This report outlines a proposed processing route for the Shovelnose South Zone mineral resource based on limited metallurgical testwork, with key design assumptions requiring confirmation through additional testwork.
Report context
This technical report for the Shovelnose Gold Property – South Zone, dated 2023, presents a proposed processing concept for the mineral resource. The report acknowledges that metallurgical testwork data are minimal, with the extent of data from test processes being limited. The proposed design is based on available test results combined with the author's experience, and the report emphasizes that a significant amount of additional test data is required before process plant design can be confirmed.
Processing route
Overview of process options
Metallurgical tests emphasized the production by flotation of a rougher gold-silver sulphide concentrate plus cyanidation of flotation tails. Recoveries, representing gold and silver reporting to a rougher flotation concentrate combined with cyanide extractions, exceeded 90%. An optional process tested was direct cyanidation of the whole mineralized feed, which resulted in average extraction slightly exceeding 89%. A third process option, which provides the basis for the proposed flowsheet, involves production of a cleaned gold-silver-sulphide flotation concentrate followed by fine grinding and intensive cyanide leaching of this concentrate, with flotation tails subject to conventional leaching. Gold and silver would be recovered from clarified solutions by a Merrill Crowe process to produce a doré product. The production of a gravity concentrate was shown to be ineffective, and the gold content is described as not refractory and finely distributed.
Feed handling and crushing
Mineralized material will be hauled to surface with underground mine trucks and stockpiled on surface according to grade. ROM material will be blended by a front-end loader and fed to a surface-installed jaw crusher with a 50–100 t crusher feed bin below a 300 mm (12 in) grizzly. The crusher is anticipated to be set at 80 to 100 mm (3 to 4 in). Crushed material will be delivered to a covered stockpile of approximately 1,500 t capacity. Mill feed will be drawn from this stockpile by at least three feeders, with a propane-fueled loader employed to homogenize the stockpile. The crushing facility would operate 60 to 75% of available time.
Grinding
Three grinding stages are considered in the overall process. For process concept consideration, primary and secondary grinding are suggested to be a conventional SAG and ball mill combination (SABC). With a potential primary grind size P80 of 150 µm, a SAG mill of approximately 7.5 m diameter by 4 m long and a ball mill of 5 m diameter by 9 m long would be adequate. The only grind performance data available from testwork is a Bond Work Index (BWi) determined to be 20 kWh/t, a moderately high value. Additional grinding and attrition characteristics are needed. Based on the author's experience, steel grinding ball consumption could be in the order of 3–4 kg/t, and grinding energy draw in the range of 25 kWh/t. A provision will be considered for the SAG mill to be equipped in the future with a pebble circuit where +20 mm pebbles are screened from SAG discharge and crushed and recycled. Pebble return is initially expected to be low, at less than 5% of feed. A single ball mill will be in closed circuit with two banks of cyclones (one operating, one standby). The third grinding component will be a circuit to finely grind the flotation concentrate, for which a tower mill could be more effective than a ball mill.
Flotation and concentrate processing
A flotation concentrate is proposed to accumulate a significant proportion of gold and silver associated with sulphides. Rougher float tests conducted at a grind size of P80 75 µm indicated average recoveries of 76% for gold and 72% for silver in a concentrate representing between 7.4% and 13% weight of feed. The absence of cleaner test data makes the degree of weight and grade improvements uncertain. Based on preliminary evaluations of gold deportment from testwork and the author's experience, fine grinding and intensive leaching of the flotation concentrate is considered a promising strategy. The flotation concentrate would be thickened in a high-rate thickener to 45–50% solids and ground to fine size. The ground concentrate would be subject to intense leaching under high sodium cyanide concentrations of 1.5 to 2% solution with strong oxidation conditions (peroxide) in multi-stages of enclosed stirred vessels. Pregnant leach solution (PLS) would be recovered by plate-and-frame filters (two in parallel), with filter cake washed twice. Filtered tailings could be treated for cyanide destruction or re-slurried and combined with flotation tailings leach feed.
