Studies On The Coupling Relationship Of The MVT Lead-zinc Deposits And The Ancient Oil(Gas) Reservoir In The Northern Margin Of The Sichuan Basin

The MVT Lead-zinc deposit and oil?gas? Reservoir often have symbiotic or associated relationships in the worldwide. The close contact of the Lead-zinc deposits and the organic matter, as a leading edge research project, has been concerned by the domestic and foreign geologists. However, the existing researches have been mostly confined to the study of the MVT Lead-zinc deposit from the view of the deposit geology, and of the oil?gas? reservoir from the view of the petroleum geology. And the combined research of the two subjects is still very weak. So, this weak point is selected by this paper. The paper does research from two different perspectives which are Lead-zinc deposit and oil?gas? reservoir. The research objects are Lead-zinc deposit and bitumen in the Northern Margin of the Sichuan Basin, and there are also some research tools such as petrology, fluid inclusion, micro analysis and geochemistry. The Paper discusses the coupling relationships of the mineralization and accumulation, and establishes the model of them. Some conclusions are drawn as follows:The Dengying Formation has two paleokarst interfaces, which effects the location of lead-zinc deposit and ancient oil?gas? reservoir in the study area. Whether in the plane or space range, ancient oil?gas? reservoir's distribution range has been far greater than the lead-zinc deposit, and both of them have the characteristics of overlapping. The lead-zinc ore and bitumen have had closely relationship, and existed in all of the pores in the ancient karst zone. The study on formation sequence of minerals in different stages by macroscopic and microscopic showed that there have been two stages of mineralization and accumulation.There were fluid inclusions in barites. The peak value of the temperature, salinity, trap pressures and density of the inclusion ranged between 140-180?, 9-13%NaCl_eqv, 15-16%NaCl_eqv, 0.06-0.97 MPa and 0.86-1.07g/cm³ respectively. The main composition of inclusions is H₂ O, then the H₂ S, and also contains less CH4 and CO₂. There has been some natural sulfur in inclusions. According to the results of inclusion test, metallogenic fluid has had the characteristics of the basin brine, which has been closely related to the oil field brine.The relationship between metal elements and reservoir forming fluid was closely, and were derived from the Qiongzhusi Formation. The sulfur which have had a genetic relationship to the Cambrian seawater was supplied by the thermochemical sulfate reduction and aquathermolysis reaction in the ancient oil reservoir. Barium was derived from the in situ fluid in the Dengying Formation.The various graphs of REE parameters, trace elements and REE distribution patterns of sphalerite and bitumen have been of high similarity. Sulfur isotope data has showed that galena, sphalerite, pyrite, barite and bitumen had the characteristics of S-richness, and the distribution range of the sulfur isotope values of the metallogenic fluid has been close to that of the bitumen. The composition and distribution characteristics of trace elements, REE, and sulfur isotopes have also indicated that metallogenic fluid and migration and accumulation fluid have been with homologous features. The MVT lead-zinc deposit and ancient oil?gas? reservoir have been with the coupling relationship of origin.The above conclusions have shown that the MVT lead-zinc deposit and ancient oil?gas? reservoir have had the coupling relationships of space and origin instead of time. The mineralization lagged behind accumulation in terms of time, and occurred in the same place.