This profile is based on the April 2022 Technical Report for the Ruby Creek Project, which summarises historical feasibility studies (2005) and HPGR design work (2006) without undertaking new testwork or plant design. The processing description is a proposed flowsheet, not an operating plant.
Report context
The 2022 Technical Report for the Ruby Creek Project, , describes no new mineral processing testwork or plant design. All processing information is drawn from earlier studies: the 2005 Wardrop Engineering preliminary feasibility, the 2006 Polysius HPGR testwork, and subsequent 2006–2007 metallurgical investigations by SGS Minnovex and G&T Metallurgical Services, which were consolidated by Golder Associates in a 2007 feasibility update. The report presents a conceptual flowsheet for producing a high-grade molybdenite (MoS₂) concentrate from a deposit with low trace-impurity mineralisation.
Processing route
Comminution circuit
Run-of-mine ore is dumped into a gyratory crusher, with crusher discharge conveyed to a coarse ore stockpile. From the stockpile, ore is reclaimed and conveyed to screens. Screen undersize becomes the finished product feeding the high-pressure grinding rolls (HPGR) in open circuit. Screen oversize is crushed in one of two cone crushers, with cone-crushed product recycled to the screens. The HPGR circuit allows for a small amount of “edge recycle,” but otherwise all HPGR product feeds directly into a ball mill. Ball mill product is classified through cyclones; oversize material is recycled to the ball mill.
The HPGR circuit replaced an earlier semi-autogenous grinding (SAG) mill design. The Polysius testwork (2006) indicated that HPGR use would increase grinding circuit availability compared with a SAG mill, with added but difficult-to-quantify benefits of reduced variability in flotation circuit operation. A design risk noted in the report is that if cone crusher availability reduces ball milling circuit availability, a storage bin between the cone crushers and HPGR would be required to restore overall availability above 90%.
Flotation and regrind
Flotation comprises rougher/scavenger tank cells. Rougher concentrate is reground in a mill to a much finer state (P80 = 20 microns). The reground product is then cleaned in a series of stages. The 2005 Wardrop design specified column cells for four cleaning stages, with two regrinding stages included in the cleaner flotation section to improve molybdenum grade in the final concentrate. The flowsheet represents a conventional molybdenum circuit.
Ruby Creek mineralisation contains minimal trace impurities: pyrite, chalcopyrite, sphalerite, galena, and bismuthinite. Extensive mineralogy work indicates that almost all these impurities are liberated during grinding and regrinding and can be mostly removed in cleaning stages with reasonable amounts of depressant. Flotation reagents include diesel (kerosene) and pine oil, used at natural pH (7.8–8.2) in the milled pulp.
Concentrate handling and tailings
Final concentrate is thickened and settled with the aid of flocculant, then dewatered in a pressure belt press. The filter cake is dried in a rotary hearth drier, cooled in a storage bin, and packaged into tote bags of approximately 2-tonne capacity. Bags are weighed and moved to a storage area.
Tailings are impounded and water is recycled for use in the mill.
Plant staffing
The mill is designed to operate seven days per week, 24 hours per day, with four crews working 12-hour shifts on a two-week turnaround. The 2005 Wardrop design specified 85 operating personnel and 35 maintenance staff, with an additional 6 persons for power supply and surface facilities, and 25 general and administrative staff, for an overall total of 151 personnel.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Plant throughput | 20,000 metric tonnes per day | Design (Wardrop, 2005) |
| Plant availability | 92% | Design assumption |
| Overall molybdenum recovery | 90% | Design (from MinnovEX testwork; G&T work projected 92%) |
| Final concentrate grade | 54% molybdenum | Predicted from MinnovEX testwork |
| Mill feed grade | 0.087% molybdenum | Basis for testwork prediction |
| Bond ball mill work index | 12.2 kWh/metric tonne | MinnovEX testing (reported by Wardrop, 2005) |
| Bond work index range (from Britton, 1969) | 8–20 kWhr/st, majority 11–14 kWhr/st | Historical testwork |
| Regrind product size (P80) | 20 microns | Design specification |
| Flotation pH | 7.8–8.2 (natural) | Design specification |
| Flotation stages | Rougher/scavenger + 4 cleaning stages | Design (Wardrop, 2005) |
| Regrind stages | 2 | Design |
| Concentrate packaging | ~2-tonne tote bags | Design |
| Plant staffing (total) | 151 | Design (includes 85 operating, 35 maintenance, 6 power/surface, 25 G&A) |
Project website: https://www.stuhini.com/rubycreekoverview55
Technical qualifications
The processing route described is a proposed design based on the 2005 Wardrop preliminary feasibility and 2006 HPGR study. No new testwork or plant design was undertaken for the 2022 report. All recovery and grade assumptions derive from historical testwork: the Britton Research testing (1969), MinnovEX testing (2005), and G&T Metallurgical Services pilot-plant work (2006). The 2022 report notes that the earlier 90% recovery assumption was retained despite G&T testwork projecting 92% recovery.
The flowsheet details (equipment sizing, specific cell geometry, mass balances) were not available to the report author, as detailed equipment listings and flowsheets were contained in appendices of the Wardrop reports that were not provided. The HPGR testwork did not include testing to quantify process efficiency downstream of comminution; grade and recovery information therefore did not change from the 2005 design basis.
The staffing total of 151 includes all site personnel (operating, maintenance, power supply, surface facilities, and general/administration). The 85 operating personnel figure is the process-plant-only component, not the entire staffing complement.
Source: “Technical Report for the Ruby Creek Project, Camp Floyd and Ophir Mining Districts, Northern British Columbia, Canada,” Mine Development Associates (a division of RESPEC), effective date April 22, 2022. Sections 13.0–13.6 (Mineral Processing and Metallurgical Testing) and Section 17.0 (Recovery Methods).
