Occurrence of Carbonate Cements and Relationship between CarbonateCementation and Uranium Mineralization of Qianjiadian Uranium Deposit,

Carbonate cements from sandstone-hosted uranium deposits have generally been considered as a tracer for ore-forming fluids. However, it is difficult to confirm whether carbonate cements occurred in the ore-forming period of the sandstone-hosted uranium deposits since they generally have characteristics of variable minerals and multiple depositional and diagenetic stages. The purpose of this study is to characterize the mineral species, occurrence, generation of the carbonate cements in the Qianjiadian uranium deposit, southern Songliao basin, based on a series of approaches such as core description, micropolariscope and scanning electron microscope (SEM). According to these data in combination with the spatial allocation of carbonate cements and uranium ore bodies, relationship between carbonate cementation and uranium mineralization are revealed. The key conclusions are summarized as follows: (1) Carbonate cements in the Qianjiadian uranium deposit are primarily composed of dolomite, siderite, ankerite and calcite. The dolomite cements with crystalline granular texture and contact cementation have the highest average content in the partial oxidation zone. Siderite cements with a large quantity of residual euhedral crystals often show as contact cementation, which have the highest average content in the reduction zone. Ankerite cements with mosaic granular structure generally present contact cementation and porous cementation. The average content of ankerite is the highest in the transition zone. Calcite cements with porous cementation and contact cementation mainly have mosaic granular texture, which have the highest average content in the weak oxidation zone. (2) The dolomite, siderite, ankerite and calcite are successively generated from early to late stages. Four evidences have been found in the thin sections. Firstly, the siderite and ankerite cements are included by the calcite. Secondly, the siderite is included by the ankerite. Thirdly, the dolomite is coated with ankerite. Finally, the dissolved pores of dolomite are filled by siderites. (3) It can be inferred that the siderite was formed during the diagenetic stage, and the dolomite may have occurred in penecontemporaneous or early diagenesis stages. It can be concluded that ankerite is associated with uranium mineralization. The calcite may have occurred after the metallogenic period. Therefore, the ankerite of carbonate cements is closely related to uranium mineralization in the Qianjiadian uranium deposit.