Olivo, G.R., Chang, F., and Kyser, T.K., 2006. Formation of the ...

©2006 Society of Economic Geologists, Inc. 

Economic Geology, v. 101, pp. 607–631 

Formation of the Auriferous and Barren North Dipper Veins in the Sigma Mine, 

Val d’Or, Canada: Constraints from Structural, Mineralogical, Fluid Inclusion, 

and Isotopic Data 

GEMA RIBEIRO OLIVO, † FELICIA CHANG, AND T. KURTIS KYSER 

Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario K7L 3N6, Canada 

Abstract 

The Sigma-Lamaque mine (>100 metric tons (t) of gold) is an example of an Archean greenstone belt gold 

deposit formed by processes related to multistage hydrothermal fluid circulation. The earliest recognized vein 

systems are steeply to moderately dipping fault-fill veins within shear zones and contemporaneous subhorizontal 

veins, which were overprinted by the late North Dipper vein system. The latter strikes east-west, dips 

moderately to the north, and exhibits complex internal geometry with features similar to fault-fill and extensional 

veins, and therefore is interpreted as extensional shear veins. This late vein system was considered one 

of the major sources of gold in the shallow underground and open-pit ore reserve estimations. 

These late North Dipper veins were studied in detail in the Sigma pit where they contain ore-grade gold 

and are hosted by the calc-alkaline tuffs of the Val d’Or Formation and in the North zone where they are barren 

and hosted by the tholeiitic volcanic rocks of the Jacola Formation. In the Sigma pit, these veins have 

apparent thicknesses of 0.8 to 3 m and very irregular contacts with the vein walls. They comprise irregular 

zones of milky quartz filling, disrupted blocks of layered quartz and tourmaline and slabs of foliated pyriterich 

wall rock. Layers with tourmaline and quartz crystals oriented perpendicular to the vein walls are 

observed close to the vein walls. The veins contain minor amounts of calcite, pyrite, rutile, and traces of chlorite, 

muscovite, pyrrhotite, chalcopyrite, galena, bismuth tellurides, and gold. Locally, the sulfide content can 

attain 10 modal percent of the vein mineralogy. In the veins, native gold (with 6 wt % Ag) occurs rarely associated 

with the main vein-filling minerals, commonly as inclusions in pyrite (main vein-filling stage), and most 

commonly filling fractures in pyrite, tourmaline, and quartz, where it is alloyed with 8 to 17 wt percent Ag 

and is associated with calcite and Bi tellurides (late auriferous stage). The proximal wall-rock alteration related 

to the auriferous North Dipper veins overprints the metamorphic assemblage and is characterized by abundant 

fine-grained plagioclase, calcite, quartz and minor chlorite, tourmaline, and pyrite in the tuffs and more 

abundant muscovite in the intrusive feldspar porphyry. In the wall rock, gold with 6 to 28 wt percent Ag is 

found locally filling fractures in pyrite, where it is associated with a late generation of calcite. The barren 

North Dipper vein also comprises mainly quartz and tourmaline but lacks calcite and gold, has a very low content 

of sulfides (100 metric tons (t) of Au) quartz-carbonate vein deposits, 

accounting for about 13 percent of the world gold production. 

In Canada, the Archean Abitibi subprovince is the main 

source of gold (4,470 t Au and 72.4% of Canadian production) 

and hosts the world-class Hollinger-McIntyre-Coniarum, 

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608 OLIVO ET AL. 

Kirkland Lake, Dome, Kerr Addison, Sigma-Lamaque, and 

Pamour mines (Jenkins et al., 1997). These deposits formed 

through complex and multistage processes, allowing for concentration 

of gold at average grades typically around 10 g/t 

and locally attaining more than 100 g/t. 

Most studies of the processes related to the gold concentration 

in these world-class deposits have focused on the ore 

zones with less attention on the related veins and alteration 

systems that are barren. The youngest vein system in the 

Sigma deposit in the Abitibi greenstone belt, the North Dipper 

system (Gaboury et al., 2001), provides an opportunity to 

evaluate the processes related to ore formation because this 

system is relatively young and less deformed than early systems, 

and auriferous and barren veins are well exposed in the 

Sigma pit and in the North zone, respectively, allowing for detailed 

mapping and sampling. 

In this study, detailed field observations reveal that the 

geometry of the plumbing system and its position relative to 

the major fluid conduit are fundamental for formation of the 

auriferous zones. Petrographic descriptions, microthermometry, 

crush-leach chemical analyses, and time-of-flight laser ablation 

induced coupled plasma-mass spectrometry (TOF-LA- 

ICPMS) of fluid inclusions, and stable isotope data also show 

that the mechanisms for gold precipitation in the North Dipper 

and related veins changed during the evolution of the system. 

Comparisons of the elements enriched in the auriferous 

fluids versus the barren fluids suggest various sources for the 

metals associated with the gold, and the isotopic composition 

of the fluids that carried the gold indicates low fluid/rock 

ratios. 

Regional Geologic and Tectonic Setting 

The Val d’Or district is located in the eastern segment of 

the southern Volcanic zone (Daigneault et al., 2002) of the 

Archean Abitibi subprovince at the boundary with the Pontiac 

subprovince (Fig. 1). This boundary is characterized by 

an extensive deformation zone, referred to as the Larder 

Lake-Cadillac break, which is interpreted as a suture zone between 

these two subprovinces (Robert et al., 1995). The 

Larder Lake-Cadillac break major fault zone dips to the north 

and is spatially associated with numerous gold deposits and 

occurrences (Robert, 1989, 1994). The geology of the Val 

d’Or district has been described by Gunning and Ambrose 

(1940), Norman 1947), Latulippe (1966), Dimroth et al. 

(1982, 1983a, b), Imreh (1984), Desrochers et al. (1993), 

Desrochers and Hubert (1996), and recently reviewed by Pilote 

et al. (1997, 1998, 1999, 2000) and Scott et al. (2002). Information 

from these sources, as well as from specific studies 

in the area, is briefly summarized below. 

The Val d’Or district comprises a complex sequence of volcanic-sedimentary 

and intrusive rocks that evolved from 

2714 to 2611 Ma. The volcanic-sedimentary sequences are 

part of the Malartic Group (i.e., La Motte-Vasson, Dubuisson, 

Lac Caste, and Jacola Formations) and the Louvicourt 

Group (Val d’Or and Héva Formations: Scott et al., 2002). 

The Malartic Group comprises mainly ocean floor komatiite 

and tholeiitic basalt flows and sills, with minor sedimentary 

rocks, which are interpreted to be formed in an extensional 

environment related to mantle plumes. The Louvicourt 

Group is composed mainly of mafic to felsic volcanic rocks 

that formed in a subduction-related deep marine volcanic 

arc. The studied barren and auriferous veins are hosted in the 

transition zone between the Jacola and Val d’Or Formations, 

which are described below. 

The Jacola Formation extends for more than 5 km and consists 

of a 1- to 2-km-thick sequence of pillowed, brecciated, 

and massive tholeiitic basalts, intercalated with komatiite and 

massive to pillowed komatiite flows (100–200 m thick). Discontinuous 

interflow volcaniclastic deposits occur locally and 

have been dated at 2703.08 ± 1.3 Ma (Pilote et al., 1999). This 

sequence is interpreted to represent fissure-style eruptions 

formed in a proto-arc environment. The contact between the 

Jacola and Val d’Or Formations to the south is gradational and 

interefingers laterally (Dimroth et al., 1982), being characterized 

by a significant increase in the volume of volcaniclastic 

deposits and a change to intermediate and felsic composition 

at the base of the Val d’Or Formation (Scott et al., 2002). 

