鄂尔多斯盆地北部中侏罗统直罗组岩石地球化学特征及其地质意义OA

The Hangjinqi area in Inner Mongolia is one of the significant uranium-bearing regions in the northern Ordos Basin,with favorable geological conditions and promising exploration prospects for mineralization.This paper conducts sedimentological,petrological and geochemical analyses on the core samples of the Middle Jurassic Zhiluo Formation from the borehole X7-6 in the Hangjinqi area,systematically studying the conditions conducive to urani-um enrichment and mineralization.The research results show the lower section of the Zhiluo Formation comprises braided river deposits,mainly composed of the thick-bedded gray sandstone and thin mudstone interbedded with thin coal seams,rich in carbonaceous debris and pyrites,while the upper section is characterized by meandering river and deltaic sedimentation,dominated by purple-red siltstone and mudstone.The geochemical characteristics exhibit a"right-inclined"pattern with enrichment of light rare earth elements and depletion of heavy rare earth ele-ments.The chemical index of alteration(CIA)values rangs from 54 to 77,indicating moderate chemical weathering of the Zhiluo Formation during deposition.The paleoenvironmental and paleoclimatic discrimination indicators Sr/Cu,U/Th,V/Cr,Ni/Co,V/(V+Ni),and Sr/Ba values suggest that the paleowater system during the deposition of the Zhiluo Formation was an oxygen-rich freshwater environment,and the paleoclimate underwent a transition from alternating dry and wet conditions to arid and semi-arid conditions.The tectonic setting of source areas of the Zhiluo Formation are continental arcs,and the provenances are primarily composed of the upper crustal felsic rock.The sedimentary environments,tectonic setting,paleoclimate and provenance characteristics can provide favorable geological conditions for uranium enrichment and mineralization in the Zhiluo Formation of the Hangjinqi area.