云南个旧白云山碱性岩地球化特征及单矿物成因研究
Study on the Geochemical Characteristics and Genesis of Single Minerals in the Alkaline Rocks of Baiyun Mountain, Gejiu, Yunnan

云南个旧的锡多金属矿床是世界上众多超大型矿床之一，其中包含马拉格、松高、卡房、松树脚和老厂等矿田。白云山碱性岩体分布于花岗质杂岩体北部的白云山林场一带，主要由碱性正长岩和霞石正长岩组成。本文对白云山霞石正长岩进行全岩元素含量分析，并且利用电子探针对岩石中的长石、霞石和辉石单矿物进行了元素含量分析。全岩元素含量分析结果说明白云山霞石正长岩为硅不饱和超钾质碱性岩，岩体起源于不均一的富集地幔源区，在成岩过程中可能发生富镁铁质矿物和少量长石的分离结晶作用。岩石中含少量辉石，电子探针分析结果表明辉石的组成结构单一，均为霓辉石。利用巴尔特二长地质温度计进行计算，得到长石结晶温度约为385.53℃左右，代表了岩石形成的最低温度。电子探针元素含量分析表明霞石符合采矿指标，可对其进行开采利用。
The Gejiu tin polymetallic ore deposits in Yunnan are among the world’s significant megadeposits, encompassing mining fields such as Malage, Songgao, Kafa, Songshujiao, and Lao Chang. The Baiyun Mountain alkaline rock mass is situated in the Baiyun Mountain Forest Farm area, north of the granitic complex, predominantly consisting of alkali feldspar granite and nepheline syenite. This study presents a comprehensive whole-rock geochemical analysis of the nepheline syenite from Baiyun Mountain, complemented by electron microprobe analysis of the feldspars, nepheline, and pyroxenes within the rock samples. The geochemical findings suggest that the nepheline syenite is a peralkaline rock characterized by silica deficiency and ultrapotassic affinity, likely derived from a heterogeneously enriched mantle source. Fractional crystallization of mafic minerals and minor feldspar may have occurred during the petrogenesis of the rock mass. The rocks contain a few of pyroxenes, and the electron microprobe data show these pyroxenes have a uniform composition, belonging to aegirine. Employing the Bart geothermometer, the crystallization temperature of the feldspar is estimated to be approximately 385.53？C, which is indicative of the minimum temperature during the rock's formation. The electron microprobe analysis confirms that the nepheline meets the mining standards, suggesting its potential for mining and utilization.