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NI-CU-(PGE) DEPOSITS IN THE RAGLAN AREA, CAPE SMITH BELT, NEW QUÉBEC C.M. LESHER Mineral Exploration Research Centre, Department of Earth Sciences, Laurentian University, 935 Ramsey Lake Road, Sudbury ON P3E2C6 Corresponding author’s e-mail: [email protected]
Abstract Nickel-Cu-(PGE) mineralization in the Raglan area occurs within a series of thick (50-200 m) mafic-ultramafic complexes that outcrop discontinuously along the contact between the Proterozoic Chukotat and Povungnituk groups in the east-central part of the Cape Smith Belt of the Ungava Peninsula between Cross Lake and Raglan Lake. All of the ores, host rocks, and country rocks have been regionally metamorphosed to lower greenschist facies, but igneous and volcanic structures and textures are extremely well preserved. The ultramafic complexes appear to comprise two principal facies assemblages: conduit facies assemblages, which are laterally more restricted and composed primarily of peridotite, and channelized sheet facies assemblages, which comprise a laterally restricted conduit facies composed primarily of peridotite flanked by laterally extensive sheet facies composed of massive gabbro or differentiated peridotite-gabbro. Mineralization occurs exclusively within conduit facies of both assemblages, but the largest deposits occur within the larger conduit facies assemblages. Conduit facies in both assemblage types are relatively massive and undifferentiated, composed primarily of olivine mesocumulate with lesser olivine orthocumulate, thin lower margins of fine-grained pyroxene-porphyritic rock, and thin upper margins of fine-grained pyroxene-porphyritic rock capped by aphyric or microspinifex-textured basalt or basalt breccia. Many units exhibit columnar jointing in their upper and lower parts and polyhedral jointing in their uppermost parts. The lateral margins are interfingered with adjacent sediments and basalts and flanked in some areas by blocky and fluidal peperites. Footwall rocks (sulphidic graphitic semipelites, gabbros, and local basalts) have been eroded thermomechanically, forming larger broader V-shaped first-order embayments in the footwall rocks and superimposed smaller highly irregular (often re-entrant) second-order embayments that localize the Ni-Cu-PGE mineralization. Sediments underlying conduit facies are strongly hornfelsed (recrystallized, bleached, spotted), especially beneath ore-localizing embayments, but sediments and basalts overlying conduit facies, and underlying and overlying sheet facies are only very rarely and very locally contact metamorphosed. The ultramafic complexes have been previously interpreted as feeder sills and lava ponds, but many may represent deeply erosive lava conduits, some may represent invasive (downward burrowing) lava flows, and one may represent a feeder conduit. The olivine mesocumulate rocks contain up to 40% MgO and rarely preserved relict olivine ranges Fo85-88, but they appear to have formed from magmas originally containing 17 to 19% MgO and Fo87-89. The high MgO and olivine contents suggest that they are petrogenetically related to olivine-phyric basalts in the lower Chukotat Group, but they are variably enriched in highly incompatible lithophile elements (Th-U-LREE) relative to moderately incompatible lithophile elements (Zr-MREE-Ti-Y-HREE) and depleted in Nb-Ta relative to Th compared to Chukotat basalts, consistent with variable degrees of local contamination by Povungnituk Group semipelites. The Ni-Cu-PGE ores are texturally quite variable, ranging from massive and semimassive through net- and reverse net-textured, and disseminated ores at or near the bases of the complexes (Type I ores) to patchy and uniformly disseminated ores within the ultramafic complexes (Type II ores). Type I ores are localized within second-order embayments within the footwall rocks, which in some cases form linear-trending belts of differing ore tenor. Ore tenors (metals in 100% sulphides) range 4-17% Ni, 1-9% Cu, 3-25 ppm Pd, 1-6 ppm Pd, and 0.1-4 ppm Au, consistent with equilibration with a parental komatiitic basaltic (Chukotat) magma at magma:sulphide ratios (R factors) in the range 300 to 1100, followed by minor fractional crystallization of monosulphide solid solution and local tectonic/metamorphic modification. Sulphur isotope compositions are primarily 4 to 5 per mil, within the range of and consistent with derivation of the majority of the S from sulphides in the footwall semipelites. The ore zones in some areas appear to define multiple trends of differing ore tenor, as observed in other deposits of this type. The ores are interpreted to have formed by thermomechanical erosion of the sulphidic graphitic semipelites at an early stage in the emplacement of the host ultramafic units.
