Conditions of Formation of Epithermal Mineralization of the Kyplatap Volcanic Field (Central Chukotka)

The article considers the geochemical features and conditions of the formation of substantially silver mineralization of the Kyplatap volcanic field (KVF), of the Chaunsky zone, of the Central Chukchi Sector, of the Okhotsk-Chukchi volcanic belt (OChVB). New data on the composition, distribution and grade of trace elements, including REE in ores, are presented. The noticeable enrichment REE of the studied samples, the predominance of light lanthanides over heavy ones, very low Eu/Sm ratios (\( \ll {\kern 1pt} 1\)), weakly inclined near–chondrite spectra with obvious Eu minima are typical for the epithermal ore-forming system of the KVF. The Ce/Ce* vary from slightly negative to moderately positive values (from 0.81 to 1.38), and the Eu/Eu* vary from 0.28 to 0.7. This combination of Ce/Ce* and Eu/Eu* indicates the oxidative conditions prevailing during ore formation. The results of thermo- and cryometric studies of fluid inclusions in quartz allowed us to establish that the ore-forming fluid contained Na, Mg and K chlorides, epithermal mineralization was deposited by homogeneous hydrothermal fluids with salt concentrations (0.3–6.2 wt. %-eq. NaCl), fluid density – 0.60–0.87 g/cm³, at temperatures from 203 to 343°C, water vapor pressure varied from 40 to 140 bar. The obtained geochemical and thermometric data confirm the assumption put forward earlier – that the studied mineralization of KVF belongs to the intermediate sulfidation epithermal class. These data point to andesite magmas and meteoric waters as the most likely sources of fluids. The information in the article is of practical importance for regional predictive metallogenic constructions, prospecting and evaluation of epithermal Au–Ag deposits.