中非赞比亚成矿带谦比希铜钴矿床钴的赋存状态与成矿规律  

Cobalt occurrence and ore-forming process in the Chambishi deposit in the Zambian Copperbelt,Central Africa

作　　者：卢宜冠 涂家润 孙凯 覃鹏 王华青 何胜飞 张航 龚鹏辉 郭硕 方科 和文言[4] LU Yiguan;TU Jiarun;SUN Kai;QIN Peng;WANG Huaqing;HE Shengfei;ZHANG Hang;GONG Penghui;GUO Shuo;FANG Ke;HE Wenyan(Tianjin Center,China Geological Survey,Tianjin 300170,China;China Nonferrous Metals(Guilin)Geology and Mining Co.,Ltd.,Guilin 541004,China;China Metallurgical Geology Bureau,Beijing 100025,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质调查局天津地质调查中心,天津300170 [2]中国有色桂林矿产地质研究院有限公司,广西桂林541004 [3]中国冶金地质总局,北京100025 [4]中国地质大学(北京)地质过程与矿产资源国家重点实验室,北京100083

出　　处：《地学前缘》2021年第3期338-354,共17页Earth Science Frontiers

基　　金：中国地质调查项目(DD20190439,1212011220910);商务部援外项目([2015]352);国家自然科学基金项目(42002110)。

摘　　要：谦比希铜钴矿床是中非赞比亚成矿带重要的超大型铜钴矿床之一,由主矿体、西矿体和东南矿体3部分组成,赋矿层位主要为下罗安亚群敏多拉组和基特韦组,岩性包括泥质板岩、泥质石英岩、板岩、石英砂岩等。现有资料对于矿床中钴的赋存状态和含钴矿物成因的研究较为薄弱,这也直接制约了对钴矿的成因认识及今后找矿方向。本次研究聚焦谦比希矿床中的富钴矿物,对该类矿物进行电子探针、微区X射线荧光光谱分析和S同位素研究,通过查明谦比希矿床中钴的赋存状态及成因机制,为今后区域上钴资源的找矿勘查提供理论依据。分析结果表明谦比希矿床中钴以独立矿物和类质同象形式存在,其中独立矿物主要为硫铜钴矿和硫钴矿。在热液黄铁矿(Py2)和磁黄铁矿中,钴含量最高分别可达4.9%和1.5%,Co与Fe含量成反比关系且Co富集区域较为均匀地分布在硫化物中,说明Co取代Fe以类质同象方式赋存于黄铁矿和磁黄铁矿中。此外,谦比希矿床热液期黄铁矿-磁黄铁矿的Co-Ni范围不同于夕卡岩型及其他几种成矿类型的黄铁矿和磁黄铁矿,结合前人对热液矿化期流体包裹体的H-O同位素研究,暗示富钴的成矿流体可能并非岩浆热液流体,而是中-高温的变质热液流体。西矿体斑铜矿和东南矿体磁黄铁矿δ^(34) S值分别为6‰~6.9‰和7.2‰~12.6‰,表明热化学硫酸盐还原作用是谦比希矿床还原性硫形成的主要机制,硫化物在经历了变质作用后δ^(34) S值具有均一化。综合本文和前人已有研究,我们认为钴的主成矿期与卢菲利安造山作用密切相关,造山期中-高温变质热液使得钴、铜等金属元素再富集。NE-SW向挤压形成的褶皱枢纽及特定走向断层的交汇处等构造发育部位可以作为钴矿体的有利找矿地段,而热液脉中的黄铁矿-磁黄铁矿组合可作为区域上寻找钴矿体的矿物标志。The Chambishi Cu-Co deposit is one of the important giant Cu-Co deposits in Copperbelt province,Zambia,Central Africa,consisting the Main,West and Southeast orebodies.Its ore-bearing horizon is mainly the Mindola and Kitwe formations of the Lower Roan group,and its lithology includes argillaceous slate,argillaceous quartzite,slate,quartz sandstone,etc.The existing data on the cobalt occurrence mode is relatively weak and the genesis of Co-bearing minerals is not well understood,which directly hinders cobalt prospecting in the deposit.Focusing on the Co-rich minerals in this study,we conducted EPMA,Micro-XRF and S isotope analyses to investigate the Co occurrence modes and formation mechanism of Co-bearing minerals,in the Chambishi deposit,aiming to provide a theoretical basis for the future exploration of Co resources in the region.Our study shows that cobalt occurs as stand-alone minerals(mainly carrollite and linnaeite)or in Co-bearing minerals via isomorphism.In pyrite(Py2)and pyrrhotite formed from hydrothermal fluid,the cobalt content was up to 4.9%and 1.5%,respectively.Cobalt enrichment via isomorphism is evident by the inverse proportion between Co and Fe contents and by the relatively even distribution of Co components in the Co-bearing minerals.Moreover,the Co/Ni ratio in pyrite and pyrrhotite differs between the Chambishi deposit and skarn or other deposit types.Together with the hydrogen and oxygen isotope studies of fluid inclusions in the hydrothermal mineralization stage,it is implied that the Co-rich ore-forming fluid might not be magmatic-hydrothermal fluid but medium-high temperature metamorphic-hydrothermal fluid.The δ^(34) S values of bornite from the West orebody and pyrrhotite from the Southeast orebody were 6‰-6.9‰and 7.2‰-12.6‰,respectively,indicating that thermochemical sulfate reduction is the main formation mechanism of reductive sulfur in the Chambishi deposit;the similar δ^(34) S values is also an indication of late metamorphism in the sulfide minerals.Based on this and previ

关 键 词：赞比亚成矿带 谦比希 钴 赋存状态 成矿规律 

分 类 号：P618.41[天文地球—矿床学] P618.62[天文地球—地质学]