The Detour Lake and West Detour deposits are considered to be examples of orogenic greenstone-hosted hydrothermal lode gold deposits.

Greenstone-hosted hydrothermal lode gold deposits are typical of the Abitibi Greenstone Belt, and in particular the gold deposits found along the Destor–Porcupine Fault Zone from Timmins, Ontario through to Destor, Québec. These deposit types are found in greenstone belts around the world and are responsible for a large proportion of past world gold production, including most of the Canadian gold production.

The majority of Archean orogenic greenstone-hosted lode gold deposits occur within volcano–plutonic domains, which are typically distributed along crustal-scale fault zones occurring along or in close proximity to terrane or sub-province boundaries (Card et al, 1989). Elongate belts of metavolcanic and some metasedimentary rocks containing subsidiary amounts of ultramafic to felsic intrusive rocks typically dominate these domains. The intrusive rocks will have typically been emplaced in multiple pulses throughout the geologic evolution of the area. Metamorphism within the belts is generally greenschist to lower amphibolite facies. The structure of the gold districts is characterized by the presence of multiple generations of structural fabrics indicating the presence of several periods of deformation.

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).

Detour Lake
Dimensions: Mineralization at Detour Lake is hosted within a broad corridor. In mine grid coordinates the mineralization extends from 16,900E to 20,650E, 19300N to 20,650N and 5,500 m elevation to 6,300 m elevation. This corresponds to a strike extent of 3.75 km, a width of 1.35 km, and an approximate elevation range of 800 m.

Mineralization
Gold is associated with quartz–carbonate–pyrite–pyrrhotite ± tourmaline veins and/or disseminated to very local semi-massive sulphides in hydrothermally-altered wall rocks. There are two main mineralized zones, defined as hanging wall mineralization and footwall mineralization.

Hanging Wall
The hanging wall gold mineralization occurs in several different rock units within broad subvertical mineralized envelopes and splits into several sub-vertical domains sub-parallel to the orientation of the Sunday Lake Deformation Zone. The Main Zone was the largest gold-bearing mineralized zone exploited in the period 1983– 1987 and consists of gold mineralization occurring in the chert marker horizon or in quartz and quartz–carbonate vein systems splaying from the Sunday Lake Deformation Zone. In the Campbell pit area, <1 m thick quartz veins, with a frequency of greater than one vein per metre, were part of a series of sub vertically dipping east–west-trending highly-strained zones. Gold generally occurred as free gold with these veins.

West of section 19,620E, mineralization is commonly associated with increased biotite alteration, shearing, narrow quartz veining and minor pyrite or pyrrhotite. Local zones of strong brecciation with sulphide infilling have also been recognized along with minor chalcopyrite, telluride minerals and visible gold. Gold mineralization is associated with a series of sub-vertical to arcuate deformation zones characterized by enhanced strained fabrics, well defined open-space breccias, and to a lesser degree sheeted shear-hosted veins and extensional veins. The QK Zone further to the west is open down plunge and has not been tested below 800 m. This mineralization is associated with narrow parallel to sub-parallel quartz veins, quartz boudins and sulphide rich veins/breccias with adjacent silicification and potassic alteration envelopes.

Footwall Mineralization
The Talc Zone varies in width from 4–15 m and tends to be less continuous along strike. Gold in the Talc Zone is dominantly associated with pyrite, pyrrhotite, and minor chalcopyrite along foliation planes, narrow discrete shears or strain zones, and in irregular lenses. The zones also contain short deformed lenses or boudinaged quartz veins. In some cases, it appears that the mineralization is controlled by strong fault structures containing several centimetres of gouge material.

West Detour and North Pit Areas
Dimensions: The West Detour mineralization extends from mine grid sections 14,500E to 17,600E and 19,100N to 21,300N and between elevation 5,300 and 6,300 m. This corresponds to a strike extent of 3.1 km, a width of 2.2 km, and an approximate elevation range of 1 km.

Mineralization
The M Zone lies approximately 400–500 m north of the chert maker horizon and is a westerly-trending gold system that is spatially associated with the margins of the chlorite schist unit. The chlorite schist stratigraphic horizon and associated gold mineralization was traced by drilling for approximately 5 km. The footwall and hanging wall sequence of the chlorite schist in the M Zone is variably biotite altered with fairly abundant fractures and well-defined foliation (local veining) with associated pyrite, pyrrhotite, and rarely chalcopyrite. The mineralized zones appear lensoidal and plunge 20° west. Mineralized lenses vary from 5–50 m in true width. Mineralization hosted in the QK zone is associated with narrow veins that are parallel to sub-parallel to stratigraphy, quartz boudins, and sulphide-rich veins/breccias within silicified and potassic alteration envelopes up to 25 m in true width. Gold mineralization in the North Walter Lake Zone is within a relatively weak quartz vein stockwork with a low pyrite and pyrrhotite sulphide content. Mineralization is associated with moderate to strong shearing, potassic alteration of the mafic volcanic units, narrow quartz veining and minor pyrite and pyrrhotite.

