The Bolivar deposit is classified as a high-grade Cu-Zn skarn and exhibits many characteristics common to this deposit type (Meinert, 2007). The term skarn refers to coarse-grained calcium or magnesian silicate alteration formed at relatively high temperatures by the replacement of the original rock, which is often carbonate-rich.

Skarn alteration and mineralization at the Bolivar property is hosted primarily in a package of sedimentary rocks that occur as a layer or lens within the LVS (Reynolds, 2008). All sedimentary units have undergone low grade metamorphism. The lowermost sedimentary horizon observed is a dolostone which ranges from 24 m to 40 m in thickness. The lower part of the dolostone horizon is interlayered with siltstone. To the south, progressively less of the sedimentary sequence is cut out by granodioritic intrusive rocks and the dolostone is observed to be underlain by a siltstone horizon. The lower siltstone unconformably overlies the LVS. The dolostone is overlain by a discrete layer of siltstone. The average thickness of this siltstone unit is 12 to 30 m. Horizons of argillaceous dolostone (50 m thick) and argillaceous limestone (9 m thick) are above the siltstone marker layer. The uppermost sedimentary horizon is a limestone with local chert and argillaceous laminations. The vertical thickness of this horizon varies considerably in cross-section (108 to 173 m) and this variation is attributed to paleo-topographic relief. The upper contact of the limestone is an unconformity with the LVS.

The most important igneous rocks on the property are the Piedras Verde granodiorite and related dikes and sills. All are slightly porphyritic but none are a true porphyry. The Piedras Verde granodiorite exhibits a range of textural variations and compositions. The average composition is very similar to plutons related to Cu skarns (Meinert, 2007). There is no indication of an Au association.

The dikes locally cut the granodiorite, have planar, chilled contacts, and are generally finely crystalline. Both their texture and crosscutting relations suggest that the dikes are younger and shallower than the granodiorite. Both granodiorite and andesite dikes have alteration and locally skarn, along their contacts. In addition, endoskarn affects both the granodiorite and in rare cases, the andesite dikes. Thus, these rocks are older than or at best coeval with alteration/mineralization. The presence of skarn veins cutting an andesite dike is clear evidence that at least some skarn is later than at least some of the andesite dikes. A closer association of granodiorite with skarn alteration and mineralization is suggested by local K-silicate veining of the granodiorite and the zonation of skarn relative to this contact.

Mineralization at the Bolivar property is hosted by skarn alteration in carbonate rocks adjacent to the Piedras Verde granodiorite (Meinert, 2007). Orientations of the skarn vary dramatically, although the majority are gently-dipping. Thicknesses vary from 2 m to over 20 m. Skarn mineralization is strongly zoned, with proximal Cu-rich garnet skarn in the South Bolivar area, close to igneous contacts, and more distal Zn-rich garnet+pyroxene skarn in the northern Bolivar and southern skarn zones near El Val. The presence of chalcopyrite+bornite dominant skarn (lacking sphalerite) in the South Bolivar area, along with K-silicate veins in the adjacent granodiorite suggests that this zone is close to a center of hydrothermal fluid activity. In contrast, the main Bolivar Mine is characterized by Zn>Cu and more distal skarn mineralogy such as pyroxene>garnet and pale green and brown garnets.

Alteration is zoned relative to fluid flow channels. From proximal to distal, the observed sequence is: red-brown garnet to brown garnet with chalcopyrite ± bornite ± magnetite to green garnet ± pyroxene with chalcopyrite + sphalerite to massive sulfide (sphalerite ± chalcopyrite ± galena) to marble with stylolites and other fluid escape structures.

Mineralization exhibits strong stratigraphic control and two stratigraphic horizons host the majority: an upper calcic horizon, which predominantly hosts Zn-rich mineralization, and a lower dolomitic horizon, which predominantly hosts Cu-rich mineralization. In both cases, the highest grade are developed where fault or vein structures and associated breccia zones cross these favorable horizons near skarn-marble contacts. Meinert (2007) suggested that hydrothermal fluids moved up along the Piedras Verdes Granodiorite contact, forming skarn and periodically undergoing phase separation that caused brecciation. Zones of breccia follow faults like the Rosario, Fernandez, and Breccia Linda trends as well as nearly vertical breccia pipes such as La Increible.

