Deposit Types
All mineralization at Cozamin occurs in veins, and fracture-controlled systems of veinlets. Currently mined mineralization at Cozamin is best described as intermediate sulphidation. The copper-rich intermediate sulphidation mineralization is an early phase that is enveloped, overprinted or brecciated by zinc-rich intermediate sulphidation mineralization. The copper veins are inferred to be higher temperature, have significantly fewer vugs and can be massive pyrrhotite-pyrite-chalcopyrite with little gangue. Zinc-rich veins also tend to be sulphide rich, like the copper-rich ones, but with slightly more gangue. Well-banded quartz, or quartz-carbonate veins are inferred to be lower temperature and best classified as low sulphidation. They often have open space filling textures with quartz druse vug linings and typically gold and silver rich with lesser base metals and are generally not being mined today, but were historically important.

This transition from intermediate sulphidation copper-dominant mineralization to intermediate sulphidation zinc-dominant mineralization is thought to be the result of an evolving, telescoped hydrothermal system. Blocks or fragments of massive chalcopyrite-pyrite-pyrrhotite mineralization enveloped by zinc-dominant mineralization are observed in drill core and in mine workings. This telescoping system is closely associated with the district’s largest center of rhyolite flow domes which may be the shallow expression of a hidden, inferred buried felsic stock.

Mineralization
Cozamin’s dominant mineralized vein systems include the MNV and the MNFWZ. On surface, the MNV was mapped for 5.5 km across the property. It strikes approximately EW and dips on average at 60° to the N. There are several shafts that provide access to the historical workings at Cozamin. The largest historical mined area is San Roberto with a strike length of 1.4 km, and the second largest mined area is San Rafael mine with a strike length of 0.5 km. Mineralization peripheral to these workings was the principal target of Capstone’s early exploration programs at Cozamin. The MNFWZ is not exposed at surface, principally because the majority of the strike extent lies beneath the tailings pond. However, based on drilling it strikes approximately 145° over a length of more than 2.2 km and dips on average 54° to the NE.

The MNV system occupies a system of anastomosing faults. The mineralized bodies within the Mala Noche Fault System appear to be strongest where the individual faults coalesce into a single fault zone. Results from exploration and mine development to date indicate that some of the strongest mineralization in the San Roberto mine plunges to the west at approximately -50° within the vein. Post mineralization offsets of the MNV are minimal and occur along high angle, normal faults that strike northeast. The MNFWZ comprises multiple veins in close spatial association with rhyolite dikes and locally cross-cut the intrusions themselves. The relative age of the copper mineralization ranges from contemporaneous with to perhaps slightly post the rhyolite magmatism. Similar to the MNV, post mineralization offsets at the MNFWZ are minimal and occur along high angle normal faults.

Mineralization in the MNV at Cozamin appears to have been episodic. Intermediate sulphidation pyrite-pyrrhotite-chalcopyrite dominant mineralization is enveloped, overprinted or brecciated by younger sphalerite dominant intermediate sulphidation epithermal alteration and mineralization in a telescoped, intrusive related hydrothermal system. Well-banded quartz, or quartz-carbonate veins, best classified as low sulphidation are also observed but are generally volumetrically insignificant in the area of the mine. These veins have open space filling textures with quartz druse vug linings. The MNV in the San Roberto mine workings shows contained sulphides to occur as disseminations, bands and masses. The San Roberto area hosts both the copper dominant and zinc dominant epithermal events, whereas the San Rafael area is only associated with the zinc dominant epithermal event. Both events are also present at MNFWZ, however unlike San Roberto the events do not overprint each other and are separated into copper dominant or zinc dominant veins. Conclusions about mineralization styles are based on observations in drill core and the exposure of the copper-silver phase of mineralization in mine workings, however a large portion of the upper parts of the mine are not accessible.

Pyrite is the dominant vein sulphide and typically comprises approximately 15% of the MNV in the San Roberto mine. It occurs as fine disseminations and veinlets, coarse crystalline replacements, and pseudomorphs of epithermal textured carbonate minerals and possible barite. Arsenopyrite typically occurs as minor, microscopic inclusions in pyrite. Pyrite content in the MNFWZ veins is typically greater than 20%.

Pyrrhotite is the second most common sulphide mineral but is present only in the intermediate and deeper levels of the San Roberto mine, and the up-dip portion of the MNFWZ. It occurs as replacement masses, pseudomorphs of platy masses and acicular replacements probably after amphibole. Pyrrhotite commonly occurs as an envelope to, or intermixed with, strong chalcopyrite mineralization. Pyrrhotite ranges from monoclinic to hexagonal, or a combination of these polytypes.

