鲁西地区沂南金矿床成因:硫化物矿石与围岩稀土和微量元素的制约

    Genesis of Yinan gold deposit in Luxi district: Constrain from REE and trace elements of sulfide ore and wall-rock

    • 摘要: 沂南金矿床为鲁西地区典型的矽卡岩型矿床,产于早白垩世中酸性杂岩与新太古界—寒武系接触带及其附近。本次利用岩/矿石稀土和微量元素组成,示踪成矿物质来源及成矿流体地球化学性质。结果显示,成矿的闪长玢岩负Eu异常不显著,且早矿化阶段发育大量磁铁矿,暗示早阶段成矿流体具有氧化性特征。晚(金)矿化阶段的黄铁矿和黄铜矿相对富集轻稀土元素和高场强元素,负Eu异常显著,Ce异常不明显,且Hf/Sm、Nb/La值大于1,显示含F的还原性流体特征。矿石的Y/Ho、Zr/Hf和Nb/Ta值变化较大,且黄铁矿Co/Ni>10,表明成矿流体源于岩浆水和大气降水的混入。矿石与赋矿围岩具有相似的稀土元素配分模式和微量元素地球化学行为,且具有相同范围/趋势的微量元素比值,说明沂南杂岩体和碳酸盐岩提供了必要的成矿物质。综上,沂南金矿床的成矿过程得到了较好的约束,同时也对区域范围内金矿成因有一定指示意义。

       

      Abstract: The Yinan gold deposit is a representative skarn deposit in the Luxi district, mainly produced in and around the contact zone between the Early Cretaceous intermediate−acid complex and the Neoarchean and Cambrian strata. The present work traces the source of ore−forming material and geochemical properties of ore−forming fluids by using rock/ore rare earth and trace element compositions. The ore−forming diorite porphyrite does not show a negative Eu anomaly, and a large amount of magnetite is developed in the early mineralized stage, suggesting that the ore−forming fluid in the early stage is oxidized. Pyrite and chalcopyrite in the late (gold) mineralization stage are relatively enriched in light rare earth elements and high field strength elements, with significant negative Eu anomaly and insignificant Ce anomaly, and Hf/Sm and Nb/La ratios greater than 1, showing the characteristics of F−bearing reductive fluids. The Y/Ho, Zr/Hf and Nb/Ta ratios in the ore are highly variable, and the Co/Ni in the pyrite is more than 10, indicating that the ore−forming fluid originated from the mixing of magmatic water and meteoric water. The ore and the ore−bearing wall rocks have similar rare earth elements partitioning patterns and trace elements geochemical behavior, with the same range/trend of trace element ratios, suggesting that the Yi’nan complex and carbonate rocks provide the necessary ore−forming material. In summary, the mineralization process of the Yi’nan gold deposit has been well constrained, and it also has certain indicative significance for the genesis of gold deposits within the region.

       

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