Athabasca Basin - Cluff Lake, Claude, Dominique-Peter, Dominique-Janine
Super Porphyry Cu and Au|
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The Cluff Lake unconformity-style uranium deposits are located in the western section of the Athabasca Basin, some NNW of Saskatoon, 80 km south of Lake Athabasca in north-western Saskatchewan, 25 km east of the Alberta border, in Canada. The Cluff Lake operation comprised a number of orebodies within a district, including the D, N and OP Zones, and the Claude, Dominique-Peter, Dominique-Janine North, and D-J South and West mines (#Location: 58° 21' 52"N 109° 31' 01"W).
The Cluff Lake deposits are located at the southern edge of the Carswell structure, a circular, 18 km diameter window through the sedimentary Athabasca Formation into the underlying metamorphic basement complex. The Carswell structure is generally interpreted to be due to a pre-Athabasca Basin meteorite impact. Shock metamorphic features, including shatter cones, pseudotachylite and suevite, are only observed in the basement, which basically consists of granitic gneisses, meta-pelites and pegmatoids which all represent retrograde metamorphism of granulite facies rocks, but are absent from the overlying Athabasca sandstones.
The core of the structure is an exposed basement high surrounded by a reduced thickness of the Athabasca Basin sequence. The exposed basement represents the central peak of a 39 km wide complex impact structure. The remainder of the impact structure comprises a surrounding annular trough beneath, and filled by the Athabasca Basin sequence. This basement peak was more or less located beneath and surrounded by a stromatolitic reefal unit which encircles the exposed basement. Palaeogeographic features, palaeocurrents and isopach maps throughout the 100 000 sq. km Athabasca Basin suggest that the sedimentation of the Athabasca Group has been controlled by a broader bowl shaped basin asymmetrically centered on the Carswell structure.
The basement to the Western Athabasca Basin belongs the Rae Province of the western Canadian Shield. The rocks of the exposed core of the Carswell Structure are near the eastern margin of the Slave-Thelon Domain which constitutes the western half of Rae Province, which in turn is bounded to the west by the Thelon-Taltson Orogen and the approximately 1.85 Ga Taltson magmatic arc/anatectic batholith. The Slave-Thelon Domain is composed of 2.64 to 2.58 Ga Archean crust. The exposed rocks of this domain are represnted in the core of the Carswell Structure by granodioritic, quartzo-feldspathic and pelitic gneisses with minor mafic gneiss, iron formations and granitic pegmatites.
In detail, two major lithostructural units have been recognised in the basement core of the Carswell Structure, namely:
The Carswell Series which is found in the north-eastern part of the structure, comprising the Northern Aluminous gneiss and the Charnockitic Complex; and
The Cluff Lake Series which includes the aluminous Peter River gneisses and the underlying mixed feldspathic gneisses and mafic gneisses of the Earl River Complex and is localised in the south-western and west-northwestern part of the metamorphic core. Granitoids and pegmatoids are ubiquitous in both series and are largely the result of in situ anatexis of the metasedimentary rocks. These gneisses are interpreted to have been produced from protoliths representing a detrital succession of arkoses and greywackes at the base, forming the Earl River Complex, and shales at the top which makeup the Peter River gneisses.
These rocks have been subjected to polymetamorphic deformation, having undergone an early granulite facies event at ~2.6 Ga, preserved in mafic tonalitic gneisses and paragneisses and to a lesser extent in the heterogeneous felsic gneisses and mafic dykes. This phase was followed by successive upper to middle amphibolite facies at 2.3 to 2.0 Ga and greenschist facies retrograde modification at 1.85 Ga reflecting the widespread reworking of the Archaean craton by the ~1.85 Ga Hudsonian Orogeny.
To the east the Slave-Thelon Domain is bounded by the western edge of the 3.5 to 2.7 Ga Western Granulite/Clearwater Domain. This eastern edge if defined by the Virgin River-Black Lake shear zone, which is occupied by a zone of granulite facies mylonites, felsic to mafic gneisses, charnockites, anorthosites and gabbros, and by blastomylonitic gneisses. The Western Granulite Domain is composed of felsic to mafic gneisses and granulites (characterised by blue quartz), charnockites, anorthosites and gabbros. The Clearwater Domain comprises fine-grained, cumulative layered leuco-gabbronorite and anorthosite which are concordantly interlayered with units of mafic garnetiferous tonalitic gneisses and heterogeneous felsic gneisses. Orange-pink megacrystic granite and homogeneous medium grained light orange-pink leucogranite intrudes the gneisses.
Following the ~1.85 Ga Hudsonian Orogeny, the crystalline basement underwent a period of prolonged tropical erosion and lateritic weathering to produce a zero to more than 50 m thick regolith which was preserved by the fluviatile and marine sediments of the Athabasca Basin which was deposited between about 1.8 and 1.65 Ga.
The thickest and most completely preserved sections of the Athabasca Basin sequence are found in the western half of the basin where up to 1400 m of a succession estimated from diagenetic studies to have originally been more than 4000 m thick remains. Sedimentation was generally from east to west across the basin. The rocks of the basin are unmetamorphosed, flat lying and generally undisturbed. The sequence within the Athabasca Basin can be summarised as follows from the basal unconformity with the early Paleoproterozoic to Archaean basement:
Fair Point Formation a marine shoreface formation composed of pebbly to cobbly sandstone to conglomerate, quartz-lithic sandstones, commonly with abundant clay matrix, that is only found between the Carswell Structure and the western margin of the basin.
Reilly Formation - a locally developed unit composed of conglomeratic quartz-arenite.
