The 2021 technical report for the Mantos Blancos Mine in Chile's Antofagasta Region describes an expansion of the copper concentrator from 4.2 Mt per year to 7.3 Mt per year, designed to sustain total copper production at 80,000 tpy to 100,000 tpy after oxide reserves are depleted.
Report context
The Mantos Blancos Mine, Antofagasta Region, Chile, Technical Report is dated 29 November 2021. At the time of reporting, ore processing comprised two plants: an oxide plant using sulphuric acid leaching to produce copper cathodes, and a copper concentrator treating sulphide ore to produce copper concentrate. Mining plans indicated that oxide reserves would be completely depleted by 2023, with only sulphides processed thereafter. The expansion project aimed to increase concentrator capacity from 4.2 Mt per year (current) to 7.3 Mt per year (20,000 tpd). Ramp-up to full tonnage was expected by 2022, with that tonnage maintained until 2037 at an average head grade of 0.69% Cu and total fine copper production in concentrate of 704,800 t. The production plan was issued as document LOM Book 2020, developed by Mantos Copper in 2020.
Processing route
General flow
The process plant included primary crushing; secondary and tertiary crushing and screening; ball milling; flotation; copper concentrate handling (thickening and filtration); and tailings classification and thickening. Two parallel crushing and milling lines were proposed: Line 1 (existing) treating 1.8 Mt per year, and Line 2 (modified from oxide ore service; used for oxide crushing until January 2021) treating 5.5 Mt per year. The milled product from both lines was to be combined and treated in the downstream flotation plant to produce a copper concentrate grading 29% to 33% Cu, with 29% Cu used for design purposes.
Crushing
The primary crushing area comprised two existing 42” x 65” gyratory crushers, each with maximum capacity of 5.5 Mt per year (897 tph nominal) with an open side setting of 125 mm. Line 1 included one belt feeder, two overland conveyors, and an 8,000 t (live) coarse ore stockpile. Line 1 fine crushing comprised one existing triple deck 8 ft x 20 ft primary screen (openings: top 60 mm, middle 30 mm, lower 6.5 mm), one existing 7 ft secondary cone crusher, four existing 8 ft x 20 ft single deck tertiary screens in closed circuit with two new H7800 tertiary crushers. Line 1 final product sizing was D100 of 6.5 mm, D80 of 4.0 mm, D50 of 2.1 mm. The fine ore stockpile for Line 1 had 15,000 t live / 50,000 t total capacity.
Line 2 was to be modified: two 10 ft x 12 ft secondary screens fed from the 12,000 t coarse ore stockpile, with screen undersize as final product; screen oversize feeding two 5½ ft secondary standard cone crushers, then four tertiary crushing lines each comprising two 6 ft x 12 ft screens and one 5½ ft short-head crusher. Tertiary closed side setting was 8 mm; Line 2 final product sizing was D100 of 17.0 mm, D80 of 11.0 mm, D50 of 5.5 mm. The fine ore stockpile for Line 2 had 11,600 t live capacity (existing, modified). Belt feeders under each primary crusher were reversible, enabling product delivery to either line.
Grinding
Line 1 product (80% passing 4 mm) was to be milled in the existing 16.5 ft x 25 ft Ball Mill N°3 (3,200 kW) at 4,932 tpd, in closed circuit with an existing cyclone cluster. Cyclone overflow at P80 of 250 µm would be pumped to the new rougher flotation cells; underflow returned to the mill feed. Lime, primary flotation collector, and dilution water were to be added to the mill circuit.
Line 2 product (80% passing 11 mm) was to be milled in a new 23 ft x 40.5 ft Ball Mill N°8 (13,000 kW motor; 12,546 kW power at shell) with a new cyclone battery. Mill discharge density (w/w) was 75% solids; critical speed 75%; ball loading 32% (power) and 40% (structural); ball size 3.0 – 3.5 in; ball consumption 655 g/t. This mill would receive 15,068 tpd of -11 mm ore and produce a product P80 of 250 µm. The Hatch mill sizing (12,000 kW) was reviewed by Fluor, which concluded the design was conservative and fit for purpose; a second independent review in 2019 (by RPA) resulted in increasing the motor size from 12,000 kW to 13,000 kW.
