Abstract

Telescoping is the process of juxtaposing or overprinting early, deep mineralization, commonly of porphyry type, and late, shallow, generally epithermal styles of precious- and base-metal mineralization. Telescoping is attributed to synhydrothermal degradation of volcanic paleosurfaces, as a result of either rapid erosion under pluvial conditions or sector (and, less probably, caldera) collapse of the volcanic edifices. Paleosurfaces may be lowered easily by 1 km during the ∼1 m.y. total life spans of hydrothermal systems, leading to the vertical compression of any contained ore deposits by at least 1 km. Sector collapse may be triggered by volcanic tumescence due to synmineralization intrusion, and it may be facilitated by hydrothermal weakening of volcanic edifices. Sector collapse causes extensive ingress of meteoric and/or ocean water to the magmatic environment and a decrease in confining pressure. The latter may induce hydrothermal brecciation, boiling and possible epithermal Au precipitation, and even accelerated efflux of magmatic fluids. Telescoped systems are believed to possess greater potential for the existence of both porphyry-type deposits at shallower than normal depths and giant ore deposits.

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