Geology of the Kirkland Lake District

The Kirkland Lake District is underlain by (1) Archean rocks (> 2.5 Ga) of the Superior Province of the Canadian Shield; (2) Proterozoic rocks of the Huronian Supergroup (2.5 to 2.22 Ga); (3) highly metamorphosed rocks of the Grenville Province (1.1 billion years old); (4) Phanerozoic sedimentary rocks of Ordovician and Silurian age; and (5) kimberlite intrusions (approximately 150 Ma).

1. Kirkland Lake District is dominated by the southern Abitibi greenstone belt. Neoarchean supracrustal rocks are composed of komatiitic, tholeiitic, calc-alkalic and alkalic ultramafic, mafic, intermediate and felsic metavolcanic rocks; related subvolcanic intrusions, chemical and clastic metasedimentary rocks. The supracrustal rocks are intruded by calc-alkalic intermediate and felsic intrusions composed of quartz diorite, quartz monzonite, tonalite and granodiorite. Alkalic intrusions composed of hornblendite, alkalic gabbro, syenite, quartz syenite and alkalic granite are the youngest Neoarchean intrusions in the area. A detailed description of these supracrustal rocks, as well as, correlation with regional assemblages can be found in OGS OFR 6154 by Ayer et al. (2002). Metasedimentary rocks/granitoid rocks of the Opatica Subprovince lie at the southern edge of the Archean Superior craton and occupy the northeastern portion of the district.

Volcanogenic massive sulphide mineralization is 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)

2. The Proterozoic Huronian Supergroup, referred to as the Cobalt Embayment, underlies most of the southern part of the Kirkland Lake District. The Cobalt Group, the uppermost sedimentary cycle of the supergroup, is dominated by the Gowganda and Lorrain formations. The Gordon Lake and Bar River formations are much more restricted in extent in the district.

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).

3. 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.
4. In the New Liskeard area, graben type block faulting, within the Lake Timiskaming Structural Zone, has preserved limestone, sandstone and shale, Middle and Upper Ordovician and Lower and Middle Silurian in age, referred to as the Lake Timiskaming Outlier.
5. Kimberlite, the host rock of diamonds, occurs in two areas. Clusters of kimberlite pipes have been discovered in the south-eastern part of the district, between Matheson and Latchford. A number of the pipes are diamondiferous, however, no economic deposits have thus far been discovered.

The map below depicts the general geology of the Kirkland Lake District.