ARTICLE

Paleomagnetic dating of magmatic phases at the Cantungtungsten deposit, Northwest Territories, CanadaK. Kawasaki and D.T.A. Symons

Abstract: The Cantung tungsten–copper (W–Cu) skarn orebodies are hosted by Proterozoic and Lower Cambrian metasedimentaryrocks next to the Cretaceous “Mine Stock” monzogranite. Paleomagnetic analyses of 283 specimens from the Open Pit scheelite–chalcopyrite orebody (17 sites) and from adjacent host rocks including the aplite dikes (11 sites) isolated a stable characteristicremanent magnetization (ChRM), mostly by alternating field and then thermal step demagnetization. The step demagnetizationresults along with rock magnetic analyses of the W concentrate show that the main remanence carriers are single- orpseudosingle-domain pyrrhotite, titanomagnetite, and (or) magnetite. There is no statistically significant difference at 95%confidence between the site mean ChRM directions for the W–Cu ore, the host rock, or the aplite dikes populations. This resultindicates that the intrusion of the Mine Stock is coeval with the genesis of the scheelite skarn ore and with dike emplacementto give an overall mean ChRM direction of declination 342.9°, inclination 82.0° (N = 22 sites, radius of cone of 95% confidence �95 =4.2°, precision parameter k = 54.7) that defines a paleopole at 76.2°N latitude, 212.2°E longitude (radius of cone of 95% confidenceA95 = 8.1°). This paleopole is concordant with the coeval 98 Ma North American paleopole at 92% confidence, which providesstrong evidence that the eastern Selwyn Basin has been an autochthonous part of North America since the mid-Cretaceous.

Résumé : Les gisements de skarns a tungstène–cuivre (W–Cu) de Cantung sont encaissés dans des roches métasédimentairesdatant du Protérozoïque et du Cambrien inférieur, a proximité du stock intrusif de monzogranite « Mine Stock » datantdu Crétacé. Des analyses paléomagnétiques sur 283 échantillons provenant du gisement nommé « Open Pit » de scheelite–chalcopyrite (17 sites) et des roches encaissantes adjacentes, incluant des dykes d'aplite (11 sites), ont permis d'isoler uneaimantation rémanente caractéristique stable (ChRM), principalement par alternance des champs puis par désaimantationthermique par étapes. Les résultats de la désaimantation par étapes, jumelés aux analyses magnétiques du concentré W,montrent que les principaux porteurs de la rémanence sont une pyrrhotite, une titano-magnétite et/ou une magnétite, adomaine unique ou pseudo-unique. Il n'y a pas de différence statistique significative, au niveau de confiance de 95 %, entre lesdirections moyennes de la ChRM pour le minerai W–Cu, la roche encaissante ou les populations de dykes d'aplite. Selon cerésultat, l'intrusion du « Mine Stock » est contemporaine de la genèse du minerai de skarns de scheelite et de la mise en place desdykes pour donner une direction moyenne générale de déclinaison de la ChRM de 342,9 °, d'inclinaison de 82,0 ° (N = 22 sites,rayon du cône de confiance a 95 % �95 = 4,2 °, paramètre de précision k = 54,7) définissant un paléopôle a une latitude de 76,2 °Net a une longitude de 212,2 °E (rayon du cône de confiance a 95 % A95 = 8,1 °). Ce paléopôle concorde avec le paléopôlenord-américain contemporain de 98 Ma avec un niveau de confiance de 92 %, ce qui fournit de fortes indications que le bassinSelwyn oriental forme une partie autochtone de l'Amérique du Nord depuis le Crétacé moyen. [Traduit par la Rédaction]

IntroductionThe 98–95 Ma Tungsten plutonic suite in the eastern Selwyn

Basin forms an �300 km long northwest-trending belt of plutonsin the western Northwest Territories (NWT) and eastern Yukonthat intrudes carbonate-rich rocks of the Selwyn Basin (Hart et al.2004; Rasmussen et al. 2007; Fig. 1). The Tungsten suite is char-acterized by the lack of large batholiths and the formation ofsmall to medium-sized circular plutons that are cut by late dikes(Rasmussen et al. 2011). The world-class scheelite–chalcopyriteskarn deposits at Cantung and Mactung are related to the Tung-sten suite intrusions. The Cantung deposit produced 6.21 Mt of orewith a grade of 1.65% WO3 from 1962 to 2009, and it still contains1.69 Mt of ore reserves with a grade of 1.17% WO3 (Fitzpatrick andBakker 2011; Rasmussen et al. 2011). Here, the first paleomagneticresults are reported from a tungsten–copper (W–Cu) skarn de-posit. Our first objective was to show that W–Cu skarn mineral-ization could be dated by paleomagnetism at the Cantung deposit.

Secondly, the Selwyn Basin has an apparently stable position asmiogeoclinal cover on the North American cratonic edge. How-ever, different tectonic scenarios have been suggested for theSelwyn Basin since the mid-Cretaceous (e.g., Symons et al. 2005;Enkin et al. 2006; Johnston 2008; Kawasaki and Symons 2012),which are based mostly on a small number of the paleomagneticstudies in the area. Symons et al. (2008) reported paleomagneticresults from the �97 Ma Ragged Pluton, another member of theTungsten Plutonic Suite. They concluded that the eastern SelwynBasin has been an autochthonous part of North America since themid-Cretaceous. Our second objective was to test their tectonicconclusion that the Selwyn Basin is autochthonous with NorthAmerica.

GeologyTwo major W–Cu orebodies have been found at Cantung: the

Open Pit and E-Zone orebodies (Fig. 2). The following brief

Received 8 July 2013. Accepted 31 October 2013.

Paper handled by Associate Editor Randolph Enkin.

K. Kawasaki. University of Toyama, Toyama-shi, Toyama, 930-8555, Japan.D.T.A. Symons. University of Windsor, Windsor, ON N9B3P4, Canada.Corresponding author: K. Kawasaki (e-mail: kkawasak@sci.u-toyama.ac.jp).

32

Can. J. Earth Sci. 51: 32–42 (2014) dx.doi.org/10.1139/cjes-2013-0119 Published at www.nrcresearchpress.com/cjes on 13 November 2013.

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Uni

vers

ity o

f Sy

dney

on

01/3

1/14

For

pers

onal

use

onl

y.

geologic description of the Cantung deposit is summarized fromreports by Blusson (1968), Cummings and Bruce (1977), Archibaldet al. (1978), Dick and Hodgson (1982), Mathieson and Clark (1984),Bowman et al. (1985), and Rasmussen et al. (2011).

