METALLOGENETIC CHARACTERISTICS OF No.2081 URANIUM DEPOSIT IN THE NORTH OF ORDOS BASIN

The No.2801 sandstone-type uranium deposit is located in the Dongsheng area in the north of the Ordos Basin.Uranium ores are characterized by contact cementation principally and then pore cementation.Cementing materials are hydromicas chiefly,followed by calcite,pyrite,goethite,hydroferrite,etc.Clay minerals from the ores are dominated by montmorillonite,accounting for 73.3%,kaolinite and illite.There is no illite-montmorillonite layer in the ores.Uranium from the ores includes adsorptive uranium and uranium minerals.Uranium minerals are coffinite with UO_2 46.72%—73.4% and brannerite with UO_2 36.01%—49.01%. The coffinite is usually associated with pyrite and sometimes with clausthalite and anatase,and such associated minerals contain uranium.As ores in different parts of the uranium deposit possess different oxidizing-reducing conditions, the contents of adsorptive uranium,U~(6+),and U~(4+) are different.In addition,there is a close connection between the formation of the uranium deposit and oil/gas migration.