新疆西天山查汗萨拉金矿地质、金赋存状态及同位素地球化学研究

Geology, mode of occurrence of gold and isotopic geochemistry of Chahansala gold deposit in West Tianshan, Xinjiang

查汗萨拉金矿是近年在新疆西天山新发现的一处金矿床,处于依连哈比尔尕构造带西端。矿体呈不规则脉状产于细晶闪长岩构造破碎蚀变带及其接触带附近的上石炭统奇尔古斯套组蚀变围岩中,围岩蚀变较弱。矿石中硫化物主要为黄铁矿,并含少量磁黄铁矿、黄铜矿、方铅矿等。硫化物矿物呈自形粗晶或半自形结构,斑杂状分布在构造蚀变岩石中。金矿物以自然金和银金矿为主,还发现有硫(碲)银金矿和金铀化物等独特矿化线索,金矿物多赋存在黄铁矿中,以包体金、裂隙金和少量粒间金形式存在。金矿物形态以粒状和长角状为主,多为细、微细粒金(粒度<10μm)。矿石中矿物流体包裹体均一温度为220~340℃。热液脉石矿物石英流体包裹体的δD为-92‰^-74‰,δ18OV-SMOW为11.8‰~12.6‰,成矿流体显示岩浆热液和变质建造水混合的特征。热液方解石脉的δ13CV-PDB为-8.92‰^-8.06‰,δ18OV-SMOW为13.45‰~17.18‰,反映成矿流体中CO2主体来源于岩浆。硫化物206Pb/204Pb为18.036~18.173,207Pb/204Pb为15.536~15.612,208Pb/204Pb为37.940~38.097,成矿金属具岩浆来源特征。矿石中硫化物δ34SV-CDT为-9.8‰^-7.3‰,显示其可能与地层有关。查汗萨拉金矿为构造蚀变岩型中温岩浆热液矿床,不同于本区阿希金矿,是西天山金矿勘查中值得关注的新类型。

The Chahansala gold deposit, a newly discovered gold deposit in West Tianshan, is located at the west edge of the Late Paleozoic Yilianhabi＇erga arc-trench belt. Ore bodies are in the form of irregular veins and mainly occur in the shatter zone of fine-grained diorite that has intruded in the Upper Carboniferous tuffaceous siltstone and subordinately exist in the contact zone, with weak wall rock alteration. The sulfide minerals are mainly pyrite and subordinately pyrrhotite, chalcopyrite and galena, assuming euhedral and subhedral crystals in the ore and displaying taxitic structure in the structural alteration rock. Gold is most commonly present as native gold and electrum, with gold-bearing sulfides, gold-sulfides （Te） and Au-U minerals also observed. The distribution of gold in ores is uneven： gold mainly assumes relatively fine grains occurring as fracture gold and encapsulated gold in pyrite, and less commonly exists as intergranular gold between pyrite and vein mineral or as encapsulated gold in pyrrhotite, constituting fine-grained dissemination （within 10 μm）. Gold minerals have varied shapes, mostly assuming granular and long angular forms. Studies of fluid inclusions in some gangue minerals show that temperatures of the ore-forming fluids are 220～340℃, δD values of the hydrothermal gangue mineral quartz are -92‰～-74‰, the δ18OV-SMOW are 11.8‰～12.6‰, suggesting that ore-forming fluids are made up of magmatic water and formational water. δ13CV-PDB values of the hydrothermal gangue mineral calcite are -8.92‰～-8.06‰, and δ18OV-SMOW values are 13.45‰～17.18‰, implying that CO2 in the ore-forming fluids was mainly derived from the mantle-derived carbon. The 206Pb/204Pb of ore sulfides are 18.036～18.173, 207Pb/204Pb are 15.536～15.612, and 208Pb/204Pb are 37.940～38.097, indicating that the ore metals were derived from the magma. The δ34SV-CDT of sulfides are -9.8‰～-7.3‰, suggesting that the mineralization H2S resulted from the crust. The Chahansala gold deposit is a tensile structural alteration type deposit formed by the structure-magma-hydrothermal process during the extension at the end of the orogenic movement. The Chahansala gold deposit is genetically different from the A＇xi gold deposit in the same area, and this new type of gold deposit in West Tianshan should deserve much attention.