Gold was discovered at the Detour Lake property in 1974 and the first mining operation on site, owned by Placer Dome, produced 1.8 million ounces of gold from 1983 to 1999, as an open pit/underground mine. Production during Detour Gold Corporation’s ownership from 2013 to January 30, 2020 was 3.6 million ounces of gold from 135.5 million tonnes grading 0.90 g/t gold.
Kirkland Lake Gold acquired Detour Gold on January 31, 2020 and carried out an extensive exploration drilling program that achieved significant success, highlighted by the announcement in September 2021 of an increase of 10.1 million ounces in open-pit measured and indicated mineral resources.
With Agnico Eagle completing its merger with Kirkland Lake Gold in February 2022, the Detour Lake mine ranks as Agnico Eagle’s largest reserve base at 20.7 million ounces and has become the Company’s largest gold producer since 2022, producing 651,182 ounces of gold to Agnico Eagle’s account (i.e., from February 8 to December 31, 2022) and 732,572 ounces of gold for the complete 12 months of 2022.
The strong growth in mineral reserves at the Detour Lake mine in 2022 is largely due to successful conversion drilling and a revised technical evaluation of the Detour open-pit, which increased the proven and probable mineral reserves by 5.6 million ounces of gold year-over-year to 20.7 million ounces of gold in proven and probable mineral reserves (850 million tonnes grading 0.76 g/t gold) as at December 31, 2022.
The Company had reported in a news release dated July 27, 2022 an updated mineral reserve and mineral resource estimate for the Detour Lake mine that increased proven and probable mineral gold reserves by 38% or 5.6 million ounces of gold to 20.4 million ounces of gold (835.1 million tonnes grading 0.76 g/t gold) from the December 31, 2021 mineral reserve estimate net of the first quarter of 2022 depletion. As at March 31, 2022, Detour Lake contained the following: proven mineral reserves of 77.59 million tonnes grading 1.12 g/t gold for approximately 2.8 million ounces of gold; probable mineral reserves of 757.5 million tonnes grading 0.72 g/t gold for approximately 17.6 million ounces of gold; combined measured and indicated mineral resources of 590.1 million tonnes grading 0.75 g/t gold (14.2 million ounces of gold); and inferred mineral resources of 75.2 million tonnes grading 0.75 g/t gold (1.8 million ounces of gold).
Geology
At the Detour Lake property, the greenstone–granite geological setting is partially aligned and disrupted along a linear, east-west-trending belt that defines the position of the Sunday Lake Deformation Zone.
Supracrustal rocks within the project area consist of a thick sequence of mafic to ultramafic lithologies, which are predominantly volcanic in origin, and are part of the Deloro assemblage. They occur within regional synclinal-anticlinal fold structures traced for over 30 km across the property and are in structural contact to the south with the younger sediments of the Caopatina assemblage. These rocks are bounded to the north and west by the Opatica basement gneissic rocks. To the east and south, the Deloro assemblage is intruded by several large, weakly foliated granodioritic to tonalitic intrusions which are intersected by numerous local felsic to mafic dikes, sills and younger regional Proterozoic diabase dikes.
Mineralization
There are two recognized episodes of gold mineralization at the Detour Lake and West Detour deposits.
The first episode consists of a wide and generally gold-bearing, low-sulphide quartz vein stockwork formed in the hanging wall of the Sunday Lake Deformation Zone. These stockworks have sub-vertical north or south dips and are parallel to a series of east-west trending high strain zones. These veins form a weak stockwork and are boudinaged and/or folded.
The second episode is a stage of gold mineralization overprinting the early gold-bearing stockwork, principally in the hanging wall of the Sunday Lake Deformation Zone, with a higher sulphide content. The sulphide-rich gold mineralization predominantly fills structural sites in deformed quartz veins, fractures and veins crosscutting the foliation fabric but also in pillow breccias and selvages. The distribution of higher sulphide mineralization is strongly controlled by the geometry of kinematic orientation (i.e., pyrite and pyrrhotite concentrations have a shallow westerly plunge similar to the plunge of the main flexure zone in the Sunday Lake Deformation Zone at an angle of about 40 degrees (in the area of the former Campbell pit), shallowing to approximately 10 degrees further to the west).
