西藏包买铜钼矿床电气石矿物学特征及其对热液流体演化的指示OA

The Baomai deposit is a medium-sized porphyry Cu-Mo deposit located in the northern segment of the Yulong copper metallogenic belt,Xizang.The characteristics and evolutionary history of its magmatic-hydrother-mal fluids remain poorly constrained,which hinders an in-depth understanding of its metallogenic mechanism.Abundant tourmaline is widely developed within this deposit,which provides critical proxies for unraveling the evolution of magmatic-hydrothermal fluids and the ore-forming processes.Based on detailed core logging,petro-graphic microscopic observation,and electron probe microanalysis(EPMA),this paper investigates the genesis of tourmaline and discusses its implications for the evolutionary path of magmatic-hydrothermal fluids.Four distinct tourmaline generations are identified in the Baomai ore district,classified by mineral assemblages and host lithol-ogy as follows:① Nodular or vesicle-like tourmaline hosted in granodiorite porphyry(Tur-Ⅰ);② Quartz-tourma-line-sericite-molybdenite-pyrite veins within gneiss(Tur-Ⅱ);③ Quartz-tourmaline-sericite-pyrite veins hosted in granodiorite porphyry(Tur-Ⅲa);④ Quartz-tourmaline-sericite-pyrite veins within gneiss(Tur-Ⅲb).Tur-Ⅰ exhib-its extremely wide compositional variations,whereas Tur-Ⅱ and Tur-Ⅲ show relatively homogeneous chemical compositions.All four tourmaline types belong to the schorl-dravite series of the alkali tourmaline group.Their compositional variability is jointly controlled by multiple coupled substitution mechanisms,including Fe2+Mg-1/Fe3+Al-1,AlO(MgOH)-1,XvacancyAl(NaR2+)-1,Ca(Fe,Mg)(NaAl)-1.The four tourmaline generations in the Baomai ore district precipitated during the phyllic alteration stage,formed by variable degrees of mixing between early magmatic-hydrothermal fluids and formation fluids.Fe and Mn were predominantly sourced from magmas,while strata supplied substantial Mg,Ca,Fe,and Ti.The influx of formation fluids constitutes a key factor controlling Cu-Mo mineralization within the phyllic alteration zone of the Baomai deposit.