characteristics and the occurrence of “garnierite” from ... · pada endapan laterit nikel...

Majalah Geologi Indonesia, Vol. 27 No. 1 April 2012: 1-11

1Naskah diterima: 03 Januari 2011, revisi terakhir: 12 Maret 2012Corresponding Author: [email protected]

Characteristics and the Occurrence of “Garnierite” from the Soroako Nickeliferous Laterite Deposits, Sulawesi, Indonesia

Karakteristik dan Keterdapatan Garnierit pada Endapan Laterit Nikel Soroako, Sulawesi

Sufriadin1, Arifudin Idrus2, I Wayan Warmada2, Irzal Nur1,Shigeki Ueno3, and Akira Imai3,4

1Mining Engineering Study Program, Hasanuddin University, Jln. Perintis Kemerdekaan Km. 10 Tamalanrea, Makasar 90245, Indonesia

2Department of Geological Engineering, Gadjah Mada University, Yogyakarta 55283 Indonesia

3Department of Earth Resources Engineering, Kyushu University, Fukuoka, Japan4Department of Earth Science and Technology, Akita University, Akita 010-8512, Japan

ABSTRACTAn investigation of Ni-Mg hydrous silicate ores called “garnierites” from the Soroako nickeliferous laterite deposits has been conducted by means of optical microscopy, X-ray diffractometry (XRD), and

-

sepiolite-falcondoite series. Nickel content of the garnierite samples studied by means of XRF methods

Keywords: garnierite, peridotite, kerolite, sepiolite, nickeliferous laterite

SARISuatu penelitian bijih Ni-Mg hidrous silikat yang dikenal dengan “garnierit” pada endapan nikel laterit Soroako telah dilakukan dengan menggunakan metode mikroskopi optis, XRD, dan XRF dengan tujuan untuk menguraikan keterdapatan, komposisi mineralogi, dan kimia garnierit. Percontoh garnierit diambil baik dari blok barat maupun Blok Petea. Blok Barat terutama disusun oleh batuan peridotit tak terserpentinisasi, sedangkan Blok Timur yang diwakili oleh daerah Petea ditutupi oleh protolit dengan tingkat serpentinisasi sedang sampai tinggi. Penelitian lapangan dan analisis mikroskopi menunjukkan bahwa garnierit pada blok barat terdapat dalam tiga bentuk yaitu: lapisan tipis pada bidang rekahan dan patahan, sebagai bahan pengisi rekahan atau urat, dan sebagai matriks pada peridotit konglomeratan. Sementara pada Blok Petea, garnierit hanya dijumpai dalam bentuk urat. Hasil analisis XRD menunjukkan bahwa komposisi mineral garnierit Soroako terdiri atas seri kerolit-pimellit, seri talk-wilemsit, Ni-serpentin, dan seri sepiolit-falkondoit. Kadar nikel pada percontoh garnierit yang ditentukan dengan metode XRF memperlihatkan nilai antara 1,8 - 19,2%. Variasi ini mungkin disebabkan oleh keterdapatan mineral gang terutama kuarsa/silika dan sedikit oksida besi.

Kata kunci: garnierit, peridotit, kerolit, sepiolit, laterit nikel


2

INTRODUCTION

Nickel laterite deposits contribute to

et al., 2011). In-donesia is one of the four largest nickel

deposits are mostly located in the eastern

Gag, and Waigeo Islands. These Nickel-

-

tropical condition. Nickel laterite ores are

et al et al.,

Ni-bearing materials.

Garnierite is a collective term for Ni-Mg hydrous silicate minerals that is commonly used by mine geologists. It is characterized

content (Proenza et al., 2008). Garnierite is eventually not a mineral approved by

Names (CNMMN), but it occurs as intimate -

ing minerals: serpentine, talc, sepiolite,

(1973) suggested that many garnierites are

(serpentine-like phase) and 2 : 1 layer sili-

7 Å and 10 Å respectively. Recent studies

reported by Wells et al. (2009) and Tauler et al. (2009).

The objectives of this paper are to describe the mode of occurrence of garnierites, to analyze their mineralogical and chemical composition of some garnierite samples col-lected from the Soroako nickeliferous laterite

protolith as host for garnierite mineralization.

