New Data on Formation Conditions and Composition of Ore-Forming Fluids in the Promezhutochnoe Gold-Silver Deposit (Central Chukotka, Russia)

摘要

According to the conventional concept based on a great body of empirical data, volcanogenic or epither-mal deposits do not grade into mesothermal or plutono-genic ones with depth. However, in the Maisk ore group of central Chukotka (Fig. 1), epithermal Promezhutochnoe (Northeast), Sil'noe, and Sopka Rudnaya gold-silver deposits have been discovered in terrigenous flysch sequences at the basement of the Okhotsk-Chukot volcanogenic belt (OCVB). Similar epithermal ore deposits and occurrences have also been discovered in the terrigenous-sedimentary framing of intrusive domes in transmagmatic reactivation zones of the central Kolyma region (e.g., Pechal'noe and Vetvistoe deposits in the Khurchan-Orotukan zone and Rogovik deposit in the Balagychan-Sugoi zone). Analogous gold-silver deposits are also known in other regions. For example, the central Kyzyl Kum region incorporates the Vysokovol'tnoe and Kosmanychi deposits, while the Transbaikal region includes the Balei and Taseevka deposits. In this connection, let us recall the Hishikari deposit, Japan (Au reserve 250 t). In terrigenous rocks of the basement beneath the volcanic cover of this deposit, geologists have discovered a second level of epithermal auriferous veins with an average grade of as much as 25-75 g/t. However, all epithermal gold-silver orebodies (except the Hishikari, Balei, and Taseevka deposits) have small and medium reserves. This phenomenon is probably related to their significant erosion.