SYNOPSIS OF THE POLARIS ZN-P B DISTRICT , C ANADIAN ARCTIC ISLANDS , N UNAVUT KEITH DEWING 1, R OBERT J. S HARP 2 , AND ELIZABETH TURNER 3 1. Geological Survey of Canada, 3303-33rd Street NW, Calgary, Alberta T2L 2A7 2. Trans Polar Geological, 60 Hawkmount Heights NW, Calgar,y Alberta T3G 3S5 3. Department of Earth Science, Laurentian University, Sudbury, Ontario, P3E 2C6 Corresponding author’s email: [email protected]

Abstract The Polaris Mine was a Mississippi Valley-type (MVT) deposit hosted in dolomitized Middle Ordovician lime - stone. Total production was 20.1 Mt at 13.4% Zn and 3.6% Pb. There are about 80 showings in the district, which stretches from Somerset Island to the Grinnell Peninsula. There are two deposit types in the Polaris District: 1) struc - turally controlled, carbonate-hosted Zn-Pb-Fe deposits typical of MVT deposits, and 2) structurally and stratigraphi - cally controlled, carbonate-hosted Cu deposits enriched by later supergene removal of Fe and S. Mineralization is paragenetically simple, with sphalerite and galena as the ore minerals, and with dolomite and mar - casite as the main gangue minerals. The deposits formed from brines at about 90 to 100°C. The age of the mineraliza - tion is constrained to post-Late Devonian folding and may be associated with the last stages of the Ellesmerian Orogeny or the opening of the Sverdrup Basin. Copper-rich mineralization is known from four showings, is associated with zinc- lead mineralization and is confined to a single interval in the Silurian. The metallogenic model for Polaris invokes a source of metal ions within the stratigraphic column since strontium shows no indication of basement involvement. Metals are then carried in sulphate-rich brines through deep aquifers. Driven by an orogenic process, circulating fluids rose along faults until they encountered organic-rich, permeable lime - stone overlain by impermeable shale. Bacterial sulphate reduction reduces sulphate to H 2S using organic matter as a reductant. The resulting H 2S has a shift in δ 34 S values of -15‰. The H 2S reacts inorganically with zinc, lead, and iron ions to produce sulphides with a δ 34 S value of about 10‰. Released hydrogen ions dissolve carbonate resulting in dis - solution breccias and other dissolution fabrics. Excess sulphate was expelled from the system and produced a halo of barite up to 10 km from the deposit with δ 34 S of 40 to 60‰. Résumé La mine Polaris consistait en un gisement de type Mississippi-Valley encaissé dans un calcaire dolomitisé de l’Ordovicien moyen. Au total, elle a produit 20,1 Mt de minerai titrant 13,4 % de Zn et 3,6 % de Pb. Le district de Polaris compte quelque 80 indices minéralisés et s’étend de l’île Somerset jusqu’à la péninsule Grinnell. On y trouve deux types de gîtes, à savoir des gîtes de Zn-Pb-Fe encaissés dans des roches carbonatées, qui affichent un contrôle structural et sont représentatifs des gîtes de type Mississippi-Valley, et des gîtes de Cu logés dans des roches carbon - atées, qui montrent des contrôles structuraux et stratigraphiques et un enrichissement supergène ultérieur par l’élimi - nation du Fe et du S. Du point de vue paragénétique, les minéralisations sont simples. Elles présentent la sphalérite et la galène comme minéraux métallifères, ainsi que la dolomite et la marcasite comme principaux minéraux de gangue. Les gîtes du dis - trict se sont formés à partir de saumures affichant des températures de 90 à 100°C environ. L’âge maximal des minéral - isations est défini par un plissement du Dévonien tardif, qui pourrait être rattaché aux dernières phases de l’orogenèse Ellesmérienne ou à l’ouverture du bassin de Sverdrup. Quatre indices minéralisées ont révélé des minéralisations riches en cuivre, qui sont associées aux minéralisations de zinc-plomb et confinées à un seul intervalle du Silurien. Le modèle métallogénique proposé pour le district de Polaris établit une source d’ions métalliques dans la colonne sédimentaire, car la composition isotopique du strontium ne témoigne d’aucune contribution du socle. Les métaux ont donc été transportés dans des saumures riches en sulfates circulant dans de profonds aquifères. Un phénomène orogénique a fait en sorte que les fluides en circulation se sont élevés le long de failles jusqu’à ce qu’ils atteignent des horizons perméables de calcaire riche en matière organique, qui sont recouverts de shale imperméable. Des bactéries ont réduit les sulfates en H 2S en se servant de la matière organique comme agent réducteur. Le H 2S résultant présente un décalage des valeurs de δ 34 S de -15 ‰. Le H 2S réagit de manière inorganique avec les ions de zinc, de plomb et de fer pour produire des sulfures dont la valeur de δ 34 S est d’environ 10 ‰. Les ions d’hydrogène émis dissolvent les car - bonates pour produire des brèches de dissolution et d’autres fabriques de dissolution. Les sulfates excédentaires ont été expulsés du système et ont produit une auréole de barytine qui s’étend jusqu’à 10 km du gisement et les valeurs de δ 34 S de ce minéral varient de 40 à 60 ‰.

Introduction and History There are about 80 individual Zn-Pb showings occur The Polaris Zn-Pb District lies in the central Arctic within the study area (Fig. 1, Table 1). The largest of these is Islands, Nunavut, and spans an area that is roughly 450 km the Polaris deposit, a carbonate-hosted Zn-Pb deposit of north-south by 130 km east-west (Fig. 1). The southern limit about 20 million tonnes grading about 17% Zn+Pb. The is the southern edge of Somerset Island; the northern edge is deposit was mined from 1982 to 2002, when it shut down the northern shore of the Grinnell Peninsula. The eastern due to depletion of reserves. During its latter days, Polaris limit runs along the longitude of Wellington Channel employed a workforce of 235 employees on an 8 week onsite between Cornwallis and Devon islands and the western limit and 4 week offsite rotation. Sphalerite and galena were sep - is on eastern Bathurst Island. arated from the gangue in a complex known as “the barge”

Dewing, K., Sharp, R.J., Turner, E., 2007, Synopsis of the Polaris Zn-Pb District, Canadian Arctice Islands, Nunavut, 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: Geological Association of Canada, Mineral Deposits Division, Special Publication No. 5, p. 655-672. K. Dewing, R.J. Sharp, and E. Turner

which in addition to the concentra - tor, housed offices, warehouse, powerhouse, and heavy equipment and other repair shops. The concen - trator complex was built on a barge 50 0 50 100 150

in Trois Rivières, Québec, and kilometres towed to Little Cornwallis Island where it was floated into an exca - vated lagoon and surrounded by rockfill. The annual mining rate of 1,040,000 tonnes per year produced Grinnell Peninsula CU 200,000 tonnes of zinc and 30,000 Aurora Canyon North tonnes of lead concentrates that JG West Trigger&JG Featherbear BK Soda were stored in a large concentrate Tiger Simba shed. Ocean-going ships docked Oceanview Liz Ridge Cu Agpan Sheills 1 Hornby Cu near the concentrate shed and were Sheills 2 Hornby Zn loaded directly with a conveyor Aquarius system. Freighters arrived in early Dundas July and departed up until late Bathurst Island October. Baillie Hamilton Exploration in the Polaris Harrison Markham Pt Eclipse Stuart District took place in five phases Bass LCI BG Polaris Rookery Caribou 210 (Fig. 2): 1) a reconnaissance explo - NW Arm Truro Cape Devon Island ration period (1960-1970) during Abbott W CD Laura Abbott E Tern W C which most surface showings on e Cornwallis Island h l l a i Muskox n n Cornwallis and Little Cornwallis g n Allen t o Bacon e n islands were found; 2) a discovery l period (1971-1979) during which Resolute Bay the Polaris orebody was drilled (Qausuittuq ) ait based on a gravity anomaly and Barrow Str feasibility studies were completed. Lanc aster Sound Also, new showings were discov - ered, and many showings received limited drill testing; 3) a production period (1980-1988), dominated by Seal drilling and mining at the Polaris Storm Cu Mine; 4) an ore-replacement explo - ration period (1989-2001) during Somerset Island which showings close to Polaris Typhoon were extensively drilled, showings on Cornwallis Island drill tested, and new showings found and Creswell drilled on Somerset and Bathurst islands and on the Grinnell Peninsula; and 5) a reclamation Prince of Wales Island period (2002-2004) during which Baffin Island Cu showing the mine site was restored and the Zn-Pbshowing infrastructure removed. Early studies on the Polaris deposit included a brief description of the geology and mineralization FIGURE 1. Lead-zinc-copper showings in the Polaris District, central Arctic Islands, Nunavut. LCI is Little by Muraro (1974), fluid inclusion Cornwallis Island. Some dots represent clusters of showings. Locations and sources are listed in Appendix 1. work by Jowett (1975), and lead isotope work on the Truro Island showing by Heal (1976). 1997), and controversial ideas related to the timing of fold - Kerr (1977) proposed a metallogenic model that required ing. Sharp et al. (1995a,b) produced a field-trip guide for the formation of karst during the Early Devonian Boothia Uplift, Polaris Mine. Savard et al. (2000) reported on fluid inclusion then migration of metal-bearing and sulphur-bearing fluids and isotopic data from the deposit and Dewing and Turner to the site of deposition during the Late Devonian. The karst (2003) looked at the relative ages of faults near Polaris. model guided exploration during much of the 1970s and Mineralization at Polaris was dated by paleomagnetics 1980s. Randell introduced a hydrothermal karst model (Symons and Sangster, 1992), and Rb-Sr dating of sphalerite (Randell, 1994; Randell and Anderson, 1997; Randell et al., (Christensen et al., 1995). Randell (1994), Disnar and

