The Surubim District, containing the Surubim OP Mine and Surubim UG Mine, located at 9°34’12”S and 39°51’52”W, also includes the C-12 OP/UG Mine, located at 9°34’44”S and 39°52’27”W, the Lagoa da Mina project, located at 9°30’13”S and 39°47’48”W adjacent to the past producing Angicos Mine, the Cercado Velho project, located at located at 9°30’36”S and 39°47’52”W and the Terra do Sal project, located at 9°38’1”S and 39°49’6”W.

The Surubim district is located in the central part of the Curaçá Valley (Figure 7-2). The C12 deposit is located 1.2 km to the SW of the Surubim mine. The Cercado Velho and Lagoa da Mina deposits are at approximately 10 km to the NE of Surubim whereas the Terra do Sal deposit is situated 8 km to the SE of Surubim. The Surubim and C12 deposits are hosted in the Surubim gneiss (alternating tonalitic and granorioditic bands with gabbro and diorite bands) whereas the other three deposits are hosted in the Caraíba gneissic complex (biotite orthogneiss with local migmatite). The geology of the Surubim and C12 deposits consists of large gabbro-dominant units with minor pyroxenite units and remnants of gneiss that are at least 400mwide (Figure 7-22 and Figure 7-23). In both deposits, the mafic-ultramafic units are intruded by late north-striking granite and pegmatite dykes. The geology of the Cercado Velho, Lagoa da Mina and Terra do Sal consist of orthogneiss and migmatites intruded by ultramafic units measuring a few centimeters up to 15m thick.

In all the deposits, the mafic-ultramafic lithological units are generally northerly oriented, and they dip steeply to moderately the west (Figure 7-24, A, B). Two main systems of easterly dipping anastomosing faults occur at the Surubim mine and are oriented NNE-SSW and NNW-SSE respectively.

The mafic-ultramafic intrusive rocks and the gneiss were subjected to variable alteration, including phlogopite, silica, chlorite, K-feldspar, epidote, serpentine, and carbonate. Moderate to intense phlogopite alteration is characteristic of the Surubim deposit whereas k-feldspar, diopside and silica alteration zones are dominant in the Cercado Velho and Lagoa da Mina deposits.
The copper mineralization at the Surubim and C12 deposits occurs as lenses that are hosted by phlogopite-altered gabbro injected by pyroxenite dykes. Sulphide minerals are chiefly chalcopyrite and bornite in a ratio of 4:1 that mainly occur as disseminations and veins (Figure 7-27). Chalcocite, covellite and cubanite also occur as minor sulphides associated with the mineralization surrounding the Surubim Mine. Magnetite and minor pyrite and pyrrhotite are also associated with the mineralization with pyrrhotite being an important sulphide at the Lagoa da Mina and Cercado Velho deposits. The Terra do Sal deposit is characterized by disseminated and veinlets of pyrrhotite, chalcopyrite with minor bornite, pyrite and pentlandite.

In the deposits, the copper mineralization lenses are oriented N-S to NW-SE and dip moderately to steeply to the west and follows the general trends of the lithological units but with an overall steeper westerly dip.

The Surubim and C12 OP mines are currently undergoing a restart operating activities, expected to restart operations in 2021.

The open pit operations of Surubim and C12 OP Mine in the Surubim District utilize conventional open pit mining, implementing proven drilling, blasting and loading / haulage equipment and technologies used in prior open pit operations within the Curaçá Valley by the Company.

To prepare sulphide copper ore for mining, the waste material located in the upper portion of the deposits (mostly comprised of waste rock and oxidized mineralization) is stripped mechanically by a bulldozer. While variable, the weathered profile is, on average, 15m to 20m in thickness throughout the Curaçá Valley. Waste material generated during stripping is stacked outside of the pit area, following the technical and environmental recommendations for each open pit mine.

After pre-stripping, hard rock mining of both barren waste and ore comprising the mineral reserves will be carried out by blasting with explosives. Primary rock drilling will be performed using hydraulic drills rigs with 127mm diameter blast holes, and a 2.40m x 4.80m staged mesh. The explosives, blasting agents and blasting accessories will be supplied by a licensed explosive supplier, readily available in the Curaçá Valley as demonstrated by the Company’s existing operations.

Ore and waste will be loaded by hydraulic backhoes with bucket capacities of 4.5 tonnes and transported from the open pit to the coarse ore stockpile using trucks with a capacity of 35 tonnes each.

Ore will be classified by grade in a near-mine stockpile then transported via dual-train haul trucks with a capacity of 70 tonne each to the Caraíba Mill for processing, as is currently performed at the Vermelhos UG Mine.

As the main loading, haul, dump and blasting operations will be carried out by contractors, consistent with Company’s prior open pit operations, the investment needed for equipment is limited to drill machines and operational support fleet.

Threestage 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 open pit mining is delivered to the surface primary cone crusher, featuring a nominal capacity of 1,600t/h. 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.

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 quarter of 2020, and a to-be-installed high pressure grinding roll (“HPGR”). In support of the LOM ........