Characteristics Of Oil,Gas,Coal And Uranium Coexisting In The Same Basin Worldwide And A Case Study Of The Ordos Basin In China

Oil,gas,coal and uranium are four of the most important energy resources nowadays.They are the basic energy guarantee for social economic development and national security.Not uncommonly,the four types of energy minerals coexist in the same basin.It is therefore of great practical value to study the coexistence law,which can provide guidance for the exploration of mines,increase the value of a single deposit and improve the efficiency in ore-prospecting.Research has demonstrated that the essence of the coexistence of multi-energy resources is organic-inorganic interaction,which involves knowledge of multiple disciplines.The study on the coexistence of the multi-energy resources therefore can contribute to various disciplines,making it a very hot research topic in the field of geoscience in recent years.The Ordos Basin is one of the reserves containing the most abundant energy resources of the four kinds in China.It is also one of the most typical basins where multi-energy resources coexist.Why is the Ordos Basin so rich in the four minerals?Is it due to the interaction among the four kinds of minerals?Or is it due to the coexistence of multiple kinds of minerals?This thesis takes the Ordos Basin as a study case to explore the coexistence of multi-energy,the results of which are of both practical and scientific significance.In this thesis,based on the academic thought of the coexistence of various energy sources and the basin Metallogenic system,we systematically reviewed the research on the worldwide coexistence of oil,gas,coal and uranium and obtained the distribution characteristics and coexistence laws of various energy sources in the world.We then chose the most typical energy coexisting basins in northern China–the Ordos Basin as a study case,and investigated the coexistence of oil and gas in the north and west of the basin,as well as the oil-gas dispersion and the uranium mineralization effect.The results of the Ordos Basin were compared with the pattern we observed from the review.This is to deepen our understanding of the mechanisms of organic and inorganic minerals in the multi-energy basin.To fundamentally answer the two basic scientific questions of"how to coexist"and"why coexist".In the thesis,through investigations of production reserves,distribution characteristics and regularities of sandstone-type uranium deposits in the world,we found that the sandstone-type uranium deposit is the largest type of deposits with the most production,and the sedimentary basins are the main geological units of uranium resources.This thesis systematically analyzed the distribution and basic characteristics of sandstone-type uranium deposits around the world,and compiled a series of maps of the plane distribution and the ore-bed distribution of sandstone-type uranium deposits in various countries?or continents?worldwide.The global distribution of sandstone-type uranium deposits presents the following five major characteristics and laws:?1?The sandstone-type uranium deposits are widely distributed but quite uneven in the world,and there are East-West mega-uranium deposits across Eurasia.?2?The number of sandstone-type uranium deposits is large,but the size of individual deposits varies from one to another.There are lots of?super?large deposits.?3?The spatial distribution of sandstone-type uranium deposits is significantly coupled with the climatic environment.Particularly,the 400mm precipitation line has a significant macroscopic restriction on the distribution of the global sandstone-type uranium deposits.?4?The uranium ore-bearing strata have a large span of time,but are dominated by the Mesozoic.The main metallogenic age is new,the location time is late and there is obvious dynamic mineralization.Moreover,the buried depth is relatively shallow,but the deep prospecting should not be neglected.?5?Sandstone-type uranium deposits mainly occur in oil-gas-bearing or coal-bearing basins and coexist with oil,gas and coal.Via systematic investigations,a list of global basins with which the oil,gas and uranium coexist have been sorted out and the coexistence distribution of multi-energy have been investigated.It is found that it is common that oil,gas,coal and uranium coexist,but the distribution is not even around the world.The coexistence is particularly concentrated in the Sino-Central Asian mineralization region and the western United States.Many basins in north China are located in the Central-East Asian Mineralization Domain,of which the Ordos Basin is particularly typical and representative.The existence of oil and gas seepage activities in the western and northern Ordos Basin was then confirmed by various methods such as field geologicalsurvey,core observation and geochemistry analysis.A comparison of the oil immersions in the uranium ore reserves in the Ningdong region of the western margin showed that they originate from the Upper Triassic Chang 7 source