内蒙双尖子山Pb- Zn- Ag矿床金属矿物学研究与银的富集机理
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本文为中国地质科学院矿产资源研究所基本业务费(编号K1705)、国家重点研发计划(编号2017YFC0601303)和国家自然科学基金青年基金项目(编号41502084)联合资助的成果。


Metallic mineralogy study and Ag enrichment mechanism of the Shuangjianzishan Pb- Zn- Ag deposit in Inner Mongolia, China
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    摘要:

    双尖子山Pb- Zn- Ag矿床位于黄岗- 甘珠尔庙多金属成矿带的东北段,是目前发现的中国最大的银矿床。本文通过野外地质调查、矿相学鉴定、电子探针背散射图像以及电子探针化学成分分析,对该矿床金属矿物的矿物学特征进行了详细研究,同时对金属矿物的化学式进行了计算,并对银的富集机理进行了探讨。银矿物主要以可见银(>50μm)的形式产出,包括独立银矿物:硫锑铜银矿、硫银锡矿、辉硒银矿、深红银矿、脆银矿、黝锑银矿、螺状硫银矿、金银矿和自然银等;不可见银含量少,主要以类质同象形式赋存在方铅矿中。矿床成矿阶段细分为:①石英- 高Fe闪锌矿- 富Se和Bi的方铅矿- 富Se富Sb富Sn的银矿物阶段;②石英- 方铅矿- 富Fe闪锌矿- 毒砂- 富Sb富Sn少Se的银矿物阶段;③石英- 闪锌矿- 方铅矿- 银矿物阶段;④黄铁- 碳酸盐阶段。金属矿物沉淀顺序为:(黄铁矿、黄铜矿、闪锌矿、方铅矿)→银的硫盐矿物→银的硫化物→自然银。矿床中的Fe+、Cu+、Zn+、Pb+、Ag+等金属离子在早期中温高硫逸度阶段主要以硫氢络合物形式搬运。随着成矿热液温度的降低,铅、锌等金属硫氢络合物开始分解,方铅矿、黄铜矿和闪锌矿等硫化物得以沉淀,此时部分银以显微和次显微包体银的形式被包裹于这些硫化物中,铅锌硫化物的大量沉淀引起成矿热液组成和性质的显著变化,最终导致银从硫氢络合物中彻底解体,并与Cu+、Sb3+等离子结合形成大量独立银矿物(如深红银矿、硫锑铜银矿等)。随着温度、盐度持续降低,硫逸度也逐渐降低,pH值升高,成矿流体中出现大量自由Ag+并逐渐达到饱和,银矿物开始大量沉淀,Ag+与H2S发生作用形成螺状硫银矿。自然银的大量出现标志着银的沉淀过程趋于结束。金属矿物沉淀顺序为:(黄铁矿、黄铜矿、闪锌矿、方铅矿)→银的硫盐矿物→银的硫化物→银的自然金属。

    Abstract:

    The Shuangjianzishan Pb- Zn- Ag deposit, located in the northeast section of the Huanggang- Ganzhuermiao polymetallic metallogenic belt, is currently the largest silver deposit discovered in China. In this paper, the mineral characteristics of metal minerals in the deposit were studied in detail using field geological survey, identification of the ore facies, back scattering image of the electronic probe and chemical composition of electronic probe. At the same time, the chemical formula of metallic minerals was calculated and the mechanism of silver enrichment was discussed. Silver- bearing minerals occur mainly in the form of visible silver (>50 μm), including independent silver minerals such as polybasite, canfieldite, aguilarite, pyrargyrite, stephanite, freibergite, argentite, kustelite and native silver. Invisible silver content is low and occurs mainly in galena in the form of homomorphism. The metallogenic stage of the deposit can be divided into four stages: (1) Quartz- high iron Se- rich and bismuth galena - rich selenium, tin and antimony silver mineral stage; (2) Quartz- galena- rich iron sphalerite- arsenopyrite- rich antimony and tin, low selenium silver mineral stage; (3) Quartz- sphalerite- galena- silver mineral stage; and (4) Pyrite- carbonate stage. Precipitation order for metallic mienrals is pyrite+chalcopyrite+sphalerite+galena → silver sulfosalt minerals → silver sulfide, and → natural silver. The metal ions such as Fe+, Cu+, Zn+, Pb+ and Ag+ in the deposit are mainly transported in the form of sulfur- hydrogen complexes in the early stage of medium temperature and high sulfur degree. With decreasing of metallogenic hydrothermal temperature, metal S- H complexes such as lead and zinc begin to decompose to form sulphides such as galena, chalcopyrite and sphalerite. During this process, some silver were entraped within these sulphides in the form of microscopic and sub- microscopic enclaves. Precipitation of a large amount of of lead- zinc sulfide significantly changed the composition and properties of metallogenic hydrothermal fluids, eventually resulting in the complete disintegration of silver from its S- H complexes and thus forming a large number of independent silver- bearing mienrals (such as pyrargyrite, polybasite, etc.) through combination with ions such as Cu+ and Sb 3+.With continuous decreasing of temperature and salinity, when sulphur fugacity decreased gradually and pH values increased, free Ag+started to accumulate in the metallogenic fluid and gradually reached saturation, resulting in the precipiation of silver minerals, i.e. argentite due to reaction of Ag+ to H2 S. The mass appearance of natural silver marks the end of the precipitation process of silver.

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权晓莹,刘春花,孙洪军,王丰翔.2019.内蒙双尖子山Pb- Zn- Ag矿床金属矿物学研究与银的富集机理[J].地质学报,93(9):2308-2329.
QUAN Xiaoying, LIU Chunhua, SUN Hongjun, WANG Fengxiang.2019. Metallic mineralogy study and Ag enrichment mechanism of the Shuangjianzishan Pb- Zn- Ag deposit in Inner Mongolia, China[J]. Acta Geologica Sinica,93(9):2308-2329.

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  • 收稿日期:2018-09-08
  • 最后修改日期:2019-01-13
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  • 在线发布日期: 2019-09-02
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