Résumé La minéralisation en Ni-Cu-(ÉGP) dans la région de Raglan se présente dans une série d’épais (50 à 200 m) complexes mafiques-ultramafiques qui affleurent de manière discontinue le long du contact entre les groupes protérozoïques de Chukotat et de Povungnituk dans la partie centrale est de la zone de Cape Smith de la péninsule d’Ungava entre les lacs Cross et Raglan. Tous les minerais, les roches hôtes et les roches encaissantes ont subi un métamorphisme régional au faciès des schistes verts inférieurs, mais les structures et textures ignées et volcaniques sont extrêmement bien conservées. Les complexes ultramafiques semblent associer deux principaux assemblages de faciès: des assemblages de faciès de conduits, latéralement moins étendus et principalement composés de péridotite, et des assemblages de faciès de nappes chenalisées, comprenant un faciès de conduit latéralement peu étendu et principalement composé de péridotite qui est flanqué de faciès de nappes étendus composés de gabbro massif ou de péridotite-gabbro différenciés. Seuls les faciès de conduits des deux assemblages sont minéralisés, mais les plus importants gisements se trouvent dans les plus grands assemblages de faciès de conduits. Dans les deux types d’assemblages, les faciès de conduits sont relativement massifs et non différenciés, composés principalement de mésocumulats d’olivine avec des quantités moindres d’orthocumulats d’olivine, de minces marges inférieures de roche porphyrique à grain fin renfermant du pyroxène et de minces marges supérieures de roche porphyrique à grain fin renfermant du pyroxène coiffées de basalte ou de brèche Lesher, C.M., 2007, Ni-Cu-(PGE) Deposits in the Raglan Area, Cape Smith Belt, New Québec, in Goodfellow, W. D., ed., Mineral Deposits of Canada: A Synthesis of Major Deposit-Types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods: Special Publication No. 5, Mineral Deposits Division, Geological Association of Canada, p. 351-386.
C.M. Lesher basaltique de texture aphyrique ou microspinifex. Un grand nombre des unités présentent une structure columnaire à leurs parties supérieure et inférieure et une structure polyédrique à leur partie sommitale. Les marges latérales sont interdigitées des sédiments et des basaltes adjacents et flanquées, dans certaines zones, de pépérites de textures polyédrique et fluidale. Les roches des épontes inférieures (semipélites graphitiques sulfurées, gabbros et basaltes par endroits) ont été thermomécaniquement érodées pour former dans les roches des épontes inférieures les plus grands rentrants de premier ordre en forme de V auxquels sont surimposés de plus petits rentrants très irréguliers de deuxième ordre dans lesquels se situent les minéralisations en Ni-Cu-ÉGP. Les sédiments sous-jacents des faciès de conduits sont intensément transformés en cornéenne (recristallisés, décolorés, tachetés), surtout sous les rentrants renfermant du minerai, mais les sédiments et les basaltes sus-jacents aux faciès de conduits ainsi que sus-jacents et sous-jacents aux faciès de nappes n’ont subi que très localement un métamorphisme de contact. Antérieurement, les complexes ultramafiques ont été interprétés comme étant des filons-couches d'alimentation et des étangs de lave, mais nombre d’entre eux pourraient s’avérer des conduits de lave très érosive, certains des coulées de lave invasives (s’enfouissant) et l’un d’entre eux en particulier pourrait être un conduit d’alimentation. La roche des mésocumulats d’olivine peut renfermer jusqu’à 40 % de MgO et l’olivine relique rarement conservée se situe dans la plage Fo85-88, mais semble s’être formée à partir de magmas renfermant de 17 à 19% de MgO dans la plage Fo87-89. Les teneur élevées en MgO et en olivine suggèrent qu’elle est pétrogénétiquement reliée aux basaltes à olivine phyriques du Groupe de Chukotat inférieur, mais elle est variablement enrichie en éléments lithophiles très incompatibles (Th-U-éléments de terres rares légers) comparativement aux éléments lithophiles modérément incompatibles (Zr-éléments de terres rares intermédiaires-Ti-Y- éléments de terres rares lourds) et appauvrie en Nb-Ta par rapport au Th comparativement aux basaltes de Chukotat, ce qui est conforme à des degrés variables de contamination par les semipélites du Groupe de Povungnituk. Les minerais de Ni-Cu-ÉGP sont de textures très variables, allant de massifs à semi-massifs, à des textures réticulées et réticulées inversées, à des minerais disséminés aux bases des complexes ou à leur proximité (minerais de type I) et à des minerais disséminés dans des bancs ou uniformément dans les complexes ultramafiques (minerais de type II). Les minerais de type I se trouvent dans les rentrants de deuxième ordre dans les roches des épontes inférieures qui forment dans certains cas des zones linéaires de minerais de différentes teneurs. Les teneurs des minerais (en métaux dans les minerais à 100 % sulfurés) varient de 4 à 17 % pour le Ni, de 1 à 9 % pour le Cu, de 3 à 25 ppm pour le Pt, de 1 à 6 ppm pour le Pd et de 0,1 à 4 ppm pour l’Au, ce qui est conforme à une équilibration avec un magma basaltique komatiitique d’origine (Chukotat) présentant des rapports magma/sulfure (facteurs R) de l’ordre de 300 à 1100, suivie d’une cristallisation fractionnaire mineure de la solution solide monosulfurée (SSM) puis d’une modification tectonique/métamorphique localisée. Les concentrations en isotopes du S sont principalement de 4 à 5 o/oo, c’est-à-dire de l’ordre de celles auxquelles on s’attendrait si la majorité du S des sulfures était dérivé des semipélites de l’éponte inférieure. Dans certains secteurs, les zones de minerai semblent se présenter en multiples bandes de teneurs différentes, tel qu’observé dans d’autres gisements de ce genre. Les minerais se seraient formés par érosion thermomécanique des semipélites graphitiques sulfurées à un stade précoce de la mise en place des unités ultramafiques hôtes.