Existing Ball Mills N°1 and N°2 would become redundant but remain available to cover maintenance periods on Mills N°3 and N°8 or for additional capacity. The regrind circuit comprised existing Ball Mills N°6 and N°7 (8.5 ft x 12.0 ft with 500 hp motor, and 9.5 ft x 12.0 ft with 600 hp motor), with specific energy consumption of 0.69 kWh/t and product size P80 of 45 µm. Regrind mill cyclones were 20” diameter, 2 operating + 2 stand-by (new), with 150%/180% nominal/design circulating load, 18 – 22% solids in overflow, 55 – 65% solids in underflow.
Flotation and concentrate regrinding
The current flotation plant comprised thirteen 42.5 m³ rougher cells, one regrind ball mill, one 3 m x 12 m cleaner column cell, and three 28 m³ plus twenty 14 m³ cells operating as scavengers. For the 7.3 Mt per year plant, four new 300 m³ tank cells were proposed for rougher flotation, treating the combined product from Lines 1 and 2. Lime, flotation reagents, and dilution water would be added to the feed box; flotation feed pulp density of 38% (w/w) was proposed.
Rougher concentrate would be sent to regrinding; rougher tailings passed to the tailings section. A new cleaner column cell (3 m x 12 m) would be installed adjacent to the existing column, doubling cleaner flotation capacity. Column concentrate would be final concentrate at 29% to 33% Cu (29% used for design). Column tailings passed to the existing three 28 m³ and twenty 14 m³ cells arranged in series for scavenger flotation. Scavenger concentrate at 10% Cu would be returned to the regrind mill or directly to cleaner flotation to avoid overgrinding. Scavenger tailings would flow by gravity to the tailings area. The regrind mill discharge box would receive rougher and scavenger concentrates, pumped to a modified existing cyclone battery producing final product (overflow) at P80 of 45 µm.
Key rougher flotation design parameters: cell volume 300 m³ (4 new units); residence time 30 minutes based on effective volume (90% effective volume factor); feed density 38% nominal / 34% design; concentrate grade 10.0% Cu. Cleaner flotation: column cells, 3 m x 12 m, quantity 2 (1 new, 1 existing), unit area 5.46 t/h/m², capacity 1.52 t concentrate/h/m², feed density 19.0 – 21.0% w/w, concentrate grade 29 – 33% Cu (29% design). Scavenger flotation: existing conventional cells, three 28 m³ plus twenty 14 m³ cells (total 23), residence time 45 minutes over effective volume, feed density 13.9% w/w, concentrate grade 20.0% Cu.
Concentrate handling
Concentrate thickening was to use three existing conventional thickeners (one 75 ft diameter and two 35 ft diameter); only one was currently used, the other two on standby. Unit area was 1.15 m²/tpd; underflow density 55 – 65% w/w (60.0% for balance). Concentrate filtration comprised filter presses (one existing 48 m² and one new 30 m²), with cycle time 15 minutes, existing filter rate 292 kg/h/m², new filter filtration rate 450 kg/h/m², 3.5 – 4 t/cycle, product moisture content 10 – 11%. Concentrate would be discharged onto the existing stockpile for truck transport to smelter or port; filtrate water returned to concentrate thickeners. New filter installation had sufficient area and access.
Tailings
Combined rougher and scavenger tailings were to be pumped to two primary tailings cyclone batteries (one existing, one new). Cyclone overflow (approximately 30% solids by weight) passed to tailings thickening; underflow (approximately 70% solids by weight) passed to dewatering ahead of dry stacking on the existing coarse tailings pad. Design objective was maximizing water recovery and reducing wet tailings dam size.
One new cyclone cluster was designed with specialist vendor input. Cyclone overflow was to feed a new high capacity thickener (32 m diameter); underflow at 60% solids pumped to the existing Pit 8 tailings dam, with one additional positive displacement tailings pump installed. Three existing tailings thickeners (one 220 ft Larox, one 175 ft Eimco, one 175 ft Dorr-Oliver) would serve as standby units.
Coarse underflow from primary tailings cyclones fed a dewatering section comprising four 6 ft x 12 ft dewatering screens (two existing, two new) plus two existing 100 m² belt filters, producing approximately 20% moisture content for dry stacking. Screen and belt filter underflow would be pumped to two secondary tailings cyclone batteries (one existing, one new), with overflow passing to tailings thickeners and underflow to dewatering screens. The secondary classification had two batteries of 100 mm/150 mm diameter cyclones (1 new, 1 existing), feed density 43.6% w/w, underflow density 61.4% w/w, overflow density 5.0% w/w. Coarse/fine separation was 70/30. Fine tailings thickening used a new 32 m diameter Hi-Rate (Outotec) thickener, underflow density 55 – 62% (60% for balance). Coarse tailings dewatering used dewatering screens (4 total; 2 existing, 2 new), 11.5 m² each, 150 t/h dry capacity, 20.0% moisture content.
