Reactivation mechanisms and related-porosity enhancement of shear zones in context of basement-hosted uranium mineralization: case of the Spitfire discovery in the Patterson Lake corridor, Canada

2021 ◽  
pp. geochem2020-082
Author(s):  
Maher Abdelrazek ◽  
Antonio Benedicto ◽  
Olivier Gerbaud ◽  
Patrick Ledru
Keyword(s):  
Structural Evolution ◽  
Shear Zones ◽  
Uranium Mineralization ◽  
Mechanical Anisotropy ◽  
Fluid Circulation ◽  
Content Type ◽  
Athabasca Basin ◽  
The North ◽  
Ductile Shear Zones ◽  
Alteration Minerals

Uranium mineralization in the Patterson Lake corridor (southwestern Churchill province, Canada) is hosted in the metamorphosed Paleoproterozoic basement covered to the North by the flat-lying sandstone formations of the Athabasca Basin. The mineralization is exclusively contained within inherited ductile structures that were reactivated under a brittle regime. Petrographic and micro-structural studies of drill core samples from the Spitfire discovery (Hook Lake Project) reveal the linkages between structural evolution of the basement, alteration and mineralization. During basement exhumation, localization of non-coaxial deformation led to the formation of a large anastomosing shear zone system made of mylonitic rocks. Strain localization associated with fluid circulation induced strong mineralogical and rheological changes, forming discontinuities in mechanical anisotropy. During and post-deposition of the Athabasca Basin after 1.80 Ga, these zones of anisotropy localized brittle reactivation, expressed by a network of micro-fractures later amplified by dissolution processes which enhanced porosity later filled with phyllosilicates and uranium oxides. Crosscutting relationships between alteration minerals and structures indicate that fluid circulation was active after the basement exhumation. Uranium-bearing fluids moved through the network of micro-fractures. As shown for the Spitfire prospect, fertile structures in the basement below the Athabasca Basin have a combined poly-phase structural and alteration history during which development of ductile shear zones followed by brittle reactivation and dissolution processes led to the formation of superimposed shear and damaged zones in which uranium orebodies are located.Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

Structural evolution and related implications for uranium mineralization in the Patterson Lake corridor, southwestern Athabasca Basin, Saskatchewan, Canada

2020 ◽  
pp. geochem2020-030
Author(s):  
Dillon Johnstone ◽  
Kathryn Bethune ◽  
Colin Card ◽  
Victoria Tschirhart
Keyword(s):  
Structural Evolution ◽  
Uranium Mineralization ◽  
Ductile Deformation ◽  
Normal Faults ◽  
Uranium Deposits ◽  
Content Type ◽  
Athabasca Basin ◽  
Basement Rocks ◽  
Transfer Faults ◽  
Dextral Strike Slip

The Patterson Lake corridor is situated along the southwest margin of the Athabasca Basin and contains several basement-hosted uranium deposits and prospects. Drill core investigations during this study have determined that granite, granodiorite, mafic and alkali intrusive basement rocks are entrained in a deep-seated northeast-striking subvertical heterogeneous high-strain zone defined by anastomosing ductile to semi-brittle shears and brittle faults. The earliest phases of ductile deformation (D1/2), linked with Taltson (1.94–1.92 Ga) orogenesis, involved interference between early fold sets (F1/2) and development of an associated ductile transposition foliation (S1/2). During subsequent Snowbird (ca. 1.91–1.90 Ga) tectonism, this composite foliation was re-folded (D3) by northeast-trending buckle-style folds (F3), including a regional fold centered on the Clearwater aeromagnetic high. In continuum with D3, a network of dextral-reverse chloritic-graphitic shears, with C-S geometry, formed initially (D4a) and progressed to more discrete, spaced semi-brittle structures (D4b; ca. 1.900–1.819 Ga). Basin development (D5a; <ca. 1.819 Ga) was marked by a set of north-striking normal faults and related east- and northeast-striking transfer faults that accommodated subsidence. Primary uranium mineralization (D5b; ∼1.45 Ga) was facilitated by brittle reactivation of northeast-striking basement shears in response to west-southwest - east-northeast-directed compressional stress (σ1). Uraninite was emplaced along σ1-parallel extension fractures and dilational zones formed at linkages between northeast- and east-northeast-striking dextral strike-slip faults. Uranium remobilization (D5c) occurred after σ1 shifted to west-northwest – east-southeast, giving rise to regional east- and southeast-striking conjugate faults, along which mafic dykes (1.27 Ga and 1.16 Ga) intruded.Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

scholarly journals Structural analysis of the Rio Preto fold belt (northwestern Bahia / southern Piauí), a doubly-vergent asymmetric fan developed during the Brasiliano Orogeny

