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Athabasca Basin - Roughrider, Midwest Northeast |
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Saskatchewan, Canada |
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U
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Roughrider uranium deposit is located in the Athabasca Basin of northern Saskatchewan, Canada, 8.5 km north of the Points North community and 25 km northwest and west respectively from the Rabbit Lake and McClean Lake deposits.
The saucer-shaped, east-west elongated, Athabasca Basin, which covers an area in excess of 85 000 square kilometres in northern Saskatchewan and north-eastern Alberta, contains the relatively undeformed and unmetamorphosed Mesoproterozoic clastic sequence of the Athabasca Group. These rocks unconformably overlie the deformed and metamorphosed rocks of the Western Churchill Province of the Archaean Canadian Shield. The basement rocks comprise Archaean orthogneisses, overlain by, and structurally intercalated with, the highly deformed supracrustal Palaeoproterozoic Wollaston Group. The Athabasca Basin straddles the boundary between two subdivisions of the Western Churchill Province, namely the Rae and Hearne subprovinces to the west and east respectively. These subprovinces are separated by the northeast trending Snowbird Tectonic Zone, which is called the Virgin River-Black Lake shear zone in the area of the Athabasca Basin. In the vicinity of the Roughrider deposit, in the eastern Athabasca Basin, the basement rocks of the Hearne Subprovince are subdivided into a number of domains, some of which are more favourable to the occurrence of uranium mineralisation than others. The Hearne Craton beneath the eastern Athabasca Basin comprises variably reworked Archaean basement, dominated by granitic domes and foliated to gneissic granitoid rocks with infolded outliers of Palaeoproterozoic metasedimentary rocks. The structural and tectonic regime of the area has been strongly influenced by the 1.9 to 1.77 Ga Palaeoproterozoic compressional Trans-Hudson Orogen separating the Hearne and Superior cratons. Prior to deposition of the Athabasca Group, rocks of the Rae and Hearne provinces that were to form the basement to to that sequence, experienced a lengthy period of weathering and non-deposition, and as a consequence, the basal Athabasca stratigraphy is underlain by a regolith of deeply weathered, hematite-stained basement, with the mineralogical and chemical characteristics of a laterite. In places, the preserved palaeoregolith can reach a thickness of 50 m deep, typically ranging from approximately 5 to 10 m. Regionally, the unconformity surface is relatively flat except where disrupted by post-Athabasca reverse faulting, or where local palaeotopography has been identified.
The unconformably overlying Palaeo- to Mesoproterozoic Athabasca Group mainly comprises up to ~1400 m of fluvial clastic sedimentary rocks central part of the basin, divided into eight formations in which four broadly fining-upward, unconformity-bound cycles can be distinguished. The overall, sedimentary provenance was from the east, south, and northwest. Lithologies are dominantly fine- to coarse-grained, partly pebbly or clay-intraclast-bearing quartz arenites. Minor conglomerates, mudstones, and dolostones also occur. Apart from faulting and local folding associated with thrusting, the strata are undeformed and unmetamorphosed. Age dating of zircons and diagenetic fluorapatite indicate an age of sedimentary deposition around 1.77 Ga, post-dating the Trans-Hudson Orogeny. In the eastern Athabasca Basin, the Manitou Falls is the only formation recognised, subdivided into four units, from bottom to top, designated MFa to MFd. These are dominantly fluvial sandstones with some interbedded conglomerates.
In the region surrounding the Roughrider deposit, the Hearne Subprovince has been sub-divided into four lithostructural domains from east to west, namely: (i) the Eastern Wollaston Domain ("EWD"); (ii) Western Wollaston Domain ("WWD"); (iii) Wollaston-Mudjatik Transition Zone ("WMTZ"), and; (iv) Mudjatik Domain ("MD"). The basement rocks in the vicinity of the deposit are part of the WMTZ. The majority of the uranium occurrences and all currently producing uranium mines in the region are hosted in rocks of the WWD and WMTZ. Certain lithologies, coupled with the deformational history of some domains, have had a strong influence on the location of the Athabasca unconformity-type uranium deposits.
The MD, in the west, is distinguished from the adjacent linear northeast trending belts of the WWD by having an arcuate pattern due to regional dome-and-basin fold interference structural pattern attributed to more intense Trans-Hudson Orogen transpressive tectonics. As a consequence it is more deeply eroded, with relatively limited preserved Paleoproterozoic supracrustal rocks. The eastern boundary with the WWD is arbitrarily drawn along the transition to mainly northeast-trending structures. The MD is dominated by variably migmatitic 3.6 to 2.92 Ga Archaean orthogneisses, although it also includes minor infolded supracrustal outliers of the Wollaston Supergroup. Pelitic to psammitic supracrustal rocks and mafic granulites, minor quartzites, calc-silicates, marbles and ultramafic rocks, as well as rare oxide, silicate and sulphide facies iron formations occur in narrow arcuate bands throughout, defining the dome-and-basin pattern. In the east, most of these supracrustal remnants have been correlated with the Wollaston Supergroup. Metamorphic grades range from upper amphibolite to granulite facies. In the surrounding district, away from the Roughrider uranium deposit, the reddish to greenish palaeoweathering profile immediately below the sub-Athabasca unconformity is variably developed, but typically extends to a depth of 10 to 35 m. It comprises a thin (less than 1 m thick) zone of bleached rock that is typically illitic to kaolinitic in composition, immediately overlying a zone of variably developed 'red-zone' hematite alteration, separated from the lowermost chlorite-altered 'green alteration zone', by a transitional 'red-green zone', a combination of hematite and chlorite alteration. Within the Roughrider deposit, the palaeoweathered regolith is overprinted and obliterated by hydrothermal alteration, although in some cases, a ghost clay signature of the kaolinitic zone is still evident.