The host rocks for the Cantung orebodies are Proterozoic andLower Cambrian metasedimentary rocks that include five majorlithologic units: (i) the lower argillite; (ii) the Swiss Cheese lime-stone; (iii) the ore limestone; (iv) the upper argillite; and (v) thedolomite (Fig. 2). The lower argillite is a member of the Protero-zoic Backbone Ranges Formation that is correlated to the Protero-zoic Hyland Group in the Cordillera. The lower argillite consists ofmetamorphosed thin laminated beds of dark gray mudstone tofine-grained sandstone. The Lower Cambrian Sekwi Formationoverlies the Backbone Ranges Formations and includes the SwissCheese limestone, ore limestone, upper argillite, and dolomitemembers. The Swiss Cheese limestone is up to 10 m thick, wasdeposited on an open shelf or carbonate ramp, and consists ofirregularly interbedded dolomitic siltstone and impure fine-grained limestone. Differential weathering of the unit has given ita strongly corrugated “Swiss cheese” appearance. Where contactmetamorphosed by the Mine Stock, the Swiss Cheese limestonehas been altered to a calc-silicate or siliceous hornfels. The LowerCambrian ore limestone member is �50 m thick and is composedof relatively pure, dark or vaguely laminated limestone with mi-nor dolomitic and argillitic horizons. The upper argillite memberis dark brownish-grey to black with interbedded carbonate and

pyritic shale lenses, and it contains interstratified medium- tocoarse-grained turbiditic quartzite horizons up to 3 m thick. Theuppermost member of the Lower Cambrian Sekwi Formation isthe dolomite member. It is �500 m thick and is composed ofinterbedded dolomite, sandstone, siltstone, limestone, and shale.These host rock strata rock have been deformed into a northwest–southeast-trending syncline within a regional overturned anti-cline; however, there are no controls on the absolute timing ofdeformation.

The skarn orebodies overlie the Mine Stock, a Cretaceous mon-zogranite, that intruded the folded and metamorphosed UpperProterozoic to Upper Paleozoic sedimentary rocks of the SelwynBasin. The skarn mineralization is located mainly next to frac-tures, faults, and lithological contacts, and it occurs as irregu-larly shaped pods or thin lenticular wavy bands. The Open Pitorebody is hosted in the upper Swiss Cheese limestone and theore limestone, and it consists predominantly of fine-grainedclinopyroxene–garnet skarn that is replaced by pyrrhotite, chal-copyrite, and scheelite. Pyrrhotite, the dominant sulphide min-eral at Cantung, is positively correlated with W grades. The OpenPit orebody is located �300 m above the E-Zone orebody. TheE-Zone skarn orebody is dominated by coarse-grained amphi-bole and biotite, and it is hosted in the ore limestone at theMine Stock – ore limestone contact. The E-Zone skarn includesfour major facies: (i) garnet–pyroxene; (ii) pyroxene–pyrrhotite;(iii) amphibole–pyrrhotite; and (iv) biotite–pyrrhotite. All four

Fig. 1. Regional map (modified from Hart et al. 2004; Symons et al. 2008). The box with dashed outline indicates the study area.

Terranes

Intermontane Belt

Yukon-Tanana

Cassiar

Selwyn Basin

Mackenzie Platform

Intrusive Suitesin Selwyn Basin

Legend

Tungsten

Mayo

contact

fault

Yukon-NWT border

major town

major tungsten deposits

N

Tombstone

km0 100

61o

62o

63o

138o 136o 134o 132o 130o 128o

Dawson

Whitehorse

Cantungdeposit

Mactungdeposit

Alaska

BritishColumbia

Yukon

NorthwestTerritories

70oN

60oN

70oN

60oN

150oW 140oW 130oW

150oW 140oW 130oW

HowardsPassdeposit

Kawasaki and Symons 33

Published by NRC Research Press

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Uni

vers

ity o

f Sy

dney

on

01/3

1/14

For

pers

onal

use

onl

y.

skarn facies contain disseminated pyrrhotite, quartz, chalcopy-rite, and scheelite. The Cantung mill uses both flotation andgravity circuits to separate scheelite from the gangue mineralsin the skarn, especially from magnetite and the sulphides includ-ing chalcopyrite and pyrrhotite that all have lower specific gravi-ties. The resulting concentrate contains 80 ± 5% scheelite (NorthAmerican Tungsten Corporation Ltd. 2011).

There are two monzogranite plutons of the Tungsten suite thatare exposed in the Cantung area. The Circular Stock is a cylindri-cal pluton that is located �650 m northwest of the mine. It con-tains rare skarn fragments. The Mine Stock is a flat-topped plutonthat consists of microcline, quartz, plagioclase, and biotite. Basedon the hydrogen and oxygen isotope data, Bowman et al. (1985)

suggested that the early skarn-forming fluids were mainly in equi-librium with either the monzogranite intrusion or the aplitedikes. Meteoric water was not a dominant component of the skarnfluids throughout most of the period of skarn development, al-though the possibility that the formation waters were isotopicallysimilar to the magmatic water cannot be ruled out.

Aplite dikes containing quartz, feldspar, and minor biotitecrosscut the Mine Stock, skarn orebodies, and sedimentary se-quence (Fig. 2). There is an empirical correlation between higherW grades and a series of aplite dikes, suggesting that these dikescould be used as indicators of pathways for W-bearing fluids, andtherefore, these intrusions might have been important in thegenesis of the Cantung mineralization (e.g., Rasmussen et al.

Fig. 2. Simplified cross section of the Cantung deposit (modified from Mathieson and Clark 1984). Scale: horizontal equals vertical.

monzogranite

aplite dikescheelite orebody

Tungsten suite

Dolomite

Swiss Cheese limestone

Upper argilliteQuartzite

Ore limestone

Lower argillite

0 100m

NS

Open Pit

E-Zone

fault

Mine Stock

Backbone Ranges FormationProterozoic

Sekwi FormationLower Cambrian

Cretaceous

GEOLOGIC COLUMN

LEGEND

contact

continue

34 Can. J. Earth Sci. Vol. 51, 2014

Published by NRC Research Press

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Uni

vers

ity o

f Sy

dney

on

01/3

1/14

For

pers

onal

use

onl

y.

2011). However, the timing of formation of these dikes is unclearbecause some of these dikes might be pre-mineralization intru-sions that provided permeable pathways for later mineralizingfluids, some might be from syn-mineralization magma in equi-librium with the mineralizing fluids, and others might be post-mineralization intrusions sealing fractures used by earliermineralizing fluids (Mathieson and Clark 1984; Bowman et al.1985). Further these dikes may be rooted in an extensive zone ofaplite in the roof of the Mine Stock, implying that late magmaticfluids were potentially available in the roof zone of the Mine Stockthroughout much of the development of the skarns.

