The Research On The Relation Between The Sedimentary Facies Of Sifangtai Formation And Uranium Mineralization In The North Of The Songliao Basin

Songliao basin is a large continental sedimentary basin in the north of China.This paper aims to study the relationship between sedimentary facies of Sifangtai formation and uranium mineralization in the north of Songliao Basin.Based on the methods of field outcrop,borehole core and micropetrology,the controlling factors of uranium mineralization such as sedimentary facies,uranium source and structure of the target layer in this area are analyzed.On this basis,the uranium mineralization in the study area is discussed,and the following conclusions are showed:There are two main types of sedimentary facies in the Taikang uplift of Songliao Basin : meandering river delta and lake facies.Among them,the meandering river delta mainly develops delta plain and delta front subfacies,which are distributed in the west,East and north of the study area;the lake facies are divided into shore shallow lake and semi deep lake deep lake subfacies,which are widely distributed in the south central part.This paper the sequence boundary characteristics of the Sifangtai formation in the area are identified,and the sequence division scheme of the Sifangtai formation in the area is determined.Sifangtai formation is divided into two third-order sequences,sequence one and sequence two from the bottom to the top,and then the system tract is divided to establish the fourth-order sequence stratigraphic framework of the study area.Based on the theory of sequence stratigraphy,the evolution of the plane sedimentary facies of Sifangtai formation is restored.The main types of the target sandstone of Sifangtai formation in the Songliao Basin are lithic arkose and feldspathic lithic sandstone,and the sediments show the characteristics of near provenance.The source structure attribute is mainly the mixed source area,followed by the cutting type island arc,which shows the multi-element provenance of the target sediments.In addition,the diagenesis degree of the target sandstone in the area is relatively high,and some of the sandstone can be seen the phenomenon of thermal fluid transformation.Sifangtai formation in the study area was formed in the compression-depauperization of the basin.At the end of the sedimentary period of the strata overlying Mingshui formation,the basin once again formed a reversal structure locally.The strata were denuded to form a structural skylight,which is conducive to the long-term inflow of uranium bearing oxygen water and is a favorable condition for uranium mineralization.In addition,a large number of granites are discovered in the western and northern uplift zones of the study area,and a small amount of volcanic debris can be seen in the basement strata,which are important uranium sources of sandstone uranium deposits.Based on the study of the structure and sandstone type uranium mineralization in the north of Songliao Basin,it is concluded that the basement faults and reverse structures are closely related to the uranium mineralization in the area.Uranium mineralization in the study area is subject to the transformation of the target layer by the upward movement of hydrocarbon reducing fluid caused by structural superposition,which has no strong selectivity for the sedimentary facies developed in the target layer.