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

The Mexican CRD belt hosts deposits in excess of 80 million tonnes. The Platosa property, with its combination of CRD and skarn mineralization, shares similarities with many of these systems and other North American manto/CRD systems and demonstrates potential for the discovery of additional mineralized zones.

The bulk of mineralization currently defined on the Platosa project occurs as shallow to steeply dipping bodies of massive carbonate-replacement deposits (CRD). These bodies have been identified and categorized as discrete pods or mantos based on structural setting and concentration of sulphides. The main manto bodies currently defined at Platosa are listed below from west to east:
• Mantos 6A/6B
• Mantos 4A-C
• Manto 5
• Guadalupe
• Guadalupe South
• Pierna
• Rodilla
• Manto 623
• Manto 674
• NE-1
• NE-1 South.

The footprint of the Platosa manto system currently measures approximately 400 by 700 metres. Mantos at Platosa 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 mine to approximately 320 metres below surface at the NE-1 manto, on the east side of the mine.

The main lead-, zinc-, and silver-bearing minerals are:
• Galena (main lead-bearing mineral)
• Sphalerite (main zinc-bearing mineral)
• 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.

The most significant mantos at Platosa are the Rodilla, Pierna, Guadalupe South, Manto 674, and 623 mantos, which are currently mined; and the NE-1 and NE-1 south mantos, which are included in the mine plan and that are open for expansion. These mantos have been defined in drilling from surface with an average drill spacing of 15 to 20 metres. In 2016, Excellon commenced a program of infill and expansion drilling ahead of production. This drilling was conducted on 10-metre-spacing in production areas and has been successful in discovering and defining additional mineralization near existing mine infrastructure, most notably in the 623 and Guadalupe South areas.

Mineralization is also seen in the form of vein, breccia, and skarn systems in the following propertyscale exploration prospects:

• San Gilberto. Anomalous mineralization of 10 g/t silver has been intersected in drilling of north-south-oriented structures in 2006 (hole EX06STS01). Other structures, believed to be parallel to this one, have been exploited by small-scale miners at San Gilberto where the target appears to be a black siliceous vein. Prospecting results in this area by Excellon geologists have returned samples with elevated silver and base metal values.

• Jaboncillo. A trend of anomalous silver and base metal values measuring more than 1.0 kilometre was identified by company geologists in 2017. This trend is believed to indicate the presence of hotter mineralized fluids venting off a sulphide bearing fluid system that could be analogous to the mineralization at Platosa.

• Saltillera North and South. Skarn mineralization including epidote, pyrite, and chalcopyrite as well as silver values in excess of 600 g/t have been intersected in a hornfelsed unit (EX08ST78). These targets are also the site of historical small-scale silver and base metal mining.

• Halcon. Multiple structural intersections have been mapped here which are believed to be related to the emplacement of deeper intrusions into this sequence. Surface samples were anomalous in silver, lead, zinc, and arsenic.

• PDN. This geophysical target is defined by a large gravity anomaly coincident with resistivity anomalies. Structures and veins (calcite veining, silica veining and jasperoids) have been mapped on surface. Grab and surface samples have returned anomalous silver, lead and zinc and elevated arsenic values.

• Refugio. Located 1.4 kilometres southwest of the Platosa mine on the western flank of the Sierra de Bermejillo where several small-scale historical mine workings are present; this prospect consists of outcrops of irregular silica breccias and jasperoid. The silica breccias cut beds of the Cuesta del Cura Formation and do not appear to be controlled by any obvious structure. Several historical samples of silica material returned gold values up to 7.79 g/t. Lead, zinc, and silver values have been reported in both the jasperoids and silica breccia boulders.

• Rincon Del Caido. Skarn mineralization was intersected in drilling at a depth of approximately 500 metres, most notably in diamond drillholes EX12LP1019, EX12LP1023A, EX12LP1024, EXLP1025 and EX12LP1030. The mineralized zone consists of green garnet with dispersed pyrite and subsidiary sphalerite and galena; it measures approximately 120 by 140 metres and extends down plunge for approximately 80 metres; it may indicate a larger skarn system in the area and the potential for additional mineralization at depth.

• Zorra. A set of old artisanal workings mined for silver, lead, and zinc.

• Cañón Colorado. Excellon drilled holes into what is believed to be a rhyolite tuff that was enriched in rare earth elements. This area, located at the intersection of two regional faults, is believed to have potential to be a high-level portion of a mineralizing system.

• Cañón de la Güera. Prospecting and mapping led to initial drilling in this area. No significant mineralization has yet been intersected, although it is located in a structurally complex part of the northern PSZ.

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.

The Platosa 2,000 tonne-per-day primary jaw crusher reduces the run-of-mine mineralized material to less than 9.5 millimetres. Once crushed, the material is shipped by truck to the Miguel Auza processing facility located 220 kilometres south of the mine. An additional 1,000 tonne-per-day jaw crusher is located at Miguel Auza and can be used if the Platosa crusher is unavailable. Material is screened at the conveyor that feeds the 600-tonne capacity fine material bin; the oversize fraction is processed in a secondary cone crusher.

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 35 µm. The ball mill operates in a closed circuit and uses cyclones to separate the fine particles and transfer them to the lead circuit.

Crushed mineralized material from Platosa 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 whe ........