Archibald et al. (1978) reported K–Ar biotite ages of 92.3 ± 2.5 Mafor the E-Zone skarn and 91.6 ± 2.6 Ma for the Mine Stock monzo-granite about 1.6 km from the E-Zone, and they concluded that theintrusion and scheelite–chalcopyrite mineralization were coeval.Recently, Rasmussen et al. (2006) reported a U–Pb zircon age of98.2 ± 0.4 Ma and a younger 40Ar–39Ar biotite age of 95.1 ± 0.4 Mafor the Mine Stock, leading them to conclude that the agedifference recorded a cooling interval of �3 million years frommagmatic temperatures of 850–900 °C to the 300 °C closure tem-perature of the argon system. Rasmussen et al. (2006) also re-ported a U–Pb zircon age of 98.3 ± 0.3 Ma from a scheelite- andpyrrhotite-bearing aplite dike that cuts the Mine Stock. Further,they noted that the U–Pb zircon age of 98.2 ± 0.4 Ma for the MineStock (Rasmussen et al. 2006) is significantly older than both theU–Pb zircon age of 92.1 ± 0.2 Ma for the Cirque Lake pluton (Selbyet al. 2003) and the U–Pb zircon age of 95.0 ± 0.6 Ma for the Lenedpluton (Rasmussen et al. 2006) that are adjacent to the Mactungand Lened W–Cu skarn deposits, respectively. Selby et al. (2003)

reported a Re–Os molybdenite age of 97.5 ± 0.5 Ma for the CirqueLake pluton that is significantly older than its U–Pb zircon age.Similarly Gebru and Lentz (2009) reported Ar–Ar dating of micaand U–Pb dating of zircons for the Mactung ore deposit. Theyconcluded that there were two magmatic episodes at Mactung,i.e., 92.1 ± 0.2 Ma for the younger leucogranite and 97.6 ± 0.2 Mafor the older biotite granite. Thus Gebru and Lentz (2009) sug-gested that an unidentified older intrusion with a similar age tothat of the Mine Stock at Cantung could be the source for theMactung mineralization and that the �92.1 Ma U–Pb age for boththe Mactung deposit and for the Cirque Lake pluton determinedby Selby et al. (2003) represents a later magmatic episode ratherthan the main-stage tungsten-mineralization episode at Mactung.

Methods

SamplingFive to seven 2.54 cm diameter cores were drilled at 25 sites and

oriented in situ with a solar and (or) magnetic compass, and threeoriented block samples were collected at each of three additionalsites. The 28 sites include 17 mineralized sites from the Open Pitorebody, three sites from the Mine Stock monzogranite, four sitesfrom aplite dikes, one site from upper argillite, two sites fromdolomite, and one site from ore limestone (Table 1). Five to 15 corespecimens, each 2.54 cm in diameter and �2.20 cm in length,were prepared for each site in the paleomagnetic laboratory at theUniversity of Windsor, providing 283 specimens. All specimenswere stored for 2 weeks in a magnetically shielded room with anambient field of �100 nT to allow their unstable and undesirable

Table 1. Site mean characteristic remanent magnetization (ChRM) directions.

Specimens ChRM directions

Site Description NE NR Dec. (°) Inc. (°) �95 (°) k Notesa

1 Aplite dike 1 3 35.1 81.1 10.9 132.5 —2 Aplite dike — — — — — — a3 Aplite dike 1 3 74.8 72.5 17.6 51.5 —4 Mineralization 5 2 21.3 76.6 12.8 24.1 —5 Mineralization 8 0 24.2 76.3 8.8 40.3 —6 Mineralization 9 0 19.7 73.9 8.7 36.2 —7 Mineralization 10 0 345.7 83.1 7.5 43.0 —8 Mineralization 4 2 359.8 67.7 4.8 215.0 —9 Mineralization 4 2 310.7 76.8 16.2 19.3 —10 Mineralization 3 2 216.4 75.9 16.1 26.7 —11 Mineralization 4 3 322.5 82.9 11.5 31.1 —12 Mineralization 3 3 79.4 82.5 12.4 34.5 —13 Mineralization 5 0 324.8 77.9 6.8 128.4 —14 Mineralization 5 3 17.5 87.3 8.7 44.3 —15 Mineralization — — — — — — a16 Mineralization 3 2 56.0 87.5 12.1 47.3 —17 Mineralization 8 0 337.3 79.0 8.5 43.8 —18 Mineralization — — — — — — a19 Mineralization — — — — — — a20 Mineralization 3 1 287.8 74.9 14.1 48.5 —21 Dolomite 3 2 127.3 −67.4 12.2 46.3 b22 Monzogranite 5 2 326.3 72.2 6.4 93.8 —23 Monzogranite 5 1 293.9 73.2 11.8 34.2 —24 Monzogranite 4 2 338.2 71.9 23.4 21.6 c25 Upper argillite 4 0 197.8 84.9 12.0 59.8 —26 Aplite dike 4 0 293.4 83.5 2.9 997.5 —27 Dolomite 12 0 325.7 71.5 4.8 82.7 —28 Ore limestone 4 0 341.3 70.8 6.5 202.2 —

Mean mineralization (N = 14) — — 346.8 82.5 5.1 62.5 —Mean host rock (N = 5) — — 319.1 76.7 10.1 58.3 —Mean aplite dike (N = 3) — — 47.7 82.8 147.9 48.5 —Mean (N = 22) — — 342.9 82.0 4.2 54.7 —

Note: Mean declination (Dec.), inclination (Inc.), and radius of cone of 95% confidence (�95) in degrees and precision parameter (k) of Fisher (1953). NE, specimen endpoints; NR, remagnetization circles; N, number of sites.

aSites omitted from average directions due to incoherent directions (a), questionable origin (b), or high �95 and low k values (c).

Kawasaki and Symons 35

Published by NRC Research Press

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Uni

vers

ity o

f Sy

dney

on

01/3

1/14

For

pers

onal

use

onl

y.

viscous remanent magnetization (VRM) components to substan-tially decay. All subsequent magnetic measurements were donewithout removing the specimens from the shielded room. Thenatural remanent magnetizations (NRM) of the specimens weremeasured on a 2G Enterprises 755R DC-SQUID magnetometerwith a specimen sensitivity limit of �2 × 10−6 A/m.

