The supernormal enrichment regularity and metallogenic conditions of hydrothermal vein-type nickel-cobalt ore deposit in the Cambrian black rock series of Jinxiu, Guangxi, South China

A hydrothermal vein-type nickel-cobalt deposit was discovered in the Cambrian black rock series in Jinxiu, Guangxi, South China.The deposit is exceptionally rare and holds significant scientific and prospecting importance.This paper introduces the geological characteristics of the Longhua deposit, the rules governing ore enrichment, as well as mineralogical and geochemical investigations.The ore-bearing rock is carbonaceous mudstone in the lower part of the Cambrian Qingxi Formation, and the ore-bodies can be classified into two types: high-grade hydrothermal veins and low-grade disseminated types.Two main mineral assemblages are identified: Ni-Co-As and Ni-Co-S, occurring within the primary vein.Their distribution aligns with NWW and NNW trending faults, respectively.The primary ore minerals consist of Ni-Co arsenide, accompanied by a minor presence of sulfide, quartz and carbonate.Elemental contents of niccolite, gersdorffite, polydymite, millerite, skutterudite, bismuthite, and native bismuth minerals were analyzed using the electron probe method.Additionally, the Fe-Co-Ni ternary diagram of the primary ore minerals was examined.Based on the internal structure and paragenetic relationships of minerals, the sequence of mineral formation is elucidated, and the formation process of ore minerals can be divided into endogenic hydrothermal stage and epigenetic stage.The results of elemental mapping analysis reveal significant zonation characteristics in Ni, Co, and S elements within niccolite, possibly indicating secondary growth as the underlying cause.The hydrothermal vein-type nickel-cobalt deposit may be the product of the old crustal material recirculation before Caledonian Movement. The relationship between granites and mineralization is still difficult to judge. The supernormal enrichment of nickel-cobalt elements may mainly come from the late tectonic-fluid reformation.