The overlying Val d’Or Formation is composed of a 3- to 5- 

km-thick sequence of discontinuous, interstratified, massive to 

pillowed lavas and volcaniclastic deposits of andesite (50%), 

dacite (30%), and rhyolite (20%). The lower units are tholeiitic 

to intermediate, and the upper units are intermediate to 

calc-alkaline in composition. The dacitic and rhyolitic units 

have an age of 2704 ± 2 Ma (Wong et al., 1991; Machado et al., 

1992; Pilote et al., 1998). The distribution and composition of 

the Val d’Or Formation rocks suggest that they formed as numerous 

small volcanic vents analogous to a modern arc setting 

(Scott et al., 2002). Primary volcanic features in both formations 

indicate younging directions toward the south. 

These volcanic and sedimentary sequences are intruded by 

felsic to mafic bodies that have been grouped into three 

classes (Pilote et al., 2000): (1) 2700 Ma synvolcanic (Wong et 

al., 1991) stocks and batholiths, (2) 2680 Ma syn- to late-tectonic 

intrusions (Jemielita et al., 1990; Pilote et al., 1998), and 

(3) late- to post-tectonic, undeformed and unmetamorphosed 

stocks and dikes intruded between 2675 and 2611 Ma (Feng 

and Kerrich, 1991; Ducharme et al., 1997). 

All these units, with the exception of the late stocks and 

dikes, have been metamorphosed to greenschist facies and 

multiply deformed in three major phases (Robert, 1990a, b; 

Desrochers and Hubert, 1996). The first phase of deformation 

(D 1 ) is recognized only locally; the second phase (D 2 ) is 

the dominant structural trend in the area and is characterized 

by tight and isoclinal folds, a regionally penetrative subvertical 

east-west foliation, faults, and shear zones. Gold deposits 

in the Val d’Or disctrict are hosted or spatially associated with 

these faults and shear zones. The D 2 deformation event is estimated 

to have occurred after 2672 Ma, the age of the detrital 

zircons in sedimentary units folded by D 2 (Robert, 2001, 

and references therein). The D 3 phase of deformation is characterized 

by steep, open folds and associated east-northeast 

crenulation cleavage and also involved the reactivation of the 

D 1 and D 2 faults and shear zones. 

Sigma Mine Geology: Host Rocks and Vein Systems 

The geology and auriferous vein systems of the Sigma mine 

have been described by Robert (1983), Robert and Brown 

(1986a, b), Robert et al. (1995), Garofalo (2000), and Gaboury 

et al. (2001). The relevant features observed by the authors, 

integrated with previous studies, are presented below. 

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FORMATION OF THE AURIFEROUS AND BARREN VEINS IN THE SIGMA MINE, VAL D’OR 609 

FIG. 1. Simplified geologic map of the Val d’Or mining district, showing the location of the Sigma mine and the North 

zone, which host of the barren veins. Twelve other gold deposits are also shown (after Imreh, 1984; Robert, 1989; Sauvé et 

al., 1993; and Pilote et al., 2000). 

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Host rocks 

The auriferous veins of the Sigma mine are hosted exclusively 

in the Val d’Or Formation and their intrusive rocks 

(Fig. 2). The Val d’Or Formation in the mine site comprises 

mainly calc-alkaline, andesitic, massive to pillow lavas intercalated 

with volcaniclastic horizons and porphyritic phases 

(Robert, 1983). The host rocks of the studied auriferous veins 

in the Sigma open pit are mainly lapilli tuffs and minor lapilli 

tuff breccias (West zone) and crystal tuffs (Central zone; Fig. 

3A-B), described in detail by Chang (2002). 

The studied barren North Dipper vein system crops out in 

the North zone property (Fig. 4), located about 500 m north 

of the Sigma mine open pit (Fig. 2). The rocks in this property 

comprise mainly pillowed basaltic andesite with minor 

massive flows and lapilli tuff. Preserved primary volcanic 

structures indicate south-facing directions. The pillows are 

deformed, showing an elongated shape, averaging 0.3 m in 

width and 1.5 m in length, with weak foliation striking eastwest 

and dipping steeply to the north. Based on their chemical 

composition, these pillowed units are interpreted as part 

of the Jacola Formation and are classified as tholeiitic, 

basaltic andesite to andesite (Chang, 2002), according to the 

criteria of Winchester and Floyd (1977) and Barrett and 

MacLean (1999), respectively. 

Three types of feldspar porphyritic intrusive rocks were 

identified in the study areas. Type 1 feldspar porphyry is 

found in the Central pit and North zones, where it forms irregular 

bodies (3–5 m thick), cutting the volcanic and volcaniclastic 

rocks. These dikes are correlated with C porphyry 

(mine nomenclature, Robert, 1983), also referred to as porphyritic 

diorite (Gaboury et al., 2001). Feldspar porphyry 

type 2 was observed only east of the North zone, where it cuts 

feldspar porphyry 1, strikes east-west, dips 84º to the south, 

FIG. 2. Geology of the Sigma-Lamaque deposit, showing the various host rocks, major shear zones, and quartz tourmaline 

veins. The zones mapped in detail are indicated by “W” and “C” (auriferous West and Central zones, respectively) and 

“NZ” (North zone which hosts the barren North Dipper vein). Modified after Gaboury et al. (2001). 

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FIG. 3. Detailed geologic sections of the Sigma pit benches, showing the geometry of the North Dipper and North 

Dipper-related veins and their host rocks and local structures. A. Composite section of the West zone looking west (the left 

side) and looking north (right side); see coordinates indicating bench direction. B. In the Central zone (NE-SW section). 

and is up to 1.5 m thick. Based on mineralogical and textural 

features (Chang, 2002), this rock is correlated with G porphyry 

(mine nomenclature, Gaboury et al., 2001). Type 3 

feldspar porphyry occurs as a very weakly foliated, irregular 

intrusive massive body in the lapilli tuff of the North zone 

(Fig. 4). 

The main foliation observed in the volcanic, volcaniclastic, 

and type 1 feldspar porphyry trends east-west, dips steeply to 

the north (72°–89°), and is correlated with the regional S 2 foliation 

described by Robert (1983) and Robert and Brown 

(1986a, b). The mineral assemblages found in the studied 

host rocks (plagioclase + chlorite + epidote + rutile; Chang, 

2002) are compatible with greenschist facies metamorphic 

conditions in mafic rocks. These metamorphic phases were 

replaced by late muscovite and calcite, as observed mainly in 

the feldspar porphyry type 2 (Chang, 2002). 

Vein systems 

The auriferous veins of the Sigma mine can be grouped in 

four distinct types based on their structural controls and internal 

geometries: (1) steeply to moderately dipping fault-fill 

veins within shear zones, (2) subhorizontal extensional veins, 

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FIG. 4. Geologic map of the North zone, which hosts the barren North Dipper vein. Modified from J. Brault (2000, 

unpub. report for Les Mines McWatters, Val d’Or, Quebec, Canada). 

(3) arrays of subhorizontal veins within the feldspar-porphyry 

dikes (dike stringers), and (4) moderately north dipping extensional 

shear veins (North Dipper veins). The first three 

types were well documented by Robert (1983) and Robert 

and Brown (1986a, b) and the fourth type (North Dipper 

veins) was structurally characterized by Gaboury et al. (2001) 

and is the subject of this detailed research. The various types 

of mineralized veins are composed mainly of quartz and tourmaline 

with variable amounts of carbonate (mainly calcite), 

pyrite, chalcopyrite, and scheelite and formed contemporaneously 

with the development of second- and third-order 

shear zones during an advanced stage of D 2 deformation 

(Robert, 1990a, b, 1994; Couture et al., 1994, Gaboury et al., 

2001). Their major characteristics are summarized in Table 1. 

