Aguablanca Technical Report

This report describes the proposed processing plan for underground ore at the Aguablanca mine, based on the existing plant design and historical operating data from 2015 and earlier.

Report context

The Aguablanca Technical Report, effective March 24, 2024, prepared for Denarius Mining Corp., details the proposed mineral processing approach for treating underground ore at an average rate of approximately 2,400 tpd. The existing process plant, originally designed for a dry feed throughput rate of 195 tph, historically operated at higher rates often exceeding 5,000 dry tpd between May 2008 and December 2015 before being shut down. The proposed milling schedule and staffing levels have been modified to match the lower underground mine production rate.

Processing route

Plant operating schedule and staffing

The proposed process plant operations cycle will include seven weeks with the plant operating Monday through Thursday. During the eighth week, the plant will operate only on Monday and Tuesday, allowing for two extra days to complete large maintenance projects. Plant startups are estimated to take one hour while shutdowns will require two hours. The plant will operate 93 hours for seven weeks and 45 hours during the eighth week.

Since the crushing plant design throughput is 450 tph, the crusher will not operate for as many hours each week as the rest of the plant, allowing crusher maintenance projects to be completed while the rest of the plant is in operation.

The proposed process plant workforce will total 66 people, compared to 111 employees in 2015. While the plant is operating, staffing will be similar to 2015 staffing including two reagent and plant employees as well as a commercial supervisor and commercial operator responsible for concentrate storage and loading. During scheduled plant downtime, the plant will be staffed by one supervisor and one operator on day shifts and one supervisor and one operator on night shifts to handle fire watch, monitor any equipment still operating, and complete cleanup projects. The sample preparation, assay, and metallurgical laboratories will be staffed with sufficient manpower to complete mine and plant sample analyses and testing.

Area 10 – Crushing

The Aguablanca crushing plant consists of two stages both operated from a central control room. The primary stage is a C160 Nordberg 250 kW (335 Hp) jaw crusher. Run-of-mine rock is dumped either by haul trucks or front-end loader on a level above the primary crusher into a crusher feed bin. The rock flows by gravity onto a variable speed pan feeder that delivers rock to the jaw crusher which reduces rock up to 900 mm (35 inches) in diameter to 100 mm (4 inches). Below the pan feeder is a belt conveyor to catch fine material spilled from the apron feeder. A 900 mm x 900 mm grate prevents rocks too large for the jaw crusher from entering the crusher. Located adjacent to the jaw crusher is a hydraulic rock breaker used to break rocks too large for the rock crusher opening.

The jaw crusher product drops onto a belt conveyor which transfers the rock to a second belt conveyor that transports rock to the secondary crusher. The first belt is equipped with a weight scale. A large electric magnet is suspended over the conveyor discharge transfer point to collect tramp iron.

Prior to 2007, the Aguablanca crushing circuit consisted only of the primary jaw crusher with the jaw crushing product being conveyed directly to the crushed ore stockpile. A 250 kW (335 Hp) Symons 5½-foot standard cone secondary crusher and associated belt conveyors were installed in 2007 to produce finer process plant feed. Cone crusher product target size is 50 mm (2 inch). Cone crusher discharge drops to a belt conveyor which transports the product to the mill feed stockpile.

Area 20 – Stockpile feed and pebble crushing

Crushed ore is stored in a 50,000-tonne total and 12,000 tonne live capacity stockpile. The crushed ore flows by gravity through six 1.83 x 1.83-meter (6 x 6 foot) hoppers onto vibratory feeders which load the material onto a variable speed conveyor housed in a galley below the crushed ore stockpile.

The conveyor below the stockpile is variable speed to control SAG mill feed rate and is equipped with a belt scale to monitor feed rate and total mill feed tonnes. The crushed ore pile conveyor discharges onto another conveyor that conveys the crushed rock to the SAG mill.

Located near the SAG mill feed conveyor are two pebble crushers. One, an HP200 132 kW (177 Hp) Metso cone crusher, was installed during original plant construction while the second crusher, a model CH 430 150 kW (200 Hp) Sandvik cone crusher, was installed in 2010. Both cone crushers are 900 mm (35½-inch).

Feed to these two crushers consists of oversize pebbles screened from the SAG mill discharge slurry. Plus 19 mm (3/4 inch) SAG mill discharge material drops to a conveyor that discharges to a second conveyor that transports the oversize product to a tower where a diverter directs the material to one of the two crushers. A magnetic separator is suspended over the second conveyor to remove reject SAG mill balls and other tramp iron. The pebble crushers produce a 12 mm (1/2 inch) product. Discharge from the Metso and Sandvik crushers are returned to the SAG mill feed conveyor.

