Development characteristics and exploration model of Xikengjing porphyry-type tin metallogenic system in Huichang County,Jiangxi Province
The Xikengjing ore field is located at the intersection of the eastern part of the Nanling metallogenic belt and the Wuyishan metallogenic belt.It is characterized by early Cretaceous magma eruption-intrusion activities and multi-type tin polymetallic mineralization.In the ore field,different types of large and medium-scale tin deposits such as Yanbei(porphyry type),Taoxiba and Kuangbei(cryptoexplosion-interlayer fracture zone type),Ku-zhudong and Fenghuangdong(greisen-altered rock type)have developed around porphyritic granite and granite porphyry.Its mineralization and alteration characteristics can be compared with those of the Bolivian tin ore belt,Yinyan,Weilasituo and Yangbin porphyry tin deposits.Therefore,the Xikengjing ore field is an ideal area to study the development characteristics and prospecting models of porphyry tin mineralization systems.Based on detailed geological work in the field,electron probe analysis and LA-ICP-MS in-situ microanalysis of cassiterites are carried out,this study systematically summarizes the characteristics and alteration structures of various tin-polymetallic mineralization combinations in the Xikengjing ore field.The results indicate positive anomalies in La,Pr,Gd,and Tb,negative anomalies in Ce and Eu,and significant Zr/Hf fractionation.The irregular rare earth partitioning pattern indicates that the ore-forming fluids experienced fluid immiscibility during the early metallo-genic stage and the precipitation stage of cassiterite.The cassiterite samples from the Yanbei deposit show higher Ti/Zr and Ti/Sc values than those from the Taoxiba deposit,indicating their closer proximity to the magmatic-hy-drothermal center.The alteration of the porphyry-type tin mineralization system successively developed topaz-quartz zone,chlorite-topaz-silicification zone,chlorite-sericite zone,and clay-carbonate zone outward from the mineralization center.Tin mineralization mainly occurs as disseminated,veinlets or stockwork veinlets.Compared with the traditional porphyry Cu-Mo mineralization system,the magmatic rocks related to the mineralization in Xikengjing ore field include not only granite porphyry but also porphyritic biotite granite.Ore bodies occur in por-phyry,granite and overlying volcanic rocks.Compared with the large-area quartz-tourmaline developed in Boliv-ia's porphyry tin mineralization system,the Xikengjing porphyry mineralization system contains high contents of F,and a large amount of topaz,fluorite,and muscovite appear in the alteration minerals.Combining the compara-tive analysis of mineralization-alteration structures of typical tin deposits at home and abroad and the study of cas-siterite mineralogy,a prospecting model for the Xikengjing porphyry mineralization system was established.
porphyry tin depositalteration zoningin-situ trace element analysismetallogenic systemXikengjing orefield
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