Geochemical characteristics of Jurassic sandstones on the southern margin of the Junggar Basin: Constraints on provenance and sandstone-type uranium mineralization

Abstract

Jurassic strata in the southern margin of the Junggar Basin are located in the piedmont zone of the North Tianshan Mountains in Xinjiang, China. Due to multiple tectonic movements, the basin has a complicated history of structural deformation. Accurate reconstructions of the tectonic setting, provenance attributes and paleoclimatic characteristics of the Jurassic strata in the area are vital to facilitate mineral resources prospecting (such as coal, oil, natural gas and uranium) in the basin. Here we used scanning electron microscopy, major and trace elements analyses (including rare earth elements; REE), clay mineralogy and heavy mineral composition in outcrop samples, to analyze the paleoclimate, tectonic setting, source rock properties and provenance characteristics in the southern margin of the Junggar Basin during the Jurassic period. The results are as follows: (1) according to major and trace elements and clay mineral assemblages, the degree of drought increased slightly from the Early Jurassic to the Late Jurassic concomitant increase. (2) Major and minor element discrimination and REE patterns indicate that the material was sourced from continental island arc and active continental margin environments, primarily from upper crustal felsic source rocks (mainly greywacke and arkose). (3) Heavy mineral and whole rock analyses show that the provenances of the Lower Jurassic sandstones were mainly from the primarily Zaire Mountain, North Tianshan Mt.-Middle Tianshan Mt., while the Upper Jurassic sediments were sourced from the primarily North Tianshan Mountain, Zaire Mountain, Middle Tianshan Mountain.