This technical report describes the Meadowbank mine processing plant as of February 2012, covering original design parameters, post-startup modifications, and metallurgical testwork-based recovery expectations.
Report context
The Meadowbank Mine Technical Report, dated February 15, 2012, documents the process plant design and operating history from early 2010 through late 2011. The plant poured first gold in early 2010 and achieved commercial production on March 1, 2010. The report describes the original flowsheet design, a secondary crusher addition completed in mid-2011, and changes associated with a new Life of Mine plan.
Processing route
Original design flowsheet
The mineral processing method at Meadowbank was originally based on a conventional gold plant flowsheet comprising primary and secondary crushing, grinding using a semi-autogenous mill – ball mill – pebble crusher (SABC) circuit, gravity concentration, cyanide leaching, and gold recovery in a carbon-in-pulp (CIP) circuit. The mill was designed to operate 365 days per year with a design capacity of 2.7 million tonnes of ore per year (7,500 tonnes per day). When Agnico-Eagle took over the Meadowbank project in the spring of 2007, Hatch Engineering used the same information to redesign the process plant, raising the process tonnage to 8,500 tonnes per day (3.1 million tonnes per year).
Secondary crusher addition
The addition of a secondary crusher in early summer 2011 increased the overall mill throughput capacity from 3.1 million tonnes per year (8,500 tonnes per day) to 3.59 million tonnes per year (9,840 tonnes per day). Since the installation of the permanent secondary crusher in June 2011, the design rate of 8,500 tonnes per day has been consistently exceeded.
Crushing circuit
A gyratory crusher (3.94 m by 6.31 m, 370 kW) reduces run-of-mine ore to about 80 percent passing 110–175 mm. Primary crushing is expected to crush an average of 833 tonnes per hour to supply the secondary crusher in order to satisfy mill feed requirements of 385 tonnes per hour. The secondary crusher (XL900, 671 kW) reduces the 110–175 mm ore from the gyratory to a product with about 80 percent passing 25–38 mm, depending on the required mill feed rate. The secondary crusher rate is about 750–850 tonnes per hour at a design operating time of 75 percent per day. A vibrating screen was installed ahead of the secondary crusher to scalp off product-sized ore prior to crushing. Crushed ore is fed to a coarse ore stockpile with a live capacity of 8,500 tonnes and then reclaimed to the SAG mill.
Grinding circuit
The SAG mill (7.925 m diameter by 3.734 m long, 3,650 kW) operates together with a ball mill (5.486 m diameter by 8.839 m long, 4,474 kW) to reduce the ore to about 80 percent passing 60–85 µm, depending on ore type and hardness. The ball mill operates in closed circuit with cyclones.
Gravity concentration
Approximately 33 percent of the cyclone underflow reports to a gravity concentrator, protected by an oversize scalping screen, followed by an intensive cyanidation unit (ICU). Gravity-recovered gold is intensively leached in concentrated cyanide solution. Gold-bearing pregnant solution from the intensive cyanidation leach tank is recovered by electrowinning, followed by smelting and doré bar production.
Leaching and carbon-in-pulp
Cyclone overflow is thickened prior to flowing into a pre-aeration and leaching circuit consisting of three pre-aeration tanks (4,200 m³ each) where air is injected, followed by six cyanide leach tanks (4,200 m³ each). Leached slurry is directed to a CIP system for gold recovery. The CIP circuit consists of seven tanks (142 m³ each) in series. Gold in solution from the leaching circuit is recovered on carbon in the CIP circuit and subsequently stripped and recovered from the strip solution by electrowinning, followed by smelting and doré bar production.
Tailings management
CIP tailings are thickened to recover cyanide from the process solution and then treated using the standard SO₂/air process to destroy residual cyanide. Tailings are pumped to the permanent tailings facility, which is designed for zero discharge, with all water reclaimed for reuse in the mill.
Recovery performance and testwork basis
The overall gold recovery was expected to be about 93.13 percent, with about 30 percent recovered in the gravity circuit. Based on an average gold head grade of 3.703 g/t, average gold production was estimated at approximately 343,000 ounces per year. The metal extraction rates established at startup, according to metallurgical testwork done in 2005 (SGS Lakefield et al., 2005), are summarized in Table 17.1 of the report. In 2011, the Meadowbank plant achieved an average gold recovery of 93.8 percent. With the new Life of Mine plan, the plant is expected to achieve a 94.0 percent gold recovery rate.
