geochemistry and paleotectonic setting of felsic volcanic...

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Geochemistry and Paleotectonic Setting of Felsic Volcanic Rocks in the Finlayson LakeVolcanic-Hosted Massive Sulfide District, Yukon, Canada*,**

STEPHEN J. PIERCEY,†,***Mineral Deposit Research Unit, Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road,

Vancouver, British Columbia, Canada V6T 1Z4

SUZANNE PARADIS, Mineral Resources Division, Geological Survey of Canada, 9860 West Saanich Road, Sidney, British Columbia, Canada V8L 4B2

DONALD C. MURPHY,Yukon Geology Program, P.O. Box 2703 (F-3), Whitehorse, Yukon, Canada Y1A 2C6

AND JAMES K. MORTENSEN

Geochronology Laboratory, Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia, Canada V6T 1Z4

AbstractThe Finlayson Lake volcanic-hosted massive sulfide (VHMS) district represents one of Canada’s most recent

VHMS discovery regions with ~34 million metric tons (Mt) of massive sulfide mineralization found since themid 1990s. Felsic volcanic rocks are associated with three units: the Fire Lake unit, the Kudz Ze Kayah unit,and the Wolverine succession. Significant accumulations of polymetallic felsic VHMS deposits (Kudz ZeKayah, GP4F, and Wolverine) have only been discovered in the Kudz Ze Kayah unit and Wolverine successionto date. In the hanging wall of the Money Creek thrust, felsic volcanic and high-level intrusive rocks in the FireLake unit have calc-alkalic and tholeiitic affinities with low high field strength element (HFSE) contents andintermediate Zr/Sc (9.4–43.4) and Zr/TiO2 (254–864) ratios. These rocks are interlayered with mafic rocks witharc geochemical signatures, to date devoid of significant VHMS mineralization, and represent bimodal mag-matism within an evolving Devonian-Mississippian continental-arc system. The Kudz Ze Kayah unit in the foot-wall of the Money Creek thrust stratigraphically overlies the Fire Lake unit and consists of felsic volcanic rockswith high HFSE contents, within-plate (A-type) signatures, and high Zr/Sc (15.3–190.3) and Zr/TiO2(630–2,185) ratios. The Kudz Ze Kayah unit felsic rocks are crosscut and overlain by alkalic mafic rocks, are as-sociated with abundant carbonaceous sedimentary rocks, and represent magmatism within a Devonian-Missis-sippian ensialic back-arc rift-basin environment. The Wolverine succession unconformably overlies the KudzZe Kayah unit. Felsic rocks below the Wolverine deposit have geochemical attributes similar to the Kudz ZeKayah unit with high HFSE contents, within-plate (A-type) signatures, and high Zr/Sc (29.9–84.2) and Zr/TiO2(391–1,220) ratios. In contrast, aphyric rhyolite flows in the hanging wall of the deposit have much lower HFSEcontents and the lowest Zr/Sc (3.5–27.7) and Zr/TiO2 (181–591) ratios in the district. All the felsic rocks of theWolverine succession are interlayered with abundant carbonaceous sedimentary rocks and are overlain by mi-docean ridge basalt (MORB)-like basaltic rocks. The Wolverine succession is interpreted to have formed withinan Early Mississippian ensialic back-arc basin environment that eventually evolved to sea-floor spreading.

The variation in the HFSE budgets of the felsic rocks of the Finlayson Lake district likely reflects variationsin the source and/or temperature of crustal melting. In particular, felsic rocks of the Fire Lake unit have higherNb/Ta and lower Ti/Sc ratios than other volcanic rocks in the district, suggesting possible derivation from maficcrustal sources and/or lower crustal fusion temperatures. The Kudz Ze Kayah unit and footwall rocks to theWolverine deposit are inferred to have formed from high-temperature partial melting of continental crust. Thehanging-wall aphyric rhyolites from the Wolverine deposit may have formed from either lower temperaturecontinental crustal melting or may have been derived from the mixing of HFSE-depleted N-MORB maficmagmas and evolved continental crust.

Polymetallic felsic volcanic-associated, VHMS deposits within the Finlayson Lake district are preferentiallyassociated with HFSE-enriched felsic rocks with high Zr/Sc (15.3–190.3) and Zr/TiO2 (391–2,105) ratios. TheHFSE and rare earth element (REE) systematics of VHMS-associated felsic rocks of the Finlayson Lake dis-trict are different from prospective felsic rocks from Archean VHMS environments in the Superior provinceand are displaced toward higher Zr/Y and La/Ybn ratios. Their HFSE and REE systematics are similar to manyPhanerozoic VHMS environments, in particular those at least partially to fully underlain by evolved continen-tal crust. The geochemical differences between the felsic rocks of the Finlayson Lake district and those fromArchean VHMS environments most likely reflect differences in the substrates from which the felsic rocks werederived (e.g., evolved versus juvenile).

Economic GeologyVol. 96, 2001, pp. 1877–1905

*Geological Survey of Canada contribution 1999166. **Mineral Deposit Research Unit, University of British Columbia contribution P-117.† Corresponding author: email, [email protected]***Current address: Mineral Exploration Research Centre, Department of Earth Sciences, Laurentian University, Ramsey Lake Road, Sudbury, Ontario,

Canada P3E 2C6.

IntroductionTHE FINLAYSON LAKE district of the Yukon-Tanana terrane,central Yukon Territory, is host to some of Canada’s most re-cent volcanic-hosted massive sulfide (VHMS) discoveries,such as the Kudz Ze Kayah, GP4F, Wolverine, Fyre Lake, andIce deposits (Fig. 1). The VHMS deposits discovered in theFinlayson Lake district have a total tonnage of ~34 millionmetric tons (Mt) with 21 Mt in the felsic volcanic- and sedi-ment-hosted Kudz Ze Kayah, GP4F, and Wolverine deposits;the other 13 Mt are in the Cu-Co-Au Fyre Lake deposit andthe Cu-rich Ice deposit. These VHMS discoveries started oneof the largest staking rushes in the history of the Yukon Terri-tory (Hunt, 1998), which in turn has spurred an integratedprogram of regional geologic mapping (Murphy, 1998; Mur-phy and Piercey, 1999, 2000), metallogenic and lithogeo-chemical studies (Piercey et al., 1999; Bradshaw et al., 2001)of the Finlayson Lake district.

Volcanic-hosted massive sulfide deposits of the FinlaysonLake district occur within a variably deformed and metamor-phosed sequence of middle to late Paleozoic volcanic, plu-tonic, and sedimentary rocks (e.g., Mortensen, 1992a; Mur-phy and Piercey, 2000). This paper presents a regionalgeochemical dataset for felsic volcanic rocks from the Fin-layson Lake district, including those that do not host signifi-cant (to date) felsic volcanic-associated VHMS mineralization(Fire Lake unit) and those spatially associated with theWolverine, GP4F, and Kudz Ze Kayah deposits. Petrochemi-cal studies of volcanic rocks in other VHMS districts (e.g.,Lesher et al., 1986; Barrie et al., 1993; Stoltz, 1995; Lentz,1998, 1999; Barrett and MacLean, 1999) have shown that vol-canic rock geochemical signatures can provide insight into the

paleotectonic setting and metallogenic evolution of host rocksto VHMS districts. Furthermore, these geochemical studieshave shown that volcanism associated with VHMS mineral-ization may provide a fingerprint of the ambient thermal andtectonic controls that govern the genesis of VHMS hy-drothermal systems. By association volcanic lithogeochemicalsignatures may be a guide to the exploration and discovery ofnew VHMS mineralization. The objectives of this study are to(1) document the geochemical signatures of felsic volcanicrocks in the Finlayson Lake district, (2) elucidate the paleo-tectonic and metallogenic settings of the Finlayson Lakedistrict and to compare the district to possible modern andancient analogues, and (3) investigate the petrologic relation-ships between felsic volcanic petrogenesis and VHMS hy-drothermal systems in the Finlayson Lake district.

Regional SettingThe Yukon-Tanana terrane in the Finlayson Lake district is

composed of foliated and lineated greenschist- to lower am-phibolite-grade metasedimentary, metavolcanic, and meta-plutonic rocks (e.g., Tempelman-Kluit, 1979; Mortensen andJilson, 1985). Although the region has been strongly de-formed and metamorphosed, regional mapping has identifieda stratigraphically intact sequence consisting of three middleto late Paleozoic unconformity bound successions: the GrassLakes, Wolverine, and Campbell Range (Murphy, 1998, 2001;Murphy and Piercey, 1999, 2000).

The Grass Lakes succession consists of unit 1, the Fire Lakeunit, the Kudz Ze Kayah unit, and unit 4 (Figs. 2 and 3). Thelowermost part of the Grass Lakes succession consists of pre-Early Mississippian (pre-365 Ma) quartz-rich, noncarbonaceous

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Yukon-Tanana Terrane

C A N A

D

AC A N

A D

A

60°

141°

YukonBC

Ala

ska

Yuk

on

Tintina Fault Zone

Denali Fault

Pelly-Cassiar

Platform

Selwyn Basin

Scalek mk m

0 100100

Dawson City

Carmacks

WatsonLake

Teslin

AishihikRossRiver

VMS Deposits

Kudz Ze Kayah GP4FWolverine

Fyre LakeMoney

Ice

Yukon

WHITEHORSEWHITEHORSE

FIG. 1. Location of the Finlayson Lake district and VHMS deposits with respect to the Yukon-Tanana terrane, Yukon,Canada (modified from Wheeler and McFeely, 1991, and Hunt, 1998).

metaclastic rocks of unit 1, which are overlain by the ~365 to360 Ma (Mortensen, 1992a, b, and unpub. data) mafic-domi-nated arc- and back-arc-related Fire Lake unit (Mortensen,1992a, b; Grant, 1997; Murphy and Piercey, 1999, 2000;Piercey et al., 1999). Boninitic rocks of the Fire Lake unithost the ~8.5 Mt Besshi-style Fyre Lake Cu-Co-Au VHMSdeposit (Figs. 2 and 3; Murphy, 1998; Murphy and Piercey,2000).

Stratigraphically overlying the Fire Lake unit is the felsicvolcanic and sedimentary rock-dominated Kudz Ze Kayahunit (Murphy, 1998). This unit consists predominantly of

Devonian-Mississippian (~360–356 Ma; Mortensen, 1983,1992a) felsic volcanic and variably carbonaceous sedimentaryrocks in the lower parts of the unit (unit 3 of Murphy, 1998;Figs. 2 and 3). The top of the Grass Lakes succession consistspredominantly of alkalic basalts and carbonaceous sedimen-tary rocks (unit 4 of Murphy, 1998; Figs. 2 and 3). Coeval withthe Kudz Ze Kayah unit and unit 4 are the Devonian-Missis-sippian (360 ± 1 Ma; Mortensen, 1992a) K feldspar por-phyritic to megacrystic granites of the Grass Lakes suite of in-trusions, which are inferred to be the subvolcanic intrusivecomplex to the Kudz Ze Kayah unit VHMS mineralization

FELSIC VOLCANIC ROCKS, FINLAYSON LAKE DISTRICT, YUKON, CANADA 1879

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Q Quaternary sediments

Chert, chert-pebble conglomerate,sandstone

Mafic volcanic, volcaniclasticand intrusive rocks

Diamictite, mafic tuff, olisostromalcarbonate, chert, sandstone

Unit 6: Felsic volcanic rocks,Fe-formation, mixed tuffs

Grass Lakes Suite: Peraluminous granitoids

Peraluminous granitoids

Simpson Range Plutonic Suite: Metaluminousgranitoids

Simpson Range Plutonic Suite: Shearedmetaluminous granitoids

Mississippian? serpentinized harzburgitesand ultramafic rocks (intrusions?)

VHMS Deposit

Faults, displacement uncertain

Money Creek Thrust Fault

Unit 5cp: Carbonaceous argilliteand phyllite

Unit 5f/qfp: Quartz-bearing felsicvolcanics and high-level intrusiverocks

Unit 5l: Quartz-feldspar+shalechip conglomeratePennsylvanian-Permian

Mississippian

Mississippian

Devonian

Intrusive Rocks

Mississippian

Cretaceous

Campbell Range Succession

Unit 1: Quartz-(+biotite)-rich metaclasticrocks calc-silicates, rare felsic horizons

Fire Lake Unit (Unit 2): Mafic volcanicand intrusive rocks, carbonaceous phyllite,lesser felsic volcanic rocks

Unit 4: Carbonaceous phyllite, rift-relatedmafic rocks, quartzite

Kudz Ze Kayah Unit (Unit 3): Felsic volcanicand shallow level intrusive rocks,carbonaceous phyllite, turbiditicsedimentary rocks

Grass Lakes Succession

Wolverine Succession

Unconformity

Other

Q

Q

QQ

QQ

Q

61 00’o

0

Kilometres

5 10

61 30’o

61 15’o

Tintina

Fault

Wolverine Lake

FyreLake

North

Lakes

N

131 45’o 131 15’o 131 00’o

Q

Wolverine

Fyre Lake

GP4FKudz Ze Kayah

FIG. 2. Regional geologic setting of the Finlayson Lake district after Murphy and Piercey (1999, 2000).

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Grass LakesSuite

SRPS

MONEY CREEK THRUST(>30 km displacement)

Unit 1Mafic + ultramafic intrusions

Intrusions

Layered RocksGrass Lakes suite intrusions

Fire Lake unit

Grass Lakes successionKudz Ze Kayah unit and unit 4

Wolverine Lake succession

Simpson Range plutonic suite (SRPS)

Campbell Range succession

unconformity

unconformity

Fyre LakeVHMS Deposit

WolverineVHMS Deposit

Kudz Ze KayahGP4F

VHMS Deposits

(a)

>36

5M

a~

360

Ma

~35

6-34

5M

aP

enn-

~27

3M

a

UC

UC

KZK GP4F

365-

360

Ma

~360 Ma

~365 Ma

Fyre Lake

Wolverine

Ice?

GrassLakes

(360+/-1Ma)U

nit

1Fi

reLa

keU

nit

KZ

KU

nit

U4

Gra

ssLa

kes

Suc

cess

ion

U-5

f/q

f p

Wo

lver

ine

S.

Cam

pb

ell

Ran

ge

Suc

cess

ion

U-6

(c)

Fire

Lake

Uni

t(~

360

Ma)

Uni

t1

360.5 +/- 0.9Ma

QFPI

RHY/DAC

345-350 Ma

SRPS

(b)

see (b)

see (c)

see (c)

FIG. 3. Schematic stratigraphic relationship of felsic rocks in the hanging wall of the Money Creek thrust in relationshipto the footwall, which forms the bulk of the Finlayson Lake district (a). Schematic stratigraphic sections for felsic rocks ofthe Fire Lake unit in the hanging wall of the Money Creek thrust fault (b), and felsic rocks of the Kudz Ze Kayah unit andWolverine succession (c). Figures modified from Murphy and Piercey (1999, 2000) and Piercey and Murphy (2000).

(Figs. 2 and 3). The VHMS deposits within the Kudz ZeKayah unit include the Kudz Ze Kayah Zn-Pb-Cu deposit (13Mt, 5.5% Zn, 1.3% Pb, 1% Cu, 125 g/t Ag, 1.2 g/t Au; Shultze,1996) and the GP4F Zn-Pb deposit (1.0 Mt, 6.4% Zn, 1.55%Pb, 0.1% Cu, 90 g/t Ag, 1.76 g/t Au; Figs. 2 and 3); both de-posits are hosted by felsic volcanic and sedimentary rocks.

Unconformably overlying the Grass Lakes succession is theWolverine succession. The Wolverine succession consists pre-dominantly of Early Mississippian (~356–346 Ma; Mortensen,1992a; Piercey and Mortensen, unpub. data) felsic volcanicand carbonaceous sedimentary rocks (Murphy and Piercey,1999, 2000), which host the Wolverine VHMS deposit (6.2Mt @ 12.96% Zn, 1.53% Pb, 1.41% Cu, 359.1 g/t Ag, 1.81 g/tAu; Tucker et al., 1997; Bradshaw et al., 2001; Figs. 2 and 3).The succession contains, from bottom to top, a lower con-glomerate unit (unit 5l), a lower felsic volcanic-dominatedunit (unit 5f/qfp), a regional carbonaceous argillite unit (unit5cp), the immediate footwall felsic volcanic and subvolcanicrocks to the Wolverine deposit (unit 6fw), and a hanging wallconsisting of aphyric rhyolitic rocks, carbonaceous sedimen-tary rocks, which near their top contain basalt flows (unit6hw; Figs. 2 and 3; Murphy and Piercey, 1999, 2000; Brad-shaw et al., 2001). The Wolverine deposit occurs at the con-tact between footwall felsic volcaniclastic rocks (unit 6hw)and either hanging-wall carbonaceous argillite or exhalativerocks (Bradshaw et al., 2001). The Wolverine succession isunconformably overlain by the upper Paleozoic (Pennsylvan-ian-Permian; Harms, in Plint and Gordon, 1997) mafic vol-canic and clastic sedimentary rock-dominated CampbellRange succession (Figs. 2 and 3; Murphy and Piercey, 1999;Murphy, 2001).