The Roughrider deposit area is underlain by 195 to 215 m of sandstone belonging to the Manitou Falls Collins Member (MFc - 70 to 100 m thickness of fine-grained, homogeneous, beige to maroon sandstone) and Bird Member (MFb - 100 to 130 m of heterogeneous sandstones, pebbly sandstones and conglomerates) of the Athabasca Group. The Read Formation (MFa) is missing. The conglomerates pf the MFb include a distinctive "Marker Conglomerate" that can be correlated regionally. The basal conglomerate is not ubiquitous throughout the district, and in places it may be absent immediately overlying the Roughrider deposit. Typically the unconformity ~196 to 221 m below the surface.
The Athabasca Basin and surrounding areas were strongly affected by Quaternary glaciation, with the northern half of Saskatchewan being deeply scoured by the southwesterly moving Pleistocene Laurentide ice sheet. Glacial erosion of the less resistant Athabasca Basin sandstones resulted in an increased sediment load in the ice, and glacial drift cover being much more extensive and thicker over the basin than the rest of the shield region. The surficial geology within the deposit area is characterised by portions of two low drumlins trending in a north-easterly direction, with overburden depths of between 9 and 12 m.
The Roughrider Uranium Deposit overlies the Wollaston-Mudjatik Transition Zone ("WMTZ") of the Wollaston Domain. The basement is structurally complex, comprising steeply dipping Wollaston Group rocks interfingered with Archaean granitic to granodioritic orthogneisses. Aeromagnetic data suggest that several Archaean granitic domes dominate the basement geology. Several basement packages are recognised in the vicinity of the Roughrider deposit, including the:
Wollaston Group - the Roughrider deposit is located in the basal part of this group, where it is dominated by garnet- and cordierite-bearing pelitic gneisses with subordinate amounts of graphitic pelitic gneisses and psammopelitic to psammitic gneisses, and rare garnetites. The pelitic gneiss varies from equigranular to porphyroblastic in texture, with porphyroblasts varying in size up to cm-scale and normally comprise red almandine-rich garnets. Variations in size and concentration of garnets allows the identification of several units that are termed the "Garnet Marker Gneiss", with micro-folding evident in variably developed foliation. The very high abundance of garnet within the gneissic rock package reflects the highly aluminous nature of the precursor sediments. These gneisses have been intruded by syn- to post-peak metamorphic felsic pegmatites, granites, and microgranites of Hudsonian age, locally containing up to 400 ppm of primary uranium. Proximal to mineralisation, graphite in graphitic pelitic gneisses has been consumed by alteration and mineralisation, although distal to mineralisation, the graphite appears to be discontinuous.
Hanging Wall Wedge ("HWW") and Foot Wall Wedge ("FWW") - both of which are complex packages comprising variable amounts of granitic to tonalitic orthogneiss that was subjected to local anatexis. The gneisses were intruded by younger pegmatites, leucogranites and microgranites. The FWW is only locally present and has been interpreted to plunge to the west and does not extend from the Roughrider West Zone eastward to the Roughrider East Zone. It is possible that several FWWs are present, representing slivers of either the MWD or the FWW that been carved off during deformation.
Midwest Dome ("MWD") - which comprises strongly foliated orthogneisses that range in composition from granitic to dioritic, with volumetrically minor amounts of partially melted material, and younger 'Hudsonian' pegmatites, leucogranites and microgranites. Local hydrothermal calc-silicate alteration of the orthogneisses is interpreted to be post-peak metamorphism and is probably related to the introduction of the Hudsonian felsic rocks.
The Athabasca sandstones and basement rocks have been subjected to several episodes of brittle deformation, including the brittle reactivation of older ductile shear zones.
Macro-scale geophysical, geological and structural modelling indicated the depsoit area is cut by a large number of structures. The two principal structures are: (1) the east-west trending Roughrider Corridor, which hosts the Roughrider West Zone, and (2) the northern extension of the NNE-SSW trending Midwest Trend, that hosts the Midwest and Midwest A Deposits immediately to the south of the deposit area. The Roughrider West Zone is centered on the Roughrider Structure, while the Roughrider East Zone is centred at or near the intersection of the Midwest Trend and Roughrider Corridor.
The Roughrider uranium deposit comprises three zones, the Roughrider West, East and Far East Zones. All three zones are basically similar, although each has subtle differences.
