滇西北兰坪金顶可能的古油气藏及对铅锌大规模成矿的作用

Possible Former Oil-gas Reservoir in the Giant Jinding Pb-Zn Deposit,Lanping,NW-Yunnan:the Role in the Ore Accumulation

滇西北兰坪中—新生代沉积盆地产有中国最大的铅锌矿床,巨量铅锌矿石集中产在金顶穹窿内,矿石中不同产状的干酪根、轻质原油、重油、烃类气、沥青等多种成熟形式的有机物质丰富。对矿区有机物质进行了岩相学、生物标志化合物、碳同位素及铅同位素分析,结果显示：有机物质中氯仿沥青“A”的质量分数为（72～395 415.42）×10^-6,w（饱和烃）/w（芳香烃）普遍大于1,饱和烃中检测出丰度较高的正构烷烃、Pr、Ph和iC18等生物标志化合物,烃源母质为藻类生物Ⅰ型有机质;相对于区域岩石,矿石中有机物质的有机转化率较低（0.5%～7.2%,平均为3.05%）,已明显受热而成熟;透射全色光和紫外光显微镜在矿石光薄片样品中鉴别出较多原油和烃类气体包裹体。研究表明：金顶穹窿具有油气成藏“生、运、储、盖、闭”等配套发育的良好条件,矿区油气显示和古油气藏遗迹明显,铅锌成矿前或成矿中可能已形成油气藏;这个可能的油气藏以富含原油、烃类和H2S等还原性气体为成分特征;金顶古油气藏中H2S等还原性气体的聚集及其导致铅锌硫化物快速集中沉淀是大规模成矿的关键,成藏—成矿是金顶穹窿中一个连续发生、发展的动力学过程,成藏是成矿的前提。

Oil-gas reservoir and metal deposits always coexist in the sedimentary basin,and the dynamic relationship between them has long been interested.The biggest zinc-lead deposit in China occurs in the Lanping Meso-Cenozoic sedimentary basin,Northwest Yunnan.Giant zinc-lead ores distribute in the Jinding dome,and cotain rich organic matters with different maturity,such as kerogen,light-and heavy crude oil,hydrocarbon gas,bitumen,and so on.Through research about lithofacies,biomarker compounds,carbon isotope and lead isotopeof organic matters in Jinding deposit, some conclusions are drawn. Chloroform bitumen “A” of the organic matters is （72～395 415.42） ×10^-6. The ratio of saturated hydrocarbon to aromatic hydrocarbon is always over 1. Lots of biomakers such as N-Alkanes, Pr, Ph and iC18 are found in saturated hydrocarbon, and the parent material of biogenesis is mainly I-type. Compared with regional rocks, organic conversion rate of organic mattersin the ores is lower, from 0. 5%to 7. 2%, showing obvious maturity. Many crude oil and hydrocarbon gas inclusions are found with transmission and ultraviolet light microscope. There are good conditions for generation, migration, storingr, covering, and trapping of oil-gas reservoir in Jinding dome, and oil-gas showings and remains of paleo-oil-gas reservoir are found in the ore region. All these indicate that a paleo-oil-gas reservoir had been formed before or during the mineralization, characterized by full of crude oil, hydrocarbon gas and hydrogen sulfide. The key points of large scale mineralization are accumulation of reducing gases, for instance, hydrogen sulfide, in Jinding oil-gas reservoir. The process from forming of oil-gas reservoir to mineralization is a continuous dynamic process, and the forming of oil-gas reservoir is the premise of mineralization.