Major, trace and rare earth element geochemistry of coal and oil shale in the Yuqia area, Middle Jurassic Shimengou Formation, northern Qaidam Basin

Abstract

Coal and oil shale in the Middle Jurassic Shimengou Formation of the northern Qaidam Basin (China) have been characterized and compared using total organic carbon (TOC) content, oil yield, and proximate as well as major, trace and rare earth element (REE) and X-ray powder diffraction (XRD) analyses. The results show that coal is represented by lignite and bituminous coal and oil shale is of medium quality. In both coal and oil shale, Si, Al, K, Ti and Na originate from a mixed clastic sedimentary component comprised of clay minerals, quartz and feldspars. In coal, rare earth elements (REEs) are related to phosphate minerals, whereas those in oil shale have inorganic affinities and are mainly associated with clay minerals and quartz. REEs in coal and oil shale are of terrigenous origin. Both coal and oil shale in the Yuqia area are possibly the products of source rocks that have experienced moderate chemical weathering during a warm and humid climate, and they have similar source rocks of felsic volcanic and sedimentary rocks.