川西李家沟伟晶岩型锂矿床锂富集机制——流体包裹体、白云母和锂辉石LA-ICP-MS成分的限定OA

The Lijiagou pegmatite-type lithium deposit,a major discovery within the Ke'eryin ore field of western Sichuan,is situated at the heart of the Songpan-Ganze fold belt and the northeastern margin of the Qinghai-Tibet Plateau.Within the No.Ⅰ ore body of the Lijiagou deposit,two distinct types of pegmatite dikes have been identified:albite pegmatite(Type Ⅰ)and albite spodumene pegmatite(Type Ⅱ).Tourmaline-bearing pegmatite dikes are rarely observed in outcrops and are typically found outside of the main ore bodies.Lithium is predominantly concentrated in spodumene within the Type Ⅱ pegmatite dikes,indicating a complex mechanism of lithium enrichment driven by multistage magma hydrothermal processes.In this study,we employed microthermometric and LA-ICP-MS analyses of fluid inclusions in quartz and spodumene from various pegmatite dikes,complemented by LA-ICP-MS mapping of the spodumene and muscovite,to elucidate the characteristics of ore-forming fluids in the Lijiagou deposit.Microthermometric analyses revealed homogenization temperatures of fluid inclusions ranging from 197℃to 429℃,with salinities(wNaCl)varying between 0.1%and 19.9%.LA-ICP-MS analyses demonstrated that fluid inclusions in quartz and spodumene from Type Ⅰ and Type Ⅱ pegmatite dikes are enriched in multiple trace elements,whereas those in quartz from tourmaline-bearing pegmatites are relatively depleted.Notably,higher lithium concentrations were detected in fluid inclusions within quartz and spodumene from Type Ⅱ pegmatite dikes,which also exhibited a positive correlation with homogenization temperature.The LA-ICP-MS mapping results revealed that spodumene is primarily enriched in lithium,while muscovite is enriched in a suite of trace elements,including Li,Be,Mn,Rb,Cs,Nb,Ti,and Ta.These findings suggest that the magmatic-hydrothermal fluids associated with Type Ⅰ and Type Ⅱpegmatite dikes share similarities in terms of temperature,salinity,and trace element composition,with the highest lithium enrichment occurring in the ore-forming fluids of Type Ⅱ pegmatite dikes.This enrichment is likely driven by fluid exsolution from magmatic sources,facilitating the formation of spodumene in Type Ⅱ pegmatite dikes,with hydrothermal alteration of muscovite also contributing to spodumene genesis.