The Kirkland Lake District is underlain by (1) Archean rocks (2.75 to 2.67 billion years old) of the Superior Province of the Canadian Shield (assemblage table and map; (2) Proterozoic, Southern Province Cobalt Group rocks of the Huronian Supergroup (2.5 to 2.22 billion years old) and associated intrusive rocks; (3) highly metamorphosed rocks of the Grenville Province (1.1 billion years old); (4) Phanerozoic sedimentary rocks, Ordovician and Silurian in age; and (5) kimberlite intrusions (approximately 150 million years old). This general geology is described in more detail below.
The Archean “granite-greenstone”-dominated Abitibi Subprovince and metasedimentary rocks/granitoid rocks of the Opatica Subprovince lie at the southern edge of the Archean Superior craton and occupy the northern half of the Kirkland Lake District. Abitibi greenstone rocks also occur in the Shining Tree and Temagami areas.
Rocks of the greenstone belts include komatiitic, tholeiitic and calc-alkalic metavolcanic rocks, which are the oldest; followed by turbidite-dominated formations; and alkalic metavolcanic rocks and associated alluvial-fluvial metasedimetary rocks. Granitoid intrusive rocks include tonalite-trondjhemite-granodiorite batholiths, smaller granodiorite intrusions and syenite stocks.
Volcanogenic massive sulphides are hosted by komatiitic, tholeiitic and calc-alkalic metavolcanic rocks; iron by komatiitic and tholeiitic metavolcanic rocks; and asbestos by komatiitic metavolcanic flows or intrusions.
Gold deposits occur in east trending metasedimentary-metavolcanic formations, intruded by syenite stocks, proximal to major deformation zones with the same general trend. The deposits preferentially occur on sub-parallel fault splays, to major deformation zones such as the Larder Lake Fault and the Destor-Porcupine Fault. The Kirkland Lake District has produced more than 40 million ounces of gold (more than 1.2 million kg)
The Cobalt Group, the uppermost sedimentary cycle of the Proterozoic Huronian Supergroup, underlies most of the southern part of the Kirkland Lake District. This sedimentary group, which constitutes most of the Cobalt Embayment, from oldest to youngest is comprised of the following four formations: Gowganda, Lorrain, Gordon Lake and Bar River formations. The Gowganda and Lorrain formations have widespread exposures, whereas the Gordon Lake and Bar River formations are much more restricted in areal extent.
The Gowganda Formation consists of distinct diverse sequences of conglomerate, pebbly wacke, wacke, siltstone, mudstone and arenite; the Lorrain Formation consists mainly of arkose and quartz arenite; the Gordon Lake Formation is made up essentially of well bedded, variegated mudstone and siltstone, chert and minor fine-grained quartz sandstone; and the Bar River Formation is characterized by mature quartz arenite, ferruginous arenite and siltstone.
Gabbroic rocks, referred to as “Nipissing Diabase”, are the most abundant and widespread igneous rocks intruding the Huronian Supergroup. Nipissing intrusive rock forms dikes, sills, undulating sheets up to several hundred metres thick and bodies, which are interpreted as cone sheets.
The Cobalt and Gowganda areas are well known for their silver-, cobalt-, copper- and minor nickel-bearing carbonate/quartz veins. These veins occur mostly in Cobalt Group rocks in close association with Nipissing Diabase intrusions. The Cobalt and Gowganda silver “camps”, together, produced about 600 million ounces of silver (about 18.7 million kg).
- Highly metamorphosed rocks of the Grenville Province occur in the south-eastern corner of the Kirkland Lake District. The rocks, many of sedimentary origin, are coarse grained, gneissic, clastic metasediments; feldspathic biotite gneiss; and quartzose, muscovite gneiss.
- In the New Liskeard area, graben type block faulting has preserved limestone, sandstone and shale, Middle and Upper Ordovician and Lower and Middle Silurian in age.
- Kimberlite, the potential host rock to diamonds, has been discovered in two areas. Clusters of 10 kimberlite pipes have so far been discovered both in the Kirkland Lake and New Liskeard areas. In the Kirkland Lake area an additional 11 kimberlite dikes occur. A number of the pipes are diamondiferous, however, no economical deposits have so far been discovered.