The principal mineral deposits in the Platosa area are high-temperature epigenetic silverlead-zinc carbonate-replacement deposits (CRD).

The Platosa Property lies in the Sierra Bermejillo, a northwest-trending anticline-syncline pair developed in Mesozoic sedimentary rocks. The Sierra Bermejillo Anticline is a relatively open fold that plunges to the southeast. The Saltillera Syncline is a doubly plunging structure located west of the anticline. The folded sequence is cut by a set of north- to northwest-striking, steeply dipping fractures and faults. Tertiary felsic to intermediate dykes and plutons intrude these structures in the western part of the Sierra Bermejillo.

The principal fault system in the property area is the Platosa Structural Zone (PSZ), a 250 to 1,500 metre-wide northwest-trending zone of fracturing and shearing that traverses the eastern margin of the Sierra Bermejillo. The PSZ includes a series of fault planes that strike north–north westerly and dip steeply east; it has been mapped along strike for five kilometres northwest and southeast of the Platosa Mine. It is characterized by brecciated, crushed, and dolomitized limestone; slickenside fracture surfaces; iron and manganese oxides; travertinefilled breccias; and coarsely crystalline selenite veins, some up to five metres thick. The faulted rocks weather recessively and create a negative topographic expression of the PSZ.

Mineralization
The bulk of mineralization currently defined on in the Platosa Property occurs as shallow to steeply dipping bodies of massive CRD. These bodies have been identified and categorized as discrete pods or mantos based on structural setting and concentration of sulphides.

The footprint of the Platosa Property manto system currently measures approximately 400 by 700 metres. Mantos at the Platosa Property dip in accordance with the stratigraphy towards the east where a series of late extensional features down-drop the mineralization so that its depth ranges from 60 metres below surface on the west side of the Platosa Mine to approximately 320 metres below surface at the NE-1 manto, on the east side of the Platosa Mine.

The main lead-, zinc-, and silver-bearing minerals are:
• Galena (main lead-bearing mineral);
• Sphalerite (main zinc-bearing mineral); and
• Acanthite and lesser proustite (main silver-bearing minerals). Acanthite is predominant; proustite is visible where grades typically exceed the average grade of the mineralized body.

These deposits are hosted in carbonate rocks, distal to felsic intrusions that are interpreted to provide the Hydrothermal source of mineralizing fluids. Deposits are characterized by irregularly shaped pods, lenses, and roughly tabular or tubular masses of massive sulphide mineralization. Discordant bodies (chimneys) and roughly concordant elongate masses (mantos) can extend for thousands of metres from the source of the mineralizing fluids and often follow complex disjointed paths through the host rocks.

The massive sulphide bodies commonly grade progressively into mineralized metasomatic skarn deposits proximal to the source intrusions. This proximal mineralization includes skarns developed along fractures, dykes and sill contacts, and as large irregular lenses at the contact with the intrusion. Locally, mineralized veins cut both the skarns and host intrusions. Contact metamorphic features (recrystallization to marble, development of hornfels and skarnoid) commonly occurs peripheral to the skarn zone. Skarnoid mineralization and indications of skarnoid or intrusion related mineralization have been noted at various targets on the project including, Saltillera, at depth below the Platosa Mine and most notable to date at Rincon del Caido. Other Skarn type targets on the property include the conceptual PDN target approximately 1.7 km north of the deposit at the Platosa Mine.

All aspects of CRD and skarn mineralization are controlled by local and regional structures such as faults, fractures, contacts, fold axes, and collapse (paleokarst) zones. Secondary host rock permeability (such as fractures, breccias, solution cavities, dolomitization) can also be an important controlling factor for mineralization (Megaw et al. 1988).

The primary mining method has historically been a modified room and pillar, with the top of the manto being accessed first. For steeply dipping mantos, the area is benched down to a maximum height of 20 metres at which point a sill pillar is established. This process is repeated below the sill pillar until the bottom of the manto is reached. Historically, sill pillars were seldom necessary considering the flat-lying nature of the mantos, although these will become necessary where the mineralized body dips more steeply.

In 2019, the Platosa Mine transitioned the mining method from cut and fill/drift and fill to an overhand cut and bench method (“OCB”) to improve the overall mining cycle efficiency.

Primary stope accessesfor the OCB method are driven into the deposit horizontally and subsequent bench cuts are conducted until the sill elevation isreached. A cemented rock fill mat is placed on the sill elevation and the remainder of the stope filled with dry rock fill. The sill pillar above is then long hole drilled and blasted on retreat and mucked with a remote scooptram. It is then filled remotely when the pillar extraction is complete. The sequence has a higher cycle efficiency requiring fewer man-hours to extract the stopes than the previous cut and fill method. Development waste from active headings as well as waste that has been stockpiled underground is used to backfill the stopes.

The completion of a dewatering project has allowed the Platosa Mine to increase mechanization. Jacklegs have been replaced with jumbos in certain production areas, improving safety and productivity.

Mineralized material is hauled to surface using one 20-tonne haul truck and three 16-tonne haul trucks. The mineralized material is placed at surface at either the low-grade or high-grade stockpile. A wheel loader transfersthe material from the stockpilesinto the crusher; the material isthen crushed to lessthan 200 millimetres. The crushed material is hauled in 40-tonne covered trucks to Miguel Auza Mill, 220 kilometres away.

Crushing and Grinding
Oversized run-of-mine ore (+200 millimetres) is fed to the Platosa 900-tonne-per-day jaw crusher and any ore greater than 400 millimetres is reduced by a rock breaker and fed to the jaw crusher at Platosa. The sized ore is then shipped in 38-tonne covered trucks to the Miguel Auza processing facility located 220 kilometers South of the mine. The ore is blended in the stockpile area using a wheel loader with a combination of metallurgical criteria to provide a more stable feed grade to the flotation circuit. Oversized ore reports to the crusher circuit at Miguel Auza, which is comprised of a jaw crusher, cone crusher and a double-deck grizzly. This crushing circuit reduces the ore to 80% passing 9.5 millimetres that feeds the 600-tonne capacity fine material bin.

From the 600-tonne bin, the crushed material is fed into a 650-tonne-per-day ball mill. The ball mill is 3.0 metres in diameter and 3.2 metres in length and reduces the material to 80% passing 45 micrometres. The ball mill operates in a closed circuit and uses cyclones to separate the fine particles and transfer the cyclone overflow to the lead conditioning tank ahead of the lead flotation circuit.

Mineralized material from the Platosa Mine is shipped to the Miguel Auza processing facility, located 220 kilometres south of the mine. The Miguel Auza mineral processing facility operates two circuits: one for lead-silver and one for zinc-silver.

The Miguel Auza processing facility has been treating silver-, lead-, and zinc-rich CRD Platosa mineralization since 2009. The facility was initially designed and constructed to process material from the lower-grade Miguel Auza mine at a rate of 650 tonnes per day. Modifications were made in 2009 to ensure that the facility would be able to process the higher-grade feed; the flotation cells have been operating at 325 to 350 tonnes per day since that time. The unused cells are still on site and can be put back into production if required. The Miguel Auza processing facility currently produces two concentrates: a lead-silver and a zinc concentrate.

Lead Flotation
Ball mill product enters a lead conditioning tank wh ........