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Detour Lake Gold
Ontario, Canada
Main commodities: Au

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The Detour Lake Archaean gold deposit is located 300 km NE of Timmins and 185 km by road NE of Cochrane in northeastern Ontario, Canada (#Location: 50° 0' 52"N, 79° 43' 30"W).

The deposit was discovered in 1974, when Amoco Canada Petroleum Company Ltd. drilled a geophysical anomaly. In 1982, further exploration under a joint venture agreement with Red Lake Mines and Dome Mines resulted in the outlining of sufficient resources to commence mining. Open pit mining commenced in 1983, followed by underground mining in 1987. From 1983 to 1987, open pit production totaled ~3.0 Mt @ 3.25 g/t Au. Approximately 1.6 Mt @ 1.40 g/t Au were blended with underground ore between 1986 and 1998. Between 1987 and 1999, underground gold production is estimated at 9.1 Mt @ 4.98 g/t Au. In 1987, Campbell, Dome and Placer Development merged to become Placer Dome Inc. By 1988, Placer acquired the remaining 50% of the Property that was owned by Amoco. In December 1998, Pelangio-Larder Mines and the Franco-Nevada Mining Company, the 'Detour Lake Joint Venture' acquired the property from Placer Dome, along with neighbouring exploration titles. In May 2000, Marl Resources Corp. acquired substantially all of the assets of Pelangio-Larder. In 1998, the open pit mining briefly resumed, extracting 0.644 Mt @ 2.20 g/t Au. In July 1999, due to low gold prices and declining economics, Placer halted mining at Detour Lake and reclamation of the Mine Property was initiated. Total production (open pit and underground) over the 17-year life of the Detour Lake mine was estimated at 54.9 tonnes of gold from milling of just over 14.3 Mt of rock @3.82 g/t Au and a mill recovery of 93.1%. In 1998, Franco-Nevada, became part of Newmont Mining Corporation Canada. In 2002, Pelangio completed the purchase of all of Newmont’s interest in the Detour Lake Joint Venture. In September 2003, Pelangio granted Trade Winds an option to acquire a 50% interest in exploration Block A. Trade Winds fulfilled the option requirements and on On January 31, 2007, Detour Gold completed the purchase agreement with Pelangio and acquired all the Detour Lake assets, including Block A. In December 2011, Detour Gold completed the acquisition of Trade Winds and acquired a 100% interest in the Block A and adjacent properties. Detour Gold amalgamated with its wholly-owned subsidiary Trade Winds, effective January 1, 2014. Detour Gold commenced operations at the Detour Lake Main Pit in 2013. Production during Detour Gold Corporation’s ownership from 2013 to January 30, 2020 was 135.5 Mt @ 0.90 g/t Au containing 122 tonnes of gold. Kirkland Lake Gold acquired Detour Gold on January 31, 2020 and carried out an extensive exploration drilling program resulting in September 2021 of an increase of 314 tonnes of contained gold in open-pit measured and indicated mineral resources. Agnico Eagle completed a merger with Kirkland Lake Gold in February 2022, and as a consequence, the Detour Lake mine ranks as Agnico Eagle’s largest reserve base of 466 tonnes of contained gold.

The deposit lies within the northwestern segment of the Abitibi Greenstone Belt in the Superior Province of the Canadian Shield. In the Detour Lake area, the underlying sequence is composed of a thick sequence of 2730 to 2724 Ma mafic to ultramafic volcanic rocks, known as the Deloro Assemblage, which is in structural contact with the younger sediments of 2690 to 2685 Ma Caopatina Assemblage to the south. This contact between the is characterized by a regional scale thrust zone known as the Sunday Lake Deformation Zone. The structures of this deformation zone are spatially related to most of the gold mineralisation known in the Detour Lake area.

