ore deposits of bor · 2019-04-19 · the conference room. the northern open pit of the deposit is...
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Ore deposits of Bor Mineral District, Serbia Field trip report 2018
Sofia University SEG Student Chapter Email: [email protected]
Supported by:
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TABLE OF CONTENTS FIELD PARTICIPANTS __________________________________________ 2
INTRODUCTION ____________________________________________________ 3 DAY 1 (22.10.2018) ____________________________________________________
BORSKO JEZERO PROSPECT _______________________________ 4
TIMOK GOLD PROJECT _______________________________________ 5
DAY 2 (23.10.2018)_____________________________________________________
VELIKI KRIVELJ DEPOSIT ____________________________________ 6 DAY 3 (24.10.2018)_____________________________________________________
MAJDANPEK DEPOSIT ________________________________________ 7 DAY 4 (25.10.2018) ____________________________________________________
ČUKARU PEKI PROSPECT _____________________________________ 8 VISITING LECTURES AND ACTIVITIES ____________________________ 9
CONCLUSION _____________________________________________________ 10 ACKNOWLEDGMENTS _____________________________________________ 10
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FIELD PARTICIPANTS This field trip was planned and organized by BSc students, PhD student and Prof. Kamen Bogdanov
from Sofia University, Department of Mineralogy, Petrology and Economic Geology.
Name: SEG Member: Academic Position: E-mail Address:
Kamen Bogdanov Academic Advisor Professor [email protected]
Yana Kancheva SEG Student
Chapter Member PhD student [email protected]
Boris Krestev SEG Student
Chapter Member BSc student [email protected]
Betina Petkova Student Chapter
Treasurer BSc student [email protected]
Kiril Mitov Student Chapter
Vise President BSc student [email protected]
Martin Marinov Student Chapter
President BSc student [email protected]
Radoslav Kalchev SEG Student
Chapter Member BSc student [email protected]
Tsvetilyana Mitova Student BSc student [email protected]
Yordan Yordanov SEG Student
Chapter Member BSc student [email protected]
Yoana Mangezova SEG Student
Chapter Member BSc student [email protected]
Table 1. Field trip participants of Sofia University, SEG Student Chapter.
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INTRODUCTION
Between 22-25th October, this year Sofia
University SEG Student Chapter has
organized a field trip to Bor Mineral District
in eastern Serbia. We have the opportunity to
visit two operating mines and three
exploration projects with an important
еconomic significance for Bor mining region.
The main purpose of the trip was to present
the diferent types of deposits such as world-
class and unique copper-gold mineral
deposits such as porphyry, hydrothermal,
еpithermal and sediment-hosted gold ones
from Bor metallogenic zone, part of Apuseni-
Banat-Timok-Srednogorie (ABTS)
magmatic-metallogenic belt. Visiting these
mineral deposits we learn about the geology
conditions of formation of them,
mineralization characteristics, tectonic
environments and processes of exploitation.
All the deposits are within thе margins of the
Timok Magmatic Complex (TMC) (Fig.1.).
We choose several characteristic types of
deposits and prospects for our trip: Borsko
Jezero prospect constitutes epithermal and
porphyry system, two world-class porphyry system deposits Veliki Krivelj and Majdanpek, Cukaru Peki
prospect, which has both epithermal high sulphidation and porphyry systems. Also the newly discovered
sedimentary rock-hosted gold prospects Bigar Hill, Korkan and Kraku Pester, associated with a large
hydrothermal system, which are previously unrecognized type of gold mineralization within the (TMC).
Our field trip guide was the academic advisor Prof. K. Bogdanov from the Sofia University. Together
with the senior and staff geologists of each deposit he helped us understand the complex regional geology
and order of events in the formation of the deposits.
