

m)

SiO2 (wt %)

0

20

40

60

80

100

120

140

160

60.00 65.00 70.00 75.00

Pb

(p

pm

)

SiO2 (wt %)

0

20

40

60

80

100

120

140

60.00 65.00 70.00 75.00

Th

(p

pm

)

SiO2 (wt %)

0

50

100

150

200

250

300

60.00 65.00 70.00 75.00

Rb

(p

pm

)

SiO2 (wt %)

0

5

10

15

20

60.00 65.00 70.00 75.00

U (

pp

m)

SiO2 (wt %)

0

5

10

15

20

25

30

60.00 65.00 70.00 75.00

Nb

(p

pm

)

SiO2 (wt %)

0

5

10

15

20

25

30

35

60.00 65.00 70.00 75.00

Y (

pp

m)

SiO2 (wt %)

Fig. 5.9 b. Harker variation diagram for trace elements in Pegmatites

115

Fig. 5.10. Primitive mantle normalized plot for trace elements in Pegmatites

(Primitive mantle value taken from McDonough and Sun 1995)

0.001

0.01

0.1

1

10

100

1000

Rb Ba Th U Nb Sr Zr Y Sc Co Ni Cu Zn Ga Pb Cr V

Ro

ck/P

rem

itiv

e M

an

tle

SP2

SP3

SP4

SP6

SP7

SP10

SP11

SP12

SP13

SP15

116

1020

1040

1060

1080

1100

1120

1140

1160

0.00 20.00 40.00 60.00

Cr

(pp

m)

SiO2 (wt %)

0

50

100

150

200

250

300

0.00 20.00 40.00 60.00

V (

pp

m)

SiO2 (wt %)

0

50

100

150

200

250

300

350

0.00 20.00 40.00 60.00

Zn

(p

pm

)

SiO2 (wt %)

0

100

200

300

400

500

600

0.00 20.00 40.00 60.00

Zr

(pp

m)

SiO2 (wt %)

0

200

400

600

800

1000

1200

0.00 20.00 40.00 60.00

Ba

(pp

m)

SiO2 (wt %)

0

50

100

150

200

250

300

350

400

0.00 20.00 40.00 60.00

Sr

(pp

m)

SiO2 (wt %)

0

5

10

15

20

25

30

0.00 20.00 40.00 60.00

Ga

(p

pm

)

SiO2 (wt %)

0

5

10

15

20

25

30

35

0.00 20.00 40.00 60.00

Sc

(pp

m)

SiO2 (wt %)

Fig. 5.11 a. Harker variation diagram for trace elements in Amphibolite

117

0

10

20

30

40

50

60

70

80

0.00 20.00 40.00 60.00

Co (

pp

m)

SiO2 (wt %)

0

100

200

300

400

0.00 20.00 40.00 60.00

Ni

(pp

m)

SiO2 (wt %)

0

20

40

60

80

100

120

140

160

180

0.00 20.00 40.00 60.00

Pb

(p

pm

)

SiO2 (wt %)

0.00

10.00

20.00

30.00

40.00

50.00

0.00 20.00 40.00 60.00

Th

(p

pm

)

SiO2 (wt %)

0

100

200

300

400

500

0.00 20.00 40.00 60.00

Rb

(p

pm

)

SiO2 (wt %)

0

0.5

1

1.5

2

2.5

0.00 20.00 40.00 60.00

U (

pp

m)

SiO2 (wt %)

0

5

10

15

20

25

30

35

0.00 20.00 40.00 60.00

Nb

(p

pm

)

SiO2 (wt %)

0

10

20

30

40

50

60

0.00 20.00 40.00 60.00

Y (

pp

m)

SiO2 (wt %)

Fig. 5.11 b. Harker variation diagram for trace elements in Amphibolite

118

Table. 5.4. Trace elements analysis of amphibolites from Lokai Indarwa area (in ppm)

Sc

ppm

Co

ppm

Ni

ppm

Cu

ppm

Zn

ppm

Ga

ppm

Pb

ppm

Th

ppm

Rb

Ppm

U

ppm

Sr

ppm

Y

ppm

Zr

ppm

Nb

ppm

Ba

ppm

Cr

ppm

V

ppm

SHR1 22 35 342 52 97 17.73 44.6 36.60 178 2.08 347 35 455 18.1 857 1147 138

SHR2 21 39 331 30 106 22.12 36.4 46.8 267 1.92 306 42 437 22.2 776 1077 166

SHR3 18 37 351 14 135 22.47 - 42.3 401 2.08 204 40 500 22.0 735 1087 164

SHR4 31 35 260 9 331 24.00 48.7 16.4 313 1.58 177 49 416 32.3 986 1028 264

SHR5 20 41 344 8 121 21.09 27.2 46.7 378 1.97 196 39 454 21.2 768 1117 161

119

The primitive mantle normalized trace element spider diagram for the

amphibolites (Fig. 5.12) suggests the rocks are enrichment in Rb, Ba, Sr, Zr, Pb,

V and Ga and depleted in Nb, Ni and Cr.

5.5 RARE EARTH GEOCHEMISTRY

Rare earth elements are a group of elements with atomic number from 57

lanthanum (La) to71 lutetium (Lu), 14 of these elements occur naturally except

Promethium-Pm. Broadly for convenience the REEs are divided into two sub

groups: (1) Light rare earth elements (LREE), from La to Sm (i.e; lower atomic

numbers and masses). (2) Heavy rare earth elements (HREE), from Gd to Lu (i.e;

higher atomic numbers and masses). Very occasionally the term middle rare earth

elements (MREE) is loosely applied to the elements from about Sm to Ho

(Henderson, 1984). In nature all the rare earth elements exhibit a 3+-oxidation

state (trivalent), except Ce4+

(oxidized) and Eu2+

(reduced) under most geological

conditions.

The REE studies are becoming more interesting in working out coeval

petrogenetic conditions under which rocks are evolved. Different REE parameters

generally used in this contest are Europium anomaly (Eu/Eu*) and Eu/Sm,

La/Sm, Gd/Yb, Lan/Ybn, Lan/Lun, Cen/Ybn ratios etc. The europium anomaly can

be positive as well as negative. A positive anomaly represents cumulate; whereas

negative anomaly one means a fractional crystallization of plagioclase and its

removal could yield REE enriched and Eu- depleted liquids (Bowden and

Whitley, 1974). Europium is the only REE element, which occur in two states

(bi- and trivalent).

A basic observation with regard to rare earth elements is that the rare

earths elements of even atomic number are more abundant than their neighboring

odd atomic number counterparts. Due to this there is a major problem in

comparing rare earth abundance data. As such it is necessary to eliminate the

Oddo-Harkins effect. The most useful method is to compare data related to the

chondrites or sedimentary rock pattern, dividing the REE abundance element by

120

Fig. 5.12. Primitive mantle normalized plot for trace elements in Amphibolite

(Primitive mantle value taken from McDonough and Sun 1995)

0.001

0.01

0.1

1

10

100

1000

Rb Ba Th U Nb Sr Zr Y Sc Co Ni Cu Zn Ga Pb Cr V

Rock

/Pre

mord

ial

Man

tle

SHR1

SHR2

SHR3

SHR4

SHR5

121

Table 5.5. Rare earth element analysis of pegmatites and amphibolites (in ppm).

Amphibolite Pegmatite

Element SHR-1 SHR-2 SHR-3 SHR-4 SHR-5 SP 2 SP 3 SP 4 SP 6 SP 7 SP 10 SP 11

La 78.9 84.2 89.6 83 96 39.4 69.8 114.4 76.2 45.3 133.2 75

Ce 166 169 174 165.3 183.5 79 132 214 151 105 255.4 144

Pr 17.2 18.4 19 19.1 19.8 7.9 13.3 22.1 15 9.7 26.2 16.5

Nd 69.1 81.8 79.1 80.4 83.8 30.4 49.5 89.6 57.8 39 104.7 70

Sm 10.98 12.05 11.07 12.79 12.75 4.61 8.25 13.11 9.13 6.66 16.85 10.77

Eu 1.86 2.08 1.92 1.95 2.03 0.84 1.77 1.76 1.78 1.09 2.72 1.78

Gd 9.53 10.61 9.71 11.36 11.42 4.18 7.78 11.57 7.8 6.12 15.35 9.99

Tb 1.08 1.27 1.12 1.3 1.28 0.5 1.09 1.26 1.02 0.78 1.93 1.28

Dy 4.49 5.37 4.79 5.38 5.27 2.24 5.54 5.25 4.39 3.63 8.66 6.15

Ho 0.79 1 0.86 0.98 0.96 0.43 1.09 0.99 0.75 0.7 1.48 1.17

Er 2.15 2.7 2.38 2.5 2.6 1.15 2.65 2.76 1.77 1.89 3.57 2.93

Tm 0.29 0.37 0.33 0.32 0.35 0.17 0.35 0.39 0.21 0.28 0.44 0.39

Yb 1.76 2.32 2.04 1.95 2.17 1 1.95 2.49 1.1 1.75 2.46 2.14

Lu 0.3 0.39 0.34 0.32 0.36 0.18 0.29 0.43 0.17 0.28 0.36 0.35

122

the corresponding meteoritic or sedimentary rock abundances. This process was

first suggested by Coryell et al., (1963). It removes the even-z and odd-z

variations. Both of the relative patterns and concentration are compared to the

standard. number and also to discernible the extent Table 5.5 shows the rare earth

element data (ppm) in respect of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm,

Yb, Lu, Sc and Y for the pegmatites and amphibolite rocks of the present study.

In order to eliminate the abundance variation between rare earth elements of odd

and even atomic number and also to discernible the extentof any fractionation

amongst the REEs, the values of the pegmatites and amphibolites is normalized

with the Chondritic concentration (Haskins et al., 1968 and Nakamura, 1974).

The chondrite normalized REEs data is given in the Table 5.6.

5.5.1 Pegmatite

The pegmatite from the Lokai-Inderwa area are characterized by LREEs

enrichment over HREEs with (La/Lu)CN ranging from 16.66-46.18 ppm. The rare

earth concentrations in the analysed samples is ranging for Ce (79-255.4 ppm),

La (39.4- 133.2 ppm), Nd (30.4-104.7 ppm), Pr (7.9-26.2 ppm), Sm (4.61-16.85

ppm), Gd (4.18-15.35 ppm), Dy (2.24-8.66 ppm), Er (1.15-3.57 ppm), Yb (1.0-

2.49 ppm), Eu (0.84-2.72 ppm), Ho (0.43-1.48 ppm), Tm (0.17-0.44 ppm), Lu

(0.17-0.43 ppm) and Tb (0.5-1.93 ppm).

The chondrite normalized REEs pattern for the pegmatites from the Lokai

Indarwa area is given in Fig. 5.13. All the samples show typical chondrite

normalized REE slopping pattern with negative Eu anomaly. The pegmatites of

the area are typically characterized by negative anomaly with Eu/Eu* varying

from 0.43 to 0.63 ppm. The broad negative Eu anomaly suggest that the melting

of the source rock involved mostly feldspar and biotite to some extent. Le/Yb

ratio of the pegmatites is varying from 60.00 to 137.27 ppm.

123

5.5.2 Amphibolite

The analyzed data for the amphibolite is represented below. The

concentration of REE,s in decreasing order is presented below Ce (165.3-183.5

ppm), La (78.9-96.0 ppm), Nd (69.1-83.8 ppm), Pr (17.7-19.8 ppm), Sm (10.98-

12.79 ppm), Gd (9.53-11.42 ppm), Dy (4.49-5.38 ppm), Er (2.15-2.38 ppm), Eu

(1.86-2.08 ppm), Yb (1.76-2.32 ppm), Tb (1.08-1.28 ppm), Ho (0.79-1.0 ppm),

Lu (0.30-0.39 ppm), and Tm (0.29-0.37 ppm).

Chondrite normalized RRE pattern for the amphibolites is plotted in

figure 5.14. The negative Eu anomaly is prominent along with the enrichment of

light rare earth elements (LREEs) over light rare earth elements (HREEs). From

the analysis of the samples, it is seen that all the suites of the pegmatites and

amphibolites exhibit similar REE patterns.

124

Table. 5.6. Chondrite normalized data of REEs for pegmatites and amphibolites in ppm. (chondrite value after Haskin et al

1968 and Nakamura 1974).

Amphibolite

Pegmatite

SHR-1 SHR-2 SHR-3 SHR-4 SHR-5 SP 2 SP 3 SP 4 SP 6 SP 7 SP 10 SP 11

La 239.09 255.15 271.52 251.52 290.91 119.39 211.52 346.67 230.91 137.27 403.64 227.27

Ce 188.64 192.05 197.73 187.84 208.52 89.77 150.00 243.18 171.59 119.32 290.23 163.64

Pr 153.57 164.29 169.64 170.54 176.79 70.54 118.75 197.32 133.93 86.61 233.93 147.32

Nd 115.17 136.33 131.83 134.00 139.67 50.67 82.50 149.33 96.33 65.00 174.50 116.67

Sm 60.66 66.57 61.16 70.66 70.44 25.47 45.58 72.43 50.44 36.80 93.09 59.50

Eu 26.96 30.14 27.83 28.26 29.42 12.17 25.65 25.51 25.80 15.80 39.42 25.80

Gd 38.27 42.61 39.00 45.62 45.86 16.79 31.24 46.47 31.33 24.58 61.65 40.12

Tb 22.98 27.02 23.83 27.66 27.23 10.64 23.19 26.81 21.70 16.60 41.06 27.23

Dy 13.09 15.66 13.97 15.69 15.36 6.53 16.15 15.31 12.80 10.58 25.25 17.93

Ho 11.29 14.29 12.29 14.00 13.71 6.14 15.57 14.14 10.71 10.00 21.14 16.71

Er 10.75 13.50 11.90 12.50 13.00 5.75 13.25 13.80 8.85 9.45 17.85 14.65

Tm 9.67 12.33 11.00 10.67 11.67 5.67 11.67 13.00 7.00 9.33 14.67 13.00

Yb 8.80 11.60 10.20 9.75 10.85 5.00 9.75 12.45 5.50 8.75 12.30 10.70

Lu 8.82 11.47 10.00 9.41 10.59 5.29 8.53 12.65 5.00 8.24 10.59 10.29

125

Fig. 5.14. Chondrite-normalized REE abundance profile of Amphibolite

(Chondrite value taken from Haskin 1968, and Nakamura 1974)

Fig. 5.13. Chondrite-normalized REE abundance profile of Pegmatites

(Chondrite value taken from Haskin 1968, and Nakamura 1974)

1.00

10.00

100.00

1000.00

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Rock

/Ch

on

drit

e

SP 2

SP 3

SP 4

SP 6

SP 7

SP 10

SP 11

1.00

10.00

100.00

1000.00

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Rock

/Ch

on

drit

e SHR-1

SHR-2

SHR-3

SHR-4

SHR-5

126

CHAPTER-6

FLUID INCLUSIONS

MICROTHERMOMETRY

127

FLUID INCLUSIONS AND MICROTHERMAMETRY

The study of fluid inclusion in rocks and minerals goes back almost 1000

years, when these were first observed by ancient Greek and Roman Scientists

(Leeder et al., 1987). The importance of fluid inclusion studies began to be

realized soon after the detailed scientific description and interpretation of fluid

inclusion provided by Henry C. Sorby (1858). But the use of fluid inclusion in

scientific studies remained unfashionable until a half century ago when interest

revived.

Fluid inclusions are almost ubiquitous in geologic samples. It is,

therefore, fluid inclusion studies are applicable to a variety of geologic problems

and area. It has now been frequently used in solving geological problems

particularly related to ore genesis, gemmology, petrogenesis, mineralogenesis,

tectanogenesis and petroleum geology. In the study of ore deposits, fluid

inclusions have provided good information that has been used in many ways both

in immediate problems of understanding the physical and chemical conditions of

ore deposition and also for the problem of mineral exploration. Roedder (1972)

summarized a good account of the developments in the fluid inclusion studies.

In gemmology, the fluid inclusions have proven to be valuable defects.

Their studies are helpful not only in distinguishing natural from synthetic

gemstone but also help in gem identification either synthetic or treated, in the

exploration for gem deposits and also in deciphering the physico-chemical

conditions of the formation of the gemstones and recognizing the source of the

fluid.

Realizing the importance of fluid inclusion in the mineral genetic studies,

the samples of quartz and feldspar of pegmatites are subjected to homogenization

and cryogenic studies on the Linkam heating/freezing stage. The result of the

heating and freezing are presented in this chapter in order to understand the

P-V-T-X parameters of the fluid that gave rise to gemstone mineralization in the

pegmatites of the of mica belt.

128

6.1 SAMPLE PREPARATION AND INSTRUMENTATION

Samples of pegmatites from the present areas of study are selected for

studying fluid inclusions in some selected minerals (quartz and feldspar). The

selected samples are subjected to initial slicing; using a thin cutter. A profuse

supply of cold water was maintained to prevent damage to the inclusions due to

local heating and cracking. Further reduction in the thickness of the sections are

carried out by coarse grinding followed by the fine grinding on a glass using

various grades of silicon carbides. Flat thin sections of uniform thickness (200-

300µm), polished on both sides (known as doubly polished wafers), were

prepared for the fluid inclusions studies.

Microthermometric measurement of the fluid inclusions of pegmatite

were carried out on a pre-calibrated Linkam Heating and Freezing Stage (model

THMSG-600) mounted on the Nikon (model ECLIPSE E600-POL) microscope

with long working distance objectives. The heating and freezing stage (Linkam-

THMSG-600) is designed using platinum resistor sensor and provides a

temperature range of -190º to +600ºC. The heating element is cased into a silver

block to form an integral heater and sensor assembly. The THMSG-600 stage is

connected to the temperature programmer (TMS-94) by stage lead. The stage is

cooled using the LNP2 cooling systems which operate directly from a source of

unpressurised liquid nitrogen .

6.2 FLUID INCLUSION PETROGRAPHY

The foremost quest in the field of Fluid inclusion studies is giving details

about the petrography, as suggested by Kerkhof (2001) that the petrographic

microscopy of a rock sample is the first and essential steps of any fluid inclusion

study. A proper interpretation of the fluid inclusion can be made only when

textural relationship between the inclusions and the host mineral is considered.

The fluid inclusion petrography therefore, is carefully carried out for the present

study of the pegmatites in order to establish the textural relationship between the

129

inclusion and the host mineral. This also helps in selecting the suitable inclusion

for microthermometric measurements and also to classify the various fluid

inclusions present in the sample.

The fluid inclusions characteristics in pegmatites were studied under a

transmitted light microscope with high power magnification objectives, combined

with long focusing light and condenser below the sample.

6.2.1 Classification and Petrographic characteristics of the Fluid Inclusions.

A substantial number of fluid inclusions are present in the quartz and

feldspar from the pegmatites of study area. These inclusions belong to primary

(P), pseudosecondary (PS) and secondary (S) inclusions categories. These P, PS,

& S inclusions are the classes related with the timing of formation of the

inclusion relative to that of the host mineral. The identification of P, PS, and S

inclusions is based on the criteria suggested by Roedder (1981) and Kerkhof

(2001). The inclusions present in different samples are further classified, based

on the phases present within the inclusions at room temperature and their

composition, into five types as given below;

Type I Multiphase aqueous inclusions

Type II Multiphase aqueous-carbonic inclusions

Type III Type IIIa Biphase aqueous inclusions

Type IIIb Biphase aqueous with nitrogen inclusions

Type IV Biphase aqueous-carbonic inclusions

Type V Type Va Monophase carbonic inclusions

Type Vb Monophase nitrogen inclusions

A summary of the characteristics of these inclusions is given in the table 6.1.