The North Dipper Systems 

The North Dipper veins exhibit complex internal geometry 

with features similar to fault-fill and extensional subhorizontal 

veins and are interpreted by Gaboury et al (2001) to be extensional 

shear veins. They strike east-west and dip moderately 

(35 º–65º) toward the north, are relatively continuous 

along strike for more than 1 km, and occur more commonly 

within a 100-m-wide zone between the Main and A-F dike 

swarm corridors (Gaboury et al., 2001, fig. 4). Their spatial 

distributions and relationships with the extensional and shear 

veins suggest that they may represent linking structures between 

subhorizontal veins, which are related to a conjugate 

pair of low-angle reverse faults formed during a more advanced 

stage of fracture development (Gaboury et al., 2001). 

The North Dipper system has recently been recognized as 

one of the four major types of auriferous veins in the evaluation 

of the ore reserves by G. A. Armbrust, P. E. Sandefir, and 

K. L. Meyer (unpub. report for Century Mining Corp., Val 

d’Or, Quebec, 2005). However, the reserve estimations do not 

explicitly outline the contributions of each vein type because 

the various types commonly occur in the same area. 

The North Dipper veins and their related veins systems 

were studied in detail at two ore-bearing areas in the Sigma 

open pit (West and Central pit zones, referred to as “Sigma 

North Dipper” veins), with average gold grades of 5 to10 g/t 

(locally 120 g/t Au), and one barren area outside of the open 

pit zones, the North zone (referred to as “North zone North 

Dipper” veins), where the vein has gold grades lower than detection 

limit (


TABLE 1. Summary of the Characteristics of Auriferous Veins of the Sigma Mine 1 

Vein type Host rocks Geometry and dimension Mineralogy/texture 

Fault-fill (shear) vein Volcanic and Occur in stepping pattern within ductile shear Quartz, tourmaline, carbonate, scheelite, 

volcanclastics rocks of zones, commonly layered and containing pyrite; minor chalcopyrite and pyrrhotite 

the Val d’Or Formation slivers of hydrothermally altered wall rock; and tellurides; layers with main vein-filling 

and intrusive rocks strike 070°–100°, dip 50°–90° S, 2-m width, minerals parallel the vein margins; locally 

200-m vertical and lateral extent and 2 cm to brecciated 

3 m thick 

. 

Extensional (flat, Volcanic and Occur in en echelon patterns with rock bridges, Quartz, tourmaline, carbonate, minor 

tension, subhorizontal) volcaniclastics rocks of commonly proximal to fault-fill veins; variable scheelite, sulfides, and tellurides, showing 

the Val d’Or Formation strike, dip shallow, 1-mm to 1-m width, up to open-filling textures with quartz and 

and intrusive rocks 75 m N-S extent or 300 m E-W extent, tourmaline fibers perpendicular to the vein 

2–3 m thick walls 

Dike stringer Feldspar porphyry Occur en echelon and pinch out abruptly, Quartz, tourmaline, carbonate, minor 

dikes only almost perpendicular to dike margins; strike: scheelite, sulfides, and tellurides, showing 

NW-SE, dip 35° SW, 10s of meters lateral open-filling textures with quartz and 

extent, up to 1 m thick 

tourmaline fibers perpendicular to the vein 

walls 

Shear-extension Volcanic and Complex internal geometry, with layered Mainly quartz and tourmaline and minor 

(oblique-tension vein, volcaniclastics rocks of segments; strike E-W, dip moderate, calcite, pyrite, chalcopyrite, and tellurides; 

North Dipper and the Val d’Or Formation up to 1 km vertical and lateral extent, early vein-filling minerals are deformed 

North Dipper-related) up to 3 m thick and rotated parallel to the vein margins; 

late phases form fibers perpendicular to 

vein walls 

1 Based on Audet (1979), Robert et al. (1983), Robert and Brown (1986a, b), Gaboury et al. (2001), and this study 

FIG. 5. A-C: Photographs of the North Dipper veins in the Sigma pit in the West zone, looking northwest. A. Detail of 

the complex shape and internal geometry of the North Dipper vein, with irregular and disrupted layers of quartz (Qtz) and 

tourmaline (To) that formed during the various stages of the North Dipper vein opening and filling. B. Detail of the contact 

of the North Dipper vein with the wall rock, illustrating the irregular distribution of the proximal alteration. C. North Dipper-related 

veins in the southeastern margin of the North Dipper vein. D. View looking toward the north of the Central zone 

North Dipper vein. In this zone, the vein is layered, with most of quartz and tourmaline layers parallel to the vein walls. 

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layers of quartz and tourmaline and centimeter-sized slabs of 

foliated, pyrite-rich wall rock. Elongated crystals of quartz 

and tourmaline oriented at high angle to the vein margins 

occur locally, close to the footwall contact. In the Central 

zone, the North Dipper vein is mainly layered with tourmaline 

and quartz ribbons oriented parallel to subparallel to the 

vein margins (Fig. 5D). The North Dipper vein in the Sigma 

mine pit comprises calcite (5 vol %), pyrite (2–5 vol %), rutile 

(1–3 vol %), and minor amounts of chlorite, muscovite, 

pyrrhotite, chalcopyrite, galena, bismuth tellurides, and gold. 

Locally the sulfide content can be as high as 10 vol percent 

(mainly pyrite). The modes of occurrence of the vein filling 

minerals are described below and illustrated in Figure 6A-F, 

and the interpreted paragenetic sequence is summarized in 

Figure 7A. 

In the milky irregular zones, quartz occurs either as grains 

up to 5 mm long or as fine-grained (


FIG. 6. Photomicrographs of the auriferous North Dipper (A-E) and North Dipper-related veins (F) and their host rocks 

(G-H). A. First recognized generation of tourmaline (To1)aligned parallel to the layer margins, with interstitial quartz (Qtz). 

B. Tourmaline layers cut by late quartz veinlets, both showing corroded zones filled with calcite (CC). C. Radially oriented 

tourmaline grains that postdate the aligned grains shown in (A) and are associated with weakly deformed quartz grains, both 

minerals being replaced by calcite. D. Rare poikiloblastic grains of pyrite with inclusions of rutile (Rt), pyrrhotite (Po), chalcopyrite 

(Cp), and gold (Au). E. Typical mode of occurrence of gold-filling fractures in pyrite where it is associated with Bi 

tellurides (BiTe). F. Gold associated with calcite-filling late fractures in quartz and tourmaline in the North Dipper-related 

vein. G. Gold, galena (Gn), chalcopyrite, pyrrhotite and Bi teluride included in pyrite from the proximal alteration zone of 

the North Dipper vein. H. Gold associated with chalcopyrite-filling fractures in a second generation of pyrite that occurs in 

the wall-rock alteration of the North Dipper-related vein. 

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FIG. 7. Paragenetic sequence for (A) Sigma (North Dipper) and North zone North Dipper veins and (B) North Dipperrelated 

veins. 

Dipper vein in order to characterize the different fluids associated 

with the mineralized and barren North Dipper systems. 

Microthermometric measurements were conducted on 

more than 400 fluid inclusions hosted in quartz (from barren 

and mineralized veins) and on a few inclusions hosted by 

scheelite (from the barren vein only), using the Linkam 

THMS-G-600 heating-freezing stage at Queen’s University. 

The stage was calibrated using the Synflinc synthetic fluid inclusion 

standards. The error associated with temperature 

measured below 30º and above 100ºC was ±0.2º and ±2ºC, respectively, 

following the equipment specifications and standard 

measurements. 