656 Synopsis of the Polaris Zn-Pb District, Canadian Arctic Islands, Nunavut

TABLE 1. Distribution of showings by formation. Phillips Embayment. The embayment received mostly grap - Formation # showings % of showings Com. tolitic shale and carbonates, but isolated microbial and coral- Bird Fiord (Dbi) 3 3.75 Zn microbial banks within the embayment kept up with sea Blue Fiord (Dbl) 15 18.75 Zn, Pb level rise at least until Early Silurian time (Wenlock). The Disappointment Bay (Ddb) 6 7.5 Zn, Pb shelf-to-basin transition was a ramp immediately following shelf retreat, but developed a steeper rimmed profile by late Prince Alfred (Dpa) 2 2.5 Zn, Pb, Cu Llandovery time (Early Silurian). The facies front is well Zn, Pb Barlow Inlet (Sbi) 2 2.5 exposed halfway up the eastern coast of Cornwallis Island. Cu Cape Storm (Scs) 5 6.25 Vertical movement along a narrow, north-south intracra - Zn, Pb Allen Bay (Osa) 8 10 tonic uplift running from Boothia Peninsula to Grinnell Thumb Mountain (Oct) 34 42.5 Zn, Pb Peninsula during Late Silurian to Middle Devonian Bay Fiord (Ocb) 2 2.5 Zn, Pb (Givetian) time produced unconformities and syntectonic Eleanor River (Oe) 2 2.5 Zn clastic sediments (the Boothia Uplift). This deformation Ship Point (Osp) 1 1.25 Zn probably was caused by stress transmitted cratonward from Total 80 100% the Caledonian Mobile Belt on East Greenland (Miall, 1986; Okulitch et al., 1986). Structures within the Boothia Uplift Héroux (1995), and Héroux et al. (1996, 1999) examined are characterized by broad synclines and narrow, evaporite- organic matter alteration from Polaris. cored anticlines (Thorsteinsson, 1986; Mayr et al., 1998). The margins of the anticlines contain abundant thrust faults Studies of individual showings apart from Polaris are (Fig. 4; Henrichsen, 2003; Jober, 2005). Dense, anastamos - restricted to showings in Devonian strata on Baillie ing arrays of subvertical normal faults with significant verti - Hamilton Island (Thorsteinsson, 1984), showings in cal offset characterize the western margin of the uplift on Devonian strata on Bathurst Island (Harrison and de Freitas, eastern Bathurst Island. 1996; Rose, 1999), the Rookery Creek showing on Cornwallis Island (Dewing and Turner, 2003), and the By early Middle Devonian time, the effects of plate con - ‘Bermuda’ showing on Grinnell Peninsula (Mitchell, 2000). vergence were widespread over most of the Arctic Islands. Shallow-marine and nonmarine syntectonic clastic rocks Geological and Tectonic Setting were deposited in a foreland basin adjacent to a southeast - ward- and southward-advancing deformation front. The Cambrian to Devonian strata of the Arctic Islands are a maximum preserved thickness of this clastic wedge is about mixed sedimentary-igneous succession, collectively referred 4000 m. Thermal maturity indicators in the area of the to as the Franklinian succession , which were deposited on a Boothia Uplift are generally low (conodont alteration index passive-to-convergent cratonic margin (Fig. 3; Trettin, of <2 and graptolite-based vitrinite equivalent reflectances 1991). The upper boundary of this succession is constrained of about 1% (Gentzis et al., 1996; Héroux et al., 1999)) indi - as latest Devonian or earliest Carboniferous, but the oldest cating that the clastic wedge could not have attained a great strata are not exposed. Trettin (1991) suggested that the mar - thickness over the Boothia Uplift. gin initiated following a widespread Proterozoic igneous event at 723 Ma (see Heaman et al., 1992). The oldest In the Arctic Islands, the youngest preserved strata are of exposed strata are late Neoproterozoic in age (Dewing et al., Famennian age. The Middle Devonian to earliest 2004). Carboniferous phase of deformation is known as the Ellesmerian Orogeny (Thorsteinsson and Tozer, 1970). East- Following Precambrian continental breakup, thick Lower west-trending folds that resulted from the Ellesmerian Cambrian clastics and carbonate rocks accumulated along Orogeny characterize Melville, Bathurst, and southern the rifted margin. The shelf-to-basin transition was estab - Ellesmere Islands. In the area of the pre-existing Boothia lished by Early Cambrian time (Trettin, 1994; Harrison, 1995). During the Cambrian and Ordovician, the Franklinian Discovery Ore-replacement shelf accumulated carbonates, evaporites, and continent- Exploration and feasibility Production exploration derived siliciclastic rocks. During this time, marked differ - 16000 Zinc price

ences in subsidence rates between shelf and basin produced 14000 2800 Z

Diamond Drilling i n an escarpment at the shelf margin (Trettin, 1994). The Polaris c

12000 2400 ( 1 ) Cambrian-Ordovician carbonate platform was bordered to Exploration 9 9 m ( 10000 2000 8 g the north by the shale-dominated Hazen Basin. U n S i l

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Cambro-Ordovician platformal strata pass southeast and o D l l 6000 1200 a south into the thin, undisturbed cratonic sedimentary cover. r s / t The boundary between these depositional realms occurs 4000 800 o n approximately at the southern and eastern boundaries of the ) 2000 400 Parry Island – Central Ellesmere fold belts. A hinge line

0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 0 0 exists between Somerset and Cornwallis islands; the 6 6 6 6 6 7 7 7 7 7 8 8 8 8 8 9 9 9 9 9 0 0 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 Cambro-Ordovician sedimentary succession thickens rap - 0 2 4 6 8 0 2 idly northward across this feature (de Freitas and Mayr, Year 1993; de Freitas et al., 1999). FIGURE 2. Exploration and ore-definition drilling in the Polaris District between 1960 and 2002. High zinc prices in 1974 and 1990 coincide with During latest Ordovician, the shelf margin retreated sub - new rounds of regional exploration. Historical zinc prices from Planchy stantially towards the south and southeast, forming the Cape (1998).

657 K. Dewing, R.J. Sharp, and E. Turner

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658 Synopsis of the Polaris Zn-Pb District, Canadian Arctic Islands, Nunavut

100° 98° 96° 94° 92°

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FIGURE 4. Generalized geological map of the central Arctic Islands, Nunavut, (after Okulitch, 1991). The base of the legend shows the time-stratigraphic dia - gram in Figure 3 colour coded to match this map legend. At the base of the diagram is a hypothetical cross-section B-B’ (shown by white line in the centre of the map). This presents a conceptual model (Henrichsen, 2003) that shows a Boothia structure with a thick, evaporite-filled core and thrusted carbonates on the flanks. No attempt was made to balance sub-Baumann Fiord units. Later extension reactivated some of the thrusts as normal faults and created small half grabens.

659 K. Dewing, R.J. Sharp, and E. Turner

50 Canadian MVT Deposits-Production showing indicate up to 2 Mt (diluted) at 7% Zn. No other Canadian MVT Deposits-Remaining Resource Prairie Creek showings had ore-grade intersections that could be corre - Polaris ) lated to nearby drillholes Monarch-Kicking Horse %

