IM 2020 July/August 20 | Page 5

Editorial Director Paul Moore B.Sc (Hons), M.Sc. Email: [email protected] Editor Daniel Gleeson BA (Hons) Email: [email protected] Advertising Sales: Phil Playle Email: [email protected] [phone] Publishing Assistant Lynne Lane Email: [email protected] Accounts Manager Nicola Shukla [email protected] Marketing Assistant Joanna English BA (Hons) [email protected] Circulation Assistant Jane Alter [email protected] Design and Production Trevor Sheldon Email: [email protected] Website: www.im-mining.com Annual Subscription Enquiries Emma Smith Email: [email protected] Annual Subscription UK and Europe £160, €230 Rest of the world US$270 International Mining (ISSN No: 1747-146X) is published monthly by Team Publishing Ltd, GBR and is distributed in the USA by Asendia USA, 17B South Middlesex Avenue, Monroe NJ 08831 and additional mailing offices. Periodicals postage paid at New Brunswick NJ. POSTMASTER: send address changes to International Mining, 17B South Middlesex Avenue, Monroe NJ 08831 Printed by The Manson Group, St Albans, UK © Team Publishing Ltd 2020 ISSN 1747 -146X IM uses, as preference, SI units throughout, so, for example, all tonnes are metric unless otherwise stated. All dollars are US unless otherwise stated THE LEADER VOLUME 15 • NUMBER 7/8 Ramp or shaft? Alamos Gold, in deciding how it was going to further expand its Island gold mine, in Ontario, Canada, to make the most of an increasing resource base, put five vertical development options on the table. The Phase III Expansion Study, soon to be filed on SEDAR, will likely prove a valuable read for anyone thinking of carrying out an underground expansion of their own. It includes insight from Hatch, Cementation, Airfinders, Golder, Halyard, SRK and DRC Estimating. Island has gone from averaging around 900 t/d throughput in 2017 to hitting an average of 1,240 t/d in the most March quarter (ahead of the nameplate 1,200 t/d), but Alamos is after more. Of the five expansion scenarios considered, three involved ramp haulage (two retaining the 1,200 t/d nameplate capacity and one at 1,600 t/d) and two would see a shaft installed (at 1,600 t/d or 2,000 t/d). All apart from one option included the addition of a paste plant. While the company settled on expanding throughput to 2,000 t/d, from 1,200 t/d, through a shaft expansion down to the 1,373 m level, like all good maths students, Alamos showed its workings. First, the paste plant. The addition of paste fill underground will allow for faster stope cycling, thereby supporting higher mining rates and providing increased geotechnical stability, according to Alamos. It will also increase mining recovery, resulting in an additional 100,000 oz of gold recovered over the 16-year life of mine (from existing pillars). This represented an in-situ value of $145 million at a gold price of $1,450/oz, Alamos said. The paste plant will have a capacity of 2,000 t/d and came with a capital cost of $34 million, Alamos said. Further, as 56% of tailings will be placed underground, the tailings dam raise requirements will be reduced, providing a capital saving of $13 million, according to Alamos. When it comes to the shaft sinking options, which Alamos evaluated with the help of Cementation, it decided a conventional blind sink methodology provided “improved schedule reliability with minimal impact on existing operations”. A combined raisebore from the 840 m level, and blind sink option below the 840 m level, was evaluated, however, this option would significantly impact existing operations, Alamos said. Alamos and Cementation successfully used raiseboring at an expansion project at Young-Davidson, also in Ontario, which recently saw the Northgate shaft commissioned. Alamos said of the raisebore option at Island: “The cuttings from the raisebore in the upper mine, and waste generated from the conventional sink in the lower mine, would displace underground throughput capacity and significantly reduce mining rates below 1,200 t/d by as much as 400 t/d over the next several years,” it said. The settled-on option will see a 5 m diameter concrete-lined shaft constructed with a steel head frame. The shaft will house two 12 t skips in dedicated compartments for ore and waste movement and a double-deck service cage for the transport of personnel and materials. The company estimated an overall shaft sinking rate of around 9.6 ft (2.9 m)/d, which included a ramp-up period. The total construction capital for the shaft installation including all supporting infrastructure is anticipated to be $232 million. While the shaft will be sunk to the hoisting plant will be designed for an ultimate depth of 2,000 m providing flexibility to accommodate future exploration success, the company said. Having gone from 1.8 Moz of mineral reserves and resources when Island was acquired in 2017, to 3.7 Moz more recently, Alamos has already set a precedent for such growth. This is likely why the shaft has been given a capacity of 4,500 t/d at, which is more than sufficient to accommodate the peak mining rates of 3,300 t/d (ore and waste), according to Alamos. The underground ore and waste handling and loading pocket will be a conventional configuration like that of Young-Davidson, the company added. Ventilation requirements will also be lower than under the ramp scenarios given the significantly smaller mobile fleet, Alamos said. This allows the shaft to serve as the only new required fresh air source. The mining rate ramp-up to 2,000 t/d after the shaft expansion will be supported by a total of five 42 t haul trucks. This compares with a peak of 18 haul trucks required to sustain ramp haulage at 1,200 t/d and 25 haul trucks for ramp haulage at 1,600 t/d. “This contributes to the lower ventilation requirements with the shaft expansion, and significantly lower diesel usage and greenhouse gas emissions,” the company said. Once skipped to surface, ore will be trucked to the mill circuit, which will also be modified. The crushing circuit will be upgraded, a second parallel ball mill will be added, and a new elution and carbon in pulp (CIP) circuit with carbon screens will be installed. The total cost of the mill expansion is expected to be around $40 million. The total capital for the whole project comes in at $1.07 billion, but this will be paid back with higher production and a longer mine life. Following the completion of the shaft construction in 2025, output would rise to 236,000 oz/y, 72% higher than the mid-point of previously issued guidance for the mine in 2020, while minesite all-in sustaining costs would fall to $534/oz, a 30% drop on the 2020 guidance. “These are also the lowest costs of any scenario evaluated reflecting the significant productivity improvements, decreased ventilation requirements, increased automation, and higher throughput rates associated with the shaft,” the company said. Combined, this made for an after-tax net present value of $1.02 billion at a 5% discount rate, and an after-tax internal rate of return of 17%, using a base case gold price assumption of $1,450/oz. For those who want to hear more about developments in the shaft sinking industry, be sure to pick up our September 2020 issue, which will feature our annual sector focus. Daniel Gleeson Editor [email protected] JULY/AUGUST 2020 | International Mining 3