Distribution, nature, and morphology of fluid inclusions 

Fluid inclusions are abundant in quartz and scheelite and 

occur mainly along healed fractures of various orientations 

that transect quartz grain boundaries and reworked grains or 

in clusters close to these fractures (Fig. 9A). Three compositional 

types of fluid inclusions were identified: (1) H 2 O-CO 2 , 

(2) CO 2 -rich, (3) monophase, two-phase, and three-phase 

H 2 O-rich. Fluid inclusions in scheelite are commonly very 

small (


FIG. 8. Features of the barren North zone North Dipper vein. A. Outcrop of the barren North zone North Dipper vein, 

showing its geometry and contact with the host rocks. B. Detail showing the tourmaline fibers in the vein margin, indicative 

of late extension. C. and D. Photomicrographs showing the complex internal geometry of the vein with various generations 

of tourmaline and quartz. Early generations are strongly deformed, however, the late generations show open-space 

filling textures. 

and high birefringence were observed in two- (AQ SL ) and 

three-phase (AQ SLV ) fluid inclusions and are interpreted to be 

carbonate crystals. Because these crystals have an uneven distribution, 

vary in proportion, and do not change their morphology 

during cooling and heating experiments, they are interpreted 

as trapped crystals. Monophase aqueous fluid 

inclusions (AQ M ) are most common in the barren North zone 

North Dipper vein and minor or rare in the auriferous North 

Dipper and North Dipper-related veins. They occur mainly 

along intersections of healed fractures or close to grain 

boundaries. 

Microthermometry: Data and interpretation 

The results of the microthermometric analyses are summarized 

in Appendix 1, represented graphically in Figure 10A- 

B, and interpreted below. Temperatures related to phase 

changes vary slightly along single healed fractures or in 

clusters of inclusions and more significantly between samples 

of a given vein type or from different vein types. 

H 2 O-CO 2 fluid inclusions (AC): Most of the aqueous-carbonic 

(AC LL and AC LLV ) fluid inclusions decrepitated before 

homogenization (90% in North Dipper and about 60% in 

North Dipper-related veins). Where observed, homogenization 

was to the liquid phase at a wide range of temperatures 

varying from 228° to 440°C, but most inclusions homogenized 

between 228° and 270°C. The highest temperatures 

were documented in the North Dipper-related veins (App. 1, 

Fig. 10B). Melting of the carbonic phase (T m(CO2 )) in inclusions 

from the North Dipper-related veins occurred at lower 

temperatures than for the inclusions from the North Dipper 

veins (–58.3°C), which indicates the presence of small concentrations 

of other gases, most likely methane (Kerkhof, 

1990, Olivo and Williams-Jones, 2002). Homogenization of 

the CO 2 (T h(CO2 )) to the liquid phase occurred from –10° to 

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FIG. 9. Photomicrographs showing fluid inclusions in the North Dipper and North Dipper-related veins. A. Fluid inclusions 

in healed fractures of various orientations; most of the inclusions trails transect quartz grains boundaries and reworked 

grains. They are rarely intragranular. B. Deformed, necked down, and decrepitated fluid inclusions along grain boundaries. 

C. Two- (AC LL) and three-phase (AC LLV) aqueous-carbonic subtypes with variable volumetric proportions coexisting in the 

same healed fracture. D. Two-phase and monophase carbonic fluid inclusions in the same healed fracture. 

30°C, with the lower temperatures measured in the North 

Dipper vein. The densities of the carbonic phase, which were 

calculated from the graphs of Valadovich and Altunin (1968) 

and Swanenberg (1979), using values of T h(CO2 ), are high for 

liquid H 2 O and liquid CO 2 inclusions (avg 0.85 g/cm 3 , AC LL ) 

and moderate for all liquid H 2 O, liquid CO 2 , and vapor CO 2 - 

H 2 O inclusions (avg 0.65g/cm 3 , AC LLV ). The molar proportions 

of CH 4 are estimated to be less than 0.2 mol percent, 

based on the Heyen et al. (1982) method, which uses the relationship 

between T m(CO2 ) and T h(CO2 ), and the highest values 

were obtained in the North Dipper-related veins. Most of the 

clathrates melted between 7° and 8°C (T m(C) ) in both North 

Dipper and North Dipper-related veins, yielding average 

salinities of 4 to 5 wt percent NaCl equiv, according to the 

method outlined in Colins (1979). Although some inclusions 

in the North Dipper-related veins with high T m(C) (and consequently 

the lowest salinities) had low T m(CO2 ) values, other inclusions 

with equally low T m(CO2 ) yielded average T m(C) . The 

first and last ice-melting temperatures were very difficult to 

document due to the formation of large clathrates during 

cooling experiments. 

CO 2 -rich fluid inclusions (C): The temperatures of melting 

of the carbonic phase (T m(CO2 )) in the CO 2 -rich inclusions 

from the North zone North Dipper, North Dipper, and North 

Dipper-related veins are consistently –56.7° ± 0.2°C, indicating 

pure CO 2 . However, in inclusions from the North Dipperrelated 

veins, T m(CO2 ) values less than –57°C are commonly 

observed, suggesting the presence of minor CH 4 , similar to 

the aqueous-carbonic fluid inclusions. T h(CO2 ) is commonly 

greater than –10°C in carbonic inclusions (C) and carbonic 

inclusions with a small amount of H 2 O (C AQ ) from North Dipper 

veins and as low as –45°C in inclusions from North Dipper-related 

veins. The calculated densities of the carbonic 

phase average 0.86 and 0.80 g/cm 3 for the C and C AQ types, 

respectively, and the CH 4 molar proportion is low (


TABLE 2. Summary of the Distribution and Morphology of Fluid Inclusion Types in the North Zone North Dipper, North Dipper, 

and North Dipper-Related Veins 

Inclusion types North zone North Dipper veins North Dipper veins North Dipper-related veins 

H 2O-CO 2 

(AC) 

2%: mostly in clusters, rare in healed 

fractures 

AC LLV: 100% 

Size: 5 to 7 µm 

Shape: elliptical 

Volumetric proportion of CO 2 phase: 15% 

Volumetric proportion of vapor CO 2 phase: 

5% 

28%: commonly in healed fractures, 

clusters, and individual inclusions 

AC LL: 53%; AC LLV: 47% 

Size: 4 to 17 µm, most from 5 to 10 µm 

Shape: rounded, elliptical, negative crystal 

Volumetric proportion of CO 2 phase: 10 to 

40%, mostly 20% 


5 to 20% 

12%: commonly in healed fractures, and 

clusters, some occur as individual 

inclusions 

AC LL: 53%; AC LLV: 47% 

Size: 3 to 13 µm, most from 3 to 6 µm 

Shape: rounded, elliptical, negative crystal 

Volumetric proportion of CO 2 phase: 5 to 

45%, most from 10 to 25% 


5 to 25%, most from 15 to 20% 

CO 2-rich 

(C) 

8%: mainly in clusters and healed fractures, 

rare as individual inclusions 

Phases: monophase, two-phase 

C AQ : dominant CO 2-rich type 

Size: 2 to 7 µm 

Shape: irregular, elliptical, negative crystal 


15% 

25%: mostly in clusters 

Phases: monophase, two-phase 

C AQ


FIG. 10. Binary plots of fluid inclusion microthermometric data and the calculated parameters for aqueous carbonic, carbonic, 

and aqueous fluid inclusions. A. Salinity vs. temperature of melting of the carbonic phase (Tm CO2 ). B. Temperature of 

total homogenization (T h) vs. salinity. See text for discussion. 

veins and barren North zone North Dipper veins: (1) a 

crush-leach technique accompanied by high resolution-inductively 

coupled plasma mass spectrometry (HR-ICPMS), 

and (2) analysis of single fluid inclusions or clusters of fluid 

inclusions of the same type using laser-ablation time-of flight 

inductively coupled plasma-mass spectrometry (LA-TOF- 

ICPMS). This is the first time the latter technique has been 

systematically applied in conjunction with microthermometric 

and crush-leach analyses to determine the composition of 

fluid inclusions. 