Ore production at Bolivar is primarily by means of underground room and pillar mining. Ore is processed at the Piedras Verdes mill located south of the mine. Mining has occurred in several mostly shallow dipping zones in the immediate Bolivar area including Bolivar, El Gallo Superior, El Gallo Superior Magnetita, and El Gallo Inferior.

Areas where room and pillar mining occurs are divided into levels measuring approximately 16 m high. Each 16 m level is further divided into sublevels of approximately 4 m. A ramp is driven and access to the middle sublevel is established in the footwall, and the initial cut in ore is developed at this middle sublevel. The roof is then drilled, blasted and mucked. The third cut is mined down to the lower sublevel floor. Ramps in ore are established whenever possible to minimize the mining of waste. The remaining 4 m of material is left as a sill pillar.

Chimenea 1, Chimenea 2 and the steeply dipping areas of Bolivar West are suitable for mining using longhole stoping techniques. Longhole stoping can provide for higher production and better recovery of the ore than the room and pillar method. However, there are currently limited zones in the Bolivar area where this mining method is applicable, and mining using this method accounts for approximately 8% of the reserves stated herein. The site has some past experience using longhole techniques in the Chimenea areas.

Ore is hauled to the surface using one of several adits or declines accessing the orebodies and dumped onto small pads outside the portals. The ore is then loaded into rigid frame over-the-road trucks, typically 18 tonne capacity, and hauled on a gravel and dirt road approximately 5.1 km south to the Piedras Verdes mill.

Dia Bras operates a conventional concentration plant consisting of crushing, grinding, flotation, thickening and filtration of the final concentrate. Flotation tails are disposed of in a conventional tailings facility.

Dump trucks of approximately 20 tonnes capacity deliver the ore from the mine to the primary crusher area. Trucks can dump directly to the primary crusher or, alternatively, in one of multiple stockpiles. A front-end loader reclaims ore from the stockpiles and feeds the jaw crusher.

The crushing circuit has been expanded recently. In its current configuration, the crushing plant consists of a jaw crusher in open circuit, with its product feeding a vibrating screen. Material passing the vibrating screen opening becomes final product that is transferred to the feed silos. The vibrating screen’s oversize feeds a secondary crushing stage consisting of two cone crushers. The cone crusher’s discharge joins the primary crusher’s discharge and feeds the vibrating screen.

The grinding stage uses two conventional ball mills operating in parallel, each one in closed circuit with a hydrocyclone battery. Ore is fed to the ball mills from two silos using conveyor belts. The hydrocyclone overflow feed the flotation circuit.

The flotation circuit operates three identical parallel flotation lines. Each flotation line includes a rougher stage where the rougher concentrate feeds the cleaning stage, and the rougher’s tails feed the rougher-scavenger stage. The cleaning circuit consists of three consecutive cleaning stages, tailings from each cleaning stage along with the rougher-scavenger’s concentrate are recirculated to the feed of the rougher stage. Tails from the rougher-scavenger become the plant’s final tails.

The flotation concentrate is thickened before being dewatered using three vacuum filters.

Final flotation tails are pumped to the tailings storage facility where they are classified using hydrocyclones. Process water is reclaimed from the tailings water pond and reused in the process plant.

Ore feed during year 2017 reached a total of 887,236 t, equivalent to an average of 74,000 tonnes per month (t/m), or 2,400 t/d. This is 6.7% lower when compared to material processed in 2016. During 2017, production of copper concentrate has ranged between approximately 1,530 and 2,950 t/m, equivalent to roughly a 3.1% mass pull. The monthly average concentrate copper grade has ranged between 22% to 27% and credit metals averaging 374 g/t silver and 3.22 g/t gold in 2017. Metal recovery for copper, silver, and gold monthly averaged 79.6%, 76.3% and 59.5%, respectively.