新疆东准噶尔顿巴斯套金矿地质特征及矿床成因
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注:本文为NSFC—新疆联合基金 “新疆北部造山型矿床成矿规律研究”(编号:U1803242)和国家重点研发计划“深地资源勘查开采”重点专项(编号:2017YFC0601203)的成果。


Geological characteristics and genesis of Dunbastau gold deposit in Eastern Junggar, Xinjiang
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    摘要:

    新疆东准噶尔地区自北向南发育额尔齐斯、阿尔曼太、卡拉麦里三条大型构造带,南北两条构造带已发现大量造山型金矿,而阿尔曼太构造带与南北构造带具有相似的成矿地质背景,却未见造山型金矿的报道。因此,笔者等选取了该构造带最重要的金矿床——顿巴斯套金矿,开展了详细的岩相学、矿相学研究以及构造解析。研究表明,该矿床具有区域性断裂的次级断裂控矿、脆—韧性剪切带控矿、背斜核部控矿“三位一体”的控矿特征,其中,NW—SE向脆—韧性剪切带是最重要的控矿构造,金矿化显著晚于矿区赋矿岩浆岩——石英闪长玢岩,且该矿床与相邻构造带典型的造山型金矿地质地球化学特征相似。结合成矿流体具有中低温、富CO2的特征,综合认为顿巴斯套金矿是典型的造山型金矿。将该矿床成矿过程划分为3期:① 以产出草莓状黄铁矿为典型特征的沉积期;② 以黄铁矿压实、结核、重结晶为特征的成岩期;③ 以产出热液脉和金的矿化为典型特征的热液期。热液期进一步划分为两个阶段:以脆—韧性变形为主的铁白云石—石英—黄铁矿阶段和由脆—韧性变形向脆性变形转变的石英—钠长石—方解石阶段。黄铁矿可划分为6个世代、毒砂可划分为3个世代:① Py1为沉积成因的黄铁矿,具有草莓状、胶状等特殊结构;② Py2为成岩作用形成的黄铁矿,具有顺层分布、呈结核状等特征;③ 热液期毒砂Apy1,粒度20~50 μm,自形、半自形,常与金共生;④ 热液期毒砂Apy2,自形,粒度80~200 μm;⑤ 热液期黄铁矿Py3,他形—自形,粒度50~150 μm,以内部包体多、孔洞多为显著特征;⑥热液期黄铁矿Py4,半自形—自形,粒度100~250 μm,以包体多,孔洞少,发育压力影为特征;⑦ 热液期Py5,以背散射下亮度高、显著富As为特征;⑧ 热液期毒砂Apy3:以颗粒粗大、自形、内部包体少、发育碎裂结构和压力影为特征;⑨ 热液期黄铁Py6:以颗粒粗大、半自形到自形、内部包体少、发育碎裂结构和压力影为特征。随着脆—韧性变形作用进行,黄铁矿、毒砂的粒度有序递增,自形程度逐渐升高,而品位逐渐降低,金的沉淀主要发生在脆—韧性变形阶段,脆性变形阶段无金矿化。主成矿阶段标志性的铁白云石化蚀变、微细浸染状的黄铁矿化、毒砂化蚀变可以作为找矿标志。

    Abstract:

    Erqis,Armantai,and Kalamaili are three major tectonic belts developed from north to south in the eastern Junggar area of Xinjiang.A large number of orogenic gold deposits have been discovered in the Erqis and Kalamaili belts.Although Armantai tectonic belt has a similar metallogenic background with the north and south tectonic belts,no orogenic gold deposit is reported. Given this problem,we focus on the most important gold deposit in this tectonic belt,the Dunbastau gold deposit. Methods:In this paper,detailed field investigation and microscopic observation are conducted to provide petrography,mineralography,and structural evidences.Results: The Dunbastau gold deposit’s metallogenic process can be divided into three periods:①The sedimentary period characterized by framboidal pyrites;②The diagenesis period characterized by compaction,nodule-formation,and recrystallization of pyrites;③The hydrothermal period characterized by hydrothermal veins production and gold mineralization.The hydrothermal period is further divided into two stages:the ankerite—quartz—pyrite stage accompanied by brittle—ductile deformation and the quartz—albite—calcite stage with the transition from brittle—ductile to brittle deformation.Pyrites can be divided into six generations.Arsenopyrite can be divided into three generations.①Py1 is of sedimentary origin,with particular structures such as framboidal and colloid;②Py2 was formed by diagenesis and distributed stratification consistently. Py2 often show recrystallization or nodule- like shape and other characteristics; ③Hydrothermal Apy1, from subhedral to euhedral,with a grain size of 50~100μm,often paragenesis with gold;④Hydrothermal Apy2 are euhedral,with a grain size of 300~700μm;⑤Hydrothermal Py3 are anhedral to euhedral,with a grain size of 50~150μm,characterized by inclusions and pores internally;⑥Hydrothermal Py4 are subhedral to euhedral,with a grain size of 150~300 μm,characterized by inclusions,few pores,and developing pressure shadow;⑦Hydrothermal Py5 are characterized by high brightness under backscattering and rich in As significantly;⑧Hydrothermal Apy3 are coarse- grained,and euhedral shaped,with few inclusions internally,developed cataclastic texture and pressure shadows; ⑨Hydrothermal Py6 are coarse-grained,from subhedral to euhedral,with few inclusions internally,developed cataclastic texture and pressure shadows.Conclusions:The Dunbastau gold deposit has the “tri-in-one”ore-controlling characteristics:secondary fractures of regional faults,brittle—ductile shear zones,and anticline cores. Among them,the brittle—ductile shear zone with NW—SE strike is the most critical ore-controlling structure.The gold mineralization is significantly later than the host magmatic rock,quartz diorite porphyrite.The geological and geochemical characteristics of the deposit are similar to those typical orogenic gold deposits in the adjacent structural belts.Combined with the nature of ore-forming fluid is medium—low temperature and CO2 rich,it can be concluded that the Dunbastau gold deposit is a typical orogenic gold deposit.Along with the brittle—ductile deformation process,the grain size of pyrites and arsenopyrites increased orderly,the degree of self-shape gradually improved,while the grade of Au gradually decreased.The precipitation of gold mainly occurred in the brittle—ductile deformation process.In contrast,there was no gold mineralization in the brittle deformation process.The fine-grained,disseminated pyrite and arsenopyrite alteration and the ankerite alteration of the main metallogenic stage can be used as indicators for prospecting.

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刘文祥,邓小华,吴艳爽,韩申,陈西,李巽,王永,陈衍景.2021.新疆东准噶尔顿巴斯套金矿地质特征及矿床成因[J].地质论评,67(3):695-721,[DOI].
LIU Wenxiang, DENG Xiaohua, WU Yanshuang, HAN Shen, CHEN Xi, LI Xun, WANG Yong, CHEN Yanjing.2021. Geological characteristics and genesis of Dunbastau gold deposit in Eastern Junggar, Xinjiang[J]. Geological Review,67(3):695-721.

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  • 收稿日期:2020-09-17
  • 最后修改日期:2021-02-03
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  • 在线发布日期: 2021-05-19
  • 出版日期: 2021-05-15