Characteristics of cobalt-rich minerals and their implications for the Luanshya Basin,Zambian Copperbelt
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(Pyl),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 pyrite δ34S values are all negative(-9.6‰～-2.8％e).The whole rock cobalt content and the δ34S 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 hydrothermal fluids released during the Lufilian orogenic period.Cobalt enrichment and mineralization is probably related to ore-forming favorable conditions provided by the rich organic-matter in the Luanshya host rocks.Due to the reduction offo2after the injection of the hydrothermal fluid,the cobalt precipitates at relatively low temperatures and thus forms the economic deposit.
万方数据
维普
