Jurassic uraniferous rocks in the eastern Transbaikal region

Abstract

The paper presents the results of lithological studies of Jurassic rocks in one of the largest basins in the eastern Transbaikal region (Olov depression). These results refined settings of the volcanosedimentary association and indicated that the Olov depression was formed in three stages: stage 1 related to tectonic activation manifested as cataclasis of granitoids in the Transbaikal region and incipience of numerous depressions (Olov included); stage 2 characterized by catastrophic events related to reactivation of tectonic motions, strong volcanism, and intense activity of geysers; and stage 3 marked by termination of volcanic activity and relative tectonic stability of the region that promoted the deposition of rocks of the middle and upper Ukurei subformations in the course of slow synsedimentary subsidence of the depression. Uranium mineralization in the rocks was governed mainly by the following conditions: (1) abundance of cataclased granitoids that delivered terrigenous material to the sedimentation basin; (2) favorable paleogeographic setting for the formation of both sedimentary and postsedimentary hydrothermal U-rich sequences. Field works in the Transbaikal region and analytical results reported in the present paper made it possible to make a videofilm shown in https://youtu.be/UOe9xzSKOEI.