黔西南微细浸染型金矿的黄铁矿矿物学研究及其成因意义:以水银洞金矿为例  

Mineralogical study on pyrites from the micro-disseminated gold deposits in the Southwest Guizhou and its significance:A case study of the Shuiyindong gold deposit

作　　者：姜欢 郗爱华[1] 于晓飞[2] 葛玉辉[1] 赵明峰[3] 王伟[3] 赵宝金 JIANG Huan;XI AiHua;YU XiaoFei;GE YuHui;ZHAO MingFeng;WANG Wei;ZHAO BaoJin(School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610000,China;Development and Research Center,China Geological Survey,Beijing 100037,China;117 Geological Party,Guizhou Bureau of Geology and Mineral Exploration and Development,Guiyang 550000,China)

机构地区：[1]西南石油大学地球科学与技术学院,成都610000 [2]中国地质调查局发展研究中心,北京100037 [3]贵州省地质矿产勘查开发局117地质大队,贵阳550000

出　　处：《岩石学报》2022年第10期3231-3245,共15页Acta Petrologica Sinica

基　　金：中国地质调查局项目(DD20190159-30)资助。

摘　　要：贵州黔西南地区的微细浸染型金矿是一种典型的中、低温热液矿床,矿床总体上受不同级别褶皱与断裂构造的控制。但是,呈透镜状、似层状展布的矿体形态与大多数热液矿床的空间分布特点差别较大,导致该区域金矿床的成因长期存疑。本文以水银洞金矿为例,通过高精度的电子探针(EPMA)与环扫电子显微镜(ESEM)等原位微区分析测试方法,查明矿石中的黄铁矿至少存在三种类型且空间上均与有机质密切伴生:(1)粗粒黄铁矿:呈稠密浸染状或条带状分布于龙潭组1段的钙质砂岩内,其内部和周围的孔洞中常见凝析油和磷灰石、金红石、方解石等热液矿物充填。其中具环带结构的黄铁矿为主要的载金矿物,微细的不可见金主要赋存在外部2~3层富As的黄铁矿环带中,测定的Au含量平均为0.06%,最高可达0.24%,揭示黄铁矿的内核和环带形成于不同的热液期次。(2)细粒黄铁矿:呈星散状或稀疏浸染状分布于龙潭组2段富含生物碎屑的钙质凝灰岩内并构成工业富矿体,富Au、As且多与毒砂等矿物共生,Au最高可达0.14%。围岩的微裂隙中可见被有机质环状包裹的5~10μm大小的自然金颗粒。(3)草莓状黄铁矿:呈微粒集合体填充于生物格架(Ty1)或者围岩微裂隙(Ty2)中,两者在龙潭组1段和2段均有分布。Ty1交代生物碎屑且自身具有有机质包壳,Ty2则充填在富含有机质的微裂隙中并部分交代粗粒和细粒黄铁矿,表明其形成略晚于主成矿阶段。水银洞矿床黄铁矿的结构、成分及空间产状研究揭示,黔西南微细浸染型金矿具有多期次热液叠加复合成矿的特点。成矿热液持续作用于龙潭组及其下伏的地层,可交代围岩中的生物碎屑并将其分解为有机质和C、P、N、Ca、Na、K等元素。一方面成矿流体携带有机质向上迁移,另一方面致密的龙潭组2段及其上部岩层作为“隔挡层”为富Au的热流体成矿提供岩相�The micro-disseminated gold mineralization in Southwest Guizhou is a typical medium-low temperature hydrothermal deposit,which is generally controlled by different levels of structures.However,the lens and lamellar orebodies,characterized by the strata-bounded nature of Au mineralization,are quite different from the spatial distribution of most hydrothermal deposits,whose genetic mechanism is not clearly understood.The morphology,composition and distribution of pyrite and the occurrence of Au in the Shuiyindong gold deposit have been analyzed through EPMA,ESEM and other high-precision in-situ test methods.The results indicated that there are at least three types of pyrites,which are all closely associated with organic matter.(1)The coarse pyrite:It is densely disseminated or banded in the calcareous sandstone of the Member I of the Longtan Formation.Condensate and hydrothermal minerals such as apatite,rutile and calcite are often found in the pores of coarse pyrite.Some coarse pyrite has a regular core with 2~3 outer layers of secondary enlarged rings containing As,which are the major gold-bearing minerals.Invisible Au mainly exists in the outer ring,and the content of Au is 0.06%on average and up to 0.24%.The elements such as S,As and Au show an annular distribution,indicating that the inner and outer zones were formed in different metallogenic stages.(2)The fine pyrite:It is distributed in a scattered or sparse fashion in the calcareous tuff,rich in bioclasts in the MemberⅡof the Longtan Formation,and constitutes the economic orebodies.It is mostly symbiotic with arsenopyrite,and rich in Au and As,with Au constituting up to 0.14%.The organic matter contains natural gold particles with sizes of 5~10μm and is found in the microcracks of the surrounding rock.(3)The framboidal pyrite:It is distributed in the Member I and II of the Longtan Formation in the microfossils(Ty1)and microfractures(Ty2)as aggregates.Ty1 has a metasomatic bioclastic formation and organic matter cladding,whereas Ty2 is found in microfract

关 键 词：黔西南地区 微细浸染型金矿 水银洞金矿 矿床成因 黄铁矿 

分 类 号：P578.292[天文地球—矿物学] P595[天文地球—地质学] P618.51