The vein-hosted mineral deposits within the San Dimas Mine district are considered to be examples of silver- and gold-bearing epithermal quartz veins that formed in a low-sulphidation setting. Epithermal veins are typically localized along structures but may also form in permeable lithologies. Upward-flaring ore zones centred on structurally controlled hydrothermal conduits are typical. Large to small veins and stockworks are common. Vein systems can be laterally extensive, but the associated ore shoots have relatively restricted vertical extent. High-grade ores are commonly form within dilational faults zones near flexures and fault splays. Textures typical of low-sulphidation quartz vein deposits include open-space filling, symmetrical and other layering, crustification, comb structure, colloform banding and complex brecciation.

Within the San Dimas district, the mineralization is typical of epithermal vein structures with banded and drusy textures. Epithermal-style veins occupy east–west-trending fractures, except in the southern part of the Tayoltita Block where they strike mainly northeast, and in the Santa Rita area where they strike north–northwest.

The silver- and gold-rich quartz veins formed in two different phases. The east–west striking veins developed first, followed by a second system of north–northeast-striking veins. Veins pinch and swell and commonly exhibit bifurcation, horse-tailing, and sigmoidal structures. The veins have been follow ........

The San Dimas mine includes five main underground gold and silver mining areas: West Block (San Antonio mine), Sinaloa Graben Block (Graben Block), Central Block, Tayoltita Block, and the Arana Hanging-wall Block (Santa Rita mine). In 2020, 68% of ROM production came from the Central Block, 29% from the Sinaloa Graben and 3% from the Tayoltita Block and other areas.

Access to the mining areas is achieved by adits and internal ramps. The Central Block and Sinaloa Graben rely solely on truck haulage, whereas Tayoltita ROM material is transported to the surface stockpile via rail. Main accesses are typically driven at 5 m wide by 5 m high, with accesses to the stopes at 3 m wide by 3 m high. Typical rail haulageway dimensions are 3.5 m wide by 3.5 m high.

Internal ramps connect stopes from both the hanging wall and foot wall, and often, when two or more veins are in close proximity, single ramps can provide access to multiple veins.

The predominant mining methods at the San Dimas mine are mechanized cut-and-fill and longhole mining. Longhole mining was introduced in 2012 and is becoming increasingly important.

Cut-and-fill mining is carried out using jumbo or jackleg drills and load-haul-dump (LHD) machines. Minimum mining widths of 2.5 m and 0.8 m for jumbo and jackleg mining, respectively, may be attainable. Waste rock is used as fill material and provides both wall support and a working base from which to take subsequent cuts afte ........

- subscription is required.

The processing plant at the San Dimas has been successfully operating for several years and continuously achieved high levels of recoveries for silver and gold. The process is based on cyanide tank leaching and Merrill-Crowe precipitation of ground plant-feed to produce silver–gold doré bars. The installed plant capacity is for 3,000 tpd. However, the current throughput levels are around 2,000 tpd. The average feed contains head grades in the order of 300 g/t Ag and 3.6 g/t Au.

The plant consists of the following operating units:
• Crushing – a two-stage crushing circuit with a primary jaw crusher followed by two cone crushers, one in operation and one in standby, in closed circuit with dry vibrating screens;
• Grinding – three ball mills, each paired with hydrocyclones in closed circuit working in parallel;
• Cyanide leaching – plant-feed is leached with cyanide in a series of agitated tanks;
• Counter current decantation (CCD) – two CCD thickeners worki ........