中非赞比亚成矿带卢安夏盆地富钴矿物特征及其指示意义  

Characteristics of cobalt-rich minerals and their implications for the Luanshya Basin,Zambian Copperbelt

作　　者：卢宜冠 涂家润 孙凯 任军平 方科 覃鹏 郭虎 和文言[5] LU YiGuan;TU JiaRun;SUN Kai;REN JunPing;FANG Ke;QIN Peng;GUO Hu;HE WenYan(Tianjin Center,China Geological Survey,Tianjin 300170,China;Southern African Mining Research Institute,China Geological Survey,Tianjin 300170,China;China Nonferrous Metals(Guilin)Geology and Mining Co.,Ltd.,Guilin 541004,China;China Nonferrous Metals Innovation Institute(Tianjin)Co.,Ltd.,Tianjin 300393,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,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]中国地质调查局南部非洲矿业研究所,天津300170 [3]中国有色桂林矿产地质研究院有限公司,桂林541004 [4]中色创新研究院(天津)有限公司,天津300393 [5]中国地质大学,地质过程与矿产资源国家重点实验室,北京100083

出　　处：《岩石学报》2024年第6期1853-1869,共17页Acta Petrologica Sinica

基　　金：中国地质调查项目(DD20190439、DD20221801、DD20230571);国家重点研发计划项目(2021YFC2901804);商务部援外项目([2015]352);国家自然科学基金项目(42002110)联合资助.

摘　　要：中非铜钴成矿带是全球规模最大、平均品位最高的沉积型铜钴成矿带,在全球钴矿产供应中占有极其重要的地位。卢安夏矿床是中非赞比亚成矿带一超大型铜(钴)矿床,但目前对于其钴的富集机制及成因模式尚不清楚。本研究聚焦于卢安夏铜钴矿床中硫铜钴矿、黄铁矿等富钴矿物,对其开展电子探针、微区X射线荧光光谱分析和S同位素分析。电子探针与微区X射线荧光光谱分析显示,卢安夏矿床中存在沉积期(Py1)、成岩期(Py2)、热液期(Py3)、表生期(Py4)四期黄铁矿。其中,钴主要富集在硫铜钴矿-黄铁矿-黄铜矿-石英脉的Py3中,其钴含量最高可达10.5%;其次为表生期黄铁矿(Py4),但其钴富集程度有限。黄铁矿Co、As含量显示富钴Py3的形成与含As流体不断与围岩发生作用有关。尽管卢安夏硫化物S同位素组成变化范围较大,但富钴的黄铁矿δ^(34)S为负值(-9.6‰~-2.8‰),且全岩钴含量与单矿物δ^(34)S值呈负相关关系。这一结果指示富钴硫化物的形成源于在热液提供热量的条件下,有机质热分解产生大量强还原性物质与硫酸盐发生反应,由此促进了硫酸盐的还原过程和硫化物的沉淀。结合近年来中非铜钴成矿带的地质演化史和钴富集机制方面的研究成果,卢安夏矿床钴的主要成矿期应为卢菲利安造山期(540~490Ma),在此造山阶段释放的氧化性高温高盐热液是钴的主要载体,而卢安夏矿床钴的富集可能源于赋矿地层中丰富的有机质成分为钴的富集成矿提供了有利条件,热液注入后由于氧逸度的降低,钴在相对低温的条件下发生沉淀而形成矿床。The Central African Coppberbelt is the world s largest sedimentary copper cobalt metallogenic belt with a highest averaged Co grade,which plays an extremely important role in the global Co mineral supply.The Luanshya is a giant Cu-(Co)deposit in the Zambian Copperbelt,however,its cobalt enrichment mechanism and genetic model are still poorly understood.This study focuses on cobalt-rich minerals such as carrollite and pyrite in the Luanshya Cu-Co deposit,and carries out EPMA,micro-XRF and S isotope analysis to solve these problems.EPMA and micro-XRF analysis show that there are four generations of pyrite in the Luanshya deposit:the sedimentary pyrite(Py1),the diagenetic pyrite(Py2),the hydrothermal pyrite(Py3)and the supergene pyrite(Py4).Cobalt is mainly enriched in Py3 in the carrollite-pyrite-chalcopyrite-quartz vein,with the highest cobalt content up to~10.5%.Supergene pyrite(Py4)has the second highest average cobalt content,but its cobalt enrichment degree is limited.The contents of Co and As in pyrite show that the formation of the cobalt-rich Py3 is related to the continuous interaction between the As-bearing fluid and the wall rocks.Although the S isotope values of Luanshya sulfides vary widely,the cobalt-rich pyriteδ^(34)S values are all negative(-9.6‰~-2.8‰).The whole rock cobalt content and theδ^(34)S value of the sulfide are negatively correlated,which indicates that the formation of cobalt-rich sulfide is resulted from the reaction between abundant reduced substances(formed by decomposition of organic matter)and sulfate under the heat provided by the hydrothermal fluid.This process promoted sulfate reduction and sulfide precipitation.Combined with the geological evolution history of the Central African Copperbelt and cobalt enrich mechanism from researches in recent years,the main mineralization stage of the cobalt in the Luanshya deposit is supposed to be the Lufilian orogenic period(540~490Ma).The main carrier of cobalt is supposed to be the oxidized high-temperature and high salinity hydrothe

关 键 词：铜钴矿床 富钴矿物 成因机制 中非铜钴带 

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