An exhalative volcanic iron sulfide stratabound deposit, near San Fernando, Azuay Province, Ecuador

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The San Fernando region (3,700 meters above sea level) mainly consists of horizontal acidic volcanic layers, intruded by andesitic and rhyodacitic dikes, and lava flows. Strong silicification has welded the pyroclastics (rhyolite tuff, ignimbrite, volcanic ash and sand) and lava flows; geyserites occur in places. These rocks discordantly overlie Mio-Pliocene sediments. Neither records of recent volcanic activity nor craters exist in the area. It is believed that the volcanic activity stopped during the Pleistocene and the volcanic topography was erased by the last glaciation. An age of Plio-Pleistocene is probable for the volcanics. Iron sulfides are concentrated in semi-massive lenses or are disseminated in the volcanics. This mineralization is accompanied by Zn and Pb sulfides; by Au, Ag and As in smaller quantities and by sporadic amounts of Sb, Bi, Co, Sn and Ni. It is suggested that this type of metal and iron sulfide concentration in volcanics is due to the action of metalliferous hot springs and emanations during the Pleistocene volcanic activity. © 1972 Society of Economic Geologists, Inc.

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Economic Geology