投稿时间：2019-09-27
修订日期：2020-03-06
网络发布日期：2020-05-14
中文摘要:甲玛矿床位于冈底斯成矿带东段，是西藏地区最大的铜多金属矿床之一。磁黄铁矿是甲玛矿床最常见的金属矿物之一，其标型特征不仅反映其自身形成环境，对其形成机制和矿床成因也具有指示意义。文章选取产于不同岩性中的磁黄铁矿矿石样品，利用矿相学、X射线衍射和电子探针分析等手段对磁黄铁矿的形态、成分和结构进行了分析研究。研究表明，甲玛矿床的磁黄铁矿主要分布在距离岩体中心较远的矿区远端矽卡岩和角岩中。磁黄铁矿的晶胞参数和粉晶X射线衍射曲线显示矽卡岩中的磁黄铁矿主要为高温六方磁黄铁矿，角岩中的磁黄铁矿为高温六方磁黄铁矿和低温单斜磁黄铁矿的交生体，但主要以低温单斜磁黄铁矿为主。通过对矽卡岩和角岩中的磁黄铁矿进行电子探针测试，结果显示：矽卡岩中的磁黄铁矿中w(Fe)为60.09%~60.71%，平均为60.38%，w(S)为38.18%~38.69%，平均38.35%，化学分子式为Fe8S9~Fe10S11；角岩中的磁黄铁矿中w(Fe)为59.05%~59.57%，平均为59.10%，w(S)为39.28%~39.95%，平均39.59%，化学分子式为Fe5S6~Fe7S8。根据以上矿物学特征，笔者进一步探讨了该矿床磁黄铁矿的沉淀机制：炽热的岩浆热液上涌，与碳酸盐岩地层和碎屑岩地层接触发生相互作用，并有大气水的加入，使得成矿流体在角岩中先快速降温，形成高温六方磁黄铁矿和低温单斜磁黄铁矿的交生体。同时，大量的含矿热液形成，并充填于有利的成矿空间(主要为层间破碎带)沉淀成矿，形成矽卡岩矿体，然后流体在矽卡岩矿段中经历缓慢降温，形成高温六方磁黄铁矿。结合矿床地质特征和相关元素地球化学特征，认为甲玛矿床类型为斑岩-矽卡岩型。
Abstract:The Jiama deposit is located in the eastern part of Gangdise metallogenic belt, and is one of the largest copper polymetallic deposits in Tibet. Pyrrhotite is one of the most common metallic minerals of the Jiama deposit. Its typomorphic characteristics not only reflect its formation environment but also indicate its formation mechanism and deposit genesis. In this paper, pyrrhotite samples from different lithologies were collected, and the morphology, composition and structure of pyrrhotite were analyzed by means of mineralogy, X-ray diffraction and electron microprobe analysis. The study shows that pyrrhotite of the Jiama deposit is mainly distributed in the skarn and hornfels, which are far away from the center of the porphyry intrusion. The powder X-ray diffraction curves and cell parameters of pyrrhotite show that the pyrrhotite in the skarn is mainly high-temperature hexagonal pyrrhotite. The pyrrhotite in the hornfels is a mixture like associated body of high-temperature hexagonal pyrrhotite and low-temperature monoclinic pyrrhotite, with the monoclinic pyrrhotite being dominant. The results of electron microprobe analysis of pyrrhotite in skarn and hornfels show that the content of Fe in pyrrhotite of skarn is 60.09%~60.71%, averaging 60.38%, and the content of S is 38.18%~38.69%, averaging 38.35%, with the corresponding chemical formula being Fe8S9~Fe10S11. At the same time, the content of Fe in pyrrhotite of hornfels is 59.05%~59.57%, averaging 59.10%, and the content of S is 39.28%~39.95%, averaging 39.59%, with the corresponding chemical formula being Fe5S6~Fe7S8. Based on the above mineralogical characteristics, the authors hold that the precipitation mechanism of pyrrhotite in the deposit is as follows:the hot magma surged and interacted with the carbonate and clasolite formation, and the addition of atmospheric water caused the ore-forming fluid to quickly cool down in the hornfels, forming associated body of high-temperature hexagonal pyrrhotite and low-temperature monoclinic pyrrhotite. At the same time, a large number of ore-bearing hydrothermal fluids formed and filled in favorable ore-forming space (mainly interlayer fracture zone) for precipitation and mineralization, forming skarn orebodies; the fluid then experienced a slow cooling in the skarn ore segment to form a high temperature hexagonal pyrrhotite. Based on geological characteristics of the deposit and geochemical characteristics of related elements, it is concluded that the Jiama deposit type is of the porphyry-skarn type.
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基金项目:本文得到国家重点研发计划-深地专项（编号：2018YFC0604101）、西藏自治区科技计划项目（编号：XZ201901-GB-24）和国家自然科学基金项目（编号：41902097）联合资助
引用文本：
杨阳,唐菊兴,吴纯能,林彬,唐攀,张泽斌,何亮,祁婧,李怡萱.2020.西藏甲玛铜多金属矿床磁黄铁矿标型矿物学特征及其地质意义[J].矿床地质,39(2):337~350YANG Yang,TANG JuXing,WU ChunNeng,LIN Bin,TANG Pan,ZHANG ZeBin,HE Liang,QI Jing,LI YiXuan.2020.Typomorphic mineralogical characteristics of pyrrhotite in Jiama Cu polymetallic deposit, Tibet, and its geological significance[J].Mineral Deposits39(2):337~350
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