The Lower Detour Lake Formation of the Deloro Assemblage comprises:
Chert Marker Horizon associated with a silicified intermediate dyke occurring within a highly strained, silicified and mineralized zone at the contact between the overlying massive basaltic volcanic sequence (usually composed of altered pillow flow) and the underlying deeply altered mafic/ultramafic sequence.
Mafic Flow Contact Unit, which is a chloritic schist, after a 5 to 20 m thick flow unit in the immediate hanging wall of the underlying ultramafic assemblages at the Detour Lake mine. It is fine grained, light to dark greenish black and lacks significant matrix feldspar. It is generally foliated with chloritic and locally potassic alteration and does not generally contain sulphides.
Ultramafic Flows and Sills, composed of a thick sequence of ultramafic flows with locally preserved spinifex textures, and coarse grained pyroxenite and finer grained ultramafic sills. Gold mineralisation hosted in this unit is in a dilatational jog or flexure zone in the area.
Mafic volcanic, a flow unit is to the south of the talc-chlorite alteration zone of the Detour Lake mine. It contains very little gold mineralisation.
Megacrystic diorite, which has coarse to very coarse feldspar phenocrysts set in a dark, fine-grained matrix, and may locally be foliated. It is always associated with the mafic volcanic unit.
Mafic sills and dykes, represented by abundant gabbroic intrusions, finer grained flows and dykes. The mafic intrusions may contain 10 to 15% disseminated magnetite, and be strongly magnetic.
The Upper Detour Lake Formation of the Deloro Assemblage comprises a thick sequence of high-Mg tholeiitic basaltic massive flows and high-Fe tholeiitic pillowed flows that have the chemical affinities of arc-related tholeiites. It comprises:
Pillow Flows, which are common throughout the Detour Lake mine and West Detour areas, extending across the entire Property through the West Detour area. It is characterised by pillow selvages, the formation of hyaloclastite and vesicles filled with calcite. The intensity of the potassic alteration varies from weak to strong. Pillow cusps and margins are preferentially altered to secondary biotite and albite, and pyrite-pyrrhotite-quartz assemblage (with local minor chalcopyrite) exhibiting an increase in intensity proximal to mineralised strained zones.
Massive Flows, which are generally grey, fine to medium grained with local porphyritic textures, and usually weak to moderately foliations. Several very massive magnesium-rich tholeiitic flow sequences are evident in the hanging wall sequence of the Detour Lake mine and West Detour deposit. These massive flows typically carry 12 to 15% matrix plagioclase, with 85% recrystallised actinolite-hornblende, commonly occurring as 2 to 4 mm elongate interlocking recrystallised lathes. Pillow-structure, hyaloclastite and vesicles filled by calcite may be present locally.
Amphibolite Dykes, which was initially classified as a coarser grained sub-unit within the mafic flow sequence.
Chloritic Greenstone, trending east-west, composed of mafic to ultramafic komatiitic volcanics, strongly altered to chlorite or talc-chlorite schist. It is moderately to well sheared and foliated, with local sulphides (pyrite, pyrrhotite ±chalcopyrite).

All lithological units in the district have undergone upper greenschist to lower amphibolite facies regional metamorphism and are hydrothermally altered proximal to major deformation zones. The principal styles of alteration include: i). the development of strong secondary biotite in mafic rocks; and ii). the formation of talc-actinolite chlorite assemblages in ultramafic sills next to the Chert Marker Horizon and across the northern edge of the Detour Lake deposit and through the West Detour deposit.

The gold mineralisation in the district is interpreted to be relatively late and emplaced after tectonic juxtaposition of the Deloro and Caopatina assemblages. At both Detour Lake and West Detour, gold mineralisation is principally observed north of the Sunday Lake Deformation Zone in its hanging wall, along an east-west strike length of >8 km, within a corridor that is several hundreds metres in width, and up to a depth of ~750 m below surface. It occurs as a stockwork of auriferous quartz veins that splay from a flexure that coincides with the northern limb of a shallow west plunging antiform.

Two types of gold mineralisation have been recognised at the adjacent Detour Lake and West Detour deposits:
  i). a wide, and generally auriferous, sulphide-poor, quartz vein stockwork formed in the hangingwall of the Sunday Lake Deformation Zone. The sulphide-poor quartz vein stockworks observed in the hanging wall have subvertical 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; and
  ii). a gold mineralisation 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 mineralisation 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 mineralisation is strongly controlled by the geometry of kinematic orientation (i.e. pyrite and pyrrhotite concentrations have a shallow westerly plunge, similar to that of the main flexure zone in the Sunday Lake Deformation Zone at an angle of ~40°, shallowing to ~10° further to the west.

The gold mineralisation is found in different rock types within broad sub-vertical mineralised envelopes, and splits into several domains, sub-parallel to the orientation of the Sunday Lake Deformation Zone. It is principally contained in discrete fault-fill or shear hosted, extensional quartz vein networks, and broad lithology controlled mineralised zones with a weaker vein association.

