The Cusi Project area lies within a possible caldera that contains a prominent rhyolite body interpreted as a resurgent dome. The rhyolite dome hosts mineralization and trends northwest-southeast with an exposure of roughly 7 by 3 km. It is bounded (cut) on the east side by strands of the NW-trending Cusi fault and on the west by the Border fault. The Cusi fault has both normal and right-lateral slip senses. Strands of the Cusi fault are intersected by NE-trending faults, some of which indicate left-lateral strike-slip shear. NE trending veins associated with these faults dip steeply either NW or SE. High-grade and wide alteration and mineralization zones exist in the areas of intersection of NW and NE structures.

The Cusi fault is a regional fault that may have controlled the location of the caldera and resurgent dome. Continued movement on the Cusi and related faults cut and brecciated the caldera and dome rocks and provided conduits for mineralizing fluids.

Numerous mineralized veins on the property, typically moderately to steeply dipping to the southeast, southwest, and north, range from less than 0.5 m to 2 m thick, extend 100 m to 200 m along strike and up to 400 m down-dip. There are at least six major mineralized veins within the Cusi area, described below. Small open pits were typically developed at vein intersections. Mineralization mainly occurs in faults, epithermal veins, breccias, and fractures ranging from 1 to 10 meters thick.

Two of the mineral resource areas, Promontorio and Santa Eduwiges, are modeled as structurally complex zones at the intersection of NW and NE trending structures that display discrete vein mineralization as well as a disseminated-style to highly fractured/stockworked mineralization surrounding discrete veins. The remaining two resource areas, San Juan and La India, are modeled as simple, typical epithermal vein deposits with one or a few easily identified, discrete veins.

The La India and San Juan resource areas are more traditional epithermal vein structures. These areas were modeled as discrete veins based on high grade intervals and surface structural mapping.

Current production at Cusi comes from the Promontorio and Santa Rosa de Lima mineralized zones.

Each mine area is accessed from a spiral ramp (4 meters square), as well as a single shaft in each area. Minimal development is needed to exploit mineralized zones, and contract miners are developing ramps at both mines to exploit ores at depth.

Mineralized material is currently hauled to the surface using one of several adits or declines accessing the mineralized zones, and is then dumped onto small pads outside of the portals.

The mining sequence through this method is of a descending type, that is, the upper levels are mined, while in the lower ones the necessary preparations are made to start mining once the mineralized material has been extracted from the upper stopes. Within a sublevel, mining is carried out in retreat, starting at the ends of the stope and retreating towards the entrance.

Bench and Fill
In veins less than 3 m wide, sublevels are vertically spaced 16 m, and the access drift is 4 m x 4 m. Blastholes are vertically drilled 8.5 m thus leaving a sill pillar of 3.5 m under the overlying stope.

In veins wider than 3 m but less than 5, sublevels are vertically spaced 16 m, and the access drift is 4 m x 4 m. Blastholes are vertically drilled 8.5 m thus leaving a sill pillar of 3.5 m under the overlying stope.

Room and Pillars
Where veins are wider than 5 m, levels are spaced every 16 m and mining is carried out using the room and pillar mining method. Pillars are 7 m x 7 m and square rooms span 7 m x 7 m.

Stopes have access drifts of 4 m x 4 m. Fanned blastholes are drilled to develop the room with a maximum vertical height excavated to 12.5 m (as measured from floor) thus leaving a 3.5 m sill pillar under the overlying stope.

Cut and fill
Mining at the Cusi Mine is completed by cut and fill method. Mined development rock is trucked 37 km via flat, paved roads to the Company’s Malpaso mill, which is a conventional flotation processing plant. [AIF 2020, p.17]

The concentrator's processing facilities include a crushing circuit consisting of a 50 t bulk hopper, a Metso TK9-32-22V vibratory feeder, a C96 Metso jaw crusher, an HP300 secondary cone crusher, a tertiary cone crusher HP300, a 6’x 20’ Trio double-bed primary vibrating screen, a 6’x20’ Trio double-bed secondary vibrating screen and a 5’x14’ double-bed secondary vibrating screen. The material is crushed to 90% passing -5/16" and is then deposited into three fine hoppers with an aggregate storage capacity of 1000 t.

The grinding circuit consists of a 7’x 10’ ball mill with a 250 HP motor, an 8’x 7’ ball mill with a 250HP motor and an 8’x14’ ball mill with a 600HP motor, and the classification system consists of D20 hydrocyclones.

The Cusi processing facilities include two interconnected process plants, which are the Mal Paso mill purchased from Rio Tinto, and the El Triunfo (Triungo) mill. Both mills are conventional ball mill and flotation plants fed from a single crushing circuit. The flotation circuit has the ability to produce lead concentrate and zinc concentrate, although the Pb circuit represents a comparably higher percentage of concentrate production.

El Triunfo includes a cyanide leach plant that has been used to process legacy tailings and, at times, fresh tails from Mal Paso. The leach plant was idled in mid2012 with no indication that it is scheduled to restart.

Cusi’s Mal Paso processing facility consists of a conventional concentration plant including crushing, grinding, flotation, dewatering of final concentrate, and a tailings disposal facility.

The Triungo circuit, which has a capacity of 400 tpd, produces a copper concentrate and a zinc concentrate. The Mal ........