rocks.The composition and properties of the fugitive fluid were also studied.The results showed that the hydrocarbons emitted from the western margin were mainly petroleum and associated gas,and some of the Paleozoic natural gas were mixed.For the first time,the different degrees of discoloration?bleaching?of sandstone,which is caused by the oil-gas dispersion effect was discovered and studied in the Shigouyi area of the western margin of the basin.We further analyzed the genesis of dolomite in the sandstone of mineralized section in the Ningdong area by means of electron probe analysis.The results showed that dolomitization is the cause of hydrothermal reformation,and the deep seeping hydrocarbon-rich heat flow provides the required thermal environment for the formation of dolomite,and promotes the release of Mg²⁺Minerals in strata.Some other hydrothermal minerals,such as sphalerite and barite,have also been formed in the ore-bearing beds of the rich-hydrocarbon hot-fluid.Analyses on the components and properties of the west margin and the northern part of the fugitive fluid showed that both of them have reductive and hydrothermal properties,but the composition of seeping hydrocarbon are mainly oil in the west margin of the basin?the Ningdong area?,and mainly natural gas in the north?the Yimeng uplift?.We also investigated the types of uranium minerals in the west margin and the north by EPMA.We found that the western margin contains mainly brannerite,followed by the uraninite?partial drill holes may be occurringas this type?.There was significantly less coffinite.But the coffinite in the north can reach more than 80%of the uranium minerals.The genesis of the representative uranium minerals in the two places was further analyzed.The metallogenic environment of brannerite and coffiniteare all considered to relate to the rich hydrocarbon fluids seeped/leaked in the deep.The environment temperature ismuch higher in the west margin,but the reduction is muchstronger in the north,relatively.The property difference of the deep seepage fluid is the main cause of the mineral type differences between the two uranium deposits.At the same time,we explored the possibility of deep uranium source in the west margin and the northern part of the oil,through deep uranium anomalies,the metal concentrations of oil field water and gas field water.It was found that the deep seeping fluid in the western margin and the North may provide some supplementary uranium sources for the shallow part in the late stage of mineralization.We also found a highly linear relationship between U and Ti in hydrocarbon-rich fluids and we then proposed a new idea of the existence and migration of uranium in these fluids in the form of uranium-titanium ion clusters.Using the method of EPMA chemical U-Th-Pb,the in-situ micro-region of brannerite in Ningdong uranium ore area was determined and the main metallogenic age was established as6.5 Ma.Together with the dating results in previous studies,we divided the age of the Ningdong area into three periods:the 59.2⁵2 ma,the 21.9 Ma and the 10.7³.9?6.5?Ma.They correspond to the Pliocene,the early Miocene and the late Miocene period respectively.We detected a series of fatty acid methyl ester compounds?mainly 16-alkyl acid methyl ester?,which are rare in geological environment,in the Hangjinqi uranium ore-bearing sandstone by means of organic geochemistry.According to previous studies,this compound can prove that natural gas is involved in the formation of the Hangjinqi uranium deposit.It may serve as a direct indicator of whether natural gas is involved in uranium mineralization after all.Based on the above findings,we established the uranium metallogenic model of the western margin of the Ning-dong region and the northern Hangjinqi area respectively and emphasized the important role of the deep oil and gas dispersion in the uranium mineralization process.Finally,we examined the dispersion characteristics and the uranium mineralization of hydrocarbon-rich fluids in the western margin and the northern part of the basin.In addition to the tectonic factors,the geochemical environment is identified as another significant factor that affects the geological characteristics of the deposits in the two places.Specifically,there are differences in the nature and seepage characteristics?composition,scale,etc.?of the dissipated fluids in the western margins and the north,which lead to differences in the geochemical environment of the uranium mineralization in the Shallow Zhiluo Formation.It in turn causes differences in the composition of uranium minerals between the two places.Overall,the coexistence of oil,gas,and coal uranium in the same basin fundamentally results from the organic-inorganic interaction.The forms and characteristics of the interactions differ,if the interaction takes place in different basins or different regions within the same basin.With proper geological environment,the oil and gas seepage activities may result in different degrees of uranium metallogenic effect.