Geoscience

Northern Superior Province Mineral Deposit Types

Content Links:

Lode Gold
Volcanic-associated Massive Sulphide
Komatiite-associated Ni-Cu-Pge
Carbonatite (updated April 2012)
Mafic Intrusion-hosted Ti-V-Fe
Rare Element-enriched Pegmatites (updated April 2012)
Diamonds

Note: The descriptions below are based in large part on Rogers et al., 1995: Descriptive mineral deposit models of metallic and industrial deposit types and related mineral potential assessment criteria; Ontario Geological Survey, Open File Report 5916, with numerous direct quotes. As well as reworked sections to reflect the types of occurrences in the Northern Superior Province of Manitoba.

 

A list of bibliographic references and cancelled assessment files pertaining to this region are included in: 1996: Georeference Information Package for the Northern Superior Geologic Province; 2nd ed.; Manitoba Industry, Trade and Mines, Geological Services, Open File 95-8, which is available for viewing at the Mineral Resources Library or for purchase from Publication Sales. For a listing of current publications, refer to the Bibliography of the northern Superior Province (1996-2001).

 

Lode Gold

Characteristics

Gold mineralization can occur in and in proximity to, quartz veins, within a wide range of rock types. A spatial association with brittle and/or ductile deformation zones is common. The gold is typically deposited from hydrothermal fluids in or in proximity to the sheared zones (Rogers et al., 1995).

 

Geological Environment and Potential Settings in the Northwestern Superior Province

A wide range of potential host rock types within the volcano-plutonic subprovinces. The potential host rocks include:

  1. Komatiitic-tholeiitic volcanic assemblages (no known occurrences in Northern Superior (NONS))
     
  2. Bimodal mafic to felsic volcanic assemblages (Knee Lake, Island Lake)
     
  3. Internal greenstone belt turbidite (NONS)
     
  4. Internal greenstone belt iron formation (Little Stull Lake, Gods Lake, Oxford Lake)
     
  5. Alluvial fluvial sedimentary rocks (Monument Bay)
     
  6. Internal quartz-feldspar porphyritic dyke or stock (Knee Lake Gold Mine)

 

Assessment Criteria

1.  Geological

  • major deformation zones within the greenstone belts or along belt or subprovince boundaries
     
  • two preferred orientations in Sachigo region - northeast and east; arcuate subsidiary faults commonly splay from the regional deformation zones
     
  • broad zones of alteration are spatially related to the structures

2.  Geophysical

  • late deformation zones are defined by low, linear magnetic response and by large scale offsets of regional patterns
     
  • gold-bearing massive sulphide mineralization may be represented by an E.M. anomaly
     
  • magnetic lows related to broad magnetite-destructive carbonate alteration

back to top

Volcanic-associated Massive Sulphide

Characteristics

Copper, zinc and lead bearing, stratabound to stratiform lenses of solid to near solid sulphide in submarine volcanic rocks of typically intermediate to felsic composition. Noranda - type: Cu-Zn; Mattabi - type: Zn-Cu- (Ag); Kuroko - type: Zn - Pb - Cu. (Rogers et al., 1995); Cyprus - type: Cu±Zn.

 

Geological Environment

District Scale: in submarine volcanic assemblages of tholeiitic and/or calc-alkalic affinities. Various associations including bimodal mafic to felsic and intermediate to felsic volcanic successions, and komatiite to tholeiite assemblages with felsic volcanic centres. Intermediate to felsic volcanic rocks are the principal hosts. Subvolcanic intrusions of mafic to felsic composition are common and may be essential features. Common occurrence of volcaniclastic and epiclastic sedimentary units in the sequence and thin exhalite horizons. (Rogers et al., 1995)

 

Archean VMS deposits have been subdivided into two main types:

1.   Noranda - type:

  • volcanic sections include both mafic to intermediate and felsic rocks - although the mafic to intermediate rocks are more abundant
     
  • rock types are dominated by mafic to intermediate pillow lavas, hyaloclastites, massive amygdaloidal flows and flow breccia
     
  • felsic rocks occur as lava flows or domes and as hyaloclastites
     
  • local bedded volcaniclastic and exhalites
     
  • generally lack or contain only minor amounts of pyroclastic rocks and subaerial rocks

2.   Mattabi - type:

  • volcanic section is dominated by felsic volcanic rocks
     
  • abundant fragmental rocks dominate; felsic tuff, massive and bedded pyroclastic flows, hyaloclastite, debris flows and dome and flow breccia
     
  • also mafic to intermediate tuff and flow breccia
     
  • pillow lava and breccia may or may not be present
     
  • lava domes and welded tuff are commonly present
     
  • high amygdule content in flows
     
  • submarine and subaerial volcanic rocks common

 

Potential Settings in the Northwestern Superior Province
  1. Central Knee Lake
     
  2. Little Stull-Rorke lakes area
     
  3. Knife Lake
     
  4. Bigstone Lake
     
  5. Oxford Lake

 

Assessment Criteria

Geological

  • Greenstone belts
     
  • Calc-alkalic and/or tholeiitic volcanic assemblages
     
  • submarine bimodal mafic to felsic or intermediate to felsic volcanic sequences; or komatiite to tholeiite volcanic sequences with isolated volcanic centres
     
  • Intermediate to felsic volcanic sequence ± sedimentary host sequence.
     
