The Charcas mining district occupies the east-central part of the Mexican Central Mesa and is part of the Sierra Madre metallogenic province. 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).

San Martin lies in the Central Mesa between two major geologic provinces, Sierra Madre Occidental and Sierra Madre Oriental. The district’s most important mineral deposits are replacement veins and bodies generated in the skarn by Cerro de la Gloria granodiorite intrusion.

The majority of production from Santa Barbara district comes from quartz veins within faults and fractures. The north to northwestern trending veins is up to several kilometers long, dips steeply to the west and is 0.5 to 30 meters wide.

Santa Eulalia mineralization corresponds in its majority to ore skarns — silicoaluminates of calcium, iron and manganese with variable quantities of lead, zinc, copper and iron sulfides, located in the planes of crossings in the interstices of the silicates. Economic ore is found as replacement in the Limestone Glen Rose in the contact with dikes and sills and replacements in diabase sills. The mineralogy is comprised predominantly of sphalerite (ZnS), galena (PbS) and small quantities of pyrargyrite (Ag SbS ).

There are four types of ore deposits found in Taxco district. In order of importance they are as follows: fissure-filling veins, replacement veins, blanket-like replacement bodies (so called “mantos”), stock works and brecciate chimneys. Economic ore is found in the deposit in veins. Ore mineral include argentiferous galena (PbS), sphalerite (ZnS), pyrargyrite (Ag3SbS3), and other sulfosalts, and replacement “mantos.” The most mineralized zones are in the vicinity of the veins with the limestone.

IMMSA unit (underground mining poly-metallic division) operates five underground mining complexes situated in central and northern Mexico and produces zinc, lead, copper, silver and gold, and has a coal mine. These complexes include industrial processing facilities for zinc, lead, copper and silver. All of IMMSA’s mining facilities employ exploitation systems and conventional equipment. IMMSA’s principal mining facilities include Charcas, Santa Barbara, San Martin, Santa Eulalia and Taxco.

The Charcas mine uses the hydraulic cut-and-fill method and the room-and-pillar mining method with descending benches. [Form 10-K 2013. P.56]

The horizontal cut-and-fill mining method is used at the San Martin mine.
[Form 10-K 2013. P.59].

The mining operations at Santa Barbara are more diverse and complex than any of the other mines in our Mexican operations, with veins that aggregate approximately 21 kilometers in length. Due to the variable characteristics of the ore bodies, four types of mining methods are used: shrinkage stoping, long-hole drilled open stoping, cut-and-fill stoping and horizontal bench stoping.


The Taxco mining complex includes several underground mines (San Antonio, Guerrero and Remedios) and employ shrinkage, cut-and-fill and the room and pillar mining methods at the mines.
[Form 10-K 2013. P.60]

The Nueva Rosita coal and coke complex began operations in 1924 and is located in the state of Coahuila, Mexico on the outskirts of the city of Nueva Rosita near the Texas border. It includes a) an underground coal mine, which has been closed as a result of an accident in 2006; b) an open-pit mine with a yearly capacity of approximately 350,000 tons of coal; c) a coal washing plant completed in 1998 with a capacity of 900,000 tons per year that produces clean coal of a higher quality; and d) a re-engineered and modernized 21 oven coke facility capable of producing 100,000 tons of coke per year (metallurgical, nut and fine) of which, 95,000 tons are metallurgical coke.
[Form 10-K 2013. P.62].

On February 19, 2020, the Company announced the decision to return the underground coal mine, (the Olivo concession), which had been closed since 2006.

The San Luis Potosi electrolytic zinc refinery was built in 1982 and was designed to produce 105,000 tons of refined zinc per year by treating up to 200,000 tons of zinc concentrate from our own mines, principally Charcas, which is located 113 kilometers from the refinery. The refinery produces special high grade zinc (99.995%), high grade zinc (over 99.9%) and zincbased alloys with aluminum, lead, copper or magnesium in varying quantities and sizes depending on market demand. Refined silver and gold production is obtained from tolling services provided by a third party mining company.

The electrolytic zinc refinery has an acid plant, a steam recovery boiler and a roaster. There is also a calcine processing area with five leaching stages: neutral, hot acid, intermediate acid, acid, purified fourth and jarosite, as well as two stages for solution purifying.