Unconformity Associated Uranium Deposits
by C.W. Jefferson, D.J. Thomas, S.S. Gandhi, P. Ramaekers, G. Delaney, D. Brisbin, C. Cutts, D. Quirts, P. Portella, and R.A. Olson

Contents of this page:

Abstract
Introduction
Definition
Grade, Tonnage and Value Statistics
Geological Attributes
Key Exploration Criteria
Genetic And Exploration Models
Knowledge Gaps
Acknowledgements
References
Tables
Appendix
Figures

Abstract

This review of the geology, geophysics, and origin of the unconformity-associated uranium deposit type is focused on the Athabasca Basin. Pods, veins, and semimassive replacements of uraninite (var. pitchblende) are located close to unconformities between late Paleo- to Mesoproterozoic conglomeratic sandstone basins and metamorphosed basement rocks. The thin, overall flat-lying, and apparently unmetamorphosed but pervasively altered, mainly fluvial strata include red to pale tan quartzose conglomerate, sandstone, and mudstone. Beneath the basal unconformity, red hematitic and bleached clay-altered regolith grades down through chloritic altered to fresh basement gneiss. The highly metamorphosed interleaved Archean to Paleoproterozoic granitoid and supracrustal basement gneiss includes graphitic metapelitic that preferentially hosts reactivated shear zones and many deposits. A broad variety of deposit shapes, sizes and compositions ranges from monometallic and generally basement-hosted veins to polymetallic lenses located just above or straddling the unconformity, with variable Ni, Co, As, Pb and traces of Au, Pt, Cu, REEs, and Fe.

Figure 1: Paleo- to Mesoproterozoic basins within the Canadian Shield that contain unconformity-associated uranium deposits (e.g. Athabasca and Thelon) or are considered to have potential for them. Figure 4a: Geological setting and unconformity-associated uranium occurrences (numbered as in the Appendix) of the Athabasca Basin region in northern Saskatchewan and Alberta, where Rae and Hearne are termed ‘Province’ rather than Subprovince (see Fig. 2). Symbols and fonts are slightly larger for more significant occurrences. Basement geology is after Portella and Annesley (2000a), Thomas et al. (2002) Card et al. (2003, 2007a, b), and Card (2006). Athabasca Basin geology and stratigraphic units (Table 3) are from Ramaekers et al. (2007). C = Carswell, D = Douglas, FP = Fair Point, LL = Locker Lake, LZ = Lazenby Lake, MF = Manitou Falls (members: b = Bird (l = lower, u = upper) c = Collins, d = Dunlop, r = Raibl (up = upper pebbly), w = Warnes (up = upper pebbly)), O = Otherside, RD = Read, S = Smart, W = Wolverine Point, d = diabase. Members of LZ, LL, and O are indicated by lines and labels but only one shade is used per formation. The western Wollaston Domain and the Wollaston ? Mudjatik transition of Portella and Annesley (2000a,b) are combined here as “Wollaston-Mudjatik transition zone”. CIS = Carswell Structure. Generalized fault zones after Ramaekers (2004) include multiple ductile movements before deposition of Athabasca Group and brittle transcurrent and dip-slip movements during and after deposition; they are named as: A = Allan, BB = Black Bay, BL = Black Lake, BR = Beatty River, BU = Bustard, CB = Cable Bay, CH = Charlot, CHB = Charbonneau, CL = Charles Lake, CT = Clut, D = Dufferin, ER = East Rim, F = Fidler, FN = Fowler?Net Lake, GR = Grease River, H = Harrison, HT = Hudsonian thrusts (general trajectory), LL = Leland Lakes, MAY = Maybelle, NF = Needle Falls, PL = Parker Lake, P2 = P2 fault at McArthur River, R = Richardson, RI = Riou, RL = Reilly Lake, RO = Robillard, RON = Robillard north, ROS = Robillard south, SL = St. Louis, T = Tabbernor, VR = Virgin River array (Dufferin is one named fault of many in VR), Y = Yaworski, YH = Yatsore-Hill Island. Arrays of faults with similar orientation and offset are indicated by colour groups. A. Simplified bedrock geology. Cross-sections of Figue 5A and B are located along dotted lines labelled NW - SE (along the basin axis) and E - W (south of Key Lake). B. Outlines of stratigraphic units of the Athabasca Group (black), basement domains (white outlines) and major reactivated fault systems (heavy coloured lines) on total magnetic field (Geological Survey of Canada, 1987; Pilkington, 1989). Faults are after Portella and Annesley (2000a), Ramaekers (2004), Card et al. (2007a), and Thomas and McHardy (2007). Many late faults have limited offsets that cannot be shown at this scale (see Card, 2007). Figure 9c: Examples of three end-point shapes and positions of unconformity-associated uranium deposits, after Thomas et al. (2000) and Andrade (2002) located in the southeastern part of Athabasca Basin (Fig. 4). (A) Cigar Lake (underground, production expected to start about August 2007) is dominantly unconformity ore with minor basement-hosted lenses and perched ore in the overlying Manitou Falls Formation. B) Deilmann (open pit, mined out) at Key Lake included both basement-hosted and unconformity ore. C) Eagle Point is mostly basement hosted (originally mined by open pit and underground; hanging wall lenses still being developed and mined underground (LeMaitre and Belyk, oral presentation 2005). Vertical scale = horizontal scale in (B) and (C). カナダ地質調査所（Geological Survey of Canada）による『Mineral Deposits of Canada　Maps of deposits and resources（world）』から