Santo Tomás Copper Project — 2024 Technical Report

This report describes the proposed two-phase processing plant design for the Santo Tomás copper-molybdenum project, based on metallurgical testwork and engineering design criteria.

Report context

The Santo Tomás Copper Project NI 43-101 Technical Report & Updated PEA is dated August 15, 2024. Section 17 of the report details the recovery methods and process plant design for the proposed mineral processing facility. The process flowsheet design is based on a review of all metallurgical testing data and reports, combined with Ausenco's design expertise.

Processing route

Overview and general arrangement

The Process Plant is initially designed for a nominal throughput of 60,000 t/d for Phase I of the Project. Phase II will essentially be a duplicated processing line, increasing total throughput to 120,000 t/d. The facility is designed to operate 24 hours a day, 365 days a year. Major equipment is designed for a nominal throughput of 60,000 t/d except the single 1.7 km conveyor, which will be shared for both Phase I and Phase II. Equipment was sized to accommodate feed grades and recoveries that are greater than the average phase period values.

Crushing circuit

The process flowsheet includes a three-stage crushing circuit. Primary crushing reduces the run-of-mine mineralized material from a top size F100 of 1,200 mm to a P80 of 143 mm. The primary crushing circuit will be integrated by two 240 t haul truck dump stations with ramps, one 1,600 x 3,300 mm gyratory crusher, one discharge conveyor, one single 1.7 km conveyor, one stockpile feed conveyor, a crushed mineralized material stockpile, and two reclaim apron feeders. Primary crushing operates as an open circuit with no recirculation. The single 1.7 km conveyor is installed within a 1.5 km long tunnel. The stockpile has a 12-hour live capacity at the design reclaim rate.

The secondary crushing circuit consists of a set of secondary cone crushers and screens to reduce material size from an F80 of 143 mm to a P80 of 42 mm. The secondary crushing circuit operates as a closed circuit. The secondary double deck screens produce a product with a top size P100 of 60 mm. The secondary crushing circuit will include one secondary screen feed conveyor, one secondary screen oversize conveyor, three secondary cone crushers, three secondary vibrating double deck screens (two operating, one standby) measuring 8.5 m length x 3.6 m width, one secondary screen feed bin with three compartments and 5 minutes live capacity with a vibrating feeder below each compartment, and one secondary crusher feed bin with three compartments and 15 minutes live capacity with a belt feeder below each compartment.

The tertiary crushing circuit uses high-pressure grinding rolls (HPGR) to reduce material size for optimum ball mill feed. The HPGR crushing circuit operates on a closed circuit using wet screens. The P80 of the final product from the tertiary crushing circuit is 5.6 mm. The HPGR circuit will include one HPGR feed bin with 15 minutes live capacity, one HPGR belt feeder, one HPGR crusher with 3.0 m diameter x 2.0 m width rolls, one HPGR screen feed bin conveyor, one HPGR screen feed bin with two compartments and 2 hours live capacity with a belt feeder below each compartment, two HPGR vibrating double deck screens for wet screening measuring 8.5 m length x 4.2 m width, two HPGR screen oversize conveyors, and one emergency screen oversize conveyor with a diverter gate chute that dumps into an emergency stockpile. The HPGR crusher reduces material from an F80 of 42 mm to a P80 of 15 mm. The HPGR screens have a top deck opening of 15 mm and a bottom deck opening of 10 mm. Process water is added for wet screening to break material clumps and wash out fines.

Grinding circuit

The grinding circuit includes two ball mills operating in parallel, each 8.23 m in diameter by 13.11 m in effective grinding length, each powered by an 18,000-kW motor. The circuit also includes two slurry pumps (one operating and one standby) to pump ball mill discharge to cyclones, and two cyclone clusters (one for each mill). The undersize mineralized material from the HPGR wet screens feeds directly into the cyclone feed boxes in a parallel grinding circuit arrangement. The cyclone underflow flows directly into the ball mill, operating with a recirculation of 250%. Quicklime slurry is added at the mill to adjust pH to 9.5, and fuel oil acting as a flotation promoter is also added at this stage. The cyclone overflow feeds the rougher flotation tank cells. The grinding circuit reduces the mineralized material from an F80 of 5,600 µm to a P80 of 150 µm.

For Phase II, two additional ball mills, slurry pumps, and cyclone clusters are planned, providing a total of four ball mills in the same configuration as Phase I.

