Gold Mineralization at the Syenite-Hosted Beattie ... - GeoScienceWorld

©2015 Society of Economic Geologists, Inc. Economic Geology, v. 110, pp. 315–335

Gold Mineralization at the Syenite-Hosted Beattie Gold Deposit, Duparquet, Neoarchean Abitibi Belt, Canada Ludovic Bigot†,* and Michel Jébrak Département des Sciences de la Terre et de l’Atmosphère, Université du Québec à Montréal (UQÀM), C.P. 8888 Succ. Centre-ville, Montréal, Québec H3C 3P8, Canada

Abstract The syenite-associated Beattie deposit (measured and indicated resources of 60.9 Mt grading 1.59 g/t Au, and inferred resources of 29.7 Mt grading 1.51 g/t Au), located in the Abitibi greenstone belt, consists of two styles of gold mineralization: lithology controlled and structure controlled. Lithology-controlled mineralization is hosted by the syenite intrusion and associated with iron carbonate and sericite alteration. Lithology-controlled mineralization is low grade (1–2 g/t Au) and associated with arsenian pyrite and arsenopyrite, with gold being in solid solution within the spongy As-rich cores of pyrite. Structure-controlled mineralization is present within fault zones that are within the syenite intrusion and adjacent to its margins. This type of ore consists of high-grade mineralization (5 g/t Au) in silicified breccia with both hydraulic and tectonic features, cherty veins, and polymetallic veins. In this facies gold is visible as electrum filling microfractures of brecciated pyrite. The deposit has a distinct paragenesis. The initial stage of alteration involved hematite alteration due to deuteric oxidation. This was followed by a shift toward more reducing conditions, triggered by the introduction of CO2rich hydrothermal fluids that led to sulfide precipitation and gold deposition in As-rich pyrite and arsenopyrite. A later-stage alteration event implies the input of silica-rich fluids that produced sulfide brecciation and their redistribution in the fault zones and gold remobilization in microfractures of brecciated pyrite. Calculated composition for δ18O and measured composition for δD on quartz veins associated with this late event are respectively 6.9 to 10.8‰ and –53 to –83‰, indicating a potential magmatic-metamorphic fluid mixing. This event is associated with enrichment in Te, Hg, Mo, As, Au, Se, Ag, and Sb. In the Beattie deposit, interaction between magmatic and hydrothermal activities, coupled with external fluid ingress, led to a multistage process of sulfide and gold deposition.

Introduction Gold mineralization in accretionary orogens requires the conjunction in time and space of three essential factors: a fertilization of the upper mantle, a favorable transient remobilization, and a favorable lithospheric-scale plumbing structure (Hronsky et al., 2012). In these convergent margins, orogenic gold deposits and intrusion-related gold deposits commonly share characteristics, including metal association, wall-rock alteration, ore fluids, and structural controls (Groves et al., 2003). Despite these similarities, Mair et al. (2011) revealed that intrusion-related gold deposits form in a very specific tectonic setting, typically during postcollisional and transitional tectonic regime, and above previously metasomatized subcontinental lithosphere mantle. This tectonic setting sets intrusion-related gold deposits apart from orogenic gold deposits, which are synorogenic in timing and have no direct relationship to such diverse lithospheric mantle-derived magmas (cf. Goldfarb et al., 2005). In the Abitibi greenstone belt, the majority of gold deposits along crustal-scale fault zones have been recognized as mesothermal (e.g., Val d’Or), according to the orogenic gold model for which deposits are commonly associated with hydrothermal fluid circulation and deposition of gold in first- and lower-order structures (Colvine, 1989; Groves et al., 1998). However, several gold deposits associated with felsic intrusion † Corresponding

author: e-mail, [email protected] *Current address: CONSOREM, Université du Québec à Chicoutimi, 555, boul. de l’Université, Chicoutimi, Québec G7H 2B1, Canada.

