Home – Home – Jornals – Russian Geology and Geophysics 2001 number 3

Stable spatial and temporal relationships of pyrite mineralization with acid volcanism make it possible to characterize rhyodacites of producing formations, no matter to which differentiates, of tholeiitic or calc-alkalic magmas, they belong. The rhyodacites of pyrite-bearing formations are distinguished by higher, as compared with average types, contents of iron (FeO* = 3.5-4% and more versus 2-2.5%), high temperatures of homogenization of melt inclusions, and contrast hematite-pyrite zoning of extrusive subvolcanic massifs. The massifs confined to deposit structures are distinguished by a wide development of the phenomena of perlite disintegration, liquation layering, and autobrecciation conjugate with autometamorphism implicately coming to hydrothermal changes of the stage of ore deposition. The extrusive subvolcanic massifs that lie far from ore fields have no such indications of fluid enrichment. In ore fields, the replacement of small-porphyry rhyodacites by large-porphyry and perlite decomposition liquation phenomena is considered evidence of active separation of fluids in connection with the origin of peripheral chambers at interparoxismal stages of ore deposition.