Fig.1. Simplified geologic map of the Timok Magmatic
Complex (after von Quadt et al. (2002), Clark and Ullrich
(2004), Lips et al. (2004), Zimmerman et al. (2008), Kolb et
al. (2013), Gallhoffer et al. (2015))
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DAY 1 - BORSKO JEZERO PROSPECT
Our first stop was at the exploration office of
“Mundoro Capital Inc”. We were introduced with
the exploration of the Borsko Jezero license area,
which is located four kilometers west from the Bor
mine, during a nice presentation (Fig.2.) from the
geology staff. The deposit is part of the Timok
Magmatic Complex which is one of the most
highly rich on metallogenic formations in the
Tethyan Belt. The formation of the deposit is
controlled mainly by tectonic settings of rotation
on the block Tisza, which opened basins where ore
mineralization is concentrated. The lithology is
presented by andesite and pyroclastic rocks with
Upper Cretaceous age, which are the host rocks. Borsko Jezero and Cukaru Peki deposits have a lot
geological similarities, both of them represent high sulphidation systems and this leads to a conclusion
that they are part of one stage of magmatism. The data of drilling core indicates that in depth there is an
advanced argillic lithocap of altered agglomerate volcanic rocks, in which advanced argillization took
place. We had the opportunity to examine
drill core (Fig.3.) and observed that most of
ore mineralization is related to hydrothermal
breccias hosted in advanced argillic altered
andesites. Hydrothermal breccias are
characterized with pyrite grains with silica
matrix in which occurs vuggy silica with
most of the Au-concentration and there is
also alunite observe. All of these features
are common for the high-sulphidation
epithermal systems.
Fig.2. Introduction and learning about the regional
geology of Borsko Jezero.
Fig.3. Examine the drill core in drill-core storage of
Borsko Jezero prospect.
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TIMOK GOLD PROJECT
The second place we visited during the first day
was the exploration office of “Avala Resources
Ltd.” that are operating Timok Gold Project and
it includes Bigar Hill, Korkan, Korkan West, and
Kraku Pester prospects, located on the west
margin of TMC. These prospects are similar to
Carlin-type sediment-hosted deposits with gold
mineralization and are unique for the (TMC). A
presentation (Fig.4.) related to the regional
geology, specifications of the deposits formation
and the exploration methods used by the geology team of “Avala Resources Ltd.” was displayed to us.
The deposits are formed between two different types of rocks, during the intrusive magmatism the
magmatic body contacted with sedimentary rocks and processes of metamorphism caused by the
circulation of hydrothermal fluids that deposed the main Au-rich mineralization. These processes are
structurally controlled by faulted zones which are a prerequisite for intrusion of the magma in the host
sedimentary rocks. The main lithologies which are common for the deposits are limestones, marbles,
sandstones, andesitic, volcanic and volcaniclastic rocks. The gold mineralization is mainly hosted within
a sedimentary rocks such as limestones, calcareous
sandstones and conglomerates (in which it is) with
an interbedded siltstone unit included. We were
kindly invited by the hosts in the core storage
(Fig.5.) to examine drill core from the Bigar Hill
deposit. During our observation, we found out that
gold mineralization appears to be associated with
pyrite which is a sign of sulphidation with
alteration zones including kaolinization,
silicification and typical dissolution of limestones
and marls, which resembles vuggy silica and the
main deposition of Au is in these dissolved carbonate rocks. The estimated mineral resources are
approximately 46.9 million tonnes with rates of 1.32 g/t Au.
Fig.4. Presenting the Timok Gold Project to students.
Fig.5. Observing drill core from Bigar Hill deposit.
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DAY 2 - VELIKI KRIVELJ DEPOSIT
The following day we drove on to Bor town
and visited the Veliki Krivelj porphyry
copper deposit which is located 3 km to the
northeast of Bor deposit. We were
welcomed by the geology staff of the mine
and with a special truck, we were
transported to the site with an opened view
to the pit so the characteristics of the deposit
were presented live to us. The formation of
the deposit was tectonically controlled by
the extensive Timok fault (Fig.6.), that
crosses sedimentary rocks, where later magmatic bodies are intruded. The main ore mineralization is
formed in systems of dykes above magmatic intruded body hosted by hydrothermally altered andesites
and dacite rocks with Upper Cretaceous age. The porphyry mineralization in the deposit is attached to
hydrothermally altered andesites and pyroclastic breccias with
Upper Cretaceous age, agglomerated with limestones. This type
of mineralization is related to quartz-diorite and andesite dykes.
