San Matías Copper-Gold-Silver Project — 2021 Technical Report

This article summarizes the processing design for the San Matías Copper-Gold-Silver Project as presented in its 2021 Technical Report, covering comminution, flotation, dewatering, and related infrastructure.

Report context

The San Matías Copper-Gold-Silver Project, located in Colombia, is the subject of a 2021 Technical Report and Prefeasibility Study. The processing facility is designed using conventional and proven technology, with the process design based on metallurgical test work completed in 2021 by Blue Coast Research in Parksville, BC, Canada, and mineralogical work by Actlabs in Ancaster, Ontario, and SGS Canada in Lakefield, Ontario. Grindability and flotation test work was conducted by Blue Coast Research and SGS Canada in Burnaby, BC, which included 71 batch flotation tests and three locked cycle flotation tests.

Processing route

Plant overview

The process plant is designed for a throughput of 22,000 metric tonnes per day at an availability of 92% per annum, equating to an annual feed of 8,030,000 metric tonnes. The beneficiation plan will operate a planned 365 days per year and produce a Cu-Au-Ag concentrate to be sold on the open market.

Run-of-mine feed from the adjacent open pit will be hauled to a primary crusher facility consisting of a gyratory crusher before being conveyed to a 25,000-tonne surface stockpile prior to the mill facility. On average, 20,000 mtpd of fresh or transition ore will be blended with 2,000 mtpd of saprolite prior to the primary crusher by mine operations on a day-to-day basis.

Primary crushing

ROM ore is transported by truck from the open pit and dumped directly onto the spider of the primary gyratory crusher, where it is reduced to a P80 size of 150 mm. The back-in arrangement of the primary crusher facility will accept ore from two haul trucks at once. ROM ore top size will be controlled by blast fragmentation to below 600 mm minus, avoiding the need for a grizzly section prior to the primary. A Superior 5475 MK-III crusher has been selected, which can pass a maximum lump size of 1,370 mm. A remote-operated rock breaker will be installed at the dump point to reduce oversize material.

A product bin is located at the primary crusher outlet; crushed ore drops into an ore bin fitted with a discharge apron feeder which feeds a loadout conveyor. A belt magnet is located on the loadout conveyor to remove tramp ferrous material. Nominal size of the troughed loadout belt is 1.37 m wide x 525 m long, reporting to the coarse ore stockpile. A belt weigh scale tracks the production rate of the crushing plant.

A baghouse collects dust at ore transfer points within the primary crusher building, reporting to the tail end of the loadout conveyor. A sump pit collects wash-up residue and is designed to be emptied periodically by vacuum truck.

Coarse ore stockpile

The coarse ore stockpile is designed to provide storage of ore prior to the concentrator and capacitance between the crushing circuit and the concentrator to allow for maintenance of the crushing circuit without interrupting mill feed. Dimensions are approximately 59 m diameter x 22 m high, at an angle of repose of 37 degrees, corresponding to a design storage capacity of 25,000 tonnes. Excess crushed material can be broadcast away from the conical stockpile via dozer to provide adequate storage capacity for routine scheduled maintenance.

Three apron feeders (two running, one spare) located within a concrete reclaim tunnel will control the outlet flow from the storage pile to feed the SAG mill feed conveyor. Feedrate control will be accomplished via VFD control of the apron feeders and VFD control of the SAG mill feed conveyor. The troughed feed conveyor will be 1.07 m wide x 98 m long. The reclaim tunnel will be large enough to accommodate a track loader for ore clean up and will have two means of egress. All conveyor transfer points will be provided with either dust collection or water sprays to minimize dust generation.

Comminution and grinding

The grinding circuit will consist of a conventional SABC arrangement designed to produce feed slurry fine enough for effective flotation. Design parameters include an F80 of 150 mm and a ball mill closed-in with hydrocyclones. A hydrocyclone overflow P80 of 200 µm will report to the roughing circuit for the first stage of flotation.

Primary grinding will be achieved with a SAG mill. The SAG mill slurry will discharge through a double deck vibrating screen where pebbles will be screened and oversized recycled to a pebble crusher. SAG mill dimensions will be 10.4 m dia. x 5.2 m EGL, with a total installed power of 12.5 MW through a dual pinion drive and VFD.

The pebble crusher will reduce SAG mill pebbles to a P80 of 14 mm, using an HP900 cone crusher with a closed side setting of 15 mm. The pebble crusher is rated for a nominal 275 mtph throughput, capable of a throughput of 367 mtph to handle process upsets. Product will be returned to the inlet chute of the SAG mill via conveyors. A secondary ball mill will work in concert to produce a particle size of P80 = 200 µm for feed to a hydrocyclone unit prior to rougher flotation.

