EROSION AND COLLAPSE OF VOLCANOS - CAUSES OF TELESCOPING IN INTRUSION-CENTERED ORE-DEPOSITS

Telescoping is the process of juxtaposing or overprinting early, deep mineralization, commonly of porphyry type, and late, shallow, generall y epithermal styles of precious- and base-metal mineralization. Telesc oping is attributed to synhydrothermal degradation of volcanic paleosu rfaces, as a result of either rapid erosion under pluvial conditions o r sector (and, less probably, caldera) collapse of the volcanic edific es. Paleosurfaces may be lowered easily by 1 km during the approximate ly 1 m.y. total life spans of hydrothermal systems, leading to the ver tical compression of any contained ore deposits by at least 1 km. Sect or collapse may be triggered by volcanic tumescence due to synminerali zation intrusion, and it may be facilitated by hydrothermal weakening of volcanic edifices. Sector collapse causes extensive ingress of mete oric and/or ocean water to the magmatic environment and a decrease in confining pressure. The latter may induce hydrothermal brecciation, bo iling and possible epithermal Au precipitation, and even accelerated e fflux of magmatic fluids. Telescoped systems are believed to possess g reater potential for the existence of both porphyry-type deposits at s hallower than normal depths and giant ore deposits.