Abstract

The Maricunga metallogenic belt in northern Chile is defined by the presence of both intrusion-related porphyry-type and volcanic-hosted high sulfidation (acid sulfate) epithermal deposits containing gold and/or silver. The nine principal mineralized centers in the belt, including the La Coipa, La Pepa, Marte, and Lobo deposits, were dated radiometrically using the K-Ar method. Hypogene alunite from advanced argillic assemblages was dated from eight of the deposits.The 18 new radiometric ages permit subdivision of the Maricunga belt into two overlapping, longitudinal subbelts: the western of early Miocene (including latest Oligocene) age (25-20 Ma) and the eastern of middle Miocene age (14-12.5 Ma). This spatial and temporal subdivision of the alteration and mineralization accords well with that defined previously for volcanic rocks in the region and is substantiated further by regional structural and volcanic relationships. The migration of the magmatic and metallogenic activity from the western to the eastern subbelt may be attributed to shallowing of the subduction zone, which was initiated at 18 to 16 Ma.The western and eastern Maricunga subbelts are broadly correlative with two discrete volcanic alteration events in the El Indio precious metal belt 300 km to the south. The Maricunga subbelts are also integral parts of an eastward-younging sequence of gold-bearing magmatic metallogenic subbelts of Paleocene to late Miocene age, which span an east-west distance of 380 km in this transect (26 degrees -28 degrees S) of the central Andes.

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