THE ROLE OF "POSTORE" BASALTOIDS IN THE FORMATION OF ORE-BEARING HYDROTHERMAL SOLUTIONS

Abstract

The study of numerous epithermal deposits ranging in age from Paleozoic (Omolon Craton) to Late Mesozoic (Okhotsk–Chukot volcanogenic belt) and Miocene–Pliocene (Kamchatka) revealed that nearly all ore fields incorporate postore dikes (sills and stocks) of basaltic andesites. Dikes of dolerites, microgabbro, and other basic rocks are developed in some places. Subvolcanic bodies show a wide range of variation in size. Thin dikes (0.3–1 m) in sedimentary rock fields extend from a few meters to 5 km or more. Domal, stratiform, and semicircular dikes in volcanogenic rock fields range from 10 to 200–300 m in diameter. The central part of subvolcanic bodies is usually composed of holocrystalline rocks (up to monzonites), while the periphery consists of vitreous varieties enriched in clinopyroxenes. In some places, the rocks (particularly, stratiform varieties) have a botryoidal structure with chalcedony, opal, quartz, calcite, and chlorite botryoids ranging from 1.5–2 cm to 0.5 m in size.