The Roughrider West Zone was discovered in a drill hole that intersected a hydrothermal clay alteration system with high-grade uranium mineralisation (11.9 m @ 5.29% U3O8). The Roughrider East Zone was discovered as a 28.0 m @ 12.71% U3O8 intersection, with the best interval in subsequent drilling of 63.5 m @ 7.75% U3O8. The Roughrider Far East Zone, was initially cut by 37.5 m @ 1.57% U3O8, with the best subsequent drill hole encountering 42.8 m @ 3.26% U3O8 (Keller and Bernier, SRK Consulting, 2011).
The Roughrider East Zone has a surface projection of approximately 120 m in length in a north-easterly direction, corresponding to a down-dip length of approximately 125 m, and an across-strike width of up to 70 m. Uranium mineralisation has a vertical extent of as much as 80 to 100 m, starting at a depth of approximately 250 m from surface, and some 30 to 50 m below the unconformity, which is slightly deeper than the Roughrider West Zone. The Roughrider East Zone is located within the same east-west deformation corridor, the Roughrider Corridor, as the Roughrider West and Far East Zones.
Resistivity and structural modelling indicate that the Roughrider East Zone is centred at or near the intersection of the Midwest Trend and the Roughrider Corridor. Mineralisation forms moderately dipping, cigar-shaped shoots along the intersection of these two controlling structures. Uranium mineralisation at the Roughrider East Zone is exclusively hosted within basement rocks, and has been intersected within altered rocks of both the Wollaston Group and in syn- to post-tectonic Hudsonian igneous rocks, including the overlying HWW and is developed above the Midwest Dome of Archaean granitic gneiss. Uranium mineralisation is hosted in a corridor or wedge of Wollaston Group rocks, sandwiched between and extending into the MWD to the southeast and the HWW on the northwest. Mineralisation has not been intersected in the Athabasca sandstone. The uranium mineralisation at the Roughrider East Zone occurs as a series of stacked, parallel lenses (defined at a cut-off of greater than 0.5% U3O8) that collectively dip and plunge moderately to the north-east. The lenses are separated by intervals of weakly mineralised or barren rock (less than 0.5% U3O8). The contacts between these mineral lenses are sharp. Unlike the Roughrider West Zone, the lenses are not uniformly mantled by an extensive rim of low grade mineralisation. Uranium mineralisation is highly variable in thickness and style. High grade mineralisation occurs primarily as medium- to coarse-grained, semi-massive to massive pitchblende with what has been termed worm-rock texture, and texturally complex redox-controlled mineralisation. This high grade mineralisation is intimately associated locally with lesser amounts of red to orange coloured oxyhydroxillised iron oxides. Yellow secondary uranium minerals, probably uranophane, are present locally as veinlets or void-filling masses within the high grade primary mineralisation. Lower grade mineralisation occurs as either disseminated grains of pitchblende, fracture-lining, or veins of pitchblende. Veinlets of galena up to 5 mm thick, possibly formed from the radioactive decay of uranium, occurs in a number of habits and is variably present in the uranium mineralisation. These veinlets either crosscut massive pitchblende as anhedral masses (less than one millimetre in size), interstitial to the massive pitchblende, or as fine-grained, sub-millimetre-scale disseminated flecks of galena present throughout the mineralised zone. Unlike many unconformity-type uranium deposits in the Athabasca Basin, variable amounts of copper mineralisation are present within the Roughrider East Zone, although the copper appears to be paragenetically younger than the primary uranium mineralisation.
Strong alteration has been recognised in both the Athabasca sandstone and in the highly deformed basement rocks. Within the overlying Athabasca Group this includes intense bleaching, limonitisation, desilicification and silicification, hydrothermal hematisation, and illitic argillisation. None of the primary hematite in the sandstone is preserved within the zone of bleaching and alteration. In the Athabasca sandstone distal from the Roughrider deposits, the dominant background clay species is the regional dickite assemblage, in contrast to the illite of the Roughrider East Zone, which is less intense that that observed at the Roughrider West Zone. In basement rocks, alteration extends to at least 180 m below the unconformity and up to 115 m laterally away from the known mineralisation. It varies in strength, ranging from weak to intense where massive clay has completely replaced the protolith. Clay alteration is predominantly white to pale green in colour and illitic in nature, and extends downward into the Archaean rocks. Chlorite alteration is variable in concentration and location with respect to high grade uranium mineralisation, while hematite alteration within the basement rocks is spatially restricted in distribution and is commonly associated with high-grade mineralisation. The hematite is locally variably altered to a limonitic iron oxide. Silicification is rare.
At November 29, 2010, resources (Hathor Exploration Ltd website after SRK Consulting) were:
Total Indicated - 0.3942 Mt @ 1.98% U3O8, 0.03% As, 0.06% Cu, 0.03% Mo, 0.02% Ni, for 6970 t U3O8, plus
Inferred - 0.0436 Mt @ 11.03% U3O8, 0.58% As, 0.08% Co, 0.48% Cu, 0.22% Mo, 0.47% Ni, for 4240 t U3O8.
This description summarises and paraphrases sections of Keller and Bernier, SRK Consulting, 2011
The most recent source geological information used to prepare this decription was dated: 2011.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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