The mineralization at San Martin occurs in a tabular breccia zone striking northeast and dipping 10° to 90°SE. It occurs within Upper Cretaceous black limestones and calcareous shales of the Soyatal Mexcala Formation and varies in width from 1 to 17 m but averages about 4 m. The breccia zone appears in a structural window on the western hillside which is composed primarily of a Tertiary Rhyolite/Dacite.

The deposit has been described as an epithermal, probably a low sulphidation precious metal (Ag-Au) type, related to a Tertiary dacitic/andesite dome. Recent work has failed to locate the postulated dome and mineralization in the troncos may be more mesothermal or fault related. Development in 2008 discovered a sub-parallel vein to the main San Martin breccias with higher grade than the San Martin tronco breccias. This structure named the Guadalupe vein seems to degrade to a series of narrow poorly mineralized veinlets in the upper levels however at levels 8 through 10 it occurs as a strong 2 meter wide vein containing gold grades greater than 3 grams per tonne and silver values greater than 20 grams per tonne.

Mineralization occurs as native gold, electrum, naumannite (Ag2Se) and argentojarosite (AgFe3(SO4)2(OH)6) associated principally with quartz and lesser calcite. The silver contained in argentojarosite is not recoverable with cyanidation. Evidence of multiple intrusions of quartz with banding and drusy crystal masses observed in the brecciated zone are indicative of open space deposition.

The San Martin operation consists of underground mining and surface milling facilities with a current daily capacity averaging 842 tpd. The San Martin Mine is economically a gold mine with enough silver content that the plant is technically a silver plant. In the period August 1 2013 to July 31, 2014 the mill processed 308,610 tonnes with a calculated head grade of 2.55 g/t gold and 24 g/t silver.

The main mine access is by tunnels and ramps with the main portal located less than 300 m from the mill site. Ventilation is provided through robins raises by surface mounted exhaust fans and aided by natural means. The mine employs mechanized cut-and-fill using waste rock from development to backfill stoping areas. During the last few years some narrow structures have been stoped using modified resuing techniques which have helped reduce dilution while providing backfill without haulage costs. The ore is transported from the stopes with load haul dump equipment to loading ramps or ore passes for loading of highway type dump trucks with capacities of 8 to 16 tonnes depending on the ramp size, for haulage to the mill. Ramps are typically 10% but in 2008 the gradient of ramps was increased to 12%.

More than 50 percent of mine development and production is by 3 single boom jumbos with the remainder by conventional jack-leg drills. Stopes use mechanized and conventional cut and fill using pivoting ramps and most blast holes are sub-horizontal. In stopes with widths greater than 5 meters pillars are left to support the ground. Pillars commonly consist of 15% of the original reserve. The use of rockbolting has increased in recent years for rock support but shotcrete continues to be the principal method of providing additional rock support, particularly in the manto areas. The shotcrete is applied with mobile units equipped with a mixer, pump and an articulated application arm.

The San Martin Mill is a conventional cyanidation mill using the Merrill Crowe recovery process, with a rated capacity of 900 tpd. The mill flowsheet employs two stage fine crushing, grinding is also two stage with both ball mills and a tower mill followed by total ore cyanide leaching in a CCD circuit. Gold and silver is recovered with zinc precipitation and is refined on site to doré.