准噶尔盆地北部晚白垩世至新近纪沉积介质环境演化特征及其对铀成矿的制约

Environmental Evolution Characteristics of Sedimentary Media from Late Cretaceous to Neogene in the Northern Junggar Basin and Its Constraints on Uranium Mineralization

沉积地层原生沉积介质的环境对砂岩型铀矿成矿作用及潜力分析具有重要意义。本文以准噶尔盆地北部铀矿地质探井N3006中上白垩统至新近系16件泥岩样品中的微量元素测试结果为基础,结合露头及钻孔岩心发育特征,选用对沉积介质环境反映比较敏感的锂(Li)、锶(Sr)、镓(Ga)、钡(Ba)、铜(Cu)、铀(U)、钒(V)、镍(Ni)等微量元素指标,探讨了研究区晚白垩世至新近纪沉积介质环境演化特征及其对铀成矿作用的制约。研究结果表明:晚白垩世至新近纪古沉积环境总体表现为干旱炎热且富氧的淡水-微咸水沉积;据原生沉积环境判断,研究区内上白垩统至新近系各层组砂体总体上不利于传统的层间氧化和潜水氧化砂岩型铀矿化的发育;强氧化的古环境有利于铀元素的迁移,局部特殊环境形成的原生灰色层和后期遭受还原流体改造的灰色层是该区砂岩型铀矿找矿的重要突破方向。

The environment of the primary sedimentary medium in the sedimentary strata is of great significance to the mineralization and potential analysis of sandstone-type uranium deposits.In this study,trace element analyses of 16 mudstoness derived from the Upper Cretaceous to Neogene in the uranium geological exploration well N3006 in the north of Junggar basin,were conducted.By combination with observations form outcrops and drill cores,the lithium(Li),strontium(Sr),gallium(Ga),barium(Ba)Copper(Cu),uranium(U),vanadium(V),nickel(Ni)and other trace element indicators are utilized to discuss the environmental evolution characteristics of the Late Cretaceous to Neogene sedimentary media in the study area and their constraints on uranium mineralization.All the results suggest that,the paleosedimentary environment from the Late Cretaceous to Neogene was generally characterized by dry,hot and oxygen rich fresh water brackish water deposits;Judging from the primary sedimentary environment,the sand bodies of each formation from Upper Cretaceous to Neogene in the study area are generally not conducive to the development of traditional interlayer oxidation and phreatic oxidation sandstone-type uranium mineralization;However,the presence of strongly oxidized paleoenvironment is conducive to the migration of uranium elements.Significantly,the primary gray layer formed in a local special environment and the gray layer transformed by reducing fluid in the later period are the important breakthrough directions for the exploration of sandstone type uranium deposits in the area.