This report details the proposed processing route for the Tower and Rail Project using the leased Bucko Mill, based on metallurgical testwork and designed flowsheets.
Report context
The report, dated January 12, 2021, presents recovery methods for a Preliminary Economic Assessment of the Tower and Rail Project owned by Rockcliff Metals Corp. in Manitoba, Canada. The proposed concentrator design utilizes the existing Bucko Mill near Wabowden, Manitoba, originally a nickel concentrator for CrowFlight Metals, adapting it for polymetallic copper-zinc separation.
Processing route
Proposed Design Overview
Mineralized material will be crushed at the mine site to a nominal -50 mm and mechanically sorted using X-ray transmission technology to reject barren rock. Approximately 1,500 tonnes per day of upgraded material, projected to be at or above Mineral Resource grade, will be trucked to the Bucko Mill. Material from the Tower Property will be processed first, followed by feed from the Rail Property after the Tower deposit is exhausted.
Sorted material received at the Bucko Mill will be cone-crushed and conveyed through the existing feed storage silo to the primary grinding circuit, which uses existing equipment. The grinding circuit is closed with cyclones for classification, with cyclone overflow reporting to flotation feed.
Proposed Flotation Circuit
Value metals will be recovered sequentially by froth flotation using metal-selective reagents. Copper is floated first, followed by a conditioning stage and zinc flotation. Copper rougher concentrate is reground in a 125/500F HIGmill and cleaned in a single cleaning stage. Cleaner tails report to a scavenger flotation stage, with the concentrate recycled to the copper cleaner regrind mill. Scavenger tails combine with copper-rougher tails and are conditioned for zinc flotation.
The zinc rougher concentrate is reground in a 75/200F HIGmill to 25 μm and floated in two stages of counter-current cleaning. The second cleaner concentrate is the final zinc concentrate. First cleaner tails are scavenged, with the scavenger concentrate recycled to the cleaning circuit regrind mill. Scavenger tails report to final tailings with zinc rougher tails.
Copper and zinc concentrates are separately thickened and dewatered in batches through the existing LAROX pressure filter.
Material Sorting Testwork
Additional material sorting testwork suggests that almost 50% of the run-of-mine material can be rejected by the sorter and returned to the mine as fill material, with less than 5% reduction in copper, zinc and gold metal values reporting to the mill.
Historical Bucko Mill Data
The existing Bucko Mill was designed to receive run-of-mine nickel ore with nominal capacity of 45 tonnes/hour feed and an operating license for 1,100 tpd. Primary grinding was sized as a 1,500 tpd circuit. The crushing circuit includes a jaw crusher in closed circuit with a triple deck screen and a cone crusher. Crushed material is stored in a 10.7 m diameter feed silo feeding a 2.7 m diameter rod mill and a 3.8 m diameter ball mill in closed circuit with cyclones.
The existing flotation circuit included five 8.5 m3 DR 300 cells for rougher and scavenger service, with cleaner stages using 1.4 m3 cells. Final concentrate was thickened and pressure filtered. A concentrate regrind circuit was designed but never installed.
Proposed Modifications to Test Flowsheet
The closed-circuit design includes copper cleaner tails recycled to the copper regrind mill, copper scavenger tails added to copper-rougher tails as zinc circuit feed, and zinc circuit final cleaner tails and scavenger concentrate recycled to the cleaning circuit regrind mill. Testwork showed only one stage of cleaning is required for the copper circuit, and regrinding copper-rougher concentrate increases zinc recovery to the zinc concentrate by more than 10 points as zinc minerals are liberated.
Reagent Scheme
Lime, metabisulphite, zinc sulphate, copper sulphate, two metal-selective collectors, and a simple frother generated excellent results. No cyanide is required. The existing reagent mixing and storage area is adequate with modest upgrades.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Sorted material feed rate | 1,500 tpd | Proposed design |
| Primary grind target (P80) | 145 μm | Proposed design |
| Material hardness (BWi) | ~14 kWh/t | Testwork result |
| Copper regrind target (P80) | 20 μm | Proposed design |
| Zinc regrind target (P80) | 25 μm | Proposed design |
| Copper recovery to Cu concentrate | 97% | Estimated closed circuit |
| Zinc recovery to Zn concentrate | 74% | Estimated closed circuit |
| Gold recovery to Cu concentrate | 55% | Estimated closed circuit |
| Silver recovery to Cu concentrate | 55% | Estimated closed circuit |
| Zinc recovery to Cu concentrate | 17% | Estimated closed circuit |
| Gold recovery to Zn concentrate | 8% | Estimated closed circuit |
| Silver recovery to Zn concentrate | 8% | Estimated closed circuit |
| Existing mill nominal capacity | 45 tonnes/hour | Historical operating data |
| Existing mill operating license | 1,100 tpd | Historical operating data |
| Existing rod mill dimensions | 2.7 m diameter x 3.7 m long | Historical equipment |
| Existing rod mill power | 373 kW | Historical equipment |
| Existing ball mill dimensions | 3.8 m diameter x 4.6 m long | Historical equipment |
| Existing ball mill power | 895 kW | Historical equipment |
| Copper rougher minimum residence time | 18 min | Proposed design, testwork basis |
| Copper 1st cleaner minimum residence time | 24 min | Proposed design, testwork basis |
| Zinc rougher minimum residence time | 15 min | Proposed design, testwork basis |
| Zinc 1st cleaner minimum residence time | 9 min | Proposed design, testwork basis |
| Zinc 2nd cleaner minimum residence time | 9 min | Proposed design, testwork basis |
| Bucko Mill personnel (steady state) | 49.5 | Proposed design |
Project website: https://miningdataonline.com/property/1431/Tower-and-Rail-Project.aspx
Technical qualifications
The estimated closed circuit metal recoveries in Table 17.3 are stated as estimated values used for PEA economics, with follow-up testwork required to confirm. Additional metallurgical testing is required to quantify variability of metallurgical response across the deposit and to confirm and optimize the current design. Testwork was conducted in an open circuit configuration with no recycle or recirculation of products from each flotation stage. The need for metabisulphite will be confirmed or rejected as part of the reagent optimization program during the next metallurgical test program.
Source: NI 43-101 Technical Report , Tower and Rail Project, Manitoba, Canada, January 12, 2021, Section 17 Recovery Methods.
