Mineralization within the Curaçá Valley is hosted by a series of irregular-shaped, layered or zoned mafic-ultramafic intrusive bodies of Archean to Proterozoic age. Determination of genetic models for the deposition of copper has been complicated by the multiple episodes of metamorphism and deformation. These deposits are generally believed to be magmatic sulphide deposits and interpreted to be similar to those found in O’okiep, South Africa, Mayer and Barnes (1996).

The Caraíba Mine (comprised of the underground Pilar Mine and integrated Caraíba Mill) is located in the southern part of the MCSA Mining Complex within the Curaçá Valley. The mine is located in a high-grade metamorphic terrain, composed by gneiss and migmatite that were intruded by mafic, ultramafic and granitic rocks. The mafic and ultramafic intrusions are mainly composed by pyroxenite, melanorite, gabbro and serpentinite. Dibasic dykes and quartz veins crosscut the metamorphic and intrusive units.

The mafic and ultramafic units as well as the granitic intrusions are oriented north-south with steeply-dipping. The gneissic country rocks show fold-interference patterns and shear-zone structures suggesting several superimposed deformation events. The mineralized bodies have two preferential directions: N-S in the west part of the deposit and NW-SE in the east portion of the deposit.

Mineralized intrusive bodies are commonly affected by various alteration assemblages including potassic (phlogopite and K-feldspar) and calc- silicate (epidote and lesser garnet). Mineralized intrusive bodies generally trend 350° to 0° and dip from 50° to 90° to the west.

Mineralization at the Caraíba Mine is composed of copper sulphides in the form of chalcopyrite, bornite and rarely chalcocite that occur in three different styles: disseminated, remobilized and massive or brecciated. Minor ore minerals include pyrite, pyrrhotite and magnetite. The sulphides are heterogeneously distributed in the pyroxenite, melanorite, variably fresh or altered. The sulphides are present in variable concentrations in the form of lenses that trend N-S, dip steeply to the west and range from less than 1 m up to 20 m in thickness. The mineralized bodies occur in sharp contact with migmatites and generally conform to the main foliation of the host-rock. However, evidence of mineralized bodies that cross-cut the foliation are observed at the local scale. Strongly foliated sub-vertical anastomosing shears appear to break and transpose the flanks of folds.

Two main styles of mineralization are described at Caraíba: (i) disseminated chalcopyrite and lesser bornite that is interpreted as “primary”; (ii) bornite-rich mineralization that is associated with phlogopitization, K-feldspar alteration, carbonatization and silicification of the pyroxenite is interpreted as “secondary”, The secondary mineralization is associated with pervasive hydrothermal alteration evidenced by the occurrence of hydrothermal breccias, chlorite alteration, metasomatites, calc-silicate rocks and phlogopite schists.

The Pilar Mine is located in the southern part of the MCSA Mining Complex within the Curaçá Valley.

Underground mining operation within the Pilar Mine have been active for approximately 34 years.
The Pilar UG Mine is divided into six main zones: Deepening Extension Zone (or Deepening), Barauna, MSBS, P1P2NE, P1P2W and the West Limb which encompasses an area known as R22UG and P1P2W.

The mine currently produces an average of 4,100 t/day and approximately 1,170m per month of development is expected starting in 2022 (average of 14k m/year) for the next 5 years.

The material (ore and waste) produced from the Deepening Extension Project will be directed to a new external vertical shaft, that will connect the underground mine at the level -1,075 to the surface. The new transportation shaft will be commissioned in early 2025.

The Pilar UG Mine has previously employed the following mining methods: Sublevel Stoping, VRM and Vertical Crater Retreat (“VCR”). VRM is the method currently employed, whereby ore is removed from the stope after it is blasted and cemented paste backfill is pumped into the mined stopes to ensure geotechnical stability prior to advancing to adjacent stopes.

The current VRM method in currently in use varies in dimensions, with an average stope height of 35m. The majority of production drilling is performed using a Fandrill with 3½” diameter hole. The holes of the freeface are widened to approximately 8” in diameter as shown in the figure below.

Design dimensions of each stope vary according to the modeled geotechnical conditions based upon calculated induced stresses and defined rock mass classifications within the areas of development. While locally variable, on average, stope parameters can be described as having the following dimensions:
• In non-faulted zones: 10m width x 20m length x 35m height; and
• In fault zones, the size of stopes is reduced to 10m width x 15m length x 35m height.

Currently, all ore extracted in the underground mine area (except ore from the near-surface mine zone of the West Limb, which is hauled to surface) is directed to the -78 level where it is discharged into an ore pass. After crushing in one of the two primary jaw crushers, the crushed material is transported by conveyor to an intermediate ore silo connected to the shaft hoisting system.

