贵州兴仁生物成因红铊矿及其地质意义

Biogenic Lorandite and Its Geological Significance in Xingren County, Guizhou Province

贵州兴仁滥木厂铊矿床中主要工业矿物红铊矿 (lorandite)是在沉积成岩时由生物富集形成的铊矿物 ,在铊矿石中可见到大量的微古动物化石 ,其中有孔虫和苔藓虫类占绝大部分。绝大部分微古动物化石都被含铊矿液交代 ,形成保留生物假像的红铊矿物斜硫砷汞铊矿。生物成因红铊矿的发现为矿床成矿模式和成矿时代的厘定提供新的证据。生物富集成矿和热液改造成矿是该矿床最主要的成矿特征。对生物群时限 ,硫同位素组成和生物富集成矿现象分析表明 ,生物富集成矿阶段发生在晚二叠世 ,即海西晚期 ,而热液改造成矿阶段则发生在中三叠世 ,即印支早期。在热液改造成矿阶段形成的矿石中见不到生物假像铊矿物 ,其完全被典型热液铊矿物所替代。

Thallium is a very dispersed element and it seldom occurs in the form of independent minerals and in independent ore deposits. Biogenic loran dite is the major industrial mineral of the Lanmuchang Tl deposit in Xingren Cou nty, Guizhou Province. It was formed as a result of bioenrichment during sedimen tary diagenesis. A large number of micro-paleofossils, especially foramina and zoaria are still observed in the Tl ores. Most of micro-paleofossils have been replaced by Tl-bearing ore fluid, hence forming T1 minerals with bio-pseudomor phs, such as lorandite and christite. Bio-enrichment and hydrothermal reworking are the two important metallogenic fe atures for the Tl deposit studied. Biogenic lorandite provides an evidence for t he ore- formation mechanism and timing. An analysis on the time-bound nature of biocoen oses, sulfur isotopic composition and bio-enrichment metallogenic phenomenon sh ows that the Lanmuchang Tl diposit was originally formed in the Late Permian, an d the hydrothermal reworking took place during the Middle Triassic. No Tl minera ls in the form of bio-pseudomorphs have been identified in the Tl ores of hydro thermal reworking stage, indicating that these minerals have been replaced by ty pical hydrothermal Tl-minerals.