Deformation has influenced rocks of the region but theseevents largely postdate the formation of the stratigraphy inthe Finlayson Lake region. The Money Creek thrust has dis-placed rocks from the Fire Lake unit a minimum of 30 km to-ward the east-northeast to their present position in the latePaleozoic (Figs. 2 and 3; Murphy and Piercey, 2000; Murphy,2001). The region has also been subject to Cretaceous ductiledeformation due to low displacement southwest-vergent fold-ing and thrusting (Murphy, 1998). A Mississippian event ofuncertain kinematics has affected the Grass Lakes succession;however, this is addressed in the context of the evolution ofthe belt in the discussion.

Geologic and Alteration Attributes of Host Rocks

Fire Lake unit

Felsic rocks comprise less than 5 percent of the Fire Lakeunit in the Money Creek thrust sheet (Piercey and Murphy,2000). Samples from the Money Creek thrust consist of kilo-meter-scale rhyolite-dacite flows interlayered with calc-alka-line arc and island-arc tholeiitic (Grant et al., 1996; Grant,1997) pillowed, massive, and vesiculated (±amygdaloidal)mafic lava flows and volcaniclastic rocks (Piercey and Murphy,2000). The felsic volcanic and high-level subvolcanic rocks inthe Money Creek thrust are fairly well preserved, weaklystrained, and have minimal alteration (Fig. 4a). Most of thefelsic rocks are reddish-pink to greenish-white subaerial toshallow subaqueous rhyolites and dacites that are variably Kfeldspar porphyritic containing millimeter-scale subhedral to

euhedral feldspar grains (Fig. 4a). They commonly constituterhyolitic lava flows that are in places associated with blockyrhyolitic hyaloclastite (Piercey and Murphy, 2000). Within theMoney Creek thrust sheet, the felsic rocks are associated withminor clastic sedimentary rocks (Piercey and Murphy, 2000),unlike rocks of the Kudz Ze Kayah unit and Wolverine suc-cession (Murphy and Piercey, 1999).

High-level quartz and quartz-feldspar subvolcanic rhyoliticintrusive rocks are spatially associated with, and are inferredto be, the feeders of the rhyolitic volcanic rocks (Piercey andMurphy, 2000). These intrusive rocks are pink-white to white-gray and are commonly K feldspar porphyritic within amedium-grained and, less commonly, fine-grained matrix.Mortensen (1992b) obtained a 360.5 ± 1 Ma age on a felsicporphyry from the Money Creek thrust; Piercey and Murphy(2000) documented magma mingling relationships betweenthese intrusions and a calc-alkaline mafic feeder dike to thebasalts, constraining the age of concomitant mafic and felsicvolcanism within the Money Creek thrust.

The felsic rocks of the Fire Lake unit are relatively pristine,have no associated VHMS mineralization and minor sericitealteration that is most likely due to seawater-rock interaction.Petrographically, most contain K feldspar phenocrysts (Fig.5a) and, locally, quartz phenocrysts within a siliceous matrix.K feldspar crystals (millimeter-scale) are euhedral to subhe-dral and in places form glomerophenocrystic aggregates (Fig.5a). Most grains are texturally well preserved with minorsericite patches on their surfaces; in one sample they are to-tally replaced by red oxides and clay minerals. Quartz grainsare typically teardrop-shaped grains or rounded within asiliceous matrix. The matrix is commonly partially replaced byFe-rich clays and minor sericite, but primary textures such asspherulitic quartz are locally preserved; pyrite is rare but pre-sent in some samples. Amygdales are typically filled withquartz, carbonate, chlorite, and/or oxide minerals. Millime-ter-scale quartz veinlets are present in more strained samples.

Kudz Ze Kayah unit

Felsic rocks in the Kudz Ze Kayah unit range from in situcoherent rocks (rhyolitic flows and/or intrusions?) and vol-caniclastic and epiclastic sedimentary rocks. Although theKudz Ze Kayah unit is generally schistose and foliated, moremassive coherent rocks preserve some textural characteristics(Fig. 4b-d). Nevertheless, the original morphology of the co-herent rocks is largely obscured by deformation and inter-preting whether they are extrusive or intrusive is difficult.Rocks interpreted as volcaniclastic are common within theKudz Ze Kayah unit and range from fine grained (tuffaceous)to coarse grained with millimeter- to centimeter-scale feldsparcrystals (Fig. 4d); coarse volcaniclastic rocks are very preva-lent within and host the GP4F deposit. The felsic rocks of theKudz Ze Kayah unit are associated with abundant fine-grained carbonaceous sedimentary rocks and lesser silicaclas-tic rocks, which contrasts with the Fire Lake unit that con-tains very little carbonaceous material. Crosscutting andoverlying the felsic rocks of the Kudz Ze Kayah unit are alka-lic mafic rocks that are interpreted to be of non-arc origin(Piercey, 2001).

Although deformed and locally recrystallized rocks in theKudz Ze Kayah unit in places have pristine textures and


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FIG. 4. Macroscopic features of felsic rocks from the various stratigraphic levels of the Finlayson Lake district. Scale is incentimeters. (a). K feldspar porphyritic rhyolitic flow from the Fire Lake unit with a massive matrix and small millimeter-scale K feldspar phenocrysts. More photos of the rocks in the Fire Lake unit can be found in Piercey and Murphy (2000).(b). Weakly to moderate chlorite-sericite altered K feldspar porphyritic high-level intrusive rocks from the Kudz Ze Kayahunit, containing well-preserved centimeter-scale K feldspar phenocrysts. (c). Moderately altered aphyric rhyolite flow and/orintrusion from the Kudz Ze Kayah unit with a network of millimeter-scale veinlets of sericite ± quartz. Slab is 20 cm wide.(d). Coarse-grained felsic volcaniclastic (tuffaceous) rock from the Kudz Ze Kayah unit, containing K feldspar phenocrysts ina siliceous matrix. The dark streaks within this sample are likely preserved sedimentary fragments. Note how the fabric ismore strongly developed in this sample and how the feldspars are elongate into an elliptical shape. (e). Coarse-grained fel-sic volcaniclastic rock from unit 5f/qfp of the Wolverine succession, containing large centimeter-scale K feldspar grains(white) and slightly smaller elliptical black to blue glassy quartz grains (darker gray to black) set within a fine-grained matrix.The matrix to this sample is weakly altered to sericite and lesser chlorite. (f). Feldspar porphyritic intrusion with centimeter-scale feldspars set in a siliceous matrix from unit 6 in the immediate footwall to the Wolverine VHMS deposit with very weaksilica-sericite-pyrite alteration. (h). Felsic volcaniclastic rock with fine-grained quartz and feldspar crystals with minorsericite-silica-carbonate alteration. This rock in places has coarse centimeter-scale feldspar crystals and forms the immediatefootwall to the Wolverine VHMS deposit (Bradshaw et al., 2001). (i). Massive aphyric rhyolite from unit 6 of the Wolverinesuccession that forms part of the hanging wall to the Wolverine VHMS deposit. This rhyolite is very silicified and has sericite-pyrite veinlets (medium gray) and carbonate veinlets (bright white, left side of the photo). These rocks are associated withiron formations and carbonate exhalative rocks and as such are typically elevated in base metals and silica relative to otherrhyolites in the district.

(a)

(c)

(e)

(g)

(b)

(d)

(f)

(h)

feldspars, and deformation and metamorphism do not appearto have significantly altered the primary mineralogy. Proximalto the Kudz Ze Kayah and GP4F VHMS deposits, there is anincrease in the intensity of alteration and the rocks havesericite, sericite-chlorite, and silica alteration.

Petrographically, most felsic rocks are variably deformedand have a matrix of recrystallized polycrystalline quartz (Fig.5b) with folia defined by muscovite (sericite) ± green tobrown biotite ± oxides ± chlorite; rarely, carbonate is inter-grown with matrix quartz. Rarely, quartz phenocrysts are pre-served; however, in most cases they are boundinaged parallelto the dominant foliation, internally recrystallized and man-tled by muscovite (± biotite ± oxide) folia. K feldspar phe-nocrysts are common and have variable states of preservation

(Fig. 5b). Most exhibit partial to full replacement by sericite,and some contain quartz granules replacing the feldspars.Many exhibit elongation to the fabric akin to quartz crystals(Fig. 5b). The elongate feldspar grains are often segmentedby polycrystalline veinlets of quartz ± sericite ± chlorite (Fig.5b). Crosscutting many of the samples are small millimeter-scale veinlets of quartz and sericite.

Wolverine succession

The Wolverine succession is similar to the Kudz Ze Kayahunit in being a felsic-volcanic and subvolcanic and sedimen-tary rock-dominated succession; however, it is younger and hasmore abundant sedimentary rocks. The succession consists ofa lower quartz-feldspar conglomerate unit that is overlain by


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FIG. 5. Photomicrographs of Finlayson Lake district felsic rocks. (a). Glomerporphyritic texture of euhedral K feldsparthat is partially replaced by finer sericite within a matrix of quartz-clay minerals and sericite within unit 2 calc-alkalic rhyo-lites (field of view = 3.9 mm; cross-polarized light). (b). Relatively unaltered K feldspar from Kudz Ze Kayah unit FPI. Thefeldspar grain is deformed and shows brittle fracturing with partial infilling by clays and quartz and is surrounded by a fab-ric of recrystallized quartz and muscovite which wraps around the feldspar (field of view = 5.1 mm; cross-polarized light).(c). Quartz crystals within unit 5f/qfp fine-grained felsic volcaniclastic rock (tuff). A boudin of quartz crystals within this rockis partially cracked and partially wrapped by a clay-quartz-sericite matrix. Note on the bottom left of the larger grain is asmaller grain with a possible resorbed edge (field of view = 5.1 mm; cross-polarized light). (d). Well-preserved euhedralfeldspar grain within a matrix of sericite and quartz from unit 6 FPI (field of view = 3.9 mm; cross-polarized light). (e). Aboudined quartz grain with possible resorbed edges partially wrapped by muscovite and within a recrystallized quartz-sericitematrix from unit 6 footwall tuff from the Wolverine deposit (field of view = 5.1 mm; cross-polarized light). (f). A boudin ofrare quartz phenocryst in the fabric of a unit 6 rhyolite from the hanging wall of the Wolverine deposit. Matrix containslargely recrystallized quartz, biotite, oxides (magnetite), and sericite (not visible; field of view = 3.9 mm; plane-polarizedlight).

(a)

(c)

(e)

(b)

(d)

(f)

a felsic volcanic-dominated unit (5f/qfp), which is in turnoverlain by a regional carbonaceous phyllite (unit 5cp; seeMurphy and Piercey, 1999). The latter carbonaceous sedi-mentary rocks form the deeper footwall to the WolverineVHMS deposit; the immediate footwall to the deposit consistsof a felsic tuffaceous unit with high-level felsic intrusions(unit 6fw; Bradshaw et al., 2001; Piercey et al., 2001); thehanging wall consists of aphyric rhyolite flows interlayeredwith carbonaceous sedimentary rocks (unit 6hw), which arecapped by basalt flows (Bradshaw et al., 2001). Although theWolverine succession is less deformed than the Kudz ZeKayah unit (Murphy and Piercey, 1999), it is deformed andthe original morphology and textures of the volcanic and in-trusive rocks are commonly obscured. Nevertheless, in someareas macroscopic textural features are preserved.

The lowermost felsic unit within the Wolverine succession(unit 5f/qfp) consists predominantly of variably strainedquartz and feldspar porphyritic felsic rocks (Figs. 4e and 5c),interpreted to be of volcaniclastic origin (tuffs and hyalo-clastitic rocks). These volcaniclastic rocks have abundantquartz and K feldspar crystals that are millimeter to centime-ter scale and heterogeneously distributed within a siliceous tomicaceous matrix (Fig. 4e). In unit 5f/qfp there are also co-herent rocks that are interpreted to be flows or high-level in-trusions, but often their margins are deformed and flow or in-trusion relationships are obscured. Typically the volcaniclasticrocks are more strained than the more coherent rocks. Thecoherent rocks typically have quartz phenocrysts (or filledamygdales?) and millimeter-scale euhedral to weakly strainedfeldspars. Notably, the rocks of unit 5f/qfp have much moreabundant quartz crystals and phenocrysts than those of theKudz Ze Kayah unit (Murphy and Piercey, 1999). Most felsicrocks of unit 5f/qfp have minor to moderately developedsericite alteration with some exhibiting silica alteration; rarelydo they exhibit chlorite or carbonate alteration.

The footwall to the Wolverine deposit consists of felsic vol-caniclastic and high-level intrusive rocks of unit 6fw (Fig. 4f-g; Bradshaw et al., 2001; Piercey et al., 2001). Fine- to coarse-grained felsic volcaniclastic rocks form the immediatefootwall to the deposit (Fig. 4g). Locally, these volcaniclasticrocks have centimeter-scale euhedral K feldspar grains andblue, elliptical quartz eyes, which are elongate in the plane ofthe foliation (Fig. 5e). Elsewhere, they consist of very finemillimeter-scale feldspar grains and micaceous material (Fig.5e). Also present in the footwall to the deposit are sill-likefeldspar and quartz-feldspar porphyritic intrusive rocks,which are relatively undeformed and have very well pre-served euhedral millimeter- to centimeter-scale K feldsparphenocrysts with or without quartz phenocrysts within asiliceous matrix (Figs. 4f and 5d). The footwall rocks to theWolverine deposit are variably altered. The tuffaceous rocksin the immediate footwall to the deposit can range from beingrelatively fresh distal to mineralization; however, proximal tothe Cu-rich zones of the deposit, they have intense sericite tochlorite rich assemblages with or without carbonate alteration(Bradshaw et al., 2001). Felsic intrusions in the footwall of thedeposit are less altered but do have a patchy distribution ofquartz-sericite ± pyrite ± sphalerite ± chlorite ± carbonateveinlets, patchy secondary K feldspar replacement of primaryK feldspar, and weak silica alteration (Piercey et al., 2001).

Felsic rocks above the Wolverine deposit are very distinc-tive and consist of highly siliceous aphyric rhyolite flows (Figs.4h and 5f) and rhyolite breccias, minor fine-grained tuffa-ceous rocks, interlayered with carbonaceous sedimentaryrocks, iron formation, and carbonate exhalite (Bradshaw etal., 2001). The aphyric rhyolites are strongly silicified andhave a siliceous matrix with partings of green waxy sericiteand in places sericite-chlorite. Many of the aphyric rhyoliticrocks near the iron formation and carbonate exhalite are char-acterized by magnetite-pyrite-carbonate alteration in additionto silica and sericite.

GeochemistryLeast altered felsic volcanic rocks of rhyolitic to dacitic

composition from the Finlayson Lake district were analyzedat the Geological Survey of Canada and details of the analyti-cal methods are presented in the Appendix. The completedataset for this paper has been placed in digital form in theEconomic Geology data repository (Table R1). The averages,ranges, and 2σ errors for the different suites and lithologiesare presented in Table 1. Major and trace element ratios arepresented in Table 2.

Although attempts were made to sample least altered rocks,many samples exhibit the effects of alteration and metamor-phism—particularly in samples that were collected proximalto the VHMS deposits. Given these constraints we have bro-ken our presentation of the geochemical data into two sec-tions, including the mobile element and the immobile ele-ment systematics. Furthermore, in Tables 1 and 2, for ease ofpresentation, the data are subdivided based on their strati-graphic position (e.g., Fire Lake unit, Kudz Ze Kayah unit,and Wolverine succession) and geologic attributes (e.g., rhyo-lite flows, subvolcanic intrusions, and volcano-sedimentaryrocks).

