云南白马寨镍矿区煌斑岩地球化学 Ⅰ.主要元素和微量元素

GEOCHEMISTRY OF LAMPROPHYRES IN BAIMAZHAI NICKEL DEPOSIT, YUNNAN PROVINCE, I . MAJOR AND TRACE ELEMENTS

云南白马寨镍矿区煌斑岩呈岩墙和岩脉穿切矿区各时代地层、基性-超基性岩和矿体,为成矿期后产物;采自矿区不同中段和不同产状的煌斑岩具有相似矿物组合,岩石类型均为云煌岩;岩石化学特征表明岩石均为钾质-富钾质钙碱性煌斑岩;微量元素配分模式为相似的“骆峰型”,与MORB相比,富集LILE和HFSE;REE配分模式为相似的LREE富集型;主要元素和微量元素与镁指数(M值)之间存在一定的相关关系;在La-La/Sm图中样品既有水平分布趋势、也有倾斜分布趋势。总体上,该区煌斑岩为相同岩浆源区的产物,源区地幔部分熔融程度和岩浆结晶分异作用对岩石主要元素和微量元素地球化学性质均有一定的影响。比较老王寨金矿区煌斑岩形成地质背景、岩石类型、主要元素和微量元素地球化学特征,认为两地区煌斑岩地幔源区具有相同(或相似)的性质。

Lamprophyres in the Baimazhai nickel deposit occurred as dyke cutting across the strata, basic-ultrabasic rocks and ore bodies, being the post-ore products. Lamprophyre samples from different levels and of different occurrences have similar paragenetic associations of minerals, and the rock type is dominated by lamprophyres. Evidence from major elements showed that the lamprophyres are potassic and potassium-rich calc-alkaline ones. The trace element patterns are of the hump type. Compared to MORB, they are characterized by enrichment in 1JT.F, and HFSE. Meanwhile, the REE patterns are of the LREE-enricnment type. There is a linear variation trend between M values and major and trace elements. There are both horizontal and oblique tendencies in the La-La/Sm diagram. In general, the lamprophyres were derived from the same magmatic source region in the Baimazhai nickel deposit. Both partial melting and fractional crystallization affected the evolution of trace and major elements in the rocks. Geological setting, rock type and the characteristics of major and trace elements of the lamprophyres in the deposit are similar to those of the Laowangzhai gold deposit. It is concluded that the mantle-source regions for the lamprophyres in the two areas have the same or similar properties.