The Thompson Creek concentrator, operating since 1983, will treat remaining ore using a conventional molybdenum flowsheet with proposed refurbishment and replacement of key equipment during a restart preparation period.
Report context
This technical report, effective September 1, 2024, describes the existing processing facilities at the Thompson Creek Molybdenum Mine (TCM). Processing operations began in 1983 and have historically produced saleable high-grade molybdenum concentrates at recoveries of 90% Mo or better. Currently, most of the plant is on care and maintenance, with only leaching and high-grade circuits operating to treat custom feeds. Prior to full-scale production, a restart preparation period will be required to bring the concentrator to a fully operational state. Where necessary, new replacement equipment will be installed, or existing equipment and circuits will be refurbished.
Processing route
Primary Crushing
Run of mine (ROM) ore from the open pit is transported via haul trucks to a primary gyratory crusher located near the pit. The 60-inch by 89-inch gyratory crusher has an installed motor power of 600 hp. A comprehensive gyratory crusher inspection was completed in 2023 and a course of actions was recommended to upgrade the crusher to reliable and stable operation. The crusher discharge apron feeder will also be refurbished during restart activities.
Overland Conveying and Coarse Ore Stockpiling
Crushed ore is conveyed via two overland conveyors and deposited onto a coarse ore stockpile for storage upstream of the processing plant. The stockpile is not covered but includes a wind fence to control fugitive dust. Total capacity is approximately five days of production, with a live capacity of approximately 24 hours. Stockpiled ore is reclaimed by two parallel process lines, each equipped with four apron feeders. A full inspection of the overland conveyors and SAG mill feed conveyors was conducted in 2023, with maintenance actions including full belt replacement for Conveyor 1, idler replacements, rip detection system upgrades, and general maintenance.
Grinding
The primary grinding circuit consists of two parallel grinding lines. Each line has one SAG mill and one ball mill in closed-circuit configuration with two classifying hydrocyclone clusters. The SAG mills are 32 ft in diameter and 13 ft in length, each with 8,000 hp of installed power driven by two 4,000 hp motors in a dual-pinion arrangement. Grinding media is 5.25-inch steel balls. The ball mills measure 16.5 ft in diameter and 26 ft in length, each with 4,000 hp of installed power in a single pinion drive arrangement. The ball mills utilize steel liners due to the use of the grinding circuit as a conditioning stage for the fuel oil reagent. Grinding media for the ball mills is 3–4-inch steel balls. The grinding cyclone clusters each have six 26-inch cyclones. Collector (fuel oil) and frother are added to the grinding circuit.
The SAG mills, cyclone clusters, and ball mills were all inspected for recommended actions. The SAG No. 2 west clutch and Ball Mill No. 2 clutch will be changed out. Ball Mill No. 1 girth gear will be flipped, and Ball Mill No. 1 pinion will be replaced. New equipment to be installed includes a new cyclone feed pump-box to increase reliability and stability, and new liner and lifter designs for the SAG mills.
Rougher Flotation
The historical rougher flotation circuit consisted of two banks, each with 11 WEMCO #164 cells providing 1,000 ft³ of volume each, operated through a self-aspirated mechanism. For restart, the rougher flotation circuit will be replaced with new cells of the same specification. Rougher flotation reagent addition includes fuel oil as a molybdenum collector and frother, which are introduced in the grinding circuit. Overall molybdenum recovery in the roughing stage will be 94%.
Concentrate Regrinding and Cleaner Flotation
Rougher concentrate is advanced to the first regrind circuit, which consists of a first regrind ball mill measuring 8 ft in diameter and 9 ft in length with 250 hp of installed power, in closed circuit with 6-inch diameter cyclones producing a P80 of 42 µm. The first regrind mill was inspected and its trunnion, bearings, pinion, and gear were reported to be in good condition.
The first cleaner flotation circuit consists of three cleaner cells and six scavenger cells (WEMCO #120 cells, 300 ft³ each). During restart activities, the first cleaner and scavenger cells will be replaced with in-kind equipment.
The first cleaner concentrate feeds a series of three 60-inch diameter flotation columns (second, third, and fourth cleaners). The cleaning system has been configured to allow a high level of flexibility. The fourth cleaner column concentrate is sent to a stock tank that feeds a fine screening circuit with an aperture size of 37 µm.
Concentrate Leaching and Dewatering
Undersize material from the concentrate screening circuit is sent to a final concentrate thickener measuring 30 ft in diameter. The existing thickener was inspected and found to be in poor condition and will be replaced with a new 30 ft diameter thickener during restart activities.
The leaching circuit consists of four agitated leach tanks, each 8.75 ft in diameter and 11.50 ft in height. The leaching process improves concentrate grade and quality by dissolving impurities such as copper and lead into the leachate at high temperature. A mixture of hydrochloric acid, ferric chloride, and salt is currently used as lixiviant. Sodium chlorate will be used as a replacement for ferric chloride for future processing.