Mobile element systematics

Numerous workers have shown that feldspar and glass de-struction, and replacement of primary phases by secondaryalteration phases, are the most common reactions during hy-drothermal alteration of felsic rocks in the VHMS environ-ment (e.g., Munha et al., 1980; Saeki and Date, 1980; Hajashand Chandler, 1981; Lentz, 1999; Large et al., 2001).Feldspar destruction reactions result in the loss of alkalis(particularly Na and Ca) during the formation of sericite(Ishikawa et al., 1976; Spitz and Darling, 1978; Munha et al.,1980; Saeki and Date, 1980); whereas, replacement offeldspars and sericite by fixation of Mg (±Fe) from solution toform chlorite leads to gains in Mg (±Fe) in the rocks (Saekiand Date, 1980; Hajash and Chandler, 1981; Date et al., 1983;Lentz, 1999). These results lead us to assume that the alkalis,SiO2, and Fe-Mg have been mobile in the rocks of the Fin-layson Lake district. Other major elements such as TiO2 andAl2O3 are considered immobile (Whitford et al., 1989; Barrettand MacLean, 1999) except under extreme conditions (Hynes,1980; Finlow-Bates and Stumpfl, 1981). However, given thelevel of preservation of samples in this study Al2O3 and TiO2are assumed to be immobile. The low field strength elements(LFSE; Ba, Rb, Cs, Sr) are considered mobile during hy-drothermal alteration (e.g., MacLean, 1990; Lentz, 1999) andare assumed to be mobile in the rocks of the Finlayson Lake

1884 PIERCEY ET AL.

0361-0128/98/000/000-00 $6.00 1884

district. The rare earth elements (REE) can be mobile duringintense hydrothermal alteration (e.g., Campbell et al., 1984;Valsami and Cann, 1992), but under low-grade alteration(sericite) conditions they remain immobile (Whitford et al.,1988), and in this study we assumed they were immobile. Theexception, however, is Eu, which can be very mobile in thehydrothermal environment (Sverjensky, 1984; Whitford et al.,1988; Wood and Williams-Jones, 1994). The high fieldstrength elements (HFSE) appear to be immobile in nearlyall circumstances (e.g., Whitford et al., 1989; MacLean, 1990;Barrett and MacLean, 1999; Lentz, 1999) with minor excep-tions (e.g., Finlow-Bates and Stumpfl, 1981). The coherentHFSE behavior in the rocks of the Finlayson Lake districtsuggests they remained immobile during alteration and meta-morphism. By virtue of their presence as essential metallicconstituents in VHMS deposits, the metals Cu, Pb, Zn, Ag,Sn, As, and Tl are considered mobile.

In Figure 6a, the samples are plotted in a total alkalies ver-sus silica plot (Le Bas et al., 1986), which shows that mostsamples retain a rhyolitic affinity but have significant scatterdue to alkali mobility (Fig. 6a). The highly silicified nature ofthe aphyric rhyolites results in many samples plotting outsidethe bounds of this diagram. In the Shand’s index (Fig. 6b; Ma-niar and Piccoli, 1989), most samples exhibit variable A/CNKand A/NK ratios (Fig. 6b; Table 2), which suggest alkali mo-bility during feldspar destruction; it is likely that most of therocks had primary A/CNK values close to 1 (cf. Lentz, 1999).Alkali mobility is also reflected in the high Al2O3/Na2O ratios(Spitz and Darling, 1978), Hashimoto alteration index values(Ishikawa et al., 1976; Date et al., 1983), and sericite indexvalues (Saeki and Date, 1980; Table 2). On an AFM plot (Fig.6c; Irvine and Baragar, 1971) most felsic rocks from the Fin-layson Lake district appear to follow calc-alkaline trendswith some exceptions (Fig. 6c). The Fire Lake unit tholeiitic


0361-0128/98/000/000-00 $6.00 1885

0.5 1.0 1.5 2.00.4

1.4

2.4

Al/(

Na+

K)

Al/(Ca+Na+K)

Peralkaline

Metaluminous

Peraluminous

Na2O+K2O MgO

FeO*

Calc-Alkaline

Tholeiitic

(b)(c)

FIG. 6. Major element plots of the Finlayson Lake district felsic volcanic rocks. (a). Total alkalis versus silica plots of LeBas et al (1986) and (b) Irvine and Baragar (1971). (c). The Shand’s index of Maniar and Piccoli (1989) and (d). AFM plot(Irvine and Baragar, 1971). Abbreviations: 2-QFPI = Fire Lake unit quartz-feldspar porphyritic intrusions, 2-RHY/DAC =Fire Lake unit calc-alkaline rhyolite-dacite flows, 2-T-RHY/DAC = Fire Lake unit tholeiitic rhyolite-dacite flows, 3-RHY =Kudz Ze Kayah unit aphyric rhyolites, 3-F(+Q)P = Kudz Ze Kayah unit feldspar-(+quartz) porphyritic rhyolites, 3-FT = KudzZe Kayah unit felsic tuffs, 5-RHY = Wolverine succession, unit 5f/qfp, rhyolite flows, 5-QFP = Wolverine succession, unit5f/qfp, quartz-feldspar porphyritic high-level intrusions, 5-FT = Wolverine succession, unit 5f/qfp, felsic tuffs; 6-FW-FT =Wolverine succession, unit 6fw, felsic tuffs; 6-FW-QFP = Wolverine succession, unit 6fw, quartz-feldspar porphyritic intru-sion, 6-HW-APRHY = Wolverine succession, unit 6hw, aphyric rhyolite flows.

(a)

35 40 45 50 55 60 65 70 750

2

4

6

8

10

12

14

16

Na 2

O +

K2O

(wt%

)

SiO2 (wt%)

Picro-basalt

BasaltBasalticandesite

Andesite Dacite

RhyoliteTrachyte

TrachydaciteTrachy-andesite

Basaltictrachy-andesite

basalt

Tephrite

Phono-Tephrite

Tephri-phonolite

Phonolite

Foidite

65 70 752-QFPI

2-RHY/DAC

2-T-RHY/DAC

3-RHY

3-F(+Q)P

3-FT

5-RHY

5-QFP

5-FT

6-FW-QFP

6-FW-FT

6-HW-APRHY

1886 PIERCEY ET AL.

0361-0128/98/000/000-00 $6.00 1886

TAB

LE

1. S

umm

ary

of G

eoch

emic

al C

hara

cter

istic

s of

Fel

sic

Roc

ks fr

om th

e F

inla

yson

Lak

e D

istr

ict (

all r

ocks

are

sep

arat

ed in

to s

trat

igra

phic

pos

ition

and

lith

olog

y)

FLU

-2f-

FLU

-2f-

FLU

-2f-

KZK-

3-KZ

K-3-

KZK-

3-W

V-5f

/qfp

-W

V-5f

/qfp

-W

V-5f

/qfp

-W

V-6

WV-

6FW

-W

V-6-

HW

-Q

FP-I

(ca)

RHY/

DAC

(ca)

DAC

/RH

Y (t)

RHY

F ±

Q-P

IFT

(f ±

q)RH

Y (±

qfp)

QFP

-IFT

(qfp

)FW

-QFP

-IFT

(qfp

)AP

RHY

Mea

n2σ

Mea

n2σ

Mea

n2σ

Mea

n2σ

Mea

n2σ

Mea

n2σ

Mea

n2σ

Mea

n2σ

Mea

n2σ

n =

1M

ean

2σM

ean

2σn

= 3

n=

4n

= 3

n=

13n

= 5

n=

9n

= 5

n=

2n

= 7

(P98

69*)

n=

6n

= 40

SiO

276

.24.

173

.61.

470

.83.

874

.81.

372

.83.

972

.91.

976

.63.

474

.40.

474

.52.

475

.771

.42.

585

.91.

7Ti

O2

0.19

0.04

0.29

0.12

0.42

0.26

0.24

0.07

0.39

0.18

0.36

0.11

0.23

0.07

0.28

0.03

0.32

0.18

0.41

0.32

0.08

0.25

0.04

Al 2O

312

.21.

013

.11.

412

.40.

612

.30.

613

.61.

513

.50.

712

.82.

713

.60.

812

.60.

613

.913

.61.

25.

00.

7F

e 2O

3T1.

901.

103.

080.

905.

373.

101.

870.

702.

540.

872.

590.

560.

820.

411.

851.

272.

341.

560.

202.

820.

942.

090.

39F

e 2O

30.

701.

201.

380.

643.

672.

370.

600.

311.

120.

741.

080.

380.

350.

490.

900.

281.

501.

040.

00F

eO0.

900.

201.

500.

971.

531.

931.

000.

341.

260.

181.

350.

320.

250.

070.

800.

850.

980.

600.

20N

AN

AF

eO*

1.71

0.99

2.77

0.81

4.83

2.79

1.69

0.62

2.27

0.78

2.33

0.50

0.78

0.28

1.61

1.10

2.10

1.40

0.20

2.53

0.84

1.88

0.35

MnO

0.02

0.02

0.05

0.01

0.12

0.08

0.03

0.02

0.02

0.02

0.03

0.01

0.00

0.00

0.06

0.07

0.02

0.02

0.00

0.02

0.03

0.08

0.09

MgO

0.59

0.16

1.25

0.31

1.09

0.37

0.58

0.19

0.52

0.24

0.79

0.23

0.47

0.43

0.67

0.49

0.70

0.15

0.09

0.95

0.73

0.77

0.13

CaO

0.84

0.61

0.69

0.37

1.71

0.93

0.65

0.23

0.33

0.21

1.06

0.57

0.07

0.06

0.41

0.23

0.38

0.27

0.11

0.99

1.00

0.49

0.23

Na 2

O4.

201.

903.

300.

422.

132.

972.

251.

211.

541.

533.

501.

210.

560.

510.

200.

001.

591.

481.

300.

550.

520.

150.

08K

2O2.

702.

902.

800.

621.

401.

065.

941.

797.

023.

033.

691.

227.

040.

827.

150.

555.

761.

807.

125.

201.

121.

220.

19H

2O0.

870.

361.

800.

493.

071.

550.

750.

121.

120.

461.

120.

281.

120.

901.

550.

141.

240.

370.

801.

900.

131.

110.

18C

O2

0.37

0.54

0.58

0.32

1.83

1.42

0.34

0.17

0.16

0.09

0.47

0.33

0.10

15.9

70.

300.

280.

240.

180.

100.

950.

970.

750.

32P 2

O5

0.05

0.02

0.07

0.03

0.09

0.07

0.05

0.02

0.13

0.05

0.09

0.05

0.06

0.04

0.15

0.00

0.10

0.04

0.05

0.11

0.04

0.04

0.01

Tota

l10

0.1

0.3

100.

50.

910

0.4

1.2

99.8

0.5

100.

20.

410

0.1

0.5

99.9

0.1

100.

60.

299

.80.

599

.897

.51.

597

.81.

2

Cr

(ppm

)28

840

2025

725

1332

3326

1151

6012

155

3291

224

626

Ni

<10

147

<10

<10

<10

<10

165

<10

<10

<10

<10

<10

5514

Co

<56

<525

720

924

328

1121

1019

5<5

<513

5Sc

4.6

2.2

7.3

0.3

14.0

3.7

4.4

1.1

8.3

4.6

6.8

1.8

3.5

1.3

4.3

0.7

5.9

3.3

5.9

5.9

2.3

9.0

1.2

V13

339

2533

113

148

167

152

81

128

922

794

14C

u15

8<1

0<1

013

2<1

047

26<1

0<1

0<1

0<1

073

7871

12Pb

108

66

11

116

2929

74

1410

1813

95

2425

86

2Zn

3022

408

7632

3115

348

250

415

246

306

3123

<540

274

210

258

Bi

<0.2

<0.2

<0.2

0.6

0.3

0.7

0.3

0.1

0.2

<0.2

0.3

<0.2

1.5

0.9

0.3

0.0

Cd

0.3

<0.2

<0.2

0.4

0.1

<0.2

7.9

<0.2

0.7

0.4

<0.2

<0.2

6.6

10.4

0.4

0.0

In0.

170.

080.

030.

110.

050.

080.

020.

060.

100.

030.

070.

010.

090.

000.

080.

020.

070.

100.

030.

070.

00Sn

2.3

1.0

2.0

0.6

1.7

0.9

7.3

1.4

4.3

0.5

7.1

2.2

5.8

1.7

6.5

1.6

6.4

1.7

3.8

22.9

29.1

1.6

0.8

Mo

0.6

0.3

1.1

0.5

0.3

0.1

1.0

0.6

1.4

0.9

1.3

0.3

1.8

1.3

0.4

0.3

1.0

0.4

1.3

2.5

1.0

1.8

1.4

As

NA

NA

NA

1.2

0.6

1.1

1.0

1.6

0.8

NA

NA

NA

NA

NA

NA

Sb0.

70.

30.

30.

1<0

.2<0

.2<0

.2<0

.24.

14.

00.

40.

01.

00.

7<0

.23.

01.

91.

00.

7A

g0.

10.

1<0

.10.

50.

20.

40.

40.

70.

11.

40.

50.

50.

10.

3<0

.10.

40.

20.

20.

0R

b96

.610

7.3

60.3

20.3

38.0

21.4

134.

641

.714

7.2

59.0

96.3

37.5

214.

057

.319

0.0

28.3

161.

335

.915

0.0

150.

021

.261

.111

.6C

s1.

341.

543.

893.

023.

131.

641.

000.

301.

921.

026.

478.

192.

640.

842.

100.

574.

354.

492.

005.

624.

634.

731.

23B

a88

079

096

840

925

385

779

214

1229

781

1071

430

1482

988

1700

566

944

525

1400

3550

2873

7183

1849

Sr13

364

140

4381

8748

1948

2773

4035

597

1039

1845

6950

109

31T

l0.

370.

440.

280.

160.

190.

110.

610.

240.

670.

250.

420.

222.

101.

420.

840.

170.

650.

230.

856.

538.

210.

760.

19G

a12

.02.

415

.31.

718

.32.

218

.22.

320

.61.

820

.82.

418

.65.

519

.02.

819

.12.

421

.021

.74.

09.

01.

3Ta

0.7

0.1

0.9

0.1

0.5

0.1

2.5

0.6

2.8

0.6

2.7

0.6

2.1

0.7

2.6

1.4

2.2

0.4

2.0

1.9

0.4

0.4

0.1

Nb

9.5

1.8

15.5

2.9

9.9

1.5

26.1

6.7

30.4

7.9

31.2

6.7

20.4

2.6

20.0

5.7

24.7

5.0

34.0

26.5

8.2

5.6

0.9

Hf

3.6

0.1

5.8

2.2

4.2

1.7

7.6

2.4

9.5

4.4

10.0

2.6

5.2

0.5

5.1

0.7

6.0

1.5

11.0

8.1

2.8

1.9

0.3

Zr11

6.7

16.3

227.

579

.118

0.0

28.3

299.

410

9.8

412.

821

4.4

392.

412

4.0

176.

018

.217

5.0

14.1

228.

189

.050

0.0

298.

313

1.3

77.1

10.9

Y18

.77.

823

.34.

050

.37.

845

.510

.637

.66.

649

.89.

528

.48.

935

.05.

743

.413

.430

.045

.511

.714

.02.

1T

h12

.71.

611

.52.

72.

81.

226

.33.

432

.410

.928

.06.

118

.05.

217

.54.

222

.02.

531

.026

.28.

14.

00.

5U

2.3

0.8

2.2

0.1

0.6

0.5

4.7

0.6

4.3

1.1

5.0

1.1

3.7

1.0

2.6

0.1

4.1

0.7

2.3

6.8

2.7

1.2

0.2

La

30.0

6.2

37.0

2.1

21.0

1.4

56.6

9.6

75.4

37.8

68.6

21.6

36.2

9.0

46.0

11.3

44.4

8.9

110.

066

.023

.313

.71.

7C

e50

.35.

071

.54.

947

.74.

311

3.2

20.0

162.

867

.013

4.2

41.6

76.4

17.5

97.5

35.4

89.6

19.2

200.

013

9.5

52.5

29.6

4.0

Pr5.

70.

97.

80.

66.

50.

212

.82.

517

.77.

715

.05.

08.

32.

610

.12.

510

.12.

323

.015

.96.

33.

50.

4N

d18

.74.

328

.31.

129

.00.

047

.19.

465

.028

.955

.616

.528

.88.

339

.011

.337

.09.

679

.056

.822

.913

.31.

7

rhyolites-dacites plot on the tholeiitic-calc-alkaline boundary(Fig. 6c). The Wolverine deposit aphyric rhyolites trend to-ward the FeO* apex of the diagram, reflecting the presenceof pyrite and/or magnetite (Fig. 6c).