  • Typically a regional association with intermediate to felsic volcanic calderas; localized volcanic centres; especially marked by coarse pyroclastic breccia, domes and flows*

back to top

Komatiite-associated Ni-Cu-Pge

Characteristics

Stratabound to Stratiform nickel, copper and minor PGE (Platinum-group elements) sulphide deposits hosted by subaqueous ultramafic flows and related shallow intrusions.

 

Geological Environment

Host rocks include ultramafic komatiite flows (dunitic and perridotitic) and related shallow intrusions. Associated rocks include tholeiitic and komatiitic basalts flows. The commonly thin, layered komatiitic flows may have olivine spinifex textures, but also include thick cumulate textured bodies. Sulphide mineralization typically occurs in the basal portions of the flows.

 

Potential Settings in the Northern Superior Province

Komatiites are known from the Island Lake area. Some of the thin ultramafic bodies intersected in drillcores throughout the Superior Province probably represent komatiite flows.

 

Assessment Criteria
  • greenstone belts with geochemical evidence of extensional tectonics.
     
  • zones of high-magnesium basalts and sulphide iron formation.
     
  • linear magnetic anomalies with coincident conductors.

    back to top


Carbonatite (updated April 2012)

Characteristics

Carbonatites are carbonate-rich, intrusive or extrusive igneous rocks consisting of more than 50 percent primary carbonate minerals. Carbonatites can contain economic concentrations of different elements and minerals: niobium (Nb), rare earth elements (REEs), iron (F), thorium (Th), copper (Cu), apatite (phosphate), fluorite, and barite.

 

Host Rocks

Carbonatites are often associated with other alkaline igneous rocks, either of which can be mineralized. The intrusions are commonly circular to elliptical-shaped, but may also occur as lenses or layers. Rocks adjacent to these complexes may be characterized by extensive sodium, potassium, and carbonate metasomatism.

 

Potential Settings in the Northern Superior Province

There is potential for alkaline intrusions throughout the Superior Province of Manitoba especially if we take into consideration the occurrences of this type of rocks in the Ontario side of the Superior Province. For example the Carb Lake Carbonatite Complex occurs near the Manitoba-Ontario border. Similar bullseye aeromagnetic anomalies occur on the Manitoba side of the border.

 

Assessment Criteria
  • May be associated with deep-seated fault systems.

  • Magnetic, gravity and radiometric highs may indicate the presence of carbonatite complexes.

back to top

Mafic Intrusion-hosted Ti-V-Fe

Characteristics

Ilmenite and vanadiferous magnetite occur as stratabound, semi-massive, massive and disseminated zones in Archean layered anorthosite, megacrystic anorthosite and anorthositic gabbro intrusions.

 

Geological Environment

Host rocks comprise (in decreasing order of abundance) anorthosite, leucogabbro, gabbro, melagabbro and pyroxenitic phases of layered, stratiform sill-like mafic intrusions; others as stock-like intrusions. Oxide concentrations tend to occur in the upper levels of the differentiated intrusions. Associated rocks include diabase and diorite and may include ultramafic intrusive rocks in the basal portions of the intrusion. Country rock to the intrusions commonly consists of metavolcanic (basalt) and metasedimentary assemblages as well as medium to high grade metamorphic gneisses, schists, amphibolites, and granulites (Pikwitonei). The southern boundary of the north-facing Pipestone Lake Anorthosite Complex (PLAC) is intruded by tonalite veins that emanate from the Whiskey Jack gneiss complex. Late Archean. (PLAC - 2758 ± 3 Ma; U-Pb zircon).

 

Host Rock Textures

May include cumulate, ophitic, subophitic, porphyritic, glomeroporphyritic (plagioclase chadacrysts), equigranular and rarely pegmatitic textures. Net-textured pyroxene oikocrysts. More highly metamorphosed phases are white, coarsely recrystallized and contain large subideoblastic garnet porphyroblasts, and boudins.

 

Tectonic Setting and Northwestern Superior Province Examples
  1. Generally cratonic. The PLAC appears to be part of a much larger anorthositic complex that extends 95 km from the Hairy and Butterfly lakes region, west to the West Channel, Kiski and Minago Lake bodies.
     
  2. Other, potentially related, extensive gabbroic and dioritic intrusions occur to the southeast in the Ponask and Gunisao lakes region.
     
  3. Similar mafic intrusions in the Superior Province in Ontario occur as synvolcanic, or younger intrusions emplaced along structural zones coincident with subprovince boundaries.

