Chemical composition of oscillatory zoned garnets from the largescale Mengya'a Pb–Zn skarn deposit: implications for fluid physicochemical conditions and formation

作     者：Yan Zhang Cuihua Chen Yulong Yang Xuhao Kang Ying Gu Xiang Lai Xiaojie Chen Yan Zhang;Cuihua Chen;Yulong Yang;Xuhao Kang;Ying Gu;Xiang Lai;Xiaojie Chen

作者机构：School of Earth SciencesChengdu University of TechnologyChengdu 610059SichuanChina 

出 版 物：《Acta Geochimica》 (地球化学学报（英文）)

年 卷 期：2022年第41卷第3期

页      面：536-550页

核心收录：

学科分类：081803[工学-地质工程] 08[工学] 0818[工学-地质资源与地质工程] 

基　　金：funded by the Surface Project of National Natural Science Foundation of China (41372093) 

主　　题：Garnet In-situ LA–ICP–MS analysis The Mengya’s Lead–Zinc skarn deposit Tibet 

摘      要：The Mengya’a Lead–zinc deposit is a large skarn deposit in the north of the eastern segment of Gangdese metallogenic *** garnet is the main altered mineral in the Mengya’a *** color of the garnet varies from chartreuse to dark yellow brown and to *** brown garnet(Grt1)is related to pyrrhotite and chalcopyrite,and the green garnet(Grt2)is associated with lead–zinc ***-ICP-MS is the induced coupled plasma mass *** paper has used this technique to investigate Grt1 and ***1 develops core–rim textures with strong oscillation zone occurring in rim,whereas Grt2lacks core–rim textures and featured by oscillation ***–ICP–MS analysis shows that garnets of Mengya’a are rich in CaO(29.90–37.52%)and FeO(21.17–33.35%),but low in Al_(2)O_(3)(0.05–4.85%).The calculated end members belong to grandite(grossular–andradite)garnets *** negative Al(IV)versus Fe^(3+),positive Al(IV)versus total Al stoichiometric number,the positive Al(IV)versus Fe^(3+),and the negative Al(IV)versus total REE,all indicate that the substitution of REEs in garnets is controlled by *** Garnets are depleted in large lithophile elements(e.g.,Rb=0.00–4.01 ppm,Sr=0.03–8.56 ppm).The total REE in Grt1 core is high(ΣREE=233–625 ppm),with HREE enriched pattern(LREE/HREE=0.33–1.69)and weak negative Eu anomalies(δEu=0.21–0.47).In contrast,the total REEs in the Grt1 rim and Grt2 are low(ΣREE=12.4–354 ppm;ΣREE=21.0–65.3 ppm),with LREE enriched pattern(LREE/HREE=0.54–34.4;LREE/HREE=11.4–682)and positive Eu anomalies(δEu=0.35–27.2;δEu=1.02–30.7).After data compilation of garnet chemicals,we found that the early fluid responsible for the core of Grt1 was a relatively closed and chloride-depleted fluid *** was close-to-neutral,with a low water–rock *** core of garnet was formed by fluid diffusion in metasomatic *** fluid was changed into a relatively open system with reduced,chloride-rich,and weakacid *** was fluid infiltration and