2014 ◽  
Vol 86 (3) ◽  
pp. 1101-1113 ◽  
Author(s):  
FABRÍCIO A. CAXITO ◽  
ALEXANDRE UHLEIN ◽  
LUIZ F.G. MORALES ◽  
MARCOS EGYDIO-SILVA ◽  
JULIO C.D. SANGLARD ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Structural Evolution ◽  
Shear Zones ◽  
Central Compartment ◽  
Strike Slip ◽  
Fold Belt ◽  
Main Structure ◽  
The North ◽  
Brasiliano Orogeny ◽  
Analog Models

The Rio Preto fold belt borders the northwestern São Francisco craton and shows an exquisite kilometric doubly-vergent asymmetric fan structure, of polyphasic structural evolution attributed exclusively to the Brasiliano Orogeny (∼600-540 Ma). The fold belt can be subdivided into three structural compartments: The Northern and Southern compartments showing a general NE-SW trend, separated by the Central Compartment which shows a roughly E-W trend. The change of dip of S2, a tight crenulation foliation which is the main structure of the fold belt, between the three compartments, characterizes the fan structure. The Central Compartment is characterized by sub-vertical mylonitic quartzites, which materialize a system of low-T strike slip shear zones (Malhadinha – Rio Preto Shear Zone) crosscutting the central portion of the fold belt. In comparison to published analog models, we consider that the unique structure of the Rio Preto fold belt was generated by the oblique, dextral-sense interaction between the Cristalândia do Piauí block to the north and the São Francisco craton to the south.

Evolution of brittle structures in plagioclase-rich rocks at high-grade metamorphic conditions – Linking laboratory results to field observations

2020 ◽  
Author(s):  
Sarah Incel ◽  
Jörg Renner ◽  
Bjørn Jamtveit
Keyword(s):  
Structural Evolution ◽  
Confining Pressure ◽  
Shear Zones ◽  
Ductile Shear Zones ◽  
Laboratory Results ◽  
Experimental Laboratory ◽  
Eclogite Facies ◽  
Ductile Shear ◽  
Host Rocks ◽  
Lower Crustal

&lt;p&gt;Plagioclase-rich lower crustal granulites exposed on the Lofoten archipelago, N Norway, display pseudotachylytes, reflecting brittle deformation, as well as ductile shear zones, highlighting plastic deformation. Pristine pseudotachylytes often show no or very little difference in mineral assemblage to their host-rocks that exhibit limited, if any, metamorphic alteration. In contrast, host-rock volumes that developed ductile shear zones exhibit significant hydration towards amphibolite or eclogite-facies assemblages within and near the shear zones. We combine experimental laboratory results and observations from the field to characterize the structural evolution of brittle faults in plagioclase-rich rocks at lower crustal conditions. We performed a series of deformation experiments on intact granulite samples at 2.5 GPa confining pressure,&amp;#160; a strain rate of 5&amp;#215;10&lt;sup&gt;-5&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;,&amp;#160; temperatures of 700 and 900 &amp;#176;C, and total strains of either ~7-8 % or ~33-36 %. Samples were either deformed &amp;#8216;as-is&amp;#8217;, i.e. natural samples without any treatment, or with ~2.5 wt.% H&lt;sub&gt;2&lt;/sub&gt;O added. Striking similarities between the experimental and natural microstructures suggest that the transformation of precursory brittle structures into ductile shear zones at eclogite-facies conditions is most effective when hydrous fluids are available in excess.&lt;/p&gt;

