Geological And Geochemical Characteristics And Determination Of Accumulation Epoch Of The Paleo-oil Reservoir In Qinglong Antimony Deposit,Guizhou Province,China

Qinglong antimony deposit is one of the most important antimony deposits in China. There are rich organic inclusions in the Qinglong antimony deposit. However, the source of these organic matters have not been able to find out. Although the relationship of the formation of antimony ore and organic matters has been discussed by some researchers, the lack of bitumen which is a important material for the study of organic matters is difficult for the research about the relationship of organic matters and antimony mineralization. A paleo-oil reservoir has been found in the Shaziling section during the prospecting in depth and outside of Qinglong antimony deposit. Paleo-oil reservoir and antimony deposit have close spatial relationship, which suggests the organic connection in origin between them. The relationship of mineralization and accumulation is not clear and accumulation chorno logy has not been studied in the Qinglong antimony deposit. To solve these problems, this study takes the paleo-oil reservoir and antimony deposit as the research object and is based on the test data of geochemical analysis to make a study. Through the discussion about the geological and geochemical characteristics of paleo-oil reservoir and the determination of accumulation epoch, the time pedigree of age of mineralization and accumulation has been established and the relationship of mineralization and accumulation has been discussed in this study. The following understandings are acquired.1.The volcanic rock paleo-oil reservoir is founded for the first time in the Shaziling section of Qinglong antimony deposit,15 layers of bitumen had been found by 5 drill holes. Paleo-oil reservoir and antimony deposit have close spatial relationship which have close distance and distribution layer. The bitumen layers occur in Emeishan basalt and "Dachang layer" tuff of Upper Permian and Maokou group limestone of Middle Premian. The bitumen is mainly distributed in the fractures, pores and caves of rock.2.A new understanding has been obtained by the geochemical analysis and testing for the paleo-oil reservoir. The bitumen of paleo-oil reservoir in the Qinglong antimony deposi is carbonaceous bitumen which has a high degree of thermal evolution by the analysis of organic elements (C,H,O,N) and reflectivity (Rb). REE geochemical characteristics of bitumen shows that the REE content of bitumen is low and the fractionation of light and heavy REE is quite obvious. In addition, the abnormal of Eu and Ce are not obvious. The REE pattern of bitumen belongs to the pattern which enrichs light REE and tilt to the right. REE characteristics indicates that the fluid property of mineralization and accumulation is different. The bitumen of paleo-oil reservoir originates from carbonaceous mudstone of Devonian through the analysis of REE characteristics and C isotope value of bitumen.3.The isochron age of 254.3±2.8Ma has been obtained for the bitumen by the Re-Os isotopic dating and The age indicates that the oil-gas reservoir(oil generation) in the Qinglong antimony deposit was formed in the early of late Permian. The accumulation epoch has been determined by the method of fluid inclusion shows that crude oil was evolved into the pattern in the early-middle of Triassic. The age of mineralization is later than the accumulation epoch of Qinglong antimony deposit. Hydrocarbon accumulation and mineralization may be a continuous geologic process, The formation of oil-gas is the foundation of antimony mineralization in the Qinglong antimony deposit.4.The relationship of accumulationand mineralization is determined. Crude oil entered the fractures and pores of Emeishan basalts (including Dachang layer) after it has been generated. As burial process deepened, crude oil has been into natural gas and migrates into the core of Dachang anticline. The hydrocarbons(CH4) in the reservoirs may have provided the S2- required for Sb mineralization through thermal chemical reduction of sulfates(SO42-). In addition, pyrite in the bitumen is also the basis which provides S " from paleo-oil reservoir to antimony mineralization. (SO42-+CH4=S2-+CO2+H2O; 3S2-+2Sb3+=Sb2S3)...