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Saskatchewan Geological Survey 1 Summary of Investigations 2004, Volume 2
Structural Controls and Temperature-Pressure Conditions of Gold-bearing Quartz Vein Systems at the Seabee Mine, Northern
Saskatchewan
Ghislain Tourigny, Guoxiang Chi 1, Chad Yuhasz 2, Rob Olson 2, Jennifer Berger 2, and Jennifer Soloman 2
Tourigny, G., Chi, G., Yuhasz, C., Olson, R., Berger, J., and Soloman, J. (2004): Structural controls and temperature-pressure conditions of gold-bearing quartz vein systems at the Seabee mine, northern Saskatchewan; in Summary of Investigations 2004, Volume 2, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2004-4.2, CD-ROM, Paper A-2, 18p.
Abstract The Seabee mine is a Paleoproterozoic vein-type gold deposit hosted by metagabbroic rocks of the Laonil Lake Intrusive Complex, northern Saskatchewan. Results from a detailed structural analysis indicate that two different styles of gold mineralization co-exist within the deposit. The principal auriferous orebody occurs in Lens 2, which is composed of anastomosing, east-northeast– to east–trending, ductile-brittle shear zones, whose internal geometry and kinematics indicate a bulk dextral transpression along the mineralized megashears. Deformed auriferous veins occur as Riedel ‘R’ and ‘P’ veins oriented 5º to 15º from the shear foliation, fault-fill veins subparallel to the foliation, and minor extension veins oriented at a high angle to the shear zone boundary. The second structural style of gold mineralization consists of conjugate quartz veins within steeply east-dipping tabular bodies developed at the margin of the east-northeast–trending Lens 5 shear zone. The conjugate vein system developed to accommodate the component of compression oblique to the general east-northeast shear direction. Vein mineralogy is similar in both east-northeast–striking shear zones and within the conjugate network, and is dominated by quartz, tourmaline, and sulphides with minor carbonate, feldspar, and white mica. Pyrite and pyrrhotite are the major sulphide phases; chalcopyrite and sphalerite are minor. Silver-bearing gold grains shows a close spatial association with tellurides that include melonite (NiTe2) and tellurobismuthite (Bi2Te3) with minute grains of calaverite (AuTe2), frohbergite (FeTe2), coloradoite (HgTe), and altaite (PbTe).
The gold-bearing quartz veins are commonly accompanied by felsic dykes, whose orientations are controlled by shear zones. The dykes were previously interpreted to be emplaced before the development of shear zones and genetically unrelated to the quartz veins. New observations suggest, however, that felsic dykes and quartz veins are coeval.
Fluid inclusions from auriferous quartz and quartz-feldspar veins include carbonic, aqueous, and aqueous + carbonic types. The melting temperatures of the carbonic phases ranged from -60.9º to -57.8ºC, indicating CO2 dominance and presence of other gases such as CH4 and N2. Relatively high-homogenization temperatures (366º to 386ºC) are found for fluid inclusions in quartz associated with K-feldspar. Isochores of paired liquid-rich and vapour-rich aqueous-carbonic fluid inclusions with homogenization temperatures of 366º to 373ºC yield pressure values of 1.1 to 1.2 kbar, whereas isochores of carbonic inclusions indicate a much wider pressure range for the same temperature range, from 1.2 to 2.5 kbar. The pressure range may be related to fluid pressure fluctuation between lithostatic and hydrostatic conditions at a depth of about 9.6 km. The fluid composition, temperature, and pressure data are compatible with orogenic-type gold deposits.
Keywords: Seabee mine, gold mineralization, shear zone, quartz veins, dykes, transpression, dextral shear, sulphides, conjugate veins, fluid inclusions.
1. Introduction The Seabee mine is located 120 km northeast of La Ronge in the northern part of the Glennie Domain, northern Saskatchewan. Since its opening in 1991, the mine has produced more than 651,128 ounces of gold at an average ore grade of 8.21 g/t Au. This ore is extracted from a complex quartz vein network within brittle-ductile shear zones truncating the gabbroic rocks of the Laonil Lake Intrusive Complex (Figure 1).
1 Department of Geology, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2. 2 Claude Resources, 200, 224-4th Avenue South, Saskatoon, SK S7K 5M5.
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Saskatchewan Geological Survey 2 Summary of Investigations 2004, Volume 2
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Saskatchewan Geological Survey 3 Summary of Investigations 2004, Volume 2
Previous studies suggested that the auriferous shear zones were either late reverse faults that were reactivated as dextral strike-slip faults, or dextral transpression zones developed between converging rigid walls (Tourigny, 2003). This paper, based on recent surface and underground mapping and extensive compilation of the geometric information of the first ten levels (0 to 680 m), shows that the Seabee shear zone system defines a well-organized, en echelon anastomosing network dominated by major east-northeast– to east–trending, subvertical shears. Strain and kinematic indicators within and along these shears and subsidiary fracture systems show that the internal structures of the Seabee shear zone system is best interpreted in terms of a zone of dextral transpression. The emplacement and deformation of the shear-hosted gold-bearing quartz veins and subsidiary conjugate vein networks is compatible with the bulk kinematic history.
Gold-bearing quartz veins at the Seabee mine are commonly associated with felsic dykes that follow the same structures. Helmstaedt (1986) proposed that the gold mineralization was initially related to the felsic dykes before shear zone development and may be compared to porphyry-style mineralization; the disseminated gold was then remobilized by shear zones and hydrothermal activities to form the gold-quartz vein system. Previous studies (e.g., Delaney, 1986, 1992; Schultz, 1990, 1996; Basnett, 1999), suggest, however, that the spatial association of the dykes and the veins is due to preferential development of shear zones along the contacts between competent felsic dykes and less competent gabbro and subsequent development of quartz veins along the shear zones. In this paper, we report the observation that some felsic dykes change along strike to gold-quartz veins, and propose that they may have been formed during the same magmatic-hydrothermal event.
Previous fluid inclusion studies by KRTA Inc. (1986) and Schultz (1996) identified carbonic, aqueous, and carbonic-aqueous fluid inclusions in the quartz veins, typical of shear zone–controlled mesothermal gold deposits. Homogenization temperatures (Th) of aqueous fluid inclusions were reported to range from 110º to 354ºC, but were mainly between 150° and 300ºC (Schultz, 1996). Using fluid-inclusion microthermometry in conjunction with oxygen isotope thermometry, Schultz (1996) estimated the temperatures of the ore-forming fluids to be between 360º and 430ºC, and the pressures ranged from 1.7 to 3.2 kbar. We report new fluid inclusion data here, using the fluid inclusion assemblage (FIA) method of Goldstein and Reynolds (1994), that provides internal constraints on the validity of microthermometric data. Our results show that some fluid inclusion assemblages have Th values from 366º to 386ºC, which are comparable to those estimated from isotopic thermometry (Schultz, 1996). Pressure values, estimated from paired liquid-rich and vapour-rich aqueous–carbonic fluid inclusions and from carbonic inclusions, range from 1.1 to 2.5 kbar, suggesting fluid pressure fluctuation between lithostatic and hydrostatic conditions at a depth of about 9.6 km.
2. Regional Geology The Seabee gold deposit occurs in the Laonil Lake Intrusive Complex, a triangle-shaped intrusion situated between the 1859 ±5 Ma granodiorite Eyahpaise Pluton (Van Schmus et al., 1987) to the south, the Pine Lake volcanic assemblage to the northeast, and the Porky Lake siliciclastic rocks to the north and east (Figure 1).
