西藏邦铺斑岩-夕卡岩钼铜铅锌矿床成矿环境研究

Metallogenic Environment of the Bangpu Porphyry-Skarn Mo-Cu-Pb-Zn Deposit,Tibet

邦铺Mo-Cu-Pb-Zn矿床位于冈底斯斑岩铜矿带东段北侧,由斑岩型Mo-Cu热液成矿作用和夕卡岩型Pb-Zn接触交代成矿作用组成。为反演斑岩-夕卡岩成矿环境的变化,探讨成矿元素沉淀机制,本文选取斑岩矿区成矿二长花岗斑岩进行锆石微量元素分析,夕卡岩矿物进行电子探针成分分析。结果显示,二长花岗斑岩锆石稀土总量为852.21×10^(-6)~2368.54×10^(-6),具有亏损LREE并逐步富集HREE的左倾配分模式;锆石的结晶温度为677.52~868.09℃,氧逸度为ΔFMQ+1.2~ΔFMQ+7.3。夕卡岩Pb-Zn矿区具有标准的钙夕卡岩矿物组合,石榴子石端元组分以钙铁榴石和钙铝榴石为主,辉石属钙铁辉石,绿泥石主要为密绿泥石。研究说明,邦铺成矿斑岩形成于高的氧逸度环境中,氧化性的长英质岩浆与斑岩型Mo矿化之间存在内在成因联系;整个夕卡岩成矿环境从碱性、氧化向酸性、还原转变,氧化还原状态的变化控制了金属的沉淀。

The Bangpu Mo-Cu-Pb-Zn deposit in Tibet is located in the northeast of the Gangdese porphyry copper belt. The deposit is composed of porphyry Mo-Cu and skarn Pb-Zn mineralization. Zircon trace element analysis of ore-bearing monzonite porphyry and electron microprobe analysis of skarn minerals have been done in order to constrain the evolution of the metallogenic environment and explore the mechanism of metal precipitation. Zircons of the monzonite porphyry have REE contents varying from 852.21× 10^-6 to 2368.54×10^-6, depleted in LREE and gradually enrich in HREE. Crystalliza- tion temperature of the zircons range from 677.52℃ to 868.09℃ , with the oxygen fugacity varying from AFMQ ＋ 1.2 to AFMQ ＋7.3. Skarn minerals are calcium skarn association. Electron microprobe analyses indicate garnets are mainly andra- dite and grossular, pyroxene is hedenbergite, chlorite is mainly pycnochlorite. The mineral association and mineral compo- sitions indicate that the monzonite porphyry is formed in a high oxygen fugacity environment. The formation of skarn experi- enced environment varying from alkaline-oxidized to acidity-reduced, triggered the precipitation of metals.