甘肃武都金坑子金矿床地球化学特征及成因探讨

甘肃武都金坑子金矿床位于碧口地块北缘西秦岭南成矿亚带。本文为探讨金坑子金矿床成因，对矿床野外地质特征，H、O、S同位素组成及流体包裹体特征进行了系统的研究。研究结果表明：矿体产于千枚岩与灰岩岩性不整合面及其附近的断裂破碎带中，主要受断裂构造控制；不同成矿阶段石英的δD_H2O-VSMOW值范围为-81.4‰~-67.5‰，δ¹⁸O_H2O-VSMOW值范围为7.51‰~10.55‰，显示成矿流体早期主要来源于深源岩浆水，晚期有大气降水的加入；黄铁矿δ³⁴S值变化范围为-0.7‰~0.6‰，显示成矿物质主要来源于深部岩浆，并有地层物质加入；流体包裹体的均一温度为155.6~304.0℃，盐度（w（NaCl））为0.53%~13.29%，显示成矿流体具中温、中低盐度和富含CO₂的特点。结合区域研究资料，认为金坑子金矿床成因类型为印支晚期的中温热液脉型金矿床。

Geochemical Characteristics and Genesis of Jinkengzi Gold Deposit in Wudu Area,Gansu Province

Jinkengzi gold deposit is located in the southern sub-belt of west Qinling metallogenic belt in the northern margin of Bikou block. In order to find out the genesis of Jinkengzi gold deposit, the field geological characteristics, hydrogen, oxygen, sulfur isotopic composition, and fluid inclusion characteristics of the deposit were systematically studied. The results show that the ore bodies occur in the unconformity of phyllite and limestone and the fracture zone nearby, which is mainly controlled by the fracture structure; the δD_H2O-VSMOW value of quartz in the different mineralization stages ranges from -81.4‰ to -67.5‰, and δ¹⁸O_H2O-VSMOW ranges from 7.51‰ to 10.55‰, indicating that the early ore-forming fluid was originated mainly from the deep source magmatic water, and added with atmospheric precipitation in the late stage. The δ³⁴S value of pyrite varies from -0.7‰ to 0.6‰, indicating that the ore-forming material is mainly derived from deep magma, with the addition of stratum material. The homogenization temperature of the fluid inclusions is 155.6-304.0 ℃, and the salinity is 0.53%-13.29%, indicating that the ore-forming fluid has the characteristics of medium temperature, medium-low salinity,and rich in CO₂. Based on this comprehensive study, it is believed that the genetic type of Jinkengzi gold deposit is a mesothermal vein-type gold deposit formed in the Late Indosinian period.