Morphology of orebodies and genesis of uranium deposits in the Khiagda ore field

The localization controls of uranium lodes at deposits in the Khiagda ore field are considered in this paper on the basis of detailed documentation of borehole cores, geological sections, and maps. Detailed mapping has been carried out at four of eight deposits of the ore field; additionally, three deposits were studied fragmentary using separate sections and boreholes. We have shown that the idea of the lenticular shape of ore-bodies in section and their ribbonlike shape in plan view only partially corresponds to reality. The revealed morphological features of orebodies along with spatial relationships with epigenetic alteration of host rocks and faults indicate that mineralization was formed by mixing of the oxygen- and uranium-bearing subsurface water descending downdip the seam and the reductive subsurface water ascending from the basement along faults. The available data on the composition of subsurface water currently contained in the basement of ore field give grounds to assume that water similar in composition could have participated in uranium ore deposition. The special properties of this water, interacting for a long time with flows of formation water under conditions of the local geological setting, have imparted those features to the studied deposits, which differentiate them from other economic sandstone-hosted deposits, including those localized in paleovalleys.