Flotation tailings leaching
Sulphide flotation tailings containing approximately 25% of the gold and silver present in process feed, with a significant residual gold content of approximately 2.5 g/t Au, would be subject to standard cyanide leaching. Oxidation would be provided by air injection or, if confirmed by test results, by oxygen injection. A series of stirred leach vessels followed by multi-stage counter-current decantation (CCD) is described as a reasonable leach and PLS recovery flowsheet.
Merrill Crowe circuit
Gold and silver recovery from PLS would be achieved in a proposed Merrill Crowe circuit, described as the preferred process when the ratio of silver to gold is 5:1 or greater (as per the mineral resource) and concentrations of arsenic and antimony are low. The process consists of solution clarification, deaeration, and precipitation with zinc dust. A precious metal precipitate is recovered by pressure filtration and smelted to produce a slag and doré product. Barren solution from the Merrill Crowe process will provide process water for grinding, leaching, and concentrate filter washing.
Tailings management
A significant portion of the 1,000 tpd leached tailings will be used as mine paste backfill, with the balance dry-stacked and placed in a designed storage facility. Over 70% of leached tailings are intended for paste backfill. Subject to test confirmation, processes could include removal of fines by cycloning and dewatering to 12–15% moisture by vacuum filtration, with addition of Portland cement for backfill. The 30% residual tailings fraction would be dewatered to approximately 10% moisture by pressure filtration for truck transport to dry-stack storage.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Combined flotation concentrate + cyanidation recovery | >90% | Testwork (rougher flotation + cyanide extraction) |
| Direct whole-ore cyanidation average extraction | >89% | Testwork |
| Rougher flotation gold recovery (P80 75 µm) | 76% average | Testwork |
| Rougher flotation silver recovery (P80 75 µm) | 72% average | Testwork |
| Flotation concentrate weight yield | 7.4%–13% of feed | Testwork |
| Bond Work Index (BWi) | 20 kWh/t | Testwork (moderately high) |
| Primary grind size P80 | 150 µm | Conceptual design |
| SAG mill dimensions | Approximately 7.5 m dia. × 4 m long | Conceptual design |
| Ball mill dimensions | 5 m dia. × 9 m long | Conceptual design |
| Steel grinding ball consumption (estimated) | 3–4 kg/t | Based on author's experience |
| Grinding energy draw (estimated) | 25 kWh/t | Based on author's experience |
| Pebble return (initial expectation) | <5% of feed | Conceptual design |
| Residual gold in flotation tails | ~2.5 g/t Au | Testwork estimate |
| Plant throughput | 1,000 tpd | Conceptual design |
| Flotation concentrate leach cyanide concentration | 1.5%–2% solution | Conceptual design |
| Tailings for paste backfill | >70% | Conceptual design |
| Residual tailings for dry-stack | ~30% | Conceptual design |
| Crusher setting | 80–100 mm (3–4 in) | Conceptual design |
| Stockpile capacity | ~1,500 t | Conceptual design |
| Crushing facility operating time | 60%–75% of available time | Conceptual design |
Project website: https://www.westhavenventures.com/projects/shovelnose-gold/details/
Technical qualifications
The report states that the extent of data from test processes is minimal. Additional grinding and attrition characteristics are needed to provide a more precise estimate of grinding circuit parameters. The absence of cleaner test data makes the degree of weight and grade improvements from flotation cleaning uncertain. Test cleaning of rougher concentrate is strongly recommended for conceptual design. The report identifies a significant number of test requirements for process plant design confirmation, including crushing, grinding and abrasion data; gold deportment characteristics; confirmation of the preferred processing approach; flotation concentrate grind size and grinding method selection; thickening and filtration rates; cyanide destruction methodology; and determination of process stages for paste backfill preparation. These test requirements suggest the need for sourcing 1–2 tonnes of fresh mineralized material and performance of bench-scale pilot testing.
Source: Shovelnose Gold Property – South Zone Technical Report, Sections 17.0–17.7
