The San Jose de Gracia and Alta Gracia gold- silver sub-districts of the Don David Mine are characterized by classic, highgrade silver-gold, epithermal vein deposits with low to intermediate-sulfidation mineralization quartz-adularia-sericite alteration. The veins are typical of most epithermal silver-gold vein deposits in Mexico with respect to the volcanic or sedimentary host rocks and the paragenesis and tenor of mineralization. The Alta Gracia mineralization is typical of a lowsulfidation deposit. The Arista mine vein systems are intermediate-sulfidation in nature and standard of many Mexican deposits, characterized by Camprubí & Albinson, 2007, and described as Polymetallic Ag-Au by Corbett. The structural geology of the Alta Gracia area is somewhat masked at the surface by the presence of expansive soils and vegetation. However, numerous quartz veins are in accessible underground workings and prospect pits at Alta Gracia. Veins are mainly hosted in rhyolite at the surface, and andesite was developed in deeper underground mine workings. Two dominant vein trends have been mapped: N30°E dipping 65° - 85°NW and N50°E dipping 65° - 85°NW. Vein widths generally average from 0.2 meters to just over 2 meters (true width). At least nine significant veins/vein systems have been identified at Alta Gracia that include the following: • Mirador Vein - The Mirador vein is a fissure filling vein hosted in andesite with a bearing 240°-250°, a dip of 60°-80°NW and a variable thickness o ........

In 2017, in addition to the Arista underground mine, DDGM completed development of the Mirador Mine at the Alta Gracia Project and began delivering development ore to the Aguila processing facility. Two mine portals were developed to provide access to the Mirador vein. Mine site offices and mobile equipment maintenance facilities were established adjacent to the mine portals. Additionally, a diesel power generation plant, compressed air and a mine water pumping stations were developed. Operations at the Mirador Alta Gracia mine were temporarily halted in June 2020.

Ore is trucked from the mine and discharged onto ground. Ore is fed in a primary jaw crusher using a front head loader. Crushed ore from the primary crusher is screened onto a double deck screen. The first deck product is crushed by the secondary cone crusher. Crushed material is recirculated to feed the double deck screen. The screen second deck oversized products are crushed by a tertiary cone crusher. The tertiary cone crusher material is also recirculated to the feed of double deck screen. Finally, the double deck fine particle (-9.5mm) is stockpiled before being fed into the ball mills. The maximum crushing rate for this plant is about 110 tonnes per hour. The fine ore is stockpiled before being fed into the crusher and ball mills. The fine crushed ore is transported via conveyor belts to the flotation plant grinding circuit. Grinding circuit consists of two parallel ball mills. Each mill is in close circuit hydrocyclones, with cyclone overflow reporting to flotation circuit. A portion of the cyclone underflow reports to the gravity circuit, while the remainder of the cyclone underflow and gravity circuit tailing reports to the ball mill for further grinding. One ball mill is 3.2m diameter and 4.29m length driven by 798 kW motor. The second ball mill is 3.2m diameter and 3.68m length driven by 597 kW motor. Concentrate recovered by the Knelson concentrator is leached in an intensive leach reactor. When leaching is complete, the leached material is combined with a based metal concentrate which corresponds to the grade.

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