The geochemical data for felsic rocks of the Finlayson Lakedistrict are illustrated in an alteration box plot in Figure 7(Large et al., 2001). This diagram relates whole-rock geo-chemistry to potential alteration minerals present in the sam-ples. The diagram is constructed with two alteration indices,the Hashimoto alteration index (AI; Ishikawa et al., 1976; seeTable 2) to account for feldspar and glass breakdown tosericite and chlorite, and a chlorite-carbonate-pyrite index(CCPI; see Table 2). The diagram also provides a box for fel-sic rocks that are typically unaltered and fields for diageneticand hydrothermal alteration reactions (Fig. 7; Large et al.,2001). In this diagram, the calc-alkalic rocks of the Fire Lakeunit (see below) plot predominantly within the least alteredbox. The tholeiitic rhyolitic to dacitic rocks of the Fire Lakeunit lie above the least altered box (Fig. 7). This most likelyreflects their intermediate compositions, which typically havehigher least altered CCPI values (Large et al., 2001). Numer-ous rocks from the Kudz Ze Kayah unit and the Wolverinesuccession lie within the least altered box; however, numer-ous samples trend toward the sericite line (Fig. 7). Notable isthat most of the hanging-wall and footwall rocks in theWolverine deposit have high AI and CCPI values (Table 2).

Immobile element systematics

Throughout the Finlayson Lake district it is clear that manyof the major elements and most likely the LFSE were mobileduring alteration and metamorphism (see above). In this sec-tion, the immobile element geochemical features of the rocksfrom the Finlayson Lake district are presented in Figures 8 to14 and Tables 1 and 2.

Grass Lakes succession: Fire Lake unit: Felsic samplesfrom the Fire Lake unit are those that are found primarily inthe Money Creek thrust sheet and are subdivided into calc-al-kaline rhyolite-dacite flows and subvolcanic intrusions andtholeiitic rhyolites. Calc-alkalic rhyolite-dacite flows from theFire Lake unit have moderate Zr/TiO2 (750–864) and Nb/Y(0.6–0.8) values that suggest a subalkaline affinity (Fig. 8a).The HFSE contents (Nb, Ta, Ga, Zr, Hf, Y) within these rocksare moderate to low and are characteristic of volcanic-arcrocks (Fig. 8b-c) with I-type affinities (Fig. 8d). Primitivemantle-normalized plots are characterized by LREE enrich-ment, strong negative Nb and Ti anomalies, weakly negativeEu anomalies, low Al, Sc, and V, and flat to weakly positive Zrand Hf anomalies (Fig. 9a; Table 2). The Fire Lake unit calc-alkalic rhyolites have moderate Zr/Nb and Zr/Y (7.6–18.3)values, similar to published values for calc-alkalic rocks (Leatet al., 1986; Barrett and MacLean, 1999; Fig. 10b; Table 2).The calc-alkaline rhyolites have moderate Zr/Sc (26.4–43.4)and Zr/TiO2 (750–864) ratios (Fig. 10c-d), moderate to lowTi/Sc (1491-347) ratios, and moderate to high Nb/Ta values(15.9–17.4; Table 2).

The geochemical attributes of the calc-alkalic quartz-feldspar porphyritic intrusions are very similar to the calc-al-kalic rhyolite flows with similar volcanic-arc (I-type) affinities(Fig. 8; Tables 1 and 2). The intrusions have primitive man-tle-normalized patterns similar to the calc-alkaline flows but


0361-0128/98/000/000-00 $6.00 1887

Sm3.

21.

35.

30.

47.

80.

58.

81.

711

.34.

210

.33.

05.

42.

06.

81.

37.

42.

112

.010

.54.

02.

80.

3E

u0.

60.

21.

00.

21.

90.

10.

90.

31.

30.

81.

20.

40.

60.

51.

30.

30.

70.

50.

91.

61.

10.

40.

1G

d3.

11.

64.

70.

68.

40.

47.

91.

78.

82.

98.

92.

04.

51.

86.

21.

46.

71.

98.

18.

52.

92.

50.

3T

b0.

50.

30.

70.

11.

40.

11.

30.

31.

30.

31.

40.

30.

70.

31.

00.

11.

20.

41.

01.

30.

40.

40.

1D

y2.

91.

33.

80.

48.

41.

37.

72.

07.

31.

28.

31.

64.

41.

75.

60.

66.

92.

14.

87.

51.

92.

40.

3H

o0.

60.

30.

80.

11.

80.

41.

50.

41.

40.

21.

70.

30.

90.

31.

20.

11.

40.

40.

91.

50.

40.

50.

1E

r1.

70.

82.

10.

34.

70.

84.

21.

13.

70.

44.

50.

82.

50.

83.

20.

43.

91.

22.

64.

01.

01.

40.

2T

m0.

30.

10.

40.

10.

80.

20.

70.

20.

60.

00.

70.

10.

40.

10.

50.

00.

60.

20.

40.

60.

10.

20.

0Yb

1.9

0.7

2.6

0.5

5.3

1.2

4.5

1.3

3.6

0.5

4.7

0.9

2.8

0.6

3.3

0.4

3.9

1.1

2.9

3.9

1.0

1.6

0.2

Lu

0.3

0.1

0.4

0.1

0.8

0.2

0.6

0.2

0.6

0.1

0.7

0.1

0.4

0.1

0.5

0.1

0.6

0.1

0.4

0.6

0.1

0.3

0.0

T-Zr

Sat1

766

584

219

833

5483

732

886

6687

535

829

2883

310

838

2393

388

036

776

18

Abb

revi

atio

ns: F

LU

-2f p

refix

= F

ire

Lak

e un

it fe

lsic

roc

ks, Q

FP-

I (c

a) =

cal

c-al

kalin

e qu

artz

-fel

dspa

r po

rphy

ritic

intr

usio

n, R

HY/

DA

C (c

a) =

rhy

olite

-dac

ite (c

alc-

alka

line)

, RH

Y/D

AC

(t) =

rhy

olite

-da

cite

(tho

leiit

ic),

KZK

-3 p

refix

= K

udz

Ze K

ayah

uni

t, R

HY

= rh

yolit

e, F

±Q-P

I =

feld

spar

±qu

artz

por

phyr

itic

intr

usio

n, F

T (f

±q)

= fe

lsic

tuff

(fel

dspa

r ±

quar

tz),

WV-

5f/q

fp p

refix

= W

olve

rine

Suc

-ce

ssio

n un

it 5f

/qfp

, RH

Y (±

qfp)

= r

hyol

ite (

±qua

rtz

and

feld

spar

por

phyr

itic)

, QF

P-I

= qu

artz

-fel

dspa

r po

rphy

ritic

intr

usio

n, F

T (

qfp)

= fe

lsic

tuff

(qu

artz

-fel

dspa

r po

rphy

ritic

), W

V-6

pref

ix =

Wol

ver-

ine

Succ

essi

on u

nit 6

, APH

RY

= ap

hyri

c rh

yolit

e1

TZr

Sat =

zir

con

satu

ratio

n te

mpe

ratu

re (

Wat

son

and

Har

riso

n, 1

983)

TAB

LE

1. (

Con

t.)

FLU

-2f-

FLU

-2f-

FLU

-2f-

KZK-

3-KZ

K-3-

KZK-

3-W

V-5f

/qfp

-W

V-5f

/qfp

-W

V-5f

/qfp

-W

V-6

WV-

6FW

-W

V-6-

HW

-Q

FP-I

(ca)

RHY/

DAC

(ca)

DAC

/RH

Y (t)

RHY

F ±

Q-P

IFT

(f ±

q)RH

Y (±

qfp)

QFP

-IFT

(qfp

)FW

-QFP

-IFT

(qfp

)AP

RHY

Mea

n2σ

Mea

n2σ

Mea

n2σ

Mea

n2σ

Mea

n2σ

Mea

n2σ

Mea

n2σ

Mea

n2σ

Mea

n2σ

n =

1M

ean

2σM

ean

2σn

= 3

n=

4n

= 3

n=

13n

= 5

n=

9n

= 5

n=

2n

= 7

(P98

69*)

n=

6n

= 40

1888 PIERCEY ET AL.

0361-0128/98/000/000-00 $6.00 1888

TAB

LE

2. S

umm

ary

of K

ey M

ajor

and

Tra

ce E

lem

ent R

atio

s fo

r F

elsi

c R

ocks

of t

he F

inla

yson

Lak

e D

istr

ict (

all r

ocks

are

sep

arat

ed in

to s

trat

igra

phic

pos

ition

and

lith

olog

y)

FL

U-2

f-F

LU

-2f-

FL

U-2

f-K

ZK-3

-K

ZK-3

-K

ZK-3

-W

V-5f

/qfp

-W

V-5f

/qfp

-W

V-5f

/qfp

-W

V-6-

WV-

6-F

W-

WV-

6-H

W-

QF

P-I

(ca)

RH

Y/D

AC

(ca)

DA

C/R

HY

(t)

RH

YF

±Q

-PI

FT

(f ±

q)R

HY

(±qf

p)Q

FP-

IF

T (q

fp)

FW

-QF

P-I

FT

(qfp

)A

PRH

YM

ean

2σM

ean

2σM

ean

2σM

ean

2σM

ean

2σM

ean

2σM

ean

2σM

ean

2σM

ean

2σn

= 1

Mea

n2σ

Mea

n2σ

n=

3n

= 4

n=

3n

= 13

n=

5n

= 9

n=

5n

= 2

n=

7(P

98-6

9*)

n=

6n

= 40

FeM

g/N

aK1

0.36

0.13

0.72

0.18

2.34

1.81

0.32

0.11

0.36

0.06

0.47

0.09

0.18

0.11

0.34

0.13

0.44

0.26

0.03

0.71

0.29

3.27

1.93

A/C

NK

21.

10.

11.

40.

21.

60.

81.

10.

11.

30.

11.

20.

11.

50.

51.

50.

11.

40.

31.

41.

80.

62.

50.

4A

/NK

21.

20.

11.

60.

24.

87.

31.

20.

11.

30.

11.

40.

11.

60.

61.

70.

01.

50.

31.

42.

20.

53.

80.

7A

l 2O3/N

a 2O

3.1

1.5

4.0

0.5

4.2

2.4

17.1

11.0

18.8

19.7

7.3

6.5

43.5

33.7

68.0

4.2

38.5

38.1

10.7

60.7

46.5

40.9

7.1

HA

SHI-

AI3

3829

502

4118

6815

7726

4914

936

933

7719

8481

1178

5SE

R-I

437

3846

856

5969

1778

2751

1793

697

078

2185

926

884

CC

PI5

257

406

6615

226

243

304

148

246

2711

338

1065

3N

a/K

64.

769.

351.

230.

411.

973.

700.

990.

910.

530.

931.

300.

630.

080.

070.

030.

000.

450.

520.

180.

090.

080.

160.

08Sc

/Nb

0.49

0.24

0.48

0.09

1.44

0.60

0.19

0.06

0.26

0.12

0.25

0.12

0.17

0.05

0.21

0.02

0.25

0.12

0.17

0.22

0.03

1.73

0.16

Ti/S

c26

511

523

587

175

5834

578

313

104

322

4641

162

396

2632

475

417

252

195

164

20Zr

/Y6.

84.

010

.46.

13.

61.

16.

41.

911

.26.

08.

02.

26.

61.

85.

00.

46.

23.

016

.76.

51.

85.

80.

5Zr

/Sc

27.4

12.7

31.1

9.5

13.3

4.7

68.5

23.9

50.2

12.7

59.2

13.4

56.2

19.0

41.3

3.5

42.5

11.3

84.7

50.6

7.2

8.8

1.1

Zr/N

b12

.30.

815

.37.

818

.22.

910

.92.

313

.05.

312

.52.

28.

70.

88.

81.

89.

63.

314

.711

.02.

214

.21.

0Zr

/TiO

261

6.4

40.2

802.

260

.248

6.7

285.

012

04.5

228.

910

14.7

265.

810

90.2

182.

581

6.4

220.

962

5.2

12.6

819.

019

6.2

1219

.592

5.9

233.

730

7.3

21.5

Zr/H

f32

.55.

739

.41.

145

.017

.737

.04.

841

.74.

838

.43.

234

.02.

034

.72.

136

.65.

045

.535

.94.

141

.11.

4N

b/Y

0.6

0.4

0.7

0.1

0.2

0.0

0.6

0.1

0.8

0.2

0.6

0.1

0.8

0.2

0.6

0.1

0.6

0.1

1.1

0.6

0.1

0.4

0.0

Nb/

Ta7

12.9

0.8

17.0

0.9

20.8

1.2

13.6

2.8

14.7

15.8

2.5

12.9

0.9

13.7

0.7

17.0

13.6

2.5

15.2

0.6

104*

Ga/

Al

1.9

0.3

2.2

0.1

2.8

0.3

2.8

0.3

2.9

0.1

2.9

0.4

2.7

0.3

2.6

0.2

2.9

0.3

2.9

3.0

0.3

3.4

0.2

Th/

Nb

1.3

0.1

0.8

0.3

0.3

0.1

1.2

0.3

1.1

0.2

1.0

0.2

0.9

0.3

0.9

0.0

1.0

0.2

0.9

1.0

0.1

0.7

0.0

La/

Ybn8

11.8

6.3

10.7

2.4

2.9

0.6

9.7

1.5

14.7

6.7

11.1

4.1

9.5

2.5

10.1

1.2

8.8

2.3

27.2

12.4

3.5

6.5

0.6

Ce/

Ybn8

7.1

3.5

7.5

2.3

2.4

0.5

7.0

1.0

11.7

5.2

7.8

2.8

7.3

2.0

7.7

1.8

6.3

1.5

17.9

9.4

2.6

5.1

0.4

Eu/

Eu*

90.

630.

080.

640.

040.

730.

050.

310.

080.

360.

120.

380.

120.

340.

150.

620.

010.

360.

240.

280.

550.

490.

400.

06N

b/N

b*9

0.14

0.01

0.24

0.07

0.44

0.05

0.19

0.04

0.18

0.03

0.21

0.04

0.22

0.05

0.21

0.01

0.22

0.05

0.18

0.18

0.01

0.23

0.01

Zr/Z

r*9

1.03

0.42

1.23

0.42

0.82

0.11

0.93

0.26

0.95

0.18

1.08

0.20

1.01

0.29

0.71

0.12

0.95

0.28

1.04

0.84

0.26

0.86

0.07

Hf/H

f*9

1.13

0.27

1.14

0.41

0.70

0.28

0.87

0.15

0.82

0.08

1.03

0.20

1.07

0.30

0.74

0.09

0.93

0.23

0.83

0.84

0.22

0.76

0.06

Ti/T

i*9

0.09

0.04

0.08

0.03

0.10

0.06

0.04

0.01

0.05

0.01

0.05

0.01

0.06

0.01

0.06

0.01

0.07

0.05

0.04

0.03

0.02

0.14

0.01

Abb

revi

atio

ns a

s in

Tab

le 1

1

(FeO

* +

MgO

)/(N

a 2O

+ K

2O)

(Len

tz, 1

999)

2

A/C

NK

and

A/N

K m

olar

Al 2O

3/CaO

+ N

a 2O

+ K

2O a

nd A

l 2O3/N

a 2O

+ K

2O (

Man

iar

and

Picc

oli,

1989

) 3

HA

SHI-

AI

= H

ashi

mot

o in

dex

= 10

0*[(

MgO

+ K

2O)/

(MgO

+ K

2O +

Na 2

O +

CaO

)] (

Ishi

kaw

a et

al.,

197

6)

4 SE

R-I

= s

eric

ite in

dex

= K

2O/(

K2O

+ N

a 2O

) (S

akai

and

Dat

e, 1

983)

5

CC

PI =

chl

orite

-car

bona

te-p

yrite

inde

x =

100*

[(M

gO +

FeO

*)/(

MgO

+ F

eO*

+ K

2O +

Na 2

O)]

(L

arge

et a

l., 2

001)

6

Na/

K =

Na 2

O/K

2O

7 N

b/Ta

= n

ote

only

sam

ples

not

cru

shed

in tu

ngst

en c

arbi

de in

clud

ed in

cal

cula

tion

8 N

orm

aliz

ed to

cho

ndri

tic v

alue

s9 E

u/E

u* =

Eu p

m/(

Gd p

m⋅S

mpm

)0.5, N

b/N

b* =

0.5

*Nb p

m/(

Th p

m+

La p

m),

Zr/Z

r* =

0.5

*Zr p

m/(

Gd p

m+

Smpm

), H

f/Hf*

= 0

.5*H

f pm

/(G

d pm

+ Sm

pm) T

i/Ti*

= 0

.5*T

i pm

/(G

d pm

+ Sm

pm);

pm =

pri

miti

ve m

antle

norm

aliz

ed


0361-0128/98/000/000-00 $6.00 1889

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

AI

CC

PI

epidotecalcite dolomite ankerite

chloritepyrite

sericite

K-feldsparAlbite

Diagenetic Field

AlterationField

least altered felsics

FIG. 7. An alteration box plot of Large et al. (2001), with vectors for various alteration minerals and alteration versus di-agenetic trajectories (further details provided in the text). CCPI = chlorite-carbonate-pyrite index, AI = Ishikawa alterationindex. Symbols as in Figure 6.

