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A Fluid Inclusion Study of Vein‐type Copper Mineralization in the East Wulasigou Pb–Zn–Cu Deposit, Altay, Northwestern China
Author(s) -
BIAN Chunjing,
XU Jiuhua,
CHEN Deping,
ZHANG Hui,
CHENG Xihui
Publication year - 2016
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.12814
Subject(s) - fluid inclusions , geology , quartz , mineralization (soil science) , geochemistry , hydrothermal circulation , mineralogy , vein , sedimentary rock , psychology , paleontology , psychiatry , seismology , soil science , soil water
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: H 2 O–CO 2 inclusions, carbonic fluid inclusions, aqueous fluid inclusions, and daughter mineral‐bearing fluid inclusions. Microthermometric studies show that solid CO 2 melting temperatures ( T m,co2 ) of H 2 O–CO 2 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 CO 2 ‐phase densities being 0.50–0.86 g/cm 3 . H 2 O–CO 2 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 CO 2 ‐phase densities being 0.48–0.89 g/cm 3 . The minimum trapping pressures of fluid inclusions in Q1 and Q2 are estimated to be 260–360 MPa and 180–370 MPa, respectively. The δ 34 S 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 δ D values of fluid inclusions in Q2 range from −121.0‰ to −100.8‰ (SMOW), and the δ 18 O H2O values calculated from δ 18 O of quartz range from −0.2‰ to 8.3‰ (SMOW). The δ D‐ δ 18 O 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.