硅孔雀石和透视石稀土元素地球化学特征及其成矿环境研究

Geochemical Characteristics of Rare Earth Elements in Chrysocolla and Dioptase and Their Metallogenetic Environments

硅孔雀石和透视石是在热液成矿作用下经过水-岩反应形成的产物,但这一认识缺少稀土地球化学研究成果的支持。本文通过电感耦合等离子体质谱分析获得两种矿物的稀土元素含量,其中硅孔雀石的稀土含量较低(∑REEs=81.2 mg/kg),透视石的稀土含量极低(∑REEs=0.65 mg/kg);两者轻重稀土间分馏较为显著,LREEs/HREEs=3.01和6.05,(La/Yb)N=3.08和7.91。球粒陨石标准化的稀土元素配分模式图均表现为轻微"负铕异常"(δEu=0.565和0.702)、轻稀土富集、重稀土稳定的右倾特征,表明两者物质来源于同一物体。硅孔雀石显著"负铈异常"(δCe=0.219),透视石无"负铈异常"(δCe=0.949),应为两者晶体结构差异所致。研究认为,硅孔雀石和透视石中的稀土元素继承了成矿岩石的稀土特征,证实了两者是在同一氧化条件下通过水-岩反应形成的产物。

Chrysocolla and dioptase were considered to be formed from hydrothermal solutions by fluid-rock interaction,but this view was not verified by REE geochemistry. In this study,the REEs contents in these two minerals were determined by Inductively Coupled Plasma-Mass Spectrometry （ ICP-MS ）. Results show that chrysocolla has total REEs of 81 mg/kg,whereas dioptase has total REEs of 0. 65 mg/kg. There is obvious fractionation of LREEs from HREEs for chrysocolla and dioptase with LREEs/HREEs ratios of 3 . 01 and 6 . 05 ,and （La/Yb）H ratios of 3. 08 and 7. 91,respectively. The chondrite-normalized REEs patterns of two minerals show weak Eu anomalies with δEu of 0. 565 and 0. 702,respectively,with LREEs enrichment and flat HREEs, indicating their similar source. Obvious Ce anomaly（δCe =0. 219）of chrysocolla and no Ce anomaly（δCe =0. 949）of dioptase are possibly due to their different crystal structures. Chrysocolla and dioptase inherit the REEs characteristics of the source rocks. These two minerals were formed by fluid-rock interaction under the same oxidized condition.