. Great Slave Reef t Eclipse 10 Nanisivik w

( Gays River Pine Point Esker Daniel’s Harbour Age n 1 0 Jubilee Seal Robb Lake Z ,0 0 + 0 Gayna River t b o n Goz Creek The age of sphalerite crystallization at Polaris has been n P e Upton s o f established as 366 ± 15 Ma, (Late Devonian to Early 1 P 0 b , + 1 1 0 Z 0 , 0 n 0 0 0 Carboniferous) based upon Rb/Sr isotopic ratios in spha - m , 0 ,0 0 0 0 e 0 ,0 0 ta 0 0 l 0 lerite (Christensen et al., 1995). This age is supported by a 1 0.1 1 10 100 1000 Late Devonian magnetic paleopole for the ore (Symons and Geological Resource (Mt) Sangster, 1992). Recent, as yet unpublished, work by FIGURE 5. Resources versus grade diagram for Canadian Mississippi Christensen indicates some showings (e.g. Dundas Island) Valley-type deposits and resources. Production at the Polaris Mine is have a Viséan (Early Carboniferous, 337 Ma) age, synchro - marked by red star. From Paradis et al. (this volume). nous with the opening of the Sverdrup Basin. Uplift, the Ellesmerian compression produced low-ampli - Deposit Morphology tude east-west folds locally forming an interference fold pat - tern with the pre-existing north-south Boothia folds. Host Rocks Rifting during the Early Carboniferous (Viséan) produced Four stratigraphic units are exposed around Polaris (Figs. the Sverdrup Basin to the north of the lower Paleozoic shelf 6, 7, 8). The oldest is the Middle Ordovician Bay Fiord margin. Regional extension related to the formation of the Formation, a 440 m thick succession of anhydrite and dolo - Sverdrup Basin may have reactivated older thrust faults stone. This is overlain by the Middle to Upper Ordovician within the Boothia Uplift as extensional faults creating half Thumb Mountain Formation, which, where unaltered, con - grabens locally on the leading edge of the older thrusts. sists of 340 m of carbonate. These shallow-water carbonates and evaporites are overlain by deeper water shale of the Mineral Deposits and Occurrences Irene Bay (60 m) and Cape Phillips (600 m) formations. The Deposit Types and Classification Thumb Mountain Formation hosts the mineralization at the Polaris Mine. There are two deposit types in the Polaris District: 1) structurally controlled, carbonate-hosted Zn-Pb-Fe The lower member of the Thumb Mountain Formation is deposits typical of the Mississippi Valley-type (MVT) approximately 250 m thick and consists of dolomitic lime - deposit, and 2) structurally and stratigraphically controlled, stone or dolostone. The basal 35 to 45 metres are composed carbonate-hosted Cu deposits enriched by later supergene of thick-bedded, burrow-mottled, lime- or dolomudstone and removal of Fe and S. This deposit type is not discussed in wackestone. Overlying strata of the lower member (approx - detail herein. imately 180 m) consist of medium- to thick-bedded, pale grey to brown, lime- or dolomudstone, peloidal grainstone, Deposit Distribution with lesser wackestone. Metre-scale cycles of mottled dolo - mudstone or wackestone overlain by plane-laminated or fen - The Ordovician Thumb Mountain Formation hosts most estral lime- or dolomudstone occur. The uppermost 10 to 30 of the Zn-Pb mineralization and includes the largest deposits m of the lower member of the Thumb Mountain Formation, at Polaris, Eclipse, and Truro. Consequently, the Thumb known as the Tetradium Interval, contain rare to abundant Mountain Formation has been extensively prospected. Tetradium (characterized by calcite-filled tubes with a 0.5 to Significant mineralization was found in the Devonian Blue 2.0 mm square cross-section). Fiord Formation only in 1995 (Harrison and de Freitas, 1996) and 14 of the 15 showings in that unit were found The upper Thumb Mountain Formation is approximately between 1996 and 2001. Copper mineralization is restricted 80 m thick. A basal chert marker (4-10 m thick) consists of to the Cape Storm, Prince Alfred, and Douro formations. thickly bedded, medium to dark brown, burrow-mottled skeletal wackestone with white-weathering silicified bur - Grade and Tonnage rows several centimetres in diameter. Above the Chert Before mining, the Polaris orebody contained a diluted in Marker, the upper Thumb Mountain Formation consists of situ ore reserve of 26 million tonnes grading 3.7% Pb and 30 to 40 m of burrow-mottled, medium-bedded skeletal 13.9% Zn based on an 8% combined Pb+Zn (cutoff over five wackestone with lesser interbeds of nodular, argillaceous metres). Total production at the end of mine life was 20.1 Mt lime mudstone and wackestone. This is followed by 15 to 20 of ore at 13.4% Zn and 3.6% Pb. This places Polaris in the m of massive to thick-bedded, fossiliferous wackestone con - upper echelon of individual carbonate-hosted Zn-Pb mines taining abundant macrofossils. The uppermost part of the in the world (Fig. 5). Thumb Mountain Formation consists of 20 to 25 m of argillaceous, nodular, skeletal wackestone with interbedded No other showing in the district was found to be economic green terrigenous mud. so their grade and tonnage are speculative. Teck Cominco estimated the Eclipse showing to contain 765,000 (undi - Within the upper Thumb Mountain at Polaris, and on luted) tonnes grading 0.89% Pb and 11.84% Zn, with a pos - western Cornwallis Island, is the organic-rich “Vr” Marker, sible additional 165,000 tonnes grading 0.07% Pb and 8.83% a 1 m thick wackestone bed with total organic carbon of Zn. Eclipse contains both sulphide and oxide ore making the between 0.5 and 1.5%, and containing abundant, dark orange recovery more difficult. Estimates of the size of the Seal to dark brown algal colonies up to 1.5 cm long and 0.5 cm 660 Synopsis of the Polaris Zn-Pb District, Canadian Arctic Islands, Nunavut high that are internally massive or 1300 m faintly laminated. The Irene Bay Formation is a 55 m thick Upper Ordovician Barlow U crinoidal grainstone Inlet Fm. sequence gradationally overlying 1200 m L f.g. sandstone the Thumb Mountain Formation. It consists of interbedded green mud - wackestone, brachiopods E stone, argillaceous grey-green trilobites, burrowed limestone, and massive to nodular 1100 m grey limestone. ? thin-bedded grey limestone with The Upper Ordovician to crinoids, brachiopods and graptolites Silurian Cape Phillips Formation I L has a lower Ridge Member (a N D 1000 m O D A thickly bedded dolomitic or cal - I I R P

careous wackestone that is 7-10 R

m), overlain by 600 to 2200 m of U L

n shale, argillaceous limestone, and I

o

i W

t

a S chert. A facies front on central 900 m O

m L r C-t thin-bedded, black graptolitic shale

o D

Cornwallis Island marks the transi - F U

s L

p

i

l

l tion from basinal Cape Phillips i

h

P K

Formation to the north to platfor - e

p C

a O mal strata of the Allen Bay, Cape C 800 m L

N C-cy

Storm, Douro, and Barlow Inlet E formations to the south. W Unconformably overlying Y

Ordovician or older Silurian strata R

E B nodular chert and dolostone are several Upper Silurian - Lower 700 m V O

Devonian alluvial conglomerate D cream to pink nodular carbonate N A

units that record the Boothia Uplift L L (Fig. 3; Miall and Gibling, 1978; thick-bedded dolostone A L L Thorsteinsson and Uyeno, 1980; 600 m I G

Muir and Rust 1982; de Freitas and H S

Mayr, 1993; Mayr et al. 1998). A Ridge Mbr

y

a

Conglomerate units are restricted B

e green shale with limestone interbeds

n

to regions in front of each Boothia- e

r

500 m I aged thrust fault. The Early Devonian Disappointment Bay U wackestone withReceptaculites and corals Formation overlies the conglomer - organic-rich limestone (Vr Marker; M-Vr)

ate, or forms the lowest Devonian thick-bedded brown limestone with chert (Chert Marker; M-Ch) n

400 m N o Tetradium Interval

unit where the conglomerate is i

t a

A m I

absent. This is, in turn, overlain by r

o F C

the dolomitic Blue Fiord and Bird n i

I

a

t n V

Fiord formations. Devonian units u o

M thin- to thick-bedded brown sit with an angular unconformity O

300 m b dolostone

m u on underlying Ordovician and D

h L T

Silurian units on Cornwall Island R

(Thorsteinsson, 1986), Little O Cornwallis Island (Turner and Dewing, 2004), and Grinnell 200 m

Peninsula (Mayr et al., 1998). thick bedded with chert andGonioceras (Lower Chert; L-Ch) Dimensions D green shale with brachiopods

n

o

i

t

a

Dimensions of the Polaris 100 m m

r

o deposit are 800 m strike length, F

d

r

o 300 m at its widest point, and a i B thin interbeds of carbonate mudstone

F

y and grey shale thickness ranging from 20 m in the a

B west to 100 m in the central por - tion. The deposit is blind, with the FIGURE 6. Stratigraphic column for Little Cornwallis Island. Ore at the Polaris Mine is hosted in the Thumb topmost ore lying 50 m below sur - Mountain Formation (red overlay). Cape Phillips Formation member C is divided on the basis of graptolites face on the west and up to 160 m into a cyrtograptid-bearing “C-cy” unit and a Bohemograptus tenuis bearing C-t unit.

661 K. Dewing, R.J. Sharp, and E. Turner

UPPER ORDOVICIAN TO UPPER SILURIAN CAPE PHILLIPS FORMATION 2800N 2400N 2000N 1600N 1200N 800N 400N thin-bedded grey limestone with crinoids, brachiopods and graptolitesparultimus to birchensis zones, 160 m thin-bedded, black graptolitic shale cy -sakmaricus to testis zones, 125 mt -dubius toz tenuis ones, 70m nodular chert and dolostone 2600E minor togriestonensis zones, 60m thin-bedded, black graptolitic shale fastigatusto sedgwickii zones, 115 m thick-bedded wackestone 7-10 m ORDOVICIAN- UPPER ORDOVICIAN

2200E green shale and nodular wackestone 55-60 m MIDDLE ANDUPPER ORDOVICIAN

nodular wackestone with Receptaculites Maclurites, coral. Chert marker atbase 80m dolomudstone, wackestone with ostracodes 1800E Tetradium zone (10-20m) at top. 260 m

Mineable ore Zn-Pbsurface projection Zn ddh intersection Dolomite distribution in upper Thumb Mountain Formation Oct-u is limestone 1400E Oct-u is mixed dolostone - limestone Oct-u is dolomite

Loon Geological contact

a

t

a Lake (defined / assumed)

D

o Fault N (defined / assumed) 1000E

al edge erosion No Data

600E

N 0 400 m

FIGURE 7. Geological map of Polaris Peninsula, Little Cornwallis Island. Plan of the mined ore shown in solid red. The limit of the drillholes containing an interval of >1% Zn are shown by a yellow line. The limits of completely and incompletely dolomitized upper Thumb Mountain Formation are shown by dashed lines and coloured dots. The mine grid is 23° east of true north. After Turner and Dewing (2004).

600E 800E 1000E 1200E 1400E 1600E

Crozier Strait O Scp -A OS cp-R

Oci

O ct-u -200 m

O ct-l

M Cape Phillips Formation - Thumb MountainFormation- -G Ore Body OScp Oci Irene Bay Formation Oct-l n -A Member A dol lower Green Marker

M - P f

OScp Ch 2 a

Cape Phillips Formation - Oct-uThumb Mountain Formation - Ocb-u Bay Fiord Formation- u l

-R t ridge-forming member dolupper Chert Marker dol upper m P1 i n w e Pan M a r ha a K n - s 3 dl G l e n t i e z e K d 2 K eel K1

FIGURE 8. Section through the Polaris Mine on mine grid 2100 N showing the outline of the mined ore, mineralized waste and the collapse of the marker beds in the orebody. The dolomitization outlines are after Randell (1994). No vertical exaggeration. Dominant lithotypes for each unit are on the legend for Figure 7. 662 Synopsis of the Polaris Zn-Pb District, Canadian Arctic Islands, Nunavut

