甘肃北山拾金坡金矿床地质特征及成因分析

Geological characteristics and genetic analysis of Shijinpo gold deposit in Beishan Mountain, Gansu Province

拾金坡金矿是甘肃北山南带较为典型的含金硫化物石英脉型金矿床,矿化富集与加里东晚期—海西早期拾金坡复式岩体密切相关。矿体产于岩体的内接触带,产出部位明显受近EW向断裂破碎带的控制。矿体主要为大脉状、脉状、透镜状。矿床中发育一套典型的中温热液成因的矿物组合,矿石以强烈的绢云母化、碳酸盐化、硅化和黄铁矿化为特征,矿石的金属矿物组合为自然金_银金矿_黄铁矿_方铅矿_闪锌矿_黄铜矿,矿化属中温热液成因。硫和铅同位素显示成矿金属物质主要来自围岩,即斑状花岗岩;氢和氧同位素组成表明成矿流体来自花岗岩浆水。成矿时代属早—中海西期。因此可推断,拾金坡金矿床属于与构造_岩浆活动有关的中温岩浆热液成因矿床。

Located in the southern part of the Beishan Mountain, the Shijinpo deposit is a typical auriferous sulfide quartz vein gold deposit in this region. The mineralization is closely related to Shijinpo complex granite rock body which is considered to have been formed in the period from late Caledonian to early Hercynian. Existent along the endo-contract zone of the rock body, the ore bodies mostly take the forms of large veins, veins, lenses and bags and are obviously controlled by nearly EW-trending faults and fracture zones. The mineral assemblage of the ore deposit resulted from activities of medium temperature hydrothermal fluids. Intense sericitization, carbonation, silicification and pyritization are closely associated with the gold ores. Native gold, electrum, pyrite, galena, sphalerite and chalcopyrite make up the metallic mineral assemblage of the gold ore. Gold mineralization took place at medium temperature. S-Pb isotopic composition shows that the ore-forming metallic materials were derived from surrounding porphyritic granite, and the H-O isotopic data indicates that the ore-forming fluids were mainly magmatic water mixed with small amounts of meteoric water at the late ore-forming stage. The metallogenie epoch should be early-middle Hercynian. It is therefore concluded that the Shijinpo gold deposit is a medium-temperature hydrothermal deposit related to tectonic-magmatic activities.