130

Table 6.1: Classification of the Fluid inclusion from the area and their characteristics

Type of inclusion

I

II

III

IV

V

Name

Multiphase

aqueous

inclusions

Multiphase

aqueous-

carbonic

inclusions

Biphase inclusions

Biphase

aqueous-

carbonic

inclusions

Monophase inclusions

No. of optically

detectable phases

Multiphase

Multiphase IIIa

IIIb

Two Va Vb

Two Two One One

Type of phases

Solid, Liquid

and Vapour

Solid, Liquid

H2O Lq.CO2

Gas CO2

Liquid and

Vapour

Liquid and

Vapour

Lq. CO2 Gas

CO2 and Lq.

H2O

Gas

Gas

Liquid (L)

Vapour (V) ratio

L >V

L >V

L >V

L >V

L >G

……

……

Shape

Subrounded to

irregular

Subrounded to

irregular

Irregular

Elongated

Elliptical to

sub rounded

Semi-circular,

circular to

elliptical

Elongated

Size

5-15µm

5-12µm

5 to 25µm

5 to 20µm

5 to 25µm.

3 to 12 µm

3 to 15 µm

131

Type I (Multiphase aqueous inclusions)

The multiphase aqueous inclusions are characterized by the presence

of two daughter crystals along with aqueous liquid and vapour. These

inclusions are common in all the samples studied, and are present in both

quartz and feldspar minerals. They mainly occur as primary inclusions, mostly

as isolated inclusions (Fig. 6.1) and rarely as group. They show sharp and

regular boundaries of the cavities which are subrounded to irregular in shape.

However a few of them are also present as negative crystals shape. The size of

inclusions varies from 5-15µm. The daughter crystals are mainly halite,

however in rare cases sylvite is also present. The identification of daughter

crystals is done on their optical properties. Halite is cubic in shape while

sylvite shows globular form with corroded edges. Both are isotropic in nature.

They have variable ratio of liquid vapour and solid. The vapour is generally

ranging between 10-20% of the total volume. The size of daughter crystals

varies between 2-5 µm.

Type II (Multiphase aqueous-carbonic inclusions)

Type II inclusions are not very common as compared to Type I

Inclusion, and are found within quartz mineral only. They are distinguished

from type I inclusions by the occurrence immiscible CO2 during freezing

cycle. They are characterized by the presence of liquid CO2, gas CO2, and

liquid H2O with only one halite crystal (Fig. 6.2). They are subrounded to

regular in shape. Negative crystals are also seen. The size of inclusions varies

from 5-18µm.The mean ratio of V: S: L is 20:20:60.

Type III (Biphase inclusions)

These types of inclusions are present in quartz and feldspar minerals.

They are characterized by the presence of liquid and vapour phases. During

Raman Spectroscopy, a rare sub type of these inclusions has also been

132

recognized. Rarely some of the inclusions were found to contain nitrogen. On

the bases of the composition they are further sub classified as Type III-A and

Type III-B. Type III-A is mostly aqueous biphase inclusions while Type III-B

is containing additional N2 along with H2O. Visually, however, no change in

both type have been recognized. During freezing no visible CO2 phase were

noticed in these inclusions. In type III inclusions the liquid gas ratio is variable

but liquid is always more than vapour (Fig. 6.3). The shape of cavity is mostly

irregular. The size of these inclusions is highly variable ranging from 5 to

25µm.These aqueous inclusions consist of only two phases. These inclusions

are mostly present as isolated inclusions or in group. Some secondary

inclusions forming trails along the healed fractures are also present. The type

III inclusions are characterized by the higher liquid/vapour ratio. They contain

about 60 to 70% liquid and 30 to 40% vapour of the total inclusion volume.

These inclusions are commonly present with all other types of inclusions.

Type IV (Biphase aqueous-carbonic inclusions)

The Biphase aqueous-carbonic inclusions are abundant among all the

samples. The host mineral is quartz as well as feldspar. These are mainly

primary, pseudosecondary and secondary inclusions. The shape of inclusions

varies from elliptical to sub rounded. Some negative and irregular shapes are

also present. The size varies from 5 to 25µm. At ambient laboratory

temperature only two phases are present in these inclusions (Fig. 6.4). But on

freezing they show three phases. These are liquid CO2, gas CO2, and aqueous

liquid. The total CO2, volumetric proportion ranges from 10 to 60%. They

occur mostly with Type III inclusions.

Type V (Monophase inclusions)

In Monophase inclusion presence of only one phase is seen with 100%

gas. Based on Raman spectra two types of gases were identified in these

inclusions and hence classified as Type V-A as Monophase carbonic

inclusions and Type V-B as monophase nitrogen inclusions (Fig. 6.5). On the

133

Fig. 6.1. Multiphase aqueous inclusions.

10µm10µm

10µm10µm

10µm10µm

Fig. 6.2. Multiphase aqueous-carbonic

inclusions.

Fig. 6.3. Biphase aqueous inclusions. Fig. 6.4. Biphase aqueous-carbonic

inclusions.

Fig. 6.5. Monophase nitrogen inclusions. Fig. 6.6. Trail of monophase carbonic

inclusions.

134

freezing of Type V-A inclusions, they are found to be carbonic in nature. They

are common in the samples from the studied area, and are present in both

quartz and feldspar minerals. They occur with type III and type IV inclusions.

Their shape varies from circular to elliptical. The size of these inclusions

varies from 3 to 12 µm. Generally they are seen isolated but in

some samples trails are also seen (Fig. 6.6). Hence they are either primary or

secondary in origin.

6.3 MICROTHERMOMETRY

As the secondary inclusions are of no use for the present objectives of

the study, only primary and pseudosecondary inclusions were selected for the

microthermometric measurements. The inclusion which showed sign of

leakage or necking down effects were discarded. Samples which showed the

presence vary small size (dust like) inclusions were also discarded. Repeated

measurements showed the standard deviation of absolute temperature always

less than + 2.5°C for temperatures greater 100°C, and < 0.2°C for cryometric

measurements i.e, lower than 20°C. The freezing and heating results are

presented below.

6.3.1 Freezing Studies

The freezing is done in the Linkam-THSMG-600 stage by passing a

flow of Oxygen-free nitrogen gas through a copper coil immersed in a 2 liter

Dewar flask of liquid N2. In order to get the best results following steps were

adopted for freezing.

1. The selected inclusion is super cooled until it was completely frozen i.e.

content of the inclusion solidify.

2. The temperature was then allowed to rise gradually. The heating rate was

kept from 3ºC/minutes to 10ºC/ minutes.

3. The number of phases that were produced during the gradual heating were

observed and recorded.

135

Different cryogenic measurement made for the different types of inclusions

are described in the following paragraphs.

TYPE I

These inclusions were supercooled up to temperature of -120ºC to

trigger the solidification. Then these inclusions were heated slowly till first

melting take place. At this point temperature of first melting (Te) was noted. In

this type the Te ranges between -32.5°C to -38.4°C in quartz and -33.2°C to -

41.2°C in feldspar within the pegmatite from the study area. On further

heating the final melting was noted. This is temperature of melting of ice (Tm

ice) which ranges between -2.0°C to -8.9°C with average of 4.04°C in quartz

and -8.7°C to -11.8°C with average 10.18°C in feldspar. However since the

halite was also present in the fluid. This temperature may not be representing

the true temperature as hydrohalite might have been developed as was evident

by the melting temperature. The melting temperature in some of inclusions

were recorded up to +2°C. The freezing data of these inclusions is given in

Table 6.2. The graphical representation in form of the histogram of the

measurement for Tm ice and Te taken for the type I inclusions are shown in Fig.

6.7 and Fig 6.8.

Table 6.2: Freezing studies of the Type-I inclusions

Sample No. Host Mineral Te (in °C) Tm ice (in °C)

SLI-6 Feldspar -33.2 -9.1

ʺ ʺ -37.4 -11.8

SLI-8 Quartz -34.3 -2.4

ʺ ʺ -37.1 -8.9

SLI-4 ʺ -32.5 -1.9

ʺ ʺ -36.7 2.0

ʺ ʺ -38.4 -5.0


ʺ ʺ -41.2 -11.0

ʺ ʺ -34.0 -8.7

136

TYPE II

The freezing data of the type II inclusions is given in table 6.3. These

multiphase aqueous-carbonic inclusions exhibit the maximum number phases

transformation during the freezing because of their limited solubility between

H2O and CO2 at room temperature. These inclusions showed typical two

immiscible liquids namely as aqueous liquid and liquid CO2 with gas CO2 with

solid. The homogenization of CO2 was carried out as a part of freezing cycle.

The inclusions are supercooled up to -130°C to trigger the solidification. The

inclusion at this stage of the freezing comprises of solid CO2, CO2 vapour,

clathrate and ice. On gradual heating of these inclusions at first the liquid CO2

appeared and then solid CO2 completely melt between -66.2°C to -56.9°C.

Histogram for the melting of CO2 is given in Fig. 6.9. On further heating the

ice crystal are completely melted but vapour bubble remains distorted in

shape. The clathrate dissociates between -3.4°C to 5.0°C (Tm clath). Histogram

for the temperature of clathrate dissociation (Tm clath) is given in Fig 6.10. The

clathrate dissociation is linked with the sudden appearance in liquid CO2

around a perfectly round gas bubble rich in CO2. On Further warming the CO2

is homogenizing in to liquid phase between 19.9°C to 26.0°C (TH CO2).

Histogram for (TH CO2) is given in Fig. 6.11.

137

0

1

2

3

4

44 40 36 32

Fre

qu

ency

Te ( C)

Quartz

Feldspar

-44 -40 -36 -32

0

1

2

3

4

5

70 65 60 55

Fre

qu

ency

Tmco2 ( C)

Quartz

-70 -65 -60 -55

Fig. 6.8. Histogram showing temperature of first melting of Type I

0

1

2

3

4

15 10 5 0 5F

req

uen

cyTmice ( C)

Quartz

Feldspar

-15 -10 -5 0 5

Fig. 6.7. Histogram showing temperature of first melting of ice of Type I

Fig. 6.9. Histogram showing temperature of first melting of CO2 of Type II

138

Table 6.3: Freezing studies of the Type -II inclusions

Sample No Host

Mineral

Tm CO2

(in °C)

Tm Clath

(in °C)

TH CO2

(in °C)

SLI-3 Quartz -65.5 -1.9 22.2

ʺ ʺ -56.9 -2.1 24.6

ʺ ʺ -66.2 4.5 19.9

ʺ ʺ -65.6 5.0 24.0

ʺ ʺ -63.1 -3.4 23.0

ʺ ʺ -64.1 -2.9 23.1

ʺ ʺ -58.2 -1.9 26.0

SLI-1 Quartz -61.1 1.8 25.0

ʺ -63.2 2.0 20.0

SLI-2 Quartz -57.1 -1.5 22.0

ʺ -58.1 -1.1 21.0

TYPE III

In the freezing studies of these biphase aqueous inclusions, (Type-

IIIa) temperature was lowered up to -120°C until the whole aqueous phase

changes into solid phase (ice crystals). After the complete freezing the

temperature was gradually increased. The first liquid appeared between the

temperature (Te) ranges between -28.3°C to -45.3°C in quartz and -29.2°C to

-41.1°C in feldspar. At this temperature the inclusion was composed of liquid

+ ice and shows distortion in vapour bubble. The heating of these inclusions

was continued and the final ice melting was noted (Tm ice) between temperature

ranges of -3.5°C to -17.9°C in quartz and -7.2°C to -11.9°C in feldspar. The

freezing data of these inclusions given in the table 6.4. The graphical

representation in form of the histogram of the measurement for Tm ice and Te

for the type III inclusions are shown in Fig. 6.12 and Fig 6.13. Those inclusion

which don’t shows any changes after freezing below -140°C (Type-IIIb) were

studied by Raman spectroscopy.

139

Table 6.4: Freezing studies of the Type-III inclusions

TYPE IV

The freezing data of the Type IV inclusions is given in Table 6.5

These carbonic aqueous inclusions showed typical two immiscible liquids

namely an aqueous liquid and liquid CO2 with gas CO2. These inclusions

were supercooled up to -120°C to trigger the solidification. At this stage one

of the CO2 phase froze to form half moon shaped white mass of solid CO2

and darker portion as CO2 gas.

Sample No Host Mineral Te (in °C) Tm ice (in °C)


ʺ ʺ -30.1 -7.2

SLI-5 Quartz -45.3 -9.8

ʺ ʺ -43.9 -15.2

ʺ ʺ -40.1 -11.7

SLI-3 ʺ -33.1 -10.8

ʺ ʺ -32.1 -11.9


ʺ ʺ -35.2 -8.4

ʺ ʺ -41.1 -9.4

SLI-4 Quartz -33.4 -13.7

ʺ ʺ -31.7 -9.4

ʺ ʺ -28.3 -3.5

SLI-8 Quartz -41.8 -9.8

ʺ ʺ -38.9 -10.9

ʺ ʺ -45.3 -6.7

ʺ ʺ -43.9 -14.2

ʺ ʺ -42.8 -17.9

ʺ ʺ -42.0 -9.5

ʺ ʺ -38.6 -10.2

ʺ ʺ -39.3 -14.6

ʺ ʺ -41.2 -13.0

140

0

1

2

3

4

5

4 2 0 2 4 6

Fre

qu

ency

T m clath ( C)

Quartz

-4 -2 0 2 4 6

0

1

2

3

4

5

19 21 23 25 27

Fre

qu

ency

THco2 ( C)

Quartz

19 21 23 25 27

Fig. 6.10. Histogram showing temperature of first melting of clathrate of Type II

Fig. 6.11. Histogram showing temperature of homogenization of CO2 of Type II

Fig. 6.12. Histogram showing temperature of first melting of ice of Type III

0

1

2

3

4

5

6

18 14 10 6 2

Fre

qu

ency

Tm ice ( C)

Quartz

Feldspar

-18 -14 -10 -6 -2

141

Table 6.5: Freezing studies of the Type-IV inclusions

Sample

No

Host

mineral

Tm CO2

(in °C)

Tm clath

(in °C)

TH CO2

(in °C)

SLI-7 Feldspar -57.4 -1.8 21.4

ʺ ʺ -57.1 -2.0 23.4

SLI-6 Feldspar -55.9 -5.5 19.8

ʺ ʺ -56.0 -2.4 15.7

ʺ ʺ -56.8 -2.3 24.0

SLI-2 Feldspar -58.2 -3.0 26.2

ʺ ʺ -59.0 -5.7 20.7

ʺ ʺ -56.2 -4.3 18.4

SLI-8 Quartz -56.4 -2.4 26.7

ʺ ʺ -57.2 1.2 24.6

ʺ ʺ -58.8 -4.1 21.7

SLI-4 Quartz -56.1 1.5 18.0

ʺ ʺ -57.4 -4.0 19.4

SLI-5 Quartz -59.4 -2.5 23.4

ʺ ʺ -58.1 -1.3 25.9

ʺ ʺ -56.7 -4.9 26.3

The inclusions at this stage of the freezing comprised of solid CO2, CO2

vapour, clathrate and ice. The clathrate was identified by its optical property

of being colourless and isotropic. On heating at first the melting of CO2 took

place at a temperature range between -56.1° C to -59.4° C (Tm CO2) in quartz

and -55.9°C to -59.0°C in feldspar. On further heating the clathrate

dissociated between -4.9°C to 1.5°C (Tm clath) in quartz and -5.7 °C to -

1.8°C in feldspar. Histogram for the temperature of clathrate dissociation (Tm

clath) and temperature of first melting of CO2 is given in Fig 6.14 and 6.15.The

clathrate dissociation is linked with the sudden appearance in liquid CO2

around a perfectly round gas bubble rich in CO2. On Further warming the

CO2 was homogenizing (TH CO2) in to liquid phase between 15.7°C to 26.2°C

in feldspar and 18.0°C to 26.7°C in quartz, as shown in the form of histogram

in Fig. 6.16.

142

0

1

2

3

4

5

60 59 58 57

Fre

qu

ency

Tmco2 ( C)

Quartz

Feldspar

-60 -59 -58 -57 -56 -55

0

1

2

3

4

5

6 3 0 3

Fre

qu

ency

Tm clath ( C)

Quartz

Feldspar

6 3 0 3

0

1

2

3

4

5

6

7

8

50 45 40 35 30 25

Fre

qu

ency

Te ( C)

Quartz

Feldspar

-50 -45 -40 -35 -30 -25

Fig. 6.13. Histogram showing temperature of first melting of Type III

Fig. 6.14. Histogram showing temperature of first melting of clathrate Type IV

Fig. 6.15. Histogram showing temperature of first melting of CO2 of Type IV

143

TYPE V

Type-Va, inclusions were supercooled upto temperature of -120.0°C to

trigger the solidification.

Table 6.6: Freezing studies of the Type-V inclusions.

Sample No Host mineral Tm CO2 (in °C)

SLI-8 Quartz -56.3

ʺ ʺ -59.0

ʺ ʺ -58.7

SLI-7 Feldspar -57.1

ʺ ʺ -56.2

SLI-4 Quartz -56.2

ʺ ʺ -57.1

SLI-3 Quartz -57.3

ʺ ʺ -57.4

ʺ ʺ -55.1

ʺ ʺ -58.0

SLI-5 Quartz -56.4

ʺ ʺ -57.3

ʺ ʺ -55.7

ʺ ʺ -58.7

At this stage the inclusions contain only freezed CO2 solid. Then the inclusion

is heated slowly till CO2 liquid appeared for the first time and CO2 melting

temperature (Tm CO2) was noted. At this stage the bubble of CO2 gas existed

with the liquid CO2. In this type of inclusions the Tm CO2 ranges between -

55.1°C to -59.0°C in quartz and 57.1°C to 56.2°C in feldspar. The freezing

data of these inclusions is given in table 6.6 and histogram for melting of CO2

is given in Fig. 6.17.

144

0

1

2

3

4

5

6

7

8

61 59 57 55

Fre

qu

ency

Tmco2 ( C)

Quartz

Feldspar

-61 -59 -57 -55

0

1

2

3

4

5

120 150 180 210 240

Fre

qu

ency

TH

Quartz

Feldspar

15 18 22 26 30

0

1

2

3

4

5

6

7

130 150 170 190 220

Fre

qu

ency

Tds

Quartz

Feldspar

130 150 170 190 220

Fig. 6.16. Histogram showing temperature of homogenization of CO2 of Type IV

Fig. 6.17. Histogram showing temperature of melting of CO2 of Type V

Fig. 6.18. Histogram showing temperature of dissolution of halite of Type I

145

Type-Vb, these inclusions did not completely freezed even upto -

140°C suggesting presence of N2 or some hydrocarbons. The Raman spectra

in such inclusions confirmed presence of N2 into it.

6.3.2 Heating Studies

The heating studies were carried out on all the types of inclusions

obtained in the quartz and feldspar from both areas of study. After every

homogenization test, the temperature was gradually lower down to check the

reappearance of the bubbles in its original form. The rate of heating was kept

at 10°C to 15°C per minute, to get uniform heating. The homogenization data

was checked at a heating rate of 1°C to 5°C per minute to minimize the

recording error. Repeated measurements were undertaken to minimize the

error in data. The results of the homogenization tests for inclusions are

discussed in the following pages.

