滇西镇康放羊山Cu-Pb-Zn多金属矿床矿物稀土元素地球化学特征及意义

Geochemical characteristics of rare earth elements of minerals in the Fangyangshan Cu-Pb-Zn polymetallic deposit in Zhenkang County,Western Yunnan and their geological significances

放羊山矿床是近年来在滇西镇康矿集区内发现的首个以富Cu为特征的Cu-Pb-Zn多金属矿床,本文在详细的矿床地质特征研究基础上厘定了成矿期次,将成矿作用划分为以Fe-Zn矿化热液成矿期和以Cu-Pb-Zn矿化为主的叠加改造期,其中热液成矿期可进一步划分为阶段Ⅰ(石英-白云石-黄铁矿-毒砂)、阶段Ⅱ(石英-方解石-闪锌矿-绿泥石)和阶段Ⅲ(石英-萤石-磁黄铁矿-黄铜矿)。对热液成矿期各阶段和叠加改造期不同金属硫化物及脉石矿物稀土元素地球化学特征的研究表明,热液成矿期阶段Ⅰ黄铁矿、阶段Ⅱ闪锌矿、阶段Ⅱ方解石、阶段Ⅲ黄铜矿均具有轻稀土富集的"右倾型"稀土配分特征,且负Eu异常明显;叠加改造期的方解石、闪锌矿和方铅矿稀土配分模式同样为"右倾型",具正Eu异常。以上特征指示热液成矿期成矿环境具还原性,而叠加改造期矿物淀积环境则与之相反,两期成矿作用的物质来源可能与地层有关。放羊山Pb-Zn-Cu多金属矿床中金属硫化物Y/Ho值较为集中,热液成矿期阶段Ⅰ黄铁矿(23.86~28.95)、阶段Ⅱ闪锌矿(23.75~31.33)、阶段Ⅲ黄铜矿(25.42~26.70)和叠加改造期方铅矿(29.2~29.63)、闪锌矿(23.75~31.33)基本落入区域花岗岩(24.58~29.63)Y/Ho值变化区间,脉石矿物方解石(热液成矿期阶段Ⅱ32.76~40.06,叠加改造期32.67~36.54)与大陆东部地壳Y/Ho值(20~35)变化范围相同,表明热液成矿期与叠加改造期成矿流体具有同源性,主要为深部岩浆热液,而方解石的形成可能有上地壳流体的参与。

The Fangyangshan deposit,discovered firstly in recent years,is a Cu-rich characterized Cu-Pb-Zn polymetallic deposit in the Zhenkang ore-concentration area in the Western Yunnan.Two mineralization periods have been determined based on the detailed study of geological features of the deposit in this paper.They are the hydrothermal period of Fe-Zn mineralization and superimposed transformation period of Cu-Pb-Zn mineralization.The hydrothermal mineralization period can be furtherly divided to three phases including PhaseⅠ(quartz-dolomite-pyrite-arsenopyrite),PhaseⅡ(quartz-calcite-sphalerite-chlorite),and PhaseⅢ(quartz-fluorite-pyrrhotite-chalcopyrite).The research on geochemical characteristics of rare earth elements of various metal sulfides and gangue minerals in each stage of the hydrothermal mineralization period and of the superimposed transformation period shows that the PhaseⅠpyrite,PhaseⅡsphalerite,PhaseⅡcalcite,and PhaseⅢchalcopyrite all have the characteristic LREE-enriched"right-inclined"REE distribution patterns with obviously negative Eu anomalies.However,the calcite,sphalerite,and galena of the superimposed transformation epoch have"right-inclined"REE patterns with positive Eu anomalies.The above characteristics indicate that the environment of hydrothermal metallogenic period is reduced,while that of the superimposed transformation period is oxidized.The source of ore-forming materials for the two mineralization periods could be related to the stratum.The Y/Ho values of metal sulfides in the Fangyangshan Pb-Zn-Cu polymetallic deposit are relatively concentrated.The ranges of Y/Ho values for the Phase I pyrite(23.86-28.95),Phase II sphalerite(23.75-31.33),PhaseⅢchalcopyrite(25.42-26.70)of the hydrothermal mineralization period,and galena(29.2-29.63)and sphalerite(23.75-31.33)of the superimposed transformation period are basically changed in the range of regional granite(24.58-29.63).The ranges of Y/Ho values for gangue mineral calcites of the hydrothermal metallogenic Phase II(32.76-40.06)and the superimposed transformation period(32.67-36.54)are similar to that of the eastern China continental crust(20-35).Therefore,it is believed that mineralization fluids of both the hydrothermal and the superimposed transformation mineralization periods could be mainly sourced from the similar deep magmatic hydrothermal fluids while the upper crustal fluid could be involved in the formation of calcite.