.01 .1 1 10

.01

.1

1

Zr/

TiO

2

Nb/Y

Basalt

Andesite/Basalt

Rhyolite/Dacite

AlkBasalt

TrachyAnd

Trachyte

AlkRhyolite

Phonolite

Tephri-phonolite

Foidite

(a)

1 10 100 10001

10

100

1000

Nb

(pp

m)

Y (ppm)

within plateA-type

ocean ridgeOR-type

M-type

volcanic arcI-type

syncollisionalS-type with

in plate &

anomalous ocean ridge

(b)

.1 1 10 100

.1

1

10

100

Ta (p

pm

)

Yb ( )

syn-collisionalS-type

within-plate(A-type)

within-plate &

anomalous ocean ridge

volcanic arcI-type

M-type

ocean ridgeOR-type

(c)

1 1010

100

1000

Zr

(pp

m)

104Ga/Al

I&S-types

A-type

(d)

Alk

alin

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FIG. 8. (a). Modified Zr/TiO2-Nb/Y plot (Pearce, 1996) of Winchester and Floyd (1977), (b). Nb-Y, and (c). Ta-Yb plotsof Pearce et al. (1984). (d). Ga/Al-Zr plot of Whalen et al. (1987). Symbols as in Figure 6.

with less strongly developed Zr and Hf anomalies (Fig. 9;Table 2). The intrusions, however, have lower Nb/Ta(12.3–13.4) and Zr/Hf (39.7–37.1) values and higher Ti/Sc(174–329) values than the calc-alkalic flows (Table 2).

Tholeiitic rhyolite flows have distinct geochemical featureswhen compared to the calc-alkalic rocks. Although the flows

have Zr/TiO2 (254–606) values similar to the calc-alkalicrocks, they are displaced to lower Nb/Y (0.2–0.2) values (Fig.8a; Table 2). In Nb-Y and Ta-Yb space, the tholeiitic flows liemore toward the ocean-floor field and are not within the con-tinuous array from the volcanic-arc to within-plate fields, re-flecting their low Nb and Ta values (Fig. 8b-c; Table 1). TheGa/Al ratios of the tholeiitic rocks straddle the I/S- to A-typeboundary with moderate Zr contents (Fig. 8d). The primitivemantle-normalized plot of the tholeiitic flows has a flatter pat-tern than the calc-alkalic rocks with minor LREE enrich-ment; however, like the calc-alkalic suites they have strongnegative Nb and Ti anomalies (Nb/Nb* = 0.40–0.47; Ti/Ti* =0.07–0.15) and depletions in Al, Sc, and V (Fig. 9c). NotablyZr and Hf are consistently lower relative to surrounding REE(Zr/Zr* = 0.75–0.90; Hf/Hf* = 0.57–0.92), which is differentfrom the calc-alkalic suites. The tholeiitic rhyolites also havehigher Zr/Nb (16.4–20.4), Nb/Ta (20.0–21.7), and Zr/Hf(32.1–57.1) values and lower Zr/Y (3.0–4.5), Zr/Sc (9.4–15.4),and Ti/Sc (150–222) values than the calc-alkalic rocks (Fig.10; Table 2).

Grass Lakes succession: Kudz Ze Kayah unit: The felsicrocks from the Kudz Ze Kayah unit have remarkable similar-ities in their geochemical characteristics regardless of lithol-ogy and as such are treated geochemically as a common en-tity. When compared to the Fire Lake unit felsic rocks, theKudz Ze Kayah unit has higher Zr/TiO2 (630–2,185) and Nb/Y(0.4–1.1) ratios that straddle the alkaline-subalkaline bound-ary (Nb/Y = 0.7; Fig. 8a; Table 2). The Kudz Ze Kayah unitrocks have elevated HFSE (Table 1) and plot in the fields forwithin-plate felsic rocks (Fig. 8b-c), with predominantly A-type affinities (Fig. 8d) and more specifically crustally derivedA-type felsic rocks (Fig. 11). The primitive mantle-normal-ized patterns of the Kudz Ze Kayah unit rocks are very simi-lar to calc-alkalic rocks of the Fire Lake unit, with LREE en-richment, negative Nb and Ti anomalies, depletions in Al, Sc,and V, weakly negative to strongly positive Zr and Hf anom-alies, and strongly negative Eu anomalies (Fig. 12). Althoughthe patterns are similar in shape to Fire Lake unit calc-alkalicrocks, they are characterized by higher total REE and HFSEand are shifted upward relative to those of the Fire Lake unit(Fig. 12). The HFSE enrichment in these rocks is illustratedby the moderate covariation of Zr and Nb; with some sampleshaving very high Zr and Nb contents (Zr >500 ppm), typicalof peralkalic rocks (Fig. 10a; Leat et al., 1986). The Kudz ZeKayah unit has a wide variation in Zr/Y (3.3–17.7) ratios, butaverage values are transitional to calc-alkalic (Fig. 10b; Table2; Barrett and MacLean, 1999). Of significant importance isthat felsic rocks of the Kudz Ze Kayah unit exhibit a strong co-variation of Zr with Sc and Ti (Fig. 10c-d), accompanied byvery high Zr/Sc (15.3–190.3) and Zr/TiO2 (630–2,185) ratios(Table 2). These high ratios result in distinctive trends relativeto the Fire Lake unit rocks and the hanging-wall rhyolitesfrom the Wolverine deposit (Fig. 10c-d). The Kudz Ze Kayahunit rocks also have high Th contents when compared to theFire Lake unit felsic rocks (Table 1). The Ti/Sc ratios(64–537) of the Kudz Ze Kayah felsic rocks overlap but haveaverage values much higher than the Fire Lake unit felsicrocks; the average Nb/Ta values (11.6–17.8) of the Kudz ZeKayah unit felsic rocks are similar to rocks derived from con-tinental crust (Nb/Ta ~11–12 and <17; Table 2; Taylor and

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FIG. 9. Primitive mantle-normalized trace element plots for the Fire Lakeunit felsic rocks. (a). Calc-alkalic rhyolite-dacite flows. (b). High-level calc-al-kalic quartz-feldspar porphyritic intrusions. (c). Tholeiitic rhyolite-daciteflows. Primitive mantle values from Sun and McDonough (1989). Symbols asin Figure 6.


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FIG. 10. High field strength element features of the Finlayson Lake district felsic rocks. (a). Zr-Nb plot of Leat et al.(1986). (b). Zr/Ti-Y/Ti plot for deciphering the tholeiitic versus calc-alkaline affinities of the rhyolites from Lentz (1998,1999). (c). Zr/Yb-Sc/Yb. (d). Zr/Yb-Ti/Yb. These plots are all normalized to Yb to minimize the effects of mass changes dueto alteration and metamorphism. Symbols as in Figure 6.

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FIG. 11. (a). Nb-Y-Ce and (b). Nb-Y-3*Ga plots of Eby (1992) to illustrate the crustal A-type nature of the felsic rocks ofthe Kudz Ze Kayah unit and the footwall Wolverine succession. Symbols as in Figure 6.

McLennan, 1985; Green, 1995; Wedepohl, 1995; Barth et al.,2000).

Wolverine succession: Unit 5f/qfp: Felsic rocks from unit5f/qfp from the Wolverine succession have geochemical at-tributes remarkably similar to those from the Kudz Ze Kayah

unit. There is considerable geochemical coherency betweenthe different lithologies within unit 5f/qfp. The unit 5f/qfpfelsic rocks have high Zr/TiO2 (391–1,067) and Nb/Y (0.4–1.0)values that straddle the alkaline-subalkaline boundary (Fig.8a; Table 2). Unit 5f/qfp rocks are HFSE enriched and strad-dle the field for within-plate to volcanic-arc rocks (Fig. 8b-c),with features typical of A- to fractionated I/S-type granitoids(Figs. 8d and 11). Their primitive mantle-normalized signa-tures are characterized by LREE-enriched patterns, negativeNb and Ti anomalies, variably negative Eu anomalies, and de-pletions in Al, Sc, and V (Fig. 13). The Zr/Y ratios (2.2–12.9)of the rhyolite flows vary, likely due to Zr compatibility (Wat-son and Harrison, 1983), but average values are transitional(Fig. 10b; Table 2; Barrett and MacLean, 1999). Similar tothe Kudz Ze Kayah unit felsic rocks, the unit 5f/qfp rockshave a moderately strong correlation of Zr with Sc and Ti andcorrespondingly high Zr/Sc (29.9–84.2) and Zr/TiO2 (391–1,067) ratios (Fig. 10c-d; Table 2). The Ti/Sc values (200–473)of unit 5f/qfp felsic rocks are high (Table 2) and are similar tothose for the upper continental crust (Taylor and McLennan,1985; Wedepohl, 1995). The Nb/Ta values of the unit5f/qfprocks are low and overlap values for the continental crust(~11–12; Table 2; Taylor and McLennan, 1985; Green, 1995;Wedepohl, 1995; Barth et al., 2000).

Wolverine succession: Unit 6: Felsic rocks of unit 6 com-prise the footwall and hanging wall to the Wolverine VHMSdeposit. Both the footwall intrusions and tuffaceous rockshave similar geochemical attributes with high Zr/TiO2(559–1,220) and moderate Nb/Y values (0.5–1.1; Fig. 8a),with HFSE systematics typical of within-plate volcanic-arcrocks (Fig. 8b-c), and crustally derived A-type felsic rocks(Figs. 8d and 11). Primitive mantle-normalized plots for theserocks are characterized by LREE enrichment, negative Nband Ti anomalies, negative but erratic Eu anomalies, and de-pletions in Al, Sc, and V (Fig. 14a-b; Table 2). The footwallfelsic rocks have high Zr and Nb contents (Table 2; Fig. 10a)and varying Zr/Y ratios (3.4–14.7) that are on average transi-tional to calc-alkalic in nature (Fig. 10b; Table 2). These fel-sic rocks also have high Zr/Sc (40.4–84.7) and Zr/TiO2(559–1,220) values similar to the unit 5f/qfp and Kudz ZeKayah unit felsic rocks (Fig. 10c-d; Table 2). The Ti/Sc ratios(248–417) for the footwall rocks are similar to values for thecontinental crust, and Nb/Ta values (10.4–17.1) vary but aretypical of rocks derived from continental crust (Table 2; Tay-lor and McLennan, 1985; Green, 1995; Wedepohl, 1995;Barth et al., 2000).

The aphyric rhyolites in the hanging wall of the Wolverinedeposit have very distinctive geochemical features when com-pared to most other felsic rocks of the Finlayson Lake district.The Wolverine aphyric rhyolites have distinctly low Zr/TiO2(181–591) values and subalkalic Nb/Y (0.2–0.9) ratios (Fig.8a; Table 2). The HFSE contents of the aphyric rhyolites arealso low and the samples plot within as volcanic-arc felsicrocks (Fig. 8b-c). The moderate Ga/Al ratios in the aphyricrhyolites are due to their low Al2O3 contents, which results inthem plotting on the boundary of the I/S- to A-type field withmoderate low Zr contents (Fig. 8d). The primitive mantle-normalized plot of the aphyric rhyolites is flatter than thefootwall rocks and is less LREE enriched but still exhibitsnegative Nb and Ti anomalies (Fig. 14c). Aluminum and Sc

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FIG. 12. Primitive mantle-normalized trace element plots for the Kudz ZeKayah unit felsic rocks. (a). Aphyric rhyolite flows and/or intrusions. (b).Feldspar (±quartz)-porphyritic rhyolite flows and/or intrusions. (c) Fine-grained volcaniclastic-tuffaceous rocks. Primitive mantle values from Sunand McDonough (1989). Symbols as in Figure 6.

are relatively depleted in these rocks, but notably the V val-ues are elevated relative to Sc that suggests possible mag-netite accumulation (Fig. 14c). The aphyric rhyolites have in-termediate Zr/Nb values and the average Zr/Y (2.4-10.0)values are transitional (Fig. 10a-b; Table 2). Zirconium co-varies with Ti and Sc but with much lower Zr/Sc (3.5–27.7)

and Zr/TiO2 (181–591) values when compared to all other fel-sic rocks in the Finlayson Lake district (Fig. 10c-d; Table 2).The average Ti/Sc values (0–370) of the aphyric rhyolites arevery low, and the average Nb/Ta values are highly variable(8.5–18.5; Table 2; Taylor and McLennan, 1985; Green, 1995;Wedepohl, 1995; Barth et al., 2000).


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FIG. 13. Primitive mantle-normalized trace element plots for unit 5f/qfpfelsic rocks of the Wolverine succesion. (a). Rhyolite flows. (b). Quartz-feldspar porphyritic high-level intrusions. (c) Fine-grained volcaniclastic-tuffaceous rocks. Primitive mantle values from Sun and McDonough (1989).Symbols as in Figure 6.

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FIG. 14. Primitive mantle-normalized trace element plots for unit 6 felsicrocks of the Wolverine succesion. (a). Quartz-feldspar porphyritic intrusions.(b). Footwall felsic volcaniclastic rocks (tuffs). (c). Hanging-wall aphyric rhy-olite flows. Primitive mantle values from Sun and McDonough (1989). Sym-bols as in Figure 6.

Discussion

Petrogenesis and tectonic setting of felsic rocks in the Finlayson Lake district

Fire Lake unit: The geochemical and geological features offelsic rocks in the Fire Lake unit are consistent with forma-tion within an ~365 to 360 Ma (Mortensen, 1992a, b; Grant,1997) continental margin-arc setting. The HFSE- and REE-depleted signatures of these rocks, coupled with negative Nband Ti anomalies on primitive mantle-normalized plots, aresimilar to felsic rocks formed in arc environments (e.g.,Pearce and Peate, 1995). Some workers have shown, how-ever, that Nb and Ti depletions and arc signatures in felsicrocks can originate from remelting of rocks with arc parent-age (e.g., Whalen et al., 1998; Morris et al., 2000) and canarise from the fractionation of HFSE-enriched accessoryphases (e.g., Green and Pearson, 1987; Ryerson and Watson,1987; Lentz, 1999), regardless of tectonic setting. Neverthe-less, the felsic rocks of the Fire Lake unit are stratigraphicallyinterlayered and magmatically comingle with calc-alkalic andisland-arc tholeiitic mafic rocks (Piercey and Murphy, 2000),typical of rocks from arc environments, suggesting they rep-resent formation within a Devonian-Mississippian arc system.

Grant (1997) suggested that this Devonian-Mississippianarc magmatism in the Yukon-Tanana terrane was built upon acomposite basement; the evidence was primarily based on themixture of juvenile and evolved geochemical and isotopic fea-tures exhibited by the sedimentary rocks and felsic and maficrocks of the Fire Lake unit. Some key HFSE ratios (Ti/Sc andNb/Ta) support the possibility of a composite basement to thisarc. For example, felsic volcanic rocks of the Fire Lake unithave greater Nb/Ta (15.9–21.7) and lower Ti/Sc (191–347)values than most other rocks of the Finlayson Lake district(Table 2). It has been established that mantle and mantle-derived rocks typically have Nb/Ta values of ~17.5 (Sun andMcDonough, 1989; Green, 1995), whereas the continental crustand rocks derived from it have values of ~11 to 12 (Taylor andMcLennan, 1985; Green, 1995). The high Nb/Ta values (20.0–21.7) for the tholeiitic rhyolitic rocks and the lower but stillhigh Nb/Ta values (15.9–17.4) for the calc-alkaline rhyoliticflows suggest possible derivation from mafic or mantle-likecrustal sources. This is also supported by the Ti/Sc ratios ofthe volcanic rocks. As Sc is more compatible than Ti, mafic ormantle-derived crustal sources will have lower Ti/Sc valuesthan more felsic sources. The tholeiitic and calc-alkaline rhy-olite flows of the Fire Lake unit have distinctly lower Ti/Scvalues than most other felsic rocks in the Finlayson Lake dis-trict (Table 2), supporting derivation from possible mafic ormantle-like crustal sources. An equally viable alternative forthe Nb/Ta and Ti/Sc behavior is that the Fire Lake unit felsicvolcanic rocks are mafic melts that have been contaminated bycontinental crust during emplacement. Preliminary Nd isotopedata on the tholeiitic and calc-alkalic rhyolites (εNd350 = +0.11to –4.80; Piercey, 2001) would support either hypothesis.

