锑的地球化学性质与华南锑矿带成因初探

锑属亲铜元素,易与硫结合。锑在地核(0. 14×10~(-6))、地幔(0. 006×10~(-6))和地壳(0. 02×10~(-6))中的丰度均很低,而在黑色页岩(5. 0×10~(-6))中明显富集。锑是一种典型的低温成矿元素。我国华南地区低温成矿域拥有世界60%的锑探明储量。研究结果显示锑的成矿主要经历两阶段富集过程:一是与风化和沉积作用有关的表生过程;二是地球内部热驱动过程。寒武纪时华南位于赤道附近,受冈瓦纳大陆的造山带的影响,是全球地表风化最强烈的地区之一。在新元古代氧化事件的驱动下,锑在表生风化过程中被氧化为更易迁移的水溶性的SbO_3~-。因埃迪卡拉生物群所产生的有机质,有利于萃取水体中的锑并沉淀在还原性沉积物(黑色页岩)中。华南中生代岩浆活动烘烤表层富锑的寒武纪黑色页岩,产生的成矿流体向上迁移,淋滤黑色页岩中的Sb或与黑色页岩变质脱水或熔融产生成矿流体混合;而后搬运至远离岩体的有利位置沉淀,最终形成大规模的华南锑矿带。

Geochemical characteristics of antimony and genesis of antimony deposits in South China

Antimony is a chalcophile element, which is easily combined with sulfur. The abundances of antimony in the core (0.14×10^-6), the mantle (0.006×10^-6) and the crust (0.02×10^-6) are all very low, while it is enriched in black shale (5.0×10^-6). The solubility of antimony is controlled by temperature, salinity, pH value and oxygen fugacity, but not to pressure. Rutile and omphacite are the main carriers of antimony in high-pressure to ultrahigh-pressure metamorphic rocks. Antimony is also a typical low-temperature metallogenic element. The low-temperature mineralization domain in South China, possesses 60% of the world''s proven antimony reserves mostly formed in the Yanshanian Period. Our studies show that the mineralization of Sb mainly experienced two stages:One is the supergene process related to weathering and sedimentation, and the other is the hydrothermal process caused by magmatism. South China, located near the equator during the Cambrian, was affected by the Gondwana continental orogenic belt, and it is one of the most weathered areas in the world. The fertile source area is very important for the formation of antimony deposits in South China, whereas organic matter plays a positive role for the extraction and migration of antimony. As a result of Neoproterozoic Oxidation Event, antimony was oxidized to water-soluble SbO₃^- during supergene weathering. The organic matter, produced by the Ediacara biota is conducive to extracting antimony from water, and precipitating it in reduced sediments (black shale). The Mesozoic magmatic activity in South China baked the surface antimony-rich Cambrian black shale, and the ore-forming fluids produced by magma migrated upward, leaching Sb from black shales or mixing with other ore-forming fluids produced by metamorphic dehydration or melting of the black shale; and then it was transported to a favorable location far from the rock mass to deposit, eventually forming a large-scale antimony ore belt in South China.