江西会昌锡坑迳斑岩型锡矿床成矿系统发育特征与找矿模型

锡坑迳矿田位于南岭成矿带东段与武夷山成矿带交会部位，以早白垩世连续的岩浆喷发-侵入活动与多类型锡多金属成矿作用为特色。矿田内围绕似斑状花岗岩和花岗斑岩发育了岩背斑岩型、淘锡坝和矿背隐爆层间裂隙带型、苦竹岽和凤凰岽云英岩-破碎带蚀变岩型等大中型锡矿床。这些矿床的矿化-蚀变特征可与玻利维亚锡矿带、银岩、维拉斯托和洋滨等国内外斑岩型锡矿床类比，又独具特色，是研究斑岩型锡成矿系统发育特征与找矿模型的理想区域。文章在详细的野外地质调查基础上，系统总结了锡坑迳矿田内各类锡多金属矿化组合特征和蚀变结构，并对岩背矿床和淘锡坝矿床锡石开展了电子探针和LA-ICP-MS原位微区分析。研究结果显示，所有锡石样品均具有La、Pr、Gd和Tb的正异常、Ce与Eu的负异常、明显的Zr/Hf分馏和不规则的稀土元素配分模式，指示成矿热液早期阶段及锡石沉淀阶段经历了流体不相容。岩背锡石较淘锡坝锡石具有高的Ti/Zr和Ti/Sc比值，指示其更为靠近矿化中心。笔者研究认为，锡坑迳斑岩型锡成矿系统矿化类型包括细脉状、浸染状和细网脉状，围岩蚀变由早到晚、由成矿中心向外依次发育黄玉石英带、绿泥石-黄玉石英岩化带、绿泥石-绢云母化带和黏土化-碳酸盐化带。与斑岩型铜钼成矿系统相比，其成矿岩浆岩不仅有花岗斑岩，还有似斑状黑云母花岗岩，矿体在斑岩、花岗岩及上覆火山岩中均有赋存。相较于玻利维亚斑岩型锡成矿带发育的大面积石英-电气石化，锡坑迳斑岩成矿系统更富F，蚀变矿物中出现了大量黄玉、萤石和白云母等。对比国内外典型锡矿床的矿化-蚀变结构和锡石矿物学特征，文章建立了锡坑迳式斑岩型锡成矿系统的找矿模型。

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), Kuzhudong 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 metallogenic 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-hydrothermal 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 porphyry, granite and overlying volcanic rocks. Compared with the large-area quartz-tourmaline developed in Bolivia''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 comparative analysis of mineralization-alteration structures of typical tin deposits at home and abroad and the study of cassiterite mineralogy, a prospecting model for the Xikengjing porphyry mineralization system was established.