San Dimas utilizes underground long-hole stoping and mechanized cut-and-fill as the primary mining methods, with LHD equipment feeding haul trucks delivering ore to the mill. Primary access takes advantage of the topographic relief, with adits driven at river level to intersect the veins at depth. Ore is transported from the mining areas to the processing plant in Tayoltita.
The Tayoltita mill has a nameplate capacity of 2,500 tonnes per day. The facility uses conventional crushing/grinding coupled with cyanidation and zinc precipitation for recovery of gold and silver. The mill uses fine crushing and single stage ball milling to achieve a fine grind before passing into the leach circuit. Leaching is completed in a series of tanks providing 72 hours of leach residence time. The pregnant solution is recovered in a CCD circuit with the gold and silver recovered from solution in a zinc precipitation circuit.
Tailings are pumped by a single stage pumping station to the tailings impoundment area located in a box canyon east of the mill site. Gold and silver precipitate is refined using an induction furnace to produce 1,000 ounce gold and silver doré bars.
The Tayoltita mill has gone through a series of expansions over its operating life. In December 2005, crushing capacity was increased to 2,100 tonnes per day, with improvements to the chemical treatment/leaching area. Primero acquired the San Dimas Mine in 2010 and implemented thorough optimizations and a two phase expansion program. Phase 1 was completed in Q1 2014 increasing nameplate throughput to 2,500 tonnes per day.