DemagnetizationOne typical pilot specimen from each site was thermally demag-

netized in 19 steps up to 600 °C using a Magnetic MeasurementsMMTD-80 oven, with the thermal steps biased into the diagnosticunblocking temperature ranges of goethite (80–140 °C), pyrrho-tite (260–340 °C), and magnetite (500–580 °C) (Dunlop andÖzdemir 1997). A second typical specimen from each site wasalternating field (AF) demagnetized in 13 steps up to 120 mT usinga Sapphire Instruments SI-4 demagnetizer. Examination of theresults from the pilot samples led to the remaining specimensbeing AF demagnetized in 1–6 steps up to 5–30 mT and thenthermally demagnetized in nine steps up to 380 °C. The specimencharacteristic remanent magnetization (ChRM) directions weredetermined using orthogonal vector component plots (Zijderveld1967), principal component analysis (Kirschvink 1980), and remag-netization circle analysis (Bailey and Halls 1984). Site and unitmean directions were calculated following Fisher (1953) (Table 1).

Ore concentrate magnetic mineralogyIt is important in paleomagnetic age dating studies of ore de-

posits to test, if possible, that the ChRM is carried by the ore and(or) ore-stage gangue minerals. For this purpose, 0.2 g of W con-centrate from Cantung’s mill was subjected to thermomagneticand saturation isothermal remanent magnetization (SIRM) analy-ses using a Petersen Instruments Magnetic Measurements Vari-able Field Translation Balance (MMVFTB). A thermomagneticcurve was obtained from room temperature to 700 °C in an argonatmosphere. To obtain an SIRM acquisition curve for the W con-centrate, a concentrate sample was magnetized in direct-current(DC) field steps up to 985 mT with 90% of the remanence intensityat 985 mT ( J985) being deemed to be magnetic saturation.

Results

Natural remanenceThe NRM intensities showed that magnetic surveys could be

useful in locating additional tungsten skarn orebodies in the area.The median NRM intensities were 3.25 × 10−3 A/m (quartiles: Q1,8.00 × 10−4 A/m; Q3, 2.84 × 10−2 A/m) for the mineralized specimenscompared with 2.70 × 10−4 A/m (quartiles: Q1, 6.84 × 10−5 A/m; Q3,1.34 × 10−3 A/m) for the host rock specimens and 4.85 × 10−4 A/m(quartiles: Q1, 1.10 × 10−4 A/m; Q3, 3.08 × 10−3 A/m) for the aplite dikesspecimens. These results show that the mineralization’s remanenceis about 10 times more intense than the host rock’s remanence.

The NRM directions proved to be widely scattered about a cen-tral cluster of northward and steeply inclined downward normaldirections (Fig. 3A). Note that a few of the more random directionsin the upper hemisphere of the stereonet have been switch fromtheir reversed polarity position to their antiparallel normal polar-ity position.

Characteristic remanenceOn thermal step demagnetization, about two-thirds of the pilot

specimens, both from the mineralized zones and host rocks, showslow to moderate decreases in remanent intensity up to �240 °Cand a sharp remanent intensity drop between �240 and �380 °C(Figs. 4A, 4B). The remaining pilot specimens show moderate torapid decreases in intensity up to �240 °C and then erratic in-creases above �240 °C, indicating the presence of hexagonal pyr-rhotite in the specimens and (or) the transformation by oxidationin the oven of iron sulphide minerals such as pyrite and pyrrhotiteto magnetite (Dunlop and Özdemir 1997). On thermal step demag-

netization, the specimen remanence directions progressively co-alesce overall up to �160 °C (Fig. 3B), are well clustered from �190to �260 °C, with a small shift towards the 270 °C position from theremoval of a modern viscous remanence (Fig. 3D), and becomerandomly directed above �360 °C as the remanence from newlyproduced magnetite overwhelms the residual primary magnetiteremanence (Fig. 3F). About half of the AF pilot specimens showinitial rapid remanence intensity decreases up to 20–30 mT(Fig. 4D), whereas the rest of the specimens show slow to moder-ate decreases up to 120 mT (Fig. 4C). The rapid decreases up to20–30 mT indicate that the main magnetic carrier in these speci-mens is multidomain (MD) magnetite and (or) pyrrhotite. Con-versely, the slow to moderate intensity decreases above �100 mTindicate the presence of pyrrhotite with coercivities of >100 mTdue to the mineral’s relatively high magnetocrystalline anisot-ropy and its domain size (Dunlop and Özdemir 1997; Symons andCioppa 2000). Overall AF step demagnetization results in a pro-gressive improvement in the definition of the characteristic rema-nence above �10 mT (Fig. 3), with the best clustering between �15and �40 mT (Fig. 3E). Because unreliable MD components in ei-ther magnetite or pyrrhotite are easily AF demagnetized up to�30 mT and because pyrrhotite is a major remanence carrier andhas a high coercivity that cannot entirely AF demagnetized, theremaining specimens were demagnetized by AF and then thermalstep demagnetization as described in the “Methods” section(Fig. 5).

Some of the specimens with NRM directions outside of thesteeply inclined downward central cluster maintained their aber-rant direction through the initial demagnetization steps before trac-ing a great-circle path towards the cluster (Fig. 6). These specimenswere deemed to retain a low blocking temperature or low coerci-vity viscous remanence of greater-than-normal stability. The Yu-kon–NWT border follows the height of land in the MackenzieMountains between the Pacific Ocean and Arctic Ocean water-sheds, and the Cantung mine study area is only �1 km from theborder. This location suffers from an abnormally high rate ofthunderstorms and lightning. We speculate that the numerouslightning strikes explain the abnormally high scatter in theNRM directions, the rapid decay of the NRM intensity in manyspecimens in the initial steps of demagnetization, and thegreater-than-normal stability of the viscous remanence in somespecimens.