Introduction The Ni-Cu-(PGE) deposits in the Raglan area of the 1.9 Ga Cape Smith Belt represent some of the best preserved and best exposed examples of magmatic sulphide mineralization associated with komatiitic rocks. They share many characteristics with other deposits of this type (Lesher, 1989; Lesher and Keays, 2002; Barnes, 2006; Barnes and Lesher, in press): 1) the host units occur at the base of the volcanic sequence and appear to represent the initial expression of komatiitic basaltic volcanism. 2) the host units are the thickest, most magnesian, and most olivine-rich rocks in the sequence, 3) the ores are localized in embayments that transgress footwall rocks, including S-rich sedimentary rocks, and 4) the ores are composed of Type I basal massive/nettextured/disseminated and lesser Type II internal disseminated Fe-Ni-Cu sulphides. However, they are different from other deposits of this type in some respects: 1) they appear to have formed in deeply erosive lava conduits, rather than in extrusive lava conduits (cf. Kambalda: Lesher et al., 1984) or feeder sills (cf. Thompson: Layton-Matthews et al., 2007) the orebodies are more pod-like than the more ribbon-like ‘shoots’ that characterize many other deposits of this type, 3) the ores have lower Ni/Cu and higher Pd/Ir ratios than deposits associated with high-Mg komatiites (e.g. Kambalda, Perseverance, Thompson: see compilation by Naldrett, 2004), and 4) the ore textural profiles are often much more complex than in other deposits of this type (e.g. Alexo, Kambalda). 352
The exploration history of the Raglan area has been summarized by Green and Dupras (1999). The first low-grade showings in this region were discovered at the western end of the Cape Smith Belt in 1898 by A.P. Low of the Geological Survey of Canada, and in 1931-1932 were confirmed to extend inland by the Cyril Knight Prospecting Company. However, it was not until 1956 that Harold Kenty and Murray Watts of LeMoyne Explorations discovered the high-grade mineralization at “Deception Creek” (Katinniq #1 showing). Additional exploration was done in the late 1950s and 1960s by a series of companies that would eventually become New Québec Raglan Nickel Mines and which led to the sinking of the Donaldson exploration shaft in 1968 to 1970. Primarily technical work was done in the 1970s, but a major program in 1981 and 1982, led by Colin Coats, mapped the entire length of the mineralized zone between Cross Lake and Donaldson at 1:12,000 scale. Falconbridge Ltd. purchased all of the minority interests in New Québec Raglan Nickel Mines in 1989 and major diamond drilling, geophysical, and mapping programs in 1989 and 1990, overseen by Michel Dufresne, led to an underground exploration program at Katinniq in 1991 and 1992, a feasibility study in 1993, and the construction of the Katinniq concentrator and accommodation complex in 1995 to 1996. Production from the Katinniq underground mine began in December 1997 and continues today under the ownership of Xstrata Ltd. Parts of the Zone 2 and Zone 3 areas have been mined as open pits and are being developed underground. As of
Ni-Cu-(PGE) Deposits in the Raglan Area, Cape Smith Belt, New Québec December 31, 2005, total production was 6.89 Mt at 3.11% Ni and 0.91% Cu, mineral reserves (proven + probable) were 14.85 Mt at 2.80% Ni and 0.77% Cu, with a mineral resource of 3.39 Mt at 2.42% Ni and 0.80% Cu (measured + indicated), and 7.7 Mt at 3.0% Ni and 0.8% Cu (inferred) (Falconbridge Ltd., Annual Report, 2005).