Type I

These inclusions contain one or more daughter crystals; therefore

during heating of these inclusions, care was taken to observe the dissolution

behavior of each daughter crystal, apart from the total homogenization of

fluid. The result for the Type I inclusions is given in Table 6.7.

Dissolution temperature of solid Tds (Halite) ranges between 139.3°C

to 196.2°C with mean temperature of 170.9°C for quartz and 168.1°C to

171.4°C with mean temperature of 169.8°C for feldspar. The total

homogenization temperature of these inclusions ranges between 185.0°C to

310.0°C with mean temperature of 256.1°C in quartz and 280.0°C to 315.0°C

with mean of 298°C in feldspar. In some inclusions vapour bubble disappeared

before daughter crystal. The histogram of the dissolution temperature of solid

(Tds) Fig. 6.18 with a peak between 170°C to 190°C. The complete

homogenization temperature of these inclusions is shown in Fig. 6.19 with a

peak between 270°C to 300°C.

146

Type II

These inclusions consist of halite daughter crystal with liquid and

vapour. During the heating of these inclusions, the dissolution of daughter

crystal and the homogenization of inclusions were considered. Their results

are listed in Table 6.8.

Table 6.7: Heating studies of the Type-I inclusions.

The dissolution temperature of halite (Tds) in these inclusions range from

182.0°C to 222.0°C. All the multiphase inclusions were homogenized into

liquid phase and daughter crystal disappear before disappearance of bubble.

The total homogenizing temperature of these inclusions ranges from 198.0°C

Sample

No.

Host

mineral

Tds Halite

(in °C)

TH

(in °C)

Homogenizat

ion Phase

SLI-8 Quartz 196.2 280.6 Liquid

ʺ ʺ 173.4 230.0 ʺ

ʺ ʺ 140.1 307.0 ʺ

ʺ ʺ 152.2 243.4 ʺ

ʺ ʺ 165.4 210.8 ʺ

SLI-6 Feldspar 171.4 280.0 Liquid

ʺ ʺ 169.2 295.0 ʺ

ʺ ʺ 170.4 310.0 ʺ

SLI-4 Quartz 184.1 295.0 Liquid

ʺ ʺ 139.3 185.0 ʺ

ʺ ʺ 169.2 236.3 ʺ

ʺ ʺ 195.5 310.0 ʺ

ʺ ʺ 172.9 210.0 ʺ

ʺ ʺ 174.4 270.9 ʺ

ʺ ʺ 177.2 270.0 ʺ

ʺ ʺ 182.4 280.1 ʺ

SLI-10 Feldspar 170.3 315.0 ʺ

ʺ ʺ 168.1 290.0 ʺ

147

0

1

2

3

4

5

6

180 210 240 270 300 330

Fre

qu

ency

TH ( C)

Quartz

Feldspar

180 210 240 270 300 330

0

1

2

3

4

5

6

7

8

180 190 200 210 220 230

Fre

qu

ency

Tds ( C)

Quartz

180 190 200 210 220 230

0

1

2

3

4

5

6

190 200 210 220 230 240

Fre

qu

ency

TH ( C)

Quartz

190 200 210 220 230 240

Fig. 6.19. Histogram showing temperature of homogenization of Type I

Fig. 6.20. Histogram showing temperature of dissolution of halite of Type II

Fig. 6.21. Histogram showing temperature of homogenization of Type II

148

to 233.0°C. Most of these inclusions shows homogenizing temperature

between 190.0°C to 210.0°C. The histogram of the dissolution temperature of

solid (Tds) and the complete homogenization temperature of these inclusions

is given in Fig. 6.20 and 6.21.

Table 6.8: Heating studies of the Type-II inclusions

Type III

The aqueous biphase inclusions are present in the quartz and feldspar

from both areas. Mostly the inclusions homogenize in liquid phase, between

temperature range of 100.1°C to 301.1°C in quartz and 175.6°C to 280.4°C in

feldspar. A summary of the heating data for Type III inclusion is given in

Sample

No.

Host

Mineral

Tds Halite

(in °C)

TH

(in °C)

Homogenization

Phase

SLI 3 Quartz 186.0 199.0 Liquid

ʺ ʺ 190.7 200.0 ʺ

ʺ ʺ 200.0 222.0 ʺ

ʺ ʺ 208.0 226.0 ʺ

ʺ ʺ 222.0 233.0 ʺ

ʺ ʺ 211.0 232.0 ʺ

ʺ ʺ 197.0 207.0 ʺ

SLI-2 Quartz 195.6 215.0 ʺ

ʺ ʺ 210.0 222.8 ʺ

ʺ ʺ 200.7 217.6 ʺ

ʺ ʺ 198.4 207.0 ʺ

SLI-1 Quartz 182.0 198.0 ʺ

ʺ ʺ 191.7 205.2 ʺ

ʺ ʺ 198.4 210.0 ʺ

ʺ ʺ 210.0 224.0 ʺ

ʺ ʺ 194.2 215.8 ʺ

ʺ ʺ 189.0 205.6 ʺ

149

Table 6.9. The complete data set for Type III inclusions is given in Appendix-

I. The maximum samples falling between 190.0°C to 220.0°C range in

feldspar and 100.0°C to 130.0°C range in quartz. The histogram showing TH

values for Type-III inclusions is given in Fig. 6.22.

Type IV

The homogenization data of Type IV inclusions is summarized in the

Table 6.10 and detailed in Appendix-II. The temperature of homogenization of

CO2 is described under freezing studies heading. In this type all inclusions

homogenize into liquid phase between temperature range of 129.2°C to

288.5.0°C for quartz with average 182.40°C and 130.2°C to 250.1°C with a

average of 206.17°C for feldspar. The histogram showing TH values for Type-

IV inclusions is given in Fig. 6.23.

Table 6.9: Heating studies of the Type-III inclusions

Type V

For the CO2 bearing monophase inclusions the first melting

temperature and homogenization of CO2 phase obtained during freezing

experiment and is already discussed under the freezing study. On heating no

phase changes are observed

Sample

No.

Host

Mineral

No. of

Inclusions

TH in °C Homogenization

Phase Min. Max.

SLI-3 Quartz 7 172.9 235.0 Liquid

SLI-5 ʺ 10 200.4 301.1 ʺ

SLI-8 ʺ 12 100.1 161.9 ʺ

SLI-4 ʺ 4 180.2 220.4 Liquid

SLI-10 Feldspar 3 175.6 210.1 ʺ

SLI-9 ʺ 5 198.1 280.4 ʺ

150

0

2

4

6

8

10

12

100 130 160 190 220 250 280 310

Fre

qu

ency

TH ( C)

Quartz

Feldspar

100 130 160 190 220 250 280 310

0

1

2

3

4

5

6

120 150 180 210 240 270 300

Fre

qu

ency

TH ( C)

Quartz

Feldspar

120 150 180 210 240 270 300

Fig. 6.23. Histogram showing temperature of homogenization of Type IV

Fig. 6.22. Histogram showing temperature of homogenization of Type III

151

Table 6.10: Heating Studies of the Type-IV inclusions.

6.4 RAMAN SPECTROSCOPY

Raman spectroscopy is an advanced tool for determining the

composition of the fluid inclusions (solid, liquid and gas) and visualizes the 3-

D shape of the inclusions for fast confocal volume imaging. A Raman system

coupled to a confocal microscope is required to obtain high spatial resolution

and to analyze inclusion located below the surface without destruction.

6.4.1 Sample and method

The Raman spectra were obtained on the uncovered and uncoated

wafers used for fluid inclusion studies, Raman analysis as well as for studying

the textural relationship between grains.

The Raman spectroscopy work for fluid inclusions is carried out at the

Laser Micro Raman Spectroscopy Laboratory of Wadia Institute of Himalayan

Geology, Dehradun. Horibe JY-Lab Ram HR Raman Spectrometer equipped

with edge filters is used for the Raman probe, The instrument is fitted with

confocal optics, 1800 and 600 lines nm grating, 1024×256 pixels

multichannels motarized stage and lab specification software. The Olympus

BX41 microscope is used to focus the excitation 514.4 nm argon ion laser

Sample

No.

Host

Mineral

No. of

Inclusions

TH in °C Homogenizat

ion Phase Min. Max.

SLI-4 Quartz 5 177.7 241.1 Liquid

SLI-5 ʺ 5 251.8 288.5 ʺ

SLI-8 ʺ 7 129.2 191.2 ʺ

SLI-2 Feldspar 3 181.1 210.2 ʺ

SLI-6 ʺ 6 130.2 225.1 ʺ

SLI-7 ʺ 4 148.0 220.1 ʺ

152

beam on the samples. The Raman signals are collected as backscattered beam

which are allowed to pass through the filters and then to the spectrometer, and

are collected in the detector. The conofocal arrangement by pinhole helps in

the focusing with a 100X objective. Labspec software is used to control the

instrument, manage and process the data and obtaining the Raman analysis

(calculation of peak position, peak intensity, band area, and band width). Two

types of inclusions, Type-IIIb and Type-Vb were analysed by Raman Probe for

studying their compositions.

6.4.2 Micro Raman Spectroscopy of Fluid inclusions

For analyzing the composition of some of the fluid inclusion Raman

spectroscopy technique was used. Those inclusion which does not shows any

changes in freezing studies despite lowering the temperature upto -140°C were

selected. Two type of inclusions, biphase and monophase classified as, Type-

IIIb and Type-Vb shows presence of nitrogen in addition to aqueous (water)

and pure nitrogen. These inclusion were found in quartz mineral within

pegmatites from the study area. This type of inclusion occurs in groups with a

heterogeneity distribution. They are around 5-15 μm in size, elliptical or

nearly circle in shape, and grows along the crystal zones of quartz grains

without orientation and co-existed with vapor-liquid inclusions, implying

these inclusions were captured with those vapor-liquid inclusions at the same

time. Moreover, there are not any N2 inclusions were found nearby the micro-

fracture in quartz grains, indicating the pure nitrogen inclusion are primary

inclusions.

The results of analyses shows that there are three major peaks, the

prominent peak belongs to the host mineral quartz, second high intensity peak

is the peak of nitrogen and third one is the H2O peak (Fig. 6.24). Apart from

this there are few monophase inclusions with 100% nitrogen. The peak value

for this type of inclusion varies between 2328.9 and 2331.8λ (cm-1

) (Fig.

6.25), which suggest belonging to the nitrogen peak. The H2O peaks on

spectrogram comes around 3430λ (cm-1

) (Fig. 6.26). The Raman signal of

153

liquid H2O is very broad and changes its shape depending on temperature and

salinity of the solution. Due to comparably low Raman intensity nitrogen is

usually not a dominant gas species in fluid inclusions. The analysis results

indicats the composition of this type inclusion is dominated by nitrogen with

minor H2O.

154

Fig. 6.24. Raman spectral peaks of Type IIIb

Fig. 6.25. Raman spectral peaks of N2

Fig. 6.26. Raman spectral peaks of H2O

N2

H2O

Quartz

N2

H2O

155

CHAPTER-7

DISCUSSION

156

DISCUSSION

The Great Mica Belt of Jharkhand and Bihar is one of the best field

laboratories for carrying out work on pegmatites. Numerous mineral

prospectors and mining companies have been exploiting the area for world

class ruby mica for more than one and half centuries. The large number of

unattended underground mine openings and artisanal mines are available in

area. This offers a unique opportunity to study the different kind of zoned and

unzoned pegmatites for their mineral potential and genesis. Mahadevan (1967)

have classified the pegmatites of Great Mica Belt into four categories:

1) Pegmatite occurring within granitic rocks;

2) Pegmatite occurring within schistose country rock;

3) Pegmatite occurring along fracture planes, and

4) Pegmatite occurring within metamorphic rocks.

The Pegmatites which occur within the granitic rock are generally present as

segregated masses, nests and dikes in the granitic rocks. They are both

unzoned and zoned pegmatite. These are mainly containing biotite and

occasionally ruby mica. The pegmatites within the schistose country rock are

generally ill defined coarse grained bodies. They are mostly unzoned and

consist mostly of quartz, perthite, plagioclase, biotite, tourmaline and

muscovite. The third type of pegmatites generally consists of sillimanite,

muscovite, quartz and subordinate amount of plagioclase. The most important

pegmatites from economic point of view are the fourth type. These types of

pegmatite occur as concordant or discordant bodies within the metamorphic

rocks. They are varying in their length from few cm to approximately 500 mts.

With few cm to more than 25 mts in width.

The present study, however, recognized a fifth kind of pegmatitic body

in the area for the first time. These pegmatites are present within the mica

schist and amphibolites. They are intruded along the foliation planes of the

mica-schist and along fractures in the amphibolites. It is mostly plagioclase

rich with less quantity of quartz and alkali feldspar. The other minerals are

biotite and apatite. The thickness of such pegmatite veins are of few cm only.

But they are numerous in Lokai- Indarwa area. Some of these pegmatites are

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enriched in blue sheen plagioclase feldspar, commercially known as

moonstone.

The artisanal mine present in the Lokai-Indarwa area provided an

excellent opportunity to understand the gemmological characteristics of the

moonstone as well as to understand the genesis of this new type of plagioclase

rich pegmatites of Great Mica Belt. The geological setting, petrographic

features of the rock types, variation in their chemical as well as mineralogical

composition, gemmological characteristics and microthermometry of fluid

inclusions have been described in preceding chapters. These results reveals

interesting and significant features of the gem bearing pegmatites which throw

light on some fundamental genesis problems for these kind of pegmatites. In

the present chapter the synthesis of the data generated in the present research

work is done to understand the genesis of moonstone bearing pegmatite of

Lokai-Indarwa area of Great Mica Belt. An attempt has also been made to

evaluate the gemstone potential of the area.

Many workers have proposed different theories for the genesis of

pegmatites, present on global level. A synthesis of the global data on

pegmatite will help to understand the genesis of pegmatites from any area.

Keeping this in mind the various modals suggested by different workers is

been given in this chapter. The physico-chemical conditions for the formation

of gemstone (moonstone) are also discussed in the following paragraphs along

with gemstone resource of the area. The genesis of the moonstone bearing

pegmatites is also discussed in following paragraphs by considering, major

and trace elements composition of the rock.

7.1 Models for the genesis of Pegmatites

Generally “pegmatites” is a rock with giant grain size. The terms

“granitic”, “alkaline”, “basic” or others, allow a better comprehension of the

nature of the pegmatitic rock. What typifies the world’s most famous

pegmatites is a combination of gigantic crystal size and extreme enrichment of

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rare elements. However, pegmatites actually have the greatest range of grain

sizes known in any rock type, from sub-millimeter to tens of meters.

Pegmatitic textures can develop in any intrusive igneous rock type from

ultramafic, to granitic, to syenitic in composition. Most commonly, the term is

used to refer to granitic pegmatites and is generally understood to refer to rock

of overall granitic composition when it is used without a qualifying adjective

(e.g. gabbroic pegmatite). Granitic pegmatites are composed predominantly of

quartz and feldspars with accessory mica.

For over a half century, different workers have made a significant

advances in the understanding of the genesis of pegmatites (Jahns and Tuttle,

1963; Jahns and Burnham, 1969; Jahns,1982; London, 1986, 1996, 2005;

Webber et al., 1997; Simmons, 2007). Although no universally accepted

model of pegmatite genesis has yet emerged that satisfactorily explains all the

diverse features of pegmatites. During early periods of work on the genesis of

pegmatites i.e. during seventies the most widely accepted model of pegmatite

genesis suggested that pegmatites formed by equilibrium crystallization of

coexisting granitic melt and hydrous fluid at or slightly below the hydrous

granite liquidus (Jahns and Burnham, 1969). More recently, the detailed

mineralogical, geochemical and experimental investigations and experimental

studies have led to a much improved understanding of the details of pegmatite

genesis (Cerny, 2005 and London, 2005).

Much of the work has been concentrated around the granitic

pegmatites but other types have also been studied. Most researchers favoured

the genesis of pegmatites from residual melts derived from the crystallization

of granitic plutons. Incompatible components, fluxes, volatiles and rare

elements, are enriched in the residual melts. The presence of fluxes and

volatiles, which lower the crystallization temperature, decrease nucleation

rates, melt polymerization and viscosity, and increase diffusion rates and

solubility, are considered to be critical to the development of large crystals

(Simmons and Webber 2008). Some of the popular models for the genesis of

pegmatites are discussed in following paragraphs.

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7.1.1 The Early Models

During early periods, Jahns, (1955) published a good review work on

pegmatites covering every conceivable mechanism to explain pegmatites. The

most widely held view in earlier time, which can be traced to Brogger (1890),

is that the distinctive features of pegmatites arise from the interplay of

coexisting silicate melt and water vapor. Jahns and Tuttle (1963) cited

experimental laboratory studies as confirmation of the essential role of water

vapor in the formation of pegmatite. Jahns’ model that changed over time,

however, was the role of a thermal gradient in promoting the segregation of

alkalis. Jahns gradually came to accept that fractionation of alkalis between

melt and vapor is an intrinsic feature of closed granitic melt-vapor systems at

equilibrium (Jahns, 1982). However the most popular model for the origin of

pegmatites was proposed by Jahns and Burnham (1969). The works of Jahns

became the fundamental precept of the Jahns and Burnham (1969) model. One

of the important features of this model is about the incongruent fractionation

of K over Na into an aqueous fluid phase in a closed granitic system close to

equilibrium. This has not been corroborated by several experimental programs

employing various methods with pure and saline aqueous fluids. London

(1992, 1996, 2005) raised and discussed other problematic features of the

Jahns model, which include numerous and significant discrepancies in the

vertical zoning sequence and the distribution of Na- and K-rich domains

within pegmatite dikes (London, 1985).

7.1.2 The Recent Models

In last 25 years significant changes in the understanding of the

pegmatite genesis has taken place. Much of the work is based on the

experimental works of different workers (Cerny, 1985, London, 2004;

Simmons et al, 1987, 2003, 2005, 2012; Cerny et al, 2012 and Thomas and

Devinson, 2012). Many researchers suggested that pegmatites crystallize at the

temperature of the water-rich granite solidus, near 650-700 °C (London,

2004). The proposed temperatures of the final stages of pegmatite

160

crystallization have declined over the last few decades. The Jahns model

suggested that pegmatites crystallize at or near the hydrous minimum melt

temperatures of about 600 °C (Jahns & Burnham, 1969). Based on stable

isotopic studies, Taylor et al. (1979) proposed temperatures of emplacement of

pegmatite melts at about 700 °C to final temperatures of 525 °C. Two-feldspar

thermometry using reintegrated perthite compositions from the intermediate

zones of pegmatites in the South Platte, Colorado NYF district gave

temperatures of 550-500 °C (Simmons et al., 1987). Two-feldspar

thermometry of feldspars showing no evidence of exsolution from the little

three pegmatite, California (Morgan & London, 1999) gave temperatures of

∼400-435 °C near the margins to 350-390 °C near the pegmatite pocket zone

and a sharp decrease to 240-275 °C in the pockets where K-feldspar is

perthitic ( Nabelek et al. 1992 a,b) reported equilibration temperatures of

about 350 °C for coexisting quartz and K-feldspar in the cores of several

Black Hills, South Dakota, pegmatites. Sirbescu & Nabelek (2003 a,b) suggest

that the Li-bearing Tin Mountain pegmatite, Black Hills, South Dakota,

crystallized from fluid rich, compositionally complex melts at ∼400-350 °C

with the low crystallization temperatures resulting from the combined fluxing

effects of Li, B, P, H2O and carbonate anions. Their determinations are based

on microthermometric data on primary fluid inclusions cogenetic with

crystallized-melt inclusions.