The Pine Lake Assemblage comprises a basal sequence of mafic to intermediate volcanics, and volcaniclastic rocks that are overlain by a package of felsic volcanic and volcaniclastic rocks, and associated sedimentary rocks (Delaney, 1986; Figure 1). Original contact relationships of the Pine Lake Assemblage with the Laonil Lake Intrusive Complex have been obscured by tight folding and related shearing. The Porky Lake sedimentary assemblage unconformably overlies the Pine Lake Assemblage and consists of layered arenites, wackes, conglomerates, and biotite schists (Delaney, 1986).
The Laonil Lake Intrusive Complex is a multiphase intrusion composed mostly of gabbro, quartz diorite, and diorite with minor granodiorite, feldspar porphyry, mafic dykes, and intermediate dykes (Delaney, 1986). A U-Pb zircon igneous crystallization age of 1889 ±8.7 Ma was obtained from the diorite (Chiarenzelli, 1989). The main phase of the complex consists of a medium- to coarse-grained, equigranular hornblende gabbro. In the Seabee mine shear zone, the gabbro has been converted to a hornblende-actinolite-biotite-chlorite schist and mylonite. Metre- to decimetre-scale xenoliths of mafic volcanic rocks, volcaniclastic rocks, and sedimentary rocks are also frequently observed in this complex.
The Laonil Lake gabbro is transected by small ultramafic to felsic dykes striking northeasterly to easterly and ranging from a few centimetres to a few metres in width. Felsic dykes are fine- to medium- grained quartzofeldspathic rock consisting of up to 60% recrystallized quartz (<1 mm), 5 to 20% of altered feldspars (<2 mm), with subsidiary amounts of hornblende-actinolite, biotite, chlorite, and sericite. All dykes are subvertical and generally subparallel but locally, the east-trending mafic dykes crosscut the felsic dykes. Most dykes have been deformed and display a weak to moderate foliation.
In the vicinity of the deposit, melanocratic gabbro and felsic dykes are commonly associated with the auriferous brittle-ductile shear zones. Xenoliths and rafts/screens of fined-grained mafic metavolcanic and metasedimentary
Saskatchewan Geological Survey 4 Summary of Investigations 2004, Volume 2
rocks are in the gabbro. The metavolcanic rocks consist almost entirely of fine-grained hornblende ± actinolite, and plagioclase. Although these rocks were intensely deformed and recrystallized, pillow selvages are still preserved locally. Xenoliths of layered pelitic to psammitic metasedimentary rocks within the main gabbro have been converted to quartz-feldspar-biotite schists that locally contain cordierite, garnet, staurolite, and anthophyllite.
All rocks in the Laonil Lake area have been metamorphosed to middle amphibolite facies and exhibit evidence of polyphase regional deformation (Figure 1). The outstanding structural features of the area include: i) an early pervasive east-northeast–striking regional foliation and a variably oriented mineral stretching lineation (D1 of Lewry, 1977); ii) a late open, north-trending regional fold, the Ray Lake Synform in the northern part of the area; and iii) a major regional high-strain zone, the Laonil Lake Shear Zone, at the contact between the Eyahpaise Pluton and the Laonil Lake Intrusive Complex (Figure 1; Lewry, 1977; Delaney, 1986). Temporal relationship between the Laonil Lake shear zone and the other major structures is still unknown.
3. Gold Mineralization and Mineralogy At the Seabee mine, gold is in syn-kinematic quartz-tourmaline-sulphide veins in, and adjacent to, metre-scale shear zones. Auriferous veins consist dominantly of quartz, tourmaline, and minor K-feldspar with subordinate amounts of sulphides, tellurides, and altered wallrock fragments. Wallrock alteration associated with gold mineralization is dominated by biotite with minor chlorite, white mica, epidote, and traces of carbonate. In the mineralized quartz veins, pyrite and pyrrhotite are the most abundant sulphides with subordinate amounts of chalcopyrite. Traces of disseminated schellite occur locally in, or associated with, chalcopyrite. Gold is typically associated with chalcopyrite, pyrrhotite, and telluride (Figure 2A). The most complex ore mineral assemblages include various tellurides in close spatial association with native gold (Figure 2B).
With the exception of altaite, all tellurides and gold have been quantitatively analyzed by electron microprobe (Table 1). A typical melonite composition is Ni1.001 to 1.004 Te1.97 to 1.99. Gold-bearing coloradoite has a nominal composition of Hg58.75Te40.15Au 1.44. Frohbergite (~ FeTe2), calaverite (~AuTe2), and tellurobismuthite (~ Bi2Te3) have also been confirmed by microprobe analysis (Table 1). In the veins, gold grains are silver-bearing (average of 4.52 wt% Ag), and show only slight variations in Ag content (4.51 to 4.58 wt% Ag).
4. Shear Zone System and Conjugate Vein Network
The following section describes the nature, pattern, and kinematics of the mineralized shear zones and adjacent vein networks at the Seabee mine. This report combines results from previous surface mapping (Tourigny, 2003) with detailed underground mapping, kinematic analysis of oriented thin sections, and an extensive compilation of geometric information from the first 10 levels (0 to 680 m below the surface).
The principal exploited gold-bearing quartz veins at Seabee occur in a brittle-ductile shear zone system developed in the southern part of the Laonil Lake Intrusive Complex (Figure 1). The gold-bearing shear zones post-date the regional D2 deformation phase (Tourigny, 2003). At the mine scale, the shear zones define a well-organized network composed of major anastomosing, en echelon, east-northeast– to east–trending brittle-ductile shear zones. There are two main mineralized shear zones: Lens 2 and Lens 5, a past producer (Figure 3).
Figure 2 - A) Optical photomicrograph showing gold (Au) associated with melonite (mel), and chalcopyrite (cp) within pyrrhotite (po); and B) optical photomicrograph showing a complex intergrowth of tellurobismuthite (tel), calaverite (calav), frohbergite (froh), coloradoite (col), and altaite (alt) in quartz (qtz).
A)A)
B)B)
Saskatchewan Geological Survey 5 Summary of Investigations 2004, Volume 2
Table 1 - Selected electron microprobe analyses of gold and tellurides from high-grade ore, from the Seabee mine.
a) Electron microprobe analyses of Ag-bearing gold.
Analysis Weight percent* Atomic percent No. n Au Ag Total Au Ag Total
Sample 436911 1 2 95.13 4.54 99.67 91.98 8.02 100 2 3 95.03 4.51 99.54 92.03 7.97 100 3 1 95.70 4.56 100.26 92.00 8.00 100 4 3 95.54 4.43 99.97 92.19 7.81 100 5 3 95.85 4.45 100.30 92.19 7.81 100 6 2 95.66 4.50 100.16 92.09 7.91 100 7 2 95.82 4.55 100.37 92.02 7.98 100 8 1 94.89 4.58 99.47 91.90 8.10 100
Average 95.45 4.52 99.97 92.04 7.96 100 Minimum 94.89 4.43 99.32 92.14 7.86 100 Maximum 95.85 4.58 100.43 91.97 8.03 100 Std Dev 0.379 0.053 0.361 * Cu, Sb, Te and Hg were sought for but were not detected, with minimum detection limits of 0.03, 0.04, 0.04, and 0.18 wt% respectively. b) Electron microprobe analyses of melonite (NiTe2), frohbergite (FeTe2), and calaverite (AuTe2).
