Summary:
The Casposo District is situated within the Cordillera Principal which runs along the border between Argentina and Chile approximately 1,500 km in a volcanic and seismic active zone. Basement is formed by Permian-Triassic rocks characterized by calk-alkaline affinity intrusive and volcanic rocks of andesitic to rhyolitic composition regionally known as Choiyoi Group. These and younger JurassicCretaceous sediments were thickened by compression and trusting since the Late Cretaceous in a thin-skinned fold trust belt.
Within the mining area, the Cordillera Frontal is underlain by marine metasediments (shales, sandstones, and conglomerates) of La Puerta Formation (Carboniferous-Lower Permian). This formation correlates with the Agua Negra Formation to the north.
The Casposo gold–silver mineralization occurs in both the rhyolite and underlying andesite, where it is associated with banded quartz–chalcedony veins, typical of Low Sulphidation Epithermal environments. Adularia in the main veins gives an age date of 280 ± 0.8 Ma (K/Ar), very close to the published age dates for the andesite unit. Post-mineralization dykes, of rhyolitic, aphanitic-felsic and trachytic compositions which affects all the deposits Manantiales, Julieta, Mercado and B-Vein often cut the vein systems. These dykes, sometimes reaching up to 30 m thickness, are usually steeply dipping and north–south oriented. The mineralization at Casposo is typical of a low sulfidation type and is interpreted to be of a multi-stage, open space filling epithermal origin resulting in mineralized veins, hydrothermal breccias, stockworks or veinlets.
The deposits exposed in the Casposo Property are typical Epithermal Low Sulphidation (LS) and they are multi-stage, open space filling events resulting in mineralized veins, breccias, stockworks and or veinlets.
This deposit type is characterized by quartz veins, hydrothermal breccia, stockworks, and veinlets units that contain gold, silver, electrum, and variable silver and iron sulphides. Alteration has been identified and ssilicification is the most common alteration type with multiple generations of quartz and chalcedony, which are typically accompanied by adularia and calcite. Pervasive silicification in the vein envelope is flanked by sericite–Illite–kaolinite assemblages. Kaolinite Illite–montmorillonite ± smectite (intermediate argillic alteration) can form adjacent to veins; kaolinite–alunite (advanced argillic alteration) may form along the tops of mineralised zones.
The mineralization framework extends along 10 km long NW-SE structural corridor. All the structures considered in this technical report are continuations of the main and previously exploited deposits known as Kamila. Moving from south to north, these structures include B-Vein, Mercado, Julieta and Manantiales. The Casposo Property is a prolific district where mineralisation remains open and further exploration efforts will contribute to advance several targets identified by the AGL Exploration team.
Casposo Property expose well developed structural systems featured by main and secondary faults in jogs or bends setting. Main faults play a secular role in the formation of the deposits.
Manantiales Vein is the north-western expression of the deposits in the Manantiales Property and is located about 5 km north-west from the main facilities.
Julieta is located south-east of the Manantiales structure and its expression is a quartz-carbonate vein breccia with several tensional structures along the main ore body.
Mercado vein is the northern expression of the main system Kamila and in the past was partially exploited by open pit. And finally, B-Vein, which is a sub-parallel mineralized structure to the Inca vein system, has been evaluated and its resources have been determined. It was previously exploited to a minor extent using underground mining methods.
Accordingly, the geological modelling shows the ore shoots in the property presents discontinuities, the vein systems were cut by several dikes and faults conditioning the shape of the mineralization mostly forming sub-vertical shoots.