The role of fluxes in the crystallization of pegmatites has been

demonstrated by experimental work which has shown that water saturation is

neither necessary nor likely in the early crystallization of pegmatites (London,

1992, 2005). Some fluxes such as B, F, P and Li in addition to H2O play a

critical role in the formation of rare element pegmatites by lowering the

crystallization temperature, decreasing nucleation rates, decreasing melt

polymerization, decreasing viscosity, increasing diffusion rates, and increasing

solubility (Simmons et al. 2003; London, 2005). The experimental work has

shown that water saturation, as proposed by Jahns & Burnham (1969) is

neither necessary nor likely in the early crystallization of pegmatites

(London,2005). The fluxes act as network modifiers that prevent or hinder the

formation of nuclei and increase the diffusion rates of ions to the few nuclei

161

that do survive and begin to grow. Thus, network modifiers act to prevent

nuclei formation and at the same time increase the effectiveness of diffusion.

These two effects combine to facilitate ion migration over greater distances

and promote the growth of the few nuclei that do manage to form, resulting in

fewer, much larger crystals.

One of the most important indicators in understanding the genesis of

pegmatites has been found in the melt inclusions. These melt inclusions (MI),

are small blebs of melt that are trapped in crystallizing minerals at magmatic

temperatures and pressures that become essentially solid at surface

temperatures, may record parental melt compositions at the time of host

mineral growth (Roedder, 1979, 1984; Lowenstern, 1995) and they may

monitor the chemical changes of the residual liquid during magma evolution

(Pettke, 2006). Fluid inclusions (FI) entrap fluid that remains in large part

fluid at surface temperatures (Roedder, 1984). Recent studies pertaining to FI

and MI are extensive (e.g. Lowenstern, 1995, 2003; Sobolev, 1996;

Peretyazhko et al., 2000; Hauri et al., 2002; Bodnar & Student, 2006). Many

additional references pertaining to igneous systems can be found in Roedder

(1984, 2003), Samson et al. (2003) and Kontak et al. (2004). Challenges

involved in interpreting MI from felsic plutons are discussed in detail by

Webster & Thomas (2006). The study of MI has advanced tremendously with

the advent of sophisticated and accurate analytical techniques enabling the

study of volatile-rich phases in igneous rocks (Thomas et al., 2005 for a

discussion of MI analytical techniques). Thomas et al. (2006a) and Veksler &

Thomas (2002) suggest that evidence for the stable coexistence of three

immiscible phases-alumino silicate melt, hydrosaline melt.

London (2005) have suggested that model based on high viscosity of

the pegmatite-forming medium (supercooled silicate liquid, gel, or glass)

explains why granitic pegmatites are far more common than those of basic or

alkaline composition. According to this the higher viscosity of granitic liquids

inhibits the diffusion necessary to nucleate crystals, as evidenced by long

incubation times before the onset of crystallization in silicic melts. The higher

viscosity of melt also impedes the diffusion of excluded components back into

162

the melt and hence makes boundary layer formation more likely. When

crystallization finally commences, granitic melts tend to be farther below their

liquidus temperatures, and pegmatitic fabrics are the result. Fluxes are

important to the process, and the more these can be concentrated in boundary

layers, as opposed to dispersed or lost from the pegmatite body, the more

effective they become.

7.2 Classification of Pegmatite

Modern pegmatite classification schemes are strongly influenced by

the depth-zone classification of granitic rocks (Buddington, 1959 and

Ginsburg et al., 1979). It categorized pegmatites according to their depth of

emplacement and relationship to metamorphism and granitic plutons. Černy

(1991) revision of that classification scheme is the most widely used

classification of pegmatites today (Table 7.1) where he classified the

pegmatites according to their depth of emplacement, metamorphic grade and

minor element content into four main categories or classes which are further

subdivided into types and subtypes according to the

mineralogical/geochemical characteristics. The classification has provided

insight into the origin of the melts and relative degrees of fractionation.

Another important contribution of the classification is the petrogenetic

component of the classification, which shows the association of LCT

pegmatites with mainly orogenic plutons, and NYF pegmatites with mainly

anorogenic plutons. Recently, Cerny and Ercit (2005) published a new

revision of the Cerny (1991) classification. They propose a number of changes

that address NYF pegmatite classification and a petrogenetic classification of

pegmatites derived from plutons (Table 7.2). According to this classification

the pegmatite of Muscovite class are largely conformable to, and in part

deformed with, host rocks of amphibolite facies (Table 7.2). Such pegmatites

are generally formed directly by partial melting (Shmakin & Makagon 1972,

Gorlov 1975, Sokolov et al. 1975) or by very restricted extent of

differentiation of palingenetic granites (Bushev 1975, Gordiyenko & Leonova

1976, Ginsburg et al. 1979, Shmakin 1976). The modern petrogenetic studies

based on isotopic evidence are, however, not available for this pegmatite class

(Cerny and Ercit, 2005). Sometimes enclosed relics of unaltered metamorphic

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Table 7.1. The pegmatite classification scheme of Cerny (1991).

Class Family Typical Minor

Elements

Metamorphic

Environment

Relation

to Granite

Structural

Features

Examples

Abyssal _ U, Th, Zr, Nb, Ti,Y,

REE, Mo

Poor (to moderate)

mineralization

(upper amphibolites

to) low- to high- P

granulite facies

~4-9 kb

~700-800°C

none

(segregations of

anatectic leucosome)

conformable to

mobilized cross-

cutting veins

Rae and Hearne

Provinces, Sask, Aldan and Anabar

Shields, Siberia Eastern Baltic

Shield

Muscovite _ Li, Be, Y, REE, Ti, U

Th, Nb>Ta

Poor (to moderate)

mineralization, micas

and ceramic minerals

High-P, Barrovian

amphibolites facies

(kyanite-sillimanite)

~5-8 kb

~650-580°C

none (anatectic

bodies) to marginal

and exterior

quasi-conformable

to cross-cutting

White Sea region, USSR,

Appalachian, Rajashtan, India

Rare- Element LCT Li, Rb, Cs, Be, Ga,

Nb<, >ta, Sn, Hf, B, P,

F

Poor to abundant

mineralization,

gemstock industrial

minerals

low-P, Abukuma

amphibolites to upper

greenschist facies

(andalusite-

sillimanite)

~2-4 kb

~650-500°C

interior to marginal

to exterior

quasi-conformable

to cross-cutting

Yellowknife field, NWT, Black

hills, South Dakota, Cat-lake-

Winnipeg River field, Manitoba

NYF Y, REE, Ti, U, Th, Zr,

Nb>Ta, F

Poor to abundant

mineralization, ceramic

minerals

Variable interior to marginal interior pods

conformable to

cross-cutting

exterior bodies

Llano Co., Texas, South Platte

district, Colorado, Western Keivy,

Kola USSR.

Miarolitic NYF Be, Y, REE, Ti, U, Th,

Zr, Nb> Ta, F

Poor mineralization,

gemstock

shallow to sub-

volcanic

~1-2 kb

interior to marginal interior pods and

cross-cutting dikes

Pikes Peak, Colorado, Sawtooth

batholiths, Idaho, Korosten pluton,

Ukraine.

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Table. 7.2 The pegmatite classification scheme of Cerny and Erict (2005).

assemblages are present in these pegmatites. This along with lack of fractionation

indicate that the conditions of magma generation, intrusion (if any) and pegmatite

consolidation were very close to those of the metamorphic grade of the high

Class Subclass Type Subtype

Abyssal (AB) AB-HREE

AB-LREE

AB-U

AB-BBe

Muscovite (MS)

Muscovite-Rare-

elements

(MSREL)

MSREL-REE

MSREL-Li

Rare-elements

(REL)

REL-REE Allanite-monazite

euxenite gadolinite

REL-Li beryl beryl-columbite

beryl-columbite-

phosphate

complex spodumene

petalite

lapidolite

elbaite

amblygonite

albite-spodumene

albite

Miarolitic (MI) MI-REE topaz-beryl

gadolinite-fergusonite

MI-Li beryl-topaz

spodumene

petalite

lepidolite

165

grade sillimanite-bearing metamorphic host rocks (Gordiyenko & Leonova 1976,

Ginsburg et al. 1979, Gordiyenko 1996). The simple mineralogy of accessory

silicates and lack of even minor mineralization in most occurrences preclude any

meaningful subdivision of this class.

The pegmatites from the Lokai-Indarwa are typically barren, carrying

feldspar quartz and mica with no metal mineralization. The pegmatites are

generally intruded along the foliation planes of the country rocks. The pegmatites

are further geochemically characterized by enrichment of the Nb, Ba and Sr with

positive Eu anomaly. The variation diagrams show that the rock are not showing

a very good differentiation trend. These field evidences along with simple silicate

mineralogy and geochemical characteristics place these pegmatites in the

Muscovite Class of Pegmatites of Cerny (1991) and Cerny and Ercit (2005).

7.3 Moonstone in the Pegmatites of Lokai-Indarwa

The effect observed with moonstones of the Lokai-Indarwa exhibiting a

blue shiller are of particular academic as well as economic interest. Microscopic

examination revealed that most of the samples show transparent blue sheen

colour and needle like inclusions and characteristic very fine albite-pericline

tartan twinning within the moonstones. A few stones also contained partially

healed fractures that had no surface expression in reflected light. The optical

effect which produces these brilliant colours is mostly due to interference of light,

the fine lamella of the repeated twinning,

The characteristic phenomenon schiller of moonstones is best seen at a

particular setting of the crystal determined by the direction in which the light is

incident on it and the direction in which it is observed. When either the setting of

the crystal or the direction of incidence of the light is altered, the direction in

which the schiller is most conspicuous also shifts. The general idea prevailed in

the literature is that the schiller owes its origin to a lamellar structure of the

feldspar in which layers of albite and orthoclase. Such a structure would reflect

light traversing the crystal in a direction varying with its angle of incidence on

166

the planes of the lamellae (Raman, 1950). The published analyses of moonstones

show that the potash and soda feldspars are their principal constituents, the

former being usually the major and the latter the minor component; a small

percentage of lime feldspar may also be present. As with all the moonstones

studied, observations show that the schiller has a maximum intensity when

viewed in a particular direction, which is related to the direction of incidence of

the light in such manner that the two directions-at least roughly-make equal

angles with and lie in the same plane as a particular direction within the crystal

which is designated as the schiller-axis (Raman, 1950).

Numerous studies, including both experimental observations and

theoretical calculations, have been published over the past 30 years on the Raman

and infrared spectral peak assignments of feldspar-group minerals. For all of

these feldspar minerals, however, the observed number of Raman peak is much

lower than that of predicted by group theory (von Stengel 1977, Dowty 1987,

McMillan et al. 1983, Matson et al 1986, McKeown 2005). Causes for the

discrepancies between predicted and actual number of Raman peaks include: (a)

Much smaller pseudo-unit-cell in the triclinic structure, which determines the

actual number of vibrational modes, (b) accidental degeneracies between the

vibrational modes, and (c) the inability to detect weak peaks in the spectra above

background noise (White 1974, Sharma et al. 1983). The results of group analysis

and force-field calculations, plus other types of vibrational studies, have

progressively developed into a general agreement on vibrational band

assignments in feldspar group minerals. The assignments [ based on Mckeown’s

(2005) calculations for low albite] show that the two strongest Raman bands in

the 450-520 cm-1

spectral region (Group I) belong to the ring – breathing modes

of the four membered rings of tetrahedra. The Raman peaks in Groups II and III

( 400cm-1

) correspond to rotation and translation modes of four membered rings

and cage- shear modes, respectively. The weaker Raman peaks in the 900-1200

cm-1

region (Group V) were assigned to the vibrational stretching modes of the

tetrahedra. The mid- to weak-strength peaks in the 700-900 cm-1

region (Group

IV) belong to the deformation modes of tetrahedra.

167

The Lokai-Indarwa moonstone showed a typical calculated unit cell

dimension, a=8.187 Å, b=8.698 Å, c=9.364 Å and α=89.81°, β=84.53°, Ƴ=82.76°

with v=658.42 Å3. The Raman Probe of the moonstones from the area gave

typical peaks with Ia peak positions varying from 509 cm-1

to 511 cm-1

. The

variations in the Ib and II peaks positions, however are relatively larger, which

may reflect changes in the composition of the samples. The data generated from

the present study showed that most samples belong to intermediate plagioclase

composition with some ternary feldspar.

Spencer (1945) discussed the characteristics of the feldspar from

Kodarma mica belt. He suggested that up to 30% of soda component can be taken

into the solid solution of feldspar at temperature of 750°C and can be brought out

again by slow cooling to 400-450°C. He further suggested that the overlap of the

crystallizing temperature of the orthoclase, microcline and plagioclase into the

exsolution temperature range given rise to the textures and characters between

plagioclase and orthoclase. Raman (1950) however suggested that the schiller is a

diffusion of light within the material which is macroscopically a monocrystal but

exhibits pronounced local variations in its composition and refractive index.

Though the potash and soda feldspars mix together when they crystallise, the

soda component tends to segregate and form tiny crystallites of which the size,

shape and orientation determine the angular distribution of the diffused light, its

spectral character, intensity and state of polarisation in various circumstances.

From the present study of optical characters, Raman Probe and EDXRF

analysis of the moonstones of Lokai-Indarwa area it is suggested that that most

samples belong to intermediate plagioclase composition (andesine to labradorite

series). However, some samples belonged to ternary feldspar. The microperthitic

textures are very common in the pegmatites. It is suggested that the schiller in the

moonstones of the area owes its origin to the diffusion of light within the

plagioclase feldspar which exhibits pronounced local variations in its

composition and refractive index. Though the potash and soda feldspars mix

together when they crystallise, the potash component tends to exsolve and form

tiny crystallites which causes light to diffuse and produce blue schiller. The

typical blue schiller and rare occurrence of alternate dark and light blue bands in

168

the moonstone alongwith the gemological characteristics of the moonstone place

Lokai-Indarwa moonstone on a better gemstones comparable to the moonstones

from Srilanka.

7.4 Physico- Chemical Conditions of Moonstone Formation

Fluid inclusions in pegmatites potentially record the history of late

magmatic fluids (Smerekanicz and Dudas, 1999). Tracing the evolution of fluids

in pegmatites therefore has been a significant focus of research, and there have

been various studies on the chemical and physical properties of the aqueous

phase and silicate melt (Manning, 1981; London and Burt, 1982; London et al.

1989; Whitworth and Rankin, 1989). Fluid inclusion studies in pegmatites are

significant and they provide information on the fluid composition and evolution

in peraluminous pegmatites (London, 2005).

The fluid inclusion study within the feldspar and quartz gives clue to the

fluids participated during the formation on the pegmatites and mineralizing

conditions of moonstone within these pegmatites. Salinity, density and

composition of the fluids along with the trapping conditions of the fluid

inclusions present in the different minerals in the pegmatite are discussed in

following paragraphs.

7.4.1 Fluid Composition

The composition of the trapped fluid is gained indirectly from measuring

the “first melting temperature (also known as the eutectic melting Te or Tme)”.

Comparing this temperature to eutectic melting points on published phase

diagrams for binary and ternary systems would allow to predict the composition

of the fluid. Fluid composition can also be determined by laser micro Raman

Spectroscopy.

169

The micro-thermometric results from the minerals of pegmatites suggest

the presence of different types of fluids in the pegmatites. They are the aqueous

fluid represented by Type-I and Type-III inclusions and the carbonic fluid

represented by Type-II and Type-IV fluid inclusions. The carbonic fluid is

represented by coexisting monophase CO2 inclusions and aqueous-carbonic

(H2O-CO2) inclusions. The composition of the fluid inclusions can be determined

by using eutectic temperature recorded during cryogenic studies of different types

of fluid inclusions.

The Tm CO2 for Type II and Type IV inclusions is varying in the similar

range from -56.2 to -66.2°C. Which clearly show a depression in the eutectic

temperature of pure CO2 i.e. -56.6 °C. This depression in the Tm CO2 is because of

the presence of some other gas apart from CO2 in the inclusion. The exact nature

of the gas can be determined with the help of Raman Probe. On the bases of

Raman spectroscopy it is established that there is presence of N2 in some of the

monophase inclusions as well as in aqueous inclusions. The monophase

inclusions, however, generally show a CO2 gas with some inclusions showing

presence of N2, where the eutectic temperature of CO2 is ranging from -56.1 to

-59.0 °C. Further the carbonic fluid is showing more depressed value for the CO2

melting with typical development of daughter crystals.

The first melting temperature of ice in the aqueous inclusions is quite

variable in the range of -28.3 to -45.3°C for Lokai-Indarwa pegmatite. The

average value for the Te suggests the presence of complex brine than the simple

H2O-NaCl fluid. Since the Te for the pure H2O-NaCl system is -21.2°C, it is

suggested that either Mg ± Ca salt are present in addition to Na and K in the

system. Moreover most of the inclusions are in plagioclase and Te is very low

possibility of additional calcium salt in form of CaCl2 is postulated in the system.

170

7.4.2 Salinity and Density

The salinity and density of the different type of inclusions are determined

by using the various equations of state for different types of systems. The

available software (PVTX software, program AqSo2e, version 03/02 of Bakker,

2003) have also been used to calculate the salinity and density.

In the Type I inclusions, halite is the only solid phase present. Though the

cryogenic studies were carried out on these types of inclusions, the final ice

melting temperature was not taken into consideration for the salinity calculation

due to the formation of hydrohalite. It is, therefore, the salinity of these inclusions

is determined by using temperature of halite dissolution method using equations

of states as suggested by Sourirajan and Kennedy (1962). Salinity of these

inclusions is found ranging from 29.8 to 31.9 eq.wt % Nacl with an average of

30.76 eq.wt % Nacl. The corresponding density of these fluids is calculated using

the PVTX software. It is ranging between 0.74 to 0.93 g/cm3. The Type II

aqueous-carbonic inclusions also have one to two solid daughter crystals. Though

the clathrates are developed during the freezing cycles, its melting temperature is

not considered for the measurement of the salinity due to possibility of the

formation of significant amount of hydrocarbonates. The salinity for such

inclusions ranges from 9.2 to 19.0 eq. wt% Nacl with a corresponding density

between 0.82 to 0.86 g/cm3 (average 0.84 g/cm

3).

The salinity of Type III inclusions is calculated using the program PVTX

using the empirical equations of Potter (1977) for freezing-point-depression of

aqueous solutions. The salinity of these inclusions ranges between 5.62 to 20.87

eq wt% NaCl with an average 14.43 eq.wt % NaCl. The corresponding density of

Type III inclusions is found varying between 0. 86 to 1.10 g/cm3 (average 0.99).

The density of these inclusions is also determined by using the Th-density binary

diagram of Shephard et.al (1985).

In the type Type IV inclusions, during freezing cycle, clatherate was

developed. Salinity based on the final ice melting temperatures recorded in the

171

presence of clathrates cannot be used. This gives an overestimation of the true

salinity due to the removal of water from the aqueous phase during clatharation.

