The principal mineral deposits in the Platosa area are high-temperature epigenetic silverlead-zinc carbonate-replacement deposits (CRD). The Platosa Mine lies in the Sierra Bermejillo, a northwest-trending anticline-syncline pair developed in Mesozoic sedimentary rocks. Platosa is underlain by folded and faulted Mesozoic sedimentary rocks, locally intruded by dykes and sills of Laramide age. 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–northwesterly and dip steeply east; it has been mapped along strike for 5 kilometres northwest and southeast of the Platosa Mine (Megaw 2002). The Platosa Mine targets polymetallic (silver, lead, and zinc) mineralization occurring as shallow to steeply dipping bodies of massive carbonate replacement deposits or mantos. The main silver-, lead- and zinc-bearing minerals are galena, sphalerite, acanthite and lesser proustite. The mantos dip in accordance with the stratigraphy towards the east where a series of late extensional features extend the mineralization to depths ranging from 60 metres on the west side of the mine, and approximately 320 metres on the east. Mineralization The bulk of mineralization currently defined on the Platosa Mine occurs as shallow to steeply dipping bodies of massive carbonate-re ........

Access to the underground mine is by ramp through a portal collared near the administration building. The primary mining method has historically been a modified room and pillar, with the top of the manto being accessed first. During late 2019 to early 2020 the Platosa Mine transitioned the mining method from cut and fill/drift and fill to an overhand cut and bench method to improve the overall mining cycle efficiency. Drift and fill is still used where the mantos are flat lying. The overhand cut and fill method is the primary mining method currently used at Platosa. The top cut is driven along the upper stope elevation to define the stope width and length. Fully grouted 5-metre post-tensioned cable bolts are installed in the hanging wall in a pattern sufficient to support the estimated final stope dimensions using the hydraulic radius as the primary ground support design parameter. The next lift is taken as a 2-metre bench with ground support installed in the hanging wall as the bench is removed. A second 2-metre bench is taken, ground support installed, and the opening backfilled with 2-metre of cemented rock fill (CRF) placed on the floor and the remaining opening filled with waste rock. The stope below is mined in the same manner. However, a 2-metre sill is left to control the back of the stope on the elevation below. After the lower stope is mined and partially backfilled the 2-metre sill is drilled from beneath with vertical blast holes. A drop raise is excavated on t ........

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