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. Exploration drilling at Detour Lake since the acquisition has 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. This tripling of open-pit measured and indicated mineral resources was a critical milestone for the operation and is expected to contribute to strong growth in mineral reserves as further progress is made towards transforming Detour Lake into one of the world’s largest and most profitable gold mines.
A new technical report (“2021 Detour Lake Technical Report”), including a new life-of-mine plan for Detour Lake, was filed on SEDAR on March 30, 2021. Highlights of the report included planned annual production of 680,000 to 720,000 ounces of gold from 2021 to 2024, increasing to approximately 800,000 ounces in 2025, with anticipated all-in sustaining costs per ounce averaging $775 through 2025 and $821 over the 22-year production life. The 2021 Detour Lake Technical Report did not include any of the exploration success achieved since the Detour Lake acquisition in January 2020 nor did it include the full impact of business improvement initiatives undertaken since the January 2020 acquisition. A new technical report and life-of-mine plan are expected to be issued in the first half of 2022, which will include the impact of exploration success and Mineral Resource growth since the acquisition and are expected to result in significant value enhancement opportunities for the Detour Lake operation.
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 15 million ounces and is expected to be the Company’s largest gold producer in 2022.
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 utilizing a fleet of 37 haul trucks, 2 electric cable shovels, 5 hydraulic shovels, 12 drills and various ancillary equipment to support the mining operation. The mining fleet will be increased in the next few years to meet the mine production schedule of the new life-of-mine plan.
Processing
The milling operation uses a conventional crushing, grinding, gravity, cyanidation and carbon-in-pulp processing facility currently operating at approximately 24 million tonnes per year, with growth to 28 million tonnes per year targeted by 2025.
The crushing circuit includes a larger gyratory crusher and the addition of a secondary crushing circuit. In addition, this system is 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. The 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 Company is using the same location for the tailings impoundment facility as the former operation. The current tailing facility will be expanded to a second and then a third containment system with capacity for approximately 650 million tonnes.
Exploration
A highlight of the program to create value at Detour Lake has been the exploration success achieved since the acquisition in 2020. A key exploration focus was the Saddle Zone, which is located between the existing Main Pit and the planned West Pit. The Saddle Zone had previously been under explored and contained no mineral reserves and only limited mineral resources. 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.
Exploration results in 2020 and 2021 demonstrate the existence of a broad and continuous corridor of mineralization extending over 4.0 kilometres from the Main Pit through the Saddle Zone to the planned West Pit location to a depth of at least 800 metres below surface with the system remaining open.
Exploration results have also expanded the mineralized corridor to at least 400 metres west of the planned West Pit, with the corridor remaining open. In addition, drill results have identified broad zones of higher-grade mineralization below the current pit shells for the Main Pit and West Pit, indicating the potential to add both open-pit and, potentially underground, mineral reserves and mineral resources. In 2021, Kirkland Lake Gold carried out a $41.2 million exploration program at Detour Lake.
On September 2, 2021, Kirkland Lake Gold released an updated mineral resource estimate, which incorporated drilling results at Detour Lake up to July 26, 2021. The new estimate included a 10.1 million ounce increase in measured and indicated open-pit mineral resources to 14.7 million ounces of gold (572.0 million tonnes at 0.80 g/t). The 14.7 million ounces of open-pit measured and indicated mineral resources consists of 12.2 million ounces of gold (386.5 million tonnes at 0.98 g/t) established using a 0.50 g/t cut-off grade and 2.5 million ounces of gold (185.5 million tonnes at 0.42 g/t) of lower-grade mineral resources established using cut-off grades between 0.35 – 0.50 g/t.
At December 31, 2021, mineral reserves at Detour Lake were estimated at 15.0 million ounces of gold (573.3 million tonnes at 0.82 g/t gold), representing mineral reserves as at December 31, 2020 less the impact of production depletion during 2021. The 15.0 million ounces of mineral reserves at December 31, 2021 includes 13.1 million ounces of gold (426.8 million tonnes at 0.96 g/t gold) established using a 0.50 g/t cut-off grade and 1.9 million ounces of gold (146.5 million tonnes at 0.41 g/t gold) using a cut-off grade of less than 0.50 g/t. Open pit measured and indicated mineral resources were estimated at 14.7 million ounces of gold (572.0 million tonnes at 0.80 g/t gold) and inferred mineral resources were estimated at 1.2 million ounces of gold (52.4 million tonnes at 0.71 g/t gold).
At the Detour Lake mine in 2022, the Company expects to spend approximately $35.8 million for 194,000 metres of capitalized drilling to expand mineral resources at depth and to the west, and $10.1 million for 40,000 metres for 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 Pit and North Pit are planned to remain active over approximately 12 years (2025-2036) and the expansion of the existing pit would extend the life of the mine to 2040. The West Detour project is located adjacent to the west of the operating Detour Lake Mine and has been purposefully designed to utilize existing infrastructure and facilities to minimize environmental disturbance.