Black shale-hosted nickel.cobalt deposit:Current understanding and outlook to future prospecting

Nickel (Ni)and cobalt (Co)are critical,strategic metals to nations worldwide. As a subtype of sedimentary rock-hosted stratiform Ni-Co deposits,the black shale-hosted Ni-Co deposit is significant to industry and scientific research. In this paper,we summarize mineralization features of the most significant Ni. and Co-rich black shale sequences worldwide,including,in order of formation ages from old to young,the Talvivaara Formation in Finland,the Gwna Group in the UK,the Niutitang Formation in South China,the Alum Shale Formation in Sweden,the Canol Formation in Canada,and the Kupferschiefer Formation in Central Europe. The Ni-Co deposits in these formations show similar laminated texture and geochemical enrichment of multiple elements,organic matter and sulfur. Initial sources of metals were either product of terrestrial weathering or seafloor hydrothermal fluids,and metal precipitation was mainly triggered by changes in the sedimentary environment in certain sedimentary basins. Both redox conditions of paleo-ocean during the syn-sedimentary stage and subsequent hydrothermal/ metamorphic processes likely controlled the paragenesis and differentiation of Ni and Co- The black shale-hosted Ni-Co deposits were all formed in the dramatic turbulence period of the Earth-s surface during the Great Oxygenation event,Neoproterozoic Oxygenation event,and Phanerozoic,suggesting that the Earth-s surface environment is the first. order control on the formation of the Ni-Co-rich black shales- Subsequent hydrothermal fluid activities further concentrated metals in Ni- and Co- rich black shales to industrial grade. Although considerable achievements have been reached in the formation context of the black shale-hosted Ni-Co deposits,many aspects,including the mechanism of Ni and Co paragenesis and differentiation,symbiotic relationship of multiple elements during syn-sedimentary processes,and subsequent rework processes,are still obscure. Multi-disciplinary research on metallogeny,sedimentology,geobiology,and geochemistry using advanced analytical techniques will be beneficial for a better understanding of the mineralization processes in the black shale-hosted Ni-Co deposits and their relations with multiple Earth spheres