Read Formation - which is restricted to the eastern half of the basin, mainly to the east of the Snowbird Tectonic Zone, over the Hearne Province basement. This unit predominantly sits directly on basement and has been mapped as unit "b" of the Manitou Falls Formation where it is host to uranium mineralisation. It is composed of quartz-lithic pebble conglomerate interbedded with quartz-arenite, quartz-pebbly quartz-arenite and quartz-pebble conglomerate with common but local interclasts of red quartz siltstone to mudstone.
Smart Formation - which overlies the Read Formation or its lateral, thinner, distal equivalent to the west of the Snowbird Tectonic Zone, over the Rae Province basement. It is composed of quartzarenite with local red mudstone and oncoid interbeds at base. It either overlies basement rocks directly, or the Far Point Formation.
Manitou Falls Formation which has been variously sub-divided as follows, from the base,
Bird or Mfb Member - interbedded quartz-pebble conglomerate and quartz-pebbly quartz-arenite, with thin mudstone and siltstone interbeds;
Raibl Member - which is only found in a restricted to the northeastern section of the basin and comprises quartz-pebbly quartzarenite, minor clay intra-clasts and quartz-pebble conglomerate;
Warnes or Mfa Member - which interfingers with and underlies the Bird Member, overlying on the Reed Formation. It has been mapped the as unit "a" of the Manitou Falls Formation and comprises quartzarenite and clay-intraclast-rich quartzarenite;
Collins or Mfc Member - which directl;y overlies the Bird Formation in the eastern part of the basin, and has a gradational contact with the underlying Warnes Member further to the west. It is composed of quartzarenite with lesser quartz-pebbly beds, mudstone interbeds, and minor clay intraclasts and conglomerate interbeds;
Dunlop or Mfd Member - which is restricted to the eastern half of the basin, having pinched out to the east of the Carswell Structure. It rests on the Collins Member and comprises quartz-arenite with clay-intraclasts and mudstone interbeds;
Lazenby Lake Formation - a marine shoreface formation composed mostly of quartz-pebbly quartz-arenite with a basal conglomerate and rare siltstones and mudstones;
Wolverine Point Formation - a marine inner to open shelf deposit with an upper mainly siltstone and clay-rich quartz-arenite member and a lower unit of interbedded mudstone and tuffaceous quartz-arenite with thin conglomerate bands;
Locker Lake Formation - a marine shoreface deposit composed mainly of quartz-pebbly quartz-arenite, thin conglomerates and sparse mudstones. Another local unit, previously mapped above the Otherside Formation as the Tuma Lake Formation, has been shown to be an up-faulted block of Locker Lake Formation;
Otherside Formation - a marine inner shelf deposit is composed of quartz-pebbly quartzarenite and quartzarenite with minor thin interbeds of dark mudstone near the top;
Douglas Formation - which has been largely eroded from the majority of the basin is only found surrounding the Carswell Structure where it is composed of black organic-rich, red and green mudstones, siltstones and interbeds of fine to very fine quartzarenite representing a marine shelf environment; and
Carswell Formation - which like the Douglas Formation is only preserved around the Carswell Structure amd comprises a stromatolitic and oolitic dolomite, dololutite, dolorudite, stromatolite, oolite, dolarenite deposited in a marine carbonate bank environment.
The rocks of the Athabasca Group are intruded by 1.3 to 1.2 Ga dolerite to gabbro dykes and sills.
The Cluff Lake deposits are clustered near the southern margin of the basement core of the Carswell Structure, close to, above and below the unconformable contact with the overlying Athabasca Basin sediments. All except the D Zone deposit are hosted by quartzo-feldspathic, pyritic and graphitic pelitic gneisses and interdigitated garnetiferous granitic pegmatites. The D Zone is instead hosted by altered conglomerate, sandstone and of the basal sections of the Manitou Falls Formation.
The main features of the mineralisation is that in all of the deposits it is close to the basal unconformity between the crystalline basement and the ovelying Athabasca Basin sediments and is structurally controlled, commonly within clay rich shear zones.
The wall rock alteration is characterised by dark green, iron rich chlorite, red-brown hematite and pale green to white, magnesian chlorite, as well as argillic alteration. Some deposits also exhibit silicification and weak tourmalinisation. Adjacent to mineralisation the lateration is intense in halos that extend outwards from a few cms to several tens of metres, and are most intende when overprinting the regolith immediately below the unconformity with the pre-Athabasca crystalline basement.
The principal ore mineral is uraninite with lesser coffinite, with accessory hematite, pyrite, pyrrhotite, marcasite, chalcopyrite, galena, clausthalite, molybdenite, jordisite, native gold, gold tellurides, sphalerite, native selenium, PB-Bi-Co selenides and Ni or Ni-Co arsenides, altaite and carbonaceous material.
Published deposit size figures of the now mined out deposits include:
Cluff Lake D zone - 0.11076 Mt @ 4.874% U3O8, for 5245 t U3O8
Cluff Lake N zone - 0.505 Mt @ 0.40% U3O8, for 2039 t U3O8
Claude - 0.640 Mt @ 0.433% U3O8, for 2770 t U3O8
Cluff Lake OP zone - 0.0255 Mt @ 0.501% U3O8, for 127 t U3O8
Dominique-Peter - 0.8681 Mt @ 0.759% U3O8, for 6593 t U3O8
Dominique-Janine: North mine - 0.230 Mt @ 0.45% U3O8, for 1030 t U3O8
D-J South and West mines - 0.950 Mt @ 0.68% U3O8, for 6498 t U
Total: Cluff Lake deposits - 3.3262 Mt @ 0.73% U, 24 302 t U
The most recent source geological information used to prepare this summary was dated: 2005.
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.
Leventhal J S, Grauch R I, Threlkeld, Lichte F E 1987 - Unusual organic matter associated with Uranium from the Claude deposit, Cluff Lake, Canada: in Econ. Geol. v82 pp 1169-1176|
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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.
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