Jurassic shallow epithermal systems from southern Patagonia, Argentina

GUIDO, D.; CAMPBELL, K.

Congreso; 16th Biennial Meeting SGA 2022; 2022

Southern Patagonia, Argentina is part of the Jurassic Chon Aike Silicic Large Igneous Province, considered a diffuse back-arc extensional zone related with slow subduction in the Pacific and the presence of a mantellic plume related to the breakup of Gondwana and the opening of the South Atlantic Ocean. Several epithermal deposits and their shallow portions are present in the Deseado Massif province. This metallogenical unit hosts economic gold and silver-bearing, mainly low sulfidation, epithermal deposits spatially and genetically related with the bimodal calc-alkaline volcanic event of the Bahía Laura Complex. In the last five years, 12 mines were operative in the province, together with three advanced projects and several projects under exploration. The Deseado Massif hosts numerous shallow epithermal systems with well-preserved fossil geothermal areas located in four regional NNW and WNW structural belts. The geological setting at these shallow epithermal systems is characterized by the presence of hydrovolcanic activity, including phreatic and phreatomagmatic breccias forming maar-diatreme volcanic centers, the formation of large shallow lakes (some hypersaline) with restricted fluvial activity, and the intrusion of late acidic extrusive or intrusive domes. Paleosurfaces are also preserved in these Jurassic shallow epithermal systems with sinters and travertine deposits, as well as a larger quantity of shallow siliceous deposits including cherts and silicified rocks, supporting the overall neutral alkali chloride dominant nature of the hydrothermal fluids. About half of the active epithermal mines are in close spatial relationship (<5 km) with the shallow epithermal geological setting and the presence of  paleosurfaces. Larger and proximal paleosurface features (sinters and phreatic breccias) are associated with mines with larger gold and silver endowment, highlighting the importance of the shallow epithermal systems model as a relevant prospecting tool.