西藏班戈县多巴区矽卡岩型铁多金属矿床含矿花岗岩LA-ICP-MS锆石U-Pb定年、地球化学及意义

选择西藏班戈县多巴区梭沙矽卡岩型矿化点与再阿矽卡岩型铁多金属矿床,在野外地质调查、室内岩相和矿相学研究的基础上,对含矿花岗岩进行了锆石LA-ICP-MS U-Pb法测年分析、主量与微量元素测试,并探讨了岩石成因及其与成矿作用的关系。梭沙地区主要矿化岩体为细粒斑状花岗闪长岩,再阿为中细粒花岗闪长岩。锆石的LA-ICP-MS定年结果表明,细粒斑状花岗闪长岩和中细粒花岗闪长岩的年龄分别为77.37±0.55 Ma和79.78±0.99 Ma,均为晚白垩世岩浆活动的产物。区内花岗岩的A/CNK值变化于0.78~1.29之间,A/NK值变化在0.88~1.51之间,为准铝质系列。花岗岩富集大离子亲石元素Rb、Th、U、K,贫Nb,总体与班公湖成矿带的同期花岗岩相一致,∑REE=199.82×10-6~274.64×10-6,LREE/HREE=3.552~7.199,δEu=0.20~0.82,Eu呈中等负异常,揭示岩浆演化过程中可能发生过斜长石的分离结晶作用。梭沙和再阿岩体的成矿作用与班公湖-怒江洋向南俯冲结束后的碰撞闭合作用有关,为班公湖-怒江缝合带闭合之后岩浆活动及相关热液作用的产物。梭沙和再阿地区具有良好的铁铋等多金属成矿地质、地球化学条件,有良好的找矿前景,应加强该区的找矿评价工作。

LA-ICP-MS zircon U-Pb dating and geochemical characteristics of ore-bearing granite in skarn-type iron polymetallic deposits of Duoba area, Baingoin County, Tibet, and their significance

Located in northwestern Baingoin County of Tibet,Duoba area is near the middle of Bangong Co-Nujiang River metallogenic belt with the distribution of a large number of skarn iron-copper polymetallic deposits(mineralization spots) characterized by good prospecting potential.Due to high elevations,traffic inconvenience and less mining,only a small amount of work has been carried out.This research is based on the systematic field geological survey,indoor petrographic and ore microscopic studies,zircon LA-ICP-MS U-Pb dating and analysis of major and trace elements.The authors chose Sousha skarn mineralization spot and Zai’a skarn iron polymetallic deposit to conduct researches on the relationship between the petrogenesis and the mineralization.There are mainly fine grained porphyritic granodiorites in Sousha area and fine grained granodiorites in Zai’a.Zircon’s LA-ICP-MS dating indicates that the age of the fine grained porphyritic granodiorite is 77.37±0.55 Ma,whereas that of the fine grained granodiorite is 79.78±0.99 Ma,suggesting products of late Cretaceous magmatism.Their A/CNK values change between 0.78 and 1.29,and A/NK values change in the range of 0.88～1.51.The rocks belong to weakly peraluminous.They are enriched in big ion incompatible elements Rb,Th,U and K,and depleted in Nb,identical overall with the same period granite in Bangong Co-Nujiang River metallogenic belt.∑ REE range from 199.82×10-6 to 274.64×10-6,LREE/HREE= 3.552～7.199,δEu=0.20～0.82,with medium negative Eu anomalies.These data indicate that the separation of plagioclase crystallization might have occurred in magmatic evolution processes.The ore-forming processes of Sousha and Zai’a rock bodies might have had something to do with the southward subduction of the Bangong Co-Nujiang Ocean Basin and acted as the products of magmatic activity after closing.With favorable iron and bismuth polymetallic ore-forming geological and geochemical conditions,this area deserves more attention in further prospecting and evaluation work.