Kirkland Lake District - Toburn, Sylvanite, Wright-Hargreaves, Lake Shore, Teck-Hughes, Macassa
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The Kirkland Lake gold mines are located in the township of Kirkland Lake, 100 km ESE of Timmins, 80 km west of Rouyn-Noranda, and 500 km north of Toronto, in Ontario, Canada (#Location: 48° 8' 12"N, 80° 4' 13"W).
Kirkland Lake is one of the classic greenstone gold fields in the Abitibi Belt of the Superior Province. Since 1913, the field has produced approximately 760 t (24.4 Moz) of gold and 125 t of silver from 7 different mines, over a 7 km strike length, located within 2 km to the north of the major Larder Lake-Cadillac Fault zone.
The seven contiguous mines, from east to west are:
Toburn, which operated from 1915 to 1953, and produced 17.75 t Au; Sylvanite, from 1927 to 1961, for 51.8 t Au; Wright-Hargreaves, between 1921 and 1965, for 150 t Au; Lake Shore, from 1918 to 1965, for 264 t Au; Teck-Hughes, from 1917 to 1968, for 114 t Au; Kirkland Lake, from 1919 until 1960, for 36.5 t Au; and Macassa, from 1933 until 1999, for 110 t Au. Head grades varied along the trend from 11 to 16, averaging 15 g/t Au (Still, 2001; Kirkland Lake Gold Inc. website, 2012)
Kirkland Lake lies within the 2.75 to 2.67 Ga Abitibi greenstone belt, part of the larger Abitibi Subprovince, a granite-greenstone-gneiss terrane that is Iocated within the south-eastern portion of the Archaean Superior Province. This part of the Abitibi Subprovince, is characterised by a supracrustal sequence of dominantly (~80%) metavolcanic rocks formed between 2.75 and 2.70 Ga (mostly between 2.72 and 2.70 Ga) that range from komatiitic and tholeiitic to calc-alkaline (Card, 1990), comprising 55% basalt, 34% andesite, 7% dacite and 4% rhyolite (Goodwin, 1977). Turbidite-dominated metasediments, which account for the balance of the supracrustal sequence, were deposited between 2.70 and 2.68 Ga. The metavolcanic-dominated and the turbidite-dominated metasedimentary assemblages are unconformably overlain by the shallow, oxidised conglomerate-clastic sediment dominated sequence of the Timiskaming Group.
Batholithic complexes of early, pre-kinematic 2.74 to 2.69 Ga tonalite gneiss are found within and surrounding the Abitibi belt (Card, 1990), while numerous plutons of 2.70 to 7.68 Ga pre- to syn-kinematic quartz diorite, tonalite and granodiorite core central volcanic complexes. Late- to post-kinematic intrusions, mostly granodioritic or monzogranitic in composition, are discordant to structural trends, frequently surrounded by amphibolite facies metamorphic aureoles (Card, 1990). Syenitic and other 2.69 to 2.67 Ga alkalic rocks intrude the younger Timiskaming-type supracrustal rocks in a number of locations, including the Kirkland Lake district (Cameron,1990).
Most penetrative fabrics and structures in supracrustal rocks within the subprovince are parallel to regional faults and structural assemblage boundaries. Thrusts, early folding and structures associated with the 2.74 to 2-68 Ga batholith emplacement predate the synmetamorphic overprint, while folding, regional shearing and steep reverse and/or thrusts developed during and after batholithic emplacement. The Archaean structures generally strike west, NW to WNW and NE to ENE, and are consistent with a north-south compressive regime. Late, brittle faults related to the formation of the Palaeoproterozoic Cobalt Embayment and the Phanerozoic Timiskaming Rift overprint earlier Archaean structures, and strike NE, NW, and NNW.
The metamorphic grade of the Abitibi Subprovince rocks is generally lower greenschist facies, with significant areas of prehnite-pumpellyite facies. Higher grade metamorphic rocks occur in contact aureoles surrounding granitoid intrusions where grades of upper greenschist and lower amphibolite to hornblende hornfels facies may be attained.
Tholeiitic volcanic rocks of the Archaean Kinojevis Group outcrop to the north of Kirkland Lake, with calcalkaline volcanic rocks of the Blake River Group further to the north again. To the south, komatiitic volcanic rocks of the Larder Lake Group are exposed. The Kinojevis Group is unconformably overlain by alkalic volcanic and sedimentary rocks of the Timiskaming Group, while to the south the contact between the Timiskaming and Larder Lake Groups is along the major regional Kirkland Lake-Larder Lake fault/break. The Timiskaming Group consists of alluvial - fluvial conglomerates and sandstones (Mueller and Donaldson, 1992), trachytic alkaline lava flows, and pyroclastic tuff units (Lackey, 1990) that are part of the northern limb of a synclinal structure (Thomson et al., 1950). The Timiskaming conglomerates contain distinctive red chert (jasper) clasts.