Narsajuaq Arc (1.86-1.83 Ga) Cape Smith Belt Parent/Spartan Groups (ca. 1.86 Ga ) Povungnituk and Chukotat Groups (>2.04-1.92 Ga) Watts Group (ca. 2.00 Ga) Superior Province (ca. 2.80 Ga)
Geologic Setting The Raglan deposits occur in the early Proterozoic Cape Smith Belt, which extends east-west for 375 km across the Ungava Peninsula of northern Québec, between the Archean Superior Province in the south and a variety of Proterozoic ‘suspect’ terranes to the north (Fig. 1). The belt is bound to the south, east, and northeast by high-grade gneisses and plutonic rocks of the Superior Province and to the northwest by volcanic rocks of the Parent Group, which are interpreted as a volcanic arc (Picard et al., 1990), fine-grained clastic sedimentary rocks of the Spartan Group which are interpreted as fore-arc basinal deposits (St-Onge and Lucas, 1993), and mafic-ultramafic volcanic and intrusive rocks of the Watts Group, which are interpreted as an ophiolite (Scott et al., 1989). The Cape Smith Belt appears to represent a thinskinned thrust belt preserved as a stack of klippen (Hoffman, 1985) in a doubly plunging synclinorium, and is interpreted as the preserved part of the foreland thrust belt to the Ungava
New Québec Orogen
78 70 74 FIGURE 1. Map of the Ungava Peninsula north of 60ºN, showing the major geological elements of the Ungava Orogen (after St-Onge and Lucas, 1993). Area of Figure 2 is outlined.
ARCHEAN Domain 1
EARLY PROTEROZOIC Domain 3 Domain 2
oblique - slip fault
tonalite, granite, amphibolite
dominantly plagioclase-phyric basalt, gabbro, peridotite dominantly pyroxene-phyric basalt, gabbro, peridotite dominantly olivine-phyric basalt, gabbro, peridotite
Upper Povungnituk Group
basalt, gabbro sills and sheeted dykes pyroxenite
Spartan Group graphitic pelite, semipelite, quartzite
basalt, gabbro, peridotite
Lower Povungnituk Group CC T BB
arkosic quartzite, ironstone, conglomerate
micaceous quartzite semipelite, quartzite, ironstone, basalt, volcaniclastic sedimentary rock, gabbro, peridotite ironstone
Lac Watts Wakeham Bay Q
74o 30' W
Lac St - Germain
C B B A
61o 10' N FIGURE 2. Geological compilation map of the eastern part of the Cape Smith Belt (after St-Onge and Lucas, 1993). Area of Figure 3 is outlined.
C.M. Lesher 10 km
61o 30' N
74 30' W
tonalite, granite, amphibolite
graphitic pelite, semipelite, quartzite
oblique - slip fault
dominantly plagioclase-phyric basalt dominantly pyroxene-phyric basalt dominantly olivine-phyric basalt
D2 thrust fault
D1 thrust fault geological boundary
Povungnituk Group semipelite plagioclase-phyric basalt semipelite, quartzite, ironstone, basalt volcaniclastic sed. rock, gabbro, peridotite
Watts Group basalt, gabbro sills, and sheeted dykes
Deposits/Showings B = Boundary CL = Cross Lake D = Donaldson EL = East Lake EU = Expo Ungava K = Katinniq WB = West Boundary M = Méquillon
FIGURE 3. Geological compilation map of the Raglan area (modified from St-Onge and Lucas, 1993), showing the locations of major deposits along the Raglan Formation (Cross Lake to Donaldson) and some of those in the Delta horizon (Méquillon and Expo Ungava). NC20S = North Claim sill.
