Nyrdvomenshor Gem Stones Deposit, Polar Urals, Russia

Abstract

We have studied quality characteristics, chemical, mineral and isotope composition of nephrite, diopsidite and rodingite of the Nyrdvomenshor deposit in the Polar Urals. We applied the visual petrographic and mineralogical studies, X-ray spectral fluorescence, ICP-MS analysis, scanning electron microscope with the dispersive microanalysis system, oxygen isotope composition was measured. According to its quality characteristics, the nephrite is substandard. Here, uvarovite, which forms idiomorphic grains, sometimes sheath-like, less often xenomorphic elongated, and substituting chromite are commonly encountered. The nephrite was formed due to both metamorphic and metasomatic processes. Serpentinite was replaced by diopsidite, which was then replaced by nephrite. Metamorphism intensified metasomatism of the serpentinite melange and provided a cryptocrystalline tangled-fibrous structure of the nephrite. Then metamorphism and metasomatism led to the formation of omphacite and cracking of the nephrite, which reduced its quality. As these processes progressed, contribution of crustal fluid increased.