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

The Wulasigou Cu-Pb-Zn deposit,located 15 km 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 PbZn 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 Ql are from-62.3℃ to-58.5C,clathrate melting temperatures（T（m,clath）l） are from 0.5 C to 7.5 C,partial homogenization temperatures（T（h,CO2）） vary from 3.3℃ to 25.9℃（to liquid）,and the total homogenization temperatures（T（h,tot）） vary from 285℃ to 378℃,with the salinities being 4.9%-15.1%NaCl eqv.and the CO2-phase densities being 0.50-0.86 g/cm-3.H2O-CO2 inclusions in Q2 have T（m,CO2） from-61.9℃ to-56.9℃,T（m,clath）from 1.3℃ to 9.5℃,T（h,CO2） from 3.4℃ to 28.7℃（to liquid）,and T（h,tot） from 242℃ to 388℃,with the salinities being 1.0%-15.5%NaCl eqv.and the CO2-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 and180-370 MPa,respectively.The δ-（34）S values of pyrite from the volcanic sedimentary period vary from2.3‰ 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 theδ-（18）O（H2O） values calculated from δ-（18）O of quartz range from-0.2‰ to 8.3‰（SMOW）.The δD-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.

Wood textures in Jinman copper deposit in western Yunnan and their genetic implications

Jinman vein copper deposit in western Yunnan occurs in a salt-bearing red clastic rock formation composed of sandstone, siltstone and shale. Wood texture is considerably developed in the ores. The metallic minerals making up the wood textures mainly include pyrite, chalcopyrite and bornite. Studies on the samples and examination of their micrographs and electron micrographs have confirmed that they belong to xenoxylon, reflecting that the ore-hosting rock series is the product of sedimentation in the terrestrial environment. Organic geochemistry and sulfur and carbon isotopic composition data indicate that the formation of the deposit is substantially related with underground hot brines and biological processes.