TABLE 2. Ore grade by division within Polaris Mine. scattered lenses and sulfide vein systems to the north and Zone Pb+Zn Fe Zn/Pb south of the orebody. P2 16.5 4.6 3.1 Only the Eclipse and Seal showings have the pervasive P1 22.4 4.5 3.5 replacement of carbonate by sulphides, which is typical of K3 19.1 3.1 5.6 the high-grade ore at Polaris, but the solution breccias that K2 17.3 1.7 4.3 are so prominent at Polaris are poorly developed at Eclipse, K1 15.5 0.8 8.1 Seal, and at other showings. Similarly, the abundant marca - site that characterized Panhandle mineralization at Polaris is below surface on the east side. It forms a continuous sul - not present at Eclipse, Seal, Truro, or most other showings. phide body. Only the JG showing on Grinnell Peninsula contained a long drill intersection of marcasite with minor sphalerite, but The Eclipse showing is 700 m long, with a 300 metre long adjacent drillholes contained little or no sulphides. western portion that is about 70 to 100 m wide and an east - ern portion about 250 m long and 25 to 50 m wide, separated Mineralogy, Textures, and Ore Chemistry by a 150 m long central portion that appears to be poorly The Polaris orebody exhibits multiple generations of mineralized. The Seal Showing has a strike length of about dolomite and sulphide precipitation and of carbonate and 400 m, daylights to the southwest, and is 50 to 100 m wide sulphide dissolution. Details of the alteration are after and 12 to 20 m thick. Other showings range in size from 100 by 80 m (Dundas Island) to many that are <10 m across. Showings often occur in clusters of 5 to 10 spread parallel to strike over roughly 10 km. Nature of Sulphide Orebodies The Polaris orebody consists of two parts (Fig. 8). The Panhandle Zone forms the upper part of the deposit and is an elongate tabular Zn>Fe>Pb body, roughly concordant with the upper Thumb Mountain Formation, in which carbonate is almost completely replaced by sulphide. The Keel Zone occupies the lower and eastern part of the orebody and con - sists of a Zn>Pb>Fe vein stockwork. Five ore types were recognized: two ore types occur in the upper Thumb Mountain and three in the lower Thumb Mountain (Sharp et al., 1995b). P1 ore was the economically most important and formed a 10 to 30 m thick, high-grade Zn-Fe-Pb, tabular unit hosted in the basal part of the upper Thumb Mountain Formation. P1 ore consisted of massive, carbonate replacement, breccia- fill and vein sulphide averaging 4 to 5% Fe with up to 30% Fe (see Table 2). Overlying the P1 ore, above the major north-south structures defining the boundaries of the Keel graben, lie blocks designated as P2 ore. This ore is composed of numerous thin to 1m thick veins of sphalerite, marcasite, and galena oriented vertically, sub-perpendicular to bedding. Marcasite halos surround most P2 veins. Directly underlying the P1 tabular body is the high-grade K3 ore composed of complex, cross-cutting veins along with massive to dissemi - nated sulphide replacing Tetradium beds with 3 to 5% Fe. Differentiation between K3 and P1 ore was based mainly on lower iron contents of K3 versus the P1 ore. K2 ore under - lies the K3 unit and is composed of fracture-filling and vein FIGURE 9. High-grade ore samples from the Polaris Mine. Designators for sulphides with lesser replacement of carbonate, and local mine location in the keel mining areas are based on elevation and mine grid pods of mineralized brecciation carrying grades of 8 to 20% coordinates. They are level, in metres, with 1000 being sealevel and Pb+Zn and 1 to 2% Fe. The lowermost ore unit is K1 ore decreasing with depth, followed by, in metres, the latitude coordinate composed of fracture-filling and vein sulphides, is discon - divided by 10. Hence 850-176 refers to 850 level at 1760 north latitude. Keel stopes, all oriented east-west, mined the keel ore zone from 1720N or tinuous and of lower grade (10 to 15% Pb+Zn, 1 % Fe). This 172 stope in the south to 237 stope in the north at 2370 north latitude. (A) ore unit follows either the north-south (mine grid) axis of Marcasite replaced carbonate and banded sphalerite. 880 level by waterline mineralization or a northeast-southwest trend and is centred cutout. 7 cm wide. (B) Sphalerite-galena vein showing banded ore on either on lower stratigraphic horizons around a green marker bed in side and crystalline galena and sphalerite in the centre. 820 Bypass, 8 cm wide.. (C) Colloform and banded ore, 820-229, 8 cm wide. (D) Mineralized the lower Thumb Mountain Formation. To the east and west collapse breccia, 820-218, 8 cm wide. (E) Marcasite-rich ore showing col - of the orebody, sulfide mineralization dies out rapidly within lapsed fragments of banded sphalerite 880-185, 11 cm high. (F) Colloform 15 m of the ore boundaries. Sulfide feathers out into small, sphalerite with dendritic galena and minor dolospar, 730-205, 9 cm high.

663 K. Dewing, R.J. Sharp, and E. Turner

20 s e s y l 15 a n a f o

r 10 e b m u N 5

0 <-7 -6 -4 -2 0 +2 +4 +6 +8 +10 +12 +14 +16 +18 +20 +22 +24 +26 +28 +30 +32 +34 +36 +38 +40 +42 +44 +46 +48 +50 >50 δ 34S Sulphur isotope values (per mil)

SPHALERITE OTHER Grinnell Peninsula Cornwallis-LCI 5 Trigger Simba Rookery Stuart Barite Evaporite BK Aurora Truro Snowblind BAY FIORD FM. Shiells JG Eclipse Bacon +18 +20 Hornby Zn Liz Polaris AllenBranch +22 +24 +26 +28 +30 Dundas Stanley Head 5 Bathurst Somerset Island Bass Fault Typhoon Seal BAUMANN FIORD FM. Harrison Markham Pt Storm +18 +20 +22 +24 +26 +28 +30

FIGURE 10. Sulphur isotopes from sphalerite in the Polaris District colour coded by location. Data from Davies and Krouse (1975), Randell (1994), and Mitchell (2000), and as well as unpublished GSC data.

Savard et al. (2000). The alteration that extends farthest from (octahedral) cubes, or as thin, polycrystalline veins. Galena the orebody is brown, Fe-poor dolomite that replaces the δ34 S ranges from 1.0 to 9.4‰ with a median of 4.5‰. Low original limestone of the host Thumb Mountain Formation. α lead occurs in galena within the Panhandle ore. This mate - Crystal size of the replacement dolomite increases towards rial was separated and sold at a premium to silicon chip man - the core of the deposit. The replacement dolomite always ufacturers who used it to make solder in which the electrons contains some sphalerite or galena, thus is considered part of in the outer orbitals would not jump to the next-closest sol - the mineralizing event. Two types of sparry dolomite are rec - der. Marcasite typically replaces carbonate, is massive, and ognized: 1) white, saddle dolomite, which fills vugs and green-brass, but also occurs as small needles on dolomite, or fractures or that can grow replacively from finer grained as submillimetre blades and aggregates. Limited sampling of replacement dolomite. It is Fe poor and inclusion rich and marcasite for δ 34 S gives a range of 4.9 to 8.9‰. the bulk of the fluid inclusion homogenization temperatures Pyrobitumen is a common, though volumetrically small, range from 85 to 105°C; 2) white to pink, Fe-rich, inclusion- component of the deposit occurring in vugs as crusts or blobs poor saddle dolomite that fills vugs and appears to post-date up to 1 cm in diameter. It occurs on top of sulphides and the the white saddle dolospar. Most homogenization tempera - two sparry dolomite phases, but predates calcite phases. tures fall in the range of 80 to 105°C. The δ 18 O (SMOW) Native sulphur ranges up to 4 wt.% (S. Grasby, GSC- and δ 13 C (PDB) values for the replacement dolomite and the Calgary, unpublished data). Dating of pyrobitumen by Re-Os two types of saddle dolomite cluster tightly with δ 18 O = gives 368 ± 15 Ma, indicating that it is part of the mineraliz - -10.0 to –8.5‰ and δ 13 C = -1.5 to +1.0‰. 87 Sr/ 86 Sr ratios ing event (Selby et al., 2005). Other evidence for hydrocar - for replacement dolomite and the two sparry dolomite phases bon generation at Polaris is found in abundant bitumen (68% range from 0.70822 to 0.70948. This is above the range for of 125 organic matter separates contain bitumen), hydrocar - Middle Ordovician seawater (0.7078 to 0.7083; Savard et al., bon fluid inclusions, thermal maturity values indicating pas - 2000). sage into the oil window, and petrographic evidence for Sphalerite occurs as small subhedral crystals disseminated localized, direct transformation of alginite into bitumen in the host dolostone; within brecciated dolostone as fine (L.V. Stasiuk, pers. comm., 1992; Randell, 1994). aggregates, yellow, grey, brown, and black crystals, and light Barite is rare within the Polaris Mine, occasionally occur - to dark brown colloform masses and banded encrustations ring as 1 to 3 mm crystals sparsely coating sphalerite in vugs, (Fig. 9). Sphalerite δ 34 S values range from +2 to +13‰ with but commonly occurs in veins, along faults, or as pore-fill in a median of +9‰ (Fig.10; Randell, 1994). Laser ablation crinoidal grainstone for up to 10 km from the deposit. Barite studies on δ 34 S in colloform sphalerite from Polaris δ34 S values range from +36 to +58‰. It commonly occurs (Jaroslaw Nowak, unpublished data, see Fig. 9B) indicate with quartz. that each band shows a systematic variation from 8‰ in the There are at three phases of calcite that post-date the main colloform centre of the mass to 12‰ at the outer crystalline mineralizing event. The first is a fine-grained, grey calcite rim. Homogenization temperatures for sphalerite range from that appears to have grown at a fluid interface and is associ - 65 to 145°C with most of the data falling between 90 and ated with small needles of pyrite. The second phase of cal - 105°C. Ice melting temperatures indicate salinity in the cite consists of small, clear crystals less than 5 mm in length. range of 24.6 to 31.3 wt.% (NaCl + CaCl 2). Hydrocarbon The third phase consists of 2 to 5 cm, often doubly termi - inclusions are rare (<0.07 mol %; Savard et al., 2000). nated, brown crystals. Small crystals of brown sphalerite Galena occurs as small dendritic and skeletal intergrowths rarely occur between the second and third phases of calcite. within colloform sphalerite, and as cubes and truncated Homogenization temperatures for calcite range from 75 to

