我国钴镍矿床的成矿规律、科学问题、勘查技术瓶颈与研究展望

钴镍矿床主要有四类: 岩浆型、红土型、沉积岩-变沉积岩容矿型和热液型。本文提出"纽带矿床"的概念, 是指兼具多种不同类型或不同成矿元素组合的矿床, 是不同矿床类型之间连接以及与成矿理论连接的结合点, 也是成矿模型与找矿模型之间的纽带。从金属共生关系的角度看, 镍矿普遍伴生钴, 但钴矿未必有镍; 从元素地球化学的角度看, 钴和镍在深部岩浆过程多共生, 而在浅表热液、风化和沉积等过程多分离。据此提出钴镍成矿的关键科学问题为钴镍共生、分离和富集机理, 主要包括: (1)岩浆-热液过程中的钴镍分离与富集机理; (2)风化-沉积过程中的钴镍共生-分离-富集机理。通过对四种类型典型矿床和纽带矿床的解剖, 结合实验岩石学及数值模拟计算与钴镍赋存状态及富集规律的研究, 有助于建立完整的钴镍成矿理论体系。同时, 从更大尺度上来看, 钴镍成矿和重大地质事件具有一定的耦合关系, 镁铁-超镁铁岩体的成矿差异与构造背景息息相关, 而热液改造在钴超常富集方面可能起到至关重要的作用。钴镍矿床赋矿地质体产状复杂多变, 含矿岩体与围岩之间物性相似, 钴-镍赋存状态多样, 迫切要求解决钴镍矿床勘查的关键技术问题为多元多尺度勘查技术体系与含矿性评价, 主要包括: (1)碳质层干扰下有效信号辨别提取技术; (2)小岩体和陡倾斜矿体的精细识别技术; (3)多元信息匹配关联与含矿性评价技术。我国钴镍资源分布特点和成矿特色要求在高效勘查技术体系的研发和集成时应优先考虑岩浆型钴镍矿, 而沉积岩-变沉积岩容矿型和热液型钴镍矿床的找矿工作应借鉴同成因矿床或主矿种矿床的勘查方法。

Mineralization regularity,scientific issues,prospecting technology and research prospect of Co-Ni deposits in China

There are four major types of Co-Ni deposits, namely, magmatic, lateritic, (meta-)sedimentary rock-hosted, and hydrothermal types. In this study, we proposed that many of these Co-Ni deposits are composite deposits that are characterized with common features of multiple deposit types or multiple-metal element assemblages, and these deposits are important bridges that can link different deposit types, metallogenic theory, and models for ore formation and their exploration. With aspects of metal element occurrences, Ni-dominated deposits mostly accompany Co enrichment up to economic grade, whereas Co-dominated deposits may not be rich in Ni. Elemental geochemistry reveals that Co and Ni commonly coexist within magmatic system, while they could separately occur during hydrothermal, weathering and sedimentary processes. Hence, the key scientific issue relevant to Co-Ni mineralization is the mechanism of coexistence and separation of Co and Ni in the above-mentioned processes. To construct a comprehensive Co-Ni metallogenic theory requires experimental petrology, numerical modeling, characterizations of occurrence and enrichment of Co and Ni in addition to studies of typical and composite deposits. Moreover, more studies are needed including coupling of Co-Ni mineralization and important global geological events in geologic time framework, petrogenesis and tectonic setting of various mafic-ultramafic massifs, and effects of hydrothermal modifications on Co super-enrichment. Most Co-Ni ore bodies and their host rocks are highly variable in occurrence and have similar geophysical properties in many cases with numerous Co- and Ni-bearing phases. These call on multiple prospecting techniques for mineral exploration and evaluation, including: (1) geophysical technology for identification and extraction of ore-related signals under the interference of the carbonaceous layer; (2) highly sensitive identification technology of small intrusions and steeply-inclined ore bodies; (3) matching correlation of multiple information and ore-bearing evaluation technology. Considering the characteristics of Co-Ni deposits in China, prospecting techniques for magmatic types should be firstly developed, while (meta-)sedimentary rock-hosted and hydrothermal Co-Ni deposits may employ exploration technology of syn-genetic deposits or main mineral deposits.