Salinities of such inclusions are estimated by using the temperature of clatherate

dissolution applying the equation of states given by Colin (1979). The salinity of

such inclusions range between 13.40 to 20.93 eq.wt % NaCl with an average of

17.74 eq.wt % Nacl.. For density calculation PVTX software is used. The density

of Type IV is 0.77 to 0.93 g /cm3 with an average 0.86 g/cm

3.

7.4.3 Trapping Conditions

The fluid inclusion data is one of the best tools for the estimation of

temperature and pressure of trapping of these fluids. To interpret conditions of

fluid trapping, some selection of data is required. Of particular interest are the

data from feldspar and quartz from the pegmatite of the studied area. These

minerals allow some insight into the physico-chemical conditions for the trapping

of fluid inclusions. A summary of the microthermometry of the fluid inclusions

trapped in quartz and feldspar from pegmatites of Lokai-Indarwa is given in table

7.3 and is diagrammatically represented in Fig. 7.1. The fluid inclusion study

from these pegmatites suggests that the moonstone forming fluid were derived

from complex brines.

The perusal of Fig 7.1 suggests that there are at least two distinct groups

of inclusions present in almost all the samples. The early high temperature high

salinity aqueous fluid and late inclusions which are low temperature and

moderate to low salinity. The boundary between the two is easily recognizable by

a change in fluid composition. The fluids with homogenization temperatures

>200°C are the earliest fluids preserved in the pegmatite and are implicated in the

formation of the pegmatite. These are the high salinity high temperature fluids.

This is followed by the low temperature and moderate to low salinity fluid. The

other types of inclusions which are scattered and present in some of the samples

are the low density monophase N2 inclusions.

In order to understand the pressure of trapping, the methods of the

intersecting isochors for coeval fluids as suggested by Roedder and Bodnar

172

Table. 7.3. Microthermometric data of fluid inclusions.

Type

Host

Mineral

Sample

no

Freezing studies data Heating studies data Salanity Density

Te (in °C) T m ice (in °C) T m co2 (in °C) T m clath (in C) T H co2 (in °C) T ds Halite(in °C) T H (in °C) H-

Ph

ase Min. Max. Min. Max. Min. Max. Min. Max. Min. Max. Min. Max. Min. Max.

I Quartz SLI-4 -38.4 -32.5 -5.0 2 - - - - - - 139.3 184.1 185.0 236.3 Liq 30.53 0.83

ʺ Quartz SLI-8 -37.1 -34.3 -8.9 -2.4 - - - - - - 173.4 196.2 230.0 280.6 ʺ 30.45 0.85

ʺ Feldspar SLI-6 -37.4 -33.2 -11.8 -9.1 - - - - - - 169.2 171.4 280.0 295.0 ʺ 30.60 0.87

ʺ Feldspar SLI-10 -41.2 -34.0 -11.0 -8.7 - - - - - - 168.1 170.4 290.0 315.0 ʺ 30.63 0.85

II Quartz SLI-1 - - - - -63.2 -61.1 1.8 2.0 20.0 25.0 182.0 191.7 198.0 205.2 ʺ 31.35 0.85

ʺ Quartz SLI-2 - - - - -58.1 -57.1 -1.5 -1.1 21.0 22.0 195.6 210.0 215.0 222.8 ʺ 32.05 0.83

ʺ Quartz SLI-3 - - - - -66.2 -56.9 -3.4 5.0 19.9 26.0 186.0 222.0 199.0 233.0 ʺ 32.14 0.83

III Feldspar SLI-3 -33.1 -32.1 -11.9 -10.8 - - - - - - - - 172.9 192.3 ʺ 15.31 0.99

ʺ Feldspar SLI-9 -35.1 -30.1 -8.1 -7.2 - - - - - - - - 198.1 280.4 ʺ 11.27 0.90

ʺ Quartz SLI-5 -45.3 -40.1 -15.2 -9.8 - - - - - - - - 211.0 281.1 ʺ 16.05 0.99

ʺ Quartz SLI-4 -33.4 -28.3 -13.7 -3.5 - - - - - - - - 137.1 169.9 ʺ 12.14 0.99

ʺ Quartz SLI-8 -45.3 -38.6 -17.9 -6.7 - - - - - - - - 100.1 128.4 ʺ 15.58 1.18

ʺ Quartz SLI-10 -41.1 -29.2 -10.1 -8.4 - - - - - - - - 175.6 210.1 ʺ 13.17 0.97

IV Feldspar SLI-2 - - - - -59.0 -56.2 -5.7 -3.0 18.4 26.2 - - 181.1 210.2 ʺ 20.4 0.86

ʺ Feldspar SLI-6 - - - - -56.8 -55.9 -5.5 -2.3 15.7 24.0 - - 130.2 225.1 ʺ 18.3 0.87

ʺ Feldspar SLI-7 - - - - -57.4 -57.1 -2.0 -1.8 21.4 23.4 - - 148.0 171.0 ʺ 16.8 0.90

ʺ Quartz SLI-4 - - - - -57.4 -56.1 -4.0 1.5 18.0 19.4 - - 177.7 210.1 ʺ 14.7 0.86

ʺ Quartz SLI-5 - - - - -59.4 -56.7 -4.9 -1.3 23.4 26.3 - - 256.3 264.8 ʺ 15.9 0.77

ʺ Quartz SLI-8 - - - - -58.8 -56.4 -2.4 1.2 21.7 26.7 - - 129.2 154.8 ʺ 13.8 0.92

V Feldspar SLI-7 - - - - -57.1 -56.2 - - - - - - - - ʺ - -

ʺ Quartz SLI-3 - - - - -58.0 -55.1 - - - - - - - - ʺ - -

ʺ Quartz SLI-4 - - - - -57.1 -56.2 - - - - - - - - ʺ - -

ʺ Quartz SLI-5 - - - - -58.7 -55.7 - - - - - - - - ʺ - -

ʺ Quartz SLI-8 - - - - -59.0 -56.3 - - - - - - - - ʺ - -

173

0

5

10

15

20

25

30

35

0 50 100 150 200 250 300 350

Sal

init

y (

equiv

ale

nt

wt

% o

f N

aCl)

TH ( C)

Type I

Type II

Type III

Type IV

Fig. 7.1 Temperature of homogenization vs salinity plot for

different types of fluid inclusions present in

the Lokai-Indarwa pegmatites.

174

(1980), is applied. It is found that the aqueous fluids inclusions and carbonic

inclusions are present in same wafer and seems to be coeval (Fig 6.4). The isochors

corresponding to the densities calculated for the appropriate aqueous and carbonic

fluids is drawn in Figure 7.2. The area of the intersection of the crosscutting isochors

defines the P-T conditions of the trapping these fluid inclusions. It is suggested that

the minimum pressure during the trapping of these fluid inclusion was ranging

between 1.08 kb to 2.15 kb with corresponding temperature of 270°C to 475°C.

The petrologic role of immiscible fluids has been reviewed by Crawford and

Hollister (1986). Mixtures of water or aqueous brines with C-, S-, or N-bearing

compounds are immiscible below 300-400°C (Franck, 1977;Pichavante t al.,

1982).The presence of salts will increase the range of fluid unmixing, as documented

experimentally (Takenouchi and Kennedy, 1965; Naumov et al., 1974; Gehrig et

al.,1979; Sternerand Bodnar, l987; Zhangand Frantz, 1988) and observed in numerous

fluid-inclusion studies (Hollister and Bumrss, 1976; Sisson et al., l98l; Hendel and

Hollister, l98l; Mercolli, 1982; Stout et al., 1986). If there has been physical

separation of an unmixed fluid, then it is possible to trap only one of the fluid

components in fluid inclusions (Mullis, 1975). Several mechanisms have been

proposed for selective entrapment including differential wetting properties of the two

fluid phases (Mullis, 1975; Crawford and Hollister, 1986; Watson and Brenan, 1987)

and density differences between the two fluid phases (Crawford and Hollister, 1986;

Trommsdorff and Skippen, 1986). As the Lokai Indarwa pegmatite is present in the

metamorphic terrains and is intruded in the amphibolites and mica schist of

amphibolites facies some of the inclusions characteristics may be governed by the

peak metamorphism of the region. For most metamorphic terrenes, CO2, is denser

than H2O, which results in the possibility that the H2O can segregate from CO2. On

the basis of differences in the wetting properties of CO2-rich fluids and H2O-NaCl

fluids, Watson and Brenan (1987) concluded that the CO2-rich phase is relatively

immobile compared to the H2O-NaCl phase. Thus, it is reasonable to expect physical

entrapment of only one of these phases.

If the aqueous fluid that infiltrated the region had a high salt content, then it is

possible that this aqueous fluid would not mix with the CO2 produced by

metamorphic reactions. In case of Lokai-Indarwa it is suggested that the high salininty

175

0 200 400 600 800 1000

Temperature (°C)

1000

0

2000

3000

4000

Pre

ssure

(b

ars) Is

ocho

res

(HO

) 2

Isoch

ores (

O)

C2

Fig. 7.2: Intersection of

.

isochores for coeval aqueous (Type-III) andcarbonic(Type-IV) inclusions.The shaded area showing the PT conditions

of entrapment of the inclusions

176

high temperature type I fluid inclusions were entrapped earlier followed by the

carbonic-aqueous fluid.

The presence of N2 rich inclusions in the pegmatite of the area is a bit

intriguing. The chances to get the nitrogen from very deep seems not be correct seeing

the trapping conditions of the fluid inclusions. There are chances that nitrogen is

entrapped due to anatectic melt generated during high grade metamorphism. Such

inclusions have been reported from Dome de I'Agout and South Central Maine

(Kreulen and Schuiling,1982; Sission and Hollister, 1990) The introduction of water

associated with the hydrothermal alteration may have triggered the breakdown of

biotite to chlorite, releasing any NH4+, from the K* site (Duit et al., 1986).

7.5 Genesis of Pegmatites

Two of the most convincing hypothesis to explain the evolution of gem

bearing pegmatites which have been prevailing are: (1) the fractional crystallization of

flux bearing granitic melt inward from the margins of the pegmatite body and (2) the

buoyant separation of an aqueous fluid from the silicate melt and its effects on the

redistribution of components. For nearly half a century, a model that emphasized the

role of a buoyant aqueous fluid interacting with a denser granitic melt (Jahns and

Burnham 1969) drew almost universal acceptance. An evaluation of this model has

challenged its principles and underscored its lack of supporting evidence and a new

model was proposed by London (2008), by combining aspects of both concepts

invokes the formation of a flux-enriched boundary layer of silicate liquid in advance

of a crystallization front. Though most of the internal chemical and textural features

of pegmatites can now be reconciled, the puzzle of pegmatites is far from solved.

London and Morgan (2012), in their research article “The Pegmatite Puzzle” strongly

supported the model proposed and developed by London (2008). However, several

important pieces of this puzzle are still missing including “when and how pegmatites are

derived from their source”. The origin of this dilemma resulted from the assumption that

at the beginnings pegmatite-forming melts had the same water content as of the source

melt. Although in the past there has been considerable disagreement among geologists

177

regarding the origin of pegmatites, there is a general consensus today that at least the

shallower ones formed by crystallization from a magma.

The pegmatite of Lokai Indarwa is enriched in plagioclage and quartz with

potash feldspar, biotite, muscovite and apatite present into it. They are emplaced

along the foliation plane of mica schist and fracture planes of amphibolites.

Plagioclase in the pegmatite is more than the microcline. When the major oxide

chemistry of the pegmatites veins from Lokai-Indarwa area are plotted in the total

Alkali-Silica diagram (TAS) of Bateman et al. (1989), which is normally used to

classify igneous rocks based on the silica content versus the alkali content, the

pegmatites are classified as quartz monzonite to granite category (Fig. 5.1). The

pegmatite has a Al/ (Na+Ca+K) value more than 1.1 and falls under the peraluminous

category. The fluid inclusion studies clearly indicate the presence of aqueous along

with some volatile phases which participated in crystallization. The variation

diagrams however do not support a very good differentiation trend for the melt.

However a cumulative crystallization of feldspar is being supported by the study.

Pegnatitic segregations are commonly associated with many regionally

metamorphosed terranes (White 1966, Mehnert 1968, Ginsburg et al. 1979, Webber et

al. 1985). The first appearance of many of the pegmatite segregations coincides with

muscovite dehydration reactions in the surrounding aluminous country-rocks. As

described in the chapter on Petrography, the reaction textures are commonly observed

in the present studied area in the country rock. It is suggested that the pegmatatic melt

might have generated due to anatexix of the country rock. Ginsburg et al. (1979)

suggested that migamatites terranes associated with high grade metamorphism contain

only barren ceramic, or allanite- and monazite-bearing pegmatites and that both the

pegmatites and migamatites were derived during the regional metamorphism.

Numerous hypotheses have been put forward to explain the derivation of

pegmatitic-granite segregations in regionally metamorphosed terranes. These

hypothesis include: (a) injection of granitic magma from an adjacent igneous intrusive

body (Page, 1968); (b) insitu partial melting and subsequent segregation during

regional metamorphism (Thompson & Norton 1968); (c) crystallization from an

aqueous fluid (Leveson & Seyfert 1969); and (d) metamorphic differentiation and

178

segregation (Hughes 1970). The complexity of melt- residuum - fluid interaction

during migmatization has been documented by Weber et al. (1985) and Shearer et al

(1987).

The graphic and myrmekytic textures are commonly observed in the studied

pegmatite (Fig.4.13 & 4.19.). Fenn (1986) observed that graphic quartz–feldspar

intergrowths form when H2O-undersaturated granitic liquids are cooled well below

the temperature of their liquidus (i.e. the temperature–composition conditions of their

crystal–melt equilibrium) before crystallization commences. Crystal nucleation and

the attainment of equilibrium in the system are inhibited by the undercooling because

of the consequent increase in the viscosity of the silicate liquid. Increasing viscosity

impedes the diffusion of components and the reorganization of the melt structure,

which are necessary precursors to stable nucleation events (London and Morgan,

2012). The temperatures of crystallization in pegmatites as recorded by feldspar

solvus thermometry also lie at ~425–450 °C, and that is the initial temperature along

the margins of pegmatite dikes based on the contact metamorphism of host rocks and

on numerical heat-flow models (London et al. 2012 in London and Morgan, 2012).

The pressure and temperature calculated by the crosscutting isochors of the coeval

fluid inclusions in the Lokai-Indarwa pegmatites (Fig. 7.2) indicated that the

mineralization took place in the minimum pressure ranging between 1.08 kb to 2.15

kb with corresponding temperature of 270°C to 475°C.

The geochemical behavior of numerous minor- and trace-element systems in

pegmatitic melts was documented by Cerny and his colleagues. The fractionation

patterns of Nb, Ta and other HFS elements in numerous pegmatite systems have been

well documented (Cerny, 1989a, 2005; Breaks et al., 2005). The fractionation patterns

of K, Rb, Cs, Li, Ga and Ti in feldspars, micas, beryl and other minerals have also

been described by Cerny and Eriot (2005). The enrichment trends of alkali elements

in feldspars and micas have proven valuable in understanding pegmatite petrogenesis

and the internal fractionation of pegmatites.

In the initial statement of their model, Jahns and Burnham (1969) called upon

thermal gradients in a static aqueous fluid to drive the mass transfer of solutes. The

concepts for which Jahns is well known, however, were developed later in

179

collaboration with C. Wayne Burnham in which the “appearance of the aqueous phase

can be regarded as the most decisive step in the genesis of pegmatites.” (Jahns and

Burnham 1969). The Jahns- Burnham model relied on the incongruent partitioning of

alkalis, such that the aqueous fluid becomes enriched in K and the melt enriched in

Na. In their model, the aqueous fluid “scoured” incompatible elements from melt in

the lower portion of the magma body and transported those components upward to

“nourish” the formation of giant crystals and exotic minerals. The silicate melt was

left to be little more than a source of components for the fluid. The quantity of H2O in

pegmatite forming melts appears to be low enough that a vapor phase exsolves only in

the waning stages of consolidation. The vast majority of common pegmatites lack any

discernable alteration envelope along their margins. Persistent alteration aureoles tend

to surround only the largest and most fractionated pegmatites, and these aureoles

entail rock volumes of less than 1% of the total pegmatite volume (e.g. Shearer et al.

1984; Morgan and London 1987).

In order to understand the geochemical peculiarities of Lokai-Indarwa

pegmatitic rocks a continental crust normalized spider diagram is presented in (Fig.

7.3). The diagram suggests enrichment Th, U, Zr, Ni, Cr in alkalies and depleted in V,

Nb, Zn and Cu. The trace element data, especially the Rb and Sr are very good

discriminant parameters to deduce the crystallization of the pegmatites (Cerny et al.,

1985). When the Rb-Sr and Ba-Sr data are plotted in Figs. 7.4 and &.7.5 they show

some peculiarities and no proper trend. Rb, Zr, Zn, Ga and Y are higher in the

amphibolites compared to the pegmatites, whereas Ba, and Pb are more abundant in

the pegmatites compared to the amphibolites. The behavior of Rb and Ba can be

attributed to high content of feldspar present in the pegmatite. These characteristics

are attributed to incongruent melting of a mica-feldspar rich source rock. (Scaillet et

al. 1990, Harris & Inger 1992). The country rock amphibolite has been enriched in

Rb and Cs in comparison to pegmatites, presumably, owing to hydrothermal fluids of

pegmatitic origin. The amphibolite protolith was probably an internally differentiated

OFB-like trachy-andesite as plotted in Fig. 7.6 and Fig. 5.5. The enrichment of Al,

Mg, and Ca in the amphibolite is proposed to be the result of abundant cumulate

plagioclase and pyroxene.

180

0.1

1

10

100

Rb Ba Th U Nb Sr Zr Y Sc Co Ni Cu Zn Cr V

Ro

ck/C

on

tin

an

tal

cru

st

SP2

SP3

SP4

SP6

SP7

SP10

SP11

SP12

SP13

SP15

Fig. 7.3. Continental crust normalized plot for trace elements in pegmatites

(Continental crust value taken from Taylor and Mclennan 1985)

181

0

50

100

150

200

250

300

350

400

450

0 100 200 300 400

Rb

(ppm

)

Sr (ppm)

Pegmatite

Amphibolite

0

50

100

150

200

250

300

350

400

0 200 400 600 800 1000 1200

Sr

(ppm

)

Ba (ppm)

Pegmatite

Amphibolite

Fig. 7.4. Plot for Rb versus Sr

Fig. 7.5. Plot for Sr versus Ba

182

Traditionally, trace element discrimination diagrams have been used to interpret the

tectonic setting of any rock. Pegmatites can be difficult to attribute to a certain

tectonic setting due to the time lag from genesis to exposure and their complicated

petrogenetic history. Pearce et al. (1984) extended the use of trace element

discrimination diagrams for use in interpreting the tectonic setting of granitic rocks.

There is a wide variety of potential tectonic settings in which granites can form for

example: syn-collisional (Syn-COLG), within plate (WPG), volcanic arc (VAG), and

mid-ocean ridge granites (ORG). To distinguish between these tectonic settings trace

element data was plotted on the Rb vs Y+Nb tectonic discrimination diagram of

Pearce et al. (1996) (Fig. 7.7). In the diagram some fields for known post-collision

granites (Pearce, 1996) have been plotted and shown in form of circle. The Lokai-

Indarwa pegmatite can be classified as within plate category with some of the samples

falling within the Post-Collission Granites circle.