Orogen, an arc-continental collisional zone (Picard et al., 1990; St-Onge and Lucas, 1990). Tectonostratigraphy Bergeron (1959) subdivided the rocks in the Cape Smith Belt into two tectonostratigraphic groups: the Povungnituk Group and the Chukotat Group (Fig. 2). The Povungnituk Group comprises a lower sequence of primarily clastic sedimentary rocks and an upper sequence of primarily mafic volcanic and sedimentary rocks intruded by gabbro, pyroxenite, and peridotite sills. The Chukotat Group comprises a thin lower unit of mafic-ultramafic rocks overlain by olivinephyric, pyroxene-phyric, and plagioclase-phyric basalts. This sequence is interpreted to represent the transition from initial rifting (lower Povungnituk Group) and continental basalt volcanism (upper Povungnituk Group) to opening of an ocean basin (Chukotat Group) (Francis and Hynes, 1979; Hynes and Francis, 1982; Francis et al., 1983; Picard et al., 1990; St-Onge and Lucas, 1993). The major lithological units in the east-central part of the Cape Smith Belt are described below, from structural and stratigraphic base (south) to structural and stratigraphic top (north). Upper Povungnituk Group Povungnituk basalt: The mafic volcanic rocks of the upper Povungnituk Group are exposed in the upper part of thrust sheet L (Figs. 2, 3; Table 1). There are excellent outcrops of these rocks along the west shore of Raglan Lake south of the Donaldson Camp and along the Deception River 354
south of Katinniq. They comprise simple and compound massive and pillowed flows of tholeiitic basalt. They are fine- to very fine-grained, light to medium green in colour, and weather to a greenish-grey colour. They are composed primarily of albite-actinolite-chlorite with trace amounts of pyrite, and commonly exhibit a recrystallized intersertal to ophitic texture. The pillows are 0.1 to 1m long and often contain multiple pillow shelves (see Fig. 4G), indicating that they are lava tubes that experienced multiple episodes of lava emplacement and drainage (Sawyer et al., 1983). The contact with the overlying semipelites is poorly exposed and has been mapped as a D1 regional thrust fault (thrust sheet M: Figs. 2, 3; Table 1) by Hynes and Francis (1979), Coats (1982), and St-Onge and Lucas (1993). However, the fault weaves back and forth across the contact and the sills above and below the contact are very similar, suggesting that the stratigraphic sequence is broadly conformable. Povungnituk slate: The 1 to 2 km thick sequence of sedimentary rocks at the top of the Povungnituk Group is exposed in the lower part of thrust sheet M, directly underlying the Raglan Formation. These rocks do not outcrop well, but they are exposed discontinuously along the entire length of the Raglan Formation. They are dominated by semipelite, fine-grained graphitic sulphidic slate (see Fig. 4F), and argillite with minor quartzite. The semipelites are composed primarily of fine-grained quartz, white mica, and chlorite, and may contain up to 5% sulphides and significant amounts of graphite. Sedimentary structures, such as graded bedding, are rare. The contact with the overlying Raglan Formation is
Ni-Cu-(PGE) Deposits in the Raglan Area, Cape Smith Belt, New Québec transgressive and locally sheared, TABLE 1. Tectonostratigraphic column for the eastern Cape Smith Belt (adapted from St-Onge but the uppermost sedimentary and Lucas, 1993). rocks are contact metamorphosed Era Group/Suite Lithologies discontinuously along the entire Late Proterozoic Diabase dykes length of the Raglan Formation Narsajuaq Tonalite between Cross Lake and Spartan Semipelite, pelite, quartzite, gabbro Donaldson, and the degree and extent of metamorphism are greater Basalt, gabbro sills, sheeted gabbroic dykes beneath thicker parts of the ultraPyroxenite mafic complexes than beneath thinWatts Layered gabbro ner parts, and greatest beneath transgressive, second-order embayLayered peridotite ments beneath the ultramafic comDominantly plagioclase-phyric basalt, gabbro plexes (e.g. Thacker, 1995; Stilson, Dominantly pyroxene-phyric basalt, gabbro 1999). This indicates that the conChukotat Dominantly olivine-phyric basalt, gabbro; thick differentiated tact is locally unconformable (i.e. peridotite-gabbro flows and massive peridotite ± gabbro lava channel thermomechanical erosional), but complexes; Ni-Cu-PGE ores Early not tectonic. Proterozoic Semipelite, layered gabbro-peridotite sills Povungnituk sills: Povungnituk Upper basalts and slates have been Povungnituk Basalt, volcaniclastic sedimentary rock, rhyolite; minor semipelite and quartzite, gabbro, peridotite, layered gabbro-peridotite sills intruded by mafic-ultramafic sills Micaceous quartzite that range up to several hundred metres in thickness. They occur in Basalt, volcaniclastic sedimentary rock, rhyolite; minor quartzite, thrust sheets I-M and O (Figs. 2, 3). dolomite, calc-silicate rock, gabbro, peridotite, layered peridotite gabbro sills Excellent examples outcrop south Lower of Zone 13-14 (Fig. 3) and east of Semipelite, pelite, micaceous