along major faults are now interpreted as intrusion-related gold deposits (e.g., Canadian Malartic; Helt et al., 2014). In Abitibi, the spatial association between small porphyritic felsic intrusions and gold deposits has been interpreted either as a structural relation in which the intrusion is acting as a competent trap for mineralized fluids (Colvine, 1989; Witt, 1992) or as a genetic link between gold and the alkaline to calc-alkaline intrusions (Cameron and Hattori, 1987; Rowins et al., 1991, 1993; Robert, 2001). On the basis of geologic relations and geochronological constraints, Robert (2001) distinguished a new group of gold deposits associated with syenites in the Abitibi greenstone belt, which includes Beattie, Holt-McDermott, Canadian-Malartic, Young-Davidson, and Douay. These deposits share common characteristics regarding the age of crystallization at about 2680 and 2672 Ma, the spatial association near major faults, the depth of emplacement, typically above 2 km, and the mineralization dominated by disseminated sulfides. Robert (2001) proposed a model in which these deposits are genetically associated with a large magmatic-hydrothermal system centered on composite granitic to syenitic stocks. This paper documents the mineralogy and geochemical signature of the different mineralization types in the Beattie deposit, one of the major deposits of the syenite-associated gold deposit family with more than 5 million ounces of gold (resources + historic production). A characterization of fluids and alteration is also proposed, using stable isotope and 3-D modeling. These results provide a new model describing the hydrothermal evolution and gold formation at Beattie.

0361-0128/15/4287/315-21 315

Submitted: March 20, 2013 Accepted: June 14, 2014

316

BIGOT AND JÉBRAK

Regional Geology The Beattie gold deposit occurs on the north-side segment of the Porcupine-Destor fault zone in the Archean Abitibi subprovince (Fig. 1A, B). The Archean Abitibi subprovince is located within the southeastern part of the Superior Province. It is the largest continuous volcanoplutonic belt of the Canadian Shield, extending 700 km east-west and 300 km north-south (Fig. 1A). The Porcupine-Destor fault zone is interpreted as a tectonic suture of allochthonous terranes (Mueller et al., 1996; Daigneault et al., 2002). It represents a geologic boundary between the North volcanic zone and the South volcanic zone. Dimroth et al. (1982) considered the South volcanic zone as a homoclinal oceanic floor-to-arc succession, whereas Chown et al. (1992) interpreted the North volcanic zone as an intact arc segment with two volcanic cycles. An alternative model proposes the Porcupine-Destor fault zone is a consequence of anticline fold detachment in a large autochthonous terrane (Benn and Peschler, 2005; Bedard et al., 2013). Early volcanism that formed the North and South volcanic zones and coeval plutonism occurred between 2750 and 2697 Ma, followed by high-level plutonism between 2694 and 2690 Ma (Corfu, 1993; Ayer et al., 2002). This episode was accompanied by flyschoid sedimentation between 2696 and 2687 Ma (Davis, 1992; Ayer et al., 2002). After the construction of volcanoplutonic edifices and the first sedimentation, a polyphased tectonic evolution affected the southern Abitbi subprovince (Bleeker and Parrish, 1996; Daigneault et al., 2002). A first contractional deformation (D1) was responsible for tilting, folding, and local thrusting, and was accompanied by the emplacement of diorite-tonalite intrusions at about 2685 Ma (Robert, 2001). A subsequent period of uplift and erosion led to the local formation of pull-apart basins along major faults between 2678.9 ± 2.8 (David et al., 2006) and 2672 Ma (Corfu et al., 1991; Davis, 1992; Corfu, 1993), and was accompanied by the emplacement of high-level alkalic intrusions (Corfu et al., 1991; Robert, 2001). This event was followed by the main episode of greenstone belt deformation that involved a major N-S shortening (D2) responsible for the development of the east-west grain of rock types, upright folds, and penetrative foliation (Robert, 2001). It evolved gradually into dextral transcurrent deformation (D3) localized along major fault zones. The D3 deformation event was partly accompanied and postdated by granitic plutonism to about 2660 Ma (Robert, 2001). After a period of exhumation between 2660 and 2642 Ma, the southern Abitibi subprovince evolved into a final dextral transpression event that produced dextral shearing along major fault zones (Daigneault et al., 2002). Regional metamorphism ranges from subgreenschist to greenschist facies and, locally, amphibolite facies around intrusions (Powell et al., 1995). The age of regional metamorphism can be bracketed between 2677 and 2643 Ma (Powell et al., 1995). Local Geology Stratigraphy The oldest unit in the area of Duparquet is the Kinojevis Group, where the main assemblage is the Deguisier