The existing shaft, completed to approximately 700m below surface, provide the conduit for delivery of power to the underground mine. Three medium voltage cables are wired, originating from the 12TR001 transformer to the 21° bypass of the underground mine.

MCSA implemented the use of pastefill in mined out stopes beginning in 1998. There are three main objectives of the pastefill production and delivery system: (i) increase the structural integrity of mining operations, (ii) reduce the deposition of tailings in the waste piles, pits or tailings dam and (iii) maximize mineral extraction.

Paste is produced on surface in the Company’s pastefill plant, where the tailings are conditioned and mixed with a binder (Portland cement) to form suitable paste according to specification for each application and then gravity fed into the stopes of the Pilar UG Mine. Currently, the pastefill plant has a batch capacity of 95m³/h. The capacity of the plant will be increased to 120m³/h with the expansion of the facility in support of the Deepening Extension Project.

Three-stage crushing is used to prepare a nominal 12.5mm top size crushed feed for the ball milling circuit that also feeds the regrind mill circuit prior to being sent to flotation for the recovery of copper-bearing minerals.

There are two primary crushing operations. Ore from other mining sites is delivered to the surface primary gyro crusher, featuring a nominal capacity of 1,600t/h. Ore from underground mining is crushed underground by one of two primary jaw crushers with a nominal capacity of 400t/h each. Feed enters the primary crushing operations with maximum size of 48” and is discharged with maximum size of 10”.

The blended product of the primary crushing operations is transported via conveyors to a feeder stockpile with a capacity of 12,000 tonnes. The stockpile feeds two primary double deck screens, configured with 100mm aperture on the top and 40mm aperture on the bottom decks. The material over 40mm feeds one of two secondary cone crushers (seven-feet (“ft.”) standard Symons; 1,400t/h of capacity each) set to 28mm aperture. Screen undersize and secondary crushers products discharge onto one conveyor in an open circuit configuration.

Secondary cone crusher discharge and primary screen fines are blended with tertiary crusher discharge and are conveyed to the seven secondary double screen decks, configured with 25mm aperture on the top and 16mm aperture on the bottom decks. Tertiary crushing is performed with four standard CH660 Sandvik cone crushers (capacity of 350t/h each) set to 20mm aperture. Oversize material passes to the tertiary crushers operating in a closed-circuit configuration. Final product from the combined crushing and screening operations is 88% passing 1/2”.

Crushed ore is conveyed to the stacker-reclaimer system to further homogenize the ore for feeding the plant. The stacker-reclaimer system is comprised of a two-armed stacker and a 16 bucket-wheel reclaimer with capacities of 1,600t/h and 1,200t/h, respectively. Crushed ore capacity of the stacker-reclaim system is currently 140,000 tonnes.

GRINDING
The grinding circuit consists of two identical lines operating with a primary ball mill operating in closed circuit with a dedicated battery of 26” hydro-cyclones. Each ball mill is 5.0 m by 7.6 m, charged with 90 mm in diameter high chrome cast steel balls. The nominal grinding capacity of each mill is 200 t/h each. Typical ball consumption is 340 g/t.

Blended ore from the stacker reclaimer is withdrawn through belt feeders below one of the 3,000 tonne ore silos that are interconnected. Ore is delivered to the ball mill over a belt weightometer to control and measure the mass of ore sent to each mill for metallurgical accounting purposes.

The coarse fraction from the cyclone underflow recycles to the ball mill feed chute for further grinding. Overflow from both grinding lines combines as feed to the high frequency screeners and regrinding circuit.

HIGH FREQUENCY SCREENS AND REGRINDING CIRCUIT
The cyclone oversize is pumped to high frequency screening operations comprised of eight screens with five decks each of 105+ micron aperture. The high frequency screening coarse fraction is gravity fed to the vertical mill (STM HIG Mill HIG2300/23000) for regrinding, operating in an open circuit. The HIG Mill (High Intensity Grinding mill) was commission in September 2020. The screening operation fines combine with the regrind mill product and are pumped to the flotation.

All ore mined from the Pilar UG Mine is transported for treatment at the Caraíba Mill.

The Caraíba Mill has been producing copper concentrate since commissioning in 1979 and has benefited from improvement projects over the years, including most recently those undertaken by Ero Copper. The mill has been designed to process ore from both the Pilar UG Mine, via a production shaft supported by two primary underground jaw crushers as well as ore from throughout the Curaçá Valley (including within the Vermelhos and Surubim Districts) via a primary cone crusher located on surface. In its current configuration, the plant is capable of processing a nominal 3.2 million tonnes of copper ore per annum assuming 91% availability. Pursuant to the current LOM plan, the milling capacity of the Caraíba Mill will be increased to 4.2 million tonnes per annum (“Mtpa”) through integration of the Company’s high intensity grinding mill (“HIG Mill”) that was successfully installed during the third q ........