Bulk rougher flotation

After grinding, the mineralized material undergoes a rougher flotation stage. The objective of rougher flotation is to maximize copper sulphide recovery to an intermediate concentrate containing 10-15% of the feed mass. The rougher flotation circuit will include six rougher flotation tank cells with 500 m³ cell volume arranged as 1-1-2-2. The cyclone overflow flows directly into the rougher flotation tank cell feed box at a pulp density of 35% solids. Methyl Isobuthyl Carbinol (MIBC) is dosed as a frother, and Aerophine 3418A is dosed as a collector into the cell feed box. Air is injected into the flotation cell, with air bubbles moving upwards to collect the sulphides. The froth overflows into a collection weir inside each tank and flows by gravity to respective pump boxes, while the barren tailings flow by gravity into the tailings thickener. Liquid level in the tank cells is controlled by dart valves installed between each tank.

Regrinding

The rougher concentrate requires regrinding to increase liberation of copper sulphides and pyrite in advance of the cleaner circuit. A stirred mill in open circuit with a hydrocyclones cluster reduces the particle size of the rougher concentrate from an F80 of 125 µm to a P80 of 23 µm. The regrind circuit will include two cyclone feed pumps (one operating, one standby), one regrind cyclone cluster, and one stirred media regrind mill with 5,500 kW. The bulk rougher concentrate regrind cyclone advances water and fine particles to the overflow, with increased density cyclone underflow discharging to the HIG mill feed box. Slurry from the regrind mill discharge and the cyclone overflow are combined in a pump box and pumped into the cleaner flotation circuit at a product sizing of 23 µm P80.

Bulk cleaner and scavenger flotation

There will be three cleaning stages per phase to increase the grade of the copper concentrate up to 24%. A scavenger cleaning stage is included to recover middling that may require further regrinding. The cleaner flotation circuit will include five first cleaner flotation tank cells with 70 m³ cell volume arranged as 1-2-2, three first cleaner scavenger flotation tank cells with 70 m³ cell volume arranged as 1-1-1, four second cleaner flotation tank cells with 70 m³ cell volume arranged as 1-1-2, four third cleaner flotation tank cells with 70 m³ cell volume arranged as 1-1-2, and one 16 m diameter bulk concentrate high-rate thickener.

Rougher concentrate is pumped from the regrind mill pump box into the first cleaner flotation tank cell feed box. The first cleaner flotation concentrate is pumped into the second cleaner flotation tank cell feed box, while the tailings flow by gravity into the first cleaner scavenger flotation cells. The cleaner scavenger cells recover copper sulphides likely associated with pyrite from the first cleaner circuit tailings. The cleaner scavenger flotation concentrate flows by gravity into the rougher flotation concentrate pump box and is recirculated back into the regrind circuit, while the cleaner scavenger tailings flow by gravity into the tailings thickener. The concentrate from the first cleaner flotation cells enters the second cleaner flotation cells. Tailings from the second cleaner flow by gravity into the first cleaner flotation cells. The third cleaner concentrate is pumped into the Cu-Mo bulk concentrate thickener. Tailings from the third cleaner flow by gravity into the second cleaner flotation cells. All cell tanks have adjustable reagent dosing pumps at each feed box.

Molybdenum flotation

The molybdenum flotation circuit will consist of three conditioning tanks, rougher flotation, scavenger flotation, and five stages of cleaner flotation. Underflow from the Cu-Mo concentrate thickener is pumped to the molybdenum rougher conditioning tank. After conditioning, Cu-Mo concentrate is pumped to molybdenum rougher flotation cells. The concentrate from rougher flotation is delivered to the molybdenum first cleaner conditioning tank. The tailings from rougher flotation report to scavenger flotation. Concentrate from scavenger flotation reports back to the molybdenum rougher conditioning tank. Tailings from scavenger flotation report to the copper concentrate thickener.

Conditioned slurry from the molybdenum first cleaner conditioning tank is pumped to molybdenum first cleaner flotation. Tailings from the first molybdenum cleaner cells report back to the molybdenum rougher conditioning tank. Concentrate from the first cleaner flotation is pumped to the molybdenum second cleaner conditioning tank. Conditioned concentrate slurry from the molybdenum second cleaner conditioning tank is pumped to the molybdenum second cleaner flotation cells. Tailings from the second cleaner flotation report to the molybdenum first cleaner conditioning tank. Concentrate from the second cleaner flotation flows by gravity to the third stage of molybdenum cleaning. Tailings from the third stage of cleaning are pumped to the molybdenum second cleaner conditioning tank. Concentrate from the third stage of cleaning flows by gravity to the fourth stage of cleaning. Tailings from the fourth stage of cleaning are pumped to the third cleaner flotation cells. Concentrate from the fourth stage of cleaning flows by gravity to the fifth stage of cleaning. Tailings from the fifth stage of cleaning are pumped to the fourth cleaner flotation cells. Concentrate from the fifth stage of cleaning flows by gravity to the molybdenum concentrate thickener.

