Contrasting Landscape Evolution and Development of Supergene Enrichment in the El Salvador Porphyry Cu and Potrerillos-El Hueso Cu-Au Districts, Northern Chile
Thomas Bissig, Rodrigo Riquelme, 2009. "Contrasting Landscape Evolution and Development of Supergene Enrichment in the El Salvador Porphyry Cu and Potrerillos-El Hueso Cu-Au Districts, Northern Chile", Supergene Environments, Processes, and Products, Spencer R. Titley
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The landscape from the Central Depression to the eastern Precordillera in the southern Atacama Desert, northern Chile (lat. 26°–27° S), is dominated by multiple pediplains which formed from the late Oligocene through the middle Miocene, followed by canyon incision in the late Miocene. The oldest such planer surfaces are observed in the eastern Precordillera and are represented by the probably late Oligocene Sierra Checos del Cobre and the ≥17.5 Ma Asientos surface. The El Hueso disseminated epithermal Au deposit and La Coya porphyry Au-Cu prospect are hosted beneath the Sierra Checos del Cobre surface. In the western Precordillera and adjacent Central Depression, planar landforms formed throughout the middle Miocene in several stages and gave rise to the Atacama pediplain, which is composite in nature. The El Salvador porphyry Cu deposit and associated exotic mineralization is situated at the back scarp of the Atacama pediplain.
Supergene activity at El Salvador occurred from the late Eocene to late middle Miocene, but, based on published ages, was most important from ~25 to ~19 and ~15 to ~12.5 Ma. The multistage landscape evolution and related supergene activity at El Salvador during the late Oligocene and middle Miocene was favorable for the efficiency of supergene enrichment and exotic mineralization but climate desiccation after 13 Ma led to cessation of supergene processes. In contrast, El Hueso, La Coya, and Potrerillos were situated below a relatively stable landscape throughout most of the Miocene. Published alunite ages from El Hueso indicate that supergene activity took place in the late Oligocene and late Miocene but was absent through most of the early and middle Miocene. Late Miocene supergene processes coincided with a time when the Precordillera was uplifted and attained an elevation sufficient to capture increased orographically controlled precipitation. This increase in rainfall led to the incision of the El Salado and Asientos canyons, which, combined with the increased availability of meteoric water, exposed new hypogene mineralization to oxidation in the late Miocene, at a time when at El Salvador supergene activity had ceased.