Mining
Conventional open pit mining methods are used to mine the Detour Lake deposit using a fleet of haul trucks, electric cable shovels, hydraulic shovels, drills and various ancillary equipment. The mining fleet will be increased in the next few years to meet the mine production schedule of the new life-of-mine plan.
The Company is investigating the potential implementation of an electric trolley assisted haulage system to improve haulage efficiency and support carbon emission reductions.
Processing
The milling operation uses a conventional crushing, grinding, gravity, cyanidation and carbon-in-pulp processing facility. The crushing circuit includes a larger gyratory crusher and a secondary crushing circuit, complemented with additional crushing capacity in the pebble crushing circuit.
The grinding circuit consists of two parallel lines, each having one twin pinion semi-autogenous-grinding mill and one twin-pinion ball mill. A gravity circuit currently recovers approximately 25% of the gold. The remaining gold in ore is sent to cyanidation followed by carbon-in-pulp gold recovery. After carbon stripping, the gold is processed through electrowinning cells prior to gold pouring. The overall gold recovery is estimated to average between 91-92% for the life of the mine.
The cyanide solution is recycled to the head of the circuit to reduce operating costs and environmental impact. The remaining stream is detoxified through an SO2/air system before tailings deposition. The current tailings facility will be expanded to a second and then a third containment system with capacity for approximately 650 million tonnes.
The Company continues to advance multiple initiatives to increase mill throughput from 23.0 Mtpa in 2020 to 28.0 Mtpa in 2025. The initiatives completed to date include improved fragmentation at the mine, improved primary crusher choke feeding, removal of the daily regulatory mill limit, the completion of the 610 conveyor re-feed and the installation of screens before the secondary crushers. All of these initiatives are expected to bring the mill throughput capacity to approximately 27.5 Mtpa in 2023.
An upgrade of the 230kV main electrical substation is also planned to improve the power quality at the mine.
Exploration
A key exploration focus is the Saddle Zone, which is located between the existing Main Pit and the planned West Pit. Other key targets included the extension at depth of both the Main Pit and planned West Pit as well as areas west of the existing West Pit mineral reserves, which was also an area that had seen limited previous drilling.
There appears to be significant underground potential associated with the mineralization outside the planned final pit limits at depth, with the underground mineralization extending more than 2.4 km west of the current mineral resource pit.
An initial underground mineral resource estimate, expected to be completed in the first half of 2023, would form the basis for potential underground mining scenarios. Underground mining operations would likely be accessed via a ramp and utilize long hole stoping methods with grades potentially ranging from 2.0 g/t to 3.0 g/t gold. The Company expects to complete an initial internal technical evaluation of the underground potential at year-end 2023.
Overall at Detour Lake in 2023, the Company expects to spend a total of approximately $33.2 million for 171,000 metres of exploration drilling that will include $29.4 million for 157,000 metres of capitalized drilling to expand mineral resources at depth and to the west in support of an internal technical evaluation of the underground project and further optimization of the open pit in the Saddle and West Pit areas, which is expected to be completed in late 2023. The remaining $3.8 million is for 14,000 metres of exploration drilling to continue to investigate the Sunday Lake Deformation Zone to the east and west of the current pit's mineral resources.
Development Project
West Detour Project
The West Detour project is a proposed expansion of the operating Detour Lake mine. The project is intended to provide additional ore to feed the existing Detour Lake processing plant by developing two satellite open pits and the additional westward expansion of the currently operating open pit.
Expansion of the reserves at the Detour Lake mine will help maintain and extend the life of mine. The West Detour project is located adjacent to the west of the operating Detour Lake mine and has been purposefully designed to use existing infrastructure and facilities to minimize environmental disturbance.