1 2 3 4 5 Sample 436911 436911 436911A 436911A 436911A
area 1 area 4 area 3 area 3b area 3b n=8 n=2 n=4 n=1 n=2
Ni (wt%) 18.74 (18.49 to 18.94) 18.81 18.81 (18.68 to 18.92) n.d. n.d. Fe n.d.* n.d. n.d. 18.34 n.d. Au n.d. n.d. n.d. n.d. 43.20 Te 80.70 (79.40 to 81.31) 79.77 81.50 (81.23 to 81.73) 82.61 56.68 Sb 0.09 (0.02 to 0.44) 0.26 0.07 (0.04 to 0.11) 0.05 0.05 Bi 0.26 (0.03 to 1.44) 0.72 0.06 (0.02 to 0.09) n.d. 0.11 Total 99.79 99.56 100.44 101.00 100.04
Average compositions based on a total of three atoms per formula unit. Ni 1.004 1.011 1.001 0.000 0.000 Fe 0.000 0.000 0.000 1.009 0.000 Au 0.000 0.000 0.000 0.000 0.990 Sum 1.004 1.011 1.001 1.009 0.990
Te 1.990 1.972 1.996 1.990 2.006 Sb 0.002 0.007 0.002 0.001 0.002 Bi 0.004 0.011 0.001 0.000 0.002 Sum 1.996 1.990 1.999 1.991 2.010 * n.d.= not detected with minimum detection limits of 0.03 (Fe and Ni), 0.10 (Au), and 0.04 wt % (Bi). c) Electron microprobe analyses of tellurobismuthite (Bi2Te3) and coloradoite (HgTe).
1 2 3 4 5 6 7 8 Sample 436911 436911 436911 436911 436911 436911 436911A 436911A
area 1 area 2 area 4 gr.1 area 7 gr.2 area 7 gr.3 area 7 area 3b area 3b n=2 n=2 n=2 n=3 n=3 n=4 n=2 n=1
Bi wt% 52.02 52.16 50.69 51.66 51.93 51.18 51.48 n.d. Hg n.d.* n.d. n.d. n.d. n.d. n.d. n.d. 58.75 Au n.d. n.d. n.d. n.d. n.d. n.d. n.d. 1.44 Sb 0.14 0.23 0.51 0.41 0.24 0.51 0.31 n.d. Te 47.44 47.64 48.32 48.09 47.65 48.15 47.46 40.15 Total 99.60 100.03 99.52 100.16 99.82 99.84 99.25 100.34
Average compositions based on totals of five (analyses 1 to 7) and two (analysis 8) atoms per formula unit. Bi 2.001 1.997 1.939 1.970 1.992 1.955 1.984 0.000 Hg 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.953 Au 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.024 Sb 0.009 0.015 0.033 0.027 0.016 0.033 0.021 0.000 Sum 2.010 2.012 1.972 1.997 2.008 1.988 2.005 0.977
Te 2.989 2.988 3.027 3.003 2.993 3.012 2.996 1.023 Sum 2.989 2.988 3.027 3.003 2.993 3.012 2.996 1.023 * n.d.= not detected with minimum detection limits of 0.10 (Hg and Au), 0.02 (Sb), and 0.05 wt% (Bi).
Saskatchewan Geological Survey 6 Summary of Investigations 2004, Volume 2
The average shear zone width in the mined zone is 3 m. All of the shear zones are subvertical to steeply (>80°) north dipping, extend up to 1.8 km along strike and have been traced to over 800 m below surface. The shear-zone boundaries commonly coincide with sharp biotitic slip planes, but may also be developed gradationally from weakly deformed gabbro. Within the shear zone, the penetrative foliation is generally subparallel (in strike and dip) to the shear zone boundaries. The foliation contains a moderately to steeply west- to southwest-plunging mineral lineation, commonly defined by elongate hornblende-biotite aggregates or by stretched pyrite crystals. For the purpose of the kinematic analysis, shear zone textures and structures were examined on both subvertical and subhorizontal sections perpendicular to the shear zone foliation.
a) Subvertical Section In vertical cross section, approximately parallel to the mineral lineation, the penetrative foliation is generally subparallel (in strike and dip) to the shear zone boundaries and the dominant S-L fabric records a strong component of coaxial strain and boundary normal shortening. Structures resulting from subvertical elongation coexist with the pervasive flattening fabric. These strain and kinematic indicators include subvertical striations developed on biotite-rich slip planes or on the vein walls, subhorizontal veinlets (quartz-sulphides) that occupy extensional fractures developed adjacent to or within the subvertical shear zones (Figure 4A). The subhorizontal fractures developed approximately perpendicular to the elongation lineation and indicate the presence of subvertical stretching in the deposit.
Other mesoscopic and microscopic structures record the non-coaxial component of the inhomogeneous deformation and comprise northwest-verging, reverse brittle faults that displaced segments of gold-bearing veins and poorly developed C-S fabric in mylonite (Figures 4B and 4C). These structures are consistent with a localized component of southeast-verging reverse displacement along the main east-northeast–trending shear zone set.
b) Subhorizontal Section Despite the predominance of coaxial strain features in vertical section, there are a number of structures suggesting that subhorizontal dextral simple shear occurred during the structural evolution of the mineralized east-northeast–striking shears. On subhorizontal outcrop surfaces approximately perpendicular to the mineral lineation, the foliation locally defines a sigmoidal C-S fabric, indicating an apparent dextral shear sense along the main mineralized east-northeast structure (Lens 2; see Figure 5A in Tourigny, 2003). Asymmetric “Z” folds of mineralized quartz veins and rotated mafic xenoliths at the margin of the shear zones also support the presence of dextral displacement along and within the mineralized structures.
Other structures produced by dextral displacement are subvertical extensional fractures oriented at a clockwise acute angle to the shear foliation and shear zone boundary, as well as east-southeast–trending splay shears and mineralized low-angle ‘Riedel’ fractures developed at 15° to 20° to the main zone of displacement (see Figures 3A to 3G). Finally, at the deposit scale, the general architecture produced by the stepping pattern of the major east-northeast shears defines a geometric pattern reminiscent of large-scale dextral strike-slip fault zones (see Figure 3; Figure 1 in Sibson, 1987).
c) Quartz-Tourmaline-Sulphide Veins Economic gold mineralization at Seabee is in subvertical east– to east-northeast–trending quartz-tourmaline-sulphide veins in the cores of shear zones. Most of the ore comes from Lens 2, which is composed of numerous quartz bodies, surrounded by zones of intense potassic alteration (biotite-rich schist).
Individual veins may extend vertically and laterally for a few hundred metres; their thicknesses range from a few centimetres to about 12 m and average of about 3 m (see Figure 3). The veins are commonly laminated and contain slivers of foliated wall rocks, which indicate that they formed after the initial development of the shear zone foliation. Quartz veins are commonly bounded by biotite-chlorite-rich slip planes oriented parallel to the veins. The slip planes contain down-dip to steeply northwest-plunging striations and/or mineral stretching lineations (biotite-chlorite-actinolite aggregates). This indicates that subvertical displacement occurred within the orebody.