A Discussion on global tectonics in Proterozoic times - Tectonics of the North Atlantic Proterozoic dyke swarm

1976 ◽  
Vol 280 (1298) ◽  
pp. 529-539 ◽  
Keyword(s):  
North Atlantic ◽  
Shear Zones ◽  
Dyke Swarm ◽  
Fracture System ◽  
West Greenland ◽  
The North ◽  
Ductile Shear Zones ◽  
The North Atlantic ◽  
Lateral Displacements ◽  
Global Tectonics

The Proterozoic North Atlantic dyke swarm occurs in Scotland, East and West Greenland, and Labrador, over an area of at least 250000 km2, and includes two dominant dyke sets which in West Greenland strike NNE-SSW, and ESE-WNW. The intrusive relations of the two sets, and their association with ductile shear zones and other lateral displacements of country rocks, show the dykes to represent a conjugate swarm emplaced along shear fractures, rather than along tensional openings. The mechanical behaviour of the Proterozoic lithosphere is considered in the context of the regional fracture system.

Structural analysis of ductile shear zones in the North Qinling Orogen and its implications for the evolution of the Proto-Tethys Ocean

2017 ◽  
Vol 52 ◽  
pp. 202-214 ◽  
Author(s):  
Shujuan Zhao ◽  
Sanzhong Li ◽  
Xiyao Li ◽  
Ian Somerville ◽  
Huahua Cao ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Shear Zones ◽  
Qinling Orogen ◽  
The North ◽  
Ductile Shear Zones ◽  
North Qinling ◽  
Ductile Shear ◽  
Tethys Ocean

Transpression in an Archean greenstone belt, northern Minnesota

1988 ◽  
Vol 25 (7) ◽  
pp. 1060-1068 ◽  
Author(s):  
P. J. Hudleston ◽  
D. Schultz-Ela ◽  
D. L. Southwick
Keyword(s):  
Volcanic Rocks ◽  
Shear Bands ◽  
Shear Zones ◽  
The North ◽  
Strain Pattern ◽  
Ductile Shear Zones ◽  
Continuous Shear ◽  
Measured Strain ◽  
Archean Greenstone Belt ◽  
North And South

Weakly metamorphosed Archean sedimentary and volcanic rocks of the Vermilion district, northern Minnesota, occupy an east–west-trending belt between gneisses of the Vermilion granitic complex to the north and the Giants Range batholith to the south. All the measured strain, a foliation, and a mineral lineation in this belt are attributed to the "main" phase of deformation (D2). Foliation strikes parallel to the belt and dips steeply, and the mineral lineation plunges moderately to steeply east or west and is parallel to the maximum stretching direction, X, and subparallel to fold hinges. An earlier, possibly nappe-forming, event (D1) left little evidence of fabric in the Vermilion district.A number of features indicate that the D2 deformation involved a significant component of dextral strike-slip shear in addition to north–south compression. They include ductile shear zones with sigmoidal foliation patterns, shear bands, asymmetric pressure shadows, and the fact that the asymmetry of the F2 folds is predominantly Z. Other features are more simply explained by a deformation involving simple shear. The S2 cleavage is locally folded, and a new spaced cleavage developed in an orientation similar to that of the old cleavage away from the folds. We consider this the result of a process of continuous shear, with perturbations of flow resulting in folding of S2 and the development of a new foliation axial planar to the folds. The same type of perturbation can lead to the juxtaposition of zones of constrictional and flattening strains, a distinctive feature of the rocks of the Vermilion district otherwise hard to account for. The strain pattern requires a north–south component of shortening in addition to shear. The D2 deformation in the Vermilion district can therefore be characterized as one of transpression: oblique compression between two more rigid lithospheric blocks to the north and south.

scholarly journals Fluid-Present Partial Melting of Paleoproterozoic Okbang Amphibolite in the Yeongnam Massif, Korea

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
pp. 1-26
Author(s):  
Yuyoung Lee ◽  
Moonsup Cho
Keyword(s):  
Partial Melting ◽  
Shear Zones ◽  
Thin Layers ◽  
The North ◽  
Ductile Shear Zones ◽  
Ductile Shearing ◽  
Basaltic Melt ◽  
Yeongnam Massif ◽  
Migmatitic Gneiss ◽  
The Times