quartzite, quartzite, conglomerate, Povungnituk Cross Lake (Romeo I and II: Fig. ironstone, dolomite, calc-silicate rock; minor basalt and volcaniclastic rocks, gabbro, peridotite, layered peridotite-gabbro sills 5A). Some are composed of massive gabbro or pyroxenite, or less Ironstone, minor quartzite, and semipelite commonly peridotite, and some are Quartzite, ironstone, conglomerate, semipelite differentiated with thinner lower Tonalite, granite, amphibolite zones of columnar-jointed peri- Archean dotite or oikocrystic olivine pyroxRaglan Formation enite, and thicker upper zones of layered melanogabbro, mesogabbro, leucogabbro, and ferrogabbro. Some of the The only economic Ni-Cu-(PGE) sulphide deposits disundifferentiated ultramafic bodies contain basal accumulacovered thus far in the Cape Smith Belt occur in the easttions of subeconomic Ni-Cu-(PGE) sulphides (e.g. Expo central part of the belt in the upper part of thrust sheet M Ungava, Bravo, Méquillon) and some of the differentiated (Figs. 2, 3). The thick mafic-ultramafic complexes that host mafic-ultramafic sills (e.g. Delta, Romeo I) contain narrow the ores in this sheet define an apparently discontinuous but PGE-rich zones associated with thin pyroxene-rich pegmastratigraphically distinct, regionally mappable unit defined toidal gabbro (e.g. Giovenazzo et al., 1989; Thibert, 1993). by Giovenazzo et al. (1989) as the Raglan Horizon and by Where exposed, the sills have contact metamorphosed both Lesher et al. (1999) as the Raglan Formation. This unit underlying and overlying sedimentary rocks and sometimes extends 85 km from Cross Lake in the west, where it is tercontain rafts of overlying sedimentary rocks (St-Onge and minated by a D2 syncline and D2 thrust fault O, across a D4 Lucas, 1993; Thibert, 1993). These sills have been previantiform centred between the 5-8 and 13-14 areas, to ously interpreted as feeders to overlying Chukotat volcanic Wakeham Lake in the east, where it is terminated by the rocks (e.g. Hynes and Francis, 1979; Francis et al., 1981, same thrust fault (Figs. 2, 3; see also St-Onge and Lucas, 1983; Bédard et al., 1983; Giovenazzo et al., 1989). Some of 1994). the undifferentiated ultramafic bodies have weighted averThere are significant variations in the continuity and qualage MgO contents greater than their chilled margins, indiity of outcrops, and in the density of diamond drill core cating an excess olivine component of 30 to 40%, consistent drilling along the Raglan Formation. There are excellent outwith them being feeder sills (e.g. Bravo: Barnes and crops in the Cross Lake and Katinniq areas, very good outGiovennazo, 1990; Méquillon: Tremblay, 1990), but most of crops in parts of the Zone 2-3, Zone 5-8, and Boundary the sills have weighted average compositions similar to their areas, and isolated outcrops in other areas, but many areas chilled margins (Thibert, 1993; C.M. Lesher and R.R. are covered by frost-heaved outcrop (felsenmeer) and glacial Keays, unpubl. data), suggesting that they did not accumurubble. There is very good diamond drill core information at late significant amounts of olivine and that they represent Katinniq, good drill core information for parts of Zone 2-3, simple sills rather than subvolcanic feeders. All of the sills Zone 5-8, and Donaldson, but only moderate drill informaanalyzed by Burnham et al. (1999) and Lesher et al. (2001) tion for most other areas along the belt. Detailed magnetic are contaminated, and could not have fed overlying unconand electrical surveys have been done on most of the areas. taminated Chukotat basalts (see below). 355
C.M. Lesher A
FIGURE 4. (A) Columnar-jointed peridotite in the lower part of the Katinniq Ultramafic Complex. Columns are ~20-30 cm in diameter. (B) Photomicrograph of olivine (lower order interference colours) mesocumulate rock with interstitial clinopyroxene (higher order interference colours), forming a heteradcumulate texture. Width of photo is 7.5 mm. Doubly polarized light. (C) Irregular lower contact of between peridotite, pyroxene-phyric basalt, and spotted hornfels along the lower margin of the Katinniq Ultramafic Complex. The contact dips ~45º to the north (right) subparallel to bedding in the upper part of the photo, but bends sharply southward, dips vertical and then ~45º westward, transgressing bedding in lower left part of photo. Underlying/adjacent metasediments are unfolded. (D) Lower contact of Katinniq Ultramafic Complex showing contact between lower pyroxene-phyric komatiitic basalt (pinkish grey, above hammer head), 20 cm thick layer of massive, completely-recrystallized semipelite (white, below hammer head), and spotted hornfels (grey, bottom). (E) Photomicrograph of pyroxene-phyric komatiitic basalt along lower contact of Katinniq Ultramafic Complex, containing small equant pyroxene phenocrysts (intermediate interference colours) in a matrix of recrystallized sprays of pyroxene (yellow interference colours) and altered interstitial ‘glass’ (light colours). Width of photo is 8 mm. Doubly polarized light.
