EPITHERMAL FLUORITE DEPOSITS IN TRANSBAIKALIA (geochemical features, sources of matter and fluids, and genesis)
E.I. Lastochkin1, G.S. Ripp1, D.S. Tsydenova1, V.F. Posokhov1, A.E. Murzintseva2
1Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakh'yanovoi 6a, Ulan-Ude, 670047, Russia
2Buryat Scientific Center, Siberian Branch of the Russian Academy of Sciences, ul. Sakh'yanovoi 8, Ulan-Ude, 670047, Russia
Keywords: Fluorite, pyrite, barite, quartz, isotopy, fluid, Transbaikalia
Abstract
We consider the isotope-geochemical features of epithermal fluorite deposits in Transbaikalia, including the REE compositions, Sr isotope ratios, Sm-Nd systems, and isotope compositions of oxygen, carbon, hydrogen, and sulfur. The 87Sr/86Sr values in fluorites are within 0.706-0.708, and the εNd values are negative. Oxygen in quartz, the main mineral of the deposits, has a light isotope composition (δ18O = -3.4 to +2.6 ‰), and the calculated isotope composition of oxygen in the fluid in equilibrium with quartz (δ18O = -9 to -16 ‰) indicates the presence of meteoric water. The latter is confirmed by analysis of the isotope compositions of oxygen and hydrogen in gas-liquid inclusions in fluorites from three deposits. These isotope compositions are due to recycling caused by the impact of shallow basic plutons. The isotope composition of sulfur indicates its deep source. During ascent, sulfur became enriched in its light isotope (δ34S = -1.8 to -7.7 ‰). We assess the association of fluorite ores with basaltoids widespread in the study area. The isotope and geochemical parameters suggest their spatial proximity. Probably, the basaltoids were responsible for the recycling of meteoric water. It is shown that the epithermal fluorite deposits formed by the same mechanism as fissure-vein thermal waters in western Transbaikalia.
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