Clusters or healed fractures representative of particular 

inclusion types (e.g., carbonic or aqueous-carbonic dominant) 

were selected after petrography and microthermometry 

investigations, and millimeter-sized hosting segments 

were cut out as individual chips for preparation in the clean 

lab. Although the samples were carefully selected to contain 

dominantly one type, some mixing of inclusion types may 

have occurred. In total, 12 samples were selected: one sample 

from the North zone North Dipper vein representing 

predominantly aqueous inclusions, seven samples from the 

North Dipper vein representing either predominantly carbonic 

or aqueous-carbonic populations, and three samples 

from the North Dipper-related vein representing predominantly 

carbonic inclusions; a procedure blank was added to 

the analysis for comparison. The preparation involves three 

steps: (1) washing the chips with deionized (DI) water, 

ethanol, then 50 percent HNO 3 ; (2) crushing the chips using 

a mortar and pestle in a DI water-10 percent HNO 3 solution; 

and (3) centrifuging and decanting the liquid into Savillex ® 

containers for evaporation. The collected precipitate is then 

diluted with approximately 1 to 2 g of 2 percent HNO 3 and 

the solutions were analyzed using the Finnigan MAT Element 

HR-ICP-MS at Queen’s Facility for Isotope Research. 

Elements that were selected for analyses (Na, Mg, K, Ca, Ni, 

Cu, Zn, Pb, As, Sb, Ag, Au, and Bi) were chosen because of 

their typical association with fluids related to auriferous 

quartz veins. Specific isotopes of each element to be measured 

were selected in order to avoid isobaric interferences 

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present during low-, medium-, and high-resolution analysis. 

Based on the size, abundance, and density of inclusions 

within each vein, an estimated 5 × 10 –6 g of inclusion fluid 

was released into 1 g of acid solution. This estimate was used 

to approximate the concentrations of each element in the 

fluid inclusion, and the results expressed in concentration 

(ppm; ng/g) were multiplied by the weight of each solution to 

obtain the actual weight of the element released from fluid 

inclusions (Table 3). 

Each element is normalized to Na (Table 4) and the ratios 

of each sample are normalized to those obtained for the barren 

North zone North Dipper vein sample, which contained 

only aqueous inclusions (NZND-AQ100) in order to evaluate 

enrichments or depletions of each element in fluids from the 

auriferous veins with respect to the aqueous fluids in the barren 

vein (Fig. 11). Procedural blanks for the crush-leach had 

high background values in Ca and Zn (>100 ng), consequently 

these elements were not considered in the discussion below. 

Aqueous-carbonic and carbonic-dominant inclusions from 

the auriferous North Dipper and North Dipper-related vein 

samples have consistently higher Ni/Na, Cu/Na, and Sb/Na 

ratios than the aqueous inclusions from the barren North 

zone North Dipper sample (Fig. 11). One sample of the auriferous 

North Dipper vein and one from the North Dipperrelated 

vein have anomalously high values of As/Na; the latter 

sample also has high Ag/Na and Au/Na ratios. 

LA-TOF-ICPMS was chosen because it has the ability to 

quickly analyze multiple elements in the transient signal that 

results from opening of a single fluid inclusion by laser ablation. 

In addition, contamination using the LA-TOF-ICPMS is 

smaller than crush-leach because in the latter, part of the host 

mineral (e.g., sulfides and carbonates within quartz) can be 

incorporated during sample crushing and dissolution to liberate 

fluids from the inclusions. These can be avoided in the 

LA-TOF-ICPMS because of the spatial resolution of the laser 

beam. 

In TOF-ICPMS, ions representing various isotopes have 

mass-dependent velocities, which enables the detector to 

measure the signal intensity of each isotope based on its arrival 

time (Balcerzak, 2003, and references therein). This 

technique allows for high data-acquisition speed, high ion 

transmission, and quasisimultaneous measurement of all 

masses for each ion extracted from the ion source. These results 

cannot be achieved by high resolution or quadruple LA- 

ICPMS. The typical detection limit and error associated with 

this technique are on the order of 10 ppb and less than 10 

percent, respectively (Mahoney et al., 1996; Leach and 

Hieftje, 2001; Balcerzak, 2003). 

Because the minimum size of the laser beam is approximately 

10 µm, samples for analysis were selected based on 

the size of their fluid inclusions and the potential to isolate 

each type along healed fractures and clusters. The auriferous 

North Dipper veins contain the most suitable fluid inclusions 

for LA-TOF-ICPMS analysis because of their large sizes and 

low abundances. Three chip segments were selected to represent 

aqueous, carbonic, and aqueous-carbonic-dominant 

inclusion populations in the auriferous veins. Data were collected 

using a Renaissance LA-TOF-ICPMS (LECO Corporation), 

with 266-nm (UV) laser system. During ablation, individual 

fluid inclusions in clusters of fluid inclusions of the 

same type were targeted. Major (Na, Mg, K, and Ca) and 

minor (Ni, Cu, Zn, Pb, As, Sb, Ba, Ag) elements that were 

most abundant in the inclusion fluids from the auriferous 

veins determined by crush-leaching analyses were selected. 

Element data are expressed in counts per second for the 

largest peak and as element ratios normalized to Na (Table 5). 

The results obtained with the LA-TOF-ICPMS were normalized 

using the crush-leach data for the aqueous fluid inclusions 

in the barren North zone North Dipper vein (sample 

NZND-AQ100 data in Table 4 and Fig. 11). The data indicate 

that the inclusion fluids in the auriferous North Dipper and 

North Dipper-related veins have consistently higher Ni/Na, 

Cu/Na, Sb/Na, Pb/Na, and Ag/Na ratios than the aqueous fluids 

in the barren veins. This finding is similar to the data obtained 

with the crush-leach technique, with exception of the 

Ag/Na and Pb/Na ratios. In addition, aqueous-carbonic fluids 

FIG. 11. Logarithmic plot showing the enrichment factor calculated from element/Na ratios of crush-leach and LA-TOF- 

ICPMS analyses of auriferous North Dipper and North Dipper-related vein samples normalized to the crush-leach analyses 

of the barren North zone North Dipper vein, which contains mainly aqueous inclusions. 

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TABLE 3. Composition of Fluids Obtained for North Zone North Dipper, North Dipper, and North Dipper-Relatded Vein Samples Using Crush-Leach Results (in nanograms) 

North zone Procedure 

North Dipper North Dipper North Dipper-related blank 

Sample name AQ100 AC55C35 AC55AQ40 AC50AQ45 AC70AQ30 AC65AQ30 C60AQ38 C80AQ15 C80AQ15 C50AC40 C60AQ38 PB 

Proportion (%) 1 AQ(66) AC(55) AC(55) AC(50) AC(70) AC(65) C(60) C(62) C(80) C(50) C(60) none 

mAQ(26) C(27) AQC(19) AQC(22) AQC(15) AQC(15) AQC(19) CAQ(18) AQ(12) AC(40) AQ(30) 

AQC(8) CAQ(8) AQ(14) AQ(16) AQ(10) AQ(10) AQ(13) AQC(8) AQC(3) AQC(8) 

mAQ(7) mAQ(7) mAQ(5) mAQ(5) mAQ(6) AQ(5) 

mAQ(2) 

Acid wt (ng) 1.21 1.10 0.87 1.29 0.85 0.89 0.87 0.85 0.85 0.99 0.93 1.38 

Major elements 

Na-23 (LR) 

Mg-25 (MR) 

K-39 (HR) 

Ca-43 (MR) 

Minor elements 

Ni-60 (MR) 

Cu-63 (MR) 

Zn-68 (MR) 

Pb-208 (LR) 

As-75 (HR) 

Sb-121 (HR) 

Ag-107 (HR) 

Au-197 (HR) 

Bi-209 (HR) 