Three distinct types of veins are observed in Lens 2: foliation-oblique veins, foliation-parallel fault-fill veins, and en echelon extension veins.
Foliation-oblique veins are slightly discordant to the shear zone foliation. The overall strike of the vein system is approximately 80°E, whereas, the average orientation of the shear zone foliation is between 60° and 75°E. In detail, the veins commonly cut the shear zone foliation at 5° to 15° in a clockwise sense (Figure 5). Combined with the evidence of dextral shearing within the host shear zones, this geometry suggests that the main veins may have formed as Riedel shear fractures and rotated clockwise during subsequent progressive dextral shearing (Figure 5). Some narrow veins may also cut the foliation at low angle into a counterclockwise direction (Figure 5). According
1500
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Lens 162
Lens 153Lens 154
Lens 5-2
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Figure 3B
Figure 3C
Figure 3D
Figure 3E
Figure 3F
Figure 3G
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Overall direction of shear zones at Seabee
Average direction = N0 75
E
C E
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E = extensional domain, gold-rich
C = contractional domain, weakly mineralized
INTERPRETATION LENS 2
Gold-bearing Quartz Vein
GabbroUndetermined Mafic Intrusive Rock
Feldspar Porphyry Dyke
LEGEND
Felsic dyke
Biotite-rich schistand mylonite bands
Shear Zone Foliation50
Lithological contact
Mineral and stretching lineation
65 Fold axis
Strike and dip of shear zone
Dyke
Quartz vein: inclined, vertical
Brittle-ductile shear zone: dextral, sinistral, displacement unknown
65
516587 E617306 N
UTM coordinates
65 Striations
A to F = Lens 2
G = Lens 5 and subsidiary orebodies
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Figure 3A
Fault-fill vein
Extension veins
R-typeshear
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7272 Conjugate veins
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Figure 3 - Synoptic structural map of the mineralized shear zone system as observed between 0 and 680 m below the surface. Note the four principal types of auriferous veins (fault-fill, R, P, and extension veins) and their geometric relationship with the shear zone foliation.
Saskatchewan Geological Survey 7 Summary of Investigations 2004, Volume 2
6060 4040 2020 4040 6060
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Saskatchewan Geological Survey 8 Summary of Investigations 2004, Volume 2
Figure 4 - A) Subhorizontal extension veins developed perpendicular to the mineral lineation in the shear zone; B) southeast-dipping brittle reverse fault (dashed line) dissecting a gold-bearing quartz vein, 290 mining level; and C) photomicrograph showing a poorly developed C-S fabric indicating a component of reverse movement parallel to the mineral lineation.
Figure 5 - Composite sketch showing the structural features of the main vein system in Lens 2. The R-type and P-type veins cut the foliation at small clockwise and counterclockwise acute angles. In the central part of the shear, transposed veins and quartz boudins result from continuous shearing and deformation of R-type veins. The insert figure shows the pattern of Riedel fractures associated with a dextral shear. The scale is omitted because the sketch is a compilation of several features that were observed in outcrop and underground on the first 10 levels (0 to 680 m below surface) (from Tourigny, 2003).
WW EE SESE
50 cm
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CC 0.15 mm
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En echelon exension veins
Foliation
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R-type shearwith transposition features
Fault-fill veinsubparallel to foliation
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Saskatchewan Geological Survey 9 Summary of Investigations 2004, Volume 2
to the orientation of the shear fractures in a dextral transpression zone, these veins correspond to mineralized P shear fractures (Figure 5).
Fault-fill veins oriented subparallel to the shear zone foliation connect both laterally with R- and P-type veins in Lens 2 (Figures 3 and 5). They are up to 3 m wide, strike ~70°E, and dip subvertically to steeply (>80°) to the north. These veins occur in the most ductile part of the shear and exhibit laminated textures defined by selvages of biotite-hornblende schist alternating with ribbons of quartz-tourmaline-sulphides (Figure 5). Fault-fill veins central to the shear probably formed as D-type shear fractures marking the zone of maximum shear strain and displacement.
R- and P-type veins and fault-fill veins record evidence of internal deformation. The most common mesoscopic structures are both vertical and lateral boudinage (i.e. “chocolate tablet structure”), transposition within the main foliation, and rare parasitic folds. These folds are mostly dextral and plunge steeply west to southwest.
Underground mapping revealed that minor subvertical en echelon extension veins are common in Lens 2. These veins have short (<2 m) lateral and vertical extents and lie between 20° and 90° to the shear zone boundaries (Figures 3A to 3G). The veins are developed in the most isotropic part of the gabbro, either adjacent to the main mineralized shear zone or within the shear zone at the margins of the main ore-bearing veins. These veins are generally weakly deformed and disposed en echelon relative to adjacent slip planes and probably reflect the original orientation of extension fractures formed in response to the dextral sense of shear along the orebody.
d) Conjugate Veins Two narrow vein orebodies were previously mined at the western end of the Lens 5 shear zone (Figure 3G). These structures, referred as 153 and 161 zones, range in strike from north-northwest to north-northeast and dip 80° and 72° respectively towards the east. The mineralized zones form tabular orebodies, which range from about 1 to 10 m wide, extend laterally up to 100 m and have a vertical extent of less than 350 m. Gold mineralization is contained within strongly deformed quartz-tourmaline-sulphides veins whose strike ranges from north to east (Figure 3). Mineralized veins form a conjugate set which is well developed in zone 161. The veins are defined by two dominant trends including a north-northeast to north and an east-northeast trend with a dihedral angle close to 90°. A number of deformed east-northeast veins within both 153 and 161 shear zones seem to have resulted from tectonic remobilization of north-northwest and north-trending veins. This deformation is indicated by isolated hook folds bounded by slip planes, transposed and dislocated fold hinges with east-northeast axial trace, and clockwise rotation of north-northwest veins along dextral east-northeast shears (Figure 3). As the tectonic structures overprinted the mineralized veins, gold mineralization in 153 and 161 shear zones must have been emplaced early during the structural evolution of the main east-northeast shear system at Seabee.
A narrow west-northwest–trending vein called 154 zone was mined to the west of the 153 zone (Figure 3G). The dihedral angle between its subvertical structure and the adjacent 153 zone is approximately 70°. This angularity suggests that the west-northwest–trending structure is probably the conjugate counterpart of the north-trending zone 153.
5. Ore-Shoot Geometry Determining the geometric relationships between the structural elements of the shear zones and the gold-bearing veins can be used to predict the attitude and the location of orebodies at depth (Robert and Poulsen, 2001). The en echelon distribution and the plunges of the mineralized orebodies is clearly illustrated by the longitudinal section of the intersected economic gold values (Figure 6). The enveloping surfaces of the economic ore zones define prolate orebodies with long axis plunging ~50° east. This axis is very close to being orthogonal to the general slip vector of the host shear zone, which is represented by the mineral stretching lineation and striations in the host shear zone.
This angular relationship between the tectonic transport direction and the plunge of the orebodies indicates that the main mineralized veins at Seabee define geometric ore shoots (cf. Robert and Poulsen, 2001). A geometric relationship such as this indicates that the Seabee gold-bearing veins are synchronous with the development of their host shear zone (Robert and Poulsen, 2001).