GEOLOGICAL SETTINGS

The rock assemblages occupied Soroako

(ii) tectonite rocks, (iii) Mezosoic sedimen-

and (iv) Tertiary sediments (Simandjuntak et al., 1991) (Figure 1).

-

(Kadarusman et al

(Monier et al., 1995). It covers an area of ap-2

the north (Surono and Sukarna, 2001).

In Soroako and Petea areas that have been

PT. Vale Indonesia), the rocks commonly -

bronze-colour crystals. With the increas-ing degree of serpentinization, the colour of the rock generally gets darker (Ahmad,

-

Characteristics and the Occurrence of “Garnierite” from the Soroako Nickeliferous Laterite Deposits, Sulawesi, Indonesia (Sufriadin et al.)

3

-

in thin veinlets or along the edges of relic olivine crystals, or distributed as dissemi-

susceptibility of the rock and the degree of serpentinization are correlated.

-tensive deformation on the basis of crystal

-larly major thrust faults in the peripheral

the surrounding sediments.

SAMPLES AND METHODS

Fourteen garnierite samples have been col-

They comprise eight samples gathered from

using optical microscopy, X-ray diffractom-

spectroscopy.

light mode by means of Nikon Eclipse LV -

a Rigaku RINT 2000 X-ray diffractometer

o

o and counting time 4o/minute. Whole rock chemical analy-

a Rigaku RIX 3100 X-ray fluorescence

conducted at Laboratory of Economic Geol-ogy, Department of Earth Resources Engi-neering, Kyushu University, Japan.

et al., 1991).

Legend

Surfical Deposits

Larona Formation

Tomata Formation

Matano Formation

Ultramafic Complex

Wasuponda Melange

Masiku Formation

Town and village

Fault and lineament

Sample location

121 05’ E

o

121 05’ E

o

2 25’ S

o

2 25’ S

o

2 35’ S

o

2 35’ S

o

2 45’ S

o

2 45’ S

o

121 15’ E

o

121 15’ E

o

121 25’ E

o

121 25’ E

o

121 35’ E

o

121 35’ E

o

121 45’ E

o

121 45’ E

o

0 0

12 km

Wowondula

Tawuti Lake

Wasuponda

Malili

Matano Lake

Mahalona Lake

Soroako

Petea

Nuha

Lohia

0

200

Km


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RESULTS AND DISCUSSION

The Occurrence and Microscopic Features

crosscutting relationship, their occurrences may be distinguished into three types: (i)

materials or veins, and (iii) matrices on peri-dotitic conglomerate (Figure 2). Garnierites

medium green colour and they appear as thin -

nierite also formed as en echelon vein arrays

and soft materials (Figure 2c). They can be

are also common to be found at Ni laterite mines. In the case of fault planes that formed at saprolite zones closed to bedrocks, they

crack opening (crack seal mechanism). In -

block. Garnierite is also found as cements/matrices in fault gouges or as garnierite matrices in peridotitic conglomerate (Figure

previously formed the brecciation zone. The presence of garnierite clasts indicate tectonic remobilization of the veins.

Figure 2. Field appearances of garnierite ores in Soroako. a. garnierite occurs as slickensided fault coating on

10 cm

10 cm

20 cm

20 cm

d

a

b

c


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Results of microscopic analysis indicate -

alternating light and dark bands (Figure 3a).

crystals of magnetite have been found to be

(Figure 3b). Vuggy quartz or silica veins are

crosscut or parallel to the colloform banding

materials are common features observed microscopically developed on the garnierite

Mineralogy

Result of XRD analysis reveals that garnier-

-

series of talc like-phases have been identi-

-

-

0.2 mm

0.4 mm

0.2 mm

0.2 mm

Magnetite

Fibrous

Ni -Srp

Silica

Fibrous Ni

sepiolite

Ker-srp

mixture

void

A

B

C

D

0.4 mm

0.2 mm

0.2 mm

0.2 mm

b

a

c

d


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at 7.10Å and 7.33Å, possibly chrysotile

analyzed samples indicate the presence of

-

strongest lines around 12 Å observed from

of sepiolite-falcondoite series.

Whole Rock Chemistry

Chemical compositions of garnierite sam-ples determined by XRF are presented in

2

2 is dependent on mineral-ogical composition particularly the presence of quartz or amorphous silica. In addition, the differences in layer silicates of minerals containing in garnierites may also contribute

2 concentrations.