The quartz-feldspar porphyritic intrusions in the Fire Lakeunit have distinctly lower Nb/Ta (12.3–13.4) and higher Ti/Sc(174–329) values than the felsic volcanic rocks with valuessimilar to the continental crust (Taylor and McLennan, 1985;Green, 1995; Wedepohl, 1995; Barth et al., 2000). Grant(1997) documented an εNd350 value of –12.8 for a Fire Lake

unit quartz-feldspar porphyritic intrusion in the Money Creekthrust, and Mortensen (1992b) documented inherited Pro-terozoic zircon in a Money Creek thrust quartz-feldspar por-phyry, both of which support their derivation from evolvedcontinental crust. The greater crustal signature in the quartz-feldspar porphyritic intrusions relative to the volcanic rocksmay be due to a longer crustal residence time for the intru-sions, allowing them to interact more extensively with conti-nental crust.

In summary, the felsic rocks of the Fire Lake unit are asso-ciated with bimodal volcanism with calc-alkaline and tholei-itic affinities that are interpreted to have formed within a De-vonian-Mississippian arc system built upon a compositebasement. Whether or not this arc was developed on the dis-tal edge of the North American craton (e.g., Mortensen,1992a; Creaser et al., 1997) is presently uncertain.

Kudz Ze Kayah unit: The felsic rocks of the Kudz Ze Kayahunit are very distinctive when compared to those in the FireLake unit or those in the hanging wall of the Wolverine de-posit; the felsic rocks of the Kudz Ze Kayah unit and in thefootwall of the Wolverine deposit have higher HFSE andΣREE contents and HFSE ratios (Tables 1 and 2), suggestingdifferent petrogenetic origins. The Nb/Ta (avg = 11.6–15.8)and Ti/Sc (avg = 313–345) ratios of the Kudz Ze Kayah unitare notably lower and higher, respectively, relative to FireLake unit felsic rocks and very similar to values for the conti-nental crust (~11–12). The close similarity of these ratios tothose of the continental crust is consistent with the hypothe-sis that Kudz Ze Kayah unit felsic rocks are derived from con-tinental crustal melting. This hypothesis is further supportedby the ubiquitous occurrence of inherited Proterozoic zirconin these felsic rocks (Mortensen, 1992a) and evolved Nd isotopesignatures (εNdt = –7.8 to –8.5; Piercey, 2001). Isotopic data forcoeval plutonic rocks in the Grass Lakes suite granitoids(87Sr/86Sri = 0.716–0.728; εNdt (avg) = –15 ± 1; Mortensen,1992a) add further support for a crustal partial melt origin forthe felsic rocks of the Kudz Ze Kayah unit.

The origin of the Kudz Ze Kayah unit felsic rocks frommelting continental (or continent derived) crust is significantbecause the nature of this melting event likely controlled theHFSE-REE characteristics of these rocks. In the continentalcrust, most HFSE and REE in the continental crust reside inHFSE-enriched accessory minerals (Green and Pearson,1987; Ryerson and Watson, 1987; Bea, 1996a, b). The effi-ciency of melting and dissolution of these minerals duringcrustal melting will control the HFSE-REE budget of the fel-sic magma (e.g., Watson and Harrison, 1983; Bea, 1996a, b).Numerous workers have shown that during crustal melting,the HFSE-REE budget of the melts is strongly controlled bythe temperature of crustal fusion (Watson and Harrison, 1983;Whalen et al., 1987; Creaser and White, 1991; Bea, 1996a, b;Watson, 1996). The high HFSE and REE contents of theKudz Ze Kayah unit felsic rocks suggest that the HFSE-REEbudget reflects high-temperature melting of continental crustand efficient dissolution of HFSE-REE-enriched accessoryphases. A high-temperature crustal melt origin is partly sup-ported by the zircon saturation temperatures (Watson and Har-rison, 1983) of the felsic rocks. Zircon saturation temperaturesreflect the temperature at which zircon saturates in a melt(Watson and Harrison, 1983). Some workers have interpreted

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zircon saturation temperatures to approximate the emplace-ment temperature of felsic magmas (Barrie, 1995) and no-tably the Kudz Ze Kayah unit felsic rocks have high zircon sat-uration temperatures (avg Zr saturation temperatures >837°C; Table 2) supportive of a high-temperature crustal meltorigin.

The elevated HFSE contents in the Kudz Ze Kayah unitfelsic rocks also results in high HFSE/compatible element ra-tios. Specifically, the Kudz Ze Kayah unit felsic rocks have dis-tinctive trajectories and high Zr/Sc and Zr/TiO2 ratios similarto the felsic rocks from the footwall of the Wolverine depositbut distinctive from those in the Fire Lake unit and hangingwall of the Wolverine deposit (Fig. 10c-d; Table 2). Barrettand MacLean (1999) have suggested that covarying Zr-TiO2arrays can reflect mass changes of a single homogeneous pro-tolith. Although there is most likely some component of masschange in the Kudz Ze Kayah unit rocks, the common in-compatible element denominator (Yb) in these plots (Fig.10c-d) suggest that the covarying Zr-Sc and Zr-TiO2 arrayscannot be accounted for solely by mass change. Thereforethis requires an alternative interpretation. In the Bathurstmining camp, Lentz (1996, 1999) found similar Zr-Sc and Zr-TiO2 arrays and high Zr/Sc and Zr/TiO2 ratios in manyVHMS-related felsic rocks and attributed the variations todifferent temperatures of crustal fusion. Furthermore, Lentz(1999) and Whalen et al. (1998) found that the Bathurst min-ing camp VHMS-related felsic rocks had elevated HFSE andREE contents similar to the Kudz Ze Kayah unit rhyolites andattributed these to high-temperature crustal fusion. Thesestudies and the data presented herein suggest that the HFSE-compatible element systematics in the Kudz Ze Kayah unitfelsic rocks represent thermal controls on crustal meltingrather than mass change variations.

The geochemical systematics of the Kudz Ze Kayah unit fel-sic rocks suggest a fundamentally different tectonic setting forthese rocks relative to the Fire Lake unit rocks. Mortensen(1992a) suggested that granitoids of the Grass Lakes suite inthe Kudz Ze Kayah unit reflected magmatism within a west-facing volcano-plutonic arc complex of Devonian-Mississippian

age. This interpretation could be bolstered by the negativeNb and Ti anomalies on primitive mantle-normalized plots(Fig. 12) of the Kudz Ze Kayah unit felsic rocks. However,many workers have shown that these signatures can arise fromthe remelting or arc crust (Whalen et al., 1998; Morris et al.,2000) and/or from the fractionation of HFSE- and Ti-enrichedphases (Green and Pearson, 1987; Ryerson and Watson, 1987;Lentz, 1999). The possibility of Ti-rich phase crystallization issupported in part by the broadly inverse relationship of thesize of the negative Nb anomaly (primitive mantle-normal-ized Th/Nb) to TiO2 and Sc (Fig. 15a-b), suggesting that thesignature does not necessarily reflect an arc signature. Theevidence for a crustal melting history also suggests that thenegative Nb signature might be inherited from its crustal sourceas the upper continental crust has a negative Nb anomaly onprimitive mantle-normalized plots (Taylor and McLennan,1985). Other lines of evidence also support a back-arc setting.For example, the Kudz Ze Kayah unit felsic rocks are inter-calated with voluminous carbonaceous sedimentary rocks ofbasinal character and are crosscut and overlain by HFSE-en-riched weakly alkaline mafic rocks with ocean-island basaltsignatures (Piercey, 2001). The presence of VHMS mineral-ization also provides indirect evidence for a back-arc or non-arc setting because in the modern environment, most hy-drothermal vent sites are located in non-arc settings (e.g.,Herzig and Hannington, 1996; Hannington et al., 1995).

The geological and geochemical characteristics of the KudzZe Kayah unit suggest formation within a back-arc basin en-vironment. Mortensen (1992a) suggested that Devonian-Mississippian Yukon-Tanana terrane arc magmatism formedabove a west-facing (east-dipping) subduction zone proximalto, but not necessarily part of, North America. The felsicrocks in the Kudz Ze Kayah unit most likely reflect rifting andsubsequent ensialic back-arc basin generation within this arc.The formation of the Kudz Ze Kayah unit back-arc environmentmost likely involved the westward migration of the Mortensen(1992a) arc, resulting in back-arc rifting and basin generation.Underplating of the crust by enriched asthenospheric orlithospheric magmas, represented by the crosscutting alkaline


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FIG. 15. Primitive mantle-normalized Th/Nb ratios (Th/Nbpm) vs. TiO2 (a) and Sc (b) for the Kudz Ze Kayah unit felsicrocks. The inverse relationship between the size of the negative Nb anomaly and TiO2 and Sc suggests that the anomaly maybe in part reflective of Ti-Sc phase crystallization (e.g., magnetite, ilmenite) as these minerals have high partition coefficientsfor the HFSE (Green and Pearson, 1987; Ryerson and Watson, 1987). Symbols as in Figure 6.

magmas of unit 4 (Piercey, 2001), resulted in high-tempera-ture melting of continental crust and the formation of the fel-sic rocks in the Kudz Ze Kayah unit. Devonian-Mississippianarc rifting and the synvolcanic faults associated with it (Mur-phy and Piercey, 2000) are interpreted to have been the re-gional-scale controls on the localization and formation of theKudz Ze Kayah and GP4F VHMS deposits (Murphy andPiercey, 2000).

Wolverine succession: The felsic volcanic rocks of the Wol-verine succession show considerable variation. Rocks in thefootwall of the Wolverine deposit have high HFSE-REE con-tents similar to the Kudz Ze Kayah unit rocks, whereas thosein the hanging wall have distinctive systematics and lowerREE and HFSE contents. Rocks in the footwall of the deposithave Ti/Sc and Nb/Ta ratios similar to values for the continen-tal crust (Table 2), inherited Proterozoic zircon (Mortensen,1992a), and evolved Nd isotope signatures (εNdt = –7.8 to–8.2; Piercey, 2001). These features all indicate an origin fromhigh-temperature melting of continental crust similar to rocksfrom the Kudz Ze Kayah unit.

The hanging-wall aphyric rhyolites in the Wolverine de-posit have lower HFSE and REE contents and distinct tra-jectories in Zr-Sc and Zr-TiO2 space (Fig. 10c-d) compared toall other felsic rocks in the Finlayson Lake district. The co-variation between Zr and Sc and TiO2 in these rocks has beeninterpreted to reflect mass changes (Barrett and MacLean,1999) or differential temperatures of crustal fusion (Lentz,1999). The silicified nature of the aphyric rhyolites points toa possible role for mass change; however, the ratio plots inFigure 10c-d minimize this mass effect by having a commonincompatible element denominator (Yb). Therefore, thelower Zr-Sc and Zr-TiO2 trajectories and accompanying Zr/Scand Zr/TiO2 ratios must reflect processes other than masschange. The lower HFSE and REE contents, and Zr/Sc andZr/TiO2 ratios, for the aphyric rhyolites may reflect melting ofthe same crustal source as the footwall rocks but at lower tem-peratures (e.g., Lentz, 1996, 1999; Watson, 1996). Lentz(1996, 1999) proposed a similar explanation for felsic rocks ofthe Bathurst mining camp. This hypothesis is partly sup-ported by Zr saturation temperatures (Table 2). An alterna-tive hypothesis is that the footwall and hanging-wall felsicrocks were derived from different crustal sources (e.g., FireLake unit felsic rocks). Preliminary Nd isotope data, however,illustrate that there is very little difference between the foot-wall tuffs (εNdt = –8.2) and the hanging-wall aphyric rhyolites(εNdt = –7.1; Piercey, 2001), supporting possible differentialtemperature melting of a common evolved crustal source.Equally viable, however, is the mixing of HFSE-depletedmafic magmas with abundant crustal material that could yieldHFSE depletions yet similar Nd isotope signatures (e.g.,Lentz, 1998). Given that the mafic magmas that overly theaphyric rhyolites have HFSE-depleted N-MORB signatures(Piercey, 2001), mixing of such a magma with evolved crustcould possibly yield the signatures observed in the aphyricrhyolites (e.g., Lentz, 1998).

The geological and geochemical features of footwall felsicrocks from the Wolverine deposit are identical to those of theKudz Ze Kayah unit and suggest the persistence of a similarensialic back-arc rift-basin geological environment. However,the two units are separated by an angular unconformity, and

temporal constraints suggest that the Wolverine succession isyounger than the Kudz Ze Kayah unit (Mortensen, 1992a).Although the lower part of the Wolverine succession had asetting similar to the Kudz Ze Kayah unit there are fragmentsof rocks from the Kudz Ze Kayah unit in the basal unit of theWolverine succession (Murphy and Piercey, 1999), requiringa period of uplift, erosion, and disruption of Kudz Ze Kayahunit back-arc magmatism before the commencement ofWolverine succession back-arc magmatism. Murphy (1998)has documented evidence for localized compression in theupper parts of the Grass Lakes succession. This localized de-formation episode was most likely responsible for the upliftand disruption of back-arc magmatism and may have beendue to slab trajectory changes (e.g., Uyeda and Kanamori,1979; Hawkins et al., 1984) or localized plate reorganizationsthat induced a brief compressive episode.

The back-arc setting for the Wolverine succession is furthersupported by basaltic rocks in the hanging wall of the Wolver-ine deposit, near the top of the Wolverine succession. Thesebasalts stratigraphically overlie the aphyric rhyolitic rocks(Bradshaw et al., 2001) and are characterized by MORB geo-chemical signatures (Piercey, 2001). The occurrence ofMORB-type basalts suggests that the Wolverine back-arcbasin most likely evolved to full sea-floor spreading. Howwide this basin eventually opened is uncertain since much ofthis record may have been removed by the unconformableoverlap of the late Paleozoic Campbell Range succession(Murphy, 2001).

Modern and ancient analogues to the Finlayson Lake district

Understanding the setting of ancient VHMS districts isoften aided by their comparison to similar ancient districtsand modern analogues (e.g., Hannington et al., 1995; Herzigand Hannington, 1996). Felsic-associated VHMS depositsfrom the Finlayson Lake district have features similar to theCambro-Ordovician Mount Windsor subprovince of Aus-tralia, the Bathurst district of Canada, and possibly the mod-ern day Okinawa trough of Japan.

The Mount Windsor subprovince exhibits strong similari-ties to the Finlayson Lake district. First, both districts havesimilar lower stratigraphic assemblages consisting of conti-nent-derived sedimentary material (Puddler Creek Forma-tion vs. unit 1 of the Grass Lake succession) (e.g., Berry et al.,1992; Murphy and Piercey, 1999, 2000). Stoltz (1995) sug-gested that felsic volcanic rocks in the Mount Windsor districtwere the products of partial melting of Precambrian crustalbasement (εNdt = -4.7 to –12.8) due to slab roll back and gen-eration of an intracontinental back-arc basin. A similar petro-genetic origin and geodynamic setting is proposed for theVHMS-related felsic volcanic rocks of the Finlayson Lake dis-trict. However, the relationship of VHMS mineralization tofelsic volcanism in the Mount Windsor subprovince differsfrom that of the Finlayson Lake district. For example, unlikethe Kudz Ze Kayah, GP4F, and Wolverine deposits, which arehosted by felsic volcanic rocks, the Mount Windsor Group de-posits occur either at the contact between the felsic-dominatedMount Windsor Formation and the overlying basalt-andesite-dacite-rhyolite-volcaniclastic-dominated Trooper Creek For-mation (e.g., Thalanga deposit) or are hosted within theTrooper Creek Formation (e.g., Highway-Reward deposit;

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Berry et al., 1992; Stoltz, 1995; Doyle and Huston, 1999).Furthermore, the felsic volcanic rocks within the MountWindsor subprovince do not exhibit HFSE contents that areas highly elevated as those of the Finlayson Lake district (seeStoltz, 1995; Lentz, 1998), suggesting a possible lower tem-perature of crustal fusion. Regardless of these differences,the overall volcano-sedimentary character of the succession,the nature and interpreted origin of the felsic volcanism, for-mation upon Precambrian continental (or continent-derived)basement, and the intracontinental back-arc basin-rift envi-ronment are analogous to the Finlayson Lake district.