Although more details are emerging from detailed exploration diamond drilling by Xstrata Ltd., the 1:2,000 surface mapping that was done prior to mine development (which included outcrops now covered by roads, buildings, and reservoirs) reported in Lesher et al. (1999) indicates that the Raglan Formation contains at least two of the facies assemblages defined by Lesher and Barnes (in press). Conduit facies assemblage: These units are very thick (up to 200 m in true thickness), laterally restricted, and are com356
posed primarily of relatively massive olivine mesocumulate rocks. Examples include the mineralized peridotite complexes at East Lake (Petch, 1999; Stewart, 2002), Zone 2 and Zone 3 (Mallinson, 1999a,b), Katinniq (Gillies, 1993; Lesher and Charland, 1999), Zone 6 and Zone 8 (Thacker, 1995; Mallinson, 1999c), Zone 13-14 (Vicker and Fedorowich, 1999), West Boundary (Charland, 1999), Boundary (Stilson and Lesher, 1999), and Donaldson (Lesher and Vicker, 1999).
Ni-Cu-(PGE) Deposits in the Raglan Area, Cape Smith Belt, New Québec F
FIGURE 4 CONTINUED. (F) Sulphidic graphitic slate ~20 m below lower contact of Katinniq Ultramafic Complex. (G) Pillow basalt with 17 shelves (drainage cavities) in upper part of Povungnituk Group, south side of Lac Raglan, Donaldson area.
D1 thrust fault N (Figs. 2, 3) sometimes occurs above and Channelized sheet facies assemblage: These units are characterized by laterally restricted zones of relatively massometimes below the discontinuous horizon of sedimentary sive olivine mesocumulates flanked by laterally more extenrock that separates the lowermost Chukotat basalts from the sive zones of differentiated olivine orthocumulates and gabRaglan Formation (see Figs. 5, 6). Consequently, the maficbros. Examples include the Cross Lake – C1-C2-C3 complex ultramafic complexes are conformably overlain by sedimen(Thibert, 1999; Fig. 5B) and the Zone 2-3 – Katinniq – Zone 5-8 A gabbro (Thacker, 1995; Mallinson, 1999a,b,c), which appears to be channelized only in the Zone 5 – Zone 7 area (Figs. 6, 7). In some areas only a channelized sheet facies assemblage appears to 6830000mN be present (e.g. Cross Lake: Fig. 5), area of Fig. 4B in some areas only a conduit facies $ assemblage appears to be present C2 C1 $ (e.g. East Lake: Petch, 1999; West $ C3 Boundary: Charland, 1999; Cross $ Lac Lake Donaldson: Lesher and Vicker, Main Cross 1999), but where both are present, II Sill Romeo conduit facies assemblages crossill eo I S Rom cut underlying channelized sheet facies assemblages (e.g. Zone 2-3: Chukotat Gp. Povungnituk Gp. N Mallinson, 1999a,b, Katinniq: kom. basalt sediment 0 1 km Lesher and Charland, 1999; Zone pyroxenite thol. basalt peridotite facing 5-8: Thacker, 1995; Mallinson, gabbro strike/dip 1999c), sometimes quite deeply Cross Lake – C1-2-3 Area fault (Figs. 6, 7, 8). The consistent stratigraphic relationships led Lesher et B al. (1999) to define the channelized C1-2-3 Area sheet facies assemblage as the $$$ Cross Lake Member and the con$ N duit facies assemblage as the $ $$ Katinniq Member. $$$$ $ $ $ $ $ $ Thus far, no mineralization has $ $ $ $ $$ $ $ Basalt $ $ C2 been found in any of the maficPyroxenite ultramafic bodies that occur in C3 Peridotite Fault Strike/Dip $ thrust sheet O (Figs. 2, 3), which is $ Gabbro Geological Contact Pilllow Facing C1 0 300m interpreted to be a duplication of Slate $ Showings Columnar Joint mineralized thrust sheet M (StFIGURE 5. (A) Simplified geological maps of the Cross Lake area based on 1:12,000 scale mapping by Onge and Lucas, 1994). Most Falconbridge Ltd., showing locations of the Cross Lake Main and C1-C2-C3 areas of the Cross Lake appear to represent sheet sills. Member, and the Romeo I and Romeo II sills in the upper Povungnituk Group. (B) Simplified geological map of the C1-C2-C3 area based on 1:2000 scale mapping by Thibert (1999).
