| Ma Yuan lead-zinc deposit is located in Beiba dome structure belt of northern sichuanbasin, lead-zinc deposit occurs in the dolomite breccia of Dengying Formation of Siniansystem, which associated with lots of natural bitumen.As the formation and evolution of theorganic matter of oil and gas products,natural bitumen on the one hand, reflects thecharacteristics of oil and gas formation, migration and accumulation, on the other hand, is animportant indication to the cause of pb-zn deposit which is widely distributed in the MVTtype pb-zn deposit. Based on the regional tectonic evolution characteristics and sedimentarycharacteristics,through field observation and indoor analysis, by using rock pyrolysis,chloroform bitumen "A" extraction and determination of organic carbon, and GC-MSmethods and techniques, this paper studied the geochemical and molecular organicgeochemistry characteristics of Ma Yuan lead-zinc deposit bitumen and possible hydrocarbonsource rocks.Through the analysis of geology and geochemical characteristics of naturalbitumen,exploring the mainly organic types and the characteristics of the sedimentarypaleoenvironment of natural bitumen, and tracing the source rock of the bitumenThe bitumen distributed in rock fracture, pore gravel,sutures,dissolution pore as nervation,spherulitic, droplets or block of Mayuan lead-zinc deposit of the Dengying Formation ofSinian.The bitumen has two generations, the first generation was less and had shallowcolor,distributing in the edge of the holes of the breccia, and the late generation content ishigh,distributing in the breccia pore with a large number of black cloddy or droplets inmineralized breccia dissolution pore.The regional distribution of hydrocarbon source rocks is mainly the carbonaceous shale ofGuojiaba Formation of Lower Cambrian which is rich in organic matter and the stratifieddolomite of Deying Formation in Beiba dome structure belt of Sichuan basin, and thecarbonaceous shale of Lujiaping Formation of lower Cambrian in the east Dabashan tectonicbelt. The black shale and mud source rocks are widely distributed in the Lower Cambrian inDabashan tectonic belt and Beiba dome structure belt, which are sets of regional hydrocarbonsource rocks.The lithology is mainly composed of dark shale, black carbonaceous shale,siliceous shale, carbon black silty shale,the thickness is bigger.Dengying Formation aremainly distributed between Zhenba fault, Chengkou and Pingba faults,the lithology is greywhite thick layer of striped dolomite angle conglomerate.The organic carbon content is low.Based on the analysis of the organic geochemical features of the hydrocarbon sourcerock(organic abundance, organic matter type and maturity of organic matter), We find that the organic carbon content of Cambrian hydrocarbon source rock is generally high in SichuanBasin.The hydrocarbon content of hydrocarbon source rock has reached the standard ofsource rock, the soluble hydrocarbon content of group composition is high, the ratio ofsaturated to aromatic is high too.Organic matter types is good, and the organic matter maturityis high.They are good hydrocarbon source rocks,which can generate organic matter, while thelayered dolomite organic carbon content in the Sinian Dengying Formation pattern is low,which belongs to the non hydrocarbon source rocks.The results of n-alkanes,isoprenoids,terpenoids and steroids of bitumen and hydrocarbonsource rock show that organic matter of bitumen and hydrocarbon source rocks derived frombacteria and algae,deposited and preserved in hypoxia with certain salinity reductionenvironment, the water has a chemical stratification which is conducive to the preservationand burial of organic matter.The comparative study on biomarker features of bitumen and hydrocarbon source rockindicate that bitumen of Mayuan lead-zinc deposit and the lower Cambrian source rocks havehigh consistency,while the consistency between bitumen of Mayuan lead-zinc deposit andlaminated dolomite of Deying Formation is low. It means that there is a genetic relationshipbetween bitumen of Mayuan lead-zinc deposit and the lower Cambrian source rocks.So thebitumen of Ma Yuan lead-zinc deposit could come from the overlying Lower Cambriansource rocks, rather than the dolostone of the Sinian Dengying Formation. |
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