Hangingwall mineralisation forms a 200 m wide (locally up to 350 m) corridor within a broad assemblage of mafic volcanics with an overall east-west trend. To date, gold has drill tested this mineralized corridor for a distance of over 5 km. The bulk of the mineralisation within this corridor is concentrated along a highly strained corridor of a moderate to strong potassic alteration envelope at the contacts between the pillowed mafic flows and massive flows.

Footwall mineralisation is hosted in highly altered, i.e. serpentinised and talcose ultramafic flows with mineralization concentrated at both the upper contact chert marker horizon, and lower contact with the Sunday Lake Deformation Zone, next to barren volcaniclastics and mafic volcanics. The gold mineralisation at the lower contact of the Talc Zone shows an increase in sulphide content. The Talc Zone varies from 4 to 15 m in width and tends to be less continuous along strike. Mineralisation is dominantly associated with pyrite, pyrrhotite and minor chalcopyrite along foliation planes, narrow discrete shears or strain zones, and in irregular lenses (Barclay, 1993).

West Detour Deposit Mineralisation is closely associated with a moderately to strongly sheared Mg-rich ultramafic komatiitic volcanic unit referred to the CG unit, a talc-chlorite schist. Shearing and gold mineralisation in this area extends several tens of metres north and south of this unit and generally it has been referred to as the M Zone. The M Zone lies ~400 to 500 m north of the Chert Marker Horizon and is a westerly trending gold system that is spatially associated with the margins of the talc-chlorite schist. Gold mineralisation styles are near identical with those of the Detour Lake mine, occuring within a relatively weak quartz vein stockwork with a low sulphide content, mainly composed of pyrite and pyrrhotite.

The gold mineralisation within Zone 58N in the Lower Detour area is hosted in a swarm of tonalitic dykes that intrude mafic volcanic rocks and are spatially controlled by the margin of a large intermediate intrusion. Gold mineralisation is found in quartz-tourmaline-carbonate veins containing <5% sulphides. The east-west mineralised system extends over a strike length of 450 m, from surface to a depth of 800 m, and remains open at depth.

The Ore Reserves and Mineral Resources at 31 December, 2020 were as follows (after Leite et al., 2020)
  Detour Main deposit  -  Proved + Probable Ore Reserves
    ≥0.50 g/t Au - 383.0 Mt @ 0.96 g/t Au;
    < 0.5, ≥0.35 g/t Au - 114.4 Mt @ 0.41 g/t Au;
    TOTAL Main Pit - 497.4 Mt @ 0.84 g/t Au for 418 t of gold.
  West Detour deposit  -  Proved + Probable Ore Reserves
    ≥0.50 g/t Au - 58.5 Mt @ 0.95 g/t Au;
    < 0.5, ≥0.35 g/t Au - 32.1 Mt @ 0.4 g/t Au;
    TOTAL West Pit - 90.7 Mt @ 0.75 g/t Au for 68 t of gold.
  North Pit deposit  -  Probable Ore Reserves - None Proved
    ≥0.50 g/t Au - 5.9 Mt @ 0.95 g/t Au;
    < 0.5, ≥0.35 g/t Au - 2.2 Mt @ 0.41 g/t Au;
    TOTAL North Pit - 8.1 Mt @ 0.80 g/t Au for 6.5 t of gold.

  All pits combined  -  Proved + Probable Ore Reserves
    ≥0.50 g/t Au - 447.4 Mt @ 0.96 g/t Au;
    < 0.5, ≥0.35 g/t Au - 148.7 Mt @ 0.41 g/t Au;
  TOTAL All Pits - 596.1 Mt @ 0.82 g/t Au for 490 tonnes of contained gold.

This summary is largely taken from: Anwyll, D., Bassotti, M., Daigle, P., Janusauskas, D., McMullen, J., Sirois, R. and Wallin, R., 2018 - Detour Lake Operation Ontario, Canada; an NI 43-101 Technical Report prepared by Detour Gold Corporation, 354p. and
Leite, A., Dupont, J.-F., Raizman, V., Fournier, P.A, 2020 - Detour Lake Operation Ontario, Canada; an NI 43-101 Technical Report prepared by Detour Gold Corporation, 367p.

The most recent source geological information used to prepare this decription was dated: 2020.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

Detour Lake

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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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