Skarns were formed on the contact with limestones. On the upper
parts of the deposit there is palaeo-surface zone (Fig.6.) of the
porphyry stockwork mineralization, exposed to oxidation due to
erosion so there is an enrichment of massive Cu-sulphides
(enargite and covellite) with 3 to 18% Cu. Main ore minerals for
this type of mineralization are chalcopyrite, pyrite, molybdenite,
enargite, bornite, covellite and chalcocite. In the skarn sections
are observed characteristic minerals like garnet, calcite, epidote,
quartz, pyrite and chalcopyrite. There is also hydrothermal change
in the andesite host rocks, predominantly from potassium feldspar
(Fig.7.), widespread injected silicification associated with strong
pyritization and sericitization on the margins of the zone. The ore grades are approximately 0.34% Cu,
0.07 g/t Au and only 0.003 to 0.005%.
Fig.7. Late hydrothermal change
mainly by potassium feldspar.
Fig.6. View to Veliki Krivelj open pit.
Timok fault Paleo-surface zone
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DAY 3 - MAJDANPEK DEPOSIT
On October 24th, we traveled northwest from Bor town to
Majdanpek world-class porphyry copper deposit. This is one of
the oldest operating deposits with signs of mining from 7000
thousand years ago. When we arrived, we were greeted by the
senior geologist of the mine, then we were invited to a
conference room (Fig.8.) so he can present us the rich history
and geology setting of the deposit. Majdanpek is the northest
deposit in Timok Magmatic Complex and it is structurally
related to the Timok fault. On several geology maps this was
shown to us together with the lithology, which consists mainly
of gneisses, amphibolites, limestones and a dyke system that
have complicated the geology relations. The Majdanpek deposit
consists of several types of mineralization, the dominating one
is porphyry copper-gold mineralization with molybdenite and massive sulphides. The mineralization in
the deposit is mainly concentrated in andesitic dykes in a depth up to 1000m. The dyke systems are
intruded along the Timok fault (Fig.9.) in a zone
with length of 5 km, cutting metamorphic rocks
and limestones. The ore mineralization is
typically developed as stockworks which’s
formation is within the contact of the andesitic
dykes with the limestones. There are also skarns
around the intrusive bodies, while more final
replacement bodies are found in the limestones.
The highest Cu and Au grades are related to K-
silicate alteration and quartz veins. There is a
small oxidation zone 8-10m. thick enriched with Cu containing minerals. We visited the south open pit
of the deposit and were able to see all the structures and lithology relations that were presented to us in
the conference room. The northern open pit of the deposit is similar to the southern one, but with more
massive ore bodies and it is a polymetallic type with more sulfides. Up to now, it’s been mined 600 Mt
from total pre-mining resource of approximately 1000 Mt with 0.6% Cu and 0.3-0.4g/t Au.
Fig.8. Discussing the geology of the
deposit.
Fig.9. Plan view of Majdanpek deposit south open pit.