-

2+

2+ (Faye, 1974). Ratio of

limit that can be used to provide the termi-nology of garnierite solid – solution series.

more than 0.5, then the better match for the

could be assigned to pimellite, a solid solu-

talc. Nickel concentrations of all samples are

presence of tiny magnetite crystals likely can contribute to increase the iron concen-tration in analyzed samples.

The concentration of Al2 3 in both Soroako

Table 1. Mineralogical Composition of Soroako Garnierite Samples analyzed by XRD Method

Minerals/phases

Sample CodeGarnierite from Soroako West Block Garnierite from Petea Block

KO1 SU2 WW3 WW-4 KO4 IN1 KR1 AN4 SG4 PG1 PG3 PG4 AS6 PB5

Kerolite-pimellite - ++ +++ ++ +++ - ++ - + - - +++ - ++

Talc- ++ - - - - +++ - - - - - ++ - +++

Ni-serpentine + + ++ ++ ++ + +++ + +++ +++ +++ - +++ -Smectite - - - - - ++ - +++ - - - - - -Quartz - +++ - +++ ++ ++ - - + + + + + -

++ - ++ - - - - + - - - - - -- - - - + - + - + - - - - +


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anomalous Al2 3

-

sample AN-4 contains predominantly Ni-

high Al2 3related to the presence of “brindleyite”, a nickel-rich aluminous serpentine (Maksi-

AN-4, the high concentration of Al2 3 could be derived from decomposition of Al-rich smectite (beidellite) and partly originated from serpentine.

2 2 2

Water content of garnierite is highly vari-

-dent on mineral proportions in the samples. The presence of anhydrous phases such as

Table 2 Whole Rock Chemistry of Garnierite Samples from Soroako determined by XRF.

Composition(wt %)

Sample IDUnserpentinized Peridotite

(West Block)Serpentinized Peridotite

(Petea Block)KO-1 SU-2 WW-3 WW-4 KO-4 IN-1 KR-1 AN-4 SG4 PG-1 PG-3 AS-6 PG-4 PB-5

2 44.95 50.08 48.39 48.48 50.07 49.19

2 0.01 0.01 0.01

Al2 3 23.28 0.10 0.20 0.42 0.49 0.11 11.21 0.04 0.05 0.10 0.87 0.11 0.24

1.80 1.45 3.70 2.98 9.27 1.87 3.93 0.42 0.28 0.40 0.15 0.28

0.03 0.02 0.07 0.05 0.14 0.02 0.20 0.01 0.01 0.07 0.11

22.15 19.84 28.70 15.82 35.79 20.81 20.81 8.87 31.94

4.33 0.02 0.09 0.01 0.43 0.02 0.01 0.02 0.02 0.03

Na2 0.13 0.02

K2 0.02 0.02 0.03 0.01 0.01 0.01 0.01 0.01 0.01 0.01

P2 5 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

H2 8.94 10.71 13.28 7.74 10.38 9.09 23.40 24.57 11.80 10.59

Total oxides 96.86 91.08 89.63 97.23 80.15 91.85 89.41 87.64 97.99 94.62 95.10 84.93 84.43 95.67

Zn 0.05 0.14 0.17 0.03 0.41 0.12 0.17 0.25 0.02 0.01 0.07 0.08 0.49 0.05

Cr 0.04 0.03 0.11 0.08 0.30 0.05 0.05 0.25 0.01 0.01 0.17

Ni 2.96 8.73 10.10 2.66 19.11 7.90 10.19 12.01 1.75 5.25 4.75 14.85 14.68 4.10

Co (ppm) 24 78 59 157 28 87 20 191 5 7 44 104

2 4.10 3.29 3.54 3.53 2.41 8.28 7.75 Ni/ 0.18 0.31 0.12 0.58 0.30 0.43 0.05 0.20 0.19 0.11


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of talc and serpentine is different. Pure talc 2 -

2high moisture content of samples PG1 (23.4

sepiolite (Weaver and Pollard (1973).

Precipitation of Garnierite

Soroako nickeliferous laterite deposits are

and the principal Ni-bearing phases are hydrated silicates occurring in the form of veins, fracture coating, and clasts or matri-ces components of the breccias. They are

of unserpentinized peridotites.

-

could be originated from dissolution of the early-formed vein type and other Ni-bearing phases.