Formation (2722–2718 Ma; Zhang et al., 1993). Rock types comprise abundant Fe-Mg tholeiitic massive and pillow basalts, with minor andesites, rhyolites, and lapilli tuffs (Goutier and Lacroix, 1992). These volcanic rocks are interpreted to represent oceanic crust formation in a back-arc rift (Kerrich et al., 2008). The overlying Porcupine Group (2696– 2692 Ma) consists of graywacke, siltstone, and mudstone, indicating deposition in a deep basin as distal turbidites. U-Pb zircon dating suggests that erosion of calc-alkaline to tholeiitic mafic volcanic rocks from the oldest assemblages of the south Abitibi greenstone belt is the source for Porcupine Group sediments (Ayer et al., 2002, 2005). The youngest assemblage, the Duparquet Formation (Fig. 1B), which belongs to the Timiskaming Group, consists of conglomerate and sandstone that record deposition in alluvial fan, fan delta, and/or braid delta adjacent in a sea or lake (Mueller et al., 1996). These rocks are unconformably deposited on older assemblages. The Duparquet Formation forms an easterly trending corridor along the Porcupine-Destor fault zone (Benn and Peschler, 2005; Peschler et al., 2006). Its maximum depositional age is 2678.9 ± 2.8 Ma (David et al., 2006), and its minimum age is 2672 Ma (Corfu et al, 1991; Davis, 1992; Corfu, 1993). This sedimentary period is known as the Timiskaming event. Based on U-Pb dating and petrological setting, David et al. (2006) suggested a proximal provenance for the volcanic and syenitic fragments. A period of plutonism occurred during the Timiskaming event (Robert, 2001). The Beattie syenite (Fig. 1B) has been dated at 2681.6 ± 1 Ma (U/Pb on zircon; Mueller et al., 1996). The U-Pb ages determined for the Timiskaming event and for the emplacement of the Beattie syenite overlap within analytical error and therefore may be considered contemporaneous. However, Robert (2001) outlined evidence that the sedimentary rocks of the Duparquet Formation unconformably overlie the Beattie syenite (Fig. 1B). Petrology of the Beattie syenite The Beattie syenite is an alkaline composite stock; several types of syenite differ in texture, composition, and morphology. Bourdeau (2013) recognized five distinct syenite units composing the Beattie intrusion: (1) equigranular magnetite-bearing syenite unit, an unaltered unit in the core of the Beattie intrusion; (2) porphyritic Beattie syenite unit, the main syenitic unit of the intrusion in terms of volume; it is strongly altered to carbonate and sericite; (3) porphyritic central Duparquet syenite unit, located in southeastern part of Duparquet; K-feldspar phenocrysts are 5 to 16 mm, which is twice the size of the phenocrysts of the porphyritic Beattie syenite unit; (4) megaporphyritic syenite unit, which is spatially associated with the porphyritic central Duparquet syenite unit and characterized by significant K-feldspar and albite megacrysts 1 to 6 cm in size; and (5) lath syenite unit, composed of 85% to 95% of K-feldspar and albite laths, strongly altered to carbonate and sericite. Despite the variability of composition and texture of syenite and phenocryst morphology, all five syenite units share a common geochemical signature, suggesting the same magmatic source (Bourdeau, 2013). The dominant unit, the porphyritic Beattie syenite, is a porphyritic rock mainly characterized by light gray phenocrysts

317

GOLD MINERALIZATION AT THE SYENITE-HOSTED BEATTIE GOLD DEPOSIT, NEOARCHEAN ABITIBI BELT, CANADA

A

ONTARIO

QUÉBEC

76°W

OPATICA

50°N

25

50km

G

RE

NV

IL L

E

KA stru PUSKA ctur al b SING oun dary

0

48°N

PONTIAC Gold deposit

80°W

Fault and shearing

ARCHEAN

Sedimentary rocks (Cobalt group)

