Geology of the Kenora District

The Kenora District is entirely underlain by Archean (i.e. greater than 2.5 billion year old) rocks of the Superior Province of the Canadian Shield. These basically fall into six categories which are generally distinguished by the subprovince/terrances in which they occur. From north to south, these are:

Uchi Subprovince rocks, located in the northwest part of the Kenora District is underlain by metavolcanics and felsic intrusive rocks;
English River Subprovince rocks, south of the Uchi Subprovince, which are predominantly metamorphosed sedimentary and minor intrusive rocks;
Winnipeg River Terranne rocks, south of the English River Subprovince, which are generally highly metamorphosed gneissic rocks;
Wabigoon Terrane rocks, south of the Winnipeg River Terrane, underlying most of the District, which are narrow, generally east or north-northeast trending belts of mixed volcanic, intrusive and sedimentary rocks--the so-called "greenstone" belts--separated by large intrusions of generally granitic rocks;
Marmion Terrane rocks, located in the southeast part of the District, mainly situated east of the Wabigoon Terrane and south of the Winnipeg River Terrane, is underlain by metamorphosed felsic intrusive rocks;
Quetico Subprovince rocks, south of the Wabigoon and Marmion terranes, situated in the southeastern part of the District, are predominantly sedimentary and minor intrusive rocks similar to those occurring in the English River Subprovince.

A majority of the rock descriptions are summarized from OGS, 2001 with revisions by Stone, D. and Davis, D.W., 2006.

Ontario Geological Survey 1991. Bedrock geology of Ontario, west-central sheet;
Ontario Geological Survey, Map 2542, scale 1:1 000 000.

Stone, D. and Davis, D.W., 2006. Revised Tectonic Domains of the South-Central Wabigoon Subprovince; in Summary of Field Work and Other Activities 2006, Ontario Geological Survey, Open File Report 6192, p.11-1 to 11-18.

Uchi Subprovince

The northwestern part of the Kenora District is underlain by metavolcanics and intrusive rocks of this subprovince. The majority of the subprovince extends and underlines the Red Lake Resident Geologist District.

Mineral deposit types which occur in the area include: Gold occurrences are related to late shear zones but there are no economic mineral concentration in the part of the subprovince.

English River Subprovince

The subprovince is composed predominantly of highly metamorphosed and migmatized clastic sedimentary rocks that are as young as 2698 Ma, minor metavolcanics rocks and granitic intrusive rocks that range from 2.65 to 2.70 billion years in age.

Mineral deposit types which occur in the area include: rare-element and uranium-bearing pegmatites with and adjacent to the Separation Rapids Pegmatite Field; copper-nickel-cobalt-palladium-platinum-bearing sulphides in meta-ultramafic pods in the Werner Lake area; zinc-lead copper-silver volcanogenic massive sulphide mineralization in the Separation Lake area.

Winnipeg River Terrane

The Winnipeg River Terrane is a dominantly a granitoid domain. The area is underlain by highly metamorphosed and deformed supracrustal rocks composed of massive and pillowed basalts and minor sedimentary rocks which are intruded by tonalitic gneisses and plutons. Granodioritic to granitic plutons, and minor dioritic to granodioritic plutons, were emplaced between 2.66 and 2.71 Ga. A sample of foliated tonalite, from the Tannis Lake area, gave an age date of 3319 Ma, which represents one of the oldest rocks in the Superior province.

Mineral deposit types which occur in the area include: the massive, equigranular medium-to coarse grained, porphyritic granite that is part of the Lount Lake Batholith are the sites of several granite deposits.

Wabigoon Terrane

The Wabigoon Terrane supracrustal rocks are subdivided into lithostratigraphic units grouped into tectonically bounded assemblages. The assemblages can be classified into four major sequences: a) lower mafic sequences composed of tholeiitic and minor komatiitic basalt with lesser amounts of andesite mafic flows, fragmental rocks and coeval intrusions (2800 to 2745 Ma); b) lower mixed metavolcanics sequence composed of pillow to massive tholeiitic flows and felsic pyroclastic rocks (2744 to 2730 Ma); c) diverse intermediate to felsic metavolcanics sequences composed of calc-alkalic rocks and lesser amounts of tholeiitic andesite to rhyolite pyroclastic rocks with subordinate epiclastic units and flows (2719 to 2705 Ma); and d) metasedimentary sequences composed of turbiditic, alluvial-fan fluvial and minor platform sequences (7404 to 2696 Ma). The extensive Warclub group of sedimentary rocks were deposited over several of these major sequences (2716 to 2700 Ma).

Felsic intrusive units comprise pre-greenstone granitoid plutons and numerous synvolcanic, batholiths and posttectonic stocks. Ultramafic intrusions were emplaced with mafic volcanism, early granitoid plutonism and late granitoid plutonism.

Mineral deposits of the terrane include: volcanogenic copper-gold and zinc-copper-silver deposits (VMS) within volcanic units. Algoma-type iron formation style mineralization is associated with metavolcanic and metsedimentary rock. Mineralization associated with plutonic rocks include: pegmatite-related rare metal, uranium and molybdenum deposits, copper, copper-nickel, chromite and platinum group element deposits associated with mafic and ultramafic intrusions. A 100 kg sample of ultramafic fragmental material returned six micro diamonds in the Fort Frances area. Lode gold deposits area related to late shear zones and contact strain aureoles developed around batholiths and gold-rich VMS environments are found throughout the terrane. Selected felsic intrusive bodies, composed of massive, equigranular granite are sites of granite deposits.

Marmion Terrane

The part of the Kenora District which is underlain by this terrane is predominately metamorphosed felsic intrusive rocks. The 3.0 to 2.7 billion year of rocks are interpreted as an assemblage of continental fragments. These rocks were once also interpreted as part of the Western Wabigoon and Winnipeg River terranes. The majority of the terrane extends and underlines the Thunder Bay South Resident Geologist District.

Mineral deposit types which occur in the area include: there are no economic mineral concentration in the part of the terrane situated in the Kenora District.

Quetico Subprovince

The Quetico Subprovince consists predominantly of metamorphosed turbiditic wacke, largely derived from, and deposited during and after, the volcanic climax in the neighbouring subprovinces and terranes during the period 2.70 to 2.69 Ga. Amphibolite-facies metamorphism, migmatite formation and granite intrusion occurred during the period 2.67 to 2.65 billion years ago.

Mineral deposit types which occur in the area include: there are no economic mineral concentration in the part of the subprovince situated in the Kenora District.

The following figure depicts the general geology and approximate boundaries of the subprovinces and terranes for the Kenora District.

Timmins Map