664 Synopsis of the Polaris Zn-Pb District, Canadian Arctic Islands, Nunavut

175°C with most of the data above 120°C. Ice melting temperatures indicate salinity in the range of 0.0 to 0.9 wt.% NaCl equiv. Calcite has δ18 O and δ 13 C values (PDB) of 5.0 to 25.4‰ and -25.1 to -5.1‰, respectively. 87 Sr/ 86 Sr ratios for replacement calcite range from 0.70796 to 0.70883 (Savard et al., 2000). Other Zn-Pb showings have simple paragenetic sequences and a subset of the ore textures seen at Polaris (Fig. 11). The smallest showings only contain fracture-fill - ing crystalline sphalerite (± galena, marcasite); larger showings exhibit some replacement of carbonate by sphalerite in addition to the frac - ture-filling phases; the largest showings (Eclipse, Truro) exhibit barite, marcasite replacement of carbonate, minor collapse breccias, banded aggregate and colloform sphalerite in addition to fracture filling and replacement crystalline sphalerite. Alteration Mineralogy/Chemistry Geology of Dolomitized Body The dolomite halo shows sharp margins on its downdip (east) and southern limits, but extends 550 m up dip where it is exposed on sur - face on the Polaris Peninsula (Figs. 7, 12; Sharp and Dewing, 2004). Carbonate beds in the overlying Irene Bay Formation are dolomi - tized directly over the orebody, but the upper surface of the dolomite halo drops to lower stratigraphic levels with increasing distance FIGURE 11. Alteration and sulphide textures from the Polaris District. Somerset Island: (A) Crackle and from the orebody. Thinning of the mosaic breccia with chalcocite and calcite. Storm showing ddh ST60 76.4 m. (B) Massive chalcocite cement - upper Thumb Mountain Formation ing brecciated Allen Bay Formation. Storm showing ddh ST60, 75.65 m (C) Solution breccia, Storm show - ing ddh ST60, 138.4 m (D) Storm Showing. Chalcopyrite and bornite in dolomite-lined vug being replaced and collapse of the overlying Irene by digenite. Storm showing ddh ST60, 45 m x10. Photo by N.S.F. Wilson, GSC Calgary. View is 5 mm wide. Bay Formation starts at the edge of (E) Pseudobrecciated Turner Cliffs Formation. Seal showing ddh AB95-2, 161 to 215 m. Dundas Island: (F) the dolomitized halo indicating the Sphalerite and marcasite on collapse breccia clast. Grinnell Peninsula: (G) Marcasite and trace sphalerite removal of some calcite material replacing carbonate. JG showing ddh 99-10, 34.0 m (H) Marcasite replacing brecciated carbonate and cemented by dolospar. Liz showing ddh LZ01, 18.4 m during the dolomitization. Collapse continues towards the centre of the event. Breccias are concentrated in certain stratigraphic deposit indicating that upper Thumb Mountain Formation intervals away from the orebody, but become thicker and continued to be thinned even after it was dolomitized. The coalesce towards the orebody. There is a general (though not Thumb Mountain Formation is thinned by 50% in the ore - infallible) progression from pseudobreccia and crackle brec - body (Figs. 8, 12). Few beds within the dolomite halo escape cia to collapse or solution breccia towards the core of the dolomitization; even apparently impermeable lime mudstone orebody (Fig. 12). Collapse breccias are common within the beds are dolomitized. All beds outside of the dolomitized orebody but pervasive overprinting and replacement by zinc- halo are limestone in the vicinity of Polaris. lead-iron sulphide mineralization makes it difficult to recog - Breccias occur only within the dolomitized halo around nize carbonate textures. the orebody and always contain at least some mineralization. The gradation from pseudobreccia to crackle breccia to Brecciation is thus considered to be part of the mineralizing collapse or solution breccia towards the orebody is presum -

665 K. Dewing, R.J. Sharp, and E. Turner

mineralized crackle breccia replacing pseudobreccia

mineralized collapse breccia cracklebreccia replacing crackle breccia from internal collapse of pseudobreccia pseudobrecciabed

unmineralized pseudobreccia complete sulphide replacement of carbonate Edge of mineable ore Edge of dolomite clasts

2700 N 2600 N 2500 N 2400 N 2300 N 2200N 2100N 2000 N 1900N 1800N 1700 N 1600 N 1500N 1400 N 1300N 1200 N 1100N 1000 N 900 N 800 N 700 N

OScp-B OScp-A

Loon Thumb Mountain Formation- Collapse Breccia Lake Oci Irene Bay Formation Oct-l SOUTH dol lower CENTER Green Marker Crackle Breccia SHOWING SHOWING NORTH Oct-1 Oct-u Thumb Mountain Formation - Pseudobreccia SHOWING dol upper Chert Marker

FIGURE 12. Lower part: Long section through Polaris Mine hung on the base of the Chert Marker (M-Ch) showing distribution of dolomitization and brec - cia types. Note the thinning of the upper Thumb Mountain Formation starting at the edge of the dolomitization and continuing towards the centre of the ore - body. Section length 2000 m, location shown on inset map. No vertical exaggeration. Upper part: Schematic figure showing the distribution of breccia fab - rics within the upper Thumb Mountain Formation at Polaris Mine (roughly between 1400 and 1650 N). Pseudobreccia forms in porous beds far from the ore - body and grades into crackle and collapse breccia closer to the ore. x2 vertical exaggeration.

ably a result of increasing dissolution. Pseudobreccia is illite/smectite>chlorite; 2) the background clay mineral formed in porous and permeable beds where acidic fluid assemblage for the Thumb Mountain Formation is migrating away from the site of ore deposition began to illite>chlorite>interstratified illite/chlorite; 3) the Irene Bay remove carbonate. Removal of carbonate reduced the Formation and less commonly the uppermost part of the strength of the pseudobrecciated beds and these began to col - Thumb Mountain Formation contains a background chlorite- lapse. Crackle breccia formed as blocks of pseudobreccia corrensite assemblage (chlorite+corrensite+chlorite/smectite crumbled and settled into the newly created void space and mixed layer)>illite, interstratified with illite/smectite; 4) as undissolved beds adjusted due to the overall thinning of directly over the main orebody in the upper part of the the Thumb Mountain Formation. The increasingly porous Thumb Mountain and in the Irene Bay formations is a pure and permeable crackle breccia zones were then further dis - illite facies (with traces of chlorite) containing well crystal - solved creating solution and collapse breccias (Fig. 12). lized illite with few swelling layers; 5) within 250 m of the Pseudobreccia is only recognized on the fringes of the ore in the Thumb Mountain Formation is a coarse kaolinite dolomitized halo as it has been overprinted by more intense assemblage. It contains kaolinite and illite, with some traces brecciation and mineralization closer to the orebody. of chlorite. The kaolinite to illite ratio is always much higher in the 2 to 16 micron fraction than in the <2 micron fraction. Clay Mineral Assemblages Scanning electronic microscopy shows that this kaolinite is There is a zonation of clay mineral assemblages within present as large vermicules filling the porosity in dolostone; the host rocks away from the ore (Fig. 13; Héroux et al., 6) within 1000 m of the orebody in the Thumb Mountain 1996, 1999). Six clay mineral assemblages are present: 1) Formation is a fine kaolinite assemblage containing illite and the background sedimentary clay assemblage in the Cape kaolinite with trace chlorite. The illite to kaolinite ratio is Phillips Formation consists of illite>interstratified

666 Synopsis of the Polaris Zn-Pb District, Canadian Arctic Islands, Nunavut

Ro-Vi.eq. graptolite reflectance at base (%) form of cryptocrystalline quartz, minor sphalerite, and of Cape Phillips Formation OScp 1.3 galena, were deposited at the margins of the alteration sys - -A tem. The second event was minor dissolution and dedolomi - 1.0 OScp-R Chlorite tization of dolomite, dissolution of galena, and precipitation Illite Co / Oci rrensite of zinc oxides, covellite, chalcocite, bornite, native copper, (background Oct-u Coarse Fine 0.7 for base of Kaolinite Kaolinite iron oxide, and malachite. Bornite, covellite and chalcocite Ore Cape Phillips) backgr replace pyrite and chalcopyrite and fill fissures within the cl ound Oct-l ay mine rals 0 500 1000 0.4 rock. These copper minerals were subsequently altered to Distance from ore body (m) malachite and azurite. Calcite precipitation accompanied the FIGURE 13. Schematic long section through the Polaris Mine showing the second event. distribution of clay mineral assemblages and graptolite reflectance in the The copper mineralization in the Polaris district is thought overlying Cape Phillips Formation. Stratigraphic column shown on the left (north) side. Details in Randell (1994) and Héroux et al. (1996). to be directly associated with the main zinc mineralizing event because 1) Zn-Pb mineralization occurs with or over - about the same in the less than 2 micron fraction as in the 2 laps copper mineralization and 2) both were formed by to 16 micron fraction. saline brines of similar composition and temperature. Copper mineralization occurs at the contact between the Organic Matter Alteration Allen Bay and Cape Storm formations, possibly reflecting a Reflectance of organic matter (R o) in the impermeable local source of metals. Cape Phillips and Irene Bay formations near the ore shows higher values than away from the ore (Fig. 13; Randell, Structure and Deformation 1994; Héroux et al., 1996, 1999). Above the orebody, grap - The primary control on the location of showings within tolites in the Cape Phillips Formation exhibit a R o of 1.35%, the Polaris District is structural. Mineralization occurs in twice the expected background value (R o=0.7%) for this four distinct structural settings: 1) along strike-slip and tear lithostratigraphic unit as determined from remote diamond faults that separate the east margin (Harrison, Agpan, drillholes and outcrops. R o values from the Irene Bay Aquarius showings) and west margin (Liz-Tiger-Simba, BK, Formation are also 50% higher than background above the Trigger) of the Boothia Uplift from the adjacent Parry Island ore zone. These values decrease away from the ore, attaining and Central Ellesmere fold belts; 2) in grabens and half background values at 1.2 km radius from the mine. In con - grabens along extensionally reactivated, Boothia-aged thrust trast, Ro values from the upper Thumb Mountain Formation faults (Eclipse, Rookery, Hornby, Dundas, Abbott, Bacon); within the ore deposit are 20% lower than the expected R o 3) in the axial region of east-west trending anticlines (Stuart background (R o=0.5% rather than 0.75%). This “suppres - River, Caribou, Baillie Hamilton, high-grade zones within sive” effect is also shown by decreasing Ro values with Polaris Mine); and 4) on an east-west-trending fault on depth. The difference between the lowest and the highest R o Somerset Island marked by a line of small grabens and facies values, occurring respectively near the bottom and the top of change (Seal, Storm). This structure directly lines up with at the same diamond drill, is twice the lower value. the southern bounding fault of the Proterozoic Borden Basin on Baffin Island and thus is presumably the reactivation of Cu-Rich Mineralization and Associated Alteration basement faults reflected in the overlying Paleozoic strata. Alteration at the copper-rich showings at Storm and There is a second-order, stratigraphic control on the loca - Hornby Zn includes fracturing to crackle breccia; small tion of mineralization within the sedimentary pile and on the zones of mosaic packbreccias with calcite, pyrite, and subor - mineralogy of the showing. Limestone units that are overlain dinate chalcocite cement; pervasive hematite staining; and by less permeable shale, evaporite, or argillaceous dolostone rare malachite/chalcocite on fractures. Mineralization is usu - units are preferentially mineralized. These include the ally accompanied by medium to coarsely crystalline dolomi - Thumb Mountain, Blue Fiord, and Allen Bay formations. tization and local dedolomitization of the host lithology; Cu-Fe±Zn-Pb mineralization (Storm Cu, Hornby Cu, minor sparry dolomite; pockets of silicification; limonite Eclipse, Tern Lake) occurs only within Silurian strata, either staining and hematization; crackle and mosaic breccias with at the contact between the Allen Bay and overlying Cape solution-rounding clasts. Chalcocite and bornite are the most Storm formations (Storm, Tern Lake), or where Early common copper sulphides, with lesser chalcopyrite (Fig. 11). Devonian synorogenic clastic strata overlie Silurian strata Accessory copper minerals include cuprite, covellite, and (Hornby Cu, Eclipse). native copper. Malachite and azurite occur as surface stain Two showings on eastern Cornwallis Island located along and are associated with iron oxides in drill core. Pyrite is the the shelf margin contact between the basinal Cape Phillips main non-copper sulphide but small veins of sphalerite and Formation and the platformal Barlow Inlet Formation (Laura galena occur. Fluid inclusion homogenization temperatures Lakes and Cape) have no obvious associated structures and on sparry dolomite yield 100 to 120°C and ice melting tem - appear to be stratigraphically controlled showings. peratures indicate salinities >35 wt.% NaCl eq. Sphalerite has a δ 34 S value of 8.5 ‰, whereas two samples of chal - Genetic Models cocite yielded δ 34 S values of –9.5 and +10.7 ‰. The model for the Polaris deposit (Fig. 14) invokes a Two diagenetic events are documented at the Storm show - source of metal ions within the stratigraphic column, since ing. The first was dolomitization accompanied by precipita - strontium or lead isotopes show no indication of basement or tion of pyrite, chalcopyrite, and lesser bornite. Silica, in the basal clastics being involved. Metals are then carried in sul -

