Enhancement Of Organic Matter Maturation Of Carbonaceous Debris Due To Radiogenic Heat From The Sandstone-type Uranium Deposits, Ordos Basin

Organic-inorganic interaction is ubiquitous in the process of formation and enrichment of various energy resources of coal,petroleum,gas and uranium.In sandstone-type uranium deposits of sedimentary basins,it has been documented that organic matter palys an important role of concentration,complexation and reduction in uranium mineralization.However,little attention is paid to influences of uranium mineralization on organic matter.Carbonaceous debris?CD?,a matter reflecting thermal evolution,is widely distributed in sandstone of uranium-bearing strata,and coexists with uranium mineralization bodies,which provide a favorable change for studying the relationship between them.In the present study,organic matter maturation of CD from the uranium-bearing stratas in the Daying and Shuanglong uranium deposits,Ordos basin,is investigated by using vitrinite reflectance?Ro?,laser raman parameters,moisture on air dried basis?Mad?and volatile matter yield on dry,ash-free basis(V_daf)in an attempt to acquire the informations about influences of uranium mineralization on organic matter maturation.CD is widely interspersed in sand bodies in the forms of lumps,bands and dispersion,and CD in lump forms is most common.Coal petrology maceral of CD from the Daying uranium deposit is similar to those from the shuanglong uranium deposit.Coal petrology maceral of CD is mostly composed of Vitrinite?V?,Inertinite?I?and minerals,and V is the major maceral.Moreover,CD can be classified into vitrite and vitrinertite-V.CD from the Daying uranium deposit is of medium-high moisture,super-high volatile matter,low-medium ash and low sulfur.It experiences the normal burial coalification,and the majority of CD is immature while only a small part of them is at a low maturity stage.CD from the Shuanglong uranium deposit is of low moisture,medium volatile matter,medium ash and medium sulfur.It undergoes the normal burial coalification,and CD is mostly low-medium mature while a small fraction is at a medium maturity stage.In the uranium mineralization areas of the Daying and Shuanglong uranium deposits,M_ad and V_daf signficantly decrease while ash yield on dried basis?A_d?and total sulfur?S_t?slightly increases,and Ro obviously increases,which indicate that uranium mineralization might have relationships with coalification indicators Ro,M_ad and V_daf.Besides,CD coexists with uranium minerals,and uranium is rich in the area which CD distributed in.In the uranium mineralization areas of the Daying and Shuanglong uranium deposits,Ro remarkably increases,and the frequency distributions of Ro are more discrete.Additionlly,Ro increases as uranium content increases,and decrease with the increasing distance to uranium mineralization bodies.In the Daying uranium deposit,Ro of CD with uranium mineralization is 0.062%higher than those without uranium mineralization.In the Shuanglong uranium deposit,Ro,laser raman parameters and uranium contents of uranium-bearing organic matrix are unevenly distributed,and the higher Ro values and the lower values of shift difference of G peaks are intensively distributed in uranium mineralization zones.Uranium content increases with an increase in Ro and a decrease in the shift difference of G peak.In the Daying and Shuanglong uranium deposits,it is found that uranium mineralization has influences on coalification indicators M_ad and V_daf.In the uranium mineralization zones,M_ad and V_daf evidently decrease.M_ad and V_daf decrease as uranium content increases,and increase with the increasing distance to uranium mineralization bodies,indicating that the coalification of CD increases as uranium content increases.On the basic,the influences of uranium mineralization on organic matter maturation are summied.Influenced by uranium mineralization,organic matter maturation increases,including that Ro increases about 0.060%,and shift difference of G peaks,M_ad and V_daf decreases about 6¹5cm^-1,4⁵%and 10¹5%,respectively.Take the Daying uranium deposit as a studied area,the mechanism about the influences of uranium mineralization on organic matter maturation is analyzed.It is found that the production of uranium decay makes FT observable in quartz grains,and the intensity of decay increases with proximity to the uranium ore body.The calculated radioactive heat production rate from the uranium mineralization body is 6.857x10^-5 W/m³.During the long-term stable decay,as the uranium ore body theoretically results in an abnormal increase in temperature of 52°C without consideration of the loss of heat conduction,heat convection and thermal radiation,this would yield a theoretical Ro increase of 0.209%,reasonably greater than the observed.Therefore,the long-term stable radiogenic heat produced by uranium mineralization body can slightly enhance organic matter maturation,which is instructive in prospecting.