Session 5 Epigenetic gold systems - Extra Materials - Springer

Chapter 5-6
Age and origin of advanced argillic alteration at the
Bor Cu-Au deposit, Serbia
C. Lerouge, L. Bailly, E. Béchu, C. Fléhoc, A. Genna, J.L. Lescuyer, G. Stein
BRGM, BP 6009, 45060 Orléans cédex 2, France
P.Y. Gillot
Laboratoire de Géochronologie, bat. 504, 91405 Orsay, France
D. Kozelj
Bor Copper Institute, Bor, Serbia
Abstract. Stable (O, S, H) isotopic data on alunite from the Bor highsulfidation
Cu-Au deposit in Serbia indicate a magmatic-hydrothermal
origin. Hydrogen and oxygen isotopes indicate fluids are dominantly
magmatic. Oxygen and sulfur isotopes suggest a H 2 S/SO 4
ratio around 7-8 that is similar to those of other high-sulfidation
ore deposits around the world. A K/Ar date on alunite of 84.6 ± 1.2
Ma is within the range of early V1 Volcanism in the district. Stable
isotopic data on alunite from the Kupjatra prospect are quite similar
to the Bor ore deposit ; fluids are dominantly magmatic with a
greater meteoric component.
Keywords. K/Ar dating, stable isotopes, advanced argillic alteration,
Bor district, Serbia
1 Introduction
Alunite is a typical mineral of advanced argillic alteration
by acidic, sulfate-bearing fluids generated by several ways
in epithermal and supergene environments. Its different
origins can be distinguished by associated minerals and
S, H, O isotope compositions (Rye et al., 1992). Advanced
argillic alteration occurs as a main alteration type in the
Bor district, Serbia. It is associated with the large coppergold
deposit of Bor, the small base metals/gold deposit at
Coka Marin, and large quartz-alunite carapaces associated
with gold anomalies identified during an extensive
exploration program in the Bor district, such as Coka
Kupjatra (Kozelj 2002). These alteration zones and ore
deposits are hosted by Upper Cretaceous Volcano-plutonic
rocks of the Timok complex in Serbia. Exhumation of
the Carpatho-Balkanic belt suggests that a part of alunite
might be supergene.
This paper presents a K-Ar date and (S, O, H) isotopic
data on alunite from the Bor ore deposit and from the prospect
of Coka Kupjatra in order to constrain the origin of
the advanced argillic alteration zones in the district.
2 Geology
The Bor district in Serbia is part of the Carpatho-Balkans
metallogenic province which lies within the larger Tethyan
Eurasian metallogenic belt (TEMB). The Bor metallogenic
zone is developed in the so-called Timok Complex (TC)
(80km long, 20 km wide) comprised of three main calcalkaline
Volcanic episodes (V1 to V3).
The major types of mineralization in the district are located
along the eastern margin of the TC mainly within the
V1 hornblende±biotite andesitic lavas and pyroclastics,
dated at around 90-80 Ma (Jankovic et al., 1981). There are
porphyry copper deposits (Majdanpek, Veliki Krivelj), a
cupriferous massive pyrite deposit (Bor) and a gold-bearing
polymetallic massive sulfide deposit (Coka Marin). Other
gold prospects associated with advanced-argillic alteration
are hosted within V2 hornblende±pyroxene andesites dated
around 80-72 Ma (Jankovic et al., 1981). They are characterized
by low volume and low grade Cu-Au mineralization,
such as Coka Kupjatra, where the Au content is around
1 g/t in surficial samples and below 0.1 g/t at deeper levels
and laterally (Kozelj, 2002). The Bor mineralization
consists of series of massive cigar-shaped and pipe-like
bodies related to fracture zones and Volcanic breccias.
The largest body is Tilva Ros. The massive ore is comprised
of up to 70 Volume % fine-grained pyrite with
chalcosite, covellite and enargite. Barite is common in
upper parts of the system, whereas anhydrite/gypsum
occur as vein networks in lower parts of the system. Associated
advanced argillic alteration contains pyrophyllite,
diaspore, alunite, andalusite, zunyite and corundum
(Karamata et al. 1983).
3 Sampling
In the BOR mine, samples were collected along a vertical
cross-section in the advanced argillic alteration of the Tilva
Ros orebody, at the 0, -16, and -31m levels, and at the deepest
-155m level of the Borska Reka orebody. At Tilva Ros,
mineralization is represented by disseminated pyrite and
veins of pyrite-covellite, pyrite-sulvanite, or enargite associated
with an advanced argillic alteration (AAA), overprinted
by a late sericitic alteration. The AAA affects massively
volcanics, with scarce relics of biotite and plagioclase
phenocrysts. It is characterized by different mineral
assemblages depending of the depth and lateral zon-
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