甘肃礼县-岷县成矿带西段寨上金矿床中自然金的发现及成因意义

位于西秦岭礼(县)-岷(县)成矿带西段的寨上金矿床是近年发现的一个大型微细浸染型金矿。在研究甘肃寨上金矿床物质组分的过程中,采用显微镜观察、电子探针扫描、化学分析等综合分析技术发现了显微自然金颗粒。矿石中的自然金颗粒形态多样,粒度变化较大(5～150μm)。电子探针分析结果显示,自然金中Au=88.23%～92.73%,Ag=7.41%～9.08%,为含银自然金,成色905～926。金的载体矿物有砷黄铁矿、方铅矿、碲汞矿、铁白云石等。金的嵌布类型有粒间金、裂隙金和连生金3种。赋矿围岩中含Fe碳酸盐矿物溶解释放出Fe和溶解Fe的大量硫化物化,可能是寨上金矿床中存在显微可见自然金的最重要因素。

Discovery and significance of native gold in the Zhaishang gold deposit, southern Gansu, China

Located in the western part of the Min-Li metallogenetic belt,western Qinling Mountains,the Zhaishang gold deposit is a recendy discovered large Carhn-type disseminated gold deposit.Examination of ores by optical microscope,electron probe,X-ray surface scanning,chemical analyses from the deposit,has revealed some nadve gold minerals.Under the reflecting microscope,the na-tive gold minerals have a variety of forms such as oval,flake,triangular,rod-like,filamentous,inegular,which range in size from 5 to erage),Ag 7.41%to 9.08%(8.08 on average),which range in finenes from 905 to 926.The carders are arsenian pyrite,galena,col-oradoite and ankerite.Gold is embodied as intergranular,fissure-filling,and intedocking form.Dissolution of ferroan limestone in the host rocks and sulfidation of the dissolved iron by H_2S introduced by ore fluids were the most important depositional mechanism for visible gold grains in the Zhaishang gold deposit.