贵州遵义下寒武统黑色岩系Ni-Mo多金属矿地球化学特征及成矿作用

华南扬子板块分布广泛的下寒武统黑色岩系中富含Ni、Mo、Cd、V、Cu、Zn、Ba、REE和铂族元素(PGE),多处Ni-Mo-PGE矿化已形成了矿化体。由于其特殊的形成时代及特殊的多金属组合特点,其成因一直是地质学家研究的热点。作者以贵州遵义黄家湾矿区的黑色岩系硫化物矿床为主要研究对象,对围岩及矿层进行了元素地球化学及不同形态硫的分离、测试分析。结果表明,钼矿层处亲硫元素Ni、Mo、Cd、V、Cu、Zn明显富集,而高场强元素Nb、Th、Hf、Zr、Ti亏损。在剖面上U/Th比值大于1,在矿层处接近70,代表了一种非正常的海水沉积作用,各形态硫与金属元素沿剖面的变化趋势相似,都在矿层处异常富集。镜下观察发现红藻囊果与金属硫化物之间有密切的共生关系。结合前人研究结果,认为镍、铜、锌等金属元素的来源与深部基岩物质有关,这些成矿元素在缺氧的还原沉积环境下,通过有机硫和硫酸盐还原细菌提供的S2-,富集形成Ni-Mo多金属硫化物矿床。红藻囊果的发现及其与各种金属矿物之间密切的空间关系进一步证实生物参与了成矿作用。

Geochemical characteristics and ore-forming processes of Ni-Mo polymetallic deposits in Lower Cambrian black shale,Zunyi,Guizhou Province

The Lower Cambrian black rock sequence widely distributed in Yangtze platform of South China is rich in Ni,Mo,V,Cu,U,Ba,REE and platinum group elements(PGE). The genesis of these ore species has aroused much interest due to their specific age and polymetallic combination. This paper deals with the Huangjiawa deposit in Zunyi. Methods used in the laboratory study included petrochemistry and elemental geochemistry. Geochemical characteristics of trace elements show that there exists obvious enrichment of such chalcophile elements as Ni,Mo,Cd,V,Cu and Zn in the Ni-Mo polymetallic deposits,while the high field intensity elements like Nb,Th,Hf,Zr and Ti are evidently deficient. The U/Th ratio is higher than 1 in the profile and up to 70 in the Ni-Mo polymetallic deposits. The variation trends of organic carbon,different forms of sulfur and main metals along the profile were analyzed. The remarkable enrichment of organic sulfur in mineralized strata suggests that organic sulfur provided sulfur for mineralization. Close relationship between algae cystocarp and metal sulfides was discovered under microscope. Based on the authors' results and previous researchers' outcomes,it is held that the sources of Ni,Mo,Cu and Zn are related to materials in the earth's depth. In an anoxic reductive environment and under the influence of the organic sulfur and S2-produced by bacterial sulfate reduction,the ore-forming elements were concentrated and formed the Ni-Mo polymetallic sulfide deposits. Red algae cystocarp was found for the first time and the discovery of the close relationship between algae cystocarp and metal sulfides has supplied the evidence for biomineralization.