Chalcopyrite is the only copper sulphide recognized visually at Cozamin. Like pyrrhotite, it is more common at the intermediate and deeper levels of the mine. It occurs as disseminations, veinlets and replacement masses. These masses appear to be fractured and brecciated at intermediate levels in the mine. Mineralization at the MNFWZ in the copper dominant veins is chalcopyrite dominant in contrast to the polymetallic nature of the main MNV.

Sphalerite is the dominant economic sulphide in the upper levels in the San Roberto mine and throughout the San Rafael mine. Most of the sphalerite is marmatitic. It occurs as disseminations and coarse crystalline masses and is commonly marginal to the chalcopyrite-dominant portion of the vein. Sphalerite is locally present in the MNFWZ copper dominant veins, shifting to the dominant sulphide in the zinc dominant veins.

Franklinite, a zinc oxide in the spinel group of minerals, accounts for some of the zinc mineralization in the MNV. Recovery of zinc is lower in areas of franklinite mineralization.

Galena is less common than sphalerite but is generally associated with it. Where it is abundant, it occurs as coarse crystalline replacement masses. Both coarse and fine crystalline masses of galena are argentiferous. Argentite is the most common silver mineral. It has been identified microscopically occurring as inclusions in chalcopyrite and pyrite. Assays indicate that silver is also probably present in sphalerite and galena. Bismuth and silver selenides occur as inclusions predominantly in chalcopyrite and pyrite.

At MNV and MNFWZ, moderate propylitic wall rock alteration is generally limited to 3 m into the hangingwall and footwall. The main gangue minerals are quartz and calcite, and in some cases rhodochrosite, gypsum, barite, or ilvaite. The quartz occurs as coarse-grained druse crystalline masses, and cross-cutting quartz veinlets.

Cozamin used LHOS as the primary bulk mining method, supported by horizontal drifting to develop the access for stoping. Historically, Cut-and-Fill mining methods and a version of the Modified AVOCA mining method have been employed at Cozamin but are not used in this Mineral Reserve estimate. The LHOS mining method has proven to be a scalable method for use at Cozamin, allowing production to steadily increase since Capstone took ownership. Major levels are separated by sill pillars and extend along strike to each extent of the vein domain being mined.

Longitudinal long-hole open stoping operates along or parallel to the strike of the vein. The orientation of the method means that the hangingwall and footwall of the vein will form the sidewalls of the stope. The method is commonly used in narrow-vein mines where the orebody continues for a large extent along strike and dip. LHOS requires competent rock in the hangingwall and footwall in order to support a large void. As employed at Cozamin, the LHOS method is entirely bottom-up extraction on retreat within stoping panels. Although the method requires high capital development ramp to access the development levels, much of the sublevel development necessary to expose stopes is mined economically as ore production as the cuts can be kept within the vein.

Cozamin backfills each stoping sublevel prior to mining the sublevel above. The backfill used is unconsolidated waste development rock from other areas of the mine.

The production schedule is based on a general rule set of mining dependencies. When ramp development reaches stoping levels, in-vein production development begins expanding from the access along strike in both directions. Each of the approximately 57 m to 60 m panels consists of three sublevel production development drifts. The stoping activity starts when the upper and lower sublevel development drifts for the lowest stoping sublevel are completed. Long-hole drills are used to drill down-holes (up-holes on third sublevel) from the upper sublevel to the lower sublevel. These holes are loaded with an explosive product (usually ANFO prill, but sometimes emulsion in wet conditions) and blasted in 2 m to 6 m strike lengths. The blasted muck is removed by load-haul-dump (“LHD”) muckers on line-of-sight remote control and then the drilling cycle repeats.

Stoping proceeds from the outside (furthest away from the access along strike) back to center. Stoping is continued uninterrupted for up to 72 m along strike (this distance varies according to local geotechnical conditions), the entire distance between rib pillars forming a stope “cell” after which a vertical rib pillar is left in-situ. The stoping resumes after leaving the rib pillar and this pattern continues until mining reaches the central access point.

After a single cell is mined, loose backfill is deposited in the empty cell from the upper sublevel by an LHD mucker. This loose fill creates the floor of the stoping activities for the next level above. After three sublevels are mined in this bottom-up, outside-in sequence, a horizontal pillar is left separating the completely mined and filled panel from the panels above and below. The mining activities continue in the panels above and/or below and the pattern is repeated. The sequence is constrained to vertical columns with a length of less than 200 m along strike as measured from the ramp access for the level. The division of columns in this manner allows for parallel mining activities to occur at several locations along strike simultaneously.

