后龙门山造山带辛家咀金矿床地质特征及成因探讨

辛家咀金矿床位于后龙门山造山带北东段,是2020年新发现的一个金矿床(年度金资源量约960 kg),找矿潜力巨大。基于详细的野外露头、探槽、钻孔编录和镜下观察,发现辛家咀金矿床中矿石类型以石英脉型为主,金主要以裂隙金和包裹金的形式赋存于黄铁矿、石英和少量多金属硫化物中。结合脉体穿插关系、矿物共生组合和矿石组构,将辛家咀金矿床的成矿作用划分为热液成矿期和表生氧化期,其中热液成矿期为主成矿期,可细分为3个成矿阶段:Ⅰ.石英-黄铁矿阶段,Ⅱ.石英-方解石-自然金-多金属硫化物阶段,Ⅲ.石英-碳酸盐阶段。此外,辛家咀金矿床发育于燕子砭—花石沟脆-韧性剪切带中,矿体的产出严格受剪切带控制,仅在脆-韧性变形强且脆性断裂发育的部位才发育高品位金矿石。综上,辛家咀金矿床属于脆-韧性剪切带型矿床。

Geological Characteristics and Genesis of the Xinjiazui Gold Deposit in Back-Longmenshan Orogenic Belt

The Xinjiazui gold deposit is located in the north-eastern section of Back-Longmenshan orogenic belt. This deposit (annual gold resources of about 960 kg) is newly discovered by the Xi’an Center of Mineral Resources Survey in 2020, and shows huge resource potential. Based on detailed study of outcrops, exploration trench, drillhole logging and microscope observation, it is found that the mineralization of primary ores in the Xinjiazui gold deposit is dominated by quartz-vein-type gold ore. In addition, gold is mainly hosted by pyrite, quartz and a small amount of polymetallic sulfides and occurs as fracture gold or gold inclusions. Combining with the crosscutting relationship of veins, the characteristics of mineral paragenetic association and typical ore fabric, mineralization of the Xinjiazui gold deposit can be divided into hydrothermal mineralization epoch and supergene oxidation epoch. The hydrothermal metallogenic epoch is the main ore event, and can be subdivided into three stages: Ⅰ.quartz-pyrite stage, Ⅱ.quartz-calcite-natural gold polymetallic sulfide stage, and Ⅲ.quartz-carbonate stage. Moreover, the Xinjiazui gold deposit is developed in Yanzibian-Huashigou brittle-ductile shear zone, the ore production is strictly controlled by the shear zone, and high-grade gold ore is developed only in the position with strong ductile deformation and brittle fracture. Therefore, the Xinjjiazui gold deposit is a brittle-ductile shear zone type gold deposit.