Bucko Lake Nickel Project PEA — 2022 Technical Report

The Bucko Lake process plant, on care and maintenance since 2012, is proposed to be reactivated at 1,500 tpd, 50% higher than its original design capacity.

Report context

The 2022 Preliminary Economic Assessment for the Bucko Lake Nickel Project addresses the reactivation of the process plant that had been designed to process nickel-rich mineralized material from the underground Bucko Lake Mine. The plant has been in care and maintenance since 2012. The proposed plan is to process mineralized material at 1,500 tpd, versus the original 1,000 tpd design capacity. Some process plant feed will be hoisted, but most will be hauled by truck up a ramp and fed to the process plant crusher circuit by a loader.

Processing route

Historical operating data (2009 to 2012)

Between 2009 and 2012, the process plant processed 435,573 t of mineralized material from the Bucko Lake Mine to produce a total of 6,928,148 lb (3,142,538 kg) of nickel. Average process recoveries ranged from 55.52% in 2009 to 75.65% in 2012. A process recovery high of 79.98% was reported for processing 22,616 t of feed grading 0.98% Ni in the second quarter of 2012. The last month of operation was May 2012.

Existing process plant components

The process plant appears to have been reasonably mothballed with apparently minimal equipment deterioration and salvage during the last decade. The plant design can be considered conventional and the flowsheet remains appropriate for processing the Bucko Lake Mineral Resource. Many of the major operating components appear to have been acquired from an equipment salvage company (Carminex) and are described as quality items suitable for producing a high-grade nickel concentrate.

Crushing and grinding. The crushing facilities include a coarse material storage silo, one Metso C100 jaw crusher and one XL300 1.1 m cone crusher, a triple deck vibratory screen and associated conveyors. The jaw crusher reduces ROM material to approximately 76 mm and the cone crusher was reported to have been set to reduce material size to 16 mm (5/8 in). The crushed fines bin is reported to be able to store 1,000 t of material.

Existing grinding facilities are composed of a rod mill in open circuit and a ball mill in closed circuit with a pair of cyclones. The mill drives were 340 and 1,130 kW, respectively, with the nominal capacity of these grinding units listed as 1,000 tpd.

Flotation and concentrate handling. The rougher-scavenger flotation circuit is believed to be composed of five 8.5 m³ cells, and the three-stage cleaner circuit is composed of ten 1.4 m³ cells. The third stage cleaner concentrate is the final product which is thickened in a 5 m diameter thickener and transferred to a concentrate storage tank that feeds a Larox pressure filter. The pressure filter was expected to dewater the concentrate to approximately 8% moisture, suitable for transport without thermal drying. The dewatered concentrate was placed in an in-plant storage area before loading onto trucks for shipment to a Sudbury smelter.

Paste backfill plant. A paste backfill plant had been installed in a building attached to the process plant building in 2012 but was not commissioned when operations were suspended in June of that year. The plant was designed to dewater tailings to 60% solids using cyclones and add sand to reduce moisture content. The report states that the backfill plant will not use sand in the future and the process will be converted to paste production from 100% tailings. Vacuum filters will be installed to dewater the tailings to the designed moisture content prior to paste backfill mixing.

Proposed process plant upgrading for 1,500 tpd

Increasing throughput to 1,500 tpd or greater will require significant investments. The report recommends that process plant capacity should be increased by at least 10% of this objective, or 1,650 tpd, to achieve the intended 1,500 tpd target.

Crushing upgrades. The C100 jaw crusher and associated conveyors, feeders and screens are expected to be capable of handling the increased tonnage by increasing daily crushing hours from 12 to between 18 to 20. The 1.1 m standard crusher should be capable of handling 1,650 tpd when operating for up to 20 hours per day at a setting of 16 mm. Tightening the crusher to 13 mm to increase grinding capacity may choke the cone crushing capacity. The capacity of the crushing and grinding circuits could be expanded by the installation of a tertiary crusher, a second cone crusher, possibly a short-head cone crusher set to produce a 10 to 13 mm crushed product.

Grinding upgrades. The current rod and ball mill combination is expected to be limited to less than 1,650 tpd. A capacity increase may be achieved by reducing the crushed mineral size to 13 mm and installing a system for recycling ball mill scats to rod mill feed. The two cyclones may not be capable of handling the increased tonnage and the anticipated high circulating load. A review of cyclone and pumping capacity should be considered. A trash screen should be installed in the cyclone overflow to remove wood and plastic debris.

