Qualified comments: |
(Applies to: discovery and development) The Cigar Lake deposit was discovred in 1981 by Cogema Resources Inc., now AREVA Resources Canada Inc., the operator of the Waterbury Lake Joint Venture. The discovery drill hole was no. 15 in a reconnaissance program of drilling to test anomalies defined by airborne and ground electromagnetic surveys. The ore intersection was at 440 m depth. The deposit was outlined over subsequent years by more than 220 surface diamond dril holes totalling 92 km of drilling. It is 200 m long, 20 to 100 m wide and up to 20 m thick. Its depth is between 410 to 450 m. The higher grade eastern part was discovered in 1983, and was outlined by drill holes 20 m apart along fences spaced at 50 m intervals. Some infill drilling has been done at closer spacing of fences at 25 m and holes at 10 m spacing. The western part of the deposit has been drilled along fences 200 m apart and holes 20 m apart along them. Development of the deposit included a test mining phase during 1987 to 2000. During 2001 to 2004 the project was on care and maintenance. At the beginning of 2002 Cameco Corporation became the operator of the project. The current owners are Cameco, Cogema, Idemitsu and Tepco, with 50, 37, 8 and 5 % interest, respectively. Construction of the production mine commenced in 2005. It is slowed by some flooding. Mining methods selected are boxhole boring and jet drilling of prefrozen orebody.
(Applies to: reserve/resource descriptions) Resources for the East + West zones in 1993: 148000 t U in 1.888 Mt ore averaging 7.84 % U; revised for East zone: recoverable 89076 t U in 0.577 Mt ore grading 15.44 % U, hence it will be mined first. The West zone has approximately 50000 t U in 0.435 Mt ore grading 11.5 % U; it includes 45620 t U in 0.318 Mt grading 14.35 % U; total of West and East zones: 134696 t U in 0.895 Mt grading 15.05 % U.
(Applies to: regional stratigraphy) Country rocks in the vicinity of the Cigar Lake Deposit include Paleoproterozoic rocks of the Lower Wollaston Supergroup, reactivated Archean granitoid gneisses, and unconformably overlying Late Paleoproterozoic-Mesoproterozoic sandstones and conglomerates of the Athabasca Group. An altered regolith marks the unconformity. The Lower Wollaston Supergroup below the unconformity is amphibolite to granulite in metamorphic grade, and includes the metamorphosed pelitic and semi-pelitic equivalents of shale and siltstone with graphitic horizons, and quartzite and meta-arkose with minor calc-silicate and metapelite. The Athabasca Group is represented by three members of the Manitou Falls Formation, the Read Formation which is present in other areas of the basin being absent. The Bird River Member, which rests directly on the regolith, contains conglomerate and sandstone with relict heavy mineral laminae and maroon-coloured late diagenetic to hydrothermal hematite. The Collins Member consists of clean, medium to course-grained sandstone with rare, thin, granule beds. The Dunlop Member is a fine-grained, well-sorted sandstone with abundant clay intraclasts. The rocks were intrudes (after mineralization) by the Mackenzie diabase dyke swarm. Extensive Quaternary till forms fields of southwest-trending drumlins across the area.
(Applies to: regional structure) The Cigar Lake deposit area was affected by the regional east-striking Cigar Lake Structural Zone, a reverse dextral proto-mylonite zone with unknown vertical displacement that is concordant with the steeply south-dipping basement units of the Wollaston Supergroup. This shear zone shows evidence of pre- and post-Athabasca Group displacement. Post-Athabasca Group faults include east-west steeply dipping normal with minor reverse faults, and low-angle, east-west reverse faults, as well as very late fractures. The basement horst upon which the main orebody is draped is located where the Cigar Lake structural zone cuts the unconformity.
(Applies to: property geology) The Cigar Lake deposit is draped over an east-west-trending ridge or horst, along the dextral Cigar Lake Fault, at the unconformity between the continental (fluviatile) Athabasca Group and the basement Paleoproterozoic Wollaston Supergroup. The basement paragneiss units comprise steeply south-dipping pelitic to psammitic gneiss, graphitic pelite, calc-silicate gneiss and meta-arkose. A funnel-shaped zone of hydrothermal chloritic and argillic alteration beneath the deposit is over 200 m wide at the unconformity and extends as much as 100 metres below the deposit. The regolith at the unconformity is about 40 m thick, consisting of an oxidized red zone grading down through a reduced green zone characterized by chlorite, sericite, and clay, to fresh basement. The regolith is strongly overprinted by hydrothermal alteration beneath the ore. The Bird Member of the Manitou Falls Formation, resting directly on the regolith, comprises trough-cross bedded quartz arenite and quartz pebble conglomerate with heavy mineral bands, and siltstone; it is gradationally overlain by the arenaceous Collins Member.
(Applies to: mineralization) The bulk of the ore forms three east-trending elongate horizontal zones with an irregular upward-convex lens-shaped cross-sections, aggregating 2150 metres long, ranging from 25-105 metres wide, and up to 40 metres thick resting on the basement high in the unconformity assemblage. Mineralization and alteration are interpreted as a result of multiphase hydrothermal processes. The first, predominant phase involved deposition of uraninite and coffinite at 1461 +/- 47 Ma followed by arsenide, sulphide and sulph-arsenide minerals. Pitchblende (sooty uraninite) and associated copper sulphate minerals were deposit during the second phase, followed by phase-three uranium silicate, oxide and hydroxide minerals. Minor ore is located in cross-cutting veins below and above, and in perched lenses in sandstone above the unconformity orebody, along steeply dipping faults. The perched mineralization is thought to represent very late-stage remobilization of the unconformity ore.
(Applies to: alteration) The Manitou Falls Formation is overprinted by a concentric domed alteration halo above the deposit. Volume loss equivalent to about 30 million tonnes of rock is associated with faulting and collapse due to dissolution of quartz and other minerals, including zircon, from the lowest 50 m of the section, leaving only residual clay. The deposit is mantled by an illite-chlorite clay cap including intense deep red hydrothermal hematite, surrounded in outward succession by extremely clay-altered sandstone, grey-coloured bleached sandstone, a zone of quartz crystals - iron sulphide - hydrocarbonaceous material (quartz precipitation marks the outer limit of quartz dissolution), and an outer zone of grey, bleached sandstone extending up to 300 metres above the deposit. This grades into the background regional sandstone - typically pink to pale red with patches and liesegang bands of hematite cement.
(Applies to: geophysical surveys) Aeromagnetic data 'see through' the Athabasca Group cover and map basement supracrustal units as lows, with granitoid rocks as highs. The graphitic metapelite in the Cigar Lake fault zone is one of many local to regional conductors within the aeromagnetic lows that can be mapped by airborne to ground electromagnetic methods. Audiomagnetotelluric methods can trace this conductivity more than a kilometre beneath the surface, and identify quartz dissolution zones by their lower resistivity. Seismic reflection can generate laterally continuous images of the unconformity and provides data for structural cross sections showing offsets of the P2 and other faults, with pseudo-3D data providing a topographic map of the unconformity surface, documenting the location of ore zones at fault intersections. The ore bodies are dense but too small to generate gravity anomalies that can be measured at surface, however the large quartz dissolution zone produces a gravity low, and the different basement rock units have different densities that can be modeled. Borehole geophysics provides bulk geophysical rock parameters that allow calibration of geological properties to geophysical properties. |
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