青海尕日力根二叠系砾岩容金矿床的地质与地球化学特征

新近在柴北缘宗务隆构造带与南祁连陆块接合部位发现了二叠系勒门沟组砾岩和含砾砂岩层容矿的尕日力根金矿床,其围岩蚀变有硅化、绿泥石化、褐铁矿化、黄钾铁矾等低温蚀变组合,矿体呈层状、似层状分布在构造破碎带内及砾岩含砾砂岩层内,金属矿物主要有黄铁矿和毒砂。结合电子探针分析数据和背散射图像观察,黄铁矿在不同阶段,其形态和元素含量均不同,金主要有两种赋存形态:第一种是极细粒自然金的形态赋存在裂隙发育的沉积阶段的破碎黄铁矿中;第二种是以不可见固溶体金赋存热液阶段的含砷黄铁矿和毒砂中。硫同位素组成暗示硫主要来自地层。综合分析认为,尕日力根金矿床成矿过程至少有两个阶段,第一阶段是沉积阶段,金来自古砂金矿床,第二阶段是热液阶段,由来自地层的变质热液活化金,使其以不可见固溶体金的形成赋存在含砷黄铁矿和毒砂中,故尕日力根金矿床的成因类型应为砾岩改造型矿床。

Geological and geochemical characteristics of the Permian conglomerate host gold deposit in Gariligen, Qinghai province

The Gariligen gold deposit which occurs in the conglomerate and pebbled sandstone of the Permian Lemengou formation was recently discovered at the junction between the Zongwulong tectonic belt and the southern Qilian landmass in the northern margin of Qaidam. The wall rock alteration of the deposit is mainly cryogenic alteration combination including silication, chlorite, limonite, jarosite and so on. The orebody appears in bedded and near bedded distributing in the feature zone and conglomerate and pebbly sandstone layer, metallic minerals are mainly pyrite and arsenopyrite. Combined with electron probe analysis data and back scattering image observation, the morphology and element content of pyrite are difference in different stages and there are two occurrence patterns of gold: the first is that the form of extremely fine natural gold occurs in the cracked pyrite in the sedimentary stage, and the second is the arsenic-bearing pyrite and arsenopyrite in the hydrothermal stage of invisible solid solution gold. The isotopic composition of sulfur suggests that sulfur is mainly derived from strata. Comprehensive analysis shows that there are at least two stages in the metallogenic process of the Gariligen gold deposit: the first stage is the sedimentary stage, the gold comes from the ancient placer gold deposit, and the second stage is the hydrothermal stage, in which the gold is activated by metamorphic hydrothermal from the stratum, so that the gold is formed in arsenic-bearing pyrite and arsenopyrite, therefore, the genetic type of the Gariligen gold deposit should be the conglomerate -reworked deposit.