Timok fault
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DAY 4 - CUKARU PEKI PROSPECT
The last day of the field trip we visited the exploration
office of “Rakita Exploration doo Bor” 7 km west of
Bor town. We had safety instructions, presentation and
a short discussion (Fig.10.) about the geology of the
deposit and the latest data from the exploration drilling
program. Cukaru Peki ore mineralization is very similar
to this in Bor deposit with massive sulfide bodies and
stockworks. The mineralization is hosted in andesites
and hydrothermal breccias with Upper Cretaceous age
and it is associated mainly with two types of deposition:
epithermal and porphyry copper-gold deposition. Cukaru Peki is divided on two zones, Upper Zone
(400-800m) and Lower Zone with significant differences in ore mineralization deposition types. In the
Upper Zone mineralization is related to high sulphidation-epithermal type with very high grades of Cu
and Au. We visited the core shelter (Fig.11.) and observed the hydrothermal breccia hosted by altered
andesite from the zone with sulfide matrix of pyrite, covellite, enargite, chalcocite and other copper
sulfides in which Au is associated. The approximate resources estimated in Upper Zone are 27 million
tonnes with average grade of 3.3% Cu and 2.1g/t Au. In the Lower Zone (500-2300m) there are two
types of mineralization, but with lower grades of Cu and Au than the Upper Zone. The porphyry
mineralization is characterized with minerals like chalcopyrite, bornite, molybdenite, galena and
sphalerite. This mineralization is by far the most important containing at over 95% of the ore at the
Lower Zone. The mineralization of Lower Zone
covered above the Upper Zone on the east side on
the contact between the high sulphidation and
porphyry types is differentiated epithermal zone
with covellite and enargite that are replacing the
primary sulphide. At the drill core logging section,
we saw the process of logging and observed that this
zone is associated with gypsum and anhydrite veins
that are typical for the high sulphidation zone. The
estimated resources of the Lower Zone are 1.1 billion
tonnes with grades 0.99% Cu and 0.21 g/t Au.
Fig.10. Presenting the regional geology of
the deposit.
Fig.11. In front the core shelter with geology
staff of the deposit.
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VISITING LECTURES AND ACTIVITIES
This year the Sofia University SEG Student Chapter had
two visits by lecturers, members of the Society of
Economic Geologists (SEG). On 27.04.2018 we had a
guest lecturer Prof. Dan Wood (Fig.12.), who gave a
lecture on the topic about: “Transforming the Business
of Gold Exploration: Adapting to Deeper Exploration “.
Тhe lecture was interesting, very useful and gathered
many people from the mining industry in Bulgaria.
The chapter had an invitation from “Dundee Precious
Metals Chelopech” on 11.05.2018 to attend a lecture”
Porphyry copper systems” of Dr. Richard Sillitoe
(Fig.13.).
Оn October 29th, 2018 arrived lecturer Dr. Alan J.
Wilson and presented (Fig.14.) two lectures. The first
lecture was about “Comparative Anatomies: Calc-
alkaline vs Alkalic Porphyry Deposits” and the second
one “Porphyry Copper Deposits: Field Criteria for
Exploration and Resourses Potential Evolution”. There
was huge interest to this lectures from people in the
mining industry and the geology staff of “Rakita
Exploration doo Bor”, Serbia also attended to the
lecture. For the students was extremely helpful to gain
experience from a proven specialist like Dr. Alan J.
Wilson. Thanks to our academic advisor Prof. Kamen
Bogdanov, in the months of July and October 2019 a
course on working with geological software for 3D
geological modelling provided by Leapfrog company
will take place. It will be free for the students from
Sofia University, and will be paid for employees from
the mining industry.
Fig.13.Presentation of Dr. Richard Sillitoe
at “Dundee Precious Metals Chelopech”
Fig.12. Discussion during the lecture of
Prof. Dan Wood
Fig.14. During the presentation of Dr. Alan
J. Wilson
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CONCLUSION To summarize, this year for Sofia University SEG Student Chapter was extremely useful and
constructive for our future as geologists. Тhe field trip to Serbia mineral deposits was an incredible
experience and opportunity to feel the atmosphere of the geologist profession and to establish contacts
with future employers. The meetings with the lecturers enriched our knowledge, strengthened our
interest in geology and for organizing new trips and future meetings with fellows from Society Economic
Geologists.
ACKNOWLEDGMENTS
Sofia University SEG Student Chapter would like to serve special thanks for the financial support from
the Society of Economic Geologists, that made this trip possible and also the commitment for better
education of the future economic geologists. In addition, we would like also to thank to the geological
staffs of RTB Bor, Dundee Precious Metals (Avala Resources Ltd.), Freeport-McMoran (Rakita
Exploration doo Bor), Mundoro Capital (Stara Planina Resources d.o.o.), for their kind support for
organizing the field trip and make it beneficial for us, by presenting, discussing and leading exceptional
tours with very open access to their work and mining base.