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TitleThe role of enigmatic deep crustal and upper mantle structures on Au and magmatic Ni-Cu-PGE-Cr mineralization in the Superior Province
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LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorHarris, L B; Adiban, P; Gloaguen, E
SourceTargeted Geoscience Initiative 5: grant program final reports (2018-2020); by Targeted Geoscience Initiative Coordination Office; Geological Survey of Canada, Open File 8755, 2021 p. 85-128, Open Access logo Open Access
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
RelatedThis publication is contained in Targeted Geoscience Initiative 5: grant program final reports (2018-2020)
File formatpdf
ProvinceOntario; Quebec; Newfoundland and Labrador
NTS22; 23; 24; 25; 31; 32; 33; 34; 35; 41; 42; 43; 44; 52; 53; 54; 62; 63; 64
Lat/Long WENS-100.0000 -64.0000 62.0000 45.0000
Subjectseconomic geology; structural geology; geophysics; extraterrestrial geology; Science and Technology; Nature and Environment; mineral exploration; mineral potential; mineral deposits; gold; nickel; copper; chromium; magmatic deposits; porphyry deposits; molybdenum; uranium; thorium; ore mineral genesis; mineralization; ore controls; basement geology; structural features; faults; faults, transverse; faults, extension; shear zones; fractures; circular structures; lineaments; lithology; metamorphic rocks; granulites; mafic rocks; ultramafic rocks; intrusive rocks; kimberlites; crustal structure; lithosphere; craton; mantle; geophysical surveys; aeromagnetic surveys; magnetic surveys, airborne; gravity surveys, ground; magnetotelluric interpretations; resistivity interpretations; gravity interpretations; radar methods; structural interpretations; structural trends; tectonic interpretations; statistical analyses; tectonic history; intrusions; faulting; plate margins; crustal shortening; crustal uplift; decollement; magmatism; fluid flow; metamorphism; deformation; fracturing; rifting; models; metallogeny; Archean; Superior Province; Oxford Stull Domain; Island Lake Domain; McFaulds Lake Greenstone Belt; Ring of Fire; Big Trout Lake Igneous Complex; Lingman Lake Deposit; Kapuskasing Structural Zone; platinum group elements; Data processing; machine learning; Artificial intelligence; Geomorphology; Precambrian; Proterozoic
Illustrationsgeoscientific sketch maps; location maps; charts; flow diagrams; 3-D diagrams; profiles; 3-D images; tables; models; satellite images; 3-D models
ProgramTargeted Geoscience Initiative (TGI-5) Knowledge Management Coordination
Released2021 10 27
AbstractAeromagnetic and ground gravity data for the Canadian Superior Province, filtered to extract long wavelength components and converted to pseudo-gravity, highlight deep, N-S trending regional-scale, rectilinear faults and margins to discrete, competent mafic or felsic granulite blocks (i.e. at high angles to most regional mapped structures and sub-province boundaries) with little to no surface expression that are spatially associated with lode ('orogenic') Au and Ni-Cu-PGE-Cr occurrences. Statistical and machine learning analysis of the Red Lake-Stormy Lake region in the W Superior Province confirms visual inspection for a greater correlation between Au deposits and these deep N-S structures than with mapped surface to upper crustal, generally E-W trending, faults and shear zones. Porphyry Au, Ni, Mo and U-Th showings are also located above these deep transverse faults.
Several well defined concentric circular to elliptical structures identified in the Oxford Stull and Island Lake domains along the S boundary of the N Superior proto-craton, intersected by N- to NNW striking extensional fractures and/or faults that transect the W Superior Province, again with little to no direct surface or upper crustal expression, are spatially associated with magmatic Ni-Cu-PGE-Cr and related mineralization and Au occurrences. The McFaulds Lake greenstone belt, aka. 'Ring of Fire', constitutes only a small, crescent-shaped belt within one of these concentric features above which 2736-2733 Ma mafic-ultramafic intrusions bodies were intruded. The Big Trout Lake igneous complex that hosts Cr-Pt-Pd-Rh mineralization west of the Ring of Fire lies within a smaller concentrically ringed feature at depth and, near the Ontario-Manitoba border, the Lingman Lake Au deposit, numerous Au occurrences and minor Ni showings, are similarly located on concentric structures. Preliminary magnetotelluric (MT) interpretations suggest that these concentric structures appear to also have an expression in the subcontinental lithospheric mantle (SCLM) and that lithospheric mantle resistivity features trend N-S as well as E-W. With diameters between ca. 90 km to 185 km, elliptical structures are similar in size and internal geometry to coronae on Venus which geomorphological, radar, and gravity interpretations suggest formed above mantle upwellings. Emplacement of mafic-ultramafic bodies hosting Ni-Cr-PGE mineralization along these ringlike structures at their intersection with coeval deep transverse, ca. N-S faults (viz. phi structures), along with their location along the margin to the N Superior proto-craton, are consistent with secondary mantle upwellings portrayed in numerical models of a mantle plume beneath a craton with a deep lithospheric keel within a regional N-S compressional regime. Early, regional ca. N-S faults in the W Superior were reactivated as dilatational antithetic (secondary Riedel/R') sinistral shears during dextral transpression and as extensional fractures and/or normal faults during N-S shortening. The Kapuskasing structural zone or uplift likely represents Proterozoic reactivation of a similar deep transverse structure.
Preservation of discrete faults in the deep crust beneath zones of distributed Neoarchean dextral transcurrent to transpressional shear zones in the present-day upper crust suggests a 'millefeuille' lithospheric strength profile, with competent SCLM, mid- to deep, and upper crustal layers. Mechanically strong deep crustal felsic and mafic granulite layers are attributed to dehydration and melt extraction. Intra-crustal decoupling along a ductile décollement in the W Superior led to the preservation of early-formed deep structures that acted as conduits for magma transport into the overlying crust and focussed hydrothermal fluid flow during regional deformation. Increase in the thickness of semi-brittle layers in the lower crust during regional metamorphism would result in an increase in fracturing and faulting in the lower crust, facilitating hydrothermal and carbonic fluid flow in pathways linking SCLM to the upper crust, a factor explaining the late timing for most orogenic Au.
Results provide an important new dataset for regional prospectively mapping, especially with machine learning, and exploration targeting for Au and Ni-Cr-Cu-PGE mineralization. Results also furnish evidence for parautochthonous development of the S Superior Province during plume-related rifting and cannot be explained by conventional subduction and arc-accretion models.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques, which will result in more effective targeting of buried mineral deposits. This compendium is the result of the TGI Grant Recipients 2018-2020.

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