澳大利亚布朗斯(Browns)Co-Cu-Ni多金属矿床地球化学特征及与中国南方黑色岩系金属矿床对比

Geochemistry of the Brwons Co-Cu-Ni Polymetallic Deposit and Comparison with the Black Shale Hosted Polymetallic Deposits in South China

黑色岩系中金属元素地球化学特征一直是矿床地质研究的重点。澳大利亚布朗斯Co-Cu-Ni多金属矿产于古元古代黑色岩系中,属典型的层控矿床;该矿床中主要成矿元素为Co、Cu、Ni和Pb,矿化分带不明显,蚀变微弱。δ34S均值范围为-5.21‰～14.78‰,估计生物成因的硫占一定比例,后期有细菌还原硫酸盐成因的高硫同位素组成硫的参与;铅同位素(206Pb/204Pb=16.20～16.22,207Pb/206Pb=15.48～15.51,208Pb/207Pb=35.86～35.92)表明矿床中铅的来源单一,均为壳源。矿床经历了沉积-成矿-后期热事件的微弱叠加改造。通过与中国南方黑色岩系对比,发现丰富的有机质在金属元素富集成矿过程中起重要作用。布朗斯多金属矿床属正常海水沉积成矿,与中国南方黑色岩系中多金属矿床有较显著区别。

The Browns Co-Cu-Ni deposit is hosted by the Whites Shale of Paleo-Preterozoic in Northern Territory of Australia,and it is a typical strata-bound deposit. Based on the analysis of the geological characters in detail,the major elements,trace elements,Pb and S isotope,and the organic matter,the enrichment mechanism of the ore metals is studied in this paper. The main Co-hosting mineral is siegenite,which is carried by pyrite. δ34S values of the sulfides range from-5.21‰ to ＋14.78‰,indicating involvement of thermochemical reduction and bacterial activity. Homogeneous lead isotope features of galena （206Pb/204Pb=16.20-16.22,207Pb/206Pb= 15.48-15.51,208Pb/207Pb=35.86-35.92） suggest that Pb was derived from the crust. Ore geochemical studies illustrate that the deposit is primarily of sedimentary origin and were somewhat reformed by later tectonic-thermal events. Compared with the deposits hosted in the South China black shales,it can be concluded that the Browns deposit is a normal sedimentation deposit,while the latter are Sedex-type deposits.