Gold was discovered at Detour Lake Mine 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 resumed at Detour Lake in 2012, when the Mine was owned and operated by Detour Gold Corporation (“Detour Gold”). Kirkland Lake Gold acquired Detour Gold on January 31, 2020 and immediately commenced 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 (“M&I”) Mineral Resources. Tripling the open-pit M&I 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 (“2021 LOMP”) for Detour Lake were filed on March 30, 2021. Highlights of the report included production of 680,000 – 720,000 ounces from 2021 to 2024, increasing to approximately 800,000 ounces in 2025, with all-in sustaining costs per ounce averaging $775 over the next five years and $821 over the 22-year production life. The 2021 Detour Lake Technical Report did not include any of the exploration success achieved since Detour Lake was acquired nor did it include the full impact of business improvement initiatives undertaken since the 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.
Geology
At Detour Lake Mine, the greenstone–granite architecture 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 Project 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 dykes, sills and younger regional Proterozoic
diabase dykes.
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 auriferous sulphide-poor quartz vein
stockwork formed in the hanging wall of the Sunday Lake Deformation Zone. The sulphidepoor quartz vein stockworks observed in the hanging wall 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 auriferous
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 sulphide-rich 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° (in the area of the former Campbell pit),
shallowing to approximately 10° further to the west)
Mining
Conventional open pit mining methods are used to mine the Detour Lake deposit utilizing a current fleet size of 37 haul trucks (CAT 795F - 300 tonnes), 2 electric cable shovels (48 m3), 5 hydraulic shovels (28 m3), 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 24,000,000 tonnes per year, with growth to 28,000,000 tonnes targeted by 2025.
The crushing circuit includes a larger gyratory crusher (60"X113" HD equipped with 1,000 kW) and the addition of a secondary crushing circuit (2X750 kW crushers). In addition, this system is complemented with additional crushing capacity in the pebble crushing circuit (2X750 kW pebble crusher).
The grinding circuit consists of two parallel lines, each having one twin pinion semi-autogenous (SAG) mill (36'X20') and one twin pinion ball mill (26'X40.5'). The gravity circuit currently recovers approximately 25% of the gold. The remaining gold in ore is sent to cyanidation followed by carbon in pulp (CIP) 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
Significant exploration success has been achieved since Kirkland Lake Gold acquired the Detour Lake Mine on January 31, 2020 as highlighted by the 10.1 million ounce increase in M&I Mineral Resources, announced in September 2021. The majority of the growth in M&I Mineral Resources was in the Saddle Zone, an area located between the existing Main Pit and planned West Pit locations, which had previously been underexplored with only limited Mineral Resources identified and no Mineral Reserves. Mineralization in the Main Pit, Saddle Zone and West Pit location remains open at depth with there also being potential to extend the known deposits to the west of the West Pit. There also remains significant exploration potential at the nearby North Pit, 58N and Zone 75 targets as well. Regionally, geophysical surveys and exploration drill holes have identified a number of gold-bearing structural trends that warrant additional exploration evaluation.
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 process 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 length of employment opportunities. The West Pit and North Pit are planned to remain active during a period of approximately 12 years (2025-2036) and the expansion of the existing pit extends the life of the mine to 2040. The West Detour Project is located adjacent to the operating Detour Lake Mine and has been purposefully designed to utilize infrastructure and facilities in place to minimize environmental disturbance as practical.