At the Lokai-Indarwa, the general coincidence of migmatites in the country

rocks and the dehydration of muscovite-quartz assemblages suggests that these

segregations may have been produced by H2O-saturated minimum melting. Redden et

al. (1982) suggested that the generation of a granitic minimum melt may, however, be

inconsistent with the approximate 500oC offset of muscovite-quartz dehydration

reactions from reactions producing a water-saturated minimum melt (Thompson

1982). Thompson & Tracy (1979) and Thompson (1982) suggested at in low-pressure

conditions, the fluid produced by mineral dehydration may migrate out of the system

prior to the attainment of temperatures necessary for melting. Searle et al (2010)

suggested similar mechanism for the formation of crustal melt granites and

migmatites in the Himalaya. The P-T conditions estimated out of the fluid inclusion

data for the Moonstone bearing pegmatites of Lokai Indarwa and their association

with migmatites confirms the formation of pegmatitic melt by anatexis. The low REE

content of the pegmatite also confirms the same. The REE pattern of the Lokai-

Indarwa pegmatite and that of the amphibolites suggests that the pegmatitic melt was

generated by the anatexix of amphibolites.

183

2150

105 20 50 100

100

200

500

1000

2000

Y (p p m )

Cr

(ppm

)

O F BW P B

A R C

W P B : W ith in -p late b asal t

A R C : Is lan d -arc b asal t

O F B : O c e an -floor b asal t

F ig .7 .6 D is trib u tio n o f P e g m a tite s d a ta o n C r-Y d ia g ra m o f G a le & P e a rc e (1 9 8 2 ).

184

Rb (

pp

m)

Y+Nb (ppm)

1000100101

10

100

1000

OceanicRidge

Granites

WithinPlateGranites

Syn-collisionGranites

VolcanicArc

Granites

Post-collisionGranites

Fig. 7.7 Tectonic discrimination diagram (Rb v/s Y+Nb) for Lokai-Indarwa Pegmatites ( after Pearce, 1996).

185

REFERENCES

186

REFERENCES

ACHARYA, S. K., (2001). Geodyanamic setting of the central, eastern & northeastern

Indian Tectonic Zone in Central, eastern & northeastern India.

ACHARYYA, S. K., (2003). The nature of Mesoproterozoic central Indian tectonic

zone with exhumed and reworked older granulites. Gondwana Research. V. 6,

No. 2, 197–214.Geol . Surv . India Spec Publ. No. 64, pp.17-35.

ANAND ALWAR, M. A and MAHADEVAN, T. M., (1969). Structure of a portion of

Bihar Mica Belt, Monghyr District, Rec. Geol. Surv. India. Vol. 95, No. 2, pp.

347-354.

BAKKER, R. J., (2003). Package Fluids 1, Computer programs for analysis of fluid

inclusion data and for modelling bulk fluid properties: Chemical Geology. V.

194, pp. 3–23.

BANERJI, A. K., (1991). Presidential address. Geology of the Chotanagpur region.

Ind. Jour. Geol. V.63, No. 4, pp.275-282.

BHATTACHARYYA, B. P., and SESHADRI, T. S., (1983). Role of barium in

geochemical exploration of mica pegmatites. A case study in Koderma area,

Bihar Mica, Belt. Geological Sury. India. Special Publication 18. pp. 24-26.

BHATTACHARYYA, B. P., (1986). Lithological characteristics of the metasedimentary

country rocks as guides to mica exploration in Bihar mica belt. Geol. Surv. Ind

Spec. Publi. No. 18, pp. 183-196.

BHATTACHARYYA, B. P., (1988). Sequence of deformation, metamorphism and

igneous intrusions in Bihar mica belt. Mem. Geol. Soc. India. No. 8, pp.113-

126.

BHOLA, K. L., (1968). Atomic mineral deposits in Bihar Mica Belt. Symp. On

Geol. & Min. of atomic minerals. V. 37, A, No. 2.

187

BISWAS, S. L., (1929). Origin of the Mica-Pegmatites of Koderma. Quart. Jour. Geol.

Min. Met. Soc. Ind, V. II, No. 2, pp. 49-54.

BODNAR, R. J., (1983). A method for calculating fluid inclusions volume based on

vapoussr diameter and PVTX properties of inclusions fluids. Economic.

Geology. V. 78, pp. 535-542.

BODNAR, R. J. and STUDENT, J. J., (2006). Melt inclusions in plutonic rocks:

petrography and microthermometry in “Melt inclusions in plutonic rocks”,

J.D. Webster, eds. Mineral. Assoc. Can. Short Course, 36, Montreal, Quebec,

pp. 1-25.

BONHAM-CARTER, G. F., (1994). Geographic Information Systems for

Geoscientists:Modelling with GIS. Pergamon, Ontario.

BROGGER, W. C., (1890). Die mineralien der syenitpegmatitga¨nge der

Sqdnorwegischen augit und nephelinsyenite. Zeitschrift fqr

Kristallographie und Mineralogie V. 16, pp. 1 – 63.

BOSE, M. K., (1990). Growth of Precambrian continental crust, A study of the

Singhbhum segment in the Eastern Indian Shield. Precambrian Continental

Crust and Its Economic Resources (Naqvi, S. M., ed.), Dev. Precambrian

Geol. V.8, pp. 267–286, Elsevier, Amsterdam.

BOWDEN, P., and WHITLEY, J. E., (1974). Rare earth element patterns in peralkaline

and associated granites, lithos. V. 7, pp. 15-21.

BOWERS, T. S., and HELGESON, H. C., (1983). Calculation of thermodynamic and

geochemical consequences of non ideal mixing in the system H2O-CO2-NaCl

on phase relation in geologic system. Equation of state for H2O-CO2-NaCL

fluid at high pressure and temperature. Geochim. Casmochim. Acta. V. 47, pp.

1247-1275.

BREAKS, F. W., SELWAY, J. B., TINDLE, A.C., (2005). Fertile peraluminous

granites and related rare-element pegmatites, Superior Province of Ontario. in

“Rare-Element Geochemistry and Mineral Deposits”, R.L. Linnen & I.M.

188

Sampson, eds. Geol. Soc. Can. Short Course Notes, St. Catharines. V.17, pp.

87-125.

BUDDINGTON, A. F., (1959). Granite emplacement with special reference

to North America. Geol. Soc. Am., Bull. V. 70, pp. 671-747.

BURTON, R. C., (1913). General report for the year 1913 Rec. Geol. Surv. Ind., V. 44,

Pt. 1, pp. 24-26.

BUSHEV, A. G., (1975). Linkage of muscovite pegmatites with granites. In Muscovite

Pegmatites of the USSR. Nauka, Leningrad, USSR (77-84; in Russ.)

CABRI, L. J., (1988). Application of proton and nuclear microbes in ore deposit

mineralogy and metallurgy. Nuclear Instruments and Methods in Physics

Research, B30, pp. 459–465.

CANNN, J. R., (1969). Spilites from Carsberg Ridge, Indian Ocean, J. Petrol. V. 10,

pp.1-19.

CARRANZA, E. J. M., (2011a). Geocomputation of mineral exploration targets.

Computers & Geosciences.V. 37, pp. 1907–1916.

CASHMAN, K.V., (1990). Textural constraints on the kinetics of crystallization

of igneous rocks in “Modern Methods of Igneous Petrology: Understanding

Magmatic Processes”, J. Nicholls & J.K. Russell, eds. Reviews in Mineralogy,

24 , Mineralogical Society of America, pp. 259-314.

CERNY, P., MEINTZER, R., and ANDERSON, A.J., (1985). Extreme fractionation in

rare element granitic pegmatites: selected examples of data and mechanism. V.

23, pp. 380-421.

CERNY, P., (1989). Exploration strategy and methods for pegmatite deposits of

tantalum: in Moller, P., !ern", P., and Saupe, F., eds., Lanthanides, Tantalum

and Niobium, Springer–Verlag, pp. 274–302.

189

CERNY, P., (1991). Rare-element granitic pegmatites. Part 1: Anatomy and internal

evolution of pegmatite deposits. Part 2: Regional to global environments and

petrogenesis. Geoscience Canada. V.18, pp. 49- 81.

CERNY, P., & Ercit, T.S., (2005). Classification of granitic pegmatites revisited. Can.

Mineral.V.43, pp. 2005-2026.

CERNY, P., London, D.,and Novak, M., (2012). Granitic pegmatites as reflections of

their sources. Elements, V. 8, pp. 289-294.

CHATTOPADHYAY, B and SAHA A. K., (1974). The Nerophar pluton in eastern India,

A mode of Precambrian diapiric intrusion. Neus Jb. Miner. Abh. V. 121,

pp.103-126.

COLLIN, P. L. F., (1979). Gas hydrate in CO2 bearing fluid inclusions and the use of

freezing data for the estimation of salinity. Econ. Geol. V. 74, pp. 1435-1444.

CORYELL, C. D., CHASE, J.W., and WINCHESTER, J.W., (1963). A procedure for

geochemical interpretation of terrestrial rare earth abundance patterns; J.

Geophys. Res. V. 68, pp. 559-566.

CRAWFORD, M. L., (1981). Phase equilibrium in aqueous fluid inclusions. Short

course in fluid inclusions; application to petrology, Mineralogical association

of Canada. V. 6, pp. 75-100.

CRAWFORD, M. L., and HOLLISTER, L.S., (1986). Metamorphic fluid: The evidence

from the fluid inclusion. In: WALTHER, J.V., WOODS, B.S. (eds.) Fluid rock

interaction during metamorphism. Springer-Verlag. New York, Berlin

Heidelberg, Tokyo, pp.1-35.

CLOUT, J. M. F., (2003). Upgrading processes in BIF-derived iron ore deposits:

implications for ore genesis and downstream mineral processing. Applied

Earth Science. V.112, pp. 89–95.

DIAMOND, L.W., (1992). Stability of CO2 hydrate + CO2 liquid + CO2 vapour +

Aqueous Kcl-Nacl solution. Experimental determination and application to

190

salinity estimation for fluid inclusions. Geochim. Cosmochin. Acta. V. 56. pp.

273-280.

DILL, H. G., (2010). The “chessboard” classification of mineral deposits: mineralogy

and geology from aluminum to zirconium. Earth-Science Reviews. V. 100,

pp.1–420.

DOWTY, E. (1987). Vibrational interactions of tetrahedra in silicate glasses and

crystals: calculations on melilites, pyroxenes, silica polymorphs and

feldspars. Phys. Chem. Minerals 14, 122-138.

DUIT, W., JANSEN, J. B. H., BREEMAN, A. V., and BOS. A., (1986). Ammonium mica

in metamorphic rocks as exemplified by Dome del Agot (France). Amercian

Journal of Science, 286, 702-732.

DUNN, J. A., (1942). Mica. Rec. Geol. Surv. Ind. V. sp, No. 10, pp. 1-80.

ERN, P., and ERCIT, T.S., (2005). Classification of granitic pegmatites revisited.

Canadian Mineralogist. V.43, pp. 2005-2026.

FENN, P. M., (1977). The nucleation and growth of alkali feldspars from hydrous

melts. Can. Mineral. V.15, pp. 135-161.

FENN, P. M., (1986). On the origin of graphic granite. Am. Mineral. V.71, pp. 325–

330.

FRANCK, E. U., (1977), Equilibra in aqueous electrolyte systems at high temperatures

and pressures. In T. S. Storvick and S. I. Sandler, Eds, Phase equlibra and

fluid properties in chemical industry. Pp- 537 American chemical Society,

Washington, D.C.

FOX, C. S., (1930-B). Koderma Excursion. Trans. Min. Geol. Inst. India. V. 24,

pp.327.

GALE, G. H., and PEARCE, J. A., (1982). Geochemical pattern in Norwegian

greenstones. Natl Research Council of Canada 1982, pp. 385-397.

191

GALESCHUK, C. R. and VANSTONE, P. J., (2005). Exploration for buried rare-element

pegmatites in the Bernic Lake area of southern Manitoba. in “Rare–Element

Geochemistry and Mineral Deposits”, R.L. Linnen & I.M. Sampson, eds.

Geol. Soc. Can.Short Course Notes, St. Catharines. V.17, pp. 159-173.

GEHRIG, M. H., LENTZ, H., and FRANCK, E. U., (1979). Thermodynomics properties

of water-carbon dioxide-sodium chloride mixtures at high temperature and

pressure. High pressure Science Technology, 6th

AIR-APT Conference, Vol,

1, In K D Timmerhaw and M S Barker, Eds, Physical properties and material

synthesis. Pp 539-542, Plenum press, New York.

GHOSH, N. C., (1983). Geology, tectonics and evolution of the Chotanagpur granite-

gneiss complex, eastern India. Structure and Tectonics of Precambrian Rocks

of India (Sinha- Roy, S., ed.), Recent Res. Geol.V. 10, pp.211–247, Hindustan

Publishing Company, India.

GHOSE, N. C., (1992). Chhotanagpur gneiss-granulite complex Eastern India: present

status and future prospect. Indian Journal of Geology. V. 84, pp. 100–121.

GHOSE, N. C., and MUKHERJEE, D., (2000). Chotanagpur gneiss-granulite complex,

Eastern India-a kaleidoscope of global events. In: Trivedi, A.N., Sarkar, B.C.,

Ghose, N.C., Dhar, Y.R. (Eds.), “Geology and Mineral Resources of Bihar and

Jharkhand”, Platinum Jubilee Commemoration Volume, Indian School

ofMines, Dhanbad,Monograph 2. Institute of Geoexploration and

Environment, Patna, pp. 33–58.

GHOSE, N. C., MUKHERJEE, D. and CHATTERJEE, N., (2005). Plume generated

Mesoproterozoic mafic-ultramafic magmatism in the Chotanagpur mobile belt

of Eastern Indian shield margin. Jour. Geol. Soc. India. V.66, pp.725-740.

GINSBURG, A. I. and RODIONOV, G. G. (1960). On the depth of formation

of granitic pegmatites. Geol. Rudn. Mestorozhd. pp. 45-54 (in Russian).

GINSBURG, A. I., TIMOFEYEV, L N., FELDMAN, L.G., (1979). Principles of geology

of the granitic pegmatites. Nedra, Moscow 296 p. (in Russian).

192

GORDIYENKO, V. V., (1996) .Granitic Pegmatites. SPGU, St. Petersburg State Univ.,

St. Petersburg, Russia (in Russ.).

GORDIYENKO, V. V., and LEONOVA, V. A., eds. (1976). Mica-Bearing Pegmatites of

Northern Karelia. Nedra, Leningrad, USSR (in Russ.).

GORLOV, N. V. (1975). Structural principles of exploration for pegmatite deposits in

northwestern White Sea region. In Muscovite Pegmatites of the USSR. Nauka,

Leningrad, USSR (146-153; in Russ.).

GUBELIN, E. J., and KOIVULA., J. I., (1986). Photoatlas of Inclusions in Gemstones,

ABC Edition, Zurich.

HARRIS, N.B.W., and INGER, S., (1992). Trace element modeling of pelite-derived

granites. Contrib. Mineral Petrol. V. 110, pp. 46-56.

HART, S. R., BROOKS, C., KROGH, T. E., DAVIS, G.L., and NAVA, D., (1970).

Anicient and modern volcanic rocks; a trace element model. Earth Planet, Sci.

Lett. V. 15, pp. 17-20.

HASKIN, L. A., and HASKIN, M. A., FREY, F.A., and WILDEMAN, T.R., (1960).

Relative and absolute terrestrial abundances of the rare earth in L H Abrens

(Editor) origin and distribution of the elements, 1. Pergamon Oxford, pp. 889-

911.

HASKIN, L. A., and HASKIN, M. A., (1968). Rare earth elements in the Skaergaard

intrusion, Geochin. Cosmochin, Acta. V. 32, pp. 433-447.

HATTORI, H., SUGISAKI, R., and TANKA, T., (1972). Nature of hydration in Japanese

Palaeozoic geosynclinal basalt. Earth Planet. Sci. Lett. V.15, pp. 271-285.

HASS, J. L., (1971). The effect of salinity on the maximum thermal gradient of a

hydrothermal system at hydrostatic pressure. Economic Geology. V. 66, pp.

940-946.

HAURI, E. H., KENT, A. J. R., ARNDT, N., (2002). Melt inclusions at the millennium:

toward a deeper understanding of magmatic processes.

193

Chem. Geol. V. 183, pp. 1-3.

HEINRICH, E. W., (1966). The geology of carbonatites (reprinted in 1980): Chicago,

Rand McNally and Company, 555 p.

HENDEL, E. M. and HOLLISTER, L. S. (1981). An empirical solvus for CO2-H2O-2.6

wt% NaCl. Geochimica et Cosmochimica Acta, 45, pp- 225-228.

HITZMAN, M. W., REYNOLDS, N.A., SANGSTER, D.F., ALLEN, C.R. and CARMAN,

C.E. (2003). Classification, genesis, and exploration guides for non sulfide

zinc deposits. Economic Geology. V. 98, pp. 685–714.

HOLLAND, T. H., (1902). The Mica Deposits of India. Mem. Geol. Surv. Ind. V. 34,

Pt. 2, pp. 11-132.

HOLLISTER, L. S. and BURRUSS, R. C. (1976). Phase equilibra in fluid inclusions

from the Khtada Lake metamorphic complex, Geochimica et Cosmochimica

Acta, V. 40, pp-163-175.

HOLLISTER, L. S., (1990). Enrichment of CO2 in fluid inclusion in quartz by removal

of H2O during crystal plastic deformation. Jou. Struct.Geol. V. 12, pp. 895-

901.

HOLMES, A., (1949). The age of uraninite and monazite from the post-Delhi

pegmatites of Rajputana. Geol. Mag. V. 86, No. 5, pp. 288-302.

HUGHES C. J. (1970). The significauce of biotite selvedges in migmatites. Geol.

Mag, 107, pp. 21-24.

IYER, L. A. N., (1939-1944). Progress reports for the years 1939 to 1944, Geological

survey of India ( unpublished).

IRVINE, T. N., and BARAGAR, W. R. D., (1971). A guide to the chemical

classification of the common volcanic rocks. Canadian Jour, Earth Sci. V.8,

pp.523-548.

194

JAHNS, R. H., (1953). The genesis of pegmatites: I. Occurrence and origin of giant

crystals. Am. Mineral. 38, 563-598.

JAHNS, R. H., (1955). The study of pegmatites. Econ. Geol., 50th

Anniversary Volume, pp. 1025-1130.

JAHNS, R. H. and TUTTLE, O. F., (1963). Layered pegmatite-aplite intrusives.

Min. Soc. Amer. Special Paper, V.1, pp.78-92.

JAHNS, R. H., BURNHAM, C. W., (1969). Experimental studies of Pegmatite genesis:

I. A model for the derivation and crystallization of granitic pegmatites,

Economic Geology. V. 64, pp. 843-864.

JAHNS, R. H., (1982). Internal evolution of pegmatite bodies. In: !ern", P. (Ed.),

Granitic Pegmatites in Science and Industry. Mineralogical Association of

Canada Short Course Handbook. V. 8, pp. 293-327.

JENKINS, R., and SNYDER, R. L., (1996). Introduction to X-ray powder diffractometry

(Wiley, New york).

JOHNSON, M. L., ELEN, S., and MUHLMEISTER, S., (1999). On the Identification of

Various Emerald Filling Substances," Gems & Gemology, Summer, V. 35,

No. 2, pp. 82-107.

