ISSN 1009-6248CN 61-1149/P 双月刊

主管单位：中国地质调查局

主办单位：中国地质调查局西安地质调查中心
中国地质学会

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    甘肃早子沟金矿床金赋存状态、成矿物质来源及矿床成因探讨

    Discussion on Gold Occurrence State, Metallogenic Material Source and Genesis of the Zaozigou Gold Deposit in Gansu Province

      摘要
    • 摘要:
      目的 早子沟金矿位于西秦岭造山带西段三叠纪陆内裂陷盆地，杂恰勒布-早子沟断裂和桑曲-地娄塘断裂之间。
      方法 前人将早子沟金矿床划分为两期四阶段，笔者重点对热液成矿期黄铁矿-毒砂-石英（Ⅱ）阶段硫化物进行电子探针分析，矿区内构造主要有NE、NW、近EW和近SN向4组，其中以NE和NW向为主。野外穿切现象表明，NE向成矿带晚于NW向，通过镜下观察发现Ⅱ阶段存在两个亚类，一类为多孔半自形黄铁矿（Ⅱ1），另一类为平整自形黄铁矿（Ⅱ2），针对Ⅱ阶段两个亚类黄铁矿开展原位硫和LA-ICP-MS微量元素实验。
      结果 研究结果显示，黄铁矿均为贫铁贫硫的含砷黄铁矿。Ⅱ1阶段As含量少于Ⅱ2阶段，主成矿期Ⅱ1阶段黄铁矿δ34Sv-CDT值为−9.92‰～−14.00‰，Ⅱ2阶段黄铁矿δ34Sv-CDT值为−15.58‰～−23.46‰，δ34Sv-CDT数值变化范围均较大，成矿物质可能先由沉积源和岩浆源为主，后期加入少量变质源。黄铁矿微量数据显示，随着主成矿期Ⅱ1向Ⅱ2成矿演化过程中，Au的赋存形式由Au+至Au0呈逐渐过渡趋势，亲Fe、Cu元素的Co、Ni、As元素变化呈下降趋势，成矿元素中Cu、Pb、Zn、Ag元素变化呈上升趋势；Co-Ni二元判别图指示成矿后期热液占比增多，Co-Ni-As投图显示两亚类黄铁矿均位于卡林型、浅成热液型与岩浆热液型的结合区，表明早子沟金矿为多期次成因。
      结论 综合矿床地质、地球化学特征，认为早子沟金矿床成因类型属于岩浆期后热液型金矿。

       

      Abstract:
      Objective‌ The Zaozigou gold deposit is located in the Triassic intracontinental rift basin at the western part of the West Qinling orogenic belt, between the Zacalebu-Zaozigou fault and the Sangqu-Diluotang fault.
      Methods The Zaozigou gold deposit has been divided into two periods and four stages, the electron probe analysis is focused on the sulfide in the pyrite - arsenopyrite - quartz (II) stage during the hydrothermal mineralization stage in this paper. There are mainly four groups of structures in the mine, such as NE, NW, near EW and near SN trending, among which NE and NW trending are the main ones. There were two types of sulfide assemblage in stage II, one is porous hemidiomorphic pyrite (II1), the other is flat idiomorphic pyrite (II2). In situ sulfur and LA-ICP-MS trace element experiments were carried out for the two subclasses in stage II.
      Results The results showed that the pyrite is arsenic-containing pyrite with poor iron and sulfur. The δ34SV-CDT of pyrite in II1 stage is −9.92‰～−14.00‰, the δ34SV-CDT of pyrite in II2 stage is −15.58‰～−23.46‰, and the δ34SV-CDT value of pyrite in II2 stage is larger. The ore-forming materials may be mainly sedimentary and magmatic sources at first, with a small amount of metamorphic sources added later. The trace data of pyrite show that the occurrence form of Au shows a gradual transition trend from Au+ to Au0, the changes of Co, Ni and As elements in iron and copper elements show a downward trend, and the changes of Cu, Pb, Zn and Ag elements in metallogenic elements show an upward trend. The Co-Ni binary discriminant map indicates that the proportion of hydrothermal deposits increased in the later ore-forming period, and the Co-Ni-As map shows that the two subpyrites are located in the combination area of Carlin type, epithermal type and magmatic hydrothermal type, indicating that the Zaozigou gold deposit has multi-stage genesis.
      Conclusion Based on the geological and geochemical characteristics of the deposit, it is considered that the Zaozigou gold deposit belongs to the post-magmatic hydrothermal type.

       

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