煎茶岭与金川硫化镍矿床的铂族元素地球化学特征对比及其意义

Comparison of platinum group elements (PGE) between Jianchaling and Jinchuan nickel sulfide deposits and its significance

采用ICP_MS方法分析了煎茶岭和金川硫化镍矿床岩石、矿石的铂族元素含量,煎茶岭岩体蛇纹岩的Cu/Pd比值低于原生地幔岩浆,说明岩浆熔离作用较弱,矿石的Pd/Ir比值较小,指示其多数矿石属于岩浆型,以岩浆成矿作用为主;而金川岩体的平均Cu/Pd比值远大于原生地幔岩浆,表明岩浆熔离作用强,矿石的Pd/Ir比值较大,体现了钯族元素矿化及成矿物质以幔源为主的特征。煎茶岭在成矿过程中有壳源物质的混染,整体上岩石、矿石铂族元素含量较低,这与岩浆熔离作用弱、铂族元素成矿作用不发育等因素有关;金川在成岩成矿过程中也有少量地壳物质的混染,但岩石、矿石铂族元素含量较高,反映了以岩浆深部熔离成矿作用为主的特征。

The PGE geochemistry of rocks and ores from the Jianchaling and the Jinchuan nickel sulfide deposits was systemically studied in this paper by new ICP-MS analytic method for the purpose of probing further into the genesis of this type of deposits and guiding their prospecting work. It is concluded that the Cu/Pd ratio of serpentinite from Jianchaling rock body is lower than that of the original mantle magma, indicating that the liquation process of magma is rather weak, and that the mean Cu/Pd ratio of Jinchuan intrusion is much higher than that of the original mantle magma, suggesting that the liquation process of magma is strong. The average Pd/Ir radio of ores from the Jianchaling nickel deposit is relatively low, implying the domination of magmatic type ores and magmatic metallogenic processes. In contrast, the ratio of the Jinchuan nickel deposit is high, embodying the characteristics of PGE mineralization and the derivation of ore-forming substance mainly from the mantle source. The platinum group element characteristic parameters Pt/（Pt ＋ Pd）, （Pt ＋ Pd） / （Ru ＋ Ir ＋ Os）, Pd/It, and Cu/（Ni ＋ Cu） of the former deposit show transitional features, which are related to the transitional tectonic environment, special magma property, and complex ore-forming process. The characteristic parameters of the latter are similar to those of the copper-nickel deposits related to basic magma. Nevertheless, it is not the ultramafic magma, but the mafic magma, that results in the formation of the superlarge sulfide copper-nickel deposits enriched in Cu and PGE. There existed crustal substance contamination during the formation of the Jianchaling ore deposit, and the PGE content of Jianchaling ores and rocks is comparatively low, which might be related to weak magmatic liquation process and PGE mineralization. There also existed some crustal substance contamination during the rock-forming and ore-forming process of the Jinchuan deposit, but its PGE content is high, suggesting the mineralization was dominated by deep magmatic liquation.