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Geological setting and timing of the Chah Zard breccia-hosted epithermal gold-silver deposit in the Tethyan belt of Iran
Citation
Kouhestani, H and Ghaderi, M and Zaw, K and Meffre, S and Emami, MH, Geological setting and timing of the Chah Zard breccia-hosted epithermal gold-silver deposit in the Tethyan belt of Iran, Mineralium Deposita: International Journal of Geology, Mineralogy, and Geochemistry of Mineral Deposits, 47, (4) pp. 425-440. ISSN 0026-4598 (2012) [Refereed Article]
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Copyright Statement
Copyright 2011 Springer-Verlag
DOI: doi:10.1007/s00126-011-0382-3
Abstract
The breccia-hosted epithermal gold–silver deposit
of Chah Zard is located within a high-K, calc-alkaline
andesitic to rhyolitic volcanic complex in the central part of
the Urumieh-Dokhtar Magmatic Arc (UDMA), west central
Iran. The total measured resource for Chah Zard is ∼2.5
million tonnes of ore at 12.7 g/t Ag and 1.7 g/t Au (28.6 t Ag,
3.8 t Au), making it one of the largest epithermal gold deposits
in Iran. Magmatic and hydrothermal activity was associated
with local extensional tectonics in a strike-slip regime formed
in transtensional structures of the Dehshir-Baft strike-slip fault
system. The host rocks of the volcanic complex consist of
Eocene sedimentary and volcanic rocks covered by Miocene
sedimentary rocks. LA-ICP–MS U–Pb zircon geochronology
yields a mean age of 6.2±0.2 Ma for magmatic activity at
Chah Zard. This age represents the maximum age of
mineralization and may indicate a previously unrecognized
mineralization event in the UDMA. Breccias and veins
formed during and after the waning stages of explosive
brecciation events due to shallow emplacement of rhyolite
porphyry. Detailed systematic mapping leads to the recognition
of three distinct breccia bodies: volcaniclastic breccia
with a dominantly clastic matrix; gray polymict breccia with a
greater proportion of hydrothermal cement; and mixed
monomict to polymict breccia with clay matrix. The polymictic
breccias generated bulk-mineable ore, whereas the
volcaniclastic breccia is relatively impermeable and largely
barren. Precious metals occur with sulfide and sulfosalt
minerals as disseminations, as well as in the veins and breccia
cements. There is a progression from pyrite-dominated (stage
1) to pyrite-base metal sulfide and sulfosalt-dominated (stages
2 and 3) to base metal sulfide-dominated (stage 4) breccias
and veins. Hydrothermal alteration and deposition of gangue
minerals progressed from illite-quartz to quartz-adularia,
carbonate, and finally gypsum-dominated assemblages. Free
gold occurs in stages 2 and 4, principally intergrown with
pyrite, quartz, chalcopyrite, galena, sphalerite, and Ag-rich
tennantite–tetrahedrite, and also as inclusions in pyrite. High
Rb/Sr ratios in ore-grade zones are closely related to sericite
and adularia alteration. Positive correlations of Au and Ag
with Cu, As, Pb, Zn, Sb, and Cd in epithermal veins and
breccias suggest that all these elements are related to the same
mineralization event.
Item Details
Item Type: | Refereed Article |
---|---|
Keywords: | Epithermal gold . Breccia .U–Pb geochronology. Hydrothermal alteration . Chah Zard . Iran |
Research Division: | Earth Sciences |
Research Group: | Geology |
Research Field: | Resource geoscience |
Objective Division: | Mineral Resources (Excl. Energy Resources) |
Objective Group: | Mineral exploration |
Objective Field: | Copper ore exploration |
UTAS Author: | Zaw, K (Professor Khin Zaw) |
UTAS Author: | Meffre, S (Professor Sebastien Meffre) |
ID Code: | 74816 |
Year Published: | 2012 |
Deposited By: | Centre for Ore Deposit Research - CODES CoE |
Deposited On: | 2011-12-14 |
Last Modified: | 2013-04-03 |
Downloads: | 3 View Download Statistics |
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