黑色页岩容矿型Ni-Co矿床:研究进展与展望

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

Ni和Co都是重要的战略性矿产资源,其中黑色页岩容矿型Ni-Co矿床是沉积岩容矿型Ni-Co矿床的重要组成部分,具有非常重要的工业价值和科学研究意义。本文按照形成时代的先后顺序综述了芬兰Talvivaara组、英国Gwna群、中国华南牛蹄塘组、瑞典Alum Shale组、加拿大Canol组以及中欧Kupferschiefer组等全球范围内几个重要黑色页岩层位赋存的Ni-Co矿床。这些矿床的矿石具有纹层状构造、多金属共生富集、富有机质和硫等共同特征。矿床中多金属的初始来源可能为陆源风化的产物或者海底热液,而导致溶解于海水中的金属发生沉淀的机制则是极端条件下海洋环境的变化。Ni-Co的共生分异受到同沉积期海水氧化还原环境和后期改造过程的共同控制。全球范围内几个重要的含Ni-Co黑色页岩层位均发育在第一次全球大氧化事件、新元古代大氧化事件和显生宙的地球表生环境突变期,显示了地球表生环境对该类型矿床的形成具有控制作用。此外,后期改造过程则有利于金属的进一步富集形成工业矿体。前人针对黑色页岩容矿型Ni-Co矿床的研究极大的推动了人们对这类矿床的认识,然而,对这类矿床中Ni-Co共生-分异机制、同沉积过程中多金属的共生关系以及后期改造过程仍需要更深入的探索。以现代分析技术为手段,开展成矿学、沉积学、地质生物学、地球化学等多学科交叉研究,将有助于深入理解黑色页岩容矿型Ni-Co矿床的成矿过程以及与地球多圈层协同演化(尤其是表生环境演化)的关系,从而推动黑色页岩容矿型Ni-Co矿床成矿理论的发展。

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.