The Timiskaming rocks in the Kirkland Lake district are thought to have been deposited in a strike-slip extensional basin elongated in a 65° direction and up to 5 km in width, possibly related to movement on the Kirkland Lake-Larder Lake fault. Deposition of the Timiskaming Group in the Kirkland Lake area commenced with the transtensional phase, which led to basin formation and sedimentation, followed by a transpressional stage where the sediments were uplifted and folded (Still, 2001). The Timiskaming sediments are intruded by numerous elongate alkaline intrusions during the extensional phase. These comprise alkali-feldspar syenite and lamprophyre as well as quartz-monzonite porphyry (Levesque et al., 1991). South of the Timiskaming sediments, a series of alkali-feldspar syenite and quartz-monzonite plutons e.g., the Otto and Murdoch Creek Stocks and the syenitic Lebel Stock intrude the Larder Lake Group (Levesque et al., 1991).
The Timiskaming group at Kirkland Lake comprises: i). conglomerates, composed of a fine-grained sandy or silty matrix that supports rounded to
sub-rounded pebbles, generally ranging in size from 2 to 10 cm in diameter, including minor, but characteristic jasper clasts. Other clasts are derived from the underlying greenstones and granitoid basement; ii). greywacke, a mine term for lenses of medium to fine-grained massive sedimentary rocks commonly dispersed as Ienses throughout
conglomerate units in the mine, including light to dark grey sandstone and mudstone layers; iii). tuffs, comprising a diverse range of pyroclastic flows and reworked waterlain tuffs, mainly fine-grained to sandy cherty tuffs with well preserved primary bedding and depositional features, and common coarser units of lapilli tuffs and agglomerates with blocks and bombs of leucite lava and pumice from several, up to 10 cm in diameter; iv). Trachyte, which, where present is mostly intercalated with the tuffs, and consists of a fine-grained, Iight grey to light brown matrix with distinctive altered pseudoleucites which gives the rock a 'spotted' texture.
Intrusive rocks at Kirkland Lake include: i). Augite (basic) syenite - a composite syenitic stock, centred near the town of Kirkland Lake and the Lake Shore mine, and extends to the west through the Sylvanite, Wright-Hargreaves, Lake Shore and Teck-Hughes mines, but plunges to the west into the Macassa mine workings parallel to the plunge of the ore. It is predominantly augite-rich with lesser felsic syenite and syenite porphyry. The fresh rock is dark grey-green with a coarse-grained equigranular texture consisting primarily of augite and alkali feldspars. The augites are well formed euhedral tabular laths to 5 mm in length, which show a distinctive light green alteration colour; ii). Felsic syenite, which is less common, has a similar texture to the augite syenite, but has lesser mafic minerals and is lighter in colour; iii). Porphyritic feldspar syenites, the youngest intrusive phase, which does not constitute a major portion of the intrusive mass at Macassa, but is the predominant igneous host rock in the central part of the Kirkland Lake trend at Lake Shore, Wright-Hargreaves and Sylvanite, which are centred on a Iargely feldspar porphyritic syenite stock. The porphyritic syenite occurs intermingled with, and intrudes both augite and felsic syenite as minor dykes and as narrow sills with sharp contacts that may exhibit chilled margins.
Mineralisation at Kirkland Lake is largely hosted within a steeply plunging composite stock of syenite, intruding Timiskaming Group conglomerate, greywacke and tuff dated at 2677 to 2680 Ma which unconformably overlies 2.72 and 2.70 Ga Kinojevis Group volcanic sequence rocks just over 1 km to the north. The Larder Lake-Kirkland Lake Fault, 2 km to the south, separates the Timiskaming from the Larder Lake Group ultramafic and mafic flows to the south. The Timiskaming Group defines an asymmetric synform, truncated by the Larder Lake-Kirkland Lake Fault. The composite syenite stock post dates the folding of the sediments, but is cut by the Kirkland Lake Main Break fault which comprises an ENE trending system of narrow steeply south dipping reverse faults with which the mineralisation is associated.