SAG mill discharge screen undersize will report to the common mill pumpbox to be pumped to the hydrocyclone. The ball mill will be fed by the cyclone underflow and will discharge into the pumpbox. A trunnion magnet will be fitted on the ball mill discharge to separate ball scats and slivers for disposal. Ball mill dimensions will be 7.3 m dia. x 10.7 m EGL, with a total installed power of 11.4 MW through a dual pinion drive and soft-start arrangement.

Flotation circuit

The flotation circuit is designed to concentrate target metals from the ROM ore and consolidate flotation products in the product stock tank prior to dewatering and storage. Equipment selected for the rougher, first, and second cleaner stages are conventional mechanical tank cells. The third cleaning stage will utilize column cell technology.

The rougher flotation circuit consists of six 200 m³ mechanical tank cells in series, equipped with 187 kW agitators. Feed will report to the roughers at a grind P80 of 200 µm via hydrocyclone overflow with an increased pH of 10.5 using lime. Sodium hexameta-phosphate (“calgon”) is introduced prior to the roughers. Reagent addition to the rougher cells will consist of MIBC (to cells #1 and 2) and potassium amyl xanthate (“PAX”) (to cells #2 and 5). Total residence time within the roughing network will be 15 minutes, provided by the total 1,200 m³ of stage capacity. Rougher float products will report to a single regrind stage closed-in with hydrocyclones. Regrinding will be accomplished with a 746 kW Vertimill (VTM1000) with a P80 of 45 µm prior to overflowing to the 1st cleaners feed box.

The 1st cleaners flotation circuit consists of six 100 m³ mechanical tank cells in series, equipped with 93 kW agitators. Feed will report from the regrind hydrocyclone overflow at a grind P80 of 45 µm, with an increased pH to 11.5 using lime (to cells #1 and 3). Additional reagents introduced to the first cleaners will consist of calgon (to cells #1, 2, and 3) and PAX (to cells #1, 2, and 3). First cleaner float products will report forward to the second stage of cleaning. First cleaner sink products will be pumped through a Knelson gravity concentrator. The dedicated Au-Ag concentrate will be available to be combined with concentrate produced at the first stage of gravity concentrations and will report to a separable and secure concentrate bagging system.

The 2nd cleaners flotation circuit consists of three 30 m³ mechanical tank cells in series, equipped with 45 kW agitators. Feed will report from the 1st cleaners concentrate. No additional reagents are introduced to the second cleaners based on PFS test work; it is recommended to review whether there is merit for additional gangue suppression prior to the final cleaning stage in the next stage of study. Total residence time within the 2nd cleaner stage will be 25 minutes, provided by the 90 m³ of total stage capacity.

The 3rd cleaner flotation circuit consists of a single 120 m³ column cell. Feed will report from the 2nd cleaner concentrate. No additional reagents are introduced to the third cleaner based on PFS test work; it is recommended to review whether there is merit for additional gangue suppression at the final cleaning stage. Total residence time within the 3rd cleaner stage will be 40 minutes, provided by the 120 m³ of stage capacity.

Regrind and gravity concentration

A regrind stage will treat rougher float product to a P80 of 45 µm prior to primary cleaning. Two stages of gravity concentration will be utilized to produce a dedicated Au-rich concentrate. One unit will be fed from a partial stream of ball mill hydrocyclone underflow, and the smaller unit will be fed from the 1st cleaner tailings. The dedicated Au-Ag concentrate may be marketed separately or recombined with the aggregate concentrate product depending on market conditions and take-off agreements.

Concentrate thickening, dewatering, and storage

Final concentrate from the 3rd cleaner concentrate is fed to an 11 m diameter high-rate concentrate thickener, where the feed slurry at 24% w/w is mixed with anionic flocculant and thickened to a target solids concentration of 63% w/w. Thickened concentrate is pumped to a concentrate pressure filter, where the solids content is further increased to a target of 91% solids w/w.

Discharge from the pressure filter is conveyed to an enclosed stockpile for bulk storage prior to being transported off site via dump truck for storage at a port facility prior to being loaded to ocean vessels for shipping to market. The bulk storage facility on site is sized to stage 2,200 m³ of concentrate and is of dimension 33 m wide x 60 m long (1,980 m²). The bulk storage facility near the chosen port facility is sized to stage 7,750 m³ of concentrate and is of dimension 36 m wide x 90 m long (3,240 m²).

Tailings and water management

Rougher tails and tails from the 1st cleaners will be pumped to a high-compression tailings thickener where the density will be increased to a target of 63% density. Flocculent will be added to the thickener at a feed rate sufficient to obtain target clarity for the thickener overflow water. Thickener underflow will be pumped to an intermediate buffer tank prior to being discharged to the WMF. Thickener overflow will join the concentrate thickener overflow to report back to the process water storage tank.

