Deposit Type
El Castillo is interpreted to be a porphyry-style gold system related to Eocene granodiorite– diorite porphyries that intrude Cretaceous clastic and carbonate sediments in an extensional tectonic setting. Gold mineralization occurs throughout the magmatic-hydrothermal system in space and time and is related to sulphide mineralization spatially associated with early potassic development and genetically related to an overprint of phyllic alteration. Supergene alteration, formed as a product of acid leaching, has resulted in argillic-quartz alteration assemblages within the oxide zone of the deposit. The main gold event is believed to be associated with magmatic hydrothermal fluids corresponding to phyllic alteration.

The El Castillo gold system is similar to that found at Andacollo, Chile (Reyes, 1991 and Oyarzun, et al., 1996). Andacollo is a Cretaceous diorite to granodiorite porphyry copper-gold system with central porphyry copper-gold mineralization related to a classic porphyry alteration assemblage and a distal sediment-hosted (manto) low sulphidation and epithermal-level gold satellite system. Fluid inclusion work by Oyarzun et al. (1996) indicates that the manto epithermal gold deposits may in fact be related to another intrusive that has not been recognized at the surface due to high temperature fluid inclusions (about 365ºC) that are found about 5 km from the porphyry centre.

Supergene oxidation of shallow (<200 m) pyrite-gold m ........

El Castillo is an Owner-operated mine using conventional equipment and conventional mining methods.

The El Castillo mine is a relatively low-grade gold deposit that benefits from a low strip ratio and disseminated mineralization that is amenable to bulk mining activities and good heap leach recoveries. The operation is situated in a semi-arid environment surrounded by moderate topography.

There are three mine phases remaining in the LOM plan:
• The Phase 10.2 design is approximately 300 m long by 100 m wide with 36 m depth. Total Mineral Reserves contained in this phase are 1.1 Mt at an average grade of 0.25 g/t Au with a strip ratio of 0.21;
• The Phase LB design is approximately 700 m long by 250 m wide with 170 m depth. Phase LB contains 3.8 Mt of Mineral Reserves grading 0.27 g/t Au and a strip ratio of 1.39;
• The Phase WP design is approximately 700 m long by 400 m wide with 150 m remaining depth. Phase WP contains 6.6 Mt of Mineral Reserves grading 0.44 g/t Au with a strip ratio of 0.61.

The mining method consists of traditional drill-and-blast operations followed by excavator loading of rigid-body haul trucks for ore transport to the crusher and waste transportation to designated WRSF locations.

Pit Design
Pit designs include a ramp width of 25 m (truck factor of 3.5), which can safely support Cat 777 (or equivalent) sized mining trucks. One-way access of 15 m was applied at the pit bottom after strippin ........

Until January 2020, Argonaut processed gold ore through a conventional heap leaching operation that included two-stage crushing of higher-grade ore (>0.25 g/t Au) to -1 ½ inch (38 mm) and coarse crushing of lower grade ore (<0.25 g/t Au) to -4 inch (100 mm). Fine crushed ore was leached on the East Heap Leach Pad and coarse crushed ore was leached on the West Heap Leach Pad.

During the latter half of 2019 the mine transitioned to a ROM only processing operation. After December 2019 crushing was discontinued, and all ore was processed as ROM, with haul trucks directly dumping ore onto the leach pads.

Both the East and West leach operations are essentially the same, processing a combined total of approximately 24,000 t/d ROM ore, generally targeted as 50% of the ore to each leach pad. The ROM ore is 24 inch (600 mm) top size and is truck-stacked on the leach pads in 8 m lifts. The ore is leached with a cyanide solution (250 ppm NaCN) for a 90-day leach cycle at a so ........