KALIA, A. N., (1952). Geological mapping in Bihar mica-field. Bull. Geol. Min. Met.

Soc. Ind., No. 11, pp. 381-390.

KARANTH, R.V., (2000). Gem and gem industry in India. Mem. 45. Geol. Soci. Ind.

KARANTH, R. V., (2008). Gemstones.Popular Science series. No. 3 Geol. Soci. Ind.

KERRICH, D. M., and JACOBS, G. K., (1981). A modified Redlich-Kwong equation

for H2O, CO2, and H2O, -CO2 mixtures at elevated pressures and

temperatures. Am. J. S. V. 281, pp.735-667.

KERKHOF, A. V., DEN and THIERY, R., (2001). Carbonic Inclusion. Lithos. V. 55,

pp. 49-68.

195

KHANNA, P. P., SAINI, N. K. , MUKHERJEE, P. K. PUROHIT, K. K., (2009). An

appraisal of ICP-Ms technique for determination of REEs: long term QC

assessment of silicate rock analysis. Himalayan Geology, V. 30, No. 1, pp 95-

99.

KONTAK, D. J., ANDERSON, A. J., MARSHALL, D., MARTIN, R. F., eds. (2004).

PACROFI VIII-Fluid Inclusions, Thematic Issue. Can.Mineral. V. 42, pp.

328.

KREULEN, R., and SCHUILING., R. D. (1982) N2-CH4-CO2 fluids during formation of

the Dome del Agout France. Geochimica et Cosmochimica Acta, 46, pp-193-

203.

KUNO, H. (1968). Differentiation of basalt magmas. In: Hess, H.H. and Poldervaart,

A. (eds.), Basalts: The Poldervaart Teatrise on Rocks of Basaltic

Composition, Vol. 2. Interscience, NewYork, pp.: 623-688.

LANDCS, K. K., (1933). Origin and classification of pegmatites, Amcr. Min., 18:33-

56, 95-103.

LE BAS, M. J., Le MAITRE, R. W., STRECKERISEN A., and ZANETTIN, B., (1986). A

chemical classification of volcanic rocks based on the total alkali-silica

diagram. Journal of Petrology. V.27, pp. 745-750.

LEEDER, O., THOMAS, R., KLEMM, W., (1987). Einschlüsse in Mineralien. VEB

Deutscher Verlag für Grundstoffenindustrie, Leipzig., 180 pp.

LEVESON, D. J. & SEYFERT, C. K. (1969). The role of metasomatism in the formation

of layering in amphibolites of Twin Island, Pelham Bay Park,-The Bronx,

New York. In Igneous and metamorphic Geology (L.H. Larsen, Ed.). Geol.

Soc. Amer. Mem. 115, pp. 379-399.

LIDDICOAT, R. T., Jr., (1981). Handbook of Gem Identification, 11th Edition, Santa

Monica, California, Gemological Institute of America.

196

LOFGREN, G. E., (1974). An experimental study of plagioclase crystal morphology:

isothermal crystallization. Am. J. Sci. V. 274, pp. 243- 273.

LOFGREN, G. E., (1980). Experimental studies on the dynamic crystallization of

silicate melts. In: Hargraves, R. B. (Ed.), Physics of Magmatic Processes.

Princeton University Press, Princeton, New Jersey, pp. 487-551.

LONDON, D. and BURT, D. M. (1982) Lithium aluminosilicate occurrences in

pegmatite and the lithium aluminosilicate phase diagram. Amer. Mineral.,

V.67, pp.483-493.

LONDON, D., MORGAN, G. B. VI. and HERVIG, R.L. (1989). Vapour undersaturated

experiments with Macusani glass +H2O at 200 MPa, and the internal

differentiation of granitic pegmatites Contrib. Mineral. Petrol., V.102, pp.1-

17.

LONDON, D., (1985). Pegmatites of the Middletown district, Connecticut. 77th

Annual

Meeting, New England Intercollegiate Geological Conference, Yale

University. Connecticut Geological and Natural History Survey Guidebook,

vol. 6, pp. 509-533.

LONDON, D., (1986b). Formation of tourmaline-rich gem pockets in miarolitic

pegmatites. Am. Mineral, V.71, pp. 396-405.

LONDON, D., MORGAN, G. B. VI. and HERVIG, R. L. (1989). Vapor undersaturated

experiments with Macusani glass +H2O at 200 MPa, and the internal

differentiation of granitic pegmatites Contrib. Mineral. Petrol., V.102, pp.1-17.

LONDON, D., (1992). The application of experimental petrology to the genesis and

crystallization of granitic pegmatites. Can. Mineral. V. 30, pp. 499-540.

LONDON, D., 1996. Granitic pegmatites. Trans. Royal Soc. Edinb. : Earth Sci. 87, 305–

319.

LONDON, D., (1999). Melt boundary layers and the growth of pegmatitic textures.

Can. Mineral. V. 37, pp. 826– 827.

197

LONDON, D., (2005). Geochemistry of Alkali and Alkaline Earth Elements in Ore

Forming Granites, pegmatites and Rhyolites, In: LINNEN, R. L. and

SAMPSON, I.M. Rare–Element Geochemistry and Mineral Deposits pp. 175-

199.

LONDON, D., (2008). Pegmatites. Canadian Mineralogist Special Publication 10, 347

pp.

LONDON, D., and MORGAN G. B. (2012). The pegmatites puzzle. Elements, Vol. 8

no. 4. Pp. 263-268.

LOWENSTERN, J. B., (1995). Applications of silicate-melt inclusions to the study of

magmatic volatiles in “Magmas, Fluids, and Ore Deposits”, J.F.H. Thompson,

ed. Mineral. Assoc. Can. Short Course. V. 23, pp.71-99.

LOWENSTERN, J. B., (2003). Melt inclusions come of age: volatiles, volcanoes, and

Sorby’s legacy. in “Melt Inclusions in Volcanic Systems: Methods,

Applications and Problems”, B. De Vito & R.J. Bodnar, eds. Elsevier,

Amsterdam, 1-21.

MACKEY, E. J. H., (1937). Bead making in ancient Sind. Jour. Am. Oriental Soc. V

.57, pp. 1-15.

MACLELLAN, H. E., and TREMBATH, L. T., (1991). The role of quartz crystallization

in the development and preservation of igneous texture in granitic rocks:

Experimental evidence at 1 kbar. Am.Mineral. V. 76, pp. 1291-1305.

MAHADEVAN, C., and ASWATHANARAYANA, U., (1955). Age levels of Archean

structural provinces. Curr. Sci. (Bangalore). V. 24, No. 3, pp. 73-74.

MAHADEVAN, T. M., (1957). Report on the progress of detailed systematic mapping

of the mica belt in parts of Monghyr district, Bihar. Geol. Surv. Ind.

(unpublished).

MAHADEVAN, T. M. (1957). A note on the occurrences of lepidolite at Bijaaiya,

Monghyr district, Bihar. Geol. Surv. Ind. (unpublished).

198

MAHADEVAN, T. M., and MAITHANI, J. P. B. , (1967). Geology and petrology of

mica pegmatites in parts of Bihar mica belt. Mem. Geol. Surv. Ind.V. 93.

MAHADEVAN, T. M., (1981). Erotation of granite pegmatites and granite pegmatite

fields in the Indian peninsular shield: a review. Unpubl, Atomic Minerals

Rept., Hyderabad.

MAHADEVAN, T. M., (2002). Geology of Bihar and Jharkhand. Geol. Surv. Ind. pp.

291.

MALLAT, F. R., (1874). Geological notes on part of northern Hazaribagh. Rec. Geol.

Surv. Ind. V.7, pt.1, pp.32-34.

MANIAR, P. D., amd PICCOLI, P. M., (1989). Tectonic discrimination of granitoids.

Geol. Soc. Am., Bull. V. 101, pp. 635-643.

MANNING, D. A. C. (1981) The effect of fluorine on liquidus phase Jour .Geol. Soc.

India, Vol.73, MARCH2009 418 F.

MAZUMDAR, S. K., (1988). Crustal evolution of the Chhotanagpur gneissic complex

and the mica belt of Bihar. In: Mukhopadhyay, D. (Ed.), Precambrian of the

Eastern Indian shield: Geological Survey of India Memoir. V. 8, pp. 49–83.

MAZUMDAR, S. K., (1996). Precambrian geology of peninsular eastern India. Indian

Minerals. V . 50, No. 3, pp. 139-174.

MATSON, D. W., SHARMA , S. K. and PHILPOTTS, J. A., (1986). Raman spectra of

some tectosilicates and of glasses along the orthoclase–anorthite and

nepheline–anorthite joins. Am. Mineral. V.71, pp. 694-704.

MCDONOUGH W. F. and SUN S. (1995). The composition of the Earth. Chemical

Geology 120, 223-253.

MCKEOWN, D. A. (2005). Raman spectroscopy and vibrational analyses of albite:

from 25°C through the melting temperature. Am. Mineral. 90, 1506-1517.

199

MCMILLAN, P., PIRIOU, B. and NAVROTSK Y, A. (1982). A Raman spectroscopic

study of glasses along the joins silica-calcium aluminate, silica – sodium

aluminate, and silica -potassium aluminate. Geochim. Cosmochim. Acta 46,

2021-2037.

MIDDLEMOST, E. A. K., (1994). Naming materials in magma/igneous rock system:

Earth Science Reviews, 37, 215–224.

MIZUHIKO, A. and HIDEHIRO, S., (1970). The lamellar structure in moonstone and

anorthoclase from Korea. Contr. Mineral. And Pettrol. V.29, pp. 28-32.

MEHNERT, K. R. (1968). Migmatites and the Origin of Granitic Rocks. Elsevier, New

York.

MERCOLLI, I. (1982) k inclusione fluide nei noduli di quarzo dei marmi dolomitici

della regione de Campolunga( Ticino). SchweizerischeM ineralogischeu nd

PetrographischeM itteilungen, 62, 24 5-3

MITCHELL and BERGMAN, (1991). Petrology of lamproites. Xvi + 447 pp. Newyork,

London Plenum.

MORGAN VI, G. B., LONDON, D., (1987). Alteration of amphibolitic wallrocks

around the Tanco rare-element pegmatite, Bernic Lake, Manitoba. Am.

Mineral.V. 72, pp.1097-1121.

MORGAN, G. B., and LONDON, D. (1999). Crystallization of the Little Three layered

pegmatite-aplite dike, Ramona District, California. Contrib. Mineral. Petrol.

V. 136, pp. 310-330.

MUKHERJEE, B., and PRASAD, U., (1958). X-ray study of rare phosphate minerals.

Nature. V. 182, pp. 472-473.

MULLIS, J. (1975) Growth conditions of quartzcrystals from Val d’lliez .

Schweizerische Mineralogische and petrographische Mitteilungen, 55 , pp.

419-429.

200

MURTHY, S. R. N., (1990). Gemmological studies in sanskrit texts (vol. I) Published

by Subbaiah Setty, Mahaveer Minerals & Chemicals, Banglore, pp. 103.

MURTHY, S. R. N., (1993). Gemmological studies in sanskrit texts (vol. I) Published

by FAAST, Trichur, 97 p.

NABELEK, P. I., RUSS-NABELEK, C., and DENISON, J. R., (1992a). The generation

and crystallization conditions of the Proterozoic Harney Peak Leucogranite,

Black Hills, South Dakota, USA: Petrologic and geochemical constraints.

Contrib. Mineral. Petrol. V. 110, pp.173-191.

NABELEK, P. I., RUSS-NABELEK, C., HAEUSSLER, G. T., (1992b). Stable isotope

evidence for the petrogenesis and fluid evolution in the Proterozoic Harney

Peak leucogranite, Black Hills, South Dakota. Geochim. Cosmochim. Acta.

V.56, pp. 403-417.

NAKAMURA, K., (1974). Volcanic alignments and their mechanism. Chidanken

Sempo. V. 18, pp. 75-81.

NAKAMURA, N. (1974). Determination of REE, Ba, Fe, Mg, Na, and K in

carbonaceous and oxidizing chondrites. Geochim. Cosmochim Acta. V. 38,

pp.287-308.

NASSAU, K., (1983). Gemstone Enhancement, London, Butterworths.

NAUMOV, V B., KHAKIMOV, A. K. H. and KHODAKOVSKIY, I. L., (1974). Solubility

of corbon dioxide in concentrated choloride solution and high temperature and

pressure. Geochemistry international. V. 11. Pp- 31-41.

OSLEN, S.N., (1988). High density CO2 inclusion in the Colorado Front range.

Contrib. Mineral Petrol. V. 100, pp. 226-235.

PAGE, L.R. (1968). Devonian plutonic rocks in New England. In Studies of

Appalachian Geology. Northern and Maritime (E-an Zen, W.S. White, J.B.

Hadley & J.B. Thompson, J r., eds.). Interscience, New York.

201

PEARCE, A., (1979). Les inclusions fluids des quartz d exsudation da la zone du

M.C.T. Himalayan au Nepal Central; de cisailleement crustal, Bulletin de

Minerakogie. V.102, pp. 537-554.

PEARCE, J. A., HARRIS, N.B. W., and TINDLE, A.G., (1984). Trace element

discrimination diagrams for the tectonic interpretation of granitic rocks:

Journal Of P etrology. V. 25, pp.956-983.

PEARCE, J.A., (1982). Trace element characteristics of lavas from destructive plate

margins, in Thorpe, R.S. (ed.), Andesites: Orogenic andesites and related

rocks: London, John Wiley & Sons, 525–548.

PEARCE, J. A., HARRIS, N. B. W., and TINDL, A. G., (1984). Trace element

discrimination diagram for the tectonic interpretation of granitic rocks.

Journal of Petrology. V.25, pp. 956-983.

PEARCE , J. A., (1996). A user’s guide to basaltic discrimination diagrams, in Wyman,

D.A., ed., Trace element geochemistry of volcanic rocks: applications for

massive sulphide exploration: Geological Association of Canada Short

Course Notes. V. 12, pp. 79-113.

PERETYAZHKO, I. S., PROKOFEV, V.Y., ZAGORSKY, V. Ye., SMIRNOV, S. Z., (2000).

Role of boric acids in the formation of pegmatite and hydrothermal minerals:

petrologic consequences of sassolite (H3BO3) discovery in fluid inclusions.

Petrol., V.8, pp.214-237.

PETTKE, T., (2006). In situ laser ablation-ICP-MS chemical analysis of melt

inclusions and prospects for constraining subduction zone magmatism. in

“Melt inclusions in plutonic rocks”, J.D. Webster, ed. Mineral. Assoc. Can.

Short Course. V. 36, pp. 189-210.

PICHAVANT, M., RAMBOZ, C., and WEISBROD, A (1982). Fluid immiscibility in

natural processes: Use and misuse of fluid inclusion data. I phase equilibra

analysis- A theoretical and geometrical approach. Chemical geology. V- 37,

pp-29-48.

202

PORWAL, A. K., and KREUZER, O. P., (2010). Introduction to the special issue:

mineral prospectively analysis and quantitative resource estimation. Ore

Geology Reviews. V. 38, pp. 121–127.

POTTER, R. W., (1977). Pressure corrections for fluid-inclusion homogenization

temperatures based on the volumetric properties of the system NaCl-H2O.

Jour. Research. U.S, Geol. Surv. V. 5, pp.603-607.

PRIYADARSHI, N., (2009). Jharkhand state of India can be the treasure trove of

gemstones. The American Chronicle.

RAMACHANDRAN, S., SRIVASTAVA, P K., RAMINAIDU, C.H., and NATESHWARA

RAO, B., (1994). Geological, structural, and geochemical studies in the Bihar

mica belt, eastern India, with special reference to mode of emplacement of

rare metal and other pegmatites. Explo.and Res. Atomic Minerals. V. 7, pp.

77-95.

RAMAN, C. V., and JAYARAMAN, A., (1950). Proc Indian Acad. Sci.,, A32, 1.

RAMCHANDRA, H. M., and ROY, A., (1998). Geology of intrusive granitoids with

particular reference to Dongargarh granite and their impact on the tectonic

evolution of the precambrian in central India. Indian Minerals. V.52, pp. 15-

32.

RAMAKRISHNAN, M., VAIDYANADHAN, R., (2008). Geology of India, V.1,

Geological Society of India. 994 p.

RAO, S.R., (1973). Lothal and Indus civilization.. Asia. Publ. House, London.

RAO, S. R. (1986). Lothal, A port town, vol. I, New Delhi: Archeological surv. India.

REDDEN, J. A, NORTON, J. J , and MCLAUGHLIN, R. J., (1982). Geology of the

Hamey Peak G ranite,B lackH ills, SouthD akota.U S. GeologicaSl urvey

Open-file Reporl 82- pp. 481, l8.

203

REINITZ, I. M., Buerki,P.R., SHIGLEY, J. E., MCCLURE, S. F., and Moses, T. M.,

(2000). "Identification of HPHT-Treated Yellow to Green Diamonds," Gems

& Gemology, Summer. V. 36, No. 2, pp. 128-137.

RODE, K. P., (1947). On the origin of mica in pegmatites. Quart Jour.Geol. Min. Met.

Soc. Ind. V. 19, pp, 1-6.

ROY, S. K., SHARMA, N. L. and CHATTOPADHYAY, G. C., (1939). The mica

pegmatites of Koderma, India. Geol. Mag. V. 76, No. 4, pp. 145-164.

ROEDDER, E., (1972). Composition of fluid inclusion. U.S. Geol. Survey Prof. Paper

440JJ, pp.164.

ROEDDER, E., (1979). Fluid inclusions on the samples of ore fluid, in Barnes, H.L.

(ed.), Geochemistry of Hydrothermal ore deposits: John Willyand sons. New

York, pp. 684-737.

ROEDDER, E., and BODNAR, R.J., (1980). Geologic pressure determination from fluid

inclusion studies. Ann. Rev. Earth plan. Sci. V. 8, pp, 263-301.

ROEDDER, E., (1981). Origin of the fluid inclusions and changes that occur after

trapping. Mineralogy in L.S. HOLLISTER and M.L.CRAWFORD (eds).

Short course in fluid inclusion: application to petrology,

ROEDDER, E., (1984). The fluid inclusion. Rev. Mineralogy. Mineralogical Soci. Of

Ame. V. 12, pp. 1-644.

ROEDDER, E., (2003). Significance of melt inclusions. in “Developments in

Volcanology, 5: Melt inclusions in volcanic systems: methods, applications

and problems”, B. De Vivo & R.J. Bodnar, eds. Elsevier, Amsterdam, xv-xvi.

ROY, S. K., SHARMA, N. L., and CHATTOPADHYAY, G. C., (1939). The Mica

Pegmatites of Koderma, India. Geol. Mag. V. 76, No. 4, H2O, pp. 145-164.

SAHA, A.K., SARKAR, S.S and REJ, S.S., (1987). Petrochemical evolution of the

Bihar mica belt granites, eastern India. Indian Jour. Earth Sci., V. 14, No. 1,

pp.22-45.

204

SAMSON, I., ANDERSON, A., MARSHALL, D., eds. (2003). Fluid Inclusions: Analysis

and Interpretation. Mineral. Assoc. Can. Short Course. V. 32, 370 p.

SANTOSH, M., (1986). Genesis of two zoned pegmatites of the Bihar Mica Belt: A

fluid inclusion study. Geol. Soc. Ind. V. 28, pp. 29-40.

