Abstract

The epithermal El Peñon gold-silver deposit consists of quartz-adularia veins emplaced within a late Upper Paleocene rhyolitic dome complex, located in the Paleocene-Lower Eocene Au-Ag belt of northern Chile. Detailed K-Ar and 40Ar/39Ar geochronology on volcano-plutonic rocks and hydrothermal minerals were carried out to constrain magmatic and hydrothermal events. The Paleocene to Lower Eocene magmatism in the El Peñon area is confined to a rhomb-shaped basin, which was controlled by N-S trending normal faults and both NE- and NW-trending transtensional fault systems. The earliest products of the basin-filling sequences comprise of Middle to Upper Paleocene (∼59-55 Ma) welded rhyolitic ignimbrites and andesitic to dacitic lavas, with occasional dacitic dome complexes. Later, rhyolitic and dacitic dome complexes (∼55-52 Ma) represent the waning stages of volcanism during the latest Upper Paleocene and the earliest Eocene. Lower Eocene porphyry intrusives (∼48-43 Ma) mark the end of the magmatism in the basin and a change to a compressive tectonomagmatic regime. 40Ar/39Ar geochronology of hydrothermal adularia from the El Peñon deposit yields ages between 51.0±0.6 and 53.1±0.5 Ma. These results suggest that mineralization occurred slightly after the emplacement of the El Peñon rhyolitic dome at 54.5±0.6 Ma (40Ar/39Ar age) and was closely tied to later dacitic-rhyodacitic bodies of 52 to 53 Ma (K-Ar ages), probably as short-lived pulses related to single volcanic events. © Springer-Verlag 2006.