6. Relationship Between Felsic Dykes and Auriferous Quartz Veins As shown in Figure 3, felsic dykes occur adjacent to the quartz veins, and both are aligned parallel to the shear zones (Figure 7A). The felsic dykes are generally deformed (boudinaged and foliated), but not as intensively as the host gabbro. Like the auriferous quartz veins, the felsic dykes crosscut shear zone–related foliations, but are themselves folded and boudinaged by shearing. Therefore, it appears that the felsic dykes occupy the same
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Saskatchewan Geological Survey 10 Summary of Investigations 2004, Volume 2
Saskatchewan Geological Survey 11 Summary of Investigations 2004, Volume 2
Figure 7 - A) A felsic dyke adjacent to an auriferous quartz vein, both occupying and being parallel to the same shear zone; and B) interfingering between a felsic dyke and quartz vein.
paragenetic position as the quartz veins, i.e., after the initial foliation, and before the termination of the shear zone movement.
Locally, felsic dykes are gradational into quartz veins (Figure 8), and the dykes and veins show an interfingering relationship (Figure 7B). The transition between the dykes and quartz veins is characterized by intense K-feldspar alteration and silicification. The unaltered part of the dyke is of dioritic to tonalitic composition, composed of mainly plagioclase and minor hornblende and quartz (Figure 9A). K-feldspar alteration and silicification are pervasive in both veinlets and dykes (Figures 9A and 9B). In addition, K-feldspar and quartz are closely associated with each other and with pyrrhotite and chalcopyrite (Figures 9B, 9C, and 9D). The elongated shape of the quartz–K-feldspar aggregates resulted from the flattening component of the finite deformation (Figure 9B).
Figure 8 - Geologic map of part of the 680 level showing the association of quartz veins with felsic dykes and shear zones. Note, that some of the dykes change along strike to quartz veins.
10 mMetagabbro
Felsic dykes
Quartz veins
Shear zones
Saskatchewan Geological Survey 12 Summary of Investigations 2004, Volume 2
Figure 9 - A) A stained slab of a dyke composed of mainly plagioclase (pink), lesser quartz, and minor hornblende and quartz cut by a K-feldspar (yellow) and quartz vein; B) a slab showing pervasive K-feldspar alteration and silicification and a quartz veinlet in a felsic dyke; note the elongated shape of the quartz-K-feldspar assemblage which may have resulted from flattening with the shear zone; C) photomicrograph illustrating the association of quartz and K-feldspar (yellow) in an altered felsic dyke; and D) same as (C), plus sulphides. The slabs and thin sections have been etched with HF and stained with amaranth, BaCl2, and sodium cobaltinitrite solutions. Plagioclase is stained pink, K-feldspar is stained yellow, and quartz is colourless.
7. Fluid Inclusion Study A limited number of “fluid inclusion assemblages” or FIA (Goldstein and Reynolds, 1994) were studied instead of collecting a large number of microthermometric data from individual fluid inclusions. The FIA method better allows us to evaluate the reliability of the fluid inclusion data, however, as in previous studies (Schultz, 1996), the main problem is finding well-defined primary fluid inclusions. Thus fluid inclusions that occur in clusters, healed fractures, and as scattered and isolated inclusions were studied. Some of these inclusions might be related to the quartz vein formation and may be classified as primary or pseudosecondary inclusions, whereas others might be secondary, but still related to gold mineralization because gold is secondary to quartz; still others may be secondary and unrelated to mineralization. Two samples were selected for fluid inclusion studies: sample 04GC103 is from an extensional vein with K-feldspar + quartz near a vein margin grading into quartz in the vein center from Level 650, and sample 04GC104 is from a quartz vein in a shear zone from Level 495.
Five types of fluid inclusions were distinguished in quartz according to composition and phase assemblages at room temperature. Type-I inclusions are composed of an aqueous phase and either one or two carbonic phases, with total homogenization to the liquid (aqueous) phase at elevated temperatures. An unidentified solid phase that does not melt in heating is present in these inclusions (Figure 10A). Type-II inclusions are also composed of an aqueous phase and either one or two carbonic phases, but the proportion of the carbonic phases is much larger than the aqueous phase (Figure 10B) and the inclusions homogenize to the vapor (carbonic) phase at elevated temperatures. Type-III inclusions are liquid + vapour aqueous inclusions that homogenize into the liquid at moderate temperatures. Type-IIIa inclusions (Figure 10C) contain minor carbonic components (in the vapor bubble) as
Saskatchewan Geological Survey 13 Summary of Investigations 2004, Volume 2
indicated by clathrate formation, whereas type-IIIb inclusions (Figure 10D) do not contain carbonic components that can be detected by the microthermometric method. Type-IV inclusions are composed of either one (Figure 10E) or two carbonic phases without a visible aqueous phase. Type-V inclusions are monophase (Figure 10F) and do not show any phase change when cooled down to -190ºC; they may be inclusions enriched in N2 and CH4. The microthermometric data of the various types of fluid inclusions are listed in Table 2.
Figure 10 - Photomicrographs of different types of fluid inclusions in quartz. A) A type-I fluid inclusion from sample 04GC103; note the solid particle on wall of the inclusion; B) a type-II fluid inclusion from sample 04GC104; note two carbonic phases occupy about 90% of the inclusion, and the aqueous phase is at the tips of the inclusion; C) a type-IIIa fluid inclusion; see text for the difference between this and type-I inclusion; D) type-IIIb fluid inclusions; E) type-IV fluid inclusions; and F) type-V fluid inclusions. Abbreviations: L, liquid; V, vapor; S, solid; cab, carbonic; and aq, aqueous.
10 µm
10 µm
A B
10 µm
C
Vcab
Vcab
Vcab
Lcab
Laq
Laq
Laq
S
10 µm
D
Vaq
Laq
E
10 µm
Lcab
10 µm
F
Saskatchewan Geological Survey 14 Summary of Investigations 2004, Volume 2
Table 2 - Fluid-inclusion microthermometric data. Abbreviations: V/T, vapor/total ratio; Tm, melting temperature; clath, clathrate; and Th, homogenization temperature.
Type-I and type-II fluid inclusions are found only in two quartz grains. The melting temperature of the carbonic phase is -57.8ºC (Table 2), indicating CO2 dominance and presence of other gases such as CH4 and N2. The melting temperatures of clathrate are 2.6º and 4.6ºC for type-I and type-II inclusions, respectively, corresponding to salinities of 9.6 and 12.4 wt.% NaCl equivalent. The total homogenization temperatures of the type-I fluid inclusions within the FIA range from 341.8° to 384.4ºC. The single type-II fluid inclusion in the neighbouring quartz crystal shows a total homogenization temperature of 372.9ºC. Because the type-I and type-II inclusions occur in neighbouring crystals as scattered and isolated inclusions, and homogenize into aqueous and carbonic phases, at similar temperatures, they are interpreted to represent two co-existent immiscible phases during the precipitation of quartz and K-feldspar. Thus the homogenization temperatures are interpreted to represent trapping temperatures. Fluid pressures calculated from isochores of type-I and type-II fluid inclusions, using the Flincor program of Brown
(1989), are 1112 bars and 1243 bars, respectively (Figure 11). The closeness of the two pressure values is consistent with the assumption that the two types of fluid inclusions were entrapped at the same time.
