| Red miscellaneous layer of the upper Cretaceous is the target horizon of uranium in southern Songliao Basin.For a long time,the problem of unclear target horizon division has been pending.Most of the previous studies only focused on the uranium ore belt,with a low degree of research on the southern region,lacking systematic understanding.In order to accurately determine the ore-bearing strata and clarify the relationship between the sedimentary filling characteristics of red miscellaneous layer and sandstone-type uranium deposits,based on the theories of stratigraphy,sedimentology and sandstone-type uranium mineralization,re-recognizing and systematic mapping are carried out using core,drilling,well logging and seismic data in this paper.Research results show that the ore bearing target layer can be identified and divided into three horizons: Quantou formation,Qingshankou formation and Yaojia formation(traditional stratigraphic division classifies it as the Yaojia formation).Stratigraphic distribution characteristics : Quantou Formation is characterized by eastern subsidence and western superelevation,Qingshankou Formation-Yaojia Formation is characterized by eastern uplift erosion-central subsidence-western uplift missing.During the sedimentary period of the red miscellaneous layer,the subsidence center and the sedimentary center gradually migrated westward.The palaeo-uplifts(Shebotu-Jiamatu Uplifts)in the middle part of the study area have the characteristics of “saddle-type” overlapped sedimentary filling and extinction.In the process of sedimentary filling of Quantou Formation → Qingshankou Formation → Yaojia Formation,the provenance system gradually moved westward from Zhangguangcailing → Kangping-Faku Hilly → southern Daxinganling.At the same time,in the sedimentary period of Qingshankou Formation – Yaojia Formation,the provenance supply from Shebotu – Jimatu uplift was accepted.In addition,the main sedimentary facies types are braided and meandering rivers,and the channels are characterized by westward migration and swing and convergence towards the saddle of palaeo-uplifts.The sedimentary filling evolution law of red miscellaneous determines the sedimentary background of sandstone-type uranium mineralization : First of all,the sedimentary pattern of “uplift in the east and subsidence in the west” have controlled the change of provenance and uranium sources,which make the main ore-bearing beds(Qingshankou and Yaojia formations)have favorable provenance and uranium sources during the sedimentary periods.Secondly,sedimentary sand bodies have the characteristics of migration to west superimposed,channel superimposed and oxidation-reduction sand body transition parts are conducive to sandstone type uranium mineralization.Moreover,the sedimentary evolution model of “palaeo-gully and monadnock” illustrates the overlap extinction process of the palaeo-uplifts,and the gray sand-bodies under the arid palaeo-climate background are formed during the water-catchment of the palaeo-uplifts.Therefore,the prospecting direction of the red miscellaneous layer in the southern Songliao Basin has been defined.The main prospecting target strata gradually move upward from the eastern(Quantou formation)to the middle and the western(Qingshankou and Yaojia formations).It is necessary to follow the rule of westward migration when predicting sand bodies.In addition,the saddle catchment landforms of palaeo-uplifts are the main positions to search for favorable gray sand-bodies for uranium mineralization.This study comprehensively and systematically expounded the filling characteristics and sedimentary evolution law of the upper cretaceous uraniumbearing red miscellaneous in southern Songliao Basin for the first time,which improved the basic geological theory research.In addition,this research can provide guidance for the further exploration of sandstone-type uranium deposits in the southern Songliao Basin. |
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