Nyrdvomenshor Nephrite Deposit, Polar Urals, Russia

Abstract

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