The Charcas mining district occupies the east-central part of the Mexican Central Mesa and is part of the Sierra Madre metallogenic province. Geological history starts in the Superior Triasic, where sandy clay sediments were deposited argilloarenaceous. Due to emersion in the beginning of the Jurassic Superior, the sediments suffered intense erosion, settling on continental sediments. This sequence was affected by tectonic effort, which folded and failed on this rock package. Later the positioning of intrusive rocks originated fractures, which gave way to positioning of mineral deposits. The site’s paragenesis suggests two stages of mineralization. First minerals are rich in silver, lead and zinc, with abundant calcite and small quantities of quartz chalcopyrite. Second, there is a link of copper and silver, where the characteristic minerals are chalcopyrite, lead ore with silver content, pyrite and scarce sphalerite. Economic ore is found as replacement sulfurs in carbonates host rock. The ore mineralogy is comprised predominantly of calcopyrite (CuFeS ), sphalerite (ZnS), galena (PbS) and silver minerals as diaphorite (Pb Ag Sb S).

The Charcas mine uses the hydraulic cut-and-fill method and the room-and-pillar mining method with descending benches. The broken ore is hauled to the underground crusher station. The crushed ore is then hoisted to the surface for processing in the flotation plant to produce lead, zinc and copper concentrates.

The complex includes three underground mines (San Bartolo, Rey-Reina and La Aurora) and one flotation plant that produces zinc, lead and copper concentrates, with significant amounts of silver.

The capacity of the flotation plant is 4,100 tons of ore per day. The lead concentrate produced at Charcas is treated at a third party refinery in Mexico. The zinc concentrates are treated at our San Luis Potosi zinc refinery and the copper concentrates are treated at our La Caridad smelter.