The homogenization temperatures of type-IIIa fluid inclusions range from 194.6° to 386.1ºC, which are significantly higher than those of type-IIIb inclusions (121.3° to 196.6ºC). It is remarkable that the homogenization temperatures within individual FIAs fall in much smaller ranges than the overall Th ranges (Table 2), suggesting that the Th values are generally valid. Note the high Th values (367.1° to 386.2ºC) of type-IIIa inclusions are similar to those of type-I and type-II inclusions, suggesting they may have been formed under similar
Figure 11 - Isochores of type-I and type-II fluid inclusions calculated from the equation of Bowers and Helgeson for H2O-CO2-NaCl using the Flincor program of Brown (1989).
0
500
1000
1500
2000
2500
3000
300 350 400 450 500
isochore of type I f
luid inclusion
T=24.0 V; v
%=25%; T=2.6; T
= 365.6 (L
)
h-CO2
m-clath
h
isochore of type II inclusion
T =28.8 L; v%=90%; T=4.6; T =372.9 (V)
h-CO2
m-clathh
1112 bars
1243 bars
Temperature ( C)º
Pre
ss
ure
(b
ars
)Host Size V/T Tm-CO2(°C) Tm-H2O(°C) Tm-clath(°C) Th CO2(°C) Th (°C)
Sample Mineral Occurrence Type (mm) % Mean (n) Mean (n) Mean (n) Range Mean (n) Range Mean (n)04GC103 Quartz Scattered I 4 to 18 25 -57.8 (2) -10.9 (1) 2.6 (1) 24.0 V 24.0 (1) 341.8 to 384.4 365.6 (4)
(assoc. Isolated II 13 90 -57.8 (1) - 4.6 (1) 28.8 L 28.8 (1) 372.9 V 372.9 (1)feldspar) Isolated IIIa 13 20 - -5.4 (1) 7.6 (1) - - 194.6 194.6 (1)
Cluster IIIa 4 to 11 30 - - 13.1 (2) - - 350.0 to 378.6 367.1 (5)Isolated IIIa 10 40 - - - - - 368.2 368.2 (1)
Healed fracture IIIa 5 to 9 40 - - 12.6 (1) - - 357.4 to 402.0 386.1 (8)Healed fracture IIIa 6 to 11 35 - - 12.0 (2) - - 371.5 to 391.9 382.8 (5)
Cluster IIIb 13 20 - -1.7 (1) - - - 192.6 to 200.6 196.6 (2)Healed fracture IIIb 5 to 9 10 - -1.6 (2) - - - 126.9 to 147.0 138.4 (4)
Isolated IV 13 100 -58.0 (1) - - 25.0 V 25.0 (1) - -Healed fracture IV 3 to 10 100 -58.0 (1) - - 25.0 to 27.9L 27.0 (8) - -
04GC104 Quartz Healed fracture IIIa 4 to 11 30 - -2.6 (1) 10.8 (1) - - 271.4 to 303.4 287.2 (4)Healed fracture IIIb 6 to 7 15 - -1.2 (3) - - - 140.8 to 164.0 155.6 (3)Healed fracture IIIb 7 to 10 15 - -1.4 (2) - - - 169.5 to 185.6 175.8 (3)Healed fracture IIIb 6 to 8 15 - -1.3 (1) - - - 121.0 to 137.8 129.4 (2)Healed fracture IIIb 4 to 8 10 - +0.4 (1) - - - 119.5 to 125.0 121.3 (3)Healed fracture IIIb 5 to 10 10 - -1.5 (4) - - - 143.9 to 178.6 167.1 (8)Healed fracture IIIb 8 to 15 15 - -4.6 (2) - - - 170.4 to 177.8 175.2 (3)Healed fracture IIIb 3 to 8 15 - -4.6 (1) - - - 169.0 to 170.6 169.6 (3)Healed fracture IIIb 6 to 11 15 - -4.7 (2) - - - 170.9 to 187.0 175.8 (7)
Cluster IV 5 to 8 100 -62.1 (3) - - 3.1 to 4.0L 3.7 (3) - -Cluster IV 4 to 5 100 -60.9 (2) - - 9.2 to 12.8 L 11.0 (2) - -Cluster IV 3 to 13 100 -56.9 (2) - - 10.0 to 25.4 L 18.3 (23) - -Cluster IV 3 to 6 100 -57.4 (1) - - 14.8 to 26.4 L 20.7 (4) - -
Type I = aq + carbonic + solid (homogenized to liquid; solid does not melt)Type II = aq + carbonic (homogenized to vapor)Type III = aq (a=clathrate detected; b=clathrate not detected; both homogenized to liquid)Type IV = carbonic (not aqueous phase is visible)
Saskatchewan Geological Survey 15 Summary of Investigations 2004, Volume 2
conditions, although not necessarily at the same time. Salinities for type-IIIb inclusions range from 2.0 to 7.4 wt.% NaCl equivalent. Salinities cannot, however, be calculated for type-IIIa inclusions because of the effect of clathrate.
The carbonic melting temperatures of type-IV fluid inclusions range from -57.4° to -60.9ºC, indicating CO2 dominance and probably higher CH4 and N2 content than in type-I and -II inclusions. Most of type-IV inclusions homogenize into the liquid carbonic phase. The overall homogenization temperatures range from 3.7° to 27.0ºC. This temperature range implies significant pressure variation, as shown by the isochores (Figure 12) calculated from the Flincor program of Brown (1989).
Whether the pressure variation shown by the isochores (Figure 12) reflects real pressure fluctuation needs to be discussed. The variations of Th values within individual FIAs vary from small ( e.g., 25.0º to 27.9ºC; 3.1° to 4.0ºC) (Table 2) to very large ( e.g., 10.0° to 25.4ºC). For FIAs that show large variation in Th values, the fluid inclusions may have been significantly modified ( e.g., stretching) and thus the isochores cannot be used to estimate fluid pressures. For other FIAs, the internal consistency of homogenization temperatures suggests that the fluid inclusions have not been significantly modified by post-trapping processes, and thus the isochores can be used to estimate fluid pressures. The uppermost and lowermost isochores shown in Figure 12 are from FIAs having consistent Th values, so the overall range of fluid pressures shown in Figure 12 is considered to reflect real pressure fluctuation. The actual trapping pressures of individual FIAs cannot be, however, determined because the trapping temperatures are not known. The maximum and minimum pressure values for temperatures of 121º, 195º, 366 to 373º, and 386ºC, which correspond to the range of homogenization temperatures of different types of aqueous inclusions (Figure 12), provide a reference for estimation of potential pressure ranges if the trapping temperatures were known. It is worth noting that the minimum pressure values for the temperature range of 366º to 373ºC are 1187 to 1209 bars (Figure 12), which are almost the same as the values calculated from the isochores of type-I and type-II inclusions (Figure 11). The maximum pressure values for the same temperature range are 2490 to 2532 bars (Figure 12). One possible explanation is that the maximum pressures record lithostatic conditions, whereas other pressure values reflect conditions between lithostatic and hydrostatic conditions. If this is the case, then the depth corresponding to the maximum pressure value is about 9.6 km (assuming a rock density of 2.7 g/cm3).