Area 30 – Grinding

The Aguablanca grinding circuit includes a SAG mill, SAG mill discharge screening, cyclones, and a ball mill. The grind and pebble crushing areas are operated from a central control room.

Crushed ore is ground in two stages. The primary stage is an Outokumpu EGL 6.45 meter in length x 5.5 meter diameter (21 foot x 18 foot) SAG mill powered by a 3,400 kW (4,560 Hp) 6,600 volt 3-phase induction motor. The SAG mill liners are steel. While design SAG mill feed rate is 195 tph, the addition of the cone crusher to the crushing circuit allowed for higher feed rates. Actual monthly mill feed rates between May 2008 and December 2015 when the plant was shut down ranged from 161 tph to 246 tph with an average feed rate of 212 tph. The mill charge is made up of 165 mm (6½ inch) cast steel grinding balls with a charge target at 28 to 30% of the mill volume. Mill speed is 14 rpm, 76.5% of critical speed.

The SAG mill runs in closed circuit with the pebble crushers with a circulating load of 35%. Water is added to the SAG mill to produce a slurry density of 65% solids by weight. SAG mill discharge particle size is 90% passing 12 mm (½ inch) and 80% passing 6 mm (¼ inch). SAG mill discharge slurry passes over a vibratory screen with the screen undersize reporting to cyclones. The oversize material is conveyed to the pebble crushers.

In addition to slurry, some grinding balls also exit the SAG mill. A rotary magnet positioned at the discharge end of the vibratory screening plant captures the fugitive balls and drops them into a collection bin. The balls are then added to the ball mill.

The cyclone bank is made up of five 500 mm (19½-inch) Warman model S15 500 mm hydrocyclones. Normally only two or three cyclones are operating with the remaining cyclones on standby. The cyclones are fitted with 100 to 110 mm (approx. 4 inch) apexes and 170 mm (6¾ inch) vortex finders.

Cyclone feed density is 60% solids by weight. Cyclone underflow slurry, with a density of 78% to 80% solids by weight, reports to the ball mill. Cyclone overflow at 30% solids by weight with a particle size target of 80% passing 80 microns flows to the pre-float flotation cell.

The second stage of the Aguablanca grinding circuit is an Outokumpu EGL 5 meter in length x 7.75 meter diameter (16½ foot x 25½ foot) rubber lined ball mill powered by a 3,400 kW (4,560 Hp) 6,600 volt 3-phase induction motor. The ball mill is charged with 63 mm (2½ inch) cast steel balls and the charge volume is maintained at between 28% and 30%.

The ball mill runs in closed circuit with the Warman hydrocyclones. Slurry discharge from the ball mill blends with SAG mill discharge and is pumped to the cyclone bank via either the Metso HR 300 CR 315 kW (422 Hp) electric motor-powered centrifugal pump or a Warman 12/10 AH centrifugal pump also powered by a 315 kW electric motor. When one pump is running, the other is on standby. Ball mill circulating load is between 250% and 350%. Water is added to the cyclone underflow to maintain a ball mill slurry density of 75% solids by weight. Potassium amyl xanthate (PAX) collector is also added to the ball mill feed slurry.

Area 40 – Flotation

The flotation plant includes a pre-float stage prior to copper rougher flotation and a nickel flotation circuit downstream from the copper flotation cells. The pre-float stage was originally used to separate naturally hydrophobic talc prior to copper flotation. The report states that option no longer exists. The flotation circuit is operated from the same control room as the grinding circuit. The copper flotation circuit includes a rougher and cleaner stage while the nickel flotation circuit includes rougher, scavenger, and cleaner stages. Flotation slurry density target ranges from 30% to 33% solids by weight and flotation slurry pH is in the neutral range.

Cyclone overflow slurry reports to the flotation circuit. An automated online sampler collects samples from twelve flotation circuit product streams which are fed to a Courier 5 On-Stream XRF Analyzer to provide real-time data allowing operators to monitor plant performance.

Cyclone overflow slurry flows to pre-float flotation consisting of two 40 cubic meter Dorr Oliver Eimco Smart Cell 40 flotation cells with agitators driven by 75 kW (100 Hp) electric motors. Reagents added to the pre-float cells include PAX, a sulfide mineral collector; carboxymethyl cellulose (CMC), a talc depressant; and glycol frother.