Mineralisation in the Kirkland Lake district is intimately associated with the Kirkland Lake fault (or Main Break) which strikes on average at 67° and dips steeply to the south at 75°. This structure is likely a local spay or branch of the regional Kirkland Lake-Larder Lake break. It has various related branches and splays which host most of the gold mineralisation in the district in quartz-rich zones within the fault zone and in related hanging wall and footwall veins. At the eastern end of the mineralised trend, an increasing number of branches splay off the strong Main Break (Thomson, 1950). These faults dissipate and reduce the overall south-vergent reverse fault/thrust displacement. The overall displacement, which is rotational, is near 450 m in the west at Macassa, to near 110 m in the east at Toburn. In the western part of the lode system, at Macassa, the '04 Break', which parallels the Main Break, hosts the bulk of the ore. Further east the ore is contained within the Main Break (which is the most consistent structure) and in the North Break, which lies about 60 m to the north. The South Break branches off the Main Break in the Wright-Hargreaves mine, and is important in the eastern mines. A series of other veins occur between these main lodes. Vein widths are generally less than 20 cm with over half of the ore-bearing veins hosted in syenite porphyry. The rest occur in Timiskaming conglomerate, greywacke and tuff.
Later, generally north-south and subvertically dipping, cross faults have displaced both the mineralised breaks and the host lithologies along the mineralised trend. Some of these structures have horizontal sinistral offsets of >100 m.
Gold occurs as a series of quartz-carbonate-sulphide veins distributed over a >5 km length of the Kirkland Lake Main Break and subsidiary structures to a depth of 2 km. Orebodies occur as shoots within these structures, and may extend up to 10 m into the wall rocks in the case of sheeted veins and stockworks. The deposits have associated extensive zones of Fe-carbonate in the syenite and sediments, while sericite and silicification forms an immediate selvedge to the quartz-carbonate veins. Post ore quartz-calcite veins carry barite, gypsum and traces of hematite and magnetite.
Three major types of gold ore are defined at Kirkland Lake; i). Break-related ore, which occurs continuously along major faults (breaks), and related branches. It typically occurs as mineralised zones of fractured and brecciated quartz and carbonate within the fault gouge or in the immediate hanging wall or footwall of the fault as fragmental quartz zones or as discrete veins, that are typically 0.3 to 1.5 m wide, with fine, native gold, accompanied by Iesser amounts of tellurides (chiefly altaite). The overall sulphide content is near 1 to 3%, the majority being pyrite. Fine native gold may also occur in chlorite fault gouge, although generally in minor amounts, rarely reaching ore grade in the absence of quartz; ii). Hanging wall and footwall veins, typically occurring as quartz-filled fracture zones from 2.5 to 60 cm wide that dip from sub-vertical to sub-horizontal, and are most common in close proximity (i.e., within 30 m) of major faults. They occur as single veins to multiple sheeted or stacked vein systems. Most veins are are defined by a sharp chlorite±molybdenum coated slip face with evidence of repeated episodes of mineralization. Gold is typically in its native form in fractured vein quartz accompanied by tellurides, predominantly altaite and calaverite, with a total sulphide content of 1 to 3%, chiefly of pyrite; and iii). Breccia ore, characterised by mineralised lensoidal and fragmental quartz in wide zones (generally up to 15 m) bounded by a significant fault in the hanging wall and footwall. The host rock is altered, between the two faults, silicified and strongly fractured, usually with 1 to 4% total sulphides, mainly as pyrite. The mineralised quartz contains native gold and tellurides. Outside the hanging wall and footwall contacts, the host rock is distinctly less altered and fractured and is not mineralised.
Resources and reserves at December 31, 2011 (Kirkland Lake Gold Inc., 2012) were:
Measured resources - 1.087 Mt @ 12.2 g/t Au
Indicated resources - 2.402 Mt @ 15.6 g/t Au
Inferred resources - 2.002 Mt @ 15.6 g/t Au
Proved reserves - 1.289 Mt @ 12.8 g/t Au
Probable reserves - 1.641 Mt @ 17.7 g/t Au
TOTAL proved & probable reserves + measured & indicated resources - 6.42 Mt @ 15.2 G/t Au.
This summary draws heavily on Sill, 2001.
The most recent source geological information used to prepare this summary was dated: 2012.
Record last updated: 20/10/2012
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.
Kirkland Lake - Macassa
References to this deposit in the PGC Literature Collection:
Kerrich R, Watson G P 1984 - The Macassa Mine Archean load gold deposit, Kirland Lake, Ontario: geology, patterns of alteration and hydrothermal regimes: in Econ. Geol. v79 pp 1104-1130|
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