四川盆地东南缘河坝MVT铅锌矿与古油气藏的成生关系

摘要

The intimate coexistence of MVT Pb-Zn deposits with oil-gas reservoir suggests a genetic linkage be-tween mineralization and hydrocarbon accumulation. The Pb-Zn deposit from Heba in southeastern Sichuan Basin occurred in the paleo-gas reservoir in Dengying Formation, and its distribution area of Pb-Zn deposit is much smaller than that of paleo-gas reservoir although both of them coexisted intimately. The mineralization fluid of Pb-Zn deposit is characterized by high salinity(21. 33%- 23. 83% NaCl) and enrichment of organic matter, and its homogeneous temperature concentrated in 122 - 134℃. The ages of Rb-Sr and Sm-Nd of fluo-rite coexisting with sphalerite suggest that the mineralization took place in 128 - 130 Ma. Multi-phase accumu-lation and destruction of hydrocarbon can be recognized in this paleo-oil/gas reservoir. The first hydrocarbon accumulation and destruction took place in the Ordovician- Middle Silurian and the end of the Silurian, respec-tively. The second accumulation of hydrocarbon took place during the Permian and the middle Triassic, the oil began thermal cracking and formed gas reservoir as the burial depth of oil reservoir increased during the late Triassic and Jurassic; the paleo-gas reservoir was destroyed during the Yanshaniaa The thermal cracking of oil and destruction of paleo-gas reservoir are responsible for mineralization of Pb-Zn deposit. The thermal cracking of oil produced some H2S and the super pressure resulting from thermal cracking had the H2S dis-solved in the water to supply sulphur for mineralization of Pb-Zn deposit; tectonic uplift resulted in the destruc-tion of the paleo-gas reservoir, and the brine with H2S lying under the paleo-gas reservoir migrated up and mixed with mineralization fluid leading to the formation of Pb-Zn deposit.%MVT铅锌矿与(古)油气藏在空间上的密切共生/伴生关系,说明成矿与成藏具有密切的成因联系.四川盆地东南缘的河坝铅锌矿产于震旦系灯影组古油气藏中,虽然二者在空间上密切共生,但铅锌矿的规模远较古油气藏的规模小.形成铅锌矿的流体具有较高的盐度(w(NaCl) =21.33％～23.83％)并富含有机质,成矿流体的峰温为122～134℃.与闪锌矿共生萤石的Rb-Sr和Sm-Nd同位素年龄显示成矿发生于128～130Ma.研究区的古油气藏先后经历了多期成藏与破坏.奥陶纪—中志留世时期第一次成藏,加里东期末被破坏；二叠纪—中三叠世时期二次生烃形成油藏,晚三叠世—侏罗纪时期随着埋藏深度增加,石油发生热裂解形成古气藏,燕山期古气藏被破坏.铅锌矿的成矿仅与石油的热裂解和古气藏的破坏密切相关.石油热裂解形成硫化氢,热裂解过程中的超压使硫化氢溶于水为铅锌矿成矿提供硫源,构造隆升造成古气藏破坏,含硫化氢的油田卤水与成矿流体混合成矿.