Texture and Geochemistry of Multi-stage Hydrothermal Scheelite in the Mamupu Cu-Au-Mo(-W)Deposit,Eastern Tibet:Implications for Tungsten Mineralization in the Yulong Belt

Multistage tungsten mineralization was recently discovered in the Mamupu copper-polymetallic deposit in the southern Yulong porphyry copper belt(YPCB),Tibet.This study reports the results of cathodoluminescence,trace element and Sr isotope analyses of Mamupu scheelite samples,undertaken in order to better constrain the mechanism of W mineralization and the sources of the ore-forming fluids.Three different types of scheelite are identified in the Mamupu deposit:scheelite A(Sch A)mainly occurs in breccias during the prograde stage,scheelite B(Sch B)forms in the chlorite-epidote alteration zone in the retrograde stage,while scheelite C(Sch C)occurs in distal quartz sulfide veins.The extremely high Mo content and negative Eu anomaly in Sch A represent high oxygen fugacity in the prograde stage.Compared with ore-related porphyries,Sch A has a similar REE pattern,but with higher ΣREE,more depleted HREE and slightly lower(^(87)Sr/^(86)Sr)i ratios.These features suggest that Sch A is genetically related to ore-related porphyries,but extensive interaction with carbonate surrounding rocks affects the final REE and Sr isotopic composition.Sch B shows dark(Sch B-I)and light(Sch B-II)domains under CL imaging.From Sch B-I to Sch B-II,LREEs are gradually depleted,with MREEs being gradually enriched.Sch C has the highest LREE/HREE ratio,which indicates that it inherited the geochemical characteristics of fluids after the precipitation of HREE-rich minerals,such as diopside and garnet,in the early prograde stage.The Mo content in Sch B and Sch C gradually decreased,indicating that the oxygen fugacity of the fluids changed from oxidative in the early stages to reductive in the later,the turbulent Eu anomaly in Sch B and Sch C indicating that the Eu anomaly in the Mamupu scheelite is not solely controlled by oxygen fugacity.The extensive interaction of magmatic-hydrothermal fluids and carbonate provides the necessary Ca^(2+)for the precipitation of scheelite in the Mamupu deposit.

Geochronology and Geochemistry of the Mamupu Cu-Au Polymetallic Deposit,Eastern Tibet:Implications for Eocene Cu Metallogenesis in the Yulong Porphyry Copper Belt

The Mamupu skarn-type Cu-Au polymetallic deposit represents the first discovery of a medium deposit in the southern Yulong porphyry copper belt(YPCB),eastern Tibet.The Cu-Au mineralization mainly occurs as chalcopyrite in breccia,within the plate-like carbonate interlayer,being closely related to chloritization(e.g.,chlorite,magnetite and epidote)and skarnization(e.g.,diopside,tremolite and garnet).The ore-related quartz syenite porphyry(QSP)and granodiorite porphyry(GP)were emplaced at 40.1±0.2 Ma and 39.9±0.3 Ma,respectively.The QSP of Mamupu is an alkaline-rich intrusion,relatively enriched in LREE,LILE,depleted in HFSE,with no significant negative Eu and Ce anomalies,slightly high(^(87)Sr/^(86)Sr)i,lowε_(Nd)(t),uniform(^(206)Pb/^(204)Pb)i andε_(Hf)(t)values,which indicates that the porphyry magma may be caused by both the mixing of metasomatized EM II enriched mantle and thickened juvenile lower crust.The QSP in the Mamupu deposit shares a similar genesis of petrology to other ore-related porphyries within the YPCB.High oxygen fugacity and water content of the magmas are essential for the formation of porphyry and skarn Cu deposits.The QSP has similar high magmatic oxidation states and water content to the Yulong deposit,which indicates that the Mamupu has a high prospecting potential.Differences in the geological characteristics and scale of mineralization between the Mamupu and other YPCB deposits may be due to the different emplacement depths of ore-related intrusions,as well as differences in the surrounding rocks.

藏东马牧普地区斑岩型铜金银多金属矿化带地球化学异常评价

藏东玉龙成矿带马牧普地区1:5万水系沉积物中的成矿元素Au、Ag、Cu、Pb、Zn的研究,采用分形方法确定异常下限,得出其异常下限值分别为10×10-9、0.48×10-6、75×10-6、120×10-6、130×10-6;用因子分析研究成矿元素的异常组合规律,指出测区西南异常区为Au、Cu、Pb、Zn、Ag组合异常,是矿致异常;中西部异常为Ag、Cu、Pb、Zn综合异常,为指示斑岩分散流的异常,是非矿致异常。

西藏玉龙铜矿带南段马牧普铜多金属矿床矿物学特征

西藏马牧普铜多金属矿床是玉龙铜矿带南段的重要组成部分,最新勘查进展揭示其铜、金资源量均已达到中型规模,但理论研究工作仍十分薄弱。本文基于系统的镜下鉴定和电子探针分析,对马牧普铜多金属矿床矿物学进行详细研究,进而探究矿床成因。马牧普矿床主矿体为中—厚层板状的角砾岩型矿体,矿石类型以角砾状为主,局部矿体呈透镜状产于角岩中。矿区发育广泛的绿泥石化、角岩化、金云母化和弱绢云母化蚀变。电子探针分析结果表明,矿区内矽卡岩矿物中辉石主要为透辉石,云母主要为金云母,角闪石则以透闪石为主。马牧普矿床成矿阶段和矿物组合为:Ⅰ进变质阶段,矿物组合为透辉石-石榴子石-磁铁矿±白钨矿;Ⅱ退变质阶段,矿物组合为透闪石-金云母±磁铁矿±绿泥石±绿帘石±白钨矿;Ⅲ硫化物阶段,矿物组合为黄铁矿-黄铜矿±辉钼矿±磁黄铁矿±辉铋矿±方铅矿±闪锌矿±萤石±石英,为主成矿阶段;Ⅳ碳酸盐阶段,矿物组合为赤铁矿±萤石±方解石±石英±玉髓。矿物学特征表明,矽卡岩演化经历了岩浆期后高温—中低温演化的过程,随着温度的降低,镁质矽卡岩矿物从进变质阶段的透辉石转变为退变质阶段的金云母;矽卡岩形成过程中经历了早期相对较为氧化的环境到晚期相对较为还原环境的转变。矿区角砾岩层为原沉积地层中存在的白云质、钙质碳酸盐夹层,广泛的热液交代作用使得大部分碳酸盐呈角砾状。含矿岩浆热液流体沿着碳酸盐岩产状侵位并发生交代作用,使得金属矿物在角砾岩层中沉淀并富集成矿。