 

Assessment Criteria
  1. Geological;
    Oxide concentrations occur in the upper levels of layered megacrystic to glomeroporphyritic anorthosite to gabbro intrusions with minor pyroxenitic phases. Compositional and igneous layering (locally rhythmic) occurs on centimetre, decimetre and metre scales. Textural layering defined by grainsize variations. Rare graded and grainsize graded layering. The PLAC is anomalously enriched in oxide phases and low in phosphates, sulphides, PGE and magnesium. Ilmenite concentrations range from 10-20% in the North Contact Zone, to 40% in the Main Central Zone, which has a drill proven strike length of 9.5 km and depths > 300 m. Current reserves estimates are 364 million tons of 4.75% Ti02 with iron and vanadium credits in two adjacent zones to a depth of 1,000 feet. The mineralization is 21,000 feet long and 150 to 300 feet wide. Included in this resource is the higher grade Main Central Zone which is estimated to contain drill indicated reserves of 25 million tons grading 8.72% Ti02, 42.75 Fe203 and 0.58% V205.
     
  2. Geophysical;
    Airborne and ground magnetic surveys - magnetite concentrations are characterized by strong magnetic highs; and ilmenite bodies are commonly represented by negative magnetic anomalies. Interlayered massive magnetite and ilmenite layers display alternating linear, magnetic highs and lows with sharp reversals. Oxide bodies have associated local, gravity highs.

    back to top


     

Rare Element-enriched Pegmatites (updated April 2012)

Characteristics

Pegmatites are coarse-grained igneous rocks with various shapes, unique mineralogy, textures and can also contain rare element-enriched minerals. In general, pegmatites can be important sources of rare-elements, such as beryllium (Be), niobium (Nb), tantalum (Ta), tin (Sn), lithium (Li), rubidium (Rb), phosphorous (P) cesium (Cs), gallium (Ga), industrial minerals (for example: quartz and feldspar), zirconium (Zr), thorium (Th), yttrium (Y), uranium (U), rare earth elements (REEs), gems and various mineral specimens.

 

Geological Environment

Granitic pegmatites, the most commonly found in the Superior Province in Manitoba, generally occur in association with chemically evolved, two- mica, S-type granitoids emplaced into low- to medium- grade metamorphic domains. Pegmatite emplacement in the country rock can be controlled by structural weaknesses, major shear zones and the presence of B, F, H2O, Li, and P.
Manitoba examples in the northern Superior Province include Cross Lake, Gods Lake, Red Cross Lake, and Red Sucker Lake. In the SE of the Superior Province, the Tanco pegmatite is a world-class Li-Cs-Ta deposit that is currently in production.

 

Mineralogy and Textures

Different types of pegmatites can display enrichment in one or more of the rare elements. This is reflected in their mineralogy. Mineral associations are variable but some examples include spodumene, petalite, pollucite, beryl, tantalite-columbite group minerals, lepidolite, elbaite, zinnwaldite and microlite. Textures are typically coarse- grained, and the textural complexity of pegmatites generally increases with progressive fractionation and enrichment in rare elements.

 

Tectonic Setting

Anorogenic granitic pegmatites (age range - late Archean 2650 - 2550 Ma), containing minerals enriched in rare elements are particularly abundant in Kenoran greenstone belts. Within the pegmatite provinces, individual pegmatite fields comprise largely post tectonic intrusions of fertile granites and their pegmatite aureoles. In the southern Superior Province, emplacement of pegmatites appears related to fault systems or lithologic boundaries in andalusite-, cordierite- and staurolite-bearing schists of mainly lower amphibolite facies. Individual granite-pegmatite groups may contain mineralization within the pegmatitic-granite cupolas of the host granites, but typically mineralization is most pronounced in the intermediate to outer parts of the aureoles. Manitoba examples in the northern Superior Province include Cross Lake, Gods Lake, Red Cross Lake, Red Sucker Lake and Ponask Lake.

 

Assessment Criteria

Rare element enrichment may occur as regular or irregular bodies in the pegmatites. Concentrations may be localized within the host pegmatites and/or in irregular contact aureoles. Zonation is common in some deposits. A variety of mineralogical and geochemical indicators can be used to define zonation, and the degree of fractionation, within individual pegmatites and/or pegmatitic granites, and pegmatite fields.

Vegetation geochemistry and basal till surveys are particularly useful for locating rare element enriched pegmatites in glaciated terrains. Regional lithogeochemistry, for example Li in supracrustal hostrocks, can be effective in detecting contact aureoles around rare element pegmatites or Li-bearing mineralized pegmatite bodies. Geophysical surveys can be used to define associated structural weaknesses; airborne gamma surveys to outline parent granites. Gravity surveys can detect blind pegmatite bodies.

back to top

Diamonds

Characteristics

Diamonds are associated with the ultramafic rocks kimberlite and lamproite. The diamond crystals commonly occur together with chromium-bearing pyroxenes, garnets and spinels. The host rocks commonly have pipe or champagne glass-shaped forms, but may also occur as tabular dykes.

 

Assessment Criteria

1.   Geological

  • areas of thick continental crust such as the western part of the Superior Province.
     
  • chromium pyroxene and magnesium garnet bearing ultramafic rock.
     
  • generally occur in clusters.

2.   Geophysical

  • "bullseye" magnetic anomalies, generally less than one km in diameter.
     
  • No reported occurrences in the Superior Province of Manitoba.

back to top