Uranium pre-concentration in Miaogou Formation,Lower Cretaceous and its prospecting significance in Chaoshui basin

Chaoshui basin experienced paleoclimate evolution period from arid,relatively humid,arid humid during Early Cretaceous.The lower member of the Miaogou Formation,Lower Cretaceous is mainly composed of alluvial fan-braided stream of fan front plain,while the upper member is characterized by meandering stream and stream lacustrine facies.The relatively stagnant environment during arid humid paleoclimate condition is favorable for the accumulation and concentration of uranium in sediments,and uranium was pre concentrated in adsorption form in thick bedded red or red grey alternate fine grained clastic sediments,upper member of Miaogou Formation and in desorption form in porous water.Authors suggest that during the process of compaction diagenesis,this previously pre concentrated uranium might be excluded and it migrated into high porous and well permeable sandstones becoming direct uranium source for the formation of sandstone hosted uranium deposit.This pre concentrated uranium plays important controlling role in uranium ore formation in sandstones of Miaogou Formation.Therefore,authors propose that sand bodies having direct contact with thick bedded red or red grey alternate fine grained clastic sediments should be important target for prospecting for sandstone hosted uranium deposit.