Zone 58N
Dimensions: The Zone 58N mineralized system has been intersected over an east–west strike length of 450 m, from surface to a depth of 800 m, and the mineralized system remains open at depth. The mineralization extends from approximately 595,300E to 595,750E and 5,533,700N to 5,533,800N (UTM coordinates). The width of the mineralization is variable, ranging from 4 m to >100 m at the centre of the deposit. Infill drilling has demonstrated that the geology and mineralization dip subvertically at 75º to the south.

Mineralization
Visible gold is often present and occurs within coarse pyrite or as free gold within quartz. Sulphide mineralization associated with gold ranges from 0.5–5% pyrite with minor chalcopyrite, bismuth-tellurides, molybdenite and scheelite. Gold is found within and at the margins of quartz ± tourmaline ± carbonate stockwork-type veins that infill areas of brittle deformation. Visible gold occurs in nearly every drill hole that intersects mineraliza

The Detour Lake Mine uses conventional truck-shovel open pit mining. The mine is operated using an Owner-operator mining equipment and labour strategy. Excluding the muskeg, overburden/till top layer, all material must be blasted. Pioneering drilling and blasting is required in the overburden/rock contact. Additionally, during winter months free digging of overburden material is not possible due to frost.

Design Constraints
The design of each one of the three final pits (Detour Lake, West Detour and North Pit) is guided by the respective optimized shells. The final pit design incorporates the geotechnical parameters prescribed by Golder (Golder 2019, 2020).

The Detour Lake pit design incorporates a double ramp access for most of the LOM. The final ramp and principal access will be located in the north wall. The West Detour and North Pit were designed using a single ramp access.

All ramps are designed to accommodate the safe operation of 795CAT super class trucks. Typical road width is 33 m with a total length of 40 m to allow for safety berm and drainage. Ramp widths are adjusted at the bottom of the pit to a one-way lane. Other design parameters include a ramp slope (10%), minimum curve radius (39 m) and construction constraints (super elevation, crowning).

There are a total of nine phases designed for the LOM: five for the Detour Lake Main Pit, three for West Detour and one for North Pit.

Overburden and Pre-Stripping
Bedrock at both Detour Lake and West Detour is overlain by overburden composed of layers of muskeg, till, gravel, and sand. These overburden layers may be as thick as 40 m. At the start of each mining phase, this material must be stripped prior to the drilling and blasting of rock material. Depending on the material quality, weather and moisture content, this overburden material is typically ‘free-digging’ and does not require drilling and blasting. A portion of the till material (subject to quality control specifications) is stockpiled and used for tailings management area (TMA) construction purposes. The remaining overburden is stockpiled either in the main overburden stockpile or within designated areas of the WRSFs. A portion of this material will be rehandled for the reclamation of various waste rock stockpiles and/or TMA cells. Whenever possible, this overburden is directly placed for the progressive reclamation of ultimate WRSF slopes.

Mining Operations
The Detour Lake Mine uses conventional truck-shovel open pit mining. Excluding the muskeg, overburden/till top layer, all material must be blasted. Pioneering drilling and blasting is required in the overburden/rock contact. Additionally, during winter months free digging of overburden material is not possible due to frost. The mine operation also requires the management of old underground workings.

Underground workings records are considered of good quality. The mine has been operating in historical underground working areas for the past years; the reconciliation of historical recordings and field observation of these workings is very good. The assumption that stopes were backfilled using sand/rock filled has also been confirmed. There are procedures in place to ensure safe operations in these areas. The procedures define zones classified by the risk of ground instability.

The Detour Lake Mine has used a 12 m bench-height since operations commenced. A 6 m sub-bench was used to mine the areas requiring pioneering to improve operational conditions related to boulders and pinnacles of bedrock.

Starting in mid-2020 the mine transited to a 14.5 m bench height for areas to be primarily mined by rope shovels and to 7.25 m benches in areas to be mined using hydraulic shovels. The revised mine design has led to improvements in shovel productivities.

The mine operates 24-hr per day year-round on 12 hr shifts for all operational crews. Operational teams work on a seven-day in/seven-day out rotation. The mine has implemented a successful hot-seating process for its main production equipment (shovel, trucks and drills). Management/supervisory and support personnel work at site on different schedules.