Abstract The waning stage of a long-lived collisional orogeny is commonly governed by an extensional regime in association with high-temperature metamorphism, anatexis, and magmatism. Such a late-orogenic process is well-recorded in the Okbang amphibolite, Yeongnam Massif, Korea, where thin layers or irregular patches of tonalitic leucosomes are widespread particularly in association with ductile shear zones. Various microstructures including interstitial felsic phases and former melt patches indicate that leucosomes are the product of partial melting. These leucosomes are aligned en echelon and contain large (up to ~2 cm) grains of peritectic hornblende, suggesting synkinematic fluid-present anatexis. The leucosomes are enriched in Na2O and Sr contents compared to the amphibolite but depleted in rare earth and high field-strength elements. P-T conditions of the anatexis were estimated at 4.6–5.2 kbar and 650–730°C, respectively, based on hornblende-plagioclase geothermobarometry. Sensitive high-resolution ion microprobe U-Pb analyses of zircon from an amphibolite and a leucosome sample yielded weighted mean 207Pb/206Pb ages of 1866±4 Ma and 1862±2 Ma, which are interpreted as the times for magmatic crystallization and subsequent anatexis of mafic protolith, respectively. The latter is consistent with the time of partial melting determined from a migmatitic gneiss and a biotite-sillimanite gneiss at 1861±4 Ma and 1860±9 Ma, respectively. The leucosomes are transected by an undeformed pegmatitic dyke dated at 1852±3 Ma; by this time, extensional ductile shearing has ceased. Initial εHft values of zircon from the amphibolite range from 4.2 to 6.0, suggesting juvenile derivation of basaltic melt from the mantle. In contrast, lower εHft values (–0.1 to 3.5) in leucosome zircons indicate a mixing of crust-derived melt. Taken together, the Okbang amphibolite has experienced synkinematic fluid-present melting during the waning stage of Paleoproterozoic hot orogenesis prevalent in the Yeongnam Massif as well as the North China Craton.

The Patterson Lake corridor of Saskatchewan, Canada: defining crystalline rocks in a deep-seated structure that hosts a giant, high-grade Proterozoic unconformity uranium system

2020 ◽  
pp. geochem2020-007
Author(s):  
Colin D. Card
Keyword(s):  
Large Scale ◽  
Shear Zones ◽  
Crystalline Rocks ◽  
Ductile Deformation ◽  
Uranium Deposits ◽  
Content Type ◽  
Athabasca Basin ◽  
Rock Types ◽  
Host Rocks ◽  
Basin Region

The Patterson Lake corridor in the Athabasca Basin region of Saskatchewan, Canada hosts a large-scale uranium system with two major deposits already delineated. The corridor developed in crystalline rocks of the southwest Rae Province, which host all of the known uranium endowment. Orthogneisses along with voluminous pegmatites are the hosts of the uranium mineralization. These rocks, however, underwent significant open-system metasomatic – hydrothermal modification. Principal amongst these alterations is early and pervasive quartz flooding of the host rocks that resulted in the development of widespread secondary quartzites and associated rock types. These secondary quartzites and their altered host rocks suffered ductile deformation, typically focussed at silicification fronts. Late carbonatite dykes exploited the associated shear zones. Semi-brittle deformation zones nucleated near the previously developed ductile high-strain zones. Graphite and associated iron-sulphides precipitated in a semi-brittle structural regime. These graphitized zones provided the necessary structural architecture to focus the uranium system, which developed may be hundreds of millions of years younger developing at ∼1.425 Ga.Host rocks of the Patterson Lake corridor prove that metasedimentary rocks are not a requirement for development of giant Proterozoic unconformity uranium deposits. Crustal-scale fault zones with access to the mantle (i.e. carbonatites) should be considered a key parameter in the exploration model for Proterozoic unconformity uranium deposits. Given the similarity of the mineral assemblages in the crystalline basement rocks of the main exploration corridor to eastern Athabasca Basin region, it is likely that a similar, cryptic geological boundary focussed the giant uranium system in that region.Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

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