-cated by XRD patterns suggests that garni-erites have been precipitated from colloidal

et al., 1977).

Variations of mineralogy observed in the garnierite samples may indicate the episodic changes in chemistry of solution particularly activities of Si, Mg, and lesser Al (Golightly, 1981). The presence of discrete magnetite

et al., 1995). Precipitation of garnierite is possible

-ter interaction (Taylor and Eggleton, 2001). The occurrence of quartz replacement may

-tion or from a retarded drainage in a more acid environment (Golightly, 1981). During the dry season, silica concentrations are very high (Harder, 1977). The pH of solution is

humid substance, therefore the precipitation of silica is possible.

-

are mainly composed of sepiolites. Their occurrences are rare and generally hosted

-tite. Sepiolite-falcondoite has been found

rather than quartz, indicating more alkaline

Neoformation of sepiolite is most favored

alkaline (pH: ~8.0 to ~9.5), high (Mg+Si)/P 2 (Galan and Pozo,

that sepiolite can be formed directly from dissolution of serpentine in the presence of

8Mg3Si2 5 4 + H4 4 Mg8Si12 30 2)4.8H2

serpentine sepiolite

Fibrous aggregates of sepiolite morphology and banded veins of kerolite-pimellite are typical of crack seal crystallization. This is considered the evidence of episodic crack

-sure (Wiltschko and Morse, 2001). Pressure

minerals dissolve as result of the pressure


9

under pressure are more susceptible to dis-solve than unstressed minerals (Cluzel and Vigier, 2008). Transport of material from dissolution site to precipitation site may take

Jessel, 1997).

In general, the scarcity of garnierites occur-

differences in physico-chemical properties

products. Peridotite bedrocks at Soroaoko

are characterized by medium- to coarse-

thereby released the Ni ion into solution.

condition becomes slightly alkaline.

typically consist of the highly serpentinized

This properties may preclude precipitation of garnierite veins because Ni2+ -ing solution is readily adsorbed onto crystal surfaces or substitutes for Mg2+ in octahedral sites of serpentine structures.

CONCLUSIONS

Garnierite at Soroako occur as thin layer or -

ing materials or veins, and as matrices in peridotitic conglomerate.

Talc-like phases (kerolite-pimelite and talc-

nepouite series), and sepiolite-falcondoite

series are the main Ni-bearing minerals -

ence of quartz or amorphous silica in the

contribution to the high silica-magnesia ratio of mined ores in particularly of the

Nickel concentrations of all analyzed sam-

presence of gangue minerals as impurities

Precipitations of garnierite are not only controlled by environmental conditions

factors such as lithology (serpentinization degree of protolith) and structures (fracture intensities and tectonic reactivation) may also be responsible for the rates and intensi-ties of garnierite formation.

ACKNOWLEDGEMENTS

permission to collect samples. Special thanks are addressed to Prof. Koichiro Watanabe at the De-partment of Earth Resources Engineering, Kyushu University for providing access in using laboratory facilities. Thanks are also due to Dr. Ade Kadarus-

Short Terms Research Scholarship at Kyushu Uni-versity, Japan.

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AGSOJournal of Australian Gology & Geophysics, 17 (4), p.81- 88.

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and faulted regolith. Resources Geology, 58 (2),

Robinson, T.E., and Devenport, W.G., 2011. Extrac-tive metallurgy of nickel, cobalt, and platinum-group metals. Elsevier, Amsterdam.

Elias, M., 2002. Nickel laterite deposits a geological -

versity of Tasmania. Centre for Ore Deposit Research Special Publication, 4, p.205-220.

Ni2+ in ganierite: A discussion. Canadian Mineralo-gist, 12, p.389-393.

Economic Geology 100th

Anniversary Volume

Galan, E. and Pozo, M., 2011. Palygorskite and sepiolite deposits in continental environments. Description, Genetic Patterns and Sedimentary Set-tings. In: Galan, E. and Siregar, A. (Eds.), Develop-ment in Palygorskite - Sepiolite Research, Elsevier, p.125-174.

Golightly, J.P., 1981, Nickeliferous laterite depos-its. Economic Geology, 75th Anniversary Volume,

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Monnier, C., Girardieau, J., Maury, R.C., and Cotton,

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AustralasianInstitute of Mining and Metallurgy Publication Se-ries,

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