LAUSR

Abstract The activity of polyvalent elements in the geochemical processes is to a considerable extent determined by the valence state. A change in the valence is dependent on many factors, but the redox conditions of the medium where magma is generated are considered the main factor. The ratio between divalent and trivalent iron in magmatic rocks is a reliable and an accessible indicator of the redox conditions that determine a whole set of mineralogical, geochemical and physical parameters including ferruginosity of dark-colored minerals, the ore mineral (magnetite–ilmenite) composition, the weight of the ore fraction, and magnetic susceptibility. Based on the above parameters, the zones are distinguished where magmatic rocks of the magnetite and ilmenite series are developed in the Sikhote Alin Orogenic Belt. All known tin and tungsten deposits and occurrences in the Sikhote Alin are confined to the ilmenite series (the axial zone of the belt). The ilmenite rock series are framed by the magmatic rocks of the magnetite series; the epithermal gold–silver and copper–porphyry deposits are associated with these rocks.