Based on XRF analyzer data, pre-float tank concentrates flow either to the copper concentrate thickener or to the copper cleaner circuit consisting of a bank of four 8 cubic meter Dorr Oliver Eimco Smart DO 300 UT flotation cleaner cells with agitators driven by 11 kW (14¾ Hp) electric motors. Collector, depressant, and frother are added at the copper cleaner circuit. Copper cleaner concentrate reports to the concentrate thickener. Copper cleaner circuit tailing can be pumped to the second copper rougher conditioning tank, the nickel rougher conditioning tanks, or the nickel scavenger conditioning tank.

Pre-float tailing slurry flows to two 40 cubic meter Dorr Oliver Eimco conditioning tanks operating in series. The conditioning tanks are fitted with 11 kW (14¾ Hp) MIXTEC mixers. Copper sulfate (CuSO4) is added to the first conditioning tank to activate sulfide minerals and CMC is added to the second mix tank to depress talc. Conditioning tank slurry flows to the copper rougher flotation stage, a single 40 cubic meter Dorr Oliver Eimco Smart Cell 40 flotation cell with an agitator driven by a 75 kW (100 Hp) electric motor. Rougher copper concentrate in turn flows by gravity to the copper cleaner flotation cells.

Copper rougher tailing reports to the nickel rougher conditioning bank, again two 40 cubic meter Dorr Oliver IMCO units with 11 kW (14¾ Hp) MIXTEC mixers. PAX, promoter, and frother are added to the first conditioning tank while CMC is added to the second tank. After conditioning, the slurry flows to the nickel rougher circuit consisting of four 40 cubic meter Dorr Oliver Eimco Smart Cell 40 flotation cells with agitators driven by a 75 kW (100 Hp) electric motor. Nickel rougher concentrate is pumped to the first nickel cleaner bank while nickel rougher tailing is sent to a single 40 cubic meter Dorr Oliver IMCO conditioning tank with an 11 kW (14¾ Hp) MIXTEC mixer. PAX and CMC are added to this conditioning tank.

The conditioned nickel rougher tailing slurry reports to the first nickel scavenger bank, once again four 40 cubic meter Dorr Oliver Eimco Smart Cell 40 flotation cells with agitators driven by 75 kW (100 Hp) electric motors. Nickel first scavenger concentrate reports to the first nickel cleaner circuit along with the nickel rougher concentrate. First nickel scavenger tailing flows to the second nickel scavenger cells, another bank of four 40 cubic meter Dorr Oliver Eimco Smart Cell 40 flotation cells with agitators driven by 75 kW (100 Hp) electric motors. The second nickel scavenger circuit was added to the process in 2010 to increase retention time and nickel recovery. Concentrate from the second nickel scavengers is pumped to the head-end of the nickel flotation circuit while second scavenger tailing slurry reports to the tailing thickener.

The first nickel cleaner bank is made up of four 40 cubic meter Dorr Oliver Eimco Smart Cell 40 flotation cells with agitators driven by 75 kW (100 Hp) electric motors. PAX and CMC are added to the first flotation cells. Concentrate from the first nickel cleaners is pumped to the final nickel cleaner circuit while tailing reports to the nickel first cleaner scavenger bank which is made up of three 40 cubic meter Dorr Oliver Eimco Smart Cell 40 flotation cells with agitators driven by 75 kW (100 Hp) electric motors. PAX is added here as well. Nickel first cleaner scavenger concentrate is pumped to the head-end of the nickel flotation circuit while tailing reports either to the final tailing thickener or is sent back to upstream nickel circuit tanks.

Final nickel cleaner flotation consists of three 16 cubic meter Dorr Oliver Eimco DO 600 UT flotation cells with agitators driven by 22 kW (30 Hp) electric motors. While the final nickel concentrate product is pumped to the concentrate thickener, final nickel cleaner tailing is sent back to the first cleaner tailing bank.

Flotation reagents

Flotation reagents and their reported consumption rates are as follows: FloMin F 650 glycol frother at 0.066 kg/tonne, Depramin 347 carboxymethyl cellulose depressant at 0.756 kg/tonne, FloMin C 3430 potassium amyl xanthate collector at 0.125 kg/tonne, Aero3894A thiocarbamate promoter at 0.004 kg/tonne, and copper sulfate activator at 0.030 kg/tonne.

Area 60 – Concentrate thickening and filtering

Concentrate slurry density ranges from 27% to 30% solids by weight. The first stage of concentrate dewatering is accomplished by a 14 m (46 foot) Outokumpu high-capacity thickener with a 7.5 kW (10 Hp) rake drive. Flocculant (N-71771) is added to thickener feed slurry to increase solids settling velocity. Clear thickener overflow solution is pumped to a reclaim water holding tank from where it is distributed throughout the process plant as makeup water.

