Structural Setting of the Sue C Uranium Deposit, McClean Lake Mine, Northern Saskatchewan 1 1 I Ghis/ain Tourigny, Steve Wilson , Guy Breton , and Philippe Portel/a Tourigny, G .. Wilson. S., Breton, G .. and Portclla, I'. (2000): Structural setting of the Sue C uranium dcposit. McClcan Lake mi_ne. no~hern Saskatchewan ; in Summary of Investigations 2000. Volume 2. Saskatchewan Gcological Survey. Sask. Energy Mmes. Misc. Rep. 2000-4.2. Abstract localized normal displacemenl. Uranium mineralization is essentially located within the The Sue C deposit is a structurally controlled, prominent thrust fault system and appears comrolled basement-hosted, high-grade uranium deposit located by ductile structures inherited.from the pre-existing at the eastern edge ofth e Athabasca Basin ofn orthern ductile deformation. Saskatchewan. Strongly foliated and /ineated metamorphic tec1onites exp osed in the pit display Northeast-southwest and northwest-southeast evidence ofa complex structural evolution involving conjugate normaljaults, minor strike-slip faults and a rhree main pre-mineralization ductile deformational set ofsubhorizontal thrust faults are the youngest events. The earliest de.formation, DI, produced aflar­ structures developed in the mine sequence. lying bedding-para/le/foliation, SI. and two styles of folds due to a single progressive deformation. Primary 1. Introduction lithological contacts have been folded by east-west­ /rending FI a folds. FI b .foldr are defined by folding of The Sue C deposit is a structurally controlled. the SO-SJ surfaces and represent recumbent, basement-hosted, high-grade uranium deposit located concenlric flexures associated with flat-lying thrust at the eastern edge of the Athabasca Basin in northern slices. The FI b flexures are obsen1ed in thin sheets of Saskatchewan ( Figure I; Baudemont et al.. 1993 ). The well-foliated gneiss and represent detached structures deposit, d iscovered in 1989, is one of a cluster of anafoguous lo rootless joldr encountered in uranium deposits spatially related to the unconformity decollement thrust-fold assemblages. The DI bulk separating the Helikian Athabasca Group sandstone strain records evidence C?( an early nappe- teconic from the underlying metasediments of the event pre-dating ore emplacement. Paleoproterozoic Wollaston Group. The Sue C mineralization is located in a north-northeast-trending The 02 generation of structures is chiefly anastomosing deformation zone straddling the characterized by the development ofa moderately to litho logical contact between the Archean Coll in s Bay steeply dipping, north-northeast- to northeast-trending granitic dome and the Aphebian Wollaston Group S2 foliation with associated F2 folds. The early DI metasedirnents (Baudemont et al .. 1993 ). This major structures are clear~v re.folded about north-norlheast­ fault zone is of great economic importance since it to northeast-trending overrurned to upright structures contains several lenses of uranium min era Ii zation (folds). Steeply plunging mineral extension linealions designated Sue A, Sue B, Sue C, Sue D, and Sue E. observed on S2 surfaces recorded a subverlical transport direction during 02 deformation. In their previous detailed studies of dri ll core, Baudemont et al. ( 1993) and Baudemont and Pacquet 03 deformation formed an east-west-trending ( 1996). illustrated the importance of ductile and brittle fracture/crenulation cleavage axial planar lo minor, structural elements to the internal geometry of ore open buckle fc!/dr that slight(V distorted and reoriented lenses as well as to the spatial distribution o f uranium D 1 and 02 structures. concentrations in these deposits. Recent open-pit exploitation of the Sue C deposit has produced newly A late phase ofcomp ressional deformation (late to exposed outcrops whic h have provided additional post-D3) is re!>ponsible.for the development ofm(1jor information on the structural setting of the Sue C north-northeast- to northeast-trending, west-verging deposit. and on the geometry of the defonnation 1hrust faults developed parallel to the pervasive S2 corridor hosting this typical basement-type uranium foliation. These faults.follow the trace ofAphebian mineralization. A detailed structural study of thi s graphitic clay-rich gneisses (Wollaston Group) deposit was undertaken as a pa11 of th e EX TECH IV - obsen•ed on the western limb (?{ the Collins Bay Dome. Athabasca Uranium Project. This paper presents the initial results of th is study and is based on detailed Post-Athabasca d~forn!alion involves reactivation of I: 100 scale structural mapping carried out between late Hudsonian norlh-northeast- to northeast-trending June and August 2000 of all open-pit exposures then faults as west-verging subverlical reverse faults and avalaible . Most of our observations are from the west 'COGF. MA Resource, Inc .. 