The Pinos Altos mine is in the northern part of the Sierra Madre geologic province, on the northeast margin of the Ocampo Caldera, which hosts many epithermal gold and silver occurrences, including the nearby Ocampo and Moris mines.

The property is underlain by Tertiary-age (less than 45 million years old) volcanic and intrusive rocks that have been disturbed by faulting. The volcanic rocks belong to the lower volcanic complex and the discordant overlying upper volcanic supergroup. The lower volcanic complex is represented on the property by the Navosaigame conglomerates (including thinly-bedded sandstone and siltstone) and the El Madrono volcanics (felsic tuffs and lavas intercalated with rhyolitic tuffs, sandy volcanoclastics and sediments). The upper volcanic group is made up of the Victoria ignimbrites (explosive felsic volcanics), the Frijolar andesites (massive to flow-banded, porphyritic flows) and the Buenavista ignimbrites (dacitic to rhyolitic pyroclastics).

Intermediate and felsic dykes as well as rhyolitic domes intrude all of these units. The Santo Nino andesite is a dyke that intrudes along the Santo Nino fault zone.

Structure on the property is dominated by a ten-kilometre by three-kilometre horst, a fault-uplifted block structure oriented west-northwest, that is bounded on the south by the south-dipping Santo Nino fault and on the north by the north-dipping Reyna de Plata fault. Quartz-gold vein deposits are emplaced along these faults and along transfer faults that splay outwards from the Santo Nino fault.

Mineralization
Gold and silver mineralization at the Pinos Altos mine consists of low sulphidation epithermal-type hydrothermal veins, breccias and bodies. The Santo Nino structure outcrops over a distance of roughly six kilometres. It strikes at 60 degrees azimuth on its eastern portion and turns to strike roughly 90 degrees azimuth on its western fringe. The structure dips at 70 degrees towards the south. The four mineralized sectors hosted by the Santo Nino structure consist of discontinuous quartz rich lenses named from east to west: El Apache, Oberon de Weber, Santo Nino and Cerro Colorado.

The El Apache lens is the most weakly mineralized. The area hosts a weakly developed white quartz dominated breccia. Gold values are low and erratic over its roughly 750 metre strike length. Past drilling suggests that this zone is of limited extent at depth.

The Oberon de Weber lens has been followed on surface and by diamond drilling over an extent of roughly 500 metres. Shallow holes drilled by the Company show good continuity both in terms of grade and thickness over roughly 550 metres. From the drilling done by a previous owner, continuity at depth appears to be erratic with a weakly defined western rake.

The Santo Nino lens is the most vertically extensive of these lenses. It has been traced to a depth of approximately 750 metres below the surface. The vein is followed continuously on surface over a distance of 550 metres and discontinuously up to 650 metres. Beyond its western and eastern extents, the Santo Nino andesite is massive and only weakly altered. Gold grades found are systematically associated with green quartz brecciated andesite.

The Cerro Colorado lens is structurally more complex than the three described above. Near the surface, it is marked by a complex superposition of brittle faults with mineralized zones which are difficult to correlate from hole to hole. Its relation to the Santo Nino fault zone is not clearly defined. Two deeper holes drilled by the Company suggest better grade continuity is possible at depth.

The San Eligio Zone is located approximately 250 metres north of Santo Nino. The host rock is brecciated Victoria Ignimbrite, occasionally with a stockwork style of mineralization. There is no andesite in this sector. Unlike the other lenses, the San Eligio lens dips towards the north. The lateral extent of the zone seems to be continuous for 950 metres. Its average width is five metres and never exceeds 15 metres. Surface mapping and prospecting has suggested that there is good potential for additional mineralization on strike and at depths below 150 metres. Visible gold has been seen in the drill core.

The Creston Mascota deposit is seven kilometres northwest of the Santo Nino deposit, and is similar, but dips shallowly to the west. The Creston Mascota deposit is approximately 1,000 metres long and four to 40 metres wide, and extends from surface to more than 200 metres depth. Several other promising zones are associated with the horst feature in the northwest part of the property.

The Cubiro deposit is a near-surface deposit located two kilometres west of the Creston Mascota deposit. Cubiro strikes northwest, has a steep dip and has been followed along strike for approximately 850 metres. Drilling has intersected significant gold and silver mineralization up to 30 metres in width. The Cubiro deposit is split by a fault that resulted in 200 metres of displacement to the west, as defined by drilling to date. The zone is still open to the southeast and possibly at depth.

The Sinter Zone is 1,500 metres north-northeast of the Santo Nino Zone and is part of the Reyna de Plata gold structure. The steeply dipping mineralization ranges from four to 35 metres in width and almost 900 metres long, with over 350 metres of vertical depth.

The Pinos Altos operation has been a series of open pits and an underground mine along the Santo Niño Fault. Surface mining was carried out at the Santo Niño, Oberon de Weber, San Eligio and El Apache pits using conventional open pit mining methods with shovels and trucks. The underground mining method is sublevel stoping (paste backfill) to extract ore from the Santo Niño, Cerro Colorado and Oberon de Weber deposits. The shaft project for hoisting underground ore was completed in mid-June 2016, increasing the planned capacity of the underground mine to 4,500 tonnes/day. Underground mining of the Santo Niño crown pillar began in late 2017, using long-hole sublevel stoping from surface to extract ore, and was completed in April 2019 — completing the transition of Pinos Altos from a combination surface and underground mine to a fully underground operation.

At the Sinter deposit, located approximately 2 km northwest of the Pinos Altos mine site, production started in the fourth quarter of 2020. The underground mine and small open pit are expected to provide additional flexibility to the Pinos Altos operation in 2021.

Ore from the Pinos Altos mine is treated by one of two processes: conventional processing in a mill for higher-grade ore; and a minor amount of heap-leaching for lower grade ore.

The conventional, 5,500-tonnes/day processing plant includes crushing, grinding, gravity concentration and agitated leaching followed by counter-current decantation. During 2017, the Company commissioned a silver flotation plant, which has increased overall silver recovery to an average of 22% in the flotation plant. Gold and silver are recovered using the Merrill-Crowe method, and a refinery produces gold/silver doré bars on site. Metals recovery in the plant averages approximately 94% for gold and 58% for silver.

In 2019, the Company began testing samples from Pinos Altos and La India at an ore sorting pilot plant at Pinos Altos, with favourable preliminary results. Similar ore sorting pilot testing has been considered at the Company's other operating sites.