A Fluid Inclusion Study of Vein-type Copper Mineralization in the East Wulasigou Pb-Zn-Cu Deposit, Altay, Northwestern China

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• 作者：Chunjing BIAN ; Jiuhua XU ; Deping CHEN ; Hui ZHANG and Xihui CHENG
• 刊名：Acta Geologica Sinica - English Edition
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：90
• 期：5
• 页码：1754-1767
• 全文大小：12695K
• ISSN：1755-6724

文摘

The Wulasigou Cu–Pb–Zn deposit, located 15km northwest of Altay city in Xinjiang, is one of many Cu–Pb–Zn polymetallic deposits in the Devonian Kelan volcanic-sedimentary basin in southern Altaids. Two mineralizing periods can be distinguished: the marine volcanic sedimentary Pb-Zn mineralization period, and the metamorphic hydrothermal Cu mineralization period, which is further divided into an early bedded foliated quartz vein stage (Q1) and a late sulfide-quartz vein stage (Q2) crosscutting the foliation. Four types of fluid inclusions were recognized in the Q1 and Q2 quartz from the east orebodies of the Wulasigou deposit: H₂O–CO₂ inclusions, carbonic fluid inclusions, aqueous fluid inclusions, and daughter mineral-bearing fluid inclusions. Microthermometric studies show that solid CO₂ melting temperatures (T_m,co2) of H₂O–CO₂ inclusions in Q1 are from −62.3°C to −58.5°C, clathrate melting temperatures (T_m,clath) are from 0.5°C to 7.5°C, partial homogenization temperatures (T_h,co2) vary from 3.3°C to 25.9°C (to liquid), and the total homogenization temperatures (T_h,tot) vary from 285°C to 378°C, with the salinities being 4.9%-15.1% NaCl eqv. and the CO₂-phase densities being 0.50–0.86 g/cm³. H₂O–CO₂ inclusions in Q2 have T_m,c02 from −61.9°C to −56.9°C, T_m,clath from 1.3°C to 9.5°C, T_h,co2 from 3.4°C to 28.7°C (to liquid), and T_h,tot from 242°C to 388°C, with the salinities being 1.0%-15.5% NaCl eqv. and the CO₂-phase densities being 0.48–0.89 g/cm³. The minimum trapping pressures of fluid inclusions in Q1 and Q2 are estimated to be 260–360 MPa and 180–370 MPa, respectively. The δ³⁴S values of pyrite from the volcanic sedimentary period vary from 2.3‰ to 2.8‰ (CDT), and those from the sulfide-quartz veins fall in a narrow range of −1.9‰ to 2.6‰ (CDT). The δD values of fluid inclusions in Q2 range from −121.0‰ to −100.8‰ (SMOW), and the δ¹⁸O_H2O values calculated from δ¹⁸O of quartz range from −0.2‰ to 8.3‰ (SMOW). The δD-δ¹⁸O_H2O data are close to the magmatic and metamorphic fields. The fluid inclusion and stable isotope data documented in this study indicate that the vein-type copper mineralization in the Wulasigou Pb–Zn–Cu deposit took place in an orogenic-metamorphic enviroment.