四川牦牛坪轻稀土矿床地幔流体特征——铅锶钕和氦氩同位素及稀土元素证据

四川牦牛坪稀土矿床是中国第二大轻稀土矿床。笔者对该矿床进行了较系统的Pb—Sr—Nd同位素、稀有气体同位素地球化学以及稀土元素地球化学研究。稀土元素地球化学特征研究显示,矿区萤石、方解石、氟碳铈矿稀土元素分布模式与区内英碱正长岩相似,表明牦牛坪稀土矿床成矿与英碱正长岩岩浆活动有关以及石英包裹体流体REE曲线平直,Eu与Ce无明显异常,曲线规律性较强,可以认为牦牛坪轻稀土矿床成矿流体稀土元素是深源的。Pb—Sr—Nd同位素组成表明成矿物质来自富集地幔,具深源甚至幔源特征。稀有气体同位素地球化学研究也在一定程度上揭示了牦牛坪轻稀土矿化与地幔过程之间存在着成因关系。

Mantle Fluids in the Maoniuping LREE Deposit,Sichuan Province:Evidence of Pb-Sr-Nd,He-Ar Isotopes and REE

The Maoniuping REE deposit is the second largest light rare earth elements deposit in China. Pb-Sr-Nd isotopic, rare gas isotope geochemical and rare earth element geochemical studies are systematically carried out on this deposit. The rare earth element geochemical studies demonstrate that the REE distribution patterns of fluorite, calcite and bastnaesite are similar to those of nordmarkite, implying that the deposit is closely related to magma of nordmarkite. In addition, REE of fluid from quartz exhibits distribution pattern of flat curve with negligible Eu and Ce anomalies, showing its deep source origin. The Pb-Sr-Nd isotopes also indicate the metallogenic materials are derived from EM I, which show characteristics of a deep or mantle source. The rare gas isotope geochemical analyses also support that there is a genetic association between the light rare earth element mineralization and mantle processes.