Changes under the new Life of Mine plan
During Q3 and Q4 of 2011, mill average throughput was 414 tonnes per hour and 413 tonnes per hour respectively, compared to 375 tonnes per hour at the end of Q2 2011. The addition of the secondary crusher between the primary crusher and the grinding circuit increased mill throughput flexibility. The grinding circuit can handle an average daily throughput above 450 tonnes per hour under the 2012 Meadowbank Mill Production Budget.
In summer 2011, SAG mill liner and grate design were reviewed to support throughput between 450 and 500 tonnes per hour. The SAG mill motor capacity was increased from 3,356 kW to 3,650 kW. Pump upgrading and optimization modifications were in progress. No major capital investments were expected under the new LOM plan, though some equipment upgrading would be required. Process plant grinding circuit simulations and a study were scheduled for completion at the end of 2012 to evaluate the impact of increasing SAG mill feed size on overall SAG mill throughput, with the objective of decreasing secondary crusher power consumption and increasing secondary crusher throughput by using a larger close side setting.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Original design capacity | 2.7 million tonnes/year (7,500 t/day) | Design |
| Post-takeover design capacity | 3.1 million tonnes/year (8,500 t/day) | Design (Hatch Engineering, 2007) |
| Post-2011 secondary crusher capacity | 3.59 million tonnes/year (9,840 t/day) | Proposed design (after June 2011) |
| Overall gold recovery (original) | 93.13% | Design expectation |
| Gravity circuit recovery contribution | ~30% | Design expectation |
| Average gold head grade | 3.703 g/t | Design assumption |
| Average annual gold production | ~343,000 oz/year | Design estimate |
| 2011 achieved gold recovery | 93.8% | Historical operating data |
| New LOM expected gold recovery | 94.0% | Proposed design |
| Grind size (Portage deposit) | 80% passing 62 µm | Testwork (SGS Lakefield et al., 2005) |
| Grind size (Goose deposit) | 80% passing 62 µm | Testwork (SGS Lakefield et al., 2005) |
| Grind size (Vault deposit) | 80% passing 80 µm | Testwork (SGS Lakefield et al., 2005) |
| Portage gold recovery | 94.1% | Testwork (SGS Lakefield et al., 2005) |
| Goose gold recovery | 96.1% | Testwork (SGS Lakefield et al., 2005) |
| Vault gold recovery | 91.3% | Testwork (SGS Lakefield et al., 2005) |
| SAG mill power (post-upgrade) | 3,650 kW | Proposed design (summer 2011) |
| SAG mill dimensions | 7.925 m diam. x 3.734 m long | Design |
| Ball mill dimensions | 5.486 m diam. x 8.839 m long | Design |
| Ball mill power | 4,474 kW | Design |
| Gyratory crusher power | 370 kW | Design |
| Secondary crusher power | 671 kW | Design |
| Pre-aeration tank volume | 4,200 m³ each (3 tanks) | Design |
| Leach tank volume | 4,200 m³ each (6 tanks) | Design |
| CIP tank volume | 142 m³ each (7 tanks) | Design |
| Coarse ore stockpile live capacity | 8,500 tonnes | Design |
| Q3 2011 average throughput | 414 tph | Historical operating data |
| Q4 2011 average throughput | 413 tph | Historical operating data |
Project website: https://www.agnicoeagle.com/English/operations-and-projects/global-operations-and-development-projects/meadowbank-complex/default.aspx
Technical qualifications
The recovery rates presented for the three main deposits (Portage, Goose, and Vault) are based on metallurgical testwork described in SGS Lakefield et al., 2005. The original LOM plan gold production estimate of 343,000 ounces per year and total of 3,258,893 ounces is based on design assumptions. The report notes that grinding circuit simulations and a study were scheduled for completion at the end of 2012 to evaluate the impact of increasing SAG mill feed size, with the objective of decreasing secondary crusher power consumption and increasing secondary crusher throughput using a larger close side setting. The report does not provide complete flowsheet details, final process performance results, project economics, or current operational status beyond February 15, 2012.
Source: Meadowbank Mine Technical Report, February 15, 2012, Sections 17.1–17.4.