667 K. Dewing, R.J. Sharp, and E. Turner

Barite amorphous colloform sphalerite, followed by slower precip - δ34S = 40-60‰ itation of crystalline sphalerite as the gas cap is depleted and gas slowly produced by ongoing bacterial sulphate reduc -

A tion. QUI TARD dolomite δ 34S This model fails to explain many of the showings on = 5- 6 B 15‰ ORG 0 S ANIC Grinnell Peninsula, at the Seal deposit on Somerset Island, or -8 R RICH 0 o 34 limestone C at Bass Point on Bathurst Island, where the δ S of sphalerite H S 2 is about the same as marine sulphate (25 to 30‰). These

ls

a t

e showings also lack barite and some have sphalerite in calcite

m & veins. Grinnell and Somerset are beyond the northern or 34 Ba 4 δ S = 25‰ y Fi O southern limits of the Baumann Fiord and Bay Fiord evapor - ord S A nhy ites and may reflect the long distance transport of thermo - drit Pb,Zn,Fe <140oC e chemical sulphate reduction generated gas. If so, the δ 34 S of individual crystals should be homogeneous. FIGURE 14. Genetic model for the Polaris Mine showing the origin of metal and sulphate-rich fluids in the sedimentary pile, transport as a single fluid Exploration Methods to site of ore precipitation, reduction and fractionation by bacterial sulphate Historical reduction (BSR), combination of isotopically light H 2S and metal ions to form ore and create acidic fluids, and expulsion of isotopically heavy sul - Exploration cycles in the district typically started with phate to produce a barite halo. Legend as for Figure 8. prospecting, stream sediment heavy mineral sampling, and more recently, airborne hyperspectral surveys. These activi - phate-rich brines through aquifers deep in the stratigraphic ties have been followed by property-scale mapping, soil column. Driven by an orogenic process, either the Late sampling, clay and thermal maturity analysis, gravity, IP, and Devonian Ellesmerian Orogeny or the mid-Carboniferous magnetic surveys. Targets identified were then drilled. opening of the Sverdrup Basin, circulating fluids rose along Geological techniques have focused on property-scale faults until they encountered the organic-rich, permeable mapping of alteration indicators, such as the distribution of Thumb Mountain Formation limestone overlain by the dolomite, carbonate dissolution fabrics, barite, and sulphide impermeable Irene Bay Formation shale. occurrences and textures. Stream sediment heavy mineral Bacterial sulphate reduction reduces sulphate to H 2S sampling has proven effective in locating showings, but soil using the abundant algal organic matter in the upper Thumb sampling often gives results that are hard to interpret, pre - Mountain Formation as a reductant. The resulting H 2S has a sumably due to the lack of soil development and chemical 34 shift in δ S values of -15‰ (Fig. 10). The H 2S reacts inor - weathering in the permafrost zone. Clay mineral and organic ganically with zinc, lead, and iron ions to produce sulphides matter alteration techniques (described above; Héroux et al., 34 with a δ S value of about 10‰. Released hydrogen ions dis - 1999) are effective in locating showings and providing vec - solve carbonate resulting in dissolution breccias and other tors to the area of maximum alteration. Airborne hyperspec - dissolution fabrics. It is proposed that excess sulphate was tral surveys employed by Noranda on Grinnell Peninsula expelled from the system and produced a halo of barite up to located numerous new showings, but other airborne tech - 34 10 km from the deposit with δ S values of 40 to 60‰. niques (e.g. EM) failed to locate any new showings. The Evidence of a temporal link between barite and ore is based Polaris Mine responded well to IP and gravity surveys, with on one sample from the 930-124 stope at Polaris that has a whopping 2.2 milligal residual gravity anomaly over the sphalerite that pre- and post-dates barite, proximity to deposit, although the gravity anomaly is influenced more by Polaris (barite is common only on southern Little Cornwallis the large body of dolomite within limestone rather than sul - Island), heavy sulphur isotope values, and occurrence with phide within dolomite. IP located the Polaris deposit, but marcasite. 1000 Temperatures measured from fluid inclusions and inferred Exploration Feasibility Production Exploration from the thermal maturity data indicate a range of 80 to 105°C. This is the appropriate range for bacterial sulphate s 136 ) g . n

i 100 reduction (Machel et al., 1995). Thermochemical sulphate m

u 82 w c o ( h s reduction is unlikely to have been active since 1) the tem - d f e r o e r peratures are too low (≥140°C is needed); 2) there is no v e o b c

13 s m blocky calcite with strongly negative δ C values, which is i Polaris u d (orebody) typically produced during thermochemical sulphate reduc - n 10

tion; 3) there is fractionation of the sulphur isotopes, a Polaris process that does not occur during thermochemical sulphate (north showing) 34 Eclipse reduction (Machel et al., 1995); and 4) the δ S in individual 1 sphalerite masses is inhomogeneous, typically showing a 1960 1980 2000 2020 2040 variation from 8‰ in the colloform centre of the mass to Year 12‰ at the outer crystalline rim. Presumably this reflects FIGURE 15. Graph of number of known showings versus year of discovery. pulses of fluid activity, with bacterial sulphate reduction pro - Eighty-two showings are known and the best-fit curve indicates that as ducing a gas cap with strongly fractionated H 2S, followed by many as fifty showings remain to be found. the introduction of metal-rich brine, rapid precipitation of

668 Synopsis of the Polaris Zn-Pb District, Canadian Arctic Islands, Nunavut

10 ° 9 ° ° ° ° elsewhere in the district has pro - 0 8 96 94 92 anticline axis - mapped at surface vided numerous false positives due PARRY CENTRAL reverse or thrust fault - mapped at surface ISLANDS ELLESMERE to salt-water lenses (taliks) within ° - inferred under water 77 FOLD FOLD BELT 77° the permafrost and remains of BELT normal fault - mapped at surface uncertain value. - inferred under water

11 CARBONIFEROUS & PERMIAN

Potential for New Targets T Sverdrup Basin F

I 10 L DEVONIAN Exploration potential exists for P

U Ellesmerian clastics Devon Is. additional deposits within the A I DEVONIAN 76° H above unconformity Polaris District. The curve showing T 76° O SILURIAN & DEVONIAN number of known showings versus O 9 year indicates that many showings B conformable base

D

e ORDOVICIAN & SILURIAN remain to be found (Fig. 15). The v 12 o basinal and platformal rocks

n

I difficult logistics and short summer s CAMBRIAN to ORDOVICIAN

l 7 8 a n passive margin carbonate &

season often governed exploration d 6 evaporite rocks instead of geology, so undiscov - 3 ARCHEAN 75° 5 75° metamorphic basement ered showings could be significant. Bathurst Prospect The district may respond well to Is. 4 a second exploration cycle built on more sophisticated exploration Cornwallis Is. 1) Cu and Zn along the Aston-Batty line 2) Cu and Zn on structures parallel to the Aston- techniques. Exploration starting Batty line with hyperspectral surveys to iden - 3) Cu at Allen Bay - Cape Storm contact on structures parallel to the Aston-Batty line on tify areas of iron oxides, barite, and 74° T 2 74° southwestern Devon Island F clay mineral alteration could be I L 4) Cu at Allen Bay - Cape Storm contact along followed by thermal maturity sam - P U structure from Bacon Zn showing A pling spatially associated with I 5)Underexplored Devonian -filled graben at Taylor

