Mineralogical Characteristics and Genesis of Green Nephrite from the World

Abstract

BACKGROUND In previous studies, due to the limited samples with specific origins and limited methods for measurement, the genesis of serpentinite-related green nephrite and its relationship with dolomite-related nephrite were unclear. OBJECTIVES To understand the genesis of serpentinite-related green nephrite. METHODS Green serpentinite-related nephrite deposits have been collected from Qinghai province in China, Russia, Canada, Australia, New Zealand and Pakistan for systematic analysis. X-ray Diffraction (XRD), Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), Electron Microprobe Analysis (EMPA), X-ray Fluorescence Spectrometry (XRF) and Stable Isotope Mass Spectrometry were employed. RESULTS ① Serpentinite-related green nephrite is mainly composed of tremolite with minor quartz, talc, biotite, chromite, chlorite, and garnet. ② O-H isotopic values of samples (δD=-69.763‰--29.251‰, δ18O=4.7‰-13.4‰) indicate that the ore-forming fluids are mainly metamorphic water. ③ whole-rock major elements of Fe2+/(Mg+Fe2+)values range from 0.11 to 0.32. The contents of Cr range from 22.9 to 3400 μg/g, whereas Ni ranges from 700 to 1800 μg/g. All of these geochemical characteristics indicate the input of the mantle material in the formation of serpentinite-related nephrite. CONCLUSIONS Geochemical characteristics of serpentinite-related and dolomite-related nephrite are different, which are related to the geological environment. For example, the composition of dolomite-related nephrite is controlled by the granite and dolomite marble, whereas the composition of serpentinite-related green nephrite is related to the mantle material and metamorphic fluids.

Keywords

• serpentinite-related green nephrite
• geochemistry
• nephrite
• genesis