Thickener underflow, with a density of between 55% to 60% solids by weight, is pumped to the filter press feed holding tank where coagulant (N-8105) is added to increase filtration time and efficiency. Coagulated slurry is pumped to one of two FSI Filtration Model B-1210/07-CM 1.2×1.2m (47¼ x 47¼-inch) plate and frame 5.5 kW (7.4 Hp) filter presses fitted with 48 filter plates. Feed slurry is alternately fed to one filter press or the other with one filter press always operating. Filter cake concentrate containing less than 10% moisture is transferred to the concentrate storage area from where it is loaded into trucks and hauled to the smelting facility.

Also included in the filtration building is a non-functional FSI Filtration Model B-1210/04-CM 1.2×1.2m (47¼ x 47¼-inch) plate and frame filter press. This filter press was used to dewater copper concentrates when the nickel and copper concentrates were kept separate.

Area 70 – Tailing disposal

Flotation tailing density ranges from 27% to 30% solids by weight. Water is removed from flotation tailing via a 15 m (49 foot) Outokumpu high compression paste thickener. The thickener rake mechanism is driven by a 47 kW (63 Hp) motor. Clear thickener overflow solution is pumped to the reclaim water holding tank.

Thickener underflow, with a density of between 70% to 72% solids by weight, flows to an Abel HMO-H-160-2000 piston diaphragm positive displacement pump powered by a 160 kW (215 Hp) motor which pumps the thickened slurry to the tailing storage facility. In addition to the Abel pump, there are two Metso HR150 centrifugal pumps driven by 90 kW (120 Hp) motors that are utilized to pump the slurry to the tailing storage facility whenever the piston pump is down for maintenance.

Tailing thickener underflow slurry is pumped through a 200 mm diameter steel pipe with 16 mm wall thickness (8-inch diameter x schedule 20) which transitions to a 200 mm HDPE pipe with 16 mm wall thickness (8-inch x SDR 13.5) for transport to the tailing storage facility. The HDPE line splits and runs along the perimeter of the impoundment. Smaller HDPE spigot lines branch from the 200 mm pipe to deposit tailing slurry along the impoundment beaches. The tailing storage facility elevation is roughly 30 meters (98 feet) above the process plant ground floor elevation and the tailing pipe line total length is approximately 3,000 meters (9,842 feet).

The tailing storage facility is lined with HDPE liner over compacted fill. Two Sulzer Model APP 23-40 37 kW (50 Hp) pumps return water from the tailing disposal facility to the process plant.

Area 82 – Services

Process water from thickener overflow solutions from the concentrate and tailing thickeners are pumped to a 1,000 cubic meter (264,172 gallon) holding tank for distribution throughout the process plant. Water from the tailing impoundment and the pressure filters is also pumped to the process water tank.

Fresh water from runoff precipitation and inert water pumped from the mine workings are collected in an earthen pond. Two Axflow NT80-250 55 kW (75 Hp) pumps are in place to pump water from the pond to a 686 cubic meter (181,222 gallon) covered steel storage tank. When necessary, water from the Caja river is used to maintain sufficient fresh water tank volume.

Process plant compressed air is provided by three Ingersoll Rand Model SRILATA 90 kW (120 Hp) screw compressors. An Electra Molins 400 kVA stand-by diesel powered generator is in place to provide emergency electrical power.

Reagents

Most concentrated reagents are received in dry form and all must be mixed with water to the desired concentration for distribution throughout the plant. Because Aguablanca slurry pH is typically neutral, hydrated lime addition is rarely necessary. Reagents and their functions include: hydrated lime for pH control (grind and flotation), FloMin F 650 glycol frother (flotation), Depramin 347 CMC depressant (flotation), FloMin C 3430 nickel sulfide collector (nickel flotation), Aero 3894A copper sulfide collector (copper flotation), copper sulfate nickel sulfide activator (nickel flotation), N-8105 coagulant settling agent (concentrate dewatering), N-71771 flocculant settling agent (concentrate dewatering), and N-9601 flocculant settling agent (tailing dewatering).

Reagent inventory is maintained at a level sufficient for two months of process operation. There is a dedicated system for each reagent which includes a dry reagent holding tank, a mixing tank, screw feeders for transferring dry reagent to the mixing tank, distribution pumps, an emergency shower and eyewash station, and a floor sump. Only filtered fresh water is used for reagent mixing.

Key reported parameters

Technical qualifications

The report describes historical operating data and design criteria; actual performance varies with ore blend and operating conditions. Parameters not reported in the source are not stated here.