西藏甲玛铜多金属矿床成矿系统元素的活动性及质量平衡

杨欢欢+唐菊兴+林彬+应立娟+郎兴海+郑文宝

基金项目：国家重点基础研究发展计划(“九七三”计划)项目(2011CB403103)；中国地质调查局青藏专项项目(12120113093700)

摘要：运用质量平衡方法，研究西藏甲玛铜多金属矿床中位于角岩和矽卡岩接触带内的矽卡岩化角岩被流体交代蚀变形成矽卡岩过程中元素的迁移特征和流体性质。对两类样品分别进行主量、微量、稀土元素分析，并运用等浓度线方程及其推导方程分别判断在交代蚀变过程中元素的带入、带出特点及元素的活动性，进而推断流体特征。结果表明：主量元素只有Al2O3、Na2O和K2O为带出元素，SiO2、Fe2O3和CaO为带入元素且带入量较大；微量元素W、V、Cr带入量较大，Bi、Ni、Pb、Ga带入量中等；稀土元素除Pr和La外均为带入元素，其带入序列趋势由强至弱依次为Eu、Er、Yb、Dy、Ho、Gd、Tm、Lu、Tb、Sm、Nd、Ce；成矿元素Ag、Cu、Mo、Pb、Zn为带入元素，带入序列趋势由强至弱依次为Mo、Ag、Cu、Pb、Zn；蚀变过程元素K、Na、Li、Be、Zr被带出与F、Cl、OH、CO2等组成络合物存在于溶液中；带入元素Cu、Mo、Pb、Zn以硫化物形式存在于矿区内，上述硫化物中硫、铁为低价态，而贫氧的流体有利于硫、铁以低价态出现。总之，推断蚀变流体富F、Cl、OH、CO2，具有富含硫和铁元素且贫氧的特征。

关键词：铜多金属矿床；元素迁移；成矿流体；交代蚀变作用；矽卡岩；甲玛；西藏

中图分类号：P618.41文献标志码：A

Element Mobility and Mass Balance of Oreforming System in Jiama Copper Polymetallic Deposit of Tibet

YANG Huanhuan1， TANG Juxing2， LIN Bin1， YING Lijuan2, LANG Xinghai1， ZHENG Wenbao2

(1. School of Earth Sciences, Chengdu University of Technology, Chengdu 610059, Sichuan, China;

2. Key Laboratory of Metallogeny and Mineral Assessment of Ministry of Land and Resources, Institute of

Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China)

Abstract: Mass balance method was used to study the characteristics of element transfer and fluid property while skarnization hornfels were replaced into skarns at the contact zone between skarnization hornfels and skarns in Jiama copper polymetallic deposit of Tibet. The major, trace and rare earth elements of two different types of samples were analyzed, and the bringin and bringout of elements under the metasomatic alteration were estimated by the isocon equation and its derivation, and the characteristics of fluid were discussed. The results show that only Al2O3, Na2O and K2O among the major elements are bringout, SiO2, Fe2O3 and CaO are bringin and the quantity is large; the bringin quantities of trace elements W, V and Cr are large, while the quantities of Bi, Ni, Pb and Ga are medium; rare earth elements are bringin except for Pr and La, and the bringin sequence trend is Eu, Er, Yb, Dy, Ho, Gd, Tm, Lu, Tb, Sm, Nd and Ce from strong to weak; the oreforming elements Ag, Cu, Mo, Pb and Zn are bringin, and the bringin sequence trend is Mo, Ag, Cu, Pb and Zn from strong to weak; K, Na, Li, Be and Zr in the process of alteration are brought out to form the complex with F, Cl, OH and CO2 existing in the solution; the bringin elements Cu, Mo, Pb and Zn in the mining area exist in the form of sulfides, in which S and Fe are low valence, and the fluid with deficient oxygen is favorable for the S and Fe with low valence. In general, it is concluded that alteration fluid is rich in F, Cl, OH and CO2, and rich in the elements S and Fe and deficient in oxygen.

Key words: copper polymetallic deposit; element transfer; oreforming fluid; metasomatic alteration; skarn; Jiama; Tibet

0引言

矿化蚀变过程中，元素质量迁移常会导致元素的富集贫化，具有固有的内在规律性［1］。对蚀变岩石进行物质组成变化的研究有助于了解成矿流体系统特征及其成矿作用过程［2］。目前，对矿床成矿体系元素迁移规律的研究较多，并且取得了丰硕成果［13］。……