8. Discussion and Conclusions A number of models have been proposed to explain the geometry and structure of the Seabee gold deposit. Helmstaedt (1986, 1987) suggested that gold mineralization was emplaced prior to the development of the shear zone and interpreted the penetrative shear zone fabric as the result of flattening and the coaxial strain component in the deposit. Gummer (1986), Schultz and Kerrich (1991), and Basnett (1999) recognized the presence of kinematic indicators of non-coaxial strain in the deposit, but did not propose a kinematic model for the structural evolution and the mode of emplacement of gold mineralization. Tourigny (2003) suggested that the coexistence of conflicting kinematic indicators of both coaxial and non-coaxial strain within and adjacent to mineralized shear zones results from a general transpressive mode of deformation.
The present study, combining both surface and underground mapping with an extensive structural compilation along with microscopic study of oriented thin sections, demonstrates that the Seabee gold deposit is best interpreted in terms of dextral transpression involving oblique convergence between rigid walls. The Seabee shear zone system and associated gold-bearing vein sets display a number of geometric characteristics of dextral transpression. These characteristics are summarized as follows:
1) the general en echelon, stepping and anastomosing pattern of the mineralized shear zone is reminiscent of typical zones of dextral transpression (e.g., Wilcox
Figure 12 - Isochores of type-IV fluid inclusions calculated from the equation of Bottinga and Richet for CO2 system using the Flincor program of Brown (1989). The maximum and minimum pressure values are indicated for temperatures of 121º, 195º, 366 to 373º, and 386ºC, which correspond to the range of homogenization temperatures of different types of aqueous inclusions. See text for discussion about the meaning of these pressure values.
0
500
1000
1500
2000
2500
3000
3500
0 100 200 300 400 500 600
664 bars
984 bars
1292 bars
1469 bars
2093 bars
2694 bars
Temperature ( C)º
Pre
ssu
re (
ba
rs)
Saskatchewan Geological Survey 16 Summary of Investigations 2004, Volume 2
et al., 1984; Sibson, 1987; Mandl, 1988); 2) steeply plunging elongation lineations and striations (e.g., Lin and Williams, 1992); 3) asymmetrical structures of dextral displacement in horizontal planes such as C-S fabrics and folded veins; 4) coexistence of fault-fill veins and foliation-oblique veins such as mineralized R and P shears (e.g., Lafrance,
2002); 5) extension veins at a high angle to the shear zone margin (Dewey et al., 1998); 6) conjugate veins (cf. mineralized veins in 153 and 161 zones) developed to accommodate the component of
shortening of the bulk transpressive deformation; and 7) the plunge of kinematic ore shoots is at a high angle to the stretching lineation (Robert and Poulsen, 2001). In the transpression model of Sanderson and Marchini (1984), the vertical elongation along the shear zone is due to pure shear component of the deformation, and no evidence of non-coaxial strain (simple shear) should be observed parallel to the lineation. In this study, localized C-S fabrics are, however, diagnostic of rotation along the direction of subvertical extension and indicate that local dip-slip movement of reverse sense occurred in the mineralized shear zones. Such a discrepancy from the general transpressive deformation can simply be explained in terms of slip partitioning which allows the simple shear component to have a dip-slip component within the shear zones (Lin et al., 1998; Jiang et al., 2001). Natural shear zones generally suggest localization of the non-coaxial component of deformation (e.g. Lin et al., 1998, 1999) as do theoretical models (England and Jackson, 1989), and observation of current plate-boundary deformation (Gordon, 1995). Therefore, the Seabee mineralized shear zones are interpreted to be natural analogues to zones of dextral transpression.
The structural data presented here may have certain implications for exploration of shear-hosted gold deposits in intrusive complexes of the Glennie Domain. The shears of the Seabee mine represent small exploration targets that may be detected initially by an increase of the strain intensity at their margin. Within isotropic gabbro, these high-strain zones can be easily identified by recognition of grain size reduction and mylonitization of the isotropic protolith with local development of C-S fabric and/or pervasive L-S fabric. The presence of felsic dykes must also be considered as an ore guideline in the area because they are systematically associated with the economic ore at Seabee. Mapping dyke density may also be useful to detect mineralized targets.
Our results demonstrate that the shear zones and associated quartz veins define a well-organized, en echelon, stepping network composed of several anastomosing branches. Careful mapping of the shear zone orientation is therefore recommended to reveal the entire mosaic of the shear zone system as well to locate intersecting fault branches that may represent zones of dilation and fluid infiltration with possible development of economic ore shoots.
The presence of important zones of fractures and veining at the lateral termination of Lens 5 is also significant for future exploration. The north-trending 153 and 161 orebodies, for example, are developed obliquely to the general east-northeast shear direction. These brittle structures probably developed because the ductile shear component of the bulk deformation was transferred into dilational conjugate fractures due to stress concentration and localized pure shear at the termination of the main Lens 5 shear zone (see Mount and Suppe, 1987). Such dilational structures represent targets discordant to the general east-northeast–trending shear zones of the Laonil Lake Intrusive Complex.
The kinematic analysis also shows good correlation between the ore-shoot plunge and the slip vector within the shear zone. The slip direction is easily determined through direct observation and measurement of stretching lineations and striations at the shear zone and vein margins. As observed at the Seabee mine, gold-bearing shear zones define ore shoots at high angle to the slip vector. Knowledge of the slip direction along the shear zones may aid the prediction of plunge of the ore shoots as well as in prediction of drill targets at depth at an early stage of an exploration program.
The spatial association of felsic dykes and gold-bearing quartz veins in the Seabee gold deposit has been previously interpreted as a mechanical relationship, reflecting preferential development of shear zones and emplacement of quartz veins in the dyke-gabbro contacts (e.g., Delaney, 1986, 1992; Schultz, 1990, 1996; Basnett, 1999), or as a genetic relationship in which both gold and quartz were initially related to felsic dykes and then remobilized (Helmstaedt, 1986). In this paper, we emphasize that both gold quartz veins and felsic dykes were emplaced after the initial development of foliation and early in the history of the shear zones. The observation that felsic dykes change along strike to quartz veins further suggests that they are continuous events. The transition between felsic dykes and quartz veins is marked by intense K-feldspar alteration and silicification, which may be related to magmatic activities. Schulz (1996) obtained a 207Pb/206Pb zircon evaporation age of 1877 ±10 Ma for a feldspar porphyry dyke, and 40Ar/39Ar plateau ages of 1769 ±7 Ma and 1728 ±5 Ma for biotite from the alteration assemblages, and concluded that gold mineralization is significantly younger than the felsic dykes. It is possible that
Saskatchewan Geological Survey 17 Summary of Investigations 2004, Volume 2
the 40Ar/39Ar ages do not represent the mineralization ages, but rather a thermal event after the emplacement of the gold-bearing quartz vein.
The mineralization temperatures have been estimated between 360ºC and 430ºC based on stable isotope data (Schultz, 1996). In this study, we have obtained fluid inclusion homogenization temperatures from 366° to 386ºC from one of the studied samples, which are believed to be close to mineralization temperatures. Fluid pressures calculated from isochores of aqueous-carbonic and carbonic fluid inclusions range from 1.1 to 2.6 kbar for the temperature range of 366° to 386ºC. Large pressure fluctuations have been documented in many other shear zone-controlled orogenic-type gold deposits and have been related to pressure change between lithostatic and hydrostatic conditions (e.g., Robert and Kelly, 1987; Wilkinson and Johnston, 1996). The fluid pressure range observed at Seabee may also be related to shear zone evolution and episodic change of fluid pressure regime from lithostatic to hydrostatic. If the maximum pressure is taken to represent the lithostatic condition, the depth is estimated about 9.6 km, which is within the range for orogenic-type gold deposits (see Groves et al., 2003).
