新疆西天山大山口金矿地质及成矿流体包裹体地球化学

Geological characteristics and the geochemistry of ore-forming fluid inclusions in Dashankou gold deposit,Western Tien Shan,Xinjiang

新疆和静县大山口金矿位于南天山成矿带东段、哈萨克斯坦—伊犁板块与塔里木板块缝合带附近。矿床处在萨恨托亥—大山口脆韧性剪切带中,矿体以脆韧性变形的上志留—下泥盆统大山口组细碎屑岩、闪长玢岩、英安斑岩为主岩,与围岩的界线模糊。矿体在走向和延深方向上常尖灭再现,局限在脆韧性变形带中,表现为彼此平行的板状、透镜状矿体群或矿带。金矿石类型主要有石英脉型和蚀变岩型,矿石中含少量黄铁矿。对含金脉石英中流体包裹体研究表明,室温下包裹体主要为水溶液包裹体和含CO2包裹体两种类型。流体包裹体气相成分以H2O和CO2为主。流体包裹体均一温度主要集中在260～320℃,盐度峰值5.0%～8.5%NaCleq.,流体密度集中变化于0.75～0.95g/cm3,成矿流体属中温低盐度低密度热液。从流体包裹体估算成矿压力为37.33～109.77MPa,对应3.73～9.00km的成矿深度。成矿流体是H2O-NaCl体系并含CO2。大山口金矿床具有造山型金矿的明显特点,找矿潜力大。

The Dashankou gold deposit in Hejing County,Xinjiang Province is located at the east part of the southern Tien Shan metallogenic belt,and near suture zone between the Tarim and Kazakhstan-Erie Plates.The deposit occurred in the Sahentuohai-Dashankou brittle-ductile shear zones,the gold ore-body is hosted in the clastic rocks of the Dashankou Formation and the Upper Silurian-lower Devonian diorite porphyry and dacite porphyry,and the host rocks had undergone the brittle-ductile deformation.The boundaries between the ore bodies and wall rock are blurred.The ore bodies which are confined to the brittle-ductile deformation zone obviously show characteristic of thin-out reappearing along its strike and tendency,presenting parallel slaty and lenticular ore grops or belts.The natural types of the ore are mainly gold-bearing mylonite and quartz veins.The ore contains a small amount of pyrite.The fluid inclusions in the vein-quartz of the main mineralization stage were studied.There are two major types of fluid inclusions at room temperature,i.e.,the aqueous and CO2-bearing inclusions.The ore-forming fluid mainly contains H2O and CO2,and the temperature is between 260-320 ℃,the salinity peak is between 5.00%-8.50% NaCleq.,and the density between 0.75-0.95 g/cm3.The ore-forming fluids is mesothermal,low salinity and low density hydrothermal system.The ore-forming pressure of 39.78-109.77 MPa and corresponding ore-forming depths of 4.99-9.00 km is estimated by the fluid inclusions.The ore-forming fluid is a H2O-NaCl system bearing CO2.The Dashankou gold deposit shows obviously characteristics of orogenic type of gold deposit with better exploration potentiality.