秦岭造山带发现新型铀多金属矿:华阳川与伟晶岩脉和碳酸岩脉有关的超大型铀-铌-铅-稀土矿床

A unique uranium polymetallic deposit discovered in the Qinling orogenic belt: The Huayangchuan super-large U-Nb-Pb-REE deposit associated with pegmatites and carbonatites

华阳川铀多金属矿位于华北板块南缘小秦岭构造带的西段,是一个以U、Nb、Pb为主并伴生有稀有稀土元素的可综合利用的超大型矿床。矿体主要赋存于太古代TTG片麻岩套中(武家坪黑云斜长片麻岩和大月坪花岗片麻岩)。矿化与伟晶岩脉、火成碳酸岩脉和碳酸盐脉紧密共生。伟晶岩脉主要由微斜长石、石英以及黑云母、角闪石、褐帘石、榍石和独居石组成。火成碳酸岩脉主要由方解石、石英、重晶石、霓辉石、钠闪石、黑云母和磷灰石等组成。碳酸盐脉主要由方解石、石英、重晶石和沸石等组成。根据脉体穿插关系和矿物组合特征,矿化可分为伟晶岩阶段、早期碳酸岩阶段和晚期碳酸盐化阶段,伟晶岩阶段和早期碳酸岩阶段以铀铌矿化为主,晚期碳酸盐化阶段则以铅矿化为主。铀矿物以铌钛铀矿为主,晶质铀矿次之;铌矿物以铌钛铀矿为主,褐钇铌矿次之;铅矿物以方铅矿为主,白铅矿次之。此外,U、Nb还以类质同像或吸附的形式赋存于褐帘石、独居石和磷灰石等富集稀土元素的矿物中。根据含矿主岩、矿石矿物以及成矿元素组合特征,认为华阳川矿床不同于世界上其他类型的铀矿床,属于与伟晶岩和碳酸岩有关的铀-铌-铅-稀土矿床。

The Huayangchuan uranium polymetallic deposit,located in the western part of the Lesser QinlingOrogenic Belt on the southern margin of the North China Block,is a super-large U-Nb-Pb depositaccompanied with rare-earth elements.All these elements can be utilized synthetically.Ore bodies are mainlyhosted in the Archaean TTG gneisses(Wujiaping biotite plagioclase gneiss and Dayueping granite gneiss).Mineralization coexists with pegmatites and carbonatites.The pegmatites are composed of microcline,quartz,biotite,amphibole,allanite,titanite and monazite.The carbonatites are made up of calcite,quartz,barite,aegirine-augite,riebeckite,biotite,apatite,etc.Developed in the carbonate veins are mainly calcite,quartz,barite,zeolite,etc.Based on the crosscutting relationship and mineral assemblage characteristics of thepegmatite and carbonatite dykes,the alteration and mineralization stages can be divided into the pegmatite stage,the early carbonatite stage and the late carbonate stage.The pegmatite and early carbonatite stages arecharacterized by uranium and niobium mineralization.The late carbonate stage is characterized by leadmineralization.The uranium minerals are mainly betafite with minor uraninite.The niobium minerals aredominated by betafite with minor fergusonite.The lead minerals are dominated by galena with minorcerussite.Moreover,uranium and niobium are presented in allanite,monazite and apatite throughisomorphism and adsorption.Allanite,monazite and apatite are also featured by REE enrichment.Accordingto the features of the host rocks,ore minerals and ore-forming elements association,the Huayangchuanuranium polymetallic deposit belongs to a U-Nb-Pb-REE deposit associated with pegmatites and carbonatites,which is different from uranium deposits found in other parts of the world.