Geological and structural features in the district are representative of large, disseminated type, porphyry copper deposits.

Mineralization in the district is extensive covering a surface area of approximately 30 square kilometers. An early pegmatitic stage associated with bornite-chalcopyrite-molybdenite assemblage was followed by a widespread flooding of hydrothermal solutions with quartz-pyrite-chalcopyrite. A pervasive quartz-sericite alteration is evident throughout the district’s igneous rock fabric.

An extensive and economically important zone of supergene enrichment, with disseminated and stockworks of chalcocite (Cu S), developed below the iron oxide capping. This zone coincides with the topography and has an average thickness of 300 meters. A mixed zone of secondary and primary sulfides underlay the chalcocite blanket. The hypogene mineralization, principally chalcopyrite (CuFeS ), extensively underlies the ore body. Molybdenite occurs throughout the deposit and the content tends to increase with depth.

The Buenavista copper porphyry is considered world-class and unique. The deepest exploration results in the core of the deposit have confirmed significant increase in copper grades. Similar porphyry copper deposits usually contain lower grades at depth. The district is also unique for the occurrence of high-grade breccia pipes, occurring in clusters following the trend of the district.

Current dimensions of the mineralized ore body are 5x3 kilometers, and projects to more than one kilometer at depth. Considering the geological and economic potential of the Buenavista porphyry copper deposit, it is expected that the operation can support a sizeable increase in copper production capacity.

The Buenavista mining unit operates an open-pit copper mine, two concentrators and three SX-EW plants.

Buenavista uses state-of-the-art computer monitoring systems at the concentrators, the crushing plant and the flotation circuit in order to coordinate inflows and optimize operations. In the original concentrator, material with a copper grade over 0.38% is loaded onto trucks and sent to the milling circuit, where giant rotating crushers reduce the size of the ore to approximately onehalf of an inch. The ore is then sent to the ball mills, which grind it to the consistency of fine powder. The finely ground powder is agitated in a water and reagents solution and is then transported to flotation cells. Air is pumped into the cells producing a froth, which carries the copper mineral to the surface but not the waste rock, or tailings. Recovered copper, with the consistency of froth, is filtered and dried to produce copper concentrates with an average copper content of approximately 24%. Concentrates are then shipped by rail to the smelter at La Caridad.

In the second concentrator, material with a copper grade over 0.555% is sent to a three-phase milling circuit, where the ore size is reduced to approximately one-half inch. The ore is then sent to a circuit of six ball mills, which grind it to the consistency of fine powder. The finely ground powder is agitated in a water and reagents solution and is then transported to flotation cells. Air is pumped into the cells producing a froth, which carries the copper mineral to the surface but not the waste rock, or tailings.

Recovered copper, with the consistency of froth, is filtered and dried to produce copper concentrates with an average copper content of approximately 24%. Concentrates are then sent by trucks or by railroad to the La Caridad smelter or to the Guaymas port, at Sonora, for exporting.

As part of the expansion program for this unit, in 2013 we completed the construction of the first molybdenum plant with an annual production capacity of 2,000 tons of molybdenum contained in concentrate. The plant was designed to process 1,500 tons of copper-molybdenum concentrates per day with a recovery of approximately 80% of copper and 50% of molybdenum content. The molybdenum plant consists of thickeners, homogenizer tanks, flotation cells, column cells and a holo-flite dryer. The second molybdenum plant was designed to process 3,040 tons of copper-molybdenum concentrates per day for a recovery between 80% and 87% of copper and 60% of molybdenum content. It obtained its first production lot in July 2016 and fully initiated operations in November 2016.

The Buenavista unit operates a leaching facility and three SX-EW plants. All copper ore with a grade lower than the mill cut-off grade of 0.38%, but higher than 0.25%, is delivered to the leach dumps. A cycle of leaching and resting occurs for approximately five years in the run-of-mine dumps and three years for the crushed leach material.

There are three irrigation systems for the dumps and eleven dams for the pregnant leach solution (PLS). Plant I has four solvent extraction tanks with a nominal capacity of 18,000 liters per minute of PLS and 54 electrowinning cells and has a daily production capacity of 30 tons of copper cathodes with 99.999% purity. Plant II has five trains of solvent extraction with a nominal capacity of 62,000 liters per minute of PLS and 220 cells distributed in two bays and has a daily production capacity of 120 tons of copper cathodes with 99.9% purity. Plant III has three trains of solvent extraction with a nominal capacity of 167,100 liters per minute of PLS and 270 cells distributed in two bays and has a daily production capacity of 328 tons of copper cathodes with 99.9% purity. The plant produces copper cathodes of LME grade A.