This technical report describes the proposed processing of Ootsa mill feed through the existing HB mill on a toll-milling basis, with no modifications to the existing flowsheet.
Report context
The report is dated 2016 and addresses the Ootsa Project located in the Omineca Mining Division, British Columbia, Canada. The project development is predicated on the amenability of Ootsa mill feed to processing using the existing HB mill without modification. Preliminary test work as discussed in Section 13 of the Preliminary Economic Assessment indicated this to be the case.
Processing route
Crushing
Mill feed excavated in the open pits at Ootsa will be hauled to a crusher station located near the edge of the Seel and Ox open pit(s). The proposed crusher is a Metso C160 or equivalent single-toggle, jaw crusher mounted in a semi-mobile, direct-dump arrangement. The crusher is capable of throughput of 700-850 tph generating a crushed product with a P80 of 150-200 mm. The crusher will discharge directly to the overland conveyor which will transfer mill feed from the mining area at Ootsa to the mill.
Mill Feed Handling
Mill feed arriving at the plant site will be conveyed to the dump pocket at the existing crusher installation. There are no plans to make use of the existing gyratory crusher for processing Ootsa mill feed although its presence offers the opportunity to maximize the throughput of the jaw crusher and use the existing gyratory in a secondary crushing role to achieve suitable size reduction. Mill feed discharged at the crusher will be conveyed by the existing conveyor and stacker system to a 30,000 t crushed mill feed surge stockpile. Two apron feeders located beneath the pile draw material onto the reclaim conveyor which carries mill feed into the mill.
Grinding
Feed from the crushed ore stockpile discharges into the SAG mill via the reclaim/SAG mill feed conveyor. The primary grinding mill is a nominal 32' x 14' high-aspect semi-autogenous grinding (SAG) mill powered by a pair of GE 5,500 HP electric motors. The SAG mill generates a P80 2-3 mm product which is discharged to a 20' x 8' Diester vibrating screen deck. Oversize from the screen deck is directed to a Metso HP 500 pebble crusher installed in close circuit with the SAG mill. Undersize is directed to secondary grinding which is performed by two 30' x 16' ball mills. Ball mill discharge is pumped up to a pair of 6 x 26" hydrocyclone clusters where underflow is returned to the ball mills and overflow is directed to flotation.
Bulk Flotation
Flotation feed will have a nominal particle size of 100 µm, delivered as a slurry with a density of 30-40% solids. The rougher flotation circuit is composed of 6 x 100 m³ Outotec Super Cells. Tailings from rougher flotation will go to tails while concentrate will be thickened and reground to about 30 µm prior to cleaning. Cleaner flotation will be performed by 2 x 10' diameter flotation columns. Cleaner column overflow is directed to bulk thickening while cleaner tails are sent to the Scavenger Flotation circuit. The Scavenger circuit is composed of 6 x 16 m³ Outotec U-cells. Concentrate from the scavenger circuit is recycled and scavenger tailings are directed to the tailings pond.
Molybdenum Recovery
Underflow from the bulk thickener is directed to the molybdenum rougher/scavenger flotation circuit. Concentrate from the molybdenum roughers is directed to flotation columns in the molybdenum cleaner circuit. Scavenger circuit tailings reports to the copper thickener. The product generated from the molybdenum cleaner circuit reports to the molybdenum thickener while the underflow from the cleaner circuit is recycled.
Dewatering and Concentrate Handling
When copper and molybdenum are being recovered, copper and molybdenum concentrate is thickened in two separate 60' diameter thickeners. In each, slurry density is increased to about 70% solids prior to filtration. Final dewatering of copper concentrate is performed with an automatic filter press before the product is stored in bulk in the concentrate storage shed prior being trucked to port. Thickened molybdenum concentrate is dewatered using a vacuum filtration system after which it is bagged and stored in advance of shipping.
Reagents
Lime is used to maintain an appropriately alkaline pH throughout the process to provide suitable conditions for copper flotation and depress the flotation of iron sulfides. The primary flotation collector will be PAX, potassium amyl xanthate. A stable flotation froth will be created with MIBC or an equivalent while the hydrophobic nature of sulfide particles will be promoted during flotation using fuel oil. Sodium hydrosulfide, NaHS, will be used as a depressant during copper-molybdenum separation.
Services
The total connected load for the mill will be about 18.8 MW including crushing but excluding the mill feed conveyor system. Based on 8,000 operating hours per year, processing will consume about 150,400,000 kW-hrs annually. The mill will utilize approximately two cubic metres of water for each tonne of mill feed processed. Free water associated with tailings will be recycled for processing while entrapped water will be made up from a combination of inflows to the process water pond and pumping from Tahtsa Reach. Fresh water consumption is expected to be similar to that cited in the Huckleberry 2011 LOM Plan of 280,000 m³ per year.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Throughput capacity | 15,500 tpd (approximately 5.6 Mtpa) | Estimated at finer primary grind (95 microns) |
| Bond grindability index | 16 kWh/t | Assumed (no comminution data developed for Ootsa) |
| Crusher throughput | 700-850 tph | Design specification |
| Crusher product P80 | 150-200 mm | Design specification |
| Crushed ore surge stockpile capacity | 30,000 t | Existing facility |
| SAG mill dimensions | 32' x 14' | Existing equipment |
| SAG mill power | 2 x 5,500 HP GE motors | Existing equipment |
| SAG mill product P80 | 2-3 mm | Operating parameter |
| Ball mill dimensions | 2 x 30' x 16' | Existing equipment |
| Hydrocyclone clusters | 2 x 6 x 26" | Existing equipment |
| Flotation feed particle size | 100 µm nominal | Design parameter |
| Flotation feed density | 30-40% solids | Design parameter |
| Rougher flotation cells | 6 x 100 m³ Outotec Super Cells | Existing equipment |
| Regrind particle size | ~30 µm | Design parameter |
| Cleaner flotation columns | 2 x 10' diameter | Existing equipment |
| Scavenger flotation cells | 6 x 16 m³ Outotec U-cells | Existing equipment |
| Copper and molybdenum thickeners | 2 x 60' diameter | Existing equipment |
| Thickener underflow density | ~70% solids | Operating parameter |
| Total connected load (including crushing) | 18.8 MW | Design estimate |
| Annual power consumption | 150,400,000 kW-hrs | Based on 8,000 operating hours/year |
| Process water consumption | ~2 m³ per tonne mill feed | Operating parameter |
| Fresh water consumption | 280,000 m³ per year | Reference to Huckleberry 2011 LOM Plan |
Project website: https://surgecopper.com/news-releases/gold-reach-announces-name-change-to-surge-copper-corp/
Technical qualifications
No comminution data have yet been developed for Ootsa and it is assumed that a Bond grindability index of 16 kWh/t applies. At the finer primary grind (95 microns) indicated for all Ootsa material, average throughput capacity is estimated at 15,500 tpd or approximately 5.6 Mtpa. The process flowsheet referenced in Figure 17.1 was sourced from a September 1, 2011 technical report on the Main Zone Optimization at the Huckleberry Mine. The process description and equipment specifications describe the existing HB mill, not new infrastructure for the Ootsa project.
Source: Ootsa Project , 2016 Technical Report, Recovery Methods sections 1.17 and 17.0 through 17.1.8.
