Petrogenesis of Chatoyant Green Nephrite from Serpentinite-Related Deposits, Ospinsk, Russia: Insights from Mineralogy and Geochemistry

Abstract

Ospinsk is an area in Russia well-known for mining the highest quality green nephrite in the world. However, the chatoyant green nephrite found here has not been studied to date. This study explores the mineralogy, geochemistry, and petrogenesis of chatoyant green nephrite collected from Ospinsk using polarizing microscope back-scattered electron images, scanning electron microscopy, Fourier transform infrared spectrometry, laser Raman spectroscopy, electron microprobe analysis, and laser ablation inductively coupled plasma mass spectrometry, and compares them with S-type green nephrite from other regions of the world. Tremolite is the main mineral constituent, and chromite, chlorite, graphite, and magnetite are accessory minerals in the samples. The chatoyant green nephrite from Ospinsk is serpentinite-related green nephrite. The Ti content of the chatoyant green nephrite from Ospinsk is significantly higher than that of green nephrite from other places. The chatoyant green nephrite deposit in Ospinsk is a contact metasomatic deposit related to ultramafic rocks. The ultramafic rocks first altered to serpentinite and later converted to tremolite after repeated thermal contact-based metasomatism. During the metasomatism of serpentinite into green nephrite, unilateral, compressive, and shear stresses caused by obduction forced directional growth of tremolite, resulting in chatoyancy.