Process water will be supplied to a 2,700 m³ process water head tank located 55 m above the concentrator plant ground floor. The primary source of process water will be the concentrate thickener and tailings thickener overflow water, which reports to a common overflow basin before being pumped to the storage tank. The secondary water source will be from the mill effluent metals and TSS removal plant, as necessary, to maintain a sufficient water level in the storage tank.

Freshwater will primarily be used for gland water for slurry pumps, fire water, cooling water for mill lubrication systems, and reagent preparation. Two separate modular treatment plants will be required for the mill influent (supply) and the mill effluent (discharge) systems. The mill influent system will draw from the San Juan River and process water at a design rate of 4.2 m³/hr. The effluent plant is designed for a flow rate of 700 m³/hr. Both plants will be located adjacent to the saddle dam that divides the WMF and WMP. The influent of both treatment plants will be treated by a combination of chemical and mechanical means to adjust pH and remove metals and suspended solids. Treatment plants will have common reagent storage and make-down systems consisting of H₂SO₄, NaOH, NaHS, coagulant, and flocculant. The mill influent WTF will utilize a ballasted flocculation clarifier prior to a series of multi-media filters, while the mill effluent treatment plant will utilize three ballasted flocculation clarifiers prior to a series of multi-media filters.

A potable water treatment system will also be fed from the discharge of the mill influent metals and TSS removal plant, consisting of a reverse osmosis unit followed by an ultraviolet light train, with antiscalant and clean in place chemical reagents. Potable water will be treated, stored, and distributed to various buildings on site, with each building having its own pressurized reservoir tank for distribution.

Reagents

Reagents will be stored dry, when possible, on site prior to being prepared and stored in a separate area adjacent to the concentrator facility for distribution to the process. Lime, calgon, PAX, and flocculant will be received and blended into solution. MIBC will be received in liquid form and stored in a dedicated tank and delivery facility. Reagents will be prepared using a dedicated fresh process water supply to avoid cross-contamination.

Assay and metallurgical laboratory

The assay and metallurgical laboratory facilities will include all necessary equipment to filter, dry, and pulverize mine and concentrator samples to prepare them for assay; to perform all digestions and analytical procedures required for tracking concentrator feed head grades (using mine samples); and to perform all digestions and analytical procedures required for tracking the day-to-day metallurgical performance of the concentrator facility (using grinding and flotation composite samples collected within the mill). Analytical instruments will include sample preparation equipment, microbalance room, weighing areas, fire assay lab, wet chemistry lab, environmental lab, and instrument room equipment.

Process control

The general approach to automation and control for the concentrator plant will be one with a moderate level of complexity with remote monitoring and control from a central control room but offering the option of local control. Instrumentation will be provided within the plant to measure and control key process parameters to minimize operator intervention in standard start-up functions and to provide key monitoring and control to minimize process excursions and maintain steady-state operations. The process control system (“PCS”) will be a programmable logic controller (“PLC”) based system. The PCS will control process interlocks and control loops for non-packaged equipment. Control loop set-point changes for non-packaged equipment will be made at operator interface terminals. Vendor-supplied packages will use vendor standard control systems and will generally have limited interface with the PCS such that control and set-point changes may have to be done locally. General equipment fault alarms for each vendor package will be monitored by the PCS and displayed on the OIT.

Key reported parameters

Technical qualifications

The process design parameters were established to define the equipment required for production and storage of concentrate adjacent to the open pit facilities. Various major equipment vendors have been consulted to vet preliminary equipment selections. Preliminary circuit configuration has been built based on the learnings from test work and configured within a notional process plant model to mitigate operational risk associated with the process. Information from the resultant processing plant model as well as vendor budget pricing contribute to the overall capital and operating cost estimates presented in Section 21 of the Technical Report.

The mill influent system will draw from the San Juan River and process water at a design rate of 4.2 m³/hr, and the effluent plant is designed for a flow rate of 700 m³/hr. The influent of both treatment plants will be treated by a combination of chemical and mechanical means to adjust pH and remove metals and suspended solids. The treatment plants will have their own common reagent storage and make-down systems consisting of H₂SO₄, NaOH, NaHS, coagulant, and flocculant.

For the 2nd cleaner stage, there are no additional reagents introduced based on PFS test work; it is recommended to review whether there is merit for additional gangue suppression prior to the final cleaning stage in the next stage of study. For the 3rd cleaner stage, there are no additional reagents introduced based on PFS test work; it is recommended to review whether there is merit for additional gangue suppression at the final cleaning stage prior to the next stage of study.

Source: NI 43-101 Technical Report & Prefeasibility Study, Nordmin Engineering Ltd, San Matías Copper-Gold-Silver Project, Colombia, Project # 21008-01, Cordoba Minerals Corp., 2021, Sections 17.1, 17.2, 17.3, 17.4, 17.5, 17.6, 17.7, 17.7.3, 17.7.4, 17.7.5, 17.8, 17.8.2, 17.8.3, 17.9, 17.10, and 17.11.