The Ordovician Bathurst mining camp in Canada is thebest ancient analogue to the Finlayson Lake district in termsof stratigraphy, geochemistry, and geodynamic setting. TheBathurst mining camp is characterized by a lower continentderived sedimentary sequence (Miramichi Group), which isdisconformably overlain by the felsic volcanic and sedimen-tary rocks of the Tetagouche Group (van Staal et al., 1991,1992). The Tetagouche Group consists of two packages of fel-sic volcanic and sedimentary rocks (Nepisiguit Falls and FlatLanding Brook Formations; van Staal et al., 1991, 1992),which are strikingly similar to the rocks of the Finlayson Lakedistrict, and host the massive sulfide deposits of the Bathurstmining camp. Although the deposits of the Bathurst miningcamp are larger and have greater tonnage (McCutcheon,1992), their volcano-sedimentary setting is similar to theWolverine, GP4F, and Kudz Ze Kayah deposits of the Fin-layson Lake district (e.g., Shultze, 1996; Bradshaw et al.,2001). Some VHMS deposits also exhibit strong similarities.For example, the Wolverine deposit bears strong similaritiesto the Brunswick 12 deposit, including the abundance of car-bonaceous rocks in the host stratigraphy, including thoseproximal to the massive sulfides (anoxic basin?; cf. Goodfel-low and Peter, 1996), the presence of felsic volcanic and vol-caniclastic rocks with similar physical and chemical composi-tions (Lentz, 1999; this study), and the abundance of ironformation and exhalative sedimentary rocks (Peter and Good-fellow, 1996; Bradshaw et al., 2001).

Felsic volcanic rocks from the Bathurst mining camp andthe Finlayson Lake district are virtually indistinguishablechemically. The felsic rocks from the Tetagouche Group, theKudz Ze Kayah unit, and the footwall Wolverine successionare characterized by similar HFSE-REE systematics, andthey are interpreted to have similar petrogenetic origins andto have formed in a similar tectonic setting (e.g., Lentz, 1999;this study). For example, van Staal et al. (1991) suggested thatmuch of the felsic volcanic rocks of the Tetagouche Grouparose from melting of crust due to asthenospheric underplat-ing during continental arc rifting. Lentz (1999) suggested atwo-stage crustal melting model within a continental arc riftto ensialic back-arc environment. Whalen et al. (1998) sug-gested that the felsic metavolcanic and metaplutonic rocks ofthe Tetagouche Group were formed in an environment wherearc activity was shut off due to arc rifting or ensialic back-arcbasin generation. Overall, the stratigraphy, deposit character-istics, felsic volcanic geochemistry, and tectonic setting of theBathurst mining camp are similar to the Finlayson Lake dis-trict and provide one of the best analogues.

Modern analogues of felsic volcanic- and volcano-sedimen-tary-hosted VHMS districts are rare (e.g., Halbach et al.,

1989, 1993). The Okinawa trough has been cited as a poten-tial analogue to both the Bathurst district (Whalen et al.,1998; Lentz, 1996, 1999) and the Mount Windsor sub-province (Stoltz, 1995). The Okinawa trough is an intraconti-nental back-arc basin southwest of Japan that hosts Kuroko-style VHMS deposits (JADE field) within a bimodalassemblage of basalt-andesite–dacite-rhyolite and sedimen-tary rocks (Stoltz, 1995). The setting and stratigraphy may beanalogous to the Finlayson Lake district, and the metal in-ventory of the sulfide mineralization within the JADE fieldhas somewhat similar mineralogy and local Au and Ag en-richment (Halbach et al., 1989, 1993), akin to the deposits ofthe Finlayson Lake district (e.g., Shultze, 1996; Tucker et al.,1997; Bradshaw et al., 2001). Similarly, E-MORB and OIBmafic magmatism within the Okinawa trough (Ishizuka et al.,1990; Chen et al., 1995; Shinjo, 1999; Shinjo et al., 1999) issimilar to the mafic magmatism spatially associated with thefelsic VHMS deposits in the Finlayson Lake district (Piercey,2001).

There are, however, numerous differences between theOkinawa trough and the Finlayson Lake district. First, thegeochemical attributes of the felsic rocks of the Okinawatrough are quite different from those in the Finlayson Lakedistrict. For example, Ishizuka et al. (1990) suggested that thefelsic volcanic rocks of the Okinawa trough were derived fromisland-arc-type source material with HFSE depletion unlikemost VHMS-associated felsic rocks of the Finlayson Lake dis-trict (Kudz Ze Kayah unit and footwall Wolverine succession).Similarly, Shinjo and Kato (2000) have shown that Okinawatrough felsic rocks have lower HFSE and juvenile initial87Sr/86Sr and 143Nd/144Nd isotope ratios (Shinjo and Kato,2000). These workers have also suggested derivation of theOkinawa trough felsic rocks from fractional crystallization ofbasaltic material or AFC processes (Shinjo and Kato, 2000),rather than derivation from crustal melting of evolved oldercrust, as proposed for the VHMS-associated felsic rocks ofthe Finlayson Lake district. There are also important differ-ences in the geology of the Okinawa trough. For example, theabundance of sedimentary rocks associated with the Fin-layson Lake district is not present in the Okinawa trough (e.g.,Halbach et al., 1993). Similarly, the abundance of carbona-ceous rocks and possibly anoxic bottom waters during forma-tion of some of the VHMS deposits of the Finlayson Lake dis-trict (e.g., Goodfellow and Peter, 1996; Bradshaw et al., 2001)are not present in the deposits of the Okinawa trough (e.g.,Halbach et al., 1993). Given these differences between theFinlayson Lake district and the Okinawa trough there maynot be an exact modern analogue to the Finlayson Lake dis-trict. Nevertheless, the Okinawa trough provides the bestmodern geodynamic analogue to the Finlayson Lake district.

Comparisons to the geochemistry of felsic volcanic rocks in Archean and Phanerozoic VHMS environments

Numerous workers have used felsic volcanic geochemistryin an attempt to decipher prospective versus nonprospectivevolcanic environments for VHMS deposits (e.g., Lesher et al.,1986; Barrie et al., 1993; Lentz, 1998). These prospectivity in-dexes were based on immobile HFSE-REE ratios and, in par-ticular, the Zr/Y and La/Ybn ratios of felsic rocks to delineateore-bearing versus barren felsic volcanic rocks. Lesher et al.


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(1986) noted that most VHMS deposits in the Abitibi green-stone belt were associated with tholeiitic felsic rocks with in-termediate to high HFSE and REE, low Zr/Y and La/Ybn ra-tios (Fig. 16a, b). They further suggested that these ratios are

characteristic of felsic rocks generated at high crustal levelsthat are associated with subvolcanic intrusive systems. Thelatter were interpreted as the source of heat for hydrothermalcirculation (Lesher et al., 1986). Barrie et al. (1993) extended

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FIIIa

FII

FI

FIIIb

0 20 40 60 80 100 120 140 1600

5

10

15

20

25

Zr/

Y

Y

(a)

0 20 40 60 80 100 120

1

10

La/Y

b n

Ybn

FIIIb

FII

FI

FIIIa

(b)

FIG. 16. Zr/Y-Y and La/Ybn-Ybn plots for outlining ore-bearing vs. barren Archean and Phanerozoic felsic volcanic rocks.Groupings in (a) and (b) are Archean Superior province felsic rocks from Lesher et al. (1986). FI, FII, FIIIa, and FIIIb aredifferent felsic volcanic groupings, with the FIIIa and FIIIb most prospective, FII moderately prospective, and FI leastprospective. Groupings in (c) and (d) are Archean Superior province felsic volcanic groupings from Barrie et al. (1993). Grayshaded fields are VHMS-bearing sequences. Groupings in (e) and (f) are for Phanerozoic VHMS environments from Lentz(1998). All of these groupings contain VHMS mineralization. Symbols as in Figure 6.

Kamiskotia

Upper Skead

Noranda

Misema

Timiskaming

Selbaie

0 20 40 60 80 100 120 140 1600

5

10

15

20

25

Zr/

Y

Y

(c)

0 20 40 60 80 100 120

1

10

La/Y

b n

Ybn

Kamiskotia

NorandaMisema

Selbaie

Upper Skead

Timiskaming (d)

Tobique Avoca

Mount Windsor

Que River

Kur

oko

West Shasta

0 20 40 60 80 100 120 140 1600

5

10

15

20

25

Zr/

Y

Y

(e)

Avoca

TobiqueKuroko

Mt Windsor

Que River

Mt Shasta

0 20 40 60 80 100 120

1

10

La/Y

b n

Ybn

(f)

the study of Lesher et al. (1986) to the bulk of the Abitibi sub-province and found similar results (Fig. 16c, d). Lentz (1998)showed that the Phanerozoic VHMS-associated felsic rockshave HFSE-REE systematics broadly similar to Archean ex-amples (Fig. 16e, f).

Felsic rocks from the Finlayson Lake district are comparedto the fields for these different Archean and Phanerozoicprospectivity indexes (Fig. 16). If one considers the felsicrocks of the Kudz Ze Kayah unit and the rocks of the footwallto the Wolverine deposit to be the VHMS-hosting felsic rocks(prospective) in the Finlayson Lake district, then these rockspartly overlap the FII and FIIIa fields of Lesher et al. (1986)and the Selbaie, Noranda, and Misema fields of Barrie et al.(1993; Fig. 16a, c). However, there is significant scatter in theZr/Y-Y systematics of the Finlayson Lake district felsic rocksthat reflects partial compatibility or melt kinetic-thermal con-trol on the HFSE distribution (Watson and Harrison, 1983).The La/Ybn systematics of the Finlayson Lake district rocksare less scattered and partly overlap the FII and Selbaie fields(Fig. 16b, d). However, for the most part they lie within fieldsfor less productive or barren sequences trending towardhigher La/Ybn values (Fig. 16b, d). When compared to Phanero-zoic indexes, a similar scattering of Zr/Y occurs with most ofthe rocks overlapping many productive fields (Fig. 16e). InLa/Ybn-Ybn space, the Finlayson Lake district rocks overlappredominantly with the fields for Que River, Kuroko, Tobique,and Mount Windsor (Fig. 16f).

The difference in the geochemical behavior of the FinlaysonLake district felsic rocks when compared to the ArcheanVHMS-hosting rocks, and to many Phanerozoic rocks (Fig.16), most likely reflects different crustal substrates fromwhich the felsic rocks were derived. For example, a featurecommon to the Finlayson Lake district, Que River, Kuroko,Tobique, and Mount Windsor deposits and/or districts is thatthey are partially to completely underlain by evolved conti-nental crust (Ohmoto and Skinner, 1983; Corbett, 1992;Stoltz, 1995; Lentz, 1998, 1999; Whalen et al., 1998). Partialmelting or contamination by continental crust during the gen-esis of felsic rocks would lead to LREE enrichment due to theLREE-enriched nature of the continental crustal reservoir(Taylor and McLennan, 1985; Wedepohl, 1995). In contrast,the felsic rocks hosting VHMS deposits in Archean green-stone belts are interpreted to have formed from remelting ofa mafic substrate in Iceland-type rift environments (Barrie etal., 1993; Prior et al., 1999). Remelting of a mafic (MORB-like) substrate would result in LREE-depleted, tholeiitic fel-sic rocks common to those hosting the Archean VHMS de-posits and districts (Lesher et al., 1986; Barrie et al., 1993;Prior et al., 1999). These contrasting results illustrate that in-dices for certain VHMS districts are not necessarily univer-sally applicable to other districts and an understanding of thepetrogenetic, tectonic, and crustal controls on felsic volcanicgenesis is more important than geochemical discriminationfields.

ConclusionsFelsic volcanic rocks from the Finlayson Lake district are

associated with three units: the Fire Lake unit, the Kudz ZeKayah unit, and the Wolverine succession. Of these units onlythe Kudz Ze Kayah unit and the Wolverine succession are

hosted with polymetallic felsic-associated VHMS deposits(Kudz Ze Kayah, GP4F, and Wolverine). Geochemical datafrom these rocks illustrate that felsic rocks from these unitshave formed under variable petrogenetic conditions within anevolving Devonian-Mississippian arc–back-arc system. Felsicvolcanic and high-level intrusive rocks in the Fire Lake unithave calc-alkalic and tholeiitic affinities with low HFSE con-tents and intermediate Zr/Sc (9.4–43.4) and Zr/TiO2 (254–864) ratios. These rocks are interlayered with mafic rockswith arc geochemical signatures, are largely VHMS barren,and represent bimodal magmatism within an evolving De-vonian-Mississippian continental-arc system. The Kudz ZeKayah unit stratigraphically overlies the Fire Lake unit andconsists of felsic volcanic rocks with high HFSE contents,within-plate (A-type) signatures, and high Zr/Sc (15.3–190.3)and Zr/TiO2 (630–2,185) ratios. Felsic rocks of the Kudz ZeKayah unit are crosscut and overlain by alkalic mafic rocksand are associated with abundant carbonaceous sedimentaryrocks. Felsic magmatism in the Kudz Ze Kayah unit is inter-preted to have formed within a Devonian-Mississippian en-sialic back-arc rift-basin environment. The Wolverine succes-sion is younger and unconformably overlies the Kudz ZeKayah unit. Felsic rocks in the footwall of the Wolverine de-posit have attributes similar to rocks of the Kudz Ze Kayahunit with high HFSE contents, within-plate (A-type) signa-tures, and high Zr/Sc (29.9–84.2) and Zr/TiO2 (391–1,220) ra-tios. In contrast, aphyric rhyolite flows in the hanging wall ofthe deposit have much lower HFSE contents and the lowestZr/Sc (3.5–27.7) and Zr/TiO2 (181–591) ratios in the district.All the felsic rocks of the Wolverine succession are interlay-ered with abundant carbonaceous sedimentary rocks and areoverlain by basaltic rocks with MORB affinities. The Wolver-ine succession is interpreted to have formed within an EarlyMississippian ensialic back-arc basin environment that even-tually evolved to a sea-floor-spreading environment.

The variation in the HFSE budgets of the felsic rocks of theFinlayson Lake district most likely reflects variations in thesource and/or temperature of crustal melting. In particular,the Fire Lake unit felsic rocks appear to have higher Nb/Taand lower Ti/Sc ratios than other volcanic rocks in the district,suggesting possible derivation from mafic crustal sourcesand/or lower crustal fusion temperatures. The Kudz Ze Kayahunit and footwall rocks of the Wolverine deposit are inter-preted to have formed from high-temperature partial meltingof continental crust. The hanging-wall aphyric rhyolites fromthe Wolverine deposit may have formed from either lowertemperature continental crustal melting or have been derivedfrom the mixing of HFSE-depleted N-MORB mafic magmasand evolved continental crust.

Polymetallic felsic volcanic-associated VHMS depositswithin the Finlayson Lake district are preferentially associ-ated with HFSE-enriched felsic rocks with high Zr/Sc andZr/TiO2 ratios. The HFSE and REE systematics of VHMS-as-sociated felsic rocks of the Finlayson Lake district are dif-feren from prospective felsic rocks of Archean VHMS envi-ronments in the Superior province and are displaced towardhigher Zr/Y and La/Ybn ratios. They have HFSE and REEsystematics, however, similar to many Phanerozoic VHMS en-vironments, in particular those partially to fully underlain bycontinental crust (e.g., Bathurst, Que River, Mount Windsor,


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Kuroko, Tobique). The deviation in the HFSE and REE sys-tematics between felsic rocks of the Finlayson Lake districtand Archean environments most likely reflects the differ-ences in the substrates from which the felsic rocks were de-rived (e.g., mafic vs. felsic). The similarities with manyPhanerozoic VHMS environments reflect their common as-sociation with evolved continental crust, either by derivationfrom or contamination by a continental substrate.

