粤北凡口超大型铅锌矿有机质成矿地球化学特征

用有机岩石学、元素分析和饱和烃气相色谱等方法,分析了凡口铅锌矿矿区有机质的有机地球化学特征,对有机质在该铅锌矿成矿地球化学过程中的作用进行了初步探讨。该矿区的主岩富含有机质,有机碳含量为0．03％-0．4％,平均为0．16％,有机碳和金属矿化有同步变化趋势。有机质具有高的演化程度,经换算,镜质体反射率为1．92％-3．55％,且绝大多数高于3．0％。饱和烃气相色谱的特征表明,含矿地段的有机质在成矿热液的作用下发生热裂解和热变质,其裂解产生的甲烷和新生成的干酪根等有机化合物作为还原剂,使硫酸根还原成硫化氢,还原生成的硫化氢进一步与成矿金属离子反应生成金属硫化物沉淀,并最终富集成矿。另外,草莓状黄铁矿的存在,说明了在沉积作用早期,细菌可能直接参与了成矿作用。

Characteristics of Organic Mineralization and Organic Matter in the Fankou Pb-Zn Deposit, North Guangdong Province, South China

The organic matter associated with Fankou Pb-Zn deposit(Northern Guangdong province, southeastern China) has been studied by petrographic，organic petrology，elements analysis and gas chromatographic methods, The host rocks of the deposit are abundant in organic carbon ranging from 0.03％ to 0.4％ ．The vitrinite reflectances (R0) are determined as 1.92％-3.55％ ，mostly above 3.0％ ．It is suggested that the maturity of the organic matter is high and most of the organic matter has become bitumen．The character of saturated hydrocarbons，extracted from host rocks and ores (Pr and Ph)shows a marine-facies reduction condition．Gas chromatographic analytical results show that the 0rganic matter in orebody experienced thermolysis and thermal metamorphism，and thus the formed CH4 and kerogen acted as reducing agents to reduce sulfate to sulfide hydrogen，which was favorable for precipitation of metal sulfides． In addition，the occurrence of pyrite in granular and “strawberry" form indicates the effect of bacteria and micro-algae during early sedimentation．