Katinniq Area KM
2-3 Area CLM
5700 00m E
Katinniq KM Member
Gabbro Layered Pyroxenite Flows Wehrlite
Chukotat Group Komatiitic Basalt
5750 00m E
5650 00m E
Gabbro Sills Pyroxenite Wehrlite/Peridotite
Cross L. Gabbro CLM Pyroxenite Member
FIGURE 6. Geological compilation map of the Zone 2-3 - Katinniq - Zone 5-8 area showing stratigraphic relationships between the Cross Lake (CLM) and Katinniq (KM) members of the Raglan Formation (modified from 1:12,000 scale mapping by Falconbridge Ltd.). Aa
10c 10c 4f (
6e 6e 10c 6e
4f 6e 6e
4f 4f es
10c oik 10c oik 4f
Zone 5-8 Area
basalt sed +
sed + b
4f 4f fels orn h . inc
Basalt breccia Pyroxene-phyric basalt
asalt ru sed + b 6e
Wehrlite (oik=oikocrystic) Peridotite Fe-Ni-Cu sulphides Gabbro
Hornfelsed slate Sulphidic graphitic slate
Zone 7 4f 4f 4f 4f Zone 5
Fault Columnar joint
~ limit of hornfels 0
FIGURE 7. (A) Simplified geological map of the Boundary Ultramafic Complex based on 1:2,000 scale mapping by C.M. Stilson and C.M. Lesher in 1997. (B) Simplified geological map of the Zone 5-8 Ultramafic Complex based on 1:2,000 scale mapping by J.L. Thacker and C.M. Lesher in 1990, and C.M. Lesher and S.L. Gillies in 1991. The apparent discontinuity of some lithologies (e.g. pyroxene-phyric basalts and wehrlites) is an artifact of discontinuous exposure: both areas contain numerous outcrops, but most areas (especially ultramafic rocks) are covered by frost-heaved outcrop and some areas (especially hanging-wall basalts and sediments) are covered by rubble.
Ni-Cu-(PGE) Deposits in the Raglan Area, Cape Smith Belt, New Québec 570000E
$ $ $$ $ $
LG MG NG
LG MG NG
Strike/Dip Columnar Joint Massive/Pillow Basalt
1 t n e
Peridotite (minor Wehrlite) Leucogabbro/Mesogabbro/ Melanogabbro/PyroxeneGabbro Hornfelsed Slate
100 200 300 400 500 m
FIGURE 8. Simplified geological map of the Katinniq area based on 1:2,000 scale mapping by C.M. Lesher in 1989-1991 (prior to development of the Katinniq mine site and flooding of the Deception River). KG = Katinniq Gabbro, KUC = Katinniq Ultramafic Complex, LC = leucogabbro, PG = pyroxene gabbro, MG = melanogabbro, NG = mesogabbro.
tary rocks and Chukotat volcanic rocks in some cases and in fault contact with them in other cases. The displacement on this fault has not been determined, but the similarity of the rocks on either side of the fault (olivine-phyric basalts and semipelites) indicates that this part of the stratigraphic sequence is broadly conformable. Lower Chukotat Group The lower part of the Chukotat Group is dominated by olivine-phyric basalts that form simple and compound flows with massive, polygonized, pillowed, or brecciated facies. Massive lavas are characterized by ropy surfaces and polyhedral jointing, very fine-grained margins, and fine- to medium-grained central parts. Pillows exhibit indistinct rims and are commonly larger and longer (1-2 m long, 3:1 to 5:1 aspect ratios) in the lower parts of pillowed zones, and smaller and shorter (0.4-0.6m long, 1:1 to 2:1 aspect ratios) in the central and upper parts of pillowed zones (see Fig. 9A). Interpillow spaces are filled with a mixture of basalt breccia, hyaloclastite, pelite, and quartz±calcite. Pillow shelves, representing horizontal drainage cavities (Sawyer et al., 1983) are commonly filled with quartz±calcite and are excellent paleohorizon indicators. Olivine-phyric basalts are composed of actinolite-chlorite-serpentine and contain light green pseudomorphs after olivine phenocrysts and fine disseminated pyrrhotite (see Fig. 9B). The lower part of the Chukotat Group is characterized by the presence of thick sheet flows (up to 100 m), comprising lower olivine cumulate zones of reddish-brown-weathering olivine pyroxenite or pinkish-grey weathering pyroxenite and upper differenti-
ated zones of grey weathering gabbro or basalt (Hynes and Francis, 1982; St-Onge and Lucas, 1993). Olivine-phyric basalts and differentiated flows are exposed in thrust sheet N and in the lower part of thrust sheet P (Figs. 2, 3). There are excellent outcrops in the core of the Cross Lake syncline (Fig. 5) and along the Deception River north of Katinniq (Figs. 6, 8). Deformation The rocks in the Cape Smith Belt record four major deformation events (Lucas, 1989; Lucas and St-Onge, 1989; StOnge and Lucas, 1993): D1 (