H 1 potential structurally controlled T River O 6) Under-explored prospects at CD and Northwest fluid conduits, pathfinder geo - O B Arm (BHP, DIAND Assessment Report chemical surveys (Zn, Pb, Cd, Cu, No. 083639) Ba, Fe), and then the more tradi - 73° 73° 7) Under-explored prospect at Rookery Creek tional methods described above. 8) Unexplained thermal anomaly at Victor Creek 9) Under-explored Devonian-filled graben on Baillie Highest priorities for additional Prince of Wales Is. Somerset Is. Hamilton Island exploration (Fig. 16) should be 1) 10) Liz-Simba trend of mineralization poorly explored, Devonian-filled 11) Icefield fault zone and associated Devonian- half grabens at Rookery Creek, 0 100 filled grabens km 12) Buried Thumb Mountain Formation on Eastern Taylor River, and Eleanor River on Bathurst Island Cornwallis Island; on Baillie 100° 98° 96° 94° 92° Hamilton Island; and along the FIGURE 16. Prospects for Zn-Pb or Cu potential within the Polaris District that these authors consider to have Icefield fault on Grinnell high potential. Peninsula; 2) Liz-Tiger-Simba trend on Grinnell Peninsula; 3) carbonate-hosted, copper- mal basin that developed and accommodated evaporites of rich showings associated with the Allen Bay-Cape Storm the Bay Fiord Formation may have resulted from the onset formational contact in the vicinity of faults northeast of of subduction under the North American continent and the Resolute Bay, and on structures parallel to the Aston-Batty associated drag from the down-going slab. The “Melville Line on Somerset Island and on southern Devon Island; and Arch” (Figs. 3, 17) might have been the resulting peripheral 4) unexplained thermal anomalies at Victor Creek northeast - bulge. ern Cornwallis Island described by Héroux et al. (1999), and Knowledge Gaps 5) buried Thumb Mountain Formation on eastern Bathurst Island The following knowledge gaps need to be addressed for There is another, as yet untested, deposit model for a sep - effective future exploration: arate type of lead-zinc mineralization in the district. Mapping Absolute dating of the Nanisivik deposit on northern Baffin Island (Sherlock et al., 2003) has yielded a Middle • 1:50 000 mapping is required on Cornwallis Island to Ordovician age (461 Ma or Chayzan) for the mineralization locate small, Ellesmerian-aged structures that are and associated alteration of volcanic dykes. This result, beyond the resolution of the current 1:250 000 map. while controversial, indicates that some potential exists for These structures controlled fluid flow at Polaris and on iron-rich, carbonate-hosted deposits in areas that overlie the northeast Cornwallis Island (Jober, 2005). Locating ancestral Borden Basin (Fig. 17). The age of mineralization these potential fluid conduits would help target explo - as determined by Sherlock et al. (2003) is synchronous with ration. the deposition of the Bay Fiord Formation. The intraplatfor - • 1:50 000 mapping is required on Somerset Island in the

669 K. Dewing, R.J. Sharp, and E. Turner

Precambrian tectonic elements • Organic matter studies to 1) characterize hydrocarbon Mesoproterozoic basins (subsurface/exposed) generation around the Polaris deposit and perform mass 75° ? A-B Aston-BattyLine ? balance calculations; and 2) continue mapping thermal BORDEN BASIN maturity indicators to look for buried orebodies in areas A ? of exploration interest. B Geophysics

e n • Higher resolution regional gravity and aeromagnetic o Z FURY &HECLA ic BASIN surveys would better locate basement structures that n o 70° t d c u partially control structures in overlying Paleozoic strata. e a y T M k a n n c B • Shallow seismic surveys of Pb-Zn prospects using a o l e o e e e l B e h u tt k low-energy source may offer an alternate way to pin - T Q i c m lo m B point drill targets. o 500 km C Acknowledgements 100° 90° 80° The authors thank Michael Gunning, Victoria Yehl, Chris N S Harrison, and Wayne Goodfellow for the many suggestions they made to improve this paper. TeckCominco Ltd. is Cambrian-EarlyOrdovician Neoproterozoic warmly thanked for providing data on the Polaris, Storm, 480 Ma Truro, and Eclipse deposits, as well as for logistical support Early Ordovician in 2001. Polar Continental Shelf Project and Technical Field and Support Services, both of Natural Resources Canada, helped with logistical support. References sub ducti Christensen, J.N., Halliday, A.N., Leigh, K.E., Randell, R.N., and Kesler, ng sl ab S.E., 1995, Direct dating of sulphides by Rb-Sr: A critical test using the 460 Ma MiddleOrdovician Polaris Mississippi-Valley-type Zn-Pb deposit: Geochimica et Cosmochimica Acta, v. 59, p. 5191-5197. Davies, G.R., and Krouse, H.R., 1975, Sulphur isotope distribution in Paleozoic sulphate evaporites, Canadian Arctic Archipelago: FIGURE 17. Top. Distribution of Precambrian tectono-stratigraphic ele - Geological Survey of Canada, Report of Activities 75-1B, p. 221-225. ments and their inferred distribution below the Paleozoic cover (modified de Freitas, T.A., and Mayr, U., 1993, Middle Paleozoic tear faulting, basin from Jackson, 2000). Outcrops of Proterozoic sedimentary basins in red. development, and basin uplift, central Canadian arctic: Canadian Location of Proterozoic sedimentary basins in blue. Nanisivik Mine shown Journal of Earth Science, v. 30, p. 603-620. by yellow star. Line A-B shows location of Aston Batty Line on northern Somerset Island. Bottom. Possible configuration of the northern margin of de Freitas, T.A., Trettin, H.P., Dixon, O.A., and Mallamo, M., 1999, Silurian Laurentia in the Early and Middle Ordovician showing the postulated onset System of the Canadian Arctic Archipelago: Bulletin of Canadian of subduction below Laurentia and the formation of an intraplatformal basin Petroleum Geology, v. 47, p. 136-193. (Bay Fiord Formation) and a peripheral bulge. Dewing, K., and Turner, E., 2003, Structural Setting of the Cornwallis Lead- Zinc District, Arctic Islands, Nunavut: Geological Survey of Canada, area of the Aston-Batty Line to better define its location Current Research. B-4, 9 p. Dewing, K., Harrison, J.C., Pratt, B.R., and Mayr, U., 2004, A probable Late and look for additional alteration indicators. Neoproterozoic age for the Kennedy Channel and Ella Bay formations, • Mapping and prospecting in stratigraphy younger than northeastern Ellesmere Island and its implications for passive margin the Middle Ordovician Thumb Mountain Formation. history of the Canadian Arctic: Canadian Journal of Earth Sciences, v. The Allen Bay-Cape Storm contact in the vicinity of 41, p. 1013-1025. Disnar, J.R., and Héroux, Y., 1995, Dégradation et lessivage des hydrocar - faults on Somerset, Cornwallis, Grinnell, and Devon bures de la formation ordovicienne de Thumb Mountain encaissant le islands may be analogous with the Storm copper show - gîte Zn-Pb de Polaris (Territoires du Nord-Ouest, Canada): Canadian ing and should be revisited. Journal of Earth Sciences, v. 32, p. 1017-1034. Gentzis, T., de Freitas, T., Goodarzi, F., Melchin, M., and Lenz, A.C., 1996, • The Devonian stratigraphy is complex and poorly Thermal maturity of lower Paleozoic sedimentary successions in Arctic understood. New data on the age of the base of each Canada: American Association of Petroleum Geologists Bulletin, v. 80, subbasin are desirable. Many of the Devonian-filled half p. 1065-1084. grabens on Cornwallis, Grinnell, and Bathurst islands Harrison, J.C., 1995, Melville Island’s Salt-Based Fold Belt, Arctic Canada: have never been mapped in detail or prospected. Geological Survey of Canada, Bulletin 472, 331 p. Harrison, J.C., and de Freitas, T., 1996, New showings and new geological Geochemistry settings for mineral exploration in the Arctic Islands: Geological Survey of Canada, Current Research 1996-B, p. 81-91. • Geochemical characterization of the alteration halo Heal, G.E.N., 1976, The Wrigley-Lou and Polaris-Truro lead zinc deposits, should be improved as a guide to exploration: 1) chem - Northwest Territories: Unpub. M.Sc. thesis, University of Alberta, istry of dolomite associated with alteration versus Edmonton, Alberta, 172 p. Heaman, L.M., LeCheminant, A.N., and Rainbird, R.H., 1992, Nature and regional burial dolomite; 2) barite distribution; 3) hyper - timing of Franklin igneous events, Canada; Implications for a late spectral, PIMA and ASTER response of alteration prod - Proterozoic mantle plume and the break-up of Laurentia: Earth and ucts (barite, dolomite, clay); and 4) thermal alteration of Planetary Science Letters, v. 109, p. 117-131. organic matter across the district