The molybdenum flotation circuit will include molybdenum rougher conditioning tanks with 10 minutes residence time, six molybdenum rougher flotation cells with 28.3 m³ cell volume (enclosed, self-aspirated), three molybdenum rougher scavenger flotation cells with 28.3 m³ cell volume (enclosed, self-aspirated), molybdenum first cleaner conditioning tanks with 12 minutes residence time, five molybdenum first cleaner flotation cells with 4.2 m³ cell volume (enclosed, self-aspirated), molybdenum second cleaner conditioning tanks with 12 minutes residence time, five molybdenum second cleaner flotation cells with 4.2 m³ cell volume (enclosed, self-aspirated), four molybdenum third cleaner flotation cells with 4.2 m³ cell volume (enclosed, self-aspirated), five molybdenum fourth cleaner flotation cells with 1.7 m³ cell volume (enclosed, self-aspirated), and a single molybdenum fifth cleaner high-intensity style flotation cell (50 m³/h).

Copper concentrate dewatering

The copper concentrate is first thickened using a high-rate thickener to a solids density of 60% and then filtered using a vertical pressure filter to obtain a final concentrate with 9% moisture. Water recovered from the filter and from the thickener is used as process water. Copper concentrate dewatering will include a 16 m diameter high-rate concentrate thickener, a static sieve bend trash screen, a copper concentrate filter feed tank with agitator with volume designed for a residence time of 12 hours at nominal feed rate, a single vertical pressure filter with a 144 m² filter area, and a filtered concentrate storage and handling facility with a 5-day dry concentrate storage capacity.

Copper concentrate is pumped onto a static sieve bend trash screen to remove any plastic or trash. The copper concentrate then enters the concentrate thickener feed well where it is mixed with flocculent. Recovered water from the thickener overflows into a thickener overflow tank and is pumped into the process water tank. The thickened copper concentrate in the thickener cone is pumped into the copper concentrate filter feed tank. Concentrate slurry from this agitated tank is pumped into the copper concentrate filter. Filter cake is discharged from the filter onto the concentrate storage and handling facility located below the filter, while the filtrate solution is recirculated as dilution water into the concentrate thickener. Final concentrate is moved into piles, sampled, assayed, and transferred to trucks using a front-end loader for final concentrate sale.

Molybdenum concentrate dewatering

The molybdenum concentrate is first thickened using a high-rate thickener to a solids density of 60% and then filtered using a vertical pressure filter to obtain a concentrate with 15% moisture. Molybdenum concentrate filter cake reports to the molybdenum concentrate dryer. Dried molybdenum concentrate, containing 5% moisture, reports to the molybdenum concentrate storage bin. For each phase, the molybdenum concentrate dewatering circuit will include a 3 m diameter high-rate concentrate thickener, a static sieve bend trash screen, a molybdenum concentrate filter feed tank with agitator with volume designed for a residence time of 24 hours at nominal feed rate, one vertical pressure filter, a concentrate dryer, a molybdenum product bin with a 24-hour dry concentrate storage capacity, and a molybdenum bagging system.

Molybdenum concentrate is pumped onto a static sieve bend trash screen. The molybdenum concentrate is then thickened in the high-rate molybdenum concentrate thickener. Molybdenum concentrate thickener overflow reports to the molybdenum process water tank. Molybdenum thickener underflow is pumped to the molybdenum filter feed tank. Molybdenum concentrate slurry is pumped from the feed tank to the molybdenum concentrate filter. Filtrate from the molybdenum concentrate filter is pumped back to the molybdenum concentrate thickener. Molybdenum concentrate filter cake reports to the molybdenum concentrate dryer. Dried molybdenum concentrate reports to the molybdenum concentrate storage bin. Molybdenum concentrate is withdrawn from the storage bin into a packaging system and bagged for transport by truck.