The calculated specimen ChRM directions for each site weredetermined and used to obtain the site mean directions (Table 1).Unfortunately sites 2, 15, 18, and 19 failed to give coherent speci-men ChRM directions, and site 24 gave a poorly clustered meandirection. Also, the site mean direction of site 21 gave a reversedinclination. There are two possibilities: (i) the remanence wasacquired during a reversed epoch of the Earth’s magnetic field; or(ii) a large block that had rolled down the mountain side wassampled. Although the possibility of a true magnetic field reversaldirection cannot be entirely excluded, only the specimens fromsite 21 consistently show a reversed inclination, and this is notenough data to interpret as a true magnetostratigraphic reversal.Therefore, the results of these six sites were excluded from fur-ther analysis, giving a mean direction for the mineralization ofdeclination (D) of 346.8°, and inclination (I) of 82.5° (number ofsites (N) is 14, radius of cone of 95% confidence (�95) is 5.1°, preci-sion parameter of Fisher (1953) (k) is 62.5), for the host rock of D =319.1°, I = 76.7° (N = 5, �95 = 10.1°, k = 58.3) and for the aplite dikesof D = 47.7°, I = 82.8° (N = 3, �95 = 17.9°, k = 48.5) (Fig. 7). Therelatively poor clustering parameters for the host rock and aplitedikes populations are due to the small number of accepted sites.There is no statistically significant difference at 95% confidencebetween the unit mean ChRM directions for the mineralizationand host rocks (correlation test; the observed F value f = 1.92 < thecritical value of the F distribution F = 3.28, McFadden and Lowes1981), for the mineralization and aplite dikes (f = 1.24 < F = 3.32), or

36 Can. J. Earth Sci. Vol. 51, 2014

Published by NRC Research Press

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Uni

vers

ity o

f Sy

dney

on

01/3

1/14

For

pers

onal

use

onl

y.

for the host rocks and aplite dikes (f = 3.44 < F = 3.89). The relativemerits of the Bailey and Halls (1984) and alternative McFadden andMcElhinny (1988) methods for combining observed endpoints andremagnetization circle data to calculate site mean directions havebeen well discussed in the literature (e.g., Bailey 1990; McFadden1990). Both methods make different theoretical distribution as-sumptions that can bias the calculated site mean directions and

the resulting unit mean direction and paleopole. Such a bias isparticularly likely when there are many more remagnetizationcircle points than true endpoints and when the remagnetizationcircles involve long extrapolations while running about parallelto each other. For this Cantung study, a statistically significantbias in the unit mean direction is unlikely to be present because�79% of the specimen directions are defined by endpoints. As a

Fig. 3. Stereocontour plots for the mineralization specimens on equal-area projections of the lower hemisphere (Kamb 1959) for (A) NRM,(B, D, F) thermal step demagnetization, and (C, E) AF step demagnetization. The initial contour is at the 4� level, and subsequent incrementsincrease by 4�. Upper-hemisphere remanence directions are reversed to their antipodal direction.

N N

N N

N N

A B

C D

E F

NRM 110 & 140oC

220, 240 & 260oC

320 & 340oC20 & 30 mT

5 & 10 mT

Kawasaki and Symons 37

Published by NRC Research Press

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Uni

vers

ity o

f Sy

dney

on

01/3

1/14

For

pers

onal

use

onl

y.

check for bias, the average direction of the nine accepted sitedirections, defined by endpoint data only in Table 1, of D = 343.1°,I = 80.0° (N = 9, �95 = 5.8°, k = 81.1) can be compared with that of the13 sites with some remagnetization circle directions of D = 342.7°,I = 83.4° (N = 13, �95 = 6.4°, k = 43.5). These two populations do notdiffer with ��95% confidence (correlation test: f = 0.49 < F = 3.23),showing no bias because of the use of remagnetization data orthe method of calculating the site mean directions. Based onthe results of these correlation tests, the site mean directionsfor all three rock units can be combined, giving a mean ChRMdirection of D = 342.9°, I = 82.0° (N = 22, �95 = 4.2°, k = 54.7) (Fig. 7;Table 1). This direction is significantly different at 95% confidencefrom the present Earth’s magnetic field at the Cantung deposit

(average in 1905–2005 is D = 33.7°, I = 78.8°; IGRF-10, InternationalGeomagnetic Reference Field), indicating that the ChRM records amajor geological event.

Rock magnetic testsThe MMVFTB test on an ore concentrate sample gave well-

defined Curie temperatures at �320 and �580 °C (Fig. 8A), iden-tifying both pyrrhotite and magnetite inclusions in the scheeliteas the predominant magnetic carriers. Similarly, the SIRM test onan ore concentrate sample showed that it was not entirely satu-rated by �300 mT, indicating that the main remanence carrier issingle-domain (SD) or pseudosingle-domain (PSD) magnetite orpyrrhotite (Fig. 8B). The continuously increasing SIRM acquisition

Fig. 4. Examples of (A, B) thermal step demagnetization and (C, D) alternating field (AF) step demagnetization of specimens with initialnatural remanent magnetization (NRM) intensities (JNRM) of 1.16 × 10−1, 2.21 × 10−4, 5.35 × 10−3, and 1.33 × 10−1 A/m, respectively. Solid circlesand open circles denote projection on the horizontal plane and vertical plane, respectively, defined by the north (N), east (E), south (S), andwest (W) (down (D) and up (U)) axes. Axial intensity values (J) are expressed as a ratio of the NRM intensity. Some steps are labeled in °C or mT.

NS

W, U

E, D

0.5

1

0.5240

NRM

3001

0.5

00 200 400

(oC)

JJNRM

1

0.5

0.5

NRM

340

600NS

W, U

E, D

1

0.5

00 200 400 600

(oC)

JJNRM

Monzogranite (220201)Mineralization (130601)

0.5 1

0.5

NS

W, U

E, D

NRM120

15

1

0.5

00 40 80 120

(mT)

JJNRM

NS

W, U

E, D

0.5

1

0.5

NRM

120

60

1

0.5

00 40 80 120

(mT)

JJNRM

Mineralization (140202)Mineralization (060701)

(A) (B)

(C) (D)

38 Can. J. Earth Sci. Vol. 51, 2014

Published by NRC Research Press

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Uni

vers

ity o

f Sy

dney

on

01/3

1/14

For

pers

onal

use

onl

y.

above 300 mT to 985 mT indicates the presence of a trace percent-age of SD pyrrhotite (Symons and Cioppa 2000) and (or) of a minorpercentage of goethite and (or) hematite. Based on the thermalstep demagnetization results and the thermomagnetic curves,there is negligible goethite in the Cantung specimens so thatthe high-coercivity mineral in the specimens is likely tracehematite.

