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Athabasca Basin - McArthur River |
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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 McArthur River unconformity-type uranium deposit is located near the town of McArthur River in the Athabasca Basin, central Saskatchewan, Canada and is situated in the vicinity of the unconformity between the sediments of the late Paleo- to Mesoproterozoic Athabasca Basin and an Archaean to early Paleoproterozoic basement.
The northeast-trending Snowbird tectonic zone separates the basement into two distinct provinces, the Rae province to the west and the Hearne province to the east. Both consist of Archaean gneisses, Paleoproterozoic platform metasedimentary rocks and mafic to felsic plutons, although the Hearne province underwent extensive thermo-tectonic reworking during the 1860 to 1720 Ma Trans-Hudson orogeny.
The majority of the known unconformity-type uranium deposits are found in the eastern part of the Athabasca Basin, in the vicinity of the graphite-rich Cable Bay shear zone that occurs between the Mudjatik (western) and the Wollaston (eastern) domains of the Hearne province. The Athabasca Basin is made up of a series of NE-SW oriented sub-basins controlled by major Hudsonian faults in the basement rocks which were reactivated after the filling of the Athabasca Basin and continued to be active until recent times. This late Palaeo- to Mesoproterozoic basin, was filled with sediments between 1750 and 1700 Ma, comprising fluvial to shallow marine quartz-rich sandstone of the Fair Point and Manitou Falls Formations, which were deposited in a near-shore, shallow shelf environment. They were overlain by marine sandstones, phosphatic siltstones and phosphatic mudstones of the Lazenby Lake and Wolverine Point Formations, which in turn were overlain by sandstones of the Locker Lake, Otherside, and Turma Lake Formations, and finally by shales of the Douglas Formation and stromatolitic carbonates of the Carswell Formation. The last two formations are only preserved around the Carswell structure, which is thought to have originated as a meteorite impact. Sedimentation within the basin is interpreted to have taken place during a number of transgressive-regressive cycles.
The basin was subsequently intruded by several northwest-trending 1227 ± 11 Ma mafic dykes, during post depositional tectonic activity.
The McArthur River deposit is located in the south-eastern part of the Athabasca Basin, close to the Cable Bay shear zone separating the Mudjatik and the Wollaston basement domains, where an approximately 500 m-thick section of the overlying Athabasca Sandstone is preserved. The sandstone comprises the four members of the Manitou Falls Formation, the basal section of which contains fanglomerates. The overlying sandstone was subjected by an early silicification that commonly preserved hematite between detrital grains and quartz overgrowths. Above the mineralisation, the sandstones are affected by a post-diagenetic, but pre-mineralisation pervasive silicification which is particularly well developed up to 150 m above the orebody and contains numerous drusy quartz veins.
The orebodies at McArthur River are structurally controlled by a graphite rich reverse fault set, and occur close to the intersection between a reverse fault zone and the unconformity between the Athabasca group and the basement. Ore is hosted within the overlying Proterozoic Athabasca Sandstone, within the shear and in the basement metamorphics.
The main fault of the reverse fault set is the P2 fault which strikes NE-SW at 45° and dips at 45° SE with a vertical displacement of 60 to 80 m. This fault superposed a block of basement to the NW over a wedge of Athabasca Sandstone, which is in turn underlain by basement. In addition to the reverse fault there are a series of steeply dipping ESE-WNW, 110° trending transcurrent faults cutting the area.
Four orebodies are known, three of which are located in the Athabasca Sandstone wedge in the footwall of the P2 Fault, while the fourth, the P2 orebody, is hosted in both the footwall meta-sediments and in the basal part of the Athabasca Sandstone and contains 50% of the reserve.
The basement lithologies comprise, from east to west:
i). biotite-quartz-garnet metapelitic gneisses of the hanging wall;
ii). a graphite-rich fault zone,
iii). garnet-and cordierite-rich ± graphitic pelitic gneisses with local fine-grained banded calcsilicates, pegmatites, and leucogranites of the footwall and
iv). feldspathic metaquartzite.
Uranium mineralisation in the P2 orebody is mainly found in cordierite-rich metapelites in the footwall of the P2 Fault, but extends upwards along the fault plane into the Athabasca Sandstone wedge between the basement and the P2 Fault, in the footwall of the overthrust basement wedge above the fault plane, to mushroom out over the upper edge of that hangingwall basement wedge. Brecciation is well developed within and around the orebodies, with most of the mineralisation occurring in chlorite-rich breccias which are commonly found as fragments in breccias cemented by drusy quartz and carbonate.
Widespread alteration halos surround the deposit, including intense silicification, Mg chlorite (sudoite), Mg tourmaline (dravite) and kaolinite which are attributed to syn- to post-mineralising hydrothermal events. The alteration in the basement sequence is characterised by illite, chlorite and dravite with local apatite and carbonate. Within the sandstone the alteration assemblage is mostly quartz, kaolinite, chlorite and dravite.
Massive uranium mineralisation is commonly cut by thin siderite veinlets that are attributed to late meteoric fluids. U-Pb geochronological studies of uranium minerals at McArthur River suggest several stages of uranium deposition and remobilisation, namely: i). The earliest recorded stage at around 1520 Ma represents the minimum age of initial crystallisation of uraninite at McArthur River, while ii). younger ages of 1327 ± 8 Ma, 1247 ± 88 Ma and 950 ± 27 Ma are believed to be recrystallisation ages.
As at December, 2000, the total proven + probable reserve at McArthur River was:
0.845 Mt @ 21.18% U3O8, containing 179 640 t U3O8.
In the same year the indicated resource was:
0.614 Mt @ 10.74% U3O8, containing 66 210 t U3O8.
As at December, 2005, the total proven + probable reserve at McArthur River was:
0.727 Mt @ 24.28% U3O8 with a metallurgical recovery of 99%, containing 177 200 t U3O8.
The most recent source geological information used to prepare this decription 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.
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Alexandre P, Kyser K, Polito P and Thomas D 2005 - Alteration Mineralogy and Stable Isotope Geochemistry of Paleoproterozoic Basement-Hosted Unconformity-Type Uranium Deposits in the Athabasca Basin, Canada: in Econ. Geol. v100 pp 1547-1563
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Derome D, Cathelineau M, Cuney M, Fabre C, Lhomme T and Banks D A, 2005 - Mixing of Sodic and Calcic Brines and Uranium Deposition at the McArthur River, Saskatchewan, Canada. A Raman and Laser-Induced Breakdown Spectroscopic Study of Fluid Inclusions : in Econ. Geol. v100 pp 1529-1545
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Ng R, Alexandre P and Kyser K, 2013 - Mineralogical and Geochemical Evolution of the Unconformity-Related McArthur River Zone 4 Orebody in the Athabasca Basin, Canada: Implications of a Silicified Zone : in Econ. Geol. v.108 pp. 1657-1689
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Richard, A., Cathelineau, M., Boiron, M.C., Mercadier, J., Banks, D.A. and Cuney, M., 2016 - Metal-rich fluid inclusions provide new insights into unconformity-related U deposits (Athabasca Basin and Basement, Canada): in Mineralium Deposita v.51 pp. 249-270
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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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