西藏祥林锡多金属矿床锡石U-Pb年代学及微量元素地球化学:对矿床成因与找矿的启示OA

The Xianglin tin polymetallic deposit represents the first large-scale tin deposit newly explored within the Himalayan orogenic belt;nevertheless,its ore-forming processes remain insufficiently constrained.Based on systematic orebody-scale geological observations,this study conducts U-Pb geochronology of cassiterite from the largest cassiterite-sulfide orebody and,for the first time,documents in-situ trace-element characteristics of cassiterite from different mineralization styles.Cassiterite U-Pb dating yields an age of approximately 14.2 Ma for the cassiterite-sulfide mineralization located proximal to the granitic intrusion.This age is indistinguishable from that of the distal cassiterite-quartz vein mineralization,suggesting that both mineralization types were produced by the same magmatic-hydrothermal system.In-situ trace-element analyses show that cassiterite from both mineralization styles is enriched in Ti,In,Nb,Ta,and Fe,with these element concentrations displaying strong negative correlations with Sn concentration.These geochemical signatures indicate that cassiterite incorporates trace elements mainly through three substitution mechanisms:Ti4+↔ Sn4+,2(Nb,Ta)5++(Fe,Mn)2+↔ 3Sn4+,and(Nb,Ta)5++In3+↔ 2Sn4+,with different mineralization types dominated by distinct substitution pathways.From cassiterite-sulfide to cassiterite-quartz vein mineralization,ratios of Ti/Zr and Zr/Hf,as well as concentrations of Nb and Fe,show a systematic decline,whereas Ta increases.These features collectively record the outward evolution of trace elements within the ore-forming fluids.Integrated results indicate that the cassiterite-sulfide and cassiterite-quartz vein mineralization in the Xianglin area are temporally consistent and exhibit a clear spatial zonation from intrusion-proximal to distal domains.Together,these mineralization styles record the stage-wise evolution of a single Miocene magmatic-hydrothermal ore-forming system.The trace-element assemblages and elemental ratios of cassiterite can serve as effective indicators for constraining ore genesis and for identifying mineralization positions and evolutionary stages during the exploration of granite-related tin deposits.