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

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

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。

Located in the western part of the Min-Li metallogenetic belt,western Qinling Mountains,the Zhaishang gold deposit is a recently discovered large Carlin-type disseminated gold deposit. Examination of ores by optical microscope,electron probe,X-ray surface scanning,chemical analyses from the deposit,has revealed some native gold minerals. Under the reflecting microscope,the na-tive gold minerals have a variety of forms such as oval,flake,triangular,rod-like,filamentous,irregular,which range in size from 5 to 150 μm. Electron microprobe analysis of seven points on native gold gave the results as follows：Au 88.23% to 92.73% （91.29 on average ）,Ag 7.41% to 9.08% （8.08 on average）,which range in fineness from 905 to 926. The carriers are arsenian pyrite,galena,coloradoite and ankerite. Gold is embodied as intergranular,fissure-filling,and interlocking form. Dissolution of ferroan limestone in the host rocks and sulfidation of the dissolved iron by H2S introduced by ore fluids were the most important depositional mechanism for visible gold grains in the Zhaishang gold deposit.