Ore Mining and Stockpiles
Whenever possible, mined ore is delivered directly to the primary crusher in order to avoid unnecessary rehandling. When the mined ore tonnage exceeds the operating capacity of the crusher, the ore is placed on one of the ROM stockpiles for later mill feed.

The ROM stockpiles are located in close proximity to the primary crusher to allow for efficient feeding into the plant. Ore in ROM stockpiles is segregated into piles consisting of similar grade material to allow for controlled feeding as required. The ROM stockpiles provide additional buffering capacity to ensure that crusher feed is maximized while also limiting excessive tramming of loading equipment between ore and waste areas in the pit.

Waste Mining
Waste mining is generally allocated to the rope shovel fleet. The grade control process also delineates waste into PAG or NAG material. PAG material must be routed to the MRS3 or MRS1 WRSFs. Overburden material is generally mined by the hydraulic shovels.

Drilling and Blasting
Drilling and blasting activities are performed by Kirkland Lake Gold personnel. Dyno Nobel is the explosives supplier. Different objectives and geological/fractural information are considered when design the patterns and loading plans. Yields vary with the different objectives (wall control, fragmentation, higher fragmentation, reduction of overcasting material) and with areas in the pit.

- subscription is required.

The process plant is based on a robust metallurgical flowsheet designed for optimum recovery with minimum operating costs. The flowsheet is based upon unit operations that are well proven in industry.

The processing plant was designed to process ore at an average throughput of 55,000 t/d or 20 Mt/a, equivalent to milling rates of 2,500 tpoh with operating time of 92% in a 24 hour day. While operating time has lagged at around 89%, the milling has far exceeded the design rate averaging 2,952 t/hr in 2020 for 23.06 Mt milled. On at least 70 occasions in 2020, a 74 kt milled per day rate was achieved.

With the upturn of current performance of the processing plant, ongoing optimization efforts and some new capital initiatives, the LOM plan assumes that the plant throughput will increase from 23 Mt/a in 2020 to 28.0 Mt/a in 2025 and thereafter. The annual plant throughput of 28.0 Mt/a is planned to be achieved by increasing the milling rate to 3,436 t/hr and improving operating time to 93%.

Leach and Carbon-in-PuIp
The gold recovery circuit selected was a “leach circuit followed by a CIP” circuit. The designed retention time for leaching is 29 hours. The leach feed size was designed at a P80 of 95 µm. Four new leach tanks are planned to be built to support the increase in throughput to 28 Mt/a. The CIP design selected uses a carrousel type system with an average design retention time of 80 minutes in this circuit. Upgrades to the pumpcells will support the 28 Mt/a throughput rate. The VSD and motors for the CIP tails pumps will be upgraded to 500 hp from 350 hp. The current adsorbtion profile and modeling support the planned increase in throughput rate.

Acid Wash, Stripping, Electrowinning, and Refining
The stripping system uses a modified version (i.e. ,on-line electrowinning and no pregnant solution tank) of the high-pressure Zadra process to recover the gold from the loaded carbon.

The circuit incorporates an acid wash stage and is designed to handle up to 10 t of carbon per day. The acid wash stage is not currently used and will be converted into a plastic removal vessel. The build up of calcium is not sufficient to warrant the use of the acid wash vessel.

The stripping circuit is designed to handle up to 10 t of carbon per stripping cycle (approximately 8–10 hours); 100% of the carbon is regenerated in two regeneration kilns designed to handle up to 20 t of carbon per day.

The electrowinning is done “in-line” with the stripping circuit. The flow of pregnant solution is split between three rows of two electrowinning cells. One dedicated electrowinning cell handles the pregnant solution from the ILR tank.

The refining equipment is designed to handle the gold from the stripping circuit and from the gravity recovery system. The electrowinning sludge is filtered, dried and mixed with fluxes, before being smelted using induction furnaces.

The current elution capacity is estimated to be 2.5 strips of 10 t per day. In 2020, 1.75 strips per day were completed. There is sufficient capacity to cover the increased throughput for the LOM.

Thickening
The feed to the leach circuit is maintained at a density of 50–55% solids by weight using one high rate thickener. The overflow of the pre-leach thickener is recycled to the process water tank. The pre-detox thickener is used to thicken the leach tails slurry to 55–60% solids and the overflow is recycled to the process water circuit.

The thickener capacity is over 90 kt/d and can support the increase throughput without any modifications. Current flocculent consumption is low at 10 g/t.