Sedimentary rocks (wacke and conglomerate)

Intermediate to felsic intrusions

Volcanic rocks

Mafic and ultramafic intrusions

631000E

B

Abitibi 400km

632000E

PROTEROZOIC

Superior Province

85

N

Beattie

5374500N

Donchester

Central Duparquet

250

500m

630500E

0

631500E

5374000N

Beattie syenite

Basalt and ultramafic rocks - Kinojevis Group

Basalt - Deguisier Formation

Basalt - Hebecourt Formation

Wacke and mudstone - Porcupine Group

Sandstone - Mont-Brun Formation

Conglomerate - Timiskaming Group

Gabbro

Porcupine-Destor fault zone

Old shaft

Shear zone

Thrusting

Principal planar fabric Younging direction Fold axial trace

Strike-slip fault

Unconformity

Fig. 1. (A) Simplified geology of the Abitibi greenstone belt (modified from Doucet et al., 2000). (B) Geology of Duparquet property (modified from Mueller et al., 1996; Bourdeau, 2013).

318

BIGOT AND JÉBRAK

that consist of albite core surrounded by orthoclase, 2 to 10 mm in size, set in a gray to reddish aphanitic groundmass of an aggregate of anhedral orthoclase and albite crystals (Fig. 2A, B; cf. Davidson and Banfield, 1944). The groundmass also contains relicts of clinopyroxene and actinolite, and titanite, which are largely altered to ankerite-siderite and leucoxene, respectively. Stockworks of chlorite, as well as minor calcite veins, are found. Iron carbonate and sericite are the dominant alteration. The Duparquet area contains greenschist facies metamorphic assemblages (Powell et al., 1995; Bourdeau, 2013). Structural geology In the area of Duparquet, stratigraphic units are deformed (Fig. 1B). Major folds with E-W axial planes occur in the Kinojevis Group; Deguisier Formation layers are upright with younging to the south (Goutier and Lacroix, 1992). Sedimentary rocks of the Duparquet Formation have strongly accommodated the deformation. The main structural characteristics include an N-S flattening with L/l ratio of about 4 to 5 as measured on clasts, E-W to ENE-WSW tight synclinal folds plunging 40° to 60° to the west, and an ENE-trending cleavage that steeply dips to the south. In addition, stretching lineations plunge shallowly to the east. In the Beattie syenite,

A

except for local flattening, deformation is not well developed. Faulting is a major structural characteristic in the area of Duparquet. The Porcupine-Destor fault zone is ESE striking (110°) with a dip ranging from 50° to 80° to the south (Graham, 1954). The Beattie syenite is bounded to the north and to the south by two faults that branch away from Porcupine-Destor fault zone (Figs. 1B, 3C). The former is the Beattie fault, which is mainly a thrust fault with a shear component; the latter is the Donchester fault, which is regarded as a shear fault. Both faults dip steeply subvertically to the north. An E-W to ENE-WSW subvertical shear zone (named the “fracture zone” by Davidson and Banfield, 1944; Figs. 1B, 3C), about 10 to 20 m wide, occurs within the intrusion. In the Beattie syenite, foliation only exists in the fracture zone. Major conjugated NW-SE dextral and NNE-SSW sinistral strike-slip movements crosscut the deposit (Fig. 1B). In addition to these main strike-slip faults, several minor faults are present in the deposit. Furthermore, jointing is common in the syenite; a widespread joint system steeply dips to the south and west. Veins are locally abundant but are not a key feature of the deposit, although some of them contain mineralization. Veins mostly occur within the syenite and the Timiskaming sedimentary rocks; only few have been observed in the volcanic

B

1 cm

D

1 cm

C

1 cm

E

5 cm

1 cm

F

2 cm

Fig. 2. Photographs of the different mineralization styles in the Beattie deposit. (A) Lithology-controlled style. Gray syenite of the porphyritic Beattie unit with iron carbonate and sericite alteration, and disseminated sulfides (1.5 g/t Au). (B) Lithology-controlled style. Reddish syenite with disseminated sulfides cut by carbonate veinlets (2.4 g/t Au). (C) and (D) Structure-controlled style. Breccia ore with disseminated and small clusters of sulfides and strong quartz alteration (C: 17.45 g/t Au, D: 18.6 g/t Au). (E) Structure-controlled style. Cherty quartz veins with fine sulfides (10.6 g/t Au). (F) Lithology-controlled style. Lath syenite unit with preserved K-feldspar and albite phenocrysts in a strongly carbonate and sericite altered matrix with disseminated sulfides.