Tailings dewatering and storage

Flotation tailings coming from the bulk rougher and bulk cleaner scavenger flotation cells are thickened to recover process water and provide an optimum slurry density for the tailings sand cyclone downstream. Tailings dewatering will include one 74 m diameter high-rate tailings thickener and two tailings thickener underflow pumps (one operating, one standby). Flotation tailings enter the thickener feed well where they are mixed with flocculent. Recovered water from the thickener overflows into a thickener overflow tank and is pumped into the process water tank. The thickened tailings are pumped to the tailings sand cyclone system.

The construction of the tailings storage facility (TSF) is an ongoing process during the life of mine. A tailings sand cyclone underflow will be used for the tailings dam wall construction, while the cyclone overflow will be thickened and deposited in the TSF. The Cyclone Sands Station will include one sand cyclone feed slurry pump and pump box, one tailings sand cyclone cluster, one 57 m high-rate tailings slimes thickener, two tailings thickener underflow pumps (one operating, one standby), one sand plant process water tank and distribution system, and one process water barge pump located on the TSF pond.

Tailings are pumped to the sand cyclone feed pump box where they are diluted with process water to achieve a suitable cyclone feed density. The sand cyclones will be operated to recover 40% of the inflow mass to the underflow. Fines recovery to the underflow will be mitigated using an apex wash arrangement. The coarse underflow flows by gravity to the sand wall of the TSF for distribution and placement. The finer material overflows into a slimes thickener feed well where it is mixed with flocculent. Recovered water from the slimes thickener overflows to the sand plant process water tank. The thickened slimes are pumped into the TSF. A barge pump located on the TSF pond returns process water back to the Cyclone Sands Station process water tank. Process water not required by the sand cyclone system is pumped up to the concentrator process water tank.

Reagent handling

The mixing and storage area for each reagent will be located proximate to various addition points throughout the flotation plant. Reagents delivered in bulk bags will be moved from storage to the mixing area by forklift. Electric hoists servicing the reagent area will lift the reagents to the respective reagent bag breaker located above the reagent mixing area. The reagent handling system will include unloading and storage facilities, mixing tanks, stock tanks, transfer pumps, and feeding equipment.

Reagents used include quicklime (delivered as powdered quicklime, stored in silo, slaked, and dosed as a slurry to control pH), fuel oil (diesel) (delivered by truck and transferred into a storage tank for dosing into the mill as a promoter), Aerophine 3418A (delivered in totes and dosed neat into bulk rougher flotation as a collector), Methyl Isobutyl Carbinol (delivered in drums and dosed neat into bulk rougher flotation as a frother), sodium hydrosulphide (delivered at 40% concentration, diluted to 20%, and dosed at various points in molybdenum flotation to depress Cu), flocculant (delivered as dry powder in bulk bags, dissolved in a mixing tank, and dosed to thickeners), and antiscalant (delivered in totes and dosed to prevent scaling of the process water circuit).

Phase II expansion

Phase II will essentially be a duplicated processing line, with the following exceptions and additions: the single 1.7 km conveyor will be shared for both Phase I and Phase II; the crushing and grinding circuit for Phase II is described as "2X Phase I arrangement"; the HPGR circuit for Phase II includes 2 closed operating lines; the grinding circuit for Phase II includes 4 ball mills in the same configuration as Phase I; the bulk rougher configuration for Phase II includes 2 operating lines with 12 tank cells; the bulk cleaner for Phase II includes 2 operating lines each with 3 stages; the Mo rougher, Mo rougher scavenger, and Mo cleaner circuits for Phase II each include 2 operating lines; and identical copper concentrate dewatering and tailings dewatering circuits are planned for Phase II.

Key reported parameters

Technical qualifications

The process flowsheet design is based on a review of all metallurgical testing data and reports combined with Ausenco's design expertise. Key process design criteria listed in Table 17-2 are stated as the basis of the process flowsheet design and selection of mechanical equipment for 60,000 t/d and 120,000 t/d. Bond work index values (crushing work index 23.4 kWh/t, ball mill work index 18.3 kWh/t, abrasion index 0.14 G) and JK Axb Parameter (30 kWh/t) are identified as design values. The report states that equipment was sized to accommodate feed grades and recoveries that are greater than the average phase period values. The design assumes an identical crushing circuit for Phase II provided the hardness properties and bond indices of the mill feed are similar.

Source: Santo Tomás Copper Project NI 43-101 Technical Report & Updated PEA, August 15, 2024, Section 17 Recovery Methods.