The mineralization is typical of epithermal vein structures with banded and drusy textures. Within the San Dimas District, the veins occupy east-west trending fractures, except in the southern part of Tayoltita where they strike mainly northeast, and in the Santa Rita mine where they strike north-northwest. The veins were formed in two different systems. The east-west striking veins were the first system developed, 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 vary from a fraction of a centimetre in width to 8 m, but average around 1.5 - 2.0 m. They have been followed underground from a few metres in strike-length to more than 1,500 m. An example of a vein with mineralization in the Favourable Zone extending for more than 2,000 m in the Tayoltita Mine, the San Luis Vein.

The San Dimas Mine operation includes four underground gold and silver mining areas: the West Block (San Antonio mine); the Sinaloa Graben Block; the Central Block and the Arana Block (the Santa Rita mine). Vein thickness varies from 0.1 metres to 8 metres with the average approximately 1.9 metres. Some veins have a strike length of more than 1,500 metres. Vein dips vary from about 35 o to sub-vertical, the latter being decidedly more prevalent. The general mining recovery factor is about 95%, while that for sill mining is about 75%.

Typical mining of the vein systems is by mechanized cut-and-fill and long-hole, using drill jumbos or jacklegs, pneumatic long-hole drills and load-haul-dump machines, with primary access provided by adits and internal ramps from an extensive tunnel system under the steep, mountainous terrain.

The basis for ore haulage at San Dimas is load-haul-dump (“LHD”) equipment feeding trucks for haulage to the portal and then plant stockpiles. In the Tayoltita mine, the LHD equipment load rail wagons for haulage to the Tayoltita mill crushing plant. Development waste is generally moved to stopes as fill.

There is one milling facility at Tayoltita to process the production from the active mining areas in San Dimas. The Tayoltita mill has a conventional Merrill Crowe process flowsheet that employs crushing and grinding followed by cyanidation and zinc precipitation for recovery of gold and silver.