772.94 

71.94 

404.21 

3687.61 

18.46 

8.54 

337.90 

2.70 

1.62 

0.22 

0.44 

0.08 

0.03 

208.57 

5.43 

320.25 

1610.57 

7.13 

5.29 

283.59 

1.74 

0.02 

3.22 

nd 

nd 

0.01 

142.16 

12.05 

138.42 

787.25 

9.02 

4.13 

326.03 

0.38 

0.02 

0.21 

nd 

0.01 

nd 

182.63 

18.63 

182.97 

408.05 

10.25 

7.49 

236.13 

0.56 

0.08 

1.34 

nd 

0.01 

nd 

163.02 

20.20 

129.53 

528.85 

11.15 

4.62 

495.88 

0.34 

1.53 

0.06 

0.06 

nd 

nd 

101.51 

7.01 

106.58 

252.49 

9.06 

4.71 

153.42 

0.31 

nd 

0.03 

nd 

nd 

nd 

104.36 

10.17 

152.84 

536.39 

13.19 

4.21 

246.51 

0.85 

0.02 

0.35 

nd 

nd 

nd 

119.26 

10.18 

115.48 

391.88 

8.79 

4.97 

259.71 

0.31 

0.00 

0.00 

nd 

nd 

nd 

125.83 

19.89 

42.35 

484.47 

10.79 

2.20 

335.84 

0.32 

0.04 

1.51 

nd 

nd 

nd 

186.24 

34.31 

31.79 

309.21 

13.31 

9.99 

210.63 

0.62 

13.63 

4.57 

2.04 

2.77 

nd 

170.37 

16.63 

116.98 

403.91 

10.19 

6.98 

132.22 

0.29 

0.46 

0.06 

nd 

nd 

nd 

78.73 

5.48 

61.82 

268.75 

9.73 

1.89 

100.20 

0.53 

nd 

nd 

nd 

nd 

nd 

1 Numbers in brackets indicate the proportion of each subtype of fluid inclusions in the analyzed chip, including AC = aqueous carbonic, AQ = aqueous, mAQ = monophase aqueous, AQC = aqueous 

with small amounts of dissolved CO2, and C = carbonic; LR, MR, and HR = low, medium, and high resolution; nd = not detected 

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TABLE 4. Element/Na Ratios of Fluids Obtained for North Zone North Dipper, North Dipper, and North Dipper-Related Vein Samples Using Crush-Leach Results 

North zone Procedure 

Ratio North Dipper North Dipper North Dipper-related blank 

Sample name AQ100 AC55C35 AC55AQ40 AC50AQ45 AC70AQ30 AC65AQ30 C60AQ38 C80AQ15 C80AQ15 C50AC40 C60AQ38 PB 

Proportion (%) 1 AQ(66) AC(55) AC(55) AC(50) AC(70) AC(65) C(60) C(62) C(80) C(50) C(60) None 

mAQ(26) C(27) AQC(19) AQC(22) AQC(15) AQC(15) AQC(19) CAQ(18) AQ(12) AC(40) AQ(30) 

AQC(8) CAQ(8) AQ(14) AQ(16) AQ(10) AQ(10) AQ(13) AQC(8) AQC(3) AQC(8) 

mAQ(7) mAQ(7) mAQ(5) mAQ(5) mAQ(6) AQ(5) 

mAQ(2) 

Na (ppm) 36780 22304 30446 31941 32161 27457 31233 24900 22186 20376 25923 N/A 

Major elements 

Mg/Na 

K/Na 

Ca/Na 

Minor elements 

Ni/Na 

Cu/Na 

Zn/Na 

Pb/Na 

As/Na 

Sb/Na 

Ag/Na 

Au/Na 

Bi/Na 

0.093 

0.523 

4.771 

0.024 

0.011 

0.437 

0.003 

0.002 


TABLE 5. TOF-ICPMS Results Showing Composition of Aqueous, 

Carbonic, and Aqueous-Carbonic Fluid Inclusion Populations for 

North Zone North Dipper, North Dipper, and North Dipper-Related Veins 

Aqueous- 

Fluids Aqueous Carbonic carbonic 

Elements Major 

(cps) 

Na 

Mg 

K 

Ca 

Minor (cps) 

Ni 

Cu 

Zn 

Pb 

As 

Sb 

Ag 

Bi 

Ba 

Element/Na 

Major 

Mg/Na 

K/Na 

Ca/Na 

Minor 

Ni/Na 

Cu/Na 

Zn/Na 

Pb/Na 

As/Na 

Sb/Na 

Ag/Na 

Bi/Na 

Ba/Na 

4592.4 

322.1 

711.5 

132.3 

476.4 

529.7 

100.2 

275.3 

bg 

bg 

1419.5 

bg 

308.8 

0.070 

0.155 

0.029 

0.104 

0.115 

0.087 

0.060 

nc 

nc 

0.309 

nc 

0.067 

5809.5 

543.5 

2213.4 

62.5 

bg 

406.4 

175.2 

500.2 

bg 

bg 

68.3 

bg 

bg 

0.094 

0.391 

0.011 

nc 

0.070 

0.030 

0.086 

nc 

nc 

0.012 

nc 

nc 

16201.8 

2389.7 

3574.9 

693.9 

1280.2 

4305.0 

956.4 

980.5 

67.8 

60.9 

62.3 

bg 

107.0 

0.148 

0.221 

0.043 

0.079 

0.266 

0.059 

0.061 

0.004 

0.004 

0.004 

nc 

0.007 

Abbreviations: bg = background values, cps = counts per second, nc = not 

calculated because of high background values; see text for explanation 

in the auriferous North Dipper and North Dipper-related 

veins have higher As/Na ratios than the fluids in the barren 

North zone North Dipper vein system. 

Stable Isotopes 

Sampling and methodology 

The δ 18 O values of quartz, tourmaline, calcite, and scheelite 

from the auriferous North Dipper and North Dipper-related 

veins and the barren North zone North Dipper vein 

were determined to further constrain the temperatures during 

vein formation and the isotopic compositions of the mineralizing 

fluids. The δ 13 C values of carbonates also were measured 

to determine the possible sources for CO 2 . The samples 

were collected from surface exposures, with the exception of 

SDC-OI-1, which is from drill core near the center or footwall 

of the North Dipper vein (at 40-m depth). Quartz-tourmaline 

pairs that exhibit textural equilibrium were chosen for 

the calculation of isotopic equilibration temperatures. 

The selected portions of the veins containing the minerals 

of interest were crushed and sieved down to


TABLE 6. Oxygen and Carbon Isotope Compositions of Mineral Separates from Barren North Zone North Dipper and 

Auriferous North Dipper and North Dipper-Related Veins (all δ values are reported in ‰) 

δ 18 O δ 18 O δ 18 O Apparent δ 18 O δ 13 C 

quartz tourmaline scheelite equilibration 1 calcite calcite 

Sample no. (VSMOW) (VSMOW) (VSMOW) Temp. (°C) (VSMOW) (V-PDB) Comments 

North Zone 11.1 Quartz: deformed grains with subgrains 

North Dipper 

Tourmaline: deformed grains parallel to vein 

vein 

margins and radial open-space filling grains 

NZND-OI-1a 

NZND-OI-1b 9.2 

NZND-OI-2 11.1 3.3 176 Quartz: highly deformed and fractured milky 

quartz oriented perpendicular to the vein 

margin near the footwall of the North zone 

North Dipper vein and in sharp contact with 

euhedral scheelite crystal 

North Dipper 11.2 Quartz: milky quartz (analyzed) adjacent to 

vein 

smoky quartz; 

SND-OI-1 12.4 –6.5 Calcite: white crystals filling corroded zones 

in quartz and tourmaline 

SND-OI-2 11.4 8.6 371 Quartz and tourmaline from early shear 

layers; milky quartz is recrystallized and in 

equilibrium with preferentially oriented 

tourmaline (indicates shearing) 

SND-OI-3 11.5 8.3 323 Deformed quartz grains with subgrains 

associated with tourmaline crystals oriented 

parallel to the vein layers 

SND-OI-4 10.8 Quartz: Two generations (smoky and milky) 

9.1 Tourmaline: late radial aggregates filling 

SND-OI-5 11.2 8.4 371 Quartz: smoky intergrown with tourmaline 

crystals oriented perpendicular to vein margin 

SND-OI-6 10.7 Deformed and fractured milky quartz 

SND-OI-7 10.6 

North Dipper- 11.7 Highly deformed and fractured milky quartz 

related vein 

SNDR-OI-1 

SNDR-OI-2 10.6 

1 Equilibrium temperature calculated using fractionation factors of Kotzer et al. (1993) 

(AC) and aqueous fluid inclusions with a small amount of CO 2 

(AQc) from North Dipper and North Dipper-related veins. 