DiscussionThe overall mean ChRM direction for the Cantung deposit gives

a pole position at 76.2°N, 212.2°E (short-axis of the oval of 95%confidence �p = 7.9°, long-axis of the oval of 95% confidence �m =8.2°) (Fig. 9). In Fig. 9, the paleopoles are surrounded by their 2�(95%) cones of confidence. The Cantung paleopole is just barelysignificantly different at 95% confidence by 0.2° from the 98 Mareference paleopole of 78.3°N, 179.7°E (radius of cone of 95% con-fidence A95 = 3.1°) for North America of Torsvik et al. (2012) usingthe test of Debiche and Watson (1995), but is not significantlydifferent at 92% confidence. Because the paleomagnetic age

agrees closely with the reported U–Pb zircon age of �98 Ma forthe Mine Stock of Rasmussen et al. (2006), the regional metamor-phic event that caused host rock’s remagnetization is likely themonzogranite intrusion, and therefore, the scheelite mineral-ization and monzogranite are coeval in origin. The timing ofintrusion of the aplite dikes is important also for the ore min-eralization of the Cantung deposit (Mathieson and Clark 1984;Rasmussen et al. 2011). The positive correlation test results ofthe unit mean ChRM directions for the mineralization, hostrock, and aplite dikes excludes the possibility that the dikes aresignificantly younger than the mineralization because it is im-probable that the small aplite dikes could carry sufficient heatto remagnetize the entire Mine Stock monzogranite and hostrock sequences.

The northern Cordilleran orogen of Yukon and Alaska is acomplex amalgamation of autochthonous North Americanrocks to the east-northeast and allochthonous terranes to thewest-southwest that were assembled and accreted between EarlyJurassic and Late Cretaceous (Mair et al. 2006; Fig. 1). Both para-

Fig. 5. Examples of AF and then thermal step demagnetization of three example specimens with initial NRM intensities (JNRM) of 2.28 × 10−3,2.20 × 10−1, and 1.07 × 10−3 A/m, respectively. Plotting conventions as in Fig. 4.

NRM

320oC

30 mT110oC

260oC

1

0.5

0.5NS

W, U

E, D

1

0.5

00 200 300

(oC)

JJNRM

50(mT)

1.5

100

Mineralization (070402)

1

0.5

0.5

NRM

320oC

380oC

30 mT220oC

NS

W, U

E, D

NS

W, U

E, D1

0.5

0.5

NRM

5 mT 190oC

380oC

Mineralization (140601)

1

0.5

00 200 400

(oC)

JJNRM

5(mT)

Ore limestone (280302)

1

0.5

00 200 400

(oC)

JJNRM

30(mT)

Kawasaki and Symons 39

Published by NRC Research Press

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Uni

vers

ity o

f Sy

dney

on

01/3

1/14

For

pers

onal

use

onl

y.

autochthonous and allochthonous tectonic models have beenproposed for the origin of the Selwyn Basin from paleomagneticdata. Kawasaki and Symons (2012) have shown, based on the post-folding ChRM direction from the Howards Pass Zn–Pb depositsthat are located about 100 km northwest of Cantung, that thebasin is either autochthonous or para-autochthonous with NorthAmerica. Their results indicate that the basin’s Paleozoic stratawere added to North America as an accretionary prism after Earlyto Middle Jurassic metamorphism, with subsequent margin-parallel northward transport of 300 ± 300 km and a clockwiserotation of �28° on docking. They noted further that the 97 MaRagged Pluton, located about 10 km east of the Cantung mine, hasgiven a concordant paleopole for North America, indicating thatthe region has been autochthonous since the mid-Cretaceous(Symons et al. 2008). The results reported for the Cantung scheel-ite ore and host rocks provides further support for the SelwynBasin being autochthonous since the mid-Cretaceous. In contrast,Johnston (2008) has proposed an allochthonous model for theformation of the Selwyn Basin. He suggested that the basin’sPaleozoic strata originated in the Late Tertiary – Early Jurassic asan accretionary prism against his proposed ribbon continent,SAYBIA (Johnston 2001). Based mainly on disparate and controversialpaleomagnetic results from the 70 Ma Carmacks volcanics restingon the Yukon–Tanana Terrane and Intermontane Belt (Enkin et al.2006; see also Symons et al. 2005; McCausland et al. 2006, andreferences therein), Johnston (2008) postulated that SAYBIA wastranslated >2000 km from southern California paleolatitudes be-tween �80 and �40 Ma to its present location. In his model, heargued that the contact aureole of the 106 Ma Glenlyon batholithprovided a pinning point to affirm that the Selwyn Basin wasrigidly attached to the Yukon–Tanana Terrane by 106 Ma, therebyjustifying his use of the Carmacks data (Gladwin and Johnston2006). Johnston (2008) places the inboard boundary of SAYBIAnear or along the northern and eastern boundary of the SelwynBasin. If his allochthonous model was correct, then the paleopolesfor the Cantung mineralization and host rocks, the Ragged Plu-ton, and the Howards Pass Zn–Pb mineralization should be verydiscordant compared with their coeval North American referencepoles, and should be displaced about 2000 km northward near the

Arctic ocean coastline of central Russia. Given that the three pa-leopoles from the central Selwyn Basin are concordant with theirreference poles, it is evident that these paleomagnetic results donot support Johnston’s (2008) allochthonous model for the basin’sorigin.

ConclusionsBased on step demagnetization and rock magnetic tests, the

main remanence carriers in the Cantung scheelite–chalcopyrite(W–Cu) mineralization are SD and (or) PSD pyrrhotite, with lessertitanomagnetite and (or) magnetite, and with trace hematite.There is no statistically significant difference at 95% confidencebetween the site mean ChRM directions of the W–Cu mineraliza-tion and host rock, indicating that the Mine Stock monzograniteintrusion and mineralization are coeval in origin. In addition, thecorrelation test results also exclude the possibility that the aplitedikes are significantly younger than the mineralization. The98 Ma Cantung paleopole is not significantly different from either

Fig. 6. An equal-area stereonet showing examples of the AF andthen thermal step demagnetization of specimens (●) and the unitmean remanence directions of mineralization (Œ) and host rock (�).Some steps are labeled in °C.

140102

230402

150301

140201

N

180o

270o 90o

NRM

220oC

NRM

300oC

NRM 340oC

NRM300oC

Fig. 7. An equal-area stereonet showing the following: (A) site meanremanence directions of the host rock (�) and aplite dikes (Œ) withtheir cones of 95% confidence; (B) site mean remanence directions ofthe mineralization (●) with their cones of 95% confidence; and(C) unit mean remanence directions of the host rock, aplite dikes,and mineralization, and overall (×) mean remanence directions withtheir cones of 95% confidence. The star shows the present Earth’smagnetic field direction in the study area.

N

270o 90o

180o

270o 90o

270o 90o

A

B

C

40 Can. J. Earth Sci. Vol. 51, 2014

Published by NRC Research Press

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Uni

vers

ity o

f Sy

dney

on

01/3

1/14

For

pers

onal

use

onl

y.

the 98 Ma North American reference paleopole at 92% confidenceor the �97 Ma Ragged Pluton paleopole at >95% confidence, sug-gesting that the Selwyn Basin has been autochthonous since themid-Cretaceous. Furthermore, the ChRM direction for the miner-alization is concordant with that of its host rocks, indicating thatscheelite ores are good candidates for further paleomagnetic stud-ies. Further, this study has shown that tungsten ore skarns pro-vide suitable samples for paleomagnetic studies of their oregenesis, tectonic history, or other aspects.

