内蒙乌拉山金矿床钾长石的矿物化学及有序度的分析

采用电子探针显微分析(EMPA)和粉末X射线衍射(XRD)分析了采自乌拉山金矿床含金钾长石石英脉、石英脉以及其他类型岩石中的10 0多个钾长石样品的化学成分和结果状态,并采用R和Q模式聚类分析、Spearman等级相关分析方法对实验数据进行了统计分析。结果表明,含金矿脉、岩浆热液脉和蚀变花岗岩中的钾长石为中等到最大微斜长石,其特征为K2 O含量高,但相对而言,Na2 O、CaO和BaO的含量低。其他岩石类型中的钾长石的化学成分和结果状态变化很大,可以从透长石、正长石到微斜长石,其特征为K2 O的含量相对较低,但Na2 O、CaO和BaO的含量相对较高。含金样品中的钾长石通常更富K2 O ,表明金的成矿作用与富钾的热液流体和碱质交代作用有关。乌拉山金矿床的成矿作用分为两个阶段,主要的含金钾长石石英脉中的钾长石富K2 O ,形成温度为30 7～379℃,平均为35 3℃;第二阶段含金石英脉中的钾长石含K2 O较低,形成温度为2 6 0～318℃,平均为2 81℃。这些结果表明成矿流体与岩浆热液作用有关,流体朝温度降低、K2 O含量降低的方向演化,K2 O含量高的热液流体和2 6 0～380℃的形成温度有利于金的成矿作用。

Chemical andstructural characteristics of K feldspars and their constrains to formation conditions ofthe Wulashan gold deposit, China

More than one hundred K feldspars were collected from gold-bearing Vein Ⅰ (K feldspar-quartz vein)and Vein Ⅱ (quartz vein) as well as various other rock types in the Wulashan gold deposit, China. Chemical compositions of K feldspars were analyzed using electron microprobe analysis (EMPA). The powder X-ray diffraction (XRD) patterns of K feldspars were collected using Cu Kα source. Au contents of the corresponding ore samples were analyzed by fire assay. Q- and R-mode cluster analysis and Spearman rank correlation analysis of the experimental data were performed. The results indicate that K feldspars from gold-bearing veins, magmatic hydrothermal veins and altered wall rocks are intermediate to maximum microclines characterized by higher content of K2O, lower contents of Na2O, CaO and BaO, and relatively small variations in chemical compositions. K feldspars from other rock types are likely sanidine, orthoclase or microclines that show greater variations in chemical compositions and are characterized by lower content of K2O but higher contents of Na2O,CaO and BaO. K feldspars from auriferous samples are much richer in K2O, indicating that gold mineralization might have been related to potassic hydrothermal fluids and intense K feldspar metasomatism. There exist two gold mineralization stages in the Wulashan deposit. K feldspars from the major K feldspar-quartz veins are characterized by higher K2O and higher formation temperatures of 307～379℃ with an average of 353℃. K feldspars from the quartz veins of the second stage are characterized by lower K2O and lower formation temperatures of 260～318℃ with an average of 281℃. These results indicate that the mineralization fluids were associated with magmatic hydrothermal events and evolved toward lower temperatures and lower content of K2O, but the hydrothermal fluids of higher K2O and the temperatures of 260～380℃ may favor gold mineralization.