They also agree with equilibration temperatures reported for 

quartz-tourmaline fault vein and extensional veins in the Val 

d’Or camp (Beaudoin and Pitre, 2005). These data suggest 

that the temperature of the hydrothermal system did not 

change much during the various stages of quartz-tourmaline 

vein filling or during the late North Dipper and North Dipper-related 

veins mineralizing stage. 

Using the fractionation factors of Zheng (1992), an isotopic 

equilibration temperature of 176°C was calculated from δ 18 O 

values for a single quartz-scheelite mineral pair from the barren 

vein, suggesting that they formed at a lower temperature 

than the quartz-tourmaline assemblage or were not in equilibrium. 

The δ 18 O H2 O values for the auriferous fluid in the North 

Dipper and North Dipper-related veins are about 9.5 per mil, 

based on the δ 18 O of calcite (12.4‰) associated with visible 

gold in the late fractures, the temperature of decripitation of 

aqueous-carbonic fluid inclusions (350° and 390°C), and 

using the fractionation factors of O’Neil et al. (1969). These 

values are higher than those calculated for the quartz-tourmaline 

fault-fill and extensional veins (Beaudoin and Pitre, 

2005) but consistent with the low water/rock ratios characteristic 

of high-grade metamorphism or magmatic fluids. 

Discussion 

Comparison between auriferous and barren 

North Dipper veins: Implications for processes 

of gold transport and deposition 

The barren and auriferous veins have similar structural attitude, 

internal geometry, and δ 18 O values for quartz and 

tourmaline, but they are hosted by different rock units, have 

distinct wall-rock alteration and host fluid inclusions with different 

compositions. Although both vein types comprise 

mainly quartz and tourmaline, the barren vein lacks calcite 

and has lower sulfide content. 

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The fact that most of the gold in the North Dipper and 

North Dipper-related veins occurs with calcite filling late 

fractures that cut quartz and tourmaline suggests that most of 

the gold postdated the main stage of vein filling and likely was 

transported by CO 2 -bearing aqueous fluids. Significantly, the 

auriferous veins have higher abundances of CO 2 -rich and 

H 2 O-CO 2 fluid inclusions in healed fractures (i.e., the same 

paragenesis as gold and calcite) than the barren vein (Table 

2). Gold was detected only in the CO 2 -bearing fluid inclusion 

of the North Dipper-related vein (Table 3, Fig. 11). 

A small proportion of gold, which occurs locally as micrometer-sized 

inclusions in pyrite, precipitated early, during the 

main vein-filling stage in the North Dipper veins. The composition 

of this gold also differs from the late gold (i.e., the 

early gold contains 6 wt % Ag, whereas the late gold contains 

8–17 wt % Ag). If gold is transported as Au (HS) – 2 complexes 

in these systems, as postulated by Benning and Seward (1996) 

and Mikucki (1998), gold precipitation in the main vein-filling 

stage and in the wall rock may have been caused by a decrease 

of the H 2 S concentration in the hydrothermal fluid 

caused by the precipitation of pyrite. However, in the barren 

North zone North Dipper vein and its wall rock, the content 

of sulfide is very low (


in the late auriferous North Dipper and North Dipper-related 

veins, but all fluid inclusions in the late veins homogenize to 

the liquid phase and show little variation in the density of the 

carbonic phase, which is commonly high. Although the types 

of fluids and vein minerals do not allow precise determination 

of pressure during vein formation, these observations suggest 

that unmixing did not occur, that the pressure fluctuation was 

not significant, and that the pressure of fluids was relatively 

high during the trapping phase. This raises the question 

whether a fault-valve model is applicable to the principal 

stage of gold precipitation in the North Dipper and North 

Dipper-related veins. Fluid pressure was probably high 

enough to facilitate some deformation by microcracking (Cox 

et al., 2001, and references therein), enhancing the permeability 

of the North Dipper and North Dipper-related veins 

and host rocks, thereby allowing for focused or enhanced 

fluid flow in these veins. 

Conclusions 

Structural, mineralogical, isotopic, and fluid inclusion investigations 

of the late barren (North zone North Dipper 

vein) and auriferous (North Dipper and North Dipper-related 

veins) at Sigma indicate that they have similar structural 

controls, internal geometry, main vein-filling mineralogy, and 

isotopic signatures. However, their minor vein-filling phases, 

wall-rock alteration, and fluid inclusion compositions are very 

different. The barren vein does not exhibit proximal wall-rock 

alteration, has lower sulfide content, lacks calcite, and contains 

mainly aqueous fluid inclusions that were trapped at 

lower temperatures (125º–225ºC). The auriferous veins contain 

mainly aqueous-carbonic fluid inclusions trapped at high 

temperatures (228º–440ºC), and these fluids have higher Ni, 

Cu, Sb, Pb, and Ag than the fluids extracted from the barren 

vein. The model proposed to explain the differences between 

the auriferous and barren veins involves circulation of hydrothermal 

fluids in secondary structures that may have 

become more restricted at the margins of the hydrothermal 

system as it evolved. Thus, during the late stages of the hydrothermal 

system, the auriferous aqueous-carbonic fluids 

may have had more restricted circulation, promoting precipitation 

proximal to the regional upflow zones (e.g., between 

the major break and the North zone). This interpretation is 

consistent with the fact the fluids observed in the barren veins 

of the North zone farther from the major regional fluid conduit 

(i.e., the Larder Lake-Cadillac break) are mainly aqueous 

and of lower temperature. The hydrothermal fluids most 

likely originated in deeper zones that were undergoing highgrade 

metamorphism or from deep magmatic bodies. Trace 

element data suggest that gold and associated elements may 

have been derived from a variety of rock types. Gold may 

have precipitated due to a decrease of the H 2 S concentration 

in the auriferous fluid caused by pyrite precipitation during 

main vein-filling stages and by dilution of the CO 2 -rich fluids 

by nonauriferous aqueous fluids in the late auriferous stage. 

Acknowledgments 

This project was funded mainly by the NSERC discovery 

grant #227487, and the facilities used for fluid inclusion 

analyses were acquired through the New Opportunities grants 

of the Canadian Foundation for Innovation and Ontario 

Innovation Trust to G.R. Olivo. D. Chipley, K. Klassen and P. 

Polito are thanked for their assistance during bulk leach and 

LA-ICP-MS analysis, H. Poulsen for his mentoring during 

field work, and F. Robert for discussions in the early stages of 

the project. We thank D. Gaboury, G. Chi, B. Dubé and M. 

Hannington for their constructive comments, which helped 

to improve this manuscript significantly. We also thank the 

McWatters Inc geologists, in particular, A. Carrier and C. Pelletier 

(now at INOVEXEXPLO), for logistical and technical 

support during field work and M. Badham for helping on the 

preparation of the figures. F. Chang acknowledges the funding 

of the Society of Economic Geologist Student Grant and 

Queen’s graduate scholarship. 