AcknowledgementsThe authors gratefully thank the North American Tungsten

Corporation Ltd. for allowing access to the mine property, MikeHarris for helping in the sample collection, Justin Hoyle for pre-paring and measuring the specimens, the Yukon Geological Sur-vey for information and logistical help, the Associate Editor Dr.R.J. Enkin and two anonymous referees for helpful suggestions

that have notably improved this manuscript, and the Natural Sci-ences and Engineering Research Council of Canada for fundingthis study through Discovery Grant 7834-2008 to D.T.A.S.

ReferencesArchibald, D.A., Clark, A.H., Farrar, E., and Zaw, U.K. 1978. Potassium-argon ages

of intrusion and scheelite mineralization, Cantung, Tungsten, NorthwestTerritories. Canadian Journal of Earth Science, 15(7): 1205–1207. doi:10.1139/e78-126.

Bailey, R.C. 1990. Comment on “The combined analysis of remagnetization cir-cles and direct observations in palaeomagnetism”. Earth and Planetary Sci-ence Letters, 101: 125–126. doi:10.1016/0012-821X(90)90132-H.

Bailey, R.C., and Halls, H.C. 1984. Estimate of confidence in paleomagnetic di-rections derived from mixed remagnetization circle and direct observationaldata. Journal of Geophysics, 54: 174–182.

Blusson, S.L. 1968. Geology and tungsten deposits near the headwaters of FlatRiver, Yukon Territory and southwestern district of Mackenzie, Canada. Geo-logical Survey of Canada, Paper 67-22, 77 p.

Bowman, J.R., Covert, J.J., Clark, A.H., and Mathieson, G.A. 1985. The CanTung EZone scheelite skarn orebody, Tungsten, Northwest Territories: Oxygen, hy-drogen, and carbon isotope studies. Economic Geology, 80: 1872–1895. doi:10.2113/gsecongeo.80.7.1872.

Cummings, W.W., and Bruce, D.E. 1977. Canada Tungsten – Change to under-ground mining and description of mine-mill procedures. Canada Mining andMetallurgy Bulletin, 70: 94–101.

Debiche, M.G., and Watson, G.S. 1995. Confidence limits and bias correction forestimating angles between directions with applications to paleomagnetism.Journal of Geophysical Research, 100(B12): 24405–24429. doi:10.1029/92JB01318.

Dick, L.A., and Hodgson, C.J. 1982. The MacTung W-Cu(Zn) contact metasomaticand related deposits of the northeastern Canadian Cordillera. Economic Ge-ology, 77: 845–867. doi:10.2113/gsecongeo.77.4.845.

Dunlop, D.J., and Özdemir, Ö. 1997. Rock Magnetism: Fundamentals and Fron-tiers. Cambridge University Press, Cambridge, U.K.

Enkin, R.J., Johnston, S.T., Larson, K.P., and Baker, J. 2006. Paleomagnetism ofthe 70 Ma Carmacks Group at Solitary Mountain, Yukon, confirms and ex-tends controversial results: Further evidence for the Baja British Columbiamodel. In Paleogeography of the North American Cordillera: Evidence Forand Against Large-Scale Displacements. Edited by J.W. Haggart, R.J. Enkin, andJ.W.H. Monger. Geological Association of Canada, pp 221–232.

Fisher, R.A. 1953. Dispersion on a sphere. Proceedings of the Royal Society ofLondon, 217: 295-305. doi:10.1098/rspa.1953.0064.

Fitzpatrick, K., and Bakker, F.J. 2011. Technical report on the Cantung mine,Northwest Territories, Canada. North American Tungsten Corporation Ltd.,Report for NI 43-101.

Gebru, A.L., and Lentz, D.R. 2009. Petrologic, geochemical characteristics, andage of skarn-related granitoids at the Mactung Tungsten Deposit, Yukon,Canada. In Proceedings of the 24th International Applied Geochemistry Sym-posium (IAGS), Fredericton, pp. 151–155.

Fig. 8. (A) Thermomagnetic heating and cooling curve in an Ar atmosphere using a simple moving average (number of readings n = 5) fortungsten concentrate. The arrows show approximate Curie temperature. (B) SIRM acquisition curve for tungsten concentrate. Jmax, maximumintensity value.

0 200 400 600 800 1000(mT)

300

0

0.5

1.0

JJ985

0.9

0 200 400 600(oC)

0

0.2

1.0

JJmax

0.8

0.6

0.4

Pyrrhotite

Magnetite

(A) (B)

Hematite

Hematite tail

Magnetite & Pyrrhotitesaturation

Fig. 9. Locations of the Cantung deposit, 98 Ma North Americanreference (Torsvik et al. 2012) and Ragged Pluton (Symons et al.2008) paleopoles with their 2� confidence limit.

270oE

180oE

90oE

0o

70o

80o

98 Ma

Ragged Pluton

Cantungdeposit

Kawasaki and Symons 41

Published by NRC Research Press

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Uni

vers

ity o

f Sy

dney

on

01/3

1/14

For

pers

onal

use

onl

y.

Gladwin, K., and Johnston, S.T. 2006. Mid-Cretaceous pinning of accreted ter-ranes to miogeoclinal assemblages in the northern Cordillera: Irreconcilablewith paleomagnetic data? In Paleogeography of the North AmericanCordillera: Evidence For and Against Large-Scale Displacements. Edited byJ.W. Haggart, R.J. Enkin, and J.W.H. Monger. Geological Association of Can-ada, pp 299–306.

Hart, C.J.R., Goldfarb, R.J., Lewis., L.L., and Mair, J.L. 2004. The northern Cordil-leran mid-Cretaceous plutonic province: Ilmenite/magnetite-series grani-toids and intrusion-related mineralization. Resource Geology, 54: 253–280.doi:10.1111/j.1751-3928.2004.tb00206.x.

Johnston, S.T. 2001. The Great Alaskan Terrane Wreck: reconciliation of paleo-magnetic and geological data in the northern Cordillera. Earth and PlanetaryScience Letters, 193: 259–272. doi:10.1016/S0012-821X(01)00516-7.

Johnston, S.T. 2008. The Cordilleran ribbon continent of North America. AnnualReview of Earth and Planetary Sciences, 36: 495–530. doi:10.1146/annurev.earth.36.031207.124331.

