Evidencias Geofísicas de la Continuidad del Volcanismo Dacítico Mioceno en el Subsuelo de la Depresión de Pozuelos, Provincia de Jujuy, y su Potencialidad Minera

Abstract

Geophysycal evidence of the underground continuity of the Miocene dacitic volcanism of the Pozuelos depression, Province of Jujuy, Argentina, and its mining potential. According to the existing geological and geophysical evidence, the Pozuelos depression, located in the northern Puna region of Argentina (22°30´ S, 66° W), hosts a large-scale volcanic caldera of Middle Miocene age. Pyroclastic sequences (14 ± 2 Ma) and base- and precious-metal rich dacitic dome complexes (12 ± 2 Ma) crop out discontinuously around part of the perimeter of the Pozuelos depression which, otherwise, is mostly covered by younger sediments. The aeromagnetic survey of the region has allowed to identify the presence of the Middle Miocene magmatic rocks at shallow depths, covered by young nonmagnetic sediments; the identification and localization of a covered portion of these magmatic rocks may increase the mineral potential of the region, as suggested by their associated mineralization. Three subvolcanic bodies and a volcanic unit (subdivided into two subunits) have been identified in terms of the configuration (geometry, magnitude, gradient, polarity) of the magnetic anomalies, and drawn onto a solid geology map. The subvolcanic bodies extend for 7, 27 and 32 km2 respectively, while the volcanic unit extends for 500 km2. The magnetic anomalies indicate that one of the subvolcanic bodies is normally magnetized, while the other two are reversely magnetized, suggesting a difference in their ages, though constrained within the Middle Miocene. The magnetic polarity of the two volcanic subunits could not be defined, but their probable association with the subvolcanic bodies provide indirect evidence of their age difference. Modelling of the profiles of the magnetic anomalies from the subvolcanic bodies has allowed to determine depths of burial of 120 to 500 m, and magnetic susceptibilities of 0.01 to 0.04 S.I., the latter being indicative of intermediate to basic compositions. The depth of one of the subvolcanic bodies has been confirmed by the interpretation of a seismic section.