8 l 7 - 825 45th Strccl West. Saskatoon. SK S7K 3 X5. l../6 Summurv of Investigations ] ()()()_ r "o/ume 2 west and the Wollaston Domain to the east (Lewry and Sibbald, 1979). This transitional structural boundary represents the curvil inear deformation front of a foreland fold and thrust belt related to the Trans-Hudson Orogen (Portella and Annesley, 2000). The outstanding geologic feature of the area is the presence of circular to elongate Archean granitic domes exposed in large antiformal structures (Figure 2). The domes comprise rocks ranging from granitoids in the core to foliated granitoids. gneissic rocks, and migmatites on the margins (Baudemont et al. 1993). They are unconformably overlain by thin units of polydefonned Aphebian parag neissic rocks of the Wollaston Group (Figure 2). T he Wollaston Group comprises a lower package of arkose, quartzite, petite, and graphitic I gneiss interlayered with calc­ I silicate and minor marble I I (Sibbald, 1983 ). This Early I I ss·:- -- -- -·- _ __ ___ t- _ _ Proterozoic metamorphic I I sequence is constrained by a I I 2075 ±2 Ma age from an inferred I I rift-related quartz-feldspar I porphyry intruding basal rift-fill I I I I rocks of the Courtenay Lake- I I s,1•L _ __ - - ··-- ·- - _\_ -· ·- - - - .1. \ , . Cairns Lake fold belt at the base of the Wollaston Group (Ansdell Figure I - Lithostructural subdivision ofnorthern Sa.Ikatchewan tmcl location ofthe et al. 2000), and is intruded by Sue uranium deposits. ca. 1930 Ma pegmatitic granite (Annesley et al.. 1997). The main wall o f the deposit where complexly defonned regional foliation strikes north-northeast to n_ortheast, basement rocks have provided important infonnation d ips steeply east, and is intense w\th p~edommant on the internal geometry and tectonic history of the down-dip mineral tectonic stretching lmeat1~rn s. host rock sequence. The present study shows th at three Prograde metamorphic assemblages ar~ typ1c_a l of the main ductile deformational events predated regional high-T/low-P upper amph1bohte fac1es. mineralization, which might have been related to reactivation of previously developed deeply seated The basement is unconfonnably overlain by the ductile faults. unmetamorphosed llelikian Athabasca Group, comprising clay-rich sandstone, mudstone. and siltstone with minor cong lomerate (Ramackers, 1990). 2. Regional Setting and Property Geology Bray er ul. ( 1987) used Ar/ Ar and K/ Ar techniques to determine minimum dates of 1484 ±55 and 1459 The Sue uranium deposits are located approximately ±4 Ma for interstitial and sedimentary-layer illites, 8.3 km northwc~t of th e Rabbit Lake Mine and 2.5 km 1482 ±49 and 1453 ±49 Ma for regolithic illite. and cast of the McClean Lake uraniu m deposit (Figure 2). 13 19 ±3 Ma for ii lite derived by alteration at the The regional geology of this area has been described McClean Lake deposits. bv a number of authors and is briefly summerized here (see Wall is et al. , 1983; Baudemont er al. 1993 ). Both the metamorphosed basement rocks and the Athabasca Group have been intruded by late, The property is situated in the central part of the north~est-trending Macke_nzie diabase dykes which I !came Province (I loffman, 1990) and straddles th e were introduced at approxunately 1267 ±2 Ma transition zone between the Mudjatik Domain to th e (S limmon. 1996). Saska/c/,('wa,1 ( il!olo1<ical S1t1T(')' 1-17 and induce variable-sized offsets of the unconformity (Haudcmont el al. , 1993 ). The economic uranium mineralizat ion is limited to two subparallel north­ northeast-trending zones of graphitic paragneiss, which arc up to about 25 m wide and marked by intense hydrothermal alteration. The Sue C and D basement-hosted m ineralization is associated with the western graphitic unit; the eastern fa u lt zone hosts the Sue A and B sandstone-unconformity mineralization. Sue E is located in the southern part of the Sue Trend at the j unction of these two anastomosing deform ation zones. Table I summarizes proven ore reserves for the Sue A, £3, and C ore bodies. Tht: geometric configuration of the orebodies appears largely 17 '•-••, con tro I led by the pcrvas ivc 0 SKm Early Proterozoic north-trending tectonic fabric and intermediate-felsic paragneiss, the regional structural elements Fault calc-silicates, meta-quartzites that prevailed w ithin the graphitic fault zones. The economic zones Uranium graphitic paragneiss are north-northeast-trending and Deposit vary from subvt:rtical to steeply Archean east- or west-dipping. All of [ill.. granite gneiss, felsic gneiss these lenses are pencil shaped Figure 2- General geology ofthe McC/ea11 lake area showing tlle locatio11 of and plunge I 0° to 15° southward. ura11ium deposits (from Baudemor,t atrd Pacquet, 1996). This pitch angle is almost perpendicular to the extension North-northeast- and north-trendino subvertical ductile lineation measured in adjacent and brittle-ductile faults zones. typically localized at rocks, but is at a very low ang lt: to fol d axes observed the contact between the C ollins Bay granitic dome and in the structural foot wall of the Sue C deposit. Woll_aston Group graphitic paragneisses, are among the dommant str_u~tural features of the district (Figure 2).