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. Mineralization 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 Favourable Zone concept for San Dimas was developed in the mid seventies in the Tayoltita Block, based on the San Luis vein, which was mined out in the late 1990s. The mine geologists observed that bonanza grades along the San Luis vein were spatially related to the Productive andesite unit and/or to the interphase between the Productive andesite and the Portal rhyolite and/or the Buelna andesite. This spatial association of vein-hosted mineralization to a favorable zone within the volcanic sequence is now recognized in other fault blocks and constitutes a major exploration criterion for the district. The veins were 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. They vary in width from a fraction of a centimeter to as much as 8 m wide, but average 1.5 ........

The San Dimas mine includes five 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). Mining activities are conducted by First Majestic and contractor personnel. Two mining methods are currently in use at San Dimas: Cut-and-Fill, and Longhole Stoping.

Cut-and-fill is carried out by either jumbo or jackleg drills, whereas longhole is carried out with pneumatic and electro-hydraulic drills. Primary access is provided by adits and internal ramps.

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. ........

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