Oxygen and Carbon Isotope Composition of Vitim Nephrite Province Rocks

The oxygen isotopic composition of dolomite type nephrite, contact and host regional rocks of Kavokta, Voimakan and Nizhne-Ollomi deposits of Vitim province was studied. The nephrite is characterized by an anomalously light oxygen isotope composition δ¹⁸O −21.5 ÷ −15.8‰. Contact metasomatic rocks showed wider variations, including also anomalously light isotope ratios −21.5 ÷ +9.2‰. The country rocks of the deposit area are characterized by heavier oxygen isotope compositions: granite and granodiorite −7.51 ÷ −0.71‰, amphibolite −8.38 ÷ +9.60‰, dolomitic marble +20.8 ÷ +26.1‰. The anomalously light isotopic composition of nephrite, is thus explained by the meteoric origin of the fluid from melt water and the removal of isotopically heavy oxygen by carbon dioxide in the process of decarbonatization of dolomitic marble. The granite mainly provided the regional heating that activated the fluid. The analyzed dolomite is characterized by a heavier carbon isotopic composition +3.2 ÷ +5.2‰ δ¹³C, explained by fermentation of organic matter and methane formation in the basin in which the dolomite was formed. Calcite from calcite-tremolite skarn is characterized by lighter carbon isotopic composition −6.4 ÷ +0.7‰ δ¹³C as a result of metasomatic process.