The Relationship between Oil-gas Organic Matter and MVT Mineralization:A Case Study of the Chipu Lead-zinc Deposit, Sichuan
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摘要: 四川赤普MVT铅锌矿床成矿与古老油气藏关系密切。通过对矿床不同成矿阶段硫化物硫同位素和热液碳酸盐碳、氧同位素系统研究,结合沥青有机质的有机地球化学特征,探讨油气参与金属成矿的详细过程。取得主要认识如下:(1)油气系统中先存的H2S是成矿早阶段主要的硫源, TSR作用启动后还原硫酸盐,为成矿提供另一硫源。Mg2+可能是控制成矿过程中TSR作用的一个因素;(2)热液碳酸盐矿物碳(氧)同位素组成指示了 TSR 作用氧化的有机碳与流体溶解围岩碳酸盐岩中碳的不均匀混合作用;(3)矿床中与成矿作用有关的有机质(沥青)具有高-过成熟度特征和低芳烃含量,或是其参与了 TSR 作用的一个标志;(4)川滇黔地区油气成藏-破坏和赤普铅锌成矿可能是盆山演化过程中不同阶段或是同一阶段不同时代的产物,铅锌矿床形成与古老油气藏破坏密切相关。Abstract: There is a close relationship between mineralization of the Chipu MVT deposit an d oil-gas reservoirs. Through a systematic study of sulfur isotope of sulfides and carbon and oxygen isotopes of hydrothermal carbonates, combined with organic geochemical characteristics of bitumen, the authors suggest a possible lead-zinc mineralization process in this deposit. The conclusions are as follows:(1) H2S, derived from cracking of crude oil was the main sulfur source for early-stage mineralization, whereas the thermochemical sulfate reduction provided reduced sulfur once TSR process was triggered. Mg2+could be a key factor controlling the TSR reaction. (2) The carbon and oxygen isotopic variation of hydrothermal sparry carbonates was contributed by heterogeneous mixture of the host-rock dolomite isotope source and the lighter organic one. (3) The bitumen has the features of high-degree degradation and low aromatics content, which is considered to have been involved in the lead-zinc mineralization of the Chipu MVT deposit as well as other deposits. (4) The Pb-Zn mineralization and oil-gas field formation in this area were products of basin fluids, corresponding to the different stages of the basin-and-range system.
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