Kamb, W.B. 1959. Ice petrofabric observations from Blue Glacier, Washington, inrelation to theory and experiment. Journal of Geophysical Research, 64:1891–1909. doi:10.1029/JZ064i011p01891.

Kawasaki., K., and Symons, D.T.A. 2012 Palaeomagnetism of the Howards PassZn–Pb deposits, Yukon, Canada. Geophysical Journal International, 190: 217–229. doi:10.1111/j.1365-246X.2012.05484.x.

Kirschvink, J.L. 1980. The least squares line and plane and the analysis of paleo-magnetic data. Geophysical Journal of the Royal Astronomical Society, 62:699–718. doi:10.1111/j.1365-246X.1980.tb02601.x.

Mair, J.L., Hart, C.J.R., and Stephens, J.R. 2006. Deformation history of the north-western Selwyn Basin, Yukon, Canada: Implications for orogen evolution andmid-Cretaceous magmatism. Bulletin of the Geological Society of America,118: 304–323. doi:10.1130/B25763.1.

Mathieson, G.A., and Clark, A.H. 1984. The Cantung E Zone scheelite skarnorebody, Tungsten, Northwest Territories; a revised genetic model. Eco-nomic Geology, 79: 883–901. doi:10.2113/gsecongeo.79.5.883.

McCausland, P.J.A., Symons, D.T.A., Hart, C.J.R., and Blackburn, W.H. 2006. As-sembly of the northern Cordillera: new paleomagnetic evidence for coher-ent, moderate Jurassic to Eocene motion of the Intermontane Belt andYukon-Tanana terranes. In Paleogeography of the North AmericanCordillera: evidence for and against large-scale displacements. Edited by J.W.Haggart, R.J. Enkin, and J.W.H. Monger. Geological Association of Canada, pp147–170.

McFadden, P.L. 1990. Reply to comment to R.C. Bailey on “The combined analysisof remagnetization circles and direct observations in palaeomagnetism”.Earth and Planetary Science Letters, 101: 127–128.

McFadden, P.L., and Lowes, F.J. 1981. The discrimination of mean directionsdrawn from Fisher distributions. Geophysical Journal of the Royal Astronom-ical Society, 67: 19–33. doi:10.1111/j.1365-246X.1981.tb02729.x.

McFadden, P.L., and McElhinny, M.W. 1988. The combined analysis of remagne-

tization circles and direct observations in palaeomagnetism. Earth and Plan-etary Science Letters, 87: 161–172. doi:10.1016/0012-821X(88)90072-6.

North American Tungsten Corporation Ltd. 2011. North American TungstenAnnounces: An Updated 43-101 Compliant Technical Report For The CantungMine [online]. Available from http://www.northamericantungsten.com/s/NewsReleases.asp.

Rasmussen, K.L., Mortensen, J.K., and Falck, H. 2006. Geochronology and geo-chemistry of intrusive rocks in the Nahanni region, southwestern NorthwestTerritories and southeastern Yukon. In Yukon Exploration and Geology 2005.Edited by D.S. Emond, G.D. Bradshaw, L.L. Lewis and L.H. Weston. YukonGeological Survey, Whitehorse, pp. 287–298.

Rasmussen, K.L., Mortensen, J.K., Falck, H., and Ullrich, T.D. 2007. The potentialfor intrusion-related mineralization within the South Nahanni River MERAarea, Selwyn and Mackenzie Mountains, Northwest Territories. In Mineraland Energy Resource Assessment of the Greater Nahanni Ecosystem UnderConsideration for the Expansion of the Nahanni National Park Reserve,Northwest Territories. Edited by D.F. Wright, D. Lemkow and J.R. Harris. Geo-logical Survey of Canada, Open File 5344, pp. 203–278.

Rasmussen, K.L., Lentz, D.R., Falck, H., and Pattison, D.R.M. 2011. Felsic mag-matic phases and the role of late-stage aplitic dykes in the formation of theworld-class Cantung Tungsten skarn deposit, Northwest Territories, Canada.Ore Geology Reviews, 41: 75–111. doi:10.1016/j.oregeorev.2011.06.011.

Selby, D., Creaser, R.A., Heaman, L.M., and Hart, C.J.R. 2003. Re–Os and U–Pbgeochronology of the Clear Creek, Dublin Gulch, and Mactung deposits,Tombstone Gold Belt, Yukon, Canada: absolute timing relationships betweenplutonism and mineralization. Canadian Journal of Earth Sciences, 40(12):1839–1852. doi:10.1139/e03-077.

Symons, D.T.A., and Cioppa, M.T. 2000. Crossover plots: a useful method forplotting SIRM data in paleomagnetism. Geophysical Research Letter, 27:1779–1782. doi:10.1029/1999GL008472.

Symons, D.T.A., Harris, M.J., and McCausland, P.J.A. 2005. Mesozoic-Cenozoicpaleomagnetism of the Intermontane and Yukon-Tanana terranes, CanadianCordillera. Canadian Journal of Earth Sciences, 42(6): 1163–1185. doi:10.1139/e04-086.

Symons, D.T.A., Kawasaki, K., Hart, C.J.R., and Harris, M.J. 2008. A paleomagnetictest for northward tectonic transport of the eastern Selwyn Basin, northernCanadian Cordillera: data from the mid-Cretaceous Ragged Pluton. CanadianJournal of Earth Science, 45(7): 860–869. doi:10.1139/E08-028.

Torsvik, T.H., Van der Voo, R., Preeden, U., Mac Nicaill, C., Steinberger, B.,Doubrovine, P.V., van Hinsbergen, D.J.J., Domeier, M., Gaina, C., Tohver, E.,Meert, J.G., McCausland, P.J.A., and Cocks, L.R.M. 2012. Phanerozoic polarwander, palaeogeography and dynamics. Earth-Science Reviews, 114: 325–368. doi:10.1016/j.earscirev.2012.06.007.

Zijderveld, J.D.A. 1967. A. C. demagnetization of rocks: analysis of results. InMethods of Paleomagnetism. Edited by D.W. Collinson, K.M. Creer and S.K.Runcorn. Elsevier, Amsterdam, The Netherlands, pp. 254–286.

42 Can. J. Earth Sci. Vol. 51, 2014

Published by NRC Research Press

Can

. J. E

arth

Sci

. Dow

nloa

ded

from

ww

w.n

rcre

sear

chpr

ess.

com

by

Uni

vers

ity o

f Sy

dney

on

01/3

1/14

For

pers

onal

use

onl

y.