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

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)_N 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.