西藏玉龙铜矿带南段马牧普铜多金属矿床矿物学特征

Mineralogical characteristics of the Mamupu copper polymetallic depositin the southern section of the Yulong copper belt,Tibet

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。

The Mamupu copper-polymetallic deposit in Tibet is an important part of the southern section of the Yulong copper belt.The latest exploration progress reveals that the amount of copper and gold resources in the Mamupu copper-polymetallic deposit has reached a medium scale,but the theoretical research is still very weak.Based on systematic microscopic identification and electron probe analysis,this paper studied the mineralogy of Mamupu copper polymetallic deposit in detail,and then explored the genesis of the deposit.The main ore body in the Mamupu deposit is a medium-thick plate breccia-type orebody.The ore type is mainly breccia,and partial lenticular ore bodies were produced in hornstones.Extensive chlorite,keratinization,phlogopite and weak sericite alteration are developed in the mining area.The results of electron probe analysis show that the pyroxene is mainly diopside,the mica is mainly phlogopite,and the amphibole is mainly tremolite in skarn minerals.The metallogenic stage and mineral assemblage of the Mamupu deposit are as follows:Ⅰprograde metamorphic stage,the mineral assemblage is diopside-garnet-magnetite±scheelite;Ⅱretrograde metamorphic stage,the mineral assemblage is tremolite-phlogopite-magnetite±chlorite±epidote±scheelite;Ⅲsulfide stage,mineral assemblage is pyrite-chalcopyrite±molybdenite±pyrrhotite±bismuthinite±galena±sphalerite±fluorite±quartz,mainly metallogenic stage;Ⅳcarbonate stage,mineral assemblage is hematite±fluorite±calcite±quartz±chalcedony.The mineralogical characteristics show that the evolution of skarn experienced a process from high temperature to medium and low temperature after the magmatic period.With the decrease of temperature,magnesian skarn minerals changed from diopside in prograde metamorphic stage to phlogopite in retrograde metamorphic stage.Skarn formation experienced a relatively oxidized environment in the early stage to a relatively reductive environment in the late stage.The breccia in the mining area are dolomitic and calcareous carbonate interlayers in the original sedimentary strata,and most of the carbonates are breccia due to extensive hydrothermal metasomatism.The ore-bearing magmatic hydrothermal fluids emplaced and metasomatism occurred along the occurrence of carbonate rocks,resulting in the precipitation and enrichment of metal minerals in breccia strata.