大冶-武山矿化夕卡岩的稀土元素地球化学研究

REE geochemistry of mineralized skarns from Daye to Wushan region, China

用ICP-MS分析了25个含矿夕卡岩样品的REE含量,其中对8个样品的石榴子石等矿物中的熔融包裹体进行了均一温度测定,还对5个夕卡岩样品石榴子石中的熔融包裹体进行了电子探针分析。在这些样品的石榴子石、辉石或方解石中都观察到熔融包裹体。夕卡岩的球粒陨石标准化REE分布模式具有两个突出特点:其一是以富集轻稀土元素(LREE)右倾为特征;其二是多数以具有Eu正异常为特征。夕卡岩球粒陨石标准化REE分布模式有三种类型:第一类型显示斜率不大的右倾直线;第二类型具有以Ce为峰值的折线的特征,即REE线段向上凸,在Ce处有一极大值(个别无峰值,LREE曲线向上凸,呈穹隆状);第三类型为过渡型REE分布模式。在当今REE资料有限的情况下,利用稀土元素地球化学特点鉴别夕卡岩成因是困难的。

REE concentrations of twenty-five mineralized skarn samples have been analyzed using ICP- MS. Homogenization temperatures of melt inclusions in garnet, secondly in pyroxene and calcite from eight samples were determined. Melt inclusions in garnet from some skarn samples have been analyzed by electron probe. They all contain melt inclusions in garnet, pyroxene or calcite. Chondrite-normalized REE distribution patterns of mineralized skarn samples have two outstanding characteristics. One is characterized by right-inclined curves of enriched LREE; the other is by positive Eu anomalies for majority of skarns. Three types of chondrite-normalized REE distribution patterns are present. Type 1 shows straight-lines with not too large slope. Type 2 is broken line with a peak at Ce, namely convex up in the light REE （LREE） with a maximum at Ce （a few samples have not peaks, and curves in the LREE display domed shape）. Type 3 is transition REE distribution patterns. It is difficult to distinguish genesis of skarns using geochemical characteristics of their rare earth elements under these circumstances of limited REE data at present.