湖南锡田矿田花岗岩时空分布与钨锡成矿关系:来自锆石U-Pb年代学与岩石地球化学的约束

Spatiotemporal Distribution of Granites in Xitian Ore Field in Hunan and Its Tungsten-Tin Mineralization:Constraints from Zircon U-Pb Dating and Geochemical Characteristics

锡田钨锡多金属矿田位于南岭成矿带中段,发育多期次岩浆活动与钨锡成矿.为了厘清花岗岩与钨锡成矿的时空关系,采用野外调查、显微鉴定、锆石U-Pb同位素定年与岩石地球化学的方法对矿田内多期次花岗岩岩体(脉)的空间分布、岩石类型、成岩时代、地球化学组成等进行了研究.结果表明,锡田矿田发生了三期岩浆事件,分别为加里东期(435~441 Ma)、印支期(220~230 Ma)、燕山期(141~160 Ma);三期花岗岩普遍富集大离子亲石元素Rb、K、U、Th等,亏损Ti、P、Sr、Ba等微量元素,具明显的负Eu异常,其中加里东期花岗岩与印支期花岗岩为S型花岗岩,而燕山期花岗岩为A型花岗岩;不同时期花岗岩中的成矿元素从加里东期→印支期→燕山期逐渐升高,特别是W、Sn元素在燕山期白云母与二云母花岗岩中最为富集,这与华南地区燕山期钨锡大爆发的时间是一致的;印支期岩体接触带发育少量矽卡岩型Fe-Cu-W多金属矿床,燕山期岩体接触带也发育矽卡岩型W-Sn多金属矿床,并在附近陡倾的张裂隙中发育多个中大型石英脉型W-Sn矿床,而加里东期岩体附近尚未发现钨锡矿化.因此,锡田矿田的多期次花岗岩与钨锡多金属成矿是时空耦合的,且成矿以燕山期矽卡岩型与石英脉型钨锡矿为主.

Xitian W-Sn polymetallic ore field is located in the middle part of the Nanning metallogenic belt,and multi-stage magmatism and W-Sn mineralization are developed in this ore field.To determine the spatial and temporal relationship between granites and W-Sn mineralization,in this paper it conducts field geological survey,microscopic observation,zircon UPb isotopic dating and geochemical analysis on the spatial distribution,lithology,intrusive age and geochemical compositions of multi-stage granites in this ore field.The results show that the Xitian ore field experienced three magmatic events,namely Caledonian(435-441 Ma),Indosinian(220-230 Ma),and Yanshanian(141-160 Ma).All of these granitoids are basically enriched in large ion lithophile elements(e.g.,Rb,K,U,Th)and depleted in Ti,P,Sr,Ba,with pronounced negative Eu anomalies.The Caledonian granite and Indosinian granite are S-type granite.The Yanshanian granite is A-type granite.The metal elements in granites of different periods gradually increase from the Caledonian→Indosinian→Yanshanian,in particular,W and Sn were extremely enriched in muscovite and two-mica granites,consistent with the timing of the W-Sn flare-up in South China.A few skarn-type Fe-Cu-W polymetallic deposits were developed in the margin of Indosinian rock,and multiple quartz vein type W-Sn polymetallic deposits were developed in faults or fractures near the Yanshanian rocks,without W-Sn mineralization found near the Caledonian granites.Therefore,the multi-stage granites and W-Sn polymetallic mineralization in Xitian ore field are spatially and temporally coupled,and the major mineralization is characterized by Yanshanian skarn-type and vein W-Sn mineralization,which is an important part of Nanling mineralization belt.