Superscript40/SuperscriptAr/Superscript39/S

Authors: Gloria Arancibia Stephen J Matthews Paula Cornejo Carlos Pérez de Arce José I Zuluaga Stabro Kasaneva

Publish Date: 2006/07/27

Volume: 41, Issue: 5, Pages: 505-516

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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 rhombshaped basin which was controlled by N–S trending normal faults and both NE and NWtrending transtensional fault systems The earliest products of the basinfilling 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 510±06 and 531±05 Ma These results suggest that mineralization occurred slightly after the emplacement of the El Peñon rhyolitic dome at 545±06 Ma 40Ar/39Ar age and was closely tied to later dacitic–rhyodacitic bodies of 52 to 53 Ma K–Ar ages probably as shortlived pulses related to single volcanic eventsRegional geological mapping and geochronology of volcanic and plutonic units were carried out under the auspices of the Servicio Nacional de Geología y Minería—Central Depression Project PC Fieldwork and dating of adularia samples were financially supported by a Postdoctoral Fondecyt Project 3030002 GA We thank the Meridian Gold Company for providing support access to the mine and permission to publish these results Comments by two anonymous reviewers and RW King as Associate Editor improved the manuscript Mauricio Belmar Universidad de Chile collaborated with the SEM and EMPA study Eugenia Fonseca Marcelo Yáñez and César Vásquez assisted with XRD and K–Ar analyses at Laboratory of the Servicio Nacional de Geología y Minería Chile

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