AcknowledgmentsPeter Bélanger (Geological Survey of Canada) is thanked

for prompt and reliable geochemical analyses of the samplespresented in this paper. Discussions and interaction with thefollowing individuals is gratefully acknowledged: MauriceColpron (Yukon Geology Program), Peter Holbek (Atna Re-sources), Harlan Meade and Terry Tucker (Expatriate Re-sources), Rob Carne and Bill Wengzynowski (Archer, Cathro,and Associates (1981) Ltd.), Geoff Bradshaw, Tom Danielson,and Kelly Russell (University of British Columbia), Paul Mac-Robbie (Cominco Ltd.), and Jan Peter and Alan Galley (Ge-ological Survey of Canada). Bruce Gemmell and Ross Large(Centre for Ore Deposit Research, Univ. of Tasmania) arethanked for providing a preprint of their alteration box plotpaper. Alan Galley and Jan Peter (Geological Survey ofCanada) are thanked for very thorough and constructive re-views of earlier drafts of this manuscript. Dave Lentz and ananonymous Economic Geology reviewer are thanked for for-mal reviews; their comments have greatly improved thispaper. This project is funded by the Yukon Geology Program(D.C.M.); Geological Survey of Canada and Ancient PacificMargin NATMAP Project (S.P.); Atna Resources and Expa-triate Resources; a Natural Sciences and Engineering Re-search Council (NSERC) of Canada operating grant (J.K.M.);and an NSERC postgraduate scholarship, a Geological Soci-ety of America student research grant, and the Hickok-Rad-ford fund of the Society of Economic Geologists (S.J.P.). May 26, 2000; July 2, 2001

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Samples were analyzed at the Geological Survey of Canada,Ottawa, Canada. Samples were ~1 kg or larger in size and col-lected from surface exposures during regional mapping orfrom diamond drill core. Surface samples had weatherededges removed by a diamond saw, whereas drill core sampleshad sufficiently fresh surfaces. Samples were then pulverizedin a steel jaw crusher with most subsequently pulped andpowdered in a ceramic mill. Some samples were pulped in aCr steel mill and others in a tungsten carbide mill. Samplesthat have been crushed by Cr steel likely have excess Cr val-ues, whereas those crushed by tungsten carbide most likelyhave excess Ta. Given these constraints we have denoted sam-ples crushed by these methods in Table R1 and when criticalelement ratios are discussed involving these elements (e.g.,Nb/Ta) samples crushed in contaminant mills were not in-cluded. Powders from the aforementioned steps were used inall other analytical techniques.

Major elements were determined on fused beads by X-rayfluorescence (XRF) with the exception of H2O and CO2,which were analyzed by infrared spectroscopy and FeO,which was analyzed by modified Wilson titration. Samples an-alyzed for trace elements were totally dissolved using a com-bination of nitric, perchloric, and hydrofluoric acids, with alithium metaborate flux if any residual material existed afterthe first acid attack. These solutions were then analyzed fortrace elements using a combination of inductively coupled

plasma emission spectrometry (ICP-ES) and inductively cou-pled plasma mass spectrometry (ICP-MS). Further details onthe methodology can be obtained from the Geological Surveyof Canada at http://132.156.95.172/chemistry.

During the course of this study repeat analyses of rock sam-ples with matrices similar to those in this study were under-taken to test precision and accuracy, including sample P98-KZK2 (quartz-feldspar porphyritic intrusion) from this study,and Mineral Deposit Research Unit internal reference mate-rials WP-1, a dacite from Watt’s Point, and P-1, a granodior-ite from the Coast Plutonic Complex, both in British Colum-bia. The means, ranges of determination, analytical precision,and comparisons to presently known values are presented inTable A1. Precision is presented as percent relative standarddeviation (%RSD = 100*standard deviation/mean) and esti-mated 2σ errors are presented for the replicate analyses. Fortrace elements of critical importance the repeat analysis ispresented in Figure A1 in relationship to the detection limit.This plot illustrates that the overall patterns are not signifi-cantly different and that the analyses are sufficiently precise(Fig. A1).

To test accuracy we have compared the average values forP-1 and WP-1 prior to 1998, which were compiled predomi-nantly from commercial laboratories, to the averages com-piled from this study (Table A1; Fig. A2). It is notable thatthere are some significant differences particularly for the

APPENDIX Analytical Methods, Precision, and Accuracy

REE and HFSE (Table A1; Fig. A2). This is largely the resultof different analytical techniques because in the pre-1998Mineral Deposit Research Unit values most of the REE andHFSE were determined by INAA or XRF, whereas thosefrom this study were by ICP-ES and ICP-MS. Shown in Fig-ure A2 are primitive mantle-normalized trace element plotsfor trace elements of petrological interest in this study. It isclear from these plots that the differences in the shapes of thepatterns, or the overall abundances of these trace elements,are not significant (Fig. A2).


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.001

.01

.1

1

10

100

1000

CsRb

BaTh

UNb

KLa

CePb

PrSr

PNd

ZrSm

EuTi

DyY

YbLu

AlV

ScCr

Ni

Roc

k/P

rimiti

veM

antle

P98-KZK2

.001

.01

.1

1

10

100

1000

CsRb

BaTh

UNb

KLa

CePb

PrSr

PNd

ZrSm

EuTi

DyY

YbLu

AlV

ScCr

Ni

Roc

k/

Prim

itive

Man

tle

P-1

.001

.01

.1

1

10

100

1000

CsRb

BaTh

UNb

KLa

CePb

PrSr

PNd

ZrSm

EuTi

DyY

YbLu

AlV

ScCr

Ni

Roc

k/P

rimiti

veM

antle

WP-1

(a)

(b)

(c)

FIG. A1. Primitive mantle-normalized trace element plots for repeatanalyses of felsic internal reference materials undertaken during the courseof this study. (a). P98-KZK2. (b). P-1. (c). WP-1. Shown for comparison insolid squares is the limit of detection for the given elements.

FIG. A2. Comparison of the average values of reference materials fromthis study (open squares) to pre-1998 Mineral Deposit Research Unit values(open diamonds). Further details are provided in the text.

.001

.01

.1

1

10

100

1000

CsRb

BaTh

UNb

KLa

CePb

PrSr

PNd

ZrSm

EuTi

DyY

YbLu

AlV

ScCr

Ni

Roc

k/P

rimiti

veM

antle

P-1

.001

.01

.1

1

10

100

1000

CsRb

BaTh

UNb

KLa

CePb

PrSr

PNd

ZrSm

EuTi

DyY

YbLu

AlV

ScCr

Ni

Roc

k/

Prim

itive

Man

tle

WP-1(b)

(a)

1904 PIERCEY ET AL.

0361-0128/98/000/000-00 $6.00 1904

TAB

LE

A1.

Sum

mar

y of

Pre

cisi

on, A

ccur

acy,

and

Rel

ated

Dat

a fo

r R

epea

t Ana

lyse

s of

Fel

sic

Inte

rnat

l Ref

eren

ce M

ater

ials

Und

erta

ken

duri

ng T

his

Stud

y

P98-

KZK

2M

in1

Max

1%

RSD

12σ

1P-

1M

in1

Max

1%

RSD

12σ

1M

DR

U1

RD

1W

P-1

Min

1M

ax1

%R

SD1

2σ1

MD

RU

1R

D1

LO

D1

n=

10n

= 5

valu

esn

= 5

valu

es

SiO

274

.64

74.1

075

.60

0.68

0.34

70.9

670

.70

71.1

00.

250.

1769

.81

1.65

65.0

664

.90

65.2

00.

180.

1264

.04

1.59

0.50

TiO

20.

300.

290.

312.

470.

000.

380.

370.

381.

300.

000.

406.

770.

500.

490.

500.

800.

000.

523.

950.

02A

l 2O3

12.1

412

.00

12.3

00.

890.

0714

.10

14.0

014

.20

0.45

0.06

14.3

81.

9816

.38

16.3

016

.50

0.60

0.10

16.5

10.

800.

40F

e 2O

3T2.

121.

902.

305.

360.

083.

903.

903.

900.

000.

003.

802.

734.

524.

504.

600.

880.

044.

392.

850.

10F

e 2O

30.

830.

601.

0013

.97

0.08

1.28

1.20

1.50

9.11

0.12

1.70

1.50

1.90

8.32

0.14

FeO

1.16

1.00

1.30

7.27

0.06

2.34

2.20

2.40

3.42

0.08

2.56

2.40

2.70

3.98

0.10

0.20

MnO

0.02

0.01

0.02

28.4

10.

000.

080.

070.

085.

130.

000.

0914

.43

0.08

0.08

0.08

0.00

0.00

0.09

12.9

70.

01M

gO0.

860.

790.

924.

790.

031.

111.

101.

120.

670.

011.

100.

952.

702.

682.

710.

410.

012.

642.

230.

10C

aO0.

200.

160.

2413

.22

0.02

3.49

3.47

3.52

0.49

0.02

3.59

2.83

5.05

5.02

5.08

0.38

0.02

5.12

1.30

0.10

Na 2

O1.

191.

101.

202.

660.

023.

803.

803.

800.

000.

004.

045.

834.

304.

304.

300.

000.

004.

402.

320.

50K

2O6.

806.

506.

871.

690.

082.

122.

112.

130.

350.

012.

044.

061.

641.

631.

660.

670.

011.

593.

220.

05P 2

O5

0.09

0.09

0.09

0.00

0.00

0.08

0.08

0.08

0.00

0.00

0.09

10.7

30.

180.

170.

182.

250.

000.

181.

320.

02H

2O0.

990.

901.

003.

370.

020.

620.

600.

706.

450.

040.

300.

300.

300.

000.

000.

10C

O2

0.10

0.10

0.10

0.00

0.00

0.10

0.10

0.10

0.00

0.00

0.10

0.10

0.10

0.00

0.00

0.10

Tota

l99

.34

98.0

010

0.20

0.65

0.43

100.

5610

0.20

100.

800.

220.

2299

.95

0.61

100.

6210

0.40

100.

900.

200.

20

Cr

(ppm

)71

6575

4.44

2.11

149

140

155

3.43

5.11

133.

7711

.54

7974

823.

352.

6469

.54

13.3

210

.00

Ni

<10

<10

<10

<10

1.65

4543

462.

601.

1736

.12

24.0

510

.00

Co

7<5

940

.41

1.89

66

76.

450.

407.

4817

.11

1210

138.

300.

9812

.54

5.89

5.00

Sc4.

94.

65.

13.

260.

1111

.011

.011

.010

.46

5.12

10.0

10.0

10.0

0.00

0.00

9.26

7.99

0.50

V13

1016

21.1

31.

8258

5859

0.69

0.40

59.7

22.

5582

8084

1.65

1.36

83.0

00.

725.

00C

u<1

0<1

016

1021

35.4

85.

504.

6723

2.14

1615

186.

050.

9810

.05

61.1

910

.00

Pb11

1012

7.69

0.55

109

1314

.41

1.47

3.78

170.

007

78

5.56

0.40

3.27

120.

242.

00Zn

3530

4411

.59

2.71

4443

452.

030.

8946

.55

5.47

5957

602.

311.

3658

.23

0.63

10.0

0B

i0.

50.

50.

50.

30.

20.

533

.53

0.11

0.6

0.4

0.8

29.9

90.

170.

20C

d<0

.2<0

.2<0

.2<0

.2<0

.2<0

.20.

20In

<0.0

5<0

.05

0.1

0.1

0.1

<0.1

<0.1

<0.1

0.05

Sn4.

33.

74.

67.

320.

212.

41.

84.

136

.16

0.88

5.00

51.2

01.

61.

12.

223

.13

0.37

6.00

73.6

70.

50M

o1.

11.

01.

514

.56

0.11

0.5

0.4

0.6

14.3

90.

070.

8941

.50

0.9

0.8

0.9

5.70

0.05

0.92

6.83

0.20

Sb<0

.20

<0.2

00.

30.

20.

317

.68

0.05

0.35

22.8

9<0

.2<0

.20.

270.

20A

g0.

30.

10.

594

.28

0.19

0.3

0.3

0.3

0.17

78.5

70.

20.

10.

233

.33

0.05

0.23

35.3

40.

10R

b20

719

022

03.

985.

4950

4756

6.22

3.14

48.0

05.

0023

2224

2.75

0.63

22.0

04.

550.

05C

s1.

21.

11.

36.

030.

051.

21.

11.

48.

030.

101.

220.

270.

50.

40.

52.

430.

010.

8144

.55

0.02

Ba

559

510

600

4.25

15.8

472

471

073

01.

108.

0070

8.00

2.26

582

550

610

3.98

23.1

560

7.00

4.12

10.0

0Sr

2620

3423

.27

4.02

256

250

260

1.91

4.90

217.

5017

.70

724

720

730

0.68

4.90

737.

001.

765.

00T

l0.

80.

11.

032

.30

0.17

0.3

0.3

0.3

5.17

0.02

0.2

0.1

0.2

8.43

0.01

0.02

Th

22.9

21.0

25.0

6.33

0.97

4.4

4.2

4.8

4.88

0.21

4.02

9.05

2.1

2.0

2.2

3.60

0.07

1.91

9.03

0.02

U6.

45.

96.

94.

740.

201.

51.

41.

65.

060.

071.

565.

280.

80.

80.

94.

710.

040.

852.

560.

02G

a19

1820

4.30

0.54

1514

177.

301.

1024

.00

37.5

019

1820

4.71

0.89

29.0

034

.48

0.10

Ta1.

71.

51.

85.

890.

060.

30.

30.

34.

870.

010.

5039

.60

0.22

0.21

0.24

5.36

0.01

0.50

55.2

00.

20N

b24

.423

.025

.03.

460.

563.

83.

64.

14.

550.

175.

9636

.59

4.04

3.9

4.2

3.36

0.14

6.56

38.3

70.

05H

f5.

75.

46.

14.

750.

183.

83.

64.

03.

610.

143.

556.

023.

33.

03.

44.

820.

163.

145.

610.

05Zr

207

190

230

8.26

11.3

912

611

014

08.

0910

.20

115.

009.

5711

211

012

03.

574.

0013

6.00

17.6

50.

50Y

3231

342.

600.

5623

2224

3.28

0.75

13.5

268

.66

1514

164.

920.

758.

6775

.38

0.02

La

40.9

38.0

43.0

3.54

0.97

13.2

13.0

14.0

3.03

0.40

13.5

82.

8013

.613

.014

.03.

600.

4913

.83

1.64

0.10

Ce

105.

797

.011

0.0

5.32

3.75

28.0

26.0

30.0

4.52

1.26

27.0

63.

4729

.829

.030

.01.

340.

4028

.37

5.03

0.10

Pr10

.39.

311

.06.

210.

433.

43.

23.

53.

040.

103.

83.

73.

91.

960.

070.

02Sm

7.1

6.2

7.8

5.99

0.28

2.9

2.8

3.1

3.99

0.12

2.65

10.2

73.

23.

13.

43.

950.

132.

8412

.58

0.10

Nd

35.3

33.0

37.0

4.64

1.09

13.0

12.0

14.0

4.87

0.63

12.2

26.

3815

.615

.016

.03.

140.

4913

.72

13.7

40.

02E

u0.

50.

50.

65.

210.

020.

80.

70.

84.

050.

030.

836.

070.

90.

80.

93.

280.

030.

955.

720.

02G

d6.

15.

56.

65.

330.

223.

13.

03.

33.

140.

102.

92.

83.

02.

600.

070.

02T

b1.

00.

91.

15.

610.

040.

50.

50.

63.

710.

020.

3740

.32

0.4

0.4

0.5

3.89

0.02

0.29

47.1

10.

02


0361-0128/98/000/000-00 $6.00 1905

Dy

6.1

5.4

6.7

5.89

0.24

3.3

3.1

3.5

4.48

0.15

2.4

2.3

2.6

4.92

0.12

0.02

Ho

1.2

1.1

1.3

4.77

0.04

0.7

0.7

0.8

5.09

0.04

0.5

0.5

0.5

2.11

0.01

0.02

Er

3.3

3.1

3.6

5.21

0.11

2.1

2.0

2.2

4.26

0.09

1.3

1.2

1.4

5.67

0.07

0.02

Tm

0.5

0.5

0.6

5.73

0.02

0.4

0.3

0.4

3.61

0.01

0.2

0.2

0.2

1.89

0.00

0.02

Yb3.

63.

43.

72.

740.

062.

52.

32.

76.

080.

152.

1613

.89

1.4

1.4

1.4

0.00

0.00

1.27

10.3

00.

05L

u0.

50.

50.

65.

630.

020.

40.

40.

41.

980.

010.

3516

.63

0.2

0.2

0.2

2.75

0.01

0.20

14.1

20.

02

1 M

in =

min

imum

val

ue, m

ax =

max

imum

val

ue, %

RSD

= p

erce

nt r

elat

ive

stan

dard

dev

iatio

n (s

ee t

ext)

, MD

RU

= M

iner

al D

epos

it R

esea

rch

Uni

t, 2σ

= er

ror

of t

he m

ean

at t

he 9

5% c

onfid

ence

leve

l, R

D =

rel

ativ

e di

ffer

ence

, LO

D =

lim

it of

det

ectio

n

TAB

LE

A1.

(C

ont.)

P98-

KZK

2M

in1

Max

1%

RSD

12σ

1P-

1M

in1

Max

1%

RSD

12σ

1M

DR

U1

RD

1W

P-1

Min

1M

ax1

%R

SD1

2σ1

MD

RU

1R

D1

LO

D1

n=

10n

= 5

valu

esn

= 5

valu

es

0361-0128/98/000/000-00 $6.00 1906

geochemistry and paleotectonic setting of felsic volcanic...

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