The leached concentrate is dewatered using filter presses. Filtered concentrate cake is collected and conveyed to a Holoflite dryer to reduce moisture before packaging.
High-Performance Molybdenum Circuit
Screen oversize from the concentrate screening circuit is fed to a hydrocyclone cluster associated with the second regrind circuit. Cyclone underflow returns to the No. 2 regrind mill while overflow is sent to 24-inch or 30-inch cleaner columns. Final concentrate from these columns is filtered, with solids reporting to a Holoflite dryer. The product can be directly bagged or, optionally, processed through a jet mill to approximately 3–4 µm, with potential further reduction in pancake mills to approximately 1–2 µm. The HPM circuit has been operated throughout the Thompson Creek care and maintenance period and can treat custom material from other operations in isolation from the rest of the plant.
Pyrite Removal
The original pyrite flotation equipment was removed when the mine was placed under care and maintenance. A new pyrite removal circuit will need to be constructed prior to restart. The new circuit will consist of a single high-capacity Jameson Cell (B8500/12) fed from the existing pyrite flotation conditioning tank. Pyrite concentrate will be pumped to the final sub-aqueous pyrite deposition site. Tailings from the pyrite flotation circuit will tie into the existing tailings piping and pumping system.
Key reported parameters
| Parameter | Unit | Value | Basis |
|---|---|---|---|
| Annual ore processing rate | Mst | 10.4 | Design |
| Nominal concentrator throughput | st/h | 1,290 | Design |
| Nominal concentrator throughput | st/d | 30,971 | Design |
| Concentrator availability | % | 92.0 | Design target |
| Historical availability (2012) | % | 91.7 | Actual operating data |
| Design specific energy | kWh/st | 11.35 | Testwork (Year 10-EOM composite) |
| Installed grinding power | hp | 24,000 | Equipment specification |
| Grinding circuit product P80 | µm | 212 | Design |
| Regrind product P80 | µm | 42 | Design |
| Head grade (molybdenum) | % | 0.08 | Design |
| Molybdenum recovery | Mo % | 90.5 | Design |
| Rougher stage molybdenum recovery | % | 94 | Design |
| Concentrate molybdenum grade | Mo % | 54.2 | Design |
| Concentrate molybdenite grade | MoS2 % | 90.4 | Design |
| Concentrate production | dry st/d | 40.5 | Design |
| Molybdenum production | dry st/d | 22.0 | Design |
| Primary crusher size | inch | 60 x 89 | Equipment specification |
| Primary crusher installed power | hp | 600 | Equipment specification |
| SAG mill size | ft | 32 x 13 | Equipment specification |
| SAG mill installed power (each) | hp | 8,000 | Equipment specification |
| Ball mill size | ft | 16.5 x 26 | Equipment specification |
| Ball mill installed power (each) | hp | 4,000 | Equipment specification |
| Ball mill product P80 | µm | 212 | Equipment specification |
| Rougher flotation cell size | ft³ | 1,000 | Equipment specification |
| Regrind mill size | ft | 8 x 9 | Equipment specification |
| Regrind mill installed power | hp | 250 | Equipment specification |
| Regrind hydrocyclone diameter | inch | 6 | Equipment specification |
| Cleaning stages | each | 4 | Equipment specification |
| Column cleaner diameter | inch | 60 | Equipment specification |
| Thickener diameter | ft | 30 | Equipment specification |
| Leach tanks (number) | each | 4 | Equipment specification |
| Leach tank size (diameter x height) | ft | 8.75 x 11.5 | Equipment specification |
| Pyrite flotation cell type | Jameson Cell B8500/12 | Equipment specification |
Project website: https://www.centerragold.com/operations/molybdenum-business-unit/
Technical qualifications
The concentrator availability is set at 92.0%, just above the 91.7% achieved in 2012, the last full operating year for which data are available for review. Based on the 2012 availability and restart activities, it is expected that Thompson Creek will be able to achieve the 92.0% availability. The design grind circuit specific energy is based on the Year 10-EOM composite, being the highest energy required of all four composites. The grinding circuit has historically been able to process ore at a greater than 11.35 kWh/st specific energy at a higher throughput than the nominal 1,290 st/h. Thompson Creek was able to achieve the 10.4 Mst/a annual throughput in 2011, but no clear availability information is available for that year. In 2012, throughput was 10.3 Mst/a at 91.7% availability. The design criteria, process description, and equipment specifications are based on the existing facilities with proposed replacement or addition of equipment highlighted in the flowsheet. Where equipment needs replacement, a like-for-like replacement will be obtained as much as practicably possible.
Source: Technical Report on Thompson Creek Molybdenum Mine, effective September 1, 2024, Sections 17 Recovery Methods.
