Metallogenic regularity of antimony-gold deposits in Longlin-Xilin district in western Guangxi, South China
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摘要: 锑矿床以矿石矿物组合简单为特点,常缺乏适合用于测试分析的矿物,因此关于锑矿床成矿时代、成矿物质来源等方面研究争议较大。华南锑矿省锑资源储量占全国83%以上,西南部的滇黔桂锑矿带是华南锑矿省的重要组成部分。本文选择滇黔桂锑矿带中部桂西隆林-西林锑金矿集区为例,系统总结了区内86个矿床(点)的赋矿层位、赋矿围岩岩性、容矿构造特征及金、锑矿床共伴生关系,结合典型矿床地质特征及岩浆岩时空分布,探讨锑成矿作用与碎屑岩、岩浆岩的内在联系。取得以下认识:(1)碳质泥页岩和富黄铁矿砂岩、粉砂岩是研究区赋锑有利层位,上述地层具有高的锑背景值,可能为锑成矿提供了物质来源。(2)岩浆对锑成矿既可以起到直接作用(Sb和S来源)也可以起到间接作用(热源),两者均有利于锑矿床的形成。(3)隆林-西林矿集区锑、金矿床统计显示,区内以独立的锑、金矿床为主,少量矿床以锑、金共伴生形式产出,表明研究区锑、金成矿流体可能为不同来源流体叠加,少部分矿床可能为同一成矿流体的演化分带。锑、金同源流体伴随着辉锑矿的沉淀,消耗流体中的H2S,使得其它以硫氢络合物形式迁移的金属(如Au、Hg)共同沉淀。由于Sb、Au对H2S的这种竞争关系,导致锑金矿床中两者的品位往往负相关。(4)研究区经历了印支期NS向挤压,随后叠加了中晚侏罗世NW-SE向挤压。NWW-SEE向与NE-SW向断裂交汇处是有利的容矿空间。锑主成矿期NW-SE向缩短变形导致NWW-SEE向断裂以走滑为主,而NE-SW向断裂表现出压扭性特征,因此NE-SW向断裂含矿性差于NWW-SEE向断裂。在上述研究基础上,本文提出桂西隆林-西林锑金矿集区勘查有利区域:新州背斜核部下泥盆统郁江组碳质泥页岩和富黄铁矿粉砂岩是锑矿勘查的重点层位;隆林县弄桑-石家寨NWW-SEE向断裂带内隐伏岩体周边和西林县NWW-SEE向斗皇-西林断裂与NE-SW向断裂的交汇部位是锑矿勘查的有利区域。以上成果为研究区内锑金矿床成因和成矿规律认识提供了新的思考,为区内锑矿床勘查提供了方向,同时丰富了锑成矿作用理论。Abstract: Antimony deposits are characterized by simple minerals assemblage, and often lack minerals suitable for testing and analysis. Therefore, the metallogenic ages, sources of ore-forming materials, and genesis of antimony deposits are controversial. The antimony metallogenic province in South China accounts for over 83% of China's antimony resources. The Dian-Qian-Gui antimony metallogenic belt is located in the western of the South China antimony metallogenic province. In this study, we summarized ore-bearing stratums, rock lithologies, host structures, and the relationship between gold and antimony of 86 deposits in the Longlin-Xilin antimony-gold district, the middle segment of the Dian-Qian-Gui antimony metallogenic belt. Combined with the geological investigation of typical deposits and the distribution of magmatic rocks, the relationships among antimony mineralization with clastic rocks and magmatic rocks were discussed. We concluded that: (1) nonographitic black shales and pyritiferous sandstones and siltstones are favorable for antimony mineralization. These strata have high antimony background values, which may have provided ore-forming materials. (2) The felsick intrusions may provide heat or Sb and S for the antimony mineralization. (3) Statistical results show that independent antimony and gold deposits dominate in the Longlin-Xilin district, and few deposits are characterized by intergrowth features of antimony with gold. These indicate that antimony deposits in the study area may be the superposition of fluids from different sources, and a small number of deposits maybe resulting by the Sb-Au separation from same ore-forming fluid. In the latter case, the precipitation of stibnite consumed H2S in the ore-forming fluid, resulting in other metals that migrated in the form of complexes (such as Au and Hg) to precipitate at the same time. The competitive relationship between Sb and Au led to that the contents of Sb, Au show a negative correlation in antimony-gold deposits. (4) The district has experienced NS-striking compression in the Indosinian, followed by the NW-SE-striking compression in the middle-late Jurassic. The intersection of NWW-SEE-striking and NE-SW-striking faults is the favorable ore-bearing space. The NWW-SEE-striking faults were strike slip in response to the NW-SE-striking shortening deformation, whereas the NE-SW-striking faults exhibited transpression. As a result, the NE-SW-striking faults are not beneficial than the NWW-SEE-striking faults. Based on these studies, we proposed the ideal direction for prospecting in Longlin-Xilin district: (1) Black shale and pyritiferous siltstones of the Yujiang Formation that in the core of the Xinzhou anticline are the favorable stratums for antimony prospecting. (2) Concealed intrusion in the NWW-SEE-striking Nongsang-Shijaizhai fault (the Longlin County) and the intersection area of the NWW-SEE-striking Douhuang-Xilin fault and the NE-SW-striking fault (the Xilin County) are the favorable spaces for antimony exploration. The abovementioned discussion will enhance our understanding of the genesis and metallogenic regularity of antimony deposits and provide the directions for exploration.
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