The Charcas district presents a complex magmatic history. The swarm dikes consist predominantly of monzogranite, granodiorite, and granite. They represent four distinctive magmatic pulses dated at 157, 50, from 48 to 45, and 30 Ma.

Two main types of mineralization are found at Charcas. IMMSA describes the mineralization as either veins or replacement bodies (in the form of skarn/mantos). The mineralization of Charcas is associated to fracture systems that strike at N65°W to N80°E and dip up to 70°NE and up to 60°SW. Near the Tiro General Mine, there is fissure-fill mineralization, which forms parallel to the contact between the intrusive and the limestones. Vein Leones is hosted in limestone, and the Santa Isabel vein is hosted in the intrusive and is characterized by reduced widths. The formation of the mineralized fissures is associated to normal faulting.

The Principal Fault (which runs parallel to the Temeroso intrusive stock boundary) cuts all the mentioned veins. Many replacement orebodies are reported to be occurring along the fault. El Rey and La Reyna replacement orebodies are generated by the Leones-Santa Isabel trend to the west of the Principal Fault. Parallel to the Temeroso intrusive contact is the Bufa Fault that controls other replacement mineralization.

Replacements occur as massive sulfide ore, breccia ore, and as banded white tiger ore (Levresse et al., 2015). The mineralization of the veins and the associated replacements are similar, including the following hypogene and supergene minerals: arsenopyrite, pyrite, sphalerite, tetrahedrite, galena, bornite, covellite, digestive, chalcocite, native silver, and hematite goethite. This mineralogy is typical of Pb-Zn-Cu-Ag deposits in carbonate rocks. The Leones vein type is considered to be the first stage of mineralization and the second related to the Santa Isabel type, which have copper and silver enrichment associated. Copper contents increase with depth, and lead and silver values decrease towards the east, whereas zinc and copper increase. Lead decreases at depths below 250 m.

The replacements have irregular forms and sometimes are tabular, indicating that some beds are more replacement favorable. The extension and distribution of the replacements following the structural trends, and the contact with the intrusive is very variable. The horizontal extension of the replacements and veins reach up to 1,000 m in the area of San Bartolo, 550 m in Leones, and 600 m in Aurora. The mineralization is open at depth, and the tested vertical extension in San Bartolo and Leones is approximately 900 and 450 m in the area of Aurora.

The Charcas deposit, as currently known, extends 2.6 km west-northwest to east-southeast and 2.8 km north-northeast to south-southwest.

The mineral deposits found within the Charcas mining district are Tertiary polymetallic skarn (Ag, Pb, Zn, and Cu) deposits hosted in carbonate rocks of the Jurassic-Cretaceous period and in shales and sandstones of the Late Triassic. In the carbonate rocks, veins and mantos form the predominant mineralization, while less-mineralized fractures tend to occur within the shales and sandstones. The varied style of mineralization largely corresponds to the lithological variety of units that serve as host rocks.

Fracture filled mineralization is a characteristic of hypothermal processes. These deposits are representative bodies as veins, with the most important veins at the mine being those of Leones and Santa Isabel veins. This group of veins occupy a fault zone in the contact between the limestones and the intrusive rock. It is evident that the original deposits were subject to the processes of oxidation and supergene enrichment in the most superficial part, which consisted of the solution and deposit of silver ores due to the percolation of surface waters.

The mineralogy of the economic mineralization is comprised predominantly of chalcopyrite, sphalerite, galena, and silver minerals as diaphorite (Pb, Ag, Sb, and S).

The Charcas complex includes three underground mines: San Bartolo, Rey-Reina and LaAurora.

Charcas is exploited underground by room and pillar with hydraulic cut and fill. The crushed ore is transported to the surface for processing in the flotation plant.

Mining is completed using a mechanized cut-and-fill mining method with rockfill. Ramps and levels are developed to provide access to the ore. Attack ramps are then driven to access each cut. The ramps and level development are performed using jumbos.

Mineral processing is completed via conventional flotation processes with three concentrates being produced (in order of scale):
• Zinc concentrate;
• Copper concentrate;
• Lead concentrate.

The mineral benefit plant was built with the purpose of concentrating the metallic minerals of interest (zinc, copper, and lead) and has a nominal capacity to process 4,100 tons/day.