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Organic Matter in Carlin-type Gold Deposits and Paleo-oil Reservoirs in Southwest Guizhou求source,Maturity and Association

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Tutor: GuXueXiang
School: Chinese Geology University (Beijing)
Course: Mineral prospecting and exploration
Keywords: Organic petrography,Organic geochemistry,Carlin-type gold deposit,Paleo-oil rese
CLC: P618.13
Type: Master's thesis
Year:  2012
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SouthEWst GuiZhou Province is tectonically located at the south edge ofYangtse Craton. It is not only a major production area of Carlin-type gold deposits inChina, but also an important district for oil-exploration in South China. Carlin-typegold deposits in this area are mostly hosted by Permian or Triassic strata, andstructurally controlled by anticlines or fractures. Taking Shuiyindong, Lannigou, Yatathree typical Carlin-type gold deposits for example, Shuiyindong gold deposit ishosted by bioclastic limestone and siltstone of Permian Longtan Formation, andorebodies are controlled by Huijiabao Anticline and syndepositional faults; Lannigouand Yata gold deposits are hosted by siltstone and mudstone in Triassic Bianyang andXinyuan Formation, orebodies are controlled by regionally fracture system. Wallrocka lteration in these deposits includes pyritization, arsenopyritization, silification,carbonatization, siallitization, and silification and pyritization show closerelatioSNhip with gold mineralization.Paleo-oil reserves generally restricted to the same tectonic units as the golddeposits, commonly at the basinal margiSN and within the intrabasinal isolatedplatforms or bioherms, and show close spactial relatioSNhip with gold mineralization.Reservoir rocks are mostly biohermal limestones of Perimian Wujiaping Formationwith EWll-developped fractures and karst caves. Taking Baiceng, Laizishan, Banjiepeleo-oil reservoirs for examples, solid bitumeSN commonly fills in reef-buildingorganism*s framework, karst caves and fractures of biohermal limestones, with itsshape restricted to the open space. BitumeSN have structures which indicating highmaturity, such as mosaic structure, spheroid structure, and wavy structure.Organic petrographic observation indicates that the organic matter in Carlin-typegold deposit can be devided into two categories, including kerogeSN and bitumeSN.KerogeSN are mainly alginite, vitrinite and fusinite, which are diagenesis products ofindigenous organic matter. Solid bitumen is commonly hosted by mineralized rocks,filling fractures and open spaces, indicates a high maturity product of migro-bitumen.Paragenesis relatioSNhip betEWen minerals and bitumen shows that bitumen areformed almostly in the same period of gold mineralization.Organic geochemistry testament shows that bitumeSN in paleo-oil reservoirsand organic matters in the hostrocks of Carlin-type gold deposits has differentcharacters, there is no proof that source rocks for bitumeSN in the paleo-oil reservoirs are from the same sedimentary strata which hosted gold mineralization in this area.But chloroform extractioSN of bitumen and some ores in gold deposits shows thesame pattern with bitumeSN in paleo-oil reservoirs, indicates that solid bitumeSN ingold deposits and paleo-oil reservoirs has the same source, probably are the productsof the same fluid system. Carlin-type gold deposits and paleo-oil reservoirs inSouthEWst Guizhou Province shows close spactial relatioSNhip, and close timingbetEWen gold mineralization and reservoir-formation, indicates that possibally theyare different products of the same basinal-fluid system in this region.
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