Genesis of the Bangbu Orogenic Gold Deposit, Tibet: Evidence from Fluid Inclusion, Stable Isotopes, and Ar-Ar Geochronology

Autor: Huang Kexian, Yang Zhusen, Pei Yingru, Li Wei, Zheng Yuanchuan, Sun Qingzhong
Rok vydání: 2016
Předmět:
Zdroj: Acta Geologica Sinica - English Edition. 90:722-737
ISSN: 1000-9515
Popis: The Bangbu gold deposit is a large orogenic gold deposit in Tibet formed during the Alpine-Himalayan collision. Ore bodies (auriferous quartz veins) are controlled by the E-W-trending Qusong-Cuogu-Zhemulang brittle-ductile shear zone. Quartz veins at the deposit can be divided into three types: pre-metallogenic hook-like quartz veins, metallogenic auriferous quartz veins, and post-metallogenic N-S quartz veins. Four stages of mineralization in the auriferous quartz veins have been identified: (1) Stage S1 quartz+coarse-grained sulfides, (2) Stage S2 gold+fine-grained sulfides, (3) Stage S3 quartz+carbonates, and (4) Stage S4 quartz+ greigite. Fluid inclusions indicate the ore-forming fluid was CO2-N2-CH4 rich with homogenization temperatures of 170–261°C, salinities 4.34–7.45 wt% NaCl equivalent. δ18Ofluid (3.98‰–7.18‰) and low δDV-SMOV (–90‰ to –44‰) for auriferous quartz veins suggest ore-forming fluids were mainly metamorphic in origin, with some addition of organic matter. Quartz vein pyrite has δ34SV-CDT values of 1.2‰–3.6‰ (an average of 2.2‰), whereas pyrite from phyllite has δ34SV-CDT 5.7‰–9.9‰ (an average of 7.4‰). Quartz vein pyrites yield 206Pb/204Pb ratios of 18.662–18.764, 207Pb/204Pb 15.650–15.683, and 208Pb/204Pb 38.901–39.079. These isotopic data indicate Bangbu ore-forming materials were probably derived from the Langjiexue accretionary wedge. 40Ar/39Ar ages for sericite from auriferous sulfide-quartz veins yield a plateau age of 49.52 ± 0.52 Ma, an isochron age of 50.3 ± 0.31 Ma, suggesting that auriferous veins were formed during the main collisional period of the Tibet-Himalayan orogen (∼65–41 Ma).
Databáze: OpenAIRE
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