Epithermal activity in brecciated Permian-Triassic? arkose: an unprecedented occurrence for the region at Los Cuatro Pozos quarry, southeastern San Luis province, Argentina

Abstract

Los Cuatro Pozos is an outcrop of silicified arkosic sandstones with fanglomerate levels, of continental origin and of probable Permian-Triassic age. A vertical fault zone crosscuts the quarry at least along 150 m with NE (25º) strike and a variable thickness of 5 to 10 m. In its SW edge, crackle-, mosaic-, and chaotic breccia types have formed, cemented by manganese oxides (hollandite), chalcedony, idiomorphic quartz and several generations of calcite. Anomalous contents of Ba in positive correlation with Mn, mimic the composition of Sr-rich hollandite. Anomalous geochemical values of Cu support the finding of supergenic Cu phases. Weakly anomalous Mo, V and Li are also registered. The positive correlation between of Cu and V with Mn suggests its affinity with Mn oxides; however, the occurrence of Li and Mo is aleatory. The Co+Ni vs. As+Cu+Mo+Pb+V+Zn binary ratios and the ternary Ni+Cu+Co(*10)-Mn-Fe ratios support a hydrothermal origin for the Mn oxides. The trapping temperatures of primary fluid inclusions in calcite range from ~ 192 to ~ 255 °C. The presence of Tl adsorbed onto the Mn oxides, together with Cu, might be pathfinders of the existence of sulfides at depth. The probable age of mineralization and the extensional tectonics as the dominant metallotect, could relate the Los Cuatro Pozos epithermal activity and the source of fluids to the A-type magmatism and related mineralization of the Permian-Triassic Intracratonic Magmatic Corridor of southern La Pampa province.