Lime and reagents
Lime was to be added as slurry to regulate flotation pH: 9.0 – 9.5 in rougher and 10 – 10.5 in cleaner, added principally to ball mills and to flotation as required. The existing lime plant would supply Line 1 (Ball Mill N°3); a new lime plant for Ball Mill N°8 was proposed as a conventional slaking and mixing system provided as a package by a specialist vendor. Lime addition rate was 500 g/t, type 80.0% CaO, slurry density 20% w/w.
Flotation reagents were to be supplied in iso-containers connected directly to dosing pumps, located in the existing reagent area. Primary collector (Aero AP-7156; mercaptobenzotiazol mixed with dithiophosphate, liquid form) at 10 g/t added to rougher flotation. Secondary collector (Aero MX-3753; modified xanthate, liquid form) at 20 g/t added to rougher flotation. Primary frother (Methyl Isobutyl Carbinol, MIBC, liquid form) at 38 g/t added to rougher flotation. Secondary frother (MB-78; generic, liquid form) at 15 g/t added to rougher flotation. Concentrate thickening used Praestol 2520 anionic polymer at 5 g/t (primary solution 2.5 g/L; addition solution 0.25 g/L). Tailings thickening (new plant) used Praestol 2520 anionic polymer at 5 – 30 g/t (primary solution 2.5 g/L; addition solution 0.25 g/L). A new flocculant plant would supply the new tailings thickener; the existing flocculant plant dedicated to concentrate thickening.
Mill balls
Ball Mill N°3 and the regrind mill would use existing ball handling systems. Ball size: 3” (primary mill) and 1” (regrind mill). A new ball handling system for Ball Mill N°8 would use 3”/3½” balls.
Fresh (make-up) water
Fresh water make-up supplied by FCAB and ADASA would feed existing fresh water tanks. Estimated make-up requirement was 8,378 m³/d, less than the current fresh water make-up requirement. This did not consider recirculation from the fine tailings dam (conservative assumption); with 50% recirculation (reclaimed water from tailings dam), fresh water make-up demand would drop to 6,411 m³/d.
Key reported parameters
| Parameter | Line 1 | Line 2 |
|---|---|---|
| Annual throughput (Mt/year) | 1.8 | 5.5 |
| Daily throughput (tpd) | 4,932 | 15,068 |
| Feed size F80 (µm) | 4,000 | 11,000 |
| Product size P80 (µm) | 250 | 250 |
| Ball mill | N°3, existing 16.5 ft x 25 ft, 3,200 kW | N°8, new 23 ft x 40.5 ft, 13,000 kW |
| Specific energy, P80=250 µm (kWh/t) | 13.54 | 15.91 |
| Specific energy, P80=277 µm (kWh/t) | 12.50 | , |
| Power at shell (kW) | , | 12,546 |
| Mill discharge density (w/w) | , | 75% |
| Critical speed | , | 75% |
| Ball loading (power/structural) | , | 32% / 40% |
| Ball size (in) | , | 3.0 – 3.5 |
| Ball consumption (g/t) | , | 655 |
| Circulating load (nominal/design) | 300% / 400% | 300% / 400% |
| Cyclone solids in overflow (w/w) | 40% | 40% |
| Cyclone solids in underflow (w/w) | 75% | 75% |
Project website: https://capstonecopper.com/operations/mantos-blancos/
| Parameter | Value |
|---|---|
| Overall design annual throughput | 7.3 Mt/year |
| Overall design daily throughput | 20,000 tpd |
| Ore specific gravity | 2.7 |
| Ore moisture content | 2.0% |
| Ball mill work index (75th percentile) | 23.55 kWh/t |
| Crushing work index | 18.0 – 22.0 kWh/t |
| Copper head grade, nominal / design | 0.897% / 0.937% |
| Primary crushing running time | 70.0% |
| Secondary/tertiary crushing running time | 80.0% |
| Grinding running time | 93.0% |
| Flotation running time | 93.0% |
| Concentrate thickening running time | 96.0% |
| Concentrate filtration running time | 80.0% |
| Fine tailings thickening running time | 96.0% |
| Coarse tailings dewatering running time | 80.0% |
| Primary gyratory crusher OSS | 5.5” – 7” (140 – 178 mm) |
| Primary gyratory CSS | 3.5” – 5” (88.9 – 125 mm) |