Ore is presently trucked from the headframe bin and underground ramps to a surface stockpile for blending to produce a consistent copper feed grade. The surface stockpile of approximately 10,000 tonnes is reclaimed by a front-end loader that feeds the material to a 100tonne bin. Ore reports to the 0.5 m x 0.9 m primary jaw crusher via belt feeder. A peak crushing capacity of 280 tph would be required based on an 85% overall crushing plant availability and a 75% utilization. The existing primary crusher is capable of sustaining this throughput rate. A second feed bin and feeder are installed that will allow the crushed underground ore, which represents approximately 45% of the total feed at the targeted production level, to bypass the surface jaw crusher. This ensures ample excess primary crushing capacity. A vibrating grizzly which would unload the surface primary crusher was planned for installation in 2019. This modification was not completed. This modification will need to be completed prior to increasing the throughput on a sustained basis in order to ensure targets are met with reasonable crushing availability and utilization rates.

Primary crusher product is conveyed to the secondary 1.52 m x 3.66 m vibrating screen ahead of the 1.22 m secondary standard head cone crusher. Screen oversize is fed to the secondary crusher with screen undersize combined with secondary crusher product. This material is conveyed to a 1.83 m x 4.88 m vibrating screen with oversize material conveyed to the tertiary crusher (Metso HP4) and undersize material being conveyed to the fine ore bins, for the two main ball mill circuits and original ball mill circuit. Tertiary crusher product is returned to the 1.83 m x 4.88 m screen. The secondary/tertiary crushing plant has been audited at steady state with throughput above the 280 tph target demonstrating the capacity of the plant to operate at this level with all motors drawing loads well below their rated maximums. Two 1,200-tonne capacity fine ore bins are available each feeding one of the two primary grinding lines in the milling circuit. Each bin provides approximately 20 hours storage for the respective grinding line at the current milling rate. This would drop to approximately 12 hours at the projected rates. This would require all extended maintenance activities in the crushing circuit to be scheduled together with the mill maintenance program. In addition, spare bowls and mantles for the secondary and tertiary crushers would be required to ensure rapid turn-around on steel changes.

Grinding
The milling section is composed of two primary ball mills operating in parallel. Each mill is 3.65 m in diameter by 4.27 m long. The original ball mill (2.8 m in diameter by 1.6 m long) grinding circuit was recommissioned to provide additional grinding capacity when mining the Avoca zone in 2013 and 2014 and again in 2018 to support the increase in throughput associated with processing the San Rafael ores. It is believed that some additional capacity would be needed to meet the grinding rates with the harder San Jose ores projected from 2021 onwards. This can be achieved by modifying the current mill discharge arrangements to increase the energy input capacity of the two primary grinding mills. This project has been approved and is scheduled during the first half of 2021. Both primary mills have 1,500 hp motors installed, but are operating at approximately 1,000 hp draft with the current internal configurations, which includes a discharge trommel insert that has allowed increasing the mill loading to approximately 40%. The modified discharge end design would increase the effective grinding length from 3.32 m to 4.12 m, a 23% increase. This modification will be completed in conjunction with a scheduled replacement of the mill discharge heads during the first half of 2021.

Grinding product size is an 80% passing (P80) 230 microns. Each ball mill is operated in closed circuit with a cyclone pack composed of 0.66 m diameter cyclones. Cyclone underflow reports back to the respective grinding mill with the cyclone overflow from both circuits reporting to a common flotation conditioning tank.

Lime is added to the grinding circuit for pH control throughout the circuit. Flotation reagents including a zinc depressant and a potential modifier are also added to the grinding circuit.

Flotation
Slurry from the grinding circuit is transported to the tank flotation cells for initial copper flotation. Concentrate from this initial stage of flotation reports directly to the copper cleaning circuit. The current mine plan does not contemplate production of lead concentrates from 2021 through 2026.

Tailings from the tank cells report by gravity to banks of rougher and scavenger flotation cells (6-OK 16 cells) for additional recovery of copper. The copper rougher concentrates report to a two-stage cleaning system. The original second stage cleaner cells have been replaced with a column cleaner which has improved the overall concentrate grade.

Copper rougher flotation tailings report to the zinc conditioner tank prior to zinc rougher flotation, where ........