Summary:
Exploration is focused principally on discovery and delineation of low sulfidation, Au-Ag epithermal mineralization of the type well documented throughout the Deseado Massif [e.g. White and Hedenquist (1990 &1994), Corbett, G.J. (2001) and Sillitoe, R.H. (1993)]. Mineralization typically comprises banded fissure veins and local vein/breccias characterized by high Au and Ag contents and ratios of Au:Ag generally greater than 1:10. Mineralized veins and breccias consist of quartz (coliform, banded, and chalcedonic morphologies), adularia, bladed carbonate (often replaced by quartz), and dark sulphidic material termed ginguro (fine grained electrum or Ag sulphosalts banded with quartz). Discrete vein deposits, such as at COSE, develop where mineralizing hydrothermal fluids are focused into dilatant structures, producing ore shoots which host the highest precious metal grades. Low sulfidation mineralization can also develop where mineralizing fluids flood permeable lithologies to generate large tonnage, low grade disseminated deposits (e.g. Round Mountain, Nevada; McDonald Meadows, Montana)
Mineralization at COSE is also assigned to the low sulfidation type, based on the presence of fine-grained replacement quartz and adularia, widespread illite alteration, bladed textures indicative of hydrothermal boiling, and a mineral assemblage dominated by marcasite, arsenopyrite and silver-bearing sulphosalts. The presence of anomalous copper and molybdenum associated with higher grade Au-Ag mineralization suggests a component of magmatic-derived fluid.
The COSE deposit occurs predominantly as hydrothermal breccia, in combination with replacement, veinlet and disseminated styles of mineralization, rather than as one or more discrete quartz veins. This is somewhat atypical for the Deseado Massif deposits, perhaps reflecting a lack of open space during hydrothermal fluid flow.
The deposit at COSE is a sub vertical, gold and silver bearing breccia that averages 0.5 m to 4 m in width and dips approximately 75° to the southwest. The interpreted ore shoot has a strike length of about 35 m, with a down dip extension of approximately 170 m. The preliminary estimate of undiluted resources is 34,000 tonnes.