Formation conditions and composition of ore-forming fluids in the Promezhutochnoe gold and silver deposit (Central Chukchi Peninsula, Russia)

The Promezhutochnoe and Sil’noe epithermal gold and silver deposits and ore bodies of eastern areas of the Sopka Rudnaya deposit have been discovered in the Maiskoe ore cluster, central Chukchi Peninsula, in terrigenous flysch strata of the basements of the Okhotsk–Chukchi volcanic belt. Fluid inclusions in quartz from gold ore veins of Promezhutochnoe have been studied. Similar deposits and occurrences have been found in the terrigenous-sedimentary framing of some intrusion domes in tectonomagmatic zones in the Upper Yana–Kolyma fold belt. Terrigenous strata of similar compositions host the Vysokovol’tnoe and Kosmanychi gold and silver deposits in central Kyzyl Kum and the Balei and Taseevka deposits in Transbaikalia. The richest Hishikari deposit (250 tons of gold, the mean content 60 g/t) in Japan also occurs in terrigenous strata of the basement beneath a volcanic rock cover. However, deposits other than Hishikari, Balei, or Taseevka are small. The causes of this fact are discussed in the context of the geologic structure, chemical composition, and ore formation conditions in the Promezhutochnoe deposit. The main physicochemical parameters of the formation of the ores in this deposit are: temperature 247–194 °C, pressure 270–30 bar, salt concentration 4.3–2.9 wt.% NaCl equiv. The composition of the ore-forming fluids has been studied by gas chromatography, ion exchange chromatography, and inductively coupled plasma mass spectrometry.