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APPENDIX 

Summary of Microthermometric Data of H2O-rich (AQ, AQC, AQSL, and AQSLV), CO2-rich (C and CAQ), and H2O-CO2 (ACLL and ACLLV) Fluid Inclusions 

in Quartz from the North Zone North Dipper, North Dipper, and North Dipper-Related Veins 1 

Fluid inclusion data North zone North Dipper veins North Dipper veins North Dipper-related veins 

Homogenization (Th) 

and decrepitation (TD) 

temperatures 

AC Th(liquid): >350°C 

AQ Th(liquid) : 137° to 303°C 

AQ Th(critical): 144° and 202°C 

AQC Th(liquid): 176° to 280°C 

TD: 345°C 

AC Th(liquid) : mainly 228° to 270°C 

AQ Th(liquid): 110° to 262°C; bimodal distribution at 

175° to 225°C and 300° to 375°C 

TD: 207° to 360°C 

AC Th(liquid) : 242° to 440°C 

Th(critical): 315° to 320°C 

AQ Th(liquid) : 86.2° to 395°C; bimodal distribution at 

175° to 225°C and 300° to 375°C 

AQ Th(critical): 140° to 258°C 

AQSLV Th: 16.4° to 327°C; AQSL Th: 195°C TD: 293° to 

400°C 

First melting 

temperature (TFM) 

AQ TFM: > –30°C, few –30° to –49.2°C 

Monophase AQ TFM: –55.6° to –18.5°C, avg –30.8°C 

AC TFM: –50° to –3.2°C 

AQ TFM: >–30°C, few –30° to –48°C 

Monophase AQ TFM: –48° to –18.5°C, avg –34.8°C 

AC TFM: –29° to –11°C 

AQ TFM: > –30°C, few –30° to –52.6°C 

AQSL and AQSLV TFM: –69.4° to –55°C 

Monophase AQ TFM: –26.2°C 

Final ice-melting 

temperature (TM) 

AC TM: not observed 

AQ TM: –33.9° to 0°C, most > –6°C 

Monophase AQ TM: –33.9° to –5°C, avg –13.2°C 

AC TM: –18° to 0°C 

AQ TM: –19.1° to –3.3°C, most > –5°C 

Monophase AQ TM: –21° to –0.1°C, avg –12.5°C 

AC TM: –11.2° to –0.5°C 

AQ TM: –31.6° to –0.4°C, most > –10°C 

AQSLV and AQSL TM: –55° to –28.7°C 

Monophase AQ TM: –8.9°C 

Clathrate-melting 

temperature (Tm(clathrate)) 

CAQ Tm(clathrate): 8.9°C 

AC Tm(clathrate): 6° to 10°C, most from 7° to 8°C 

AQC Tm(clathrate): 6.7° to 9.7°C, avg 8°C 

CAQ Tm(clathrate): 4.6° to 8.4°C 

AC Tm(clathrate): 6° to 10°C, most from 7° to 8°C 

AQC Tm(clathrate): 3.75° to 9.8°C, avg 6.5°C 

CAQ Tm(clathrate): 5.7° to 9°C 

Salinity 

AC: 1.3 wt % NaCl 

Aqueous: 0 to 23 wt % NaCl, avg 9.4 wt % NaCl 

AQC: 0 to 5.7 wt % NaCl, avg 2.7 wt % NaCl 

Monophase AQ: avg 12.8 wt % NaCl 

CAQ: 2.6 wt % NaCl 

AC: avg from 4 to 5 wt % NaCl 

Aqueous: 0 to 23 wt % NaCl, avg 12.3 wt % NaCl 

AQC: 0.9 to 7 wt % NaCl, avg 3.4 wt % NaCl 


CAQ: 3.1 to 10 wt % NaCl 

AC: avg 4 to 5 wt % NaCl 

Aqueous: 0 to 23 wt % NaCl, 9.1 wt % NaCl 

AQC: 0.2 to 11.2 wt% NaCl, avg 6.5 wt% NaCl 


CAQ: 2.1 to 8.1 wt % NaCl 

Solid CO2 melting 

temperature (Tm(CO 2 

)) 

AC Tm(CO 2 

): –56.8°C 

Carbonic Tm(CO 2 

): –56.6° ± 0.2°C. 

AC Tm(CO 2 

): –57° to –56.2°C 


) Tm(CO 2 

): –57.5° to –56.3°C, most 

from –57° to –56.6°C 

AC Tm(CO 2 

): –58.3° to –56.3°C 


): –57.5° to –56.3°C 

CO2 homogenization 

temperature (Th(CO 2 

)) 

Not observed AC Th(CO 2 

): –9.8° to 30°C, most from 20° to 30°C 

Carbonic Th(CO 2 

): –11.3° to 30°C, most from 12° to 

29°C 

CAQ Th(CO 2 

): 5.2° to 29.1°C 

AC Th(CO 2 

): 7.3° to 30°C, most from 20° to 30°C 

Carbonic Th(CO 2 

): –42.5° to 28.6°C, most around –2°C 

CAQ Th(CO 2 

): around 25°C 

CO2 density 2 

ACLLV: 0.70 g/cm 3 ACLL [1] : 0.58 to 0.86 g/cm 3 , avg 0.84 g/cm 3 

ACLL [2] : 0.76 to 0.91 g/cm 3 , avg 0.85 g/cm 3 



ACLLV [1] : 0.74 to 0.98 g/cm 3 , avg 0.69 g/cm 3 

ACLLV [1] : 0.59 to 0.73 g/cm 3 , avg 0.66 g/cm 3 

C [1] : 0.58 to 0.99 g/cm 3 , avg 0.81 g/cm 3 

C [1] : 0.64 to 1.0 g/cm 3 , avg 0.92 g/cm 3 

C [2] : 0.82 to 0.91 g/cm 3 , avg 0.86 g/cm 3 

C [2] : 0.62 to 1.045 g/cm 3 , avg 0.91g/cm 3 

CAQ [1} : 0.62 to 0.90 g/cm 3 , avg 0.80 g/cm 3 

CAQ [1] : 0.71 to 0.72 g/cm 3 

XCH 4 

3 

Not calculated ACLL: 0.003 to 0.006, avg 0.004 

Equiv CO2 density: 0.82 to 0.91 


C: 0.006 to 0.007 

ACLL: 0.02 to 0.037 



C: 0.001 to 0.013, avg 0.006 

CAQ: 0.007 

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APPENDIX (Cont.) 

Fluid inclusion data North zone North Dipper veins North Dipper veins North Dipper-related veins 

CH4 molar proportion 4 

ACLLV : 0.028% 

C: 0.019 to 0.092%, avg 0.062% 

CAQ: 0.032 to 0.07%, avg 0.043% 

ACLL: 0.029 to 0.191%, 0.083% 

ACLLV : 0.017% 

C: 0.0105 to 0.242%, avg 0.087% 

Bulk CO2 density 

and wt % CO2 5 

ACLLV: 0.96 g/cm 3 , 10.99 wt % CO2 ACLL: 0.91 to 1.0 g/cm 3 , avg 0.96 g/cm 3 ; 9.82 to 38.02 

wt % CO2, avg 23.26 wt % CO2 

ACLLV : 0.86 to 0.97 g/cm 3 , avg 0.93 g/cm 3 ; 8.62 to 

31.82 wt % CO2, avg 16.78 wt % CO2 

ACLL: 0.8875 to 0.994 g/cm 3 , avg 0.96 g/cm 3 ; 3.99 to 

38.03 wt % CO2, avg 16.96 wt % CO2 

ACLLV : 0.88 to 0.967 g/cm 3 , avg 0.94 g/cm 3 ; 6.15 to 

31.82 wt % CO2, avg 14.74 wt % CO2 

Abbreviations of fluid inclusions types: AC = aqueous-carbonic, ACLL = aqueous-carbonic with liquid phases, ACLLV = aqueous-carbonic with liquid and vapor phases, AQ = aqueous, AQC = aqueous 

with small amounts of dissolved CO2, AQSL = aqueous with solid and liquid phases, AQSLV = aqueous with solid, liquid, and vapor phases, C = carbonic, CAQ =carbonic with small proportion of water 

ACLLV: 0.03% ACLL: 0.04 to 0.082%, avg 0.063% 

1 Complete data set and histograms are reported in Chang (2002) 

2 Valadovich and Altunin (1968) 

3 Swanenberg (1979) 

4 Heyen et al. (1982) 

5 Shepard et al. (1985) 

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