Lead isotopes from Gondwanan polymetallic ore vein deposits, San Rafael Massif, Argentina

The San Rafael Massif in the province of Mendoza, Argentina, is characterized by widespread volcanic and pyroclastic rocks of Gondwanan age, known as the Choiyoi Group, that reflect a transition from a magmatic arc to a rift tectonic setting. Many ore deposits, according to stratigraphic constraints, are genetically related to this major magmatic episode. Lead isotopes of polymetallic ore vein deposits and mineralized country rock were analyzed to confirm their genetic link with the Gondwanan magmatic cycle and establish possible sources of the lead. The resulting linear array of the data is interpreted as a mixing scheme. The calculated model age of 279 Ma (very close to that obtained for one of the analyzed deposits) is consistent with previous geochronological data and the stratigraphic evidence, so it could be considered the age of the deposits and remobilization of lead. Lead isotope compositions reflect a mixing process between a mantle-derived component, probably from a depleted mantle, and a dominant upper crustal component. On the basis of this new information, it is possible to conclude that the ores were emplaced during arc evolution, though the upper crust was critically involved in the genesis.