SANTOSH, M., and COLLINS. A. S., (2003). Gemstone Mineralization in the Palghat-

Cauvery Shear Zone system (Karur- Kangayam Belt), Southern India.

Gondwana Research,. V. 6, No. 4, pp. 911-918.

SARKAR, S. S., CHATTERJEE, A., NANDY, S., and SAHA, A. K., (1988).

Classifications of the Granites of the Bihar Mica Belt, Eastern India, using

stepwise Multigroup Discriminant Analysis and Cluster Analysis. Indian Jour.

Earth Sci., V. 15, pp. 189-200.

SCAILLET, B., FRANCE-LANORD, C., and LEFORT, P., (1990). Badrinath-Gangotri

plutons (Garhwal, India): Petrological and geochemical evidence for

fractionation processes in a High Himalayan Leucogranite. J. Volc. Geotherm.

Res. V.44, pp.163-158.

SCHALLER, W.T., (1927). Mineral replacement in pegmatites. Amer. Min. V. 12, pp.

59-63.

SCHNEIDER, G. (2004). The roadside geology of Nambia, V.97, Gebr. Borntraeger.

SCHWARTZ, M.O., (1989). Determining phase volumes of mixed CO2- H2O

inclusions using micro thermometric measurements. Mineral Deposita. V. 24,

pp. 43-47.

SEAL, R.R., and FOLEY, N.K., (eds) (2002). Progress on Geo environmental Models

for Selected Mineral Deposit Types. U.S. Geological Survey Open-File Report

02-195, U.S. Geological Survey, Reston (VA).

SEARLE, M. P. COTTLE, J. M. STREULE, M. J. and WATERS, D. J. (2010) Crustal melt

granites and migmatites along the Himalaya: melt source, segregation,

205

transport and granite emplacement mechanisms. Earth and Environmental

Science Transactions of the Royal Society of Edinburgh, 100, 219–233, 2010.

SEN, S., and SAHA, A. K., (1961). Deformation features in the minerals of the

pegmatites of the bihar mica belt, India. Proc. 48th

Ind. Sci. Congr.Pt. III, p.

195.

SHARMA, N.L., (1938). Feldspars from the pegmatites of Koderma, Bihar. Pros. Ind.

Acad. Sci., Sec. B. V. 8, No. 4, pp.266-279.

SHARMA, N.L., (1940). The petrology of the Government Reserve Forest Koderma,

Bihar. Geol. Mag., V. 77, pp. 113-140.

SHARMA, S., SIMONS, B. and YODER , H.S., Jr. (1983): Raman study of anorthite,

calcium Tschermak’s pyroxene, and gehlenite in crystalline and glassy states.

Am. Mineral. 68, 1113-1125.

SHEARER, C. K., PAPIKE, J. J., SIMON, S. B, LAUL, J. C, and CHRISTIAN, R. (1984).

Pegmatite/wallrockin teractions:B lack Hills, South Dakota: Progressiveb

oron metasomatisma djacent to the Tip Top pegmatite Geochimicae t

CosmochimicaA cta, V. 48, pp. 2563-2580.

SHEARER, C. K., PAPIKE, J.J., LAUL, J. C. (1987). Mineralogical and chemical

evolution of a rare-element granite-pegmatite system: Harney Peak Granite,

Black Hills, South Dakota. Geochim. Cosmochim. Acta, V.51, pp.473-486.

SHEPHARD, T. J., (1981).Temperature-Programmable heating and freezing stage for

micro thermometric analysis of fluid inclusion. Econ. Geol. V. 76, pp. 1244-

1247.

SHEPHARD, T. J., RANKIN, A. H., and ALDERTON, D. H. M., (1985). A practical

guide to fluid inclusion studies. Blackies and Sons Ltd; Glassgow, pp. 88.

SHMAKIN, B., (1976). Muscovite and Rare-Metal Muscovite Pegmatites

(Mineralogical-Geochemical and Genetic Characteristics of Pegmatites in

206

Eastern Siberia and India), Nauka publishing house, Novosibirsk, 367 p. (in

Russian).

SIMMONS, W. B., LEE, M.T., BREWSTER, R. H. (1987). Geochemistry and evolution

of the South Platte granite-pegmatite system, Jefferson County, Colorado.

Geochim. Cosmochim. Acta. V.51, pp. 455-472.

SIMMONS, W. B., et al., (1995). Evidence for an anatectic origin of granitic

pegmatites western Maine, USA. Geol. Soc. Amer. Annual Meeting., Abstr

Program. V. 27, No.6, A411

SIMMONS, W. B, WEBBER, K. L, FALSTER, A. U, and NIZAMOFF, J. W., (2003).

Pegmatology: Pegmatite Mineralogy, Petrology and Petrogenesis. Rubellite

Press, New Orleans, LA, 176 pp.

SIMMONS, W. B., LAURS, B. M., FALSTER, A. U., KOIVULA, J. I., and WEBBER, K.

L., (2005) Mt. Mica: a renaissance in Maine’s gem tourmaline production.

Gems & Gemology. V.41, pp. 150-163.

SIMMONS, W.B., (2007): Gem-bearing pegmatites. In: Groat LA (ed) Geology of

Gem Deposits. Mineralogical Association Canada Short Course.V. 37, pp

.169-206.

SIMMONS, W.B., PEZZOTTA, F., SHIGLEY, J.E., and BEURLEN, H., (2012). Granitic

pegmatites as sources of colored gemstones. Elements 8: 281-287.

SISSON, V. B. CRAFORD, M. L. and THOMPSON P. H. (1981). CO2-brine

immiscibility at high temperature: evidence from calcareous metasedimentary

rock. Contribution to mineralogy and petrology, V.78, pp, 371-378.

SIMMONS, S., (2007). Pegmatite genesis: Recent advances and areas for future

research. Granitic pegmatites: The state of art-international symposism. 6-

12th May, 2007, proto, Portugal.

SIMMONS, W.B., and WEBBER, K.L., (2008). Pegmatite genesis state of the art.

European Journal of Mineralogy; July/August; V. 20, No. 4, pp. 421-438.

207

SINGH, S. P., (1998). Precambrian stratigraphy of Bihar-An overview in B.S

Paliwal (Ed). The Indian Precambrian (Scientific Publisher, Jodhpur, India,

pp. 376-408).

SINGH, R. N., THORPE, R., and KRISTIC, D., (2001). Galena Pb-isotope data of base

metal occurrences in the Hesatu-Belbathan belt, eastern Precambrian shield.

Jour. Geol. Soc. India. V.57, pp.535-538.

SIRBESCU, M. L., and NABELEK, P., (2003a). Crustal melts below 400 ◦C. Geology.

V.31, pp. 685-688.

SIRBESCU, M. L., and NABELEK, P., (2003b). Crystallization conditions and evolution

of magmatic fluids in the Harney Peak Granites and associated pegmatites,

Black Hills, South Dakota – evidence from fluid inclusions. Geochim.

Cosmochim. Acta, V.67, pp. 2443-2465.

SMEREKANICZ, J. R. and DUDAS, F. O. (1999) Reconnaissance fluid inclusion study

of Morefield pegmatite, Amelia County, Virginia. Am. Mineral, V.84, pp.746-

753.

SOBOLEV, A.V., (1996). Melt inclusions in minerals as a source of principle

petrological information. Petrology, V.4, pp. 209-220.

SOKOLOV, Y.M., KRATZ, K.O. & GLEBOVITSKYI, V.A. (1975): Regularities in the

formation and distribution of the muscovite and muscovite – rare metal

pegmatite formations in metamorphic belts. In Muscovite Pegmatites of the

USSR. Nauka, Leningrad, Russia (5-15; in Russ.).

SORBY, H.C., (1858). On the microscopical structure of crystals indicating the the

origin of rock and minerals. Q.J. Geol. Soc. London, V. 14, pp. 453-500.

SOURIRANJAN, S., and KENNEDY, G.C., (1962). The system of H2O-NaCL at

elevated temperature and pressure. Ame. Jour. Sci. V. 260, pp. 115-141.

SPENCER, E., (1945). Myrmekite in graphic granite and vein perthite. Min-mag.

V.XXVII, pp. 79-98.

208

SPOONER, E. T. C., (1981). Fluid inclusion studies of hydrothermal ore deposits. In

L.S Hollister and Mineralogical association of Canada, pp. 209-240.

STERNER. S. M., and BODNAR, R. J. (1987), Determination of phase equilibra and

volumetric properties in the system H2O-CO2-NaCl. American Current

Research in Fluid inclusions, Abstracts, 1, 68.

STOUT, M. Z., CRAWFORD, M. L., and GHENT, E. D. (1986). Pressure-temperature,

and evolution of fluid composition of Al2SiO5- bearing rocks, Mica Creek, B.

C. in light of fluid inclusion data and mineral equilbra. Contribution to

mineralogy and petrology. V.92, pp. 236-247.

SVERJENSKY, D. A., (1987). Calculation of thermodynamic properties of aqueous

species and solubility of mineral supercritical electrolyte in Carmichael I.S.E

and Eugester, H.P eds; Thermodynamic modeling of geological material ;

Mineral fluid and melt ; Rev. Mineralogy. V. 17, pp. 177-210.

SWANSON, S. E. and FENN, P. M., (1986). Quartz crystallization in igneous rocks.

Am. Mineral., V.71, 331-342.

SWANSON, S. E., and FENN, P. M., (1992). The effect of F and Cl on albite

crystallization: a model for granitic pegmatites. Can. Mineral. V. 30, pp. 549-

559.

TAKENOUCHI, S, and KENNEDY, G. C. (1965). The solubility of corbon dioxide in

NaCl solution at high temperature and pressure. American Journal of Science.

262, pp-445-454.

TANGER, J. C., and HELEGESON, H. C., (1988). Calculation of thermodynamic and

transport properties of aqueous species at high pressure and temperature.

Revised equation of state for the standard partial molal properties of ions and

electrolytes. Am. Jour. Sci. V. 288, pp.19-98.

TAYLOR, B. E., FOORD, E. E., and FRIEDRICHSEN, H., (1979). Stable isotope and

fluid inclusion studies of gem-bearing granitic pegmatiteaplite dikes, San

Diego Co., California. Contrib. Mineral.Petrol. V. 68, pp. 187-205.

209

TAYLOR, S. R., and MCLENNAN, S. H., (1985). The continental crust , its composition

and evolution Black well, Oxford, 312p.

THIAGARAJAN, R., (1961). Progress report for the year 1959-60. Geol. Surv. Ind.,

(unpublished)

THOMAS, R., WEBSTER, J. D., HEINRICH, W., (2000). Melt inclusions in pegmatite

quartz: complete miscibility between silicate melts and hydrous fluids at low

pressure. Contrib. Mineral. Petrol. V. 139, pp. 394-401.

THOMAS, R., (2002). Determination of the H3BO3 concentration in fluid and melt

inclusions in granite pegmatites by laser Raman microprobe spectroscopy.

Am. Mineral. V.87, pp. 56-68.

THOMAS, R., FORSTER, H.J., and HEINRICH, W., (2003). The behavior of boron in a

peraluminous granite-pegmatite system and associated hydrothermal solutions:

a melt and fluid inclusion study. Contrib. Mineral. Petrol. V.144, pp. 457-472.

THOMAS, R., FORSTER, H., RICKERS, K., and WEBSTER, J. D. (2005). Formation of

extremely F-rich hydrous melt fractions and hydrothermal fluids during

differentiation of highly evolved tingranite magmas: a melt/fluid-inclusion

study. Contrib. Mineral. Petrol., 148, 582-601.

THOMAS, R., WEBSTER, J.D., DAVIDSON, P., (2006a). Understanding pegmatite

formation: the melt and fluid inclusion approach. In “Melt inclusions in

plutonic rocks”, J.D. Webster, ed. Mineral. Assoc. Can. Short Course, V. 36,

pp. 189-210.

THOMAS, R., and DAVIDSON, P., (2012). Water in granite and pegmatite-forming

melts. Ore Geology Reviews 46: 32-46.

THOMPSON, A. B., (1982). Dehydration melting of pelitic rocks and the generation of

H2O-undersatuated granitic liquids. Amer. J. Sci. 282, 1567-1595.

THOMPSON, J. B., JR. & NORTON, S.A. (1968). Paleozoic regional metamorphism in

New England and adjacent areas. In Studies of Appalachian Geology.

210

Northern and Maritime (E-Zen W. S. White and J. B. Hadley and J. B.

Thompson Jr, eds. Intersciences New York.

THOMPSON, A. B., & TRACY, R.J. (1999). Model system for anatexis of pelitic rocks.

II. Facies series melting and reactions in the system CaO-KAlO2-NaAlO2-

SiO2-H2O. Contr. Mineral. Petrology, 70, pp. 429-438.

TIPPER, G. H., (1919). Pitchblende, monazite and other minerals from Pichhli, Gaya

district, Bihar and Orissa. Rec. Geol. Surv. Ind., V. 50, pt. 4 pp. 255-262.

TROMMSDORFF, V, and SKIPPEN, G., (1986). Vapour loss (boiling) as amechanism

for fluid evolution in metamorphic rocks. Contribution to mineralogy and

petrology, V.94, pp. 317-322.

TRUEMAN, D. L. and Cerny, P., (1982). Exploration for rare-element granitic

pegmatites. in “Granitic Pegmatites in Science and Industry”, P. Cerny, ed.

Mineral. Assoc. Can. Short Course Handbook, Vol.8, pp. 463-494.

VEMBAN, N. A., (1951). Progress report for the year 1950-51. Geol. Surv. Ind.,

(unpublished).

VEKSLER, I. V. and THOMAS, R., (2002). An experimental study of B, P and Frich

synthetic granite pegmatite at 0.1 and 0.2 GPa. Contrib. Mineral. Petrol.

V.143, pp. 673-68.

VON STENGE l, M.O. (1977). Normalschwingungen von Alkalifeldspäten.Z.

Kristallogr. 146, 1-18.

WATSON, E. B. and BRENAN, J. M. (1987) Fluid in the lithosphere, 1. Experimentally

determined wetting characteristics of CO2-H2O fluids and their implication

for fluid transport, host rock physical properties, and fluid inclusion formation.

Earth and Planetary Science Letters. V.85, pp. 497-515.

WEBER, C., BARBEY, P., CUNEY, M. & MARTIN, H. (1985). Trace element behaviour

during migmatization. Evidence for a complex melt - residuum- fluid

211

interaction in the St. Malo migmatitis dome (France). Contr. Mineral,

Petrology 90, 52-62.

WEBBER, K. L., FALSTER, A. U., SIMMONS, W. B., FOORD, E. E., (1997). The role of

diffusion-controlled oscillatory nucleation in the 302 D. London / Lithos 80

(2005) 281–303 formation of line rock in pegmatite-aplite dikes. J. Petrol. 38,

1777–1791

WEBSTER, R., (1994). Gems, Their Sources, Descriptions and Identification, 5th

Edition, Oxford, Butterworths,..

WEBSTER, J.D. and THOMAS, R., (2006). Silicate melt inclusions in felsic plutons: a

synthesis and review. in “Melt inclusions in plutonic rocks”, J.D. Webster, ed.

Mineral. Assoc. Can. Short Course, V. 36, pp.165-188.

WESTRA, G., and KEITH, S. B., (1981). Classification and genesis of stockwork

molybdenum deposits. Economic Geology. V. 76, pp.844-873.

WHITE, A. J. R. (1960). Genesis of migmatites from the Palmer region of south

Australia. Chem, Geol. 1, 165-200.

WHITE, E. B. (1974). Order disorder effects. In The Infrared Spectra of Minerals

(V.C. Farmer, ed.). The Mineralogical Society, London, U.K. pp. 87-110.

WHITWORTH, M. P. and RANKIN, A. H. (1989). Evolution of fluid phases associated

with lithium pegmatites from SE Ireland. Mineral. Mag., V.53, pp.271-284.

ZHANG, Z., and FRANZ, Z. E., (1987). Determination of the homogenization

temperature and densities of supercritical fluid in the system. Nacl-KCl-CaCl2-

H2O, using synthetic fluid inclusion. Chem. Geol. V. 64, pp. 335-350.

ZHANG, Y. G. and FRANTZ, J. D. (1988). Experimental determination of the

compositional limits of the immiscibility in the system CaCl2-H2O-CO2 at

high temperature and pressure using synthetic fluid inclusions. Chemical

geology.V.74, pp. 289-308.

212

APPENDIX

213

APPENDIX

Heating studies of the Type-III inclusions.

Sample No

Host Mineral TH in °C T Phase

SLI-10 Feldspar 175.6 Liquid

ʺ ʺ 181.2 ʺ

ʺ ʺ 210.1 ʺ


ʺ ʺ 198.1 ʺ

ʺ ʺ 210.1 ʺ

ʺ ʺ 205.7 ʺ

ʺ ʺ 250.0 ʺ

SLI-4 Quartz 162.4 Liquid

ʺ ʺ 137.1 ʺ

ʺ ʺ 169.9 ʺ

ʺ ʺ 183.3 ʺ


ʺ ʺ 192.3 ʺ

ʺ ʺ 199.9 ʺ

ʺ ʺ 224.0 ʺ

ʺ ʺ 205.5 ʺ

ʺ ʺ 220.0 ʺ

ʺ ʺ 235.0 ʺ


ʺ ʺ 126.4 ʺ

ʺ ʺ 128.4 ʺ

214

ʺ ʺ 127.2 ʺ

ʺ ʺ 114.5 ʺ

ʺ ʺ 118.1 ʺ

ʺ ʺ 121.6 ʺ

ʺ ʺ 120.0 ʺ

ʺ ʺ 100.1 ʺ

ʺ ʺ 124.1 ʺ

ʺ ʺ 139.6 ʺ

ʺ ʺ 161.9 ʺ

LI-5 Quartz 281.1 Liquid

ʺ ʺ 219.5 ʺ

ʺ ʺ 211.0 ʺ

ʺ ʺ 200.4 ʺ

ʺ ʺ 301.1 ʺ

ʺ ʺ 270.1 ʺ

ʺ ʺ 276.9 ʺ

ʺ ʺ 229.8 ʺ

ʺ ʺ 288.5 ʺ

ʺ ʺ 299.5 ʺ

Heating studies of the Type-IV inclusions.

Sample No

Host Mineral TH in °C T Phase


ʺ ʺ 171.0 ʺ

ʺ ʺ 180.9 ʺ

ʺ ʺ 220.1 ʺ


ʺ ʺ 210.2 ʺ

ʺ ʺ 130.2 ʺ

ʺ ʺ 140.5 ʺ

215

ʺ ʺ 181.7 ʺ

ʺ ʺ 177.1 ʺ


ʺ ʺ 181.1 ʺ

ʺ ʺ 195.2 ʺ


ʺ ʺ 210.1 ʺ

ʺ ʺ 189.0 ʺ

ʺ ʺ 237.2 ʺ

ʺ ʺ 241.1 ʺ


ʺ ʺ 154.8 ʺ

ʺ ʺ 129.2 ʺ

ʺ ʺ 189.5 ʺ

ʺ ʺ 191.2 ʺ

ʺ ʺ 143.6 ʺ

ʺ ʺ 177.9 ʺ


ʺ ʺ 264.8 ʺ

ʺ ʺ 256.3 ʺ

ʺ ʺ 251.8 ʺ

ʺ ʺ 288.5 ʺ

genesis of gemstone bearing pegmatites of great mica belt, jharkhand

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