北祁连山寒山金矿床成矿作用同位素地质年代学

Isotopic Geochronology of the Ore-forming Process in the Hanshan Gold Deposit of the North Qilian Mountains

位于北祁连山西段安西县的寒山金矿是一个较特殊的、以剪切带容矿的中浅成低温热液蚀变岩型金矿床,它赋存于下奥陶统安山英安质火山碎屑岩中,金矿体受韧脆性剪切带内的强变形带控制。根据矿脉矿物组合及相互穿插关系,原生热液成矿期成矿作用可分为5个矿化阶段。其中,金毒砂石英阶段和金黝铜矿多金属硫化物阶段为主要金成矿阶段。年代学研究表明,金毒砂黄铁矿石英阶段含金石英脉RbSr等时线年龄为372±8Ma,热液蚀变岩RbSr等时线年龄为339±10Ma,矿区辉长闪长岩及南侧青山花岗闪长岩锆石UPb年龄分别为370±25Ma和347.1±6.4Ma,表明区内岩浆侵入活动与成矿作用均发生在晚泥盆世—早石炭世,相当于北祁连山碰撞造山向陆内伸展转变时期,从而揭示了成矿作用是后碰撞造山阶段构造岩浆流体“三位一体”共同作用之产物。

The Hanshan gold deposit, located in Anxi County within the western part of the Qinlian Mountains, is a typical epithermal and ifitermediate-shallow altered rock type gold deposit with gold orebodies produced in the shear zone. It occurs in Lower Ordovician andesitic-dacitic pyroclastic rocks and is controlled by the ductile-brittle shear zone. According to the mineral assemblage and the intercalation relationship, the ore-forming process of the primary hydrothermal phase can be divided into five mineralization Among them, the gold arsenomarcasite quartz stage and the gold-stylotyp-polymetallic sulfide stage are the major gold-forming stages. Chronologic studies show that the Rb-Sr isochron age of auriferous quartz at the gold-arsenomarcasite-quartz stage is 372 ± 8 Ma and that of thermally altered rock is 339 ± 10 Ma. These data suggest that the igneous intrusion and the ore-forming process took place between Late Devonian and Early Carboniferous, corresponding to the period when the North Qianlian Mountains were formed and extended inland. It is therefore considered that the ore-forming process resulted from the ＂trinity＂ joint action of postorogenic structure-magma-fluids.