670 Synopsis of the Polaris Zn-Pb District, Canadian Arctic Islands, Nunavut

Henrichsen, M., 2003, Structural geometry and kinematics of deformation Randell, R.N., 1994, Geology of the Polaris Zn-Pb Mississippi Valley-Type in the Stanley Head Region, western Cornwallis Island, Nunavut: Deposit, Canadian Arctic Archipelago: Unpub. Ph.D. thesis, University Unpub. M.Sc. thesis, University of British Columbia, Vancouver, of Toronto, Toronto, Ontario, 736 p. British Columbia, 147 p. Randell, R.N., and Anderson, G.M., 1997, Geology of the Polaris Zn-Pb Héroux, Y., Chagnon, A., and Savard, M., 1996, Organic matter and clay deposit and surrounding area, Canadian Arctic Archipelago, in anomalies associated with base-metal sulfide deposits: Ore Geology Sangster, D.F., ed., Carbonate-Hosted Lead-Zinc Deposits: Society of Reviews, v. 11, p. 157-173. Economic Geologists, Special Publication No. 4, p. 307-319. Héroux, Y., Chagnon, A., Dewing, K., and Rose, H.R., 1999, The carbon - Randell, R.N., Héroux , Y., Chagnon, A., and Anderson, G.M., 1997, ate-hosted base-metal sulphide Polaris deposit in the Canadian Arctic: Organic matter and clay minerals at the Polaris Zn-Pb deposit, Organic matter alteration and clay diagenesis, in Glikson, M., and Canadian Arctic Archipelago, in Sangster, D.F., ed., Carbonate-Hosted Mastalerz, M., eds., Organic Matter and Mineralisation: Thermal Lead-Zinc Deposits, Society of Economic Geologists, Special Alteration, Hydrocarbon Generation and Role in Metallogenesis: Publication No. 4, p. 320-329. Kluwer Academic Publisher, p. 260-295. Rose, S.R.A., 1999, Sedimentology and diagenesis of the lower Blue Fiord Jackson, G.D., 2000, Geology of the Clyde-Cockburn Land map area, north- Formation carbonates in a prospective Mississippi-Valley-type (Pb-Zn) central Baffin Island, Nunavut: Geological Survey of Canada, Memoir setting, Bathurst Island, N.W.T.: Unpub. M.Sc. thesis, University of 440. 303 p. Calgary, Calgary, Alberta, 172 p. Jober, S.-A. 2005, Structural geology of the Stuart River – Caribou Lake Sanford, B.V., and Grant, A.C., 2000, Geological framework of the region, eastern Cornwallis Island, Nunavut: Unpub. M.Sc. thesis, Ordovician System in the southeast Arctic Platform, Nunavut, in University of New Brunswick, Fredricton, New Brunswick, 104 p. McCracken, A.D., and Bolton, T.E., eds., Geology and Paleontology of Jowett, C., 1975, Nature of the ore-forming fluids of the Polaris lead-zinc the Southeast Arctic Platform and Southern Baffin Island, Nunavut: deposit, Little Cornwallis Island, N.W.T., from fluid inclusion studies: Geological Survey of Canada, Bulletin 557, p. 13-38. Canadian Institute of Mining and Metallurgy Bulletin, v. 68, p. 124- Savard, M.M., Chi, G., Sami, T., Williams-Jones, A.E., and Leigh, K., 2000, 129. Fluid inclusion and carbon, oxygen, and strontium isotope study of the Kerr, J.W., 1977, Cornwallis lead-zinc district; Mississippi Valley-type Polaris Mississippi Valley-type Zn-Pb deposit, Canadian Arctic deposits controlled by stratigraphy and tectonics: Canadian Journal of Archipelago: Implications for ore genesis: Mineralium Deposita, v. 35, Earth Sciences, v. 14, p. 1402-1426. p. 495-510. Machel, H.G., Krouse, H.R., and Sassen R., 1995, Products and distin - Selby, D., Creaser, R.A., Dewing, K., and Fowler, M., 2005. Evaluation of guishing criteria of bacterial and thermochemical sulfate reduction: bitumen as a 187Re-187Os geochronometer for hydrocarbon matura - Applied Geochemistry, v. 10, p. 373-389. tion and migration: A case study from the Polaris MVT deposit, Mayr, U., 1978, Stratigraphy and Correlation of Lower Paleozoic Canada: Earth and Planetary Science Letters, v. 235, p. 1-15. Formations, Subsurface of Cornwallis, Devon, Somerset, and Russell Sharp, R.J., and Dewing, K., 2004, Dolomitization and brecciation at the Islands, Canadian Arctic Archipelago: Geological Survey of Canada, Mississippi-Valley type Zn-Pb Polaris Mine, central Arctic Islands, Bulletin 276, 55 p. Nunavut, in Packard, J.J., and Davies, G.R., eds., Dolomites: The Mayr, U., Packard. J.J., Goodbody, Q.H., Okulitch, A.V., Rice, R.J., Spectrum - Mechanisms, Models, Reservoir Development: Canadian Goodarzi, F., and Stewart, K.R., 1994, The Phanerozoic Geology of Society of Petroleum Geology Core Conference, p. 27. Southern Ellesmere and Northern Kent Islands, Canadian Arctic Sharp, R.J., Ste-Marie, C.P., and Lorenzini, C., 1995a, Field study of Polaris Archipelago: Geological Survey of Canada, Bulletin 470, 298 p. Mine area, NWT, Canada, in Misra, K.C., ed., Carbonate-Hosted Lead- Mayr, U., de Freitas, T., Beauchamp, B., and Eisbacher, G., 1998, The Zinc-Fluorite-Barite Deposits of North America: Guidebook Series, v. Geology of Devon Island North of 76°, Canadian Arctic Archipelago: 22, p. 38-41. Geological Survey of Canada, Bulletin 526, 500 p. Sharp, R.J., Ste-Marie, C.P., Lorenzini, C., Leigh, K.E., Dewing, K., Héroux Miall, A.D., 1986, Effects of Caledonian tectonism in Arctic Canada: , Y., and Chagnon, A., 1995b, A field guide to the geology of the Polaris Geology, v. 14, p. 904-907. Mine, Little Cornwallis Island, Northwest Territories, Canada, in Misra, K.C., ed., Carbonate-Hosted Lead-Zinc-Fluorite-Barite Deposits Miall, A.D., and Gibling, M., 1978, The Siluro-Devonian clastic wedge of of North America: Guidebook Series, v. 22, p. 19-37. Somerset Island, Arctic Canada, and some regional paleogeographic implications: Sedimentary Geology, v. 21, p. 85-127. Sherlock, R.L., Lee, J.K.E., and Cousens, B., 2003, Geological and geochronological constraints on the timing of mineralization at the Mitchell, I., 2000, The Mineralising Fluids, Stable Sulphur Isotopes, and Nanisivik Zinc-Lead Mississippi Valley-type deposit, Northern Baffin Radiogenic Age of the Bermuda Pb-Zn showing, Nunavut, Canada: Island, Nunavut, Canada: Geological Association of Canada, Annual Unpub. B.Sc. thesis, University of Waterloo, Waterloo, Ontario, 65 p. Meeting, Vancouver, Abstract no. 124, 1 p. Muir, I.D, and Rust, B.R., 1982, Sedimentology of a Lower Devonian Stewart, W.D., 1987, Late Proterozoic to Early Tertiary Stratigraphy of coastal alluvial fan complex; the Snowblind Bay Formation of Somerset Island and Northern Boothia Peninsula, District of Franklin, Cornwallis Island, Northwest Territories, Canada: Bulletin of Canadian N.W.T.: Geological Survey of Canada, Paper 83-26, 78 p. Petroleum Geology. v. 30, p. 245-263. Symons, D.T.A., and Sangster, D.F., 1992, Late Devonian paleomagnetic Muraro, T.W., 1974, Lead-zinc mining on Little Cornwallis Island, in Wren, age for the Polaris Mississippi Valley-type Zn-Pb deposit, Canadian A.E., and Cruz, R.B., eds., Proceedings of the 1973 National Arctic Archipelago: Canadian Journal of Earth Sciences, v. 29, p. 15- Convention, Canadian Society of Exploration Geophysists, p. 230-234. 25. Nentwich, F.W., 1987, Stratigraphy and Sedimentology of the Ordovician Thorsteinsson, R., 1984, A sulphide deposit containing galena, in the Lower and Silurian Brodeur Group, Northern Brodeur Peninsula, Baffin Devonian Disappointment Bay Formation on Baillie Hamilton Island, Island, Unpub. Ph.D. thesis, University of Alberta, Edmonton, Alberta, Canadian Arctic Archipelago: Geological Survey of Canada, Paper 84- 457 p. 1B, p. 269-274. Nentwich, F.W., and Jones, B., 1989, Stratigraphy and sedimentology of ——— 1986, Geology of Cornwallis Island and neighbouring smaller Ordovician and Silurian strata, northern Brodeur Peninsula, Baffin islands, Canadian Arctic Archipelago: Geological Survey of Canada, Island: Bulletin of Canadian Petroleum Geology, v. 37, 428-442. Map 1626A, scale 1:250,000. Okulitch, A.V., comp., 1991, Geology of the Canadian Arctic Archipelago, Thorsteinsson, R., and Mayr, U., 1987, The Sedimentary Rocks of Devon Northwest Territories and North Greenland, Figure 2 in Trettin, H.P., Island, Canadian Arctic Archipelago: Geological Survey of Canada, ed., Geology of the Innuitian Orogen and Arctic Platform of Canada Memoir 411, 182 p. and Greenland: Geological Survey of Canada, Geology of Canada No. 3 (also Geological Society of America, Geology of North America, v. Thorsteinsson, R., and Tozer, E.T., 1970, Geology of the Arctic E). 1:2,000,000 scale, 1 sheet. Archipelago, in Douglas, R.J.W., ed., Geology and Economic Minerals of Canada: Geological Survey of Canada, Economic Geology Report Okulitch, A.V., Packard, J.J., and Zolnai, A.I., 1986, Evolution of the no. 1, p. 547-590. Boothia Uplift, Arctic Canada: Canadian Journal of Earth Sciences, v. 23, p. 350-358. Thorsteinsson, R., and Uyeno, T.T., 1980, Stratigraphy and Conodonts of Upper Silurian and Lower Devonian Rocks in the Environs of the Planchy, J., 1998, Zinc, in Sachs, J., ed., Metal prices in the United States through Boothia Uplift, Canadian Arctic Archipelago: Geological Survey of 1998: minerals.usgs.gov/ minerals/pubs/commodity/zinc/720798.pdf Canada, Bulletin 292, 75p. 671 K. Dewing, R.J. Sharp, and E. Turner

Trettin, H.P., 1969, Lower Paleozoic sediments of northwestern Baffin Trettin, H.P., 1994, Pre-Carboniferous Geology of the Northern Part of the Island, District of Franklin. Geological Survey of Canada, Bulletin 157, Arctic Islands: Hazen Fold Belt and Adjacent Parts of central Ellesmere 70 p. Fold Belt, Ellesmere Island: Geological Survey of Canada, Bulletin Trettin, H.P. (ed.) 1991: Geology of the Innuitian Orogen and Arctic 430, 248 p. Platform of Canada and Greenland: Geological Survey of Canada, Turner, E.C., and Dewing, K. 2004, Geology, Little Cornwallis Island and Geology of Canada no. 3 (also Geological Society of America, Geology Rookery Creek (Cornwallis Island), High Arctic, Nunavut: Geological of North America v. E), 569 p. Survey of Canada, Open File 1780, 1:50 000 scale.

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