| Line 1 primary screen openings | 60 / 30 / 6.5 mm (triple deck) |
| Line 1 tertiary screen openings | 6.5 / 8.0 mm (double deck) |
| Line 1 tertiary crushers | 2 new, Hydro-cone CH870 EF, CSS 15 mm |
| Line 1 fine ore stockpile (live/total) | 15,000 t / 50,000 t |
| Line 2 secondary screens | 2 new, Sandvik LF1850T, openings 50/17 mm |
| Line 2 secondary crushers | 2 new, Sandvik 660, CSS 28 mm |
| Line 2 tertiary screens | 8, 6’ x 12’ single deck, opening 15 mm |
| Line 2 tertiary crushers | 4 new, Sandvik 440, CSS 8 mm |
| Line 2 fine ore stockpile (live) | 11,600 t |
| Coarse ore stockpiles (live/total) | 8,000/20,000 t (Line 1); 12,000/40,000 t (Line 2) |
| Regrind specific energy | 0.69 kWh/t |
| Regrind product P80 | 45 µm |
| Rougher residence time | 30 min |
| Rougher feed density (nominal/design) | 38% / 34% w/w |
| Rougher concentrate grade | 10.0% Cu |
| Cleaner columns | 2 (1 new, 1 existing), 3 m x 12 m |
| Cleaner unit area | 5.46 t/h/m² |
| Cleaner capacity | 1.52 t conc/h/m² |
| Cleaner feed density | 19.0 – 21.0% w/w |
| Scavenger cells | 23 total (3 x 28 m³ + 20 x 14 m³) |
| Scavenger residence time | 45 min |
| Scavenger feed density | 13.9% w/w |
| Scavenger concentrate grade | 20.0% Cu |
| Concentrate thickeners | 3 existing (75 ft, 35 ft, 35 ft) |
| Concentrate thickener unit area | 1.15 m²/tpd |
| Concentrate thickener underflow density | 55 – 65% w/w (60% for balance) |
| Concentrate filters | 2 (1 existing 48 m², 1 new 30 m²) |
| Filter cycle time | 15 min |
| Existing filter rate | 292 kg/h/m² |
| New filter rate | 450 kg/h/m² |
| Filter capacity | 3.5 – 4 t/cycle |
| Concentrate moisture | 10 – 11% |
| Tailings thickener | 1 new, 32 m diameter, Hi-Rate (Outotec) |
| Tailings thickener underflow density | 55 – 62% w/w (60% for balance) |
| Fine tailings cyclone batteries | 2 (1 existing, 1 new), 100/150 mm diameter |
| Fine tailings cyclone feed density | 43.6% w/w |
| Fine tailings cyclone underflow density | 61.4% w/w |
| Fine tailings cyclone overflow density | 5.0% w/w |
| Coarse/fine separation | 70/30 |
| Dewatering screens | 4 (2 existing, 2 new), 11.5 m², 150 t/h dry |
| Dewatered coarse tailings moisture | 20.0% |
| Fresh water make-up | 8,378 m³/d (without dam recirculation); 6,411 m³/d (with 50% recirculation) |
Technical qualifications
The report stated that the expanded plant was designed on the basis of existing plant operating data, together with limited testwork on samples and geometallurgical models representing material to be mined over the next 5 years, with less data available for the period after that. The geometallurgical model was tested by comparing results to actual plant results and found to be a reliable indicator of recovery.
Cautionary comments in the report included:
- Predicted recoveries for future years were higher than actual results achieved over recent years. In the qualified person’s opinion, this was achievable because the new equipment would remove bottlenecks in the current operation.
- New equipment, especially the crushers, Ball Mill N°8, and the rougher flotation cells, should improve plant operating efficiency.
- There was only limited testwork on samples after 2025.
The report also noted that this was a brownfield project where new equipment must be tied into an old plant, requiring a very detailed commissioning plan, with ramp-up to full tonnage potentially taking longer than customary.
The design criteria were considered correct, well supported, and conservative.
Source: Mantos Blancos Mine, Antofagasta Region, Chile, Technical Report, 29 November 2021, Sections 17 (Recovery Methods), including Sections 17.1, 17.2, 17.3, 17.4, 17.5, 17.6, 17.7, 17.8, 17.9, 17.10, 17.11 (17.11.1 – 17.11.9), 17.12, and 17.13.
