Abstract

A descriptive account is presented of the principal characteristics of, and time-space interrelationships between, hydrothermal alteration and lead-silver sulfide, native sulfur, and manganese oxide mineralization in the El Queva area, located on the Puna block of northwest Argentina. Alteration and mineralization are genetically related to the final stages of activity of a complex Quaternary stratovolcano of andesitic to rhyodacitic composition. Glacial erosion of the volcanic superstructure has exposed areas of argillic and advanced argillic alteration and silicification, containing pyrite-galena-silver sulfosalt mineralization accompanied by chalcedonic silica, dickite, alunite, and barite, that were formed some 400 to 500 m beneath the original volcanic surface. The sulfide mineralization is transitional upward to an accumulation of native sulfur. Around the uneroded periphery of the volcanic edifice, small manganese oxide and travertine deposits were subsequently precipitated at the orifices of thermal springs, one of which is still weakly active.This geometrical array of subvolcanic and volcanic mineralization types, preserved because of unusual erosional circumstances and well exposed in the El Queva area, is believed to be typical of that to be expected in the surficial parts of large hydrothermal systems that may include the development of porphyry copper deposits in depth at the level of a source stock. The relationships exhibited at El Queva confirm that "epithermal" mineral deposits are not related exclusively to caldera development, as in many parts of the San Juan Mountains of Colorado, but also occur within uncollapsed volcanic cones.

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