赣东北朱溪钨(铜)矿床两期石榴石研究及其对成矿作用的指示

本文对朱溪超大型钨(铜)矿床中两类与白钨矿密切相关的石榴石进行了研究。研究表明,这两类共存的石榴石与夕卡岩型矿床中常见的同期热液在不同阶段形成的两种石榴石不同。早期石榴石相对更加富Fe(Ad_37.17~41.84Gr_54.83~59.57Sp_3.10~4.62),而晚期石榴石更加富Al(Ad_12.69~14.42Gr_77.56~79.03Sp_0.44~0.92),成分上更接近钙铝榴石端员,具有更低的Sn含量,更高的U含量,并在稀土配分曲线中显示出更明显的正Eu异常,表明晚期石榴石形成时的氧逸度明显低于早期石榴石形成时的氧逸度。晚期石榴石相对于早期石榴石具有更高的Cu、Pb、Zn、Li、Be、B、Rb、Cs、Sr含量和更低的W、Mo、Ga、Ge含量,并且与成矿相关岩体具有相似的稀土配分模式曲线,表明晚期石榴石与朱溪矿床的成矿相关岩浆演化而形成的残余岩浆热液流体具有更加密切的相关性。本文研究的两类共存的石榴石可能是两期成矿热液流体作用的产物,暗示朱溪矿床的成矿作用可能与多期岩浆活动有关。

Study on the two-stage garnets and their indication of mineralization in the Zhuxi W(Cu) deposit,northeastern Jiangxi Province

We present in this study our research on two types of coexisting scheelite-bearing garnet from the giant Zhuxi W(Cu) deposit. The results showed that the coexisting scheelite-bearing garnets are different from paragenetic garnets in other skarn deposits, as these two types of garnet commonly formed at different evolutionary stages from the same hydrothermal fluid in the Zhuxi deposit. The early-stage garnet was rich in Fe (Ad_37.17-41.84Gr_54.83-59.57Sp_3.10-4.62); whereas the late-stage one was rich in Al (Ad_12.69-14.42Gr_77.56-79.03Sp_0.44-0.92), close to grossularite with higher U and lower Sn concentrations, and exhibited obvious positive Eu anomalies in the chondrite-normalized REE patterns. These results indicated that the oxygen fugacity of the late-stage garnet is lower than that of the early-stage one. The late-stage garnet was characterized by having higher Cu, Pb, Zn, Li, Be, B, Rb, Cs and Sr and lower W, Mo, Ga and Ge concentrations. It had normalized rare earth elemental patterns roughly subparallel to the ore-related granite in the Zhuxi deposit, indicating its genetic relation with the residual magma hydrothermal fluid. These two types of coexisting scheelite-bearing garnet are the products of different ore-forming hydrothermal fluid, suggesting that at least two periods of metallogenic events related to the granitic magma are present in the Zhuxi deposit.