From an operational perspective, the ideal change in crushing and grinding would be the installation of a SAG mill to replace cone crushing, screening and rod milling. An optional and less costly configuration could be the installation of a secondary cone crusher with associated screens, conveyors and dust collection. A second rod mill operating in parallel to the existing rod mill could be considered but is not recommended. The installation of a second cone crusher, a SAG, or a second rod mill would require an expansion of the process plant building and electrical power supply.

Flotation upgrades. The rougher-scavenger cell volume is described as barely adequate for processing 1,650 tpd, and cleaner capacity is dependent on process plant feed grade. A rationing of the cleaner cells can be expected and additional cleaning capacity would be needed. This extra capacity could be achieved by the installation of a column cell for the final cleaning stage.

Concentrate regrind. Regrinding of rougher concentrate or first cleaner concentrate could be considered. A small ball mill or a tower mill could perform this task. The regrinding mill for processing the first cleaner concentrate would be much smaller than for rougher concentrate. There appears to be a significant amount of unoccupied space between the rod and ball mill grinding and the flotation equipment that could be a location for a small ball mill or a tower mill to regrind rougher flotation concentrate.

Concentrate thickening and filtration. The 5 m diameter concentrate thickener is designed for 1,500 tpd of process plant feed grading 2.2% nickel. This thickener and the 5.1 m filter stock tank may be close to adequate for the higher tonnage throughput at a slightly lower grade feed. The capacity of the Larox filter is uncertain, and having only one filter is described as operationally risky. A standby pressure filter should be considered.

Metallurgical tools and automation. It is assumed that a belt weightometer was installed in the proper configuration on the rod mill feed conveyor. A safe location near the weightometer for grab sampling for moisture is expected to be available. If not already installed, automatic Vezin-type samplers could be considered for sampling grinding cyclone overflow, concentrate between flotation and the thickener, and the tailings slurry. It is expected that the final concentrate will be hand-pipe-sampled for moisture and metal content. In advance of process plant restart, there may be an opportunity to install a low-cost monitoring and control network.

Process plant restart strategy

The report presents two general options for reviving the process plant: reinstall missing or derelict components and restart the plant at nameplate capacity (1,000 tpd), or make capacity and efficiency upgrades and commence operation. Given uncertainty about what the bottlenecks would be and that significant upgrades may be completed while the plant is operating, the report indicates that the best option would be to revive the plant in its constructed flowsheet, identify bottlenecks, and appropriately remediate these during the initial months of operation. Capacity and efficiency equipment and upgrades could be installed prior to restart, and not brought online until the nameplate capacity is re-established. The underground mine is planned to supply an average of 835 tpd in the first year of production, ramping up to 1,500 tpd by the beginning of the third year.

Rehabilitation requirements

Restarting a process plant that has been dormant for a decade will require sequential examination and test operation of all units. Major components likely to require repair or upgrade include: receipt and screening of underground mineralized material haulage (exposure to weather would have deteriorated conveyors and led to seized bearings); replacement or freeing-up of seized conveyor bearings, pump shafts, sensors, safety devices and lighting; replacement of the 1,130 kW ball mill drive motor; inspection of ball and rod mill gears and bearings, check mill internals such as liners, and determine if rod and ball loads were removed (remaining grinding media would corrode and bond together); restoring tool and spare parts inventories; re-equipping the sample preparation and assay laboratories; and modifications and completion of the paste backfill plant.

Key reported parameters

Technical qualifications

The report notes that the process plant has been on care and maintenance since 2012 and that many of the major operating components appear to have been acquired from an equipment salvage company (Carminex). The condition of equipment after a decade of dormancy is noted as uncertain, with several major components likely to require repair or upgrade before restarting mineral processing.

The report states that there is some uncertainty of what the bottlenecks would exactly be when increasing throughput. The capacity of the Larox filter is described as uncertain. No information is available on the status of the decade-old reagent mixing and distribution system, which may need extensive cleaning and maintenance. The condition and capacity of low- and higher-pressure blowers, switchgear and the reclaim- and fresh-water management systems are described as uncertain.

The rougher-scavenger flotation cell volume is described as barely adequate for processing 1,650 tpd, and cleaner capacity is noted as dependent on process plant feed grade. The two cyclones may not be capable of handling the increased tonnage and the anticipated high circulating load.

Source: Bucko Lake Nickel Project PEA , 2022 Technical Report, Section 17.0 Recovery Methods, pages 180-187.