GEOCHEMICAL CHARACTERISTICS OF CLAYSTONE TYPE GALLIUM DE-POSITS AT THE BOTTOM OF THE UPPER PERMIAN XUANWEI FORMA-TION IN SOUTHERN SICHUAN AND ORIGIN OF GALLIUM ENRICHMENT
A suite of gallium-rich clay rocks developed at the base of the Upper Permian Xuanwei Forma-tion in Sichuan,Yunnan,and Guizhou regions,yet their sedimentary environment and genesis of gallium enrichment remain extremely limited understood.This paper investigates the Ga-rich clay rocks at the base of the Upper Permian Xuanwei Formation in the Muchuan area of southern Sichuan Province.The investi-gation employs field geological surveys,petrology,and petrogeochemistry,accompanied by summarizing the vertical variation of gallium content and discussing the sedimentary environment and origin of gallium enrichment.The results reveal that the gallium-bearing rock series primarily consists of purplish-red ferric claystone-type gallium,miscellaneous ferric aluminous claystone-type gallium,light grayish-green alumi-nous claystone-type gallium,grayish-white aluminous claystone-type gallium,grey claystone-type galli-um,and dark grey carbonaceous claystone-type gallium.Data from three boreholes indicates an average thickness of the gallium layer of 12.14 meters,with an average grade of Ga at 70 × 10-6,with Ga being most enriched in the gray-white aluminous clay rock.Geochemical analysis reveals that the ΣREE of galli-um-bearing rocks ranges from 263.87 × 10-6 to 12 820.56 × 10-6,ΣLREE/ΣHREE ranges from 4.31 to 24.67,and LaN/YbN ranges from 3.83 to 122.71,indicating a high degree of enrichment of light rare earth elements.The source of gallium deposits is related to the formation of the Emei Mountain igneous prov-ince,with the lower purplish-red iron claystone-type gallium deposit sourced from weathering and denuda-tion products of Emeishan basalt.The upper gray,light gray-green,gray,and dark gray claystone-type gallium deposits are mainly derived from alkaline volcanic ash and a small amount of weathering products of basalt.The gallium-bearing rock series formed in a terrestrial lacustrine environment that has been sub-merged by seawater multiple times,and is restricted by lithofacies paleogeography.The enrichment process of Ga element is controlled by both leaching and sedimentation,and the genetic type of ore deposit belongs to paleo-weathering crust and sedimentation type.These research results are of significant impor-tance in enriching and improving the understanding of the Emei Mountain mantle plume metallogenic sys-tem,and provide important clues for prospecting gallium deposits in the Sichuan-Yunnan-Guizhou area.
Upper Permian Xuanwei FormationEmeishan basaltscattered elementsMuchuan County
万方数据
维普
