新疆西天山喇嘛苏铜锌矿床矽卡岩矿物学与还原性流体演化  

Skarn mineralogy and revolution of reduced fluid in the Lamasu Cu-Zn deposit,West Tianshan,Xinjiang

作　　者：李文广 申萍[1,2,3] 潘鸿迪 LI WenGuang;SHEN Ping;PAN HongDi(Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;University of Chinese Academy of Sciences,Beijing 100049,China;Innovation Academy of Earth Sciences,Chinese Academy of Sciences,Beijing 100029,China;College of Earth Sciences,Chang an University,Xi'an 710054,China)

机构地区：[1]中国科学院地质与地球物理研究所,中国科学院矿产资源重点实验室,北京100029 [2]中国科学院大学,北京100049 [3]中国科学院地球科学研究院,北京100029 [4]长安大学地球科学与资源学院,西安710054

出　　处：《岩石学报》2024年第3期927-949,共23页Acta Petrologica Sinica

基　　金：新疆重点研发任务专项(2023B03006-1);中国科学院国际合作局国际伙伴计划(132A11KYSB20190070)联合资助.

摘　　要：喇嘛苏铜锌矿位于中亚成矿域西段,为新疆西天山地区相对较早发现的斑岩-矽卡岩铜锌矿床。本文对喇嘛苏铜锌矿矽卡岩和矽卡岩化大理岩中的矽卡岩矿物进行了岩相学及主微量成分分析,首次发现了喇嘛苏铜锌矿床发育的黑榴石和富钛钙铝榴石。对矽卡岩中发育震荡环带的钙铁榴石进行主量元素和电子探针mapping分析,发现钙铁榴石发育不均一的核部,环带部分表现为Al-Fe元素此消彼长的耦合震荡关系;对钙铁榴石从核部中央向边缘环带进行定向原位微量元素LA-ICPMS分析,发现∑REE表现为连续略有降低的趋势、δEu表现出震荡变化。黑榴石和富钛钙铝榴石表现为核幔结构,显示流体氧逸度的降低,流体从超常富集Ti转变为富集Ti。对富钛钙铝榴石进行原位微量元素LA-ICPMS测试,发现富钛钙铝榴石∑REE高于钙铁榴石(钙铝榴石:58.4×10^(-6)~408.4×10^(-6);钙铁榴石28.2×10^(-6)~108.7×10^(-6)),富钛钙铝榴石具有强烈正Eu异常(δEu=11.3~15.0),钙铁榴石和富钛钙铝榴石均表现为富集轻稀土而亏损重稀土。喇嘛苏铜锌矿中的原生辉石为透辉石,后经退蚀变流体交代发生Mg元素丢失和Fe元素富集,转变为次透辉石-铁次透辉石,随交代程度加深,进一步转变为铁角闪石,最后在退蚀变流体中直接沉淀出铁镁钙闪石。在背散射下,原生透辉石、次透辉石-铁次透辉石、铁角闪石、铁镁钙闪石表现为亮度不同的明暗结构。矽卡岩矿物的显微结构和主微量成分表明,蚀变流体为酸性和富Cl、REE、Ti的流体,蚀变阶段早期为氧化性流体,晚期为还原性流体。喇嘛苏铜锌矿流体中CH_(4)、C_(2)H_(6)等还原性物质、共生的磁黄铁矿-磁铁矿低氧逸度组合及还原状态矽卡岩矿物组合表明喇嘛苏铜锌矿可能为一还原性斑岩-矽卡岩铜锌矿。Lamasu deposit,a relatively early discovered copper porphyry-skarn deposit in western Central Asian Metallogenic Domain,is located in the West Tianshan,Xinjiang.The melanite and Ti-rich grossularite were discovered by petrography and major-trace elements analysis on those skarn minerals in skarn and skarnoid marble.EPMA mapping and major-element quantitative analysis on andradite with zoning in skarn have showed the inhomogenetic core and coupled relation of Al with Fe in zoning.The oriental test from central core to marginal zone of andradite by in-situ LA-ICPMS has shown the subsequent downturn trend of∑REE and the shaking trend ofδEu.Melanite and Ti-rich grossularite are in core-mantle structure,and it shows the decreasing of f O_(2)with the shift of fluid composition from super rich in Ti to rich in Ti.The in-situ LA-ICPMS trace elements test on Ti-rich grossularite has showed higher∑REE compared to andradite,in terms of 58.4×10^(-6)~408.4×10^(-6)for Ti-rich grossularite and 28.2×10^(-6)~108.7×10^(-6)for andradite.Ti-rich grossularite has strong positive Eu anomaly(δEu:11.3~15.0).Ti-rich grossularite and andradite have higher amount of LREE than HREE.The pyroxene in Lamasu Cu deposit is diopside.Fe is enriching and Mg is losing during the altered process of diopside,and the original diopside turns into baikalite-Fe baikalite after altered.With the deepening of alteration,the altered diopside turns into ferrohornblende,and ferritschermakite is precipitated in the retrogradation fluid directly.Original diopside together with altered diopside,ferrohornblende and ferritschermakite is in light-dark structure with varied lightness under SEM.The micro texture and major-trace elements of skarn minerals have showed that the fluid performing alteration is rich in Cl,REE and Ti,and it is acidic.In early alteration,the fluid is oxidized,and it turns reduced in late stage.The reduced material of CH_(4)and C_(2)H_(6),and low f O_(2)of pyrrhotite-magnetite assemblage imply that Lamasu Cu-Zn deposit could be a redu

关 键 词：还原性黑榴石 富钛钙铝榴石 核幔结构 喇嘛苏铜锌矿 

分 类 号：P578.947[天文地球—矿物学] P618.41[天文地球—地质学] P618.43