9. Acknowledgments The author would like to thank Claude Resources Inc. for full access to the mine, for logistical assistance, and for permission to publish this paper. Many thanks to Dan Studer and Phil Olson for their collaboration in the field. Constructive discussions with Dr. Bruno Lafrance are much appreciated. Thanks also to Breanna Uzelman and Andrew Mitchell for assistance in the field and to Mike O’Brien and Bill Slimmon for help with the figures. Natalie Thompson is greatly acknowledged for assistance in editing the final version of this paper. We also thank Charlie Happer and Sheldon Modeland for their constructive comments on earlier drafts of this paper. Gilles Laflamme from CANMET Mining and Mineral Sciences Laboratories is greatly acknowledged for his assistance with the microprobe analysis.
10. References Basnett, R. (1999): Seabee Mine; in Ashton, K.E. and Harper, C.T. (eds.), Minexpo’96 Symposium–Advances in
Saskatchewan Geology and Mineral Exploration, Sask. Geol. Soc., Spec. Publ. No. 14, p72-79.
Brown, P.E. (1989): FLINCOR: A microcomputer program for the reduction and investigation of fluid inclusion data; Amer. Mineral., v74, p1390-1393.
Chiarenzelli, J.R. (1989): The Nistowiak and Guncoat gneises: Implication for tectonics of the Glennie and La Ronge domains, northern Saskatchewan, Canada; unpubl. Ph.D. thesis, Univ. Kansas, 229p.
Delaney, G. (1986): Bedrock geological mapping, Laonil Lake area; in Summary of Investigations 1986, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 86-4, p32-44.
__________ (1992): Gold in the Glennie Domain; Sask. Energy Mines, Misc. Rep. 93-5, 71p.
Dewey, J.F., Holdsworth, R.E., and Strachan, R.A (1998): Transpression and transtension zones; in Holdsworth, R.E., Strachan R.A., and Dewey, J.F. (eds.), Continental Transpressional and Transtensional Tectonics, Geol. Soc. London, Spec. Pub. 135, p1-14.
England, P.C. and Jackson, J. (1989): Active deformation of the continents; Earth Planet. Sci., Annu. Rev., v17, p197-226.
Goldstein R.H. and Reynolds T.J. (1994): Systematics of fluid inclusions in diagenetic minerals; SEPM Short Course, v31, p1-199.
Gordon, R.G. (1995): Plate motions, crustal and lithospheric mobility, and paleomagmatism: Prospective viewpoint; J. Geophys. Resear., v93, p24,367-24,392.
Groves, D.I., Goldfarb, R.J., Robert, F., and Hart, G.J.R. (2003): Gold deposits in metamorphic belts: Overview of current understanding, outstanding problems, future research, and explorations significance; Econ. Geol., v98, p1-29.
Gummer, P.K. (1986): Geology of the Seabee gold deposit, Tabernor Lake Belt, Saskatchewan; in Clark, L.A. (ed.), Gold in the Western Shield, Can. Inst. Min. Metall., Spec. Vol. 28, p272-284.
Saskatchewan Geological Survey 18 Summary of Investigations 2004, Volume 2
Helmstaedt, H. (1986): Report on the geology and structure of the Seabee and Currie Rose properties, Laonil Lake, Saskatchewan; internal report, Placer Development Limited, 14p.
__________ (1987): Report on the geology of the No. 2 zone on the Seabee property, Laonil Lake, Saskatchewan; internal report, Placer Development Limited, 13p.
Jiang, D., Lin, S., and Willians, P. (2001): Deformation path in high-strain zones, with reference to slip portioning in transpressional plate-boundary regions; J. Struc. Geol., v23, p991-1005.
KRTA Inc. (1986): Fluid inclusion study of nine quartz samples from Seabee gold property, Saskatchewan; internal report, Placer Development Limited, 27p.
Lafrance, B. (2002): Shear-hosted gold occurrences in the Proterozoic La Ronge volcanic belt, northern Saskatchewan; Geol. Assoc. Can./Min. Assoc. Can., Jt. Annu. Meet., Field Trip Guidebook A3, Saskatoon, May 27 to 29, 37p.
Lewry, J.F. (1977): The Geology of the Glennie Lake Area, Saskatchewan; Dept. Min. Resour., Rep. 143, 59p.
Lin, S., Jiang, D., and Williams, P. (1998): Transpression (or transtension) zones of triclinic symmetry: Natural examples and theoretical modeling; in Holdsworth, R.E., Strachan, R., and Dewey, J.F. (eds.), Continental Transpressional and Transtensional Tectonics, Geol. Soc., Spec. Publ. 135, p41-57.
__________ (1999). Discussion on transpression and transtension zones; J. Geol. Soc. London, v156, p1045-1048.
Lin, S. and Williams, P.F. (1992): The geometric relationships between stretching lineations and the movement direction of shear zones; J. Struc. Geol., v14, p491-497.
Mandl, G. (1988): Mechanics of Tectonic Faulting; Elsevier, Amsterdam, 407p.
Mount, V.S. and Suppe, J. (1987): State of stress near the San Andreas Fault: Implications for wrench tectonics; Geol., v15, p1143-1146.
Robert, F. and Kelly, W.C. (1987): Ore-forming fluids in Archean gold-bearing quartz veins at Sigma Mine, Abitibi greenstone belt, Quebec, Canada; Econ. Geol., v82, p1464-1482.
Robert, F. and Poulsen, K.H. (2001): Vein formation and deformation in greenstone gold deposits; Rev. Econ. Geol., v14, p111-152
Sanderson, D.J. and Marchini, W.R.D. (1984): Transpression; J. Struc. Geol., v6, p449-458.
Schultz, D.J. (1990): Reconnaissance geological study of the Seabee gold deposit, Glennie Domain; in Summary of Investigations 1990, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 90-4, p70-73.
___________ (1996): The fluid history of the Seabee mesothermal gold deposit, northern Saskatchewan; unpubl. M.Sc. thesis, Univ. Saskatchewan, 122p.
Schultz, D.J. and Kerrich, R. (1991): Structural controls and geochemical character of the Seabee gold mine, Laonil Lake, Glennie Domain; in Summary of Investigations 1991, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 91-4, p101-108.
Sibson, R.H. (1987): Earthquake rupturing as a mineralizing agent in hydrothermal systems; Geol., v15, p701-704.
Tourigny, G. (2003): Preliminary structural study of the gold-bearing shear zone system at the Seabee Mine, northern Saskatchewan; in Summary of Investigations 2003, Volume 2, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2003-4.2, CD-ROM, Paper B-1, 11p.
Van Schmus, W.R., Bickford, M.E., Lewry, J.F., and Macdonald, R. (1987): U-Pb zircon geochronology in the Trans-Hudson Orogen, northern Saskatchewan, Canada; Can. J. Earth Sci., v24, p407-424.
Wilcox, R.E., Harding, T.P., and Seely, D.R. (1984): Basic wrench tectonics; in Sylvester, A.G. (ed.), Wrench Fault Tectonics, AAPG, Reprint Series No. 28, p291-314.
Wilkinson, J.J. and Johnston, J.D. (1996): Pressure fluctuations, phase separation, and gold precipitation during seismic fracture propagation; Geol., v24, p395-398.