+631000 E

+630500 E

A

GOLD MINERALIZATION AT THE SYENITE-HOSTED BEATTIE GOLD DEPOSIT, NEOARCHEAN ABITIBI BELT, CANADA +630000 E

319

Anomalous SVD areas

+5374500 N

Margin of the syenite

+5374500 N

Second Vertical Derivative (nT/m^2): 0.0293 to 0.2685 0.0025 to 0.0037 -0.0020 to -0.0015

+631000 E

+630500 E

+630000 E

-0.1191 to -0.0225 0

Looking down 125 250m

B +5374600

+5374500

Margin of the syenite

+5374400

Mineralization at 0.67 g/t Au

+5374300

+631400

+631200

+631000 +631000 E

+630800

+630600

+630400

+630500 E

C

Section 630200

Elev (Z)

+630000 E

+5374100

+630000

+5374200

Anomalous SVD areas +5374500 N

Margin of the syenite Carbonate Hematite Sericite Quartz Fault

+5374000 N

Fig. 3. Comparison at the same scale: (A) Airborne geophysics (second vertical derivative, SVD). (B) Mineralized zones in the Beattie deposit at 0.67 g/t Au (cutoff grade used for this study). (C) Dominant alteration halos on the surface, with the Beattie fault (north), the Donchester fault (south), and the fracture zone (center of the syenite), and with anomalous second vertical derivative areas.

320

BIGOT AND JÉBRAK

rocks. Studied veins have three main orientations: ENEWSW, ESE-WNW, and NNW-SSE (Table 1; Bigot, 2012). Sampling and Analytical Techniques Mineralization, alteration, and veins were examined both in surface and in drill holes over the deposit. The north margin of the Beattie syenite, as well as the western portion inside the intrusion, was the main area of study for understanding the mineralogy and geochemistry of the orebody. Whole-rock major and trace elements were determined by inductively coupled plasma-mass spectrometry (ICP-MS) and by inductively coupled plasma-emission spectrometry (ICPES) following lithium metaborate/tetraborate fusion and dilute nitric acid digestion at Acme Analytical Laboratories in Vancouver, Canada, and at ALS Chemex in Val d’Or, Canada. Ore textures were examined under a Leica DMLP transmitted-reflected light polarizing microscope and a Hitachi S-4300SE/N (VP-SEM) with energy-dispersive X-ray spectrometry and backscattered electron (BSE) images at the SEM laboratory of UQAM, Montreal, Canada. Pyrite, arsenopyrite, and gold were analyzed using a JXA JEOL-8900L electron microprobe (EMP) that includes five wavelengthdispersive spectrometers at the microprobe laboratory of McGill University, Montreal, Canada. Measurements were done with a 20-kV accelerating voltage, 50-nA current, and a 3-µm beam. Elements analyzed with their counting time and detection limit are as follows: Au (540 s, 0.0065 wt %), As (60 s, 0.0491 wt %), Ag (60 s, 0.035 wt %), Fe (10 s, 0.034 wt %), S (10 s, 0.0121 wt %), Cu (60 s, 0.0229 wt %), Hg (340 s, 0.0337 wt %), Te (60 s, 0.0215 wt %), and Se (60 s, 0.0156 wt %). Oxygen and hydrogen isotope compositions were measured in the three types of quartz veins (Table 2). Fourteen bulk fluid samples from quartz veins have been analyzed at the Queen’s Facility for Isotope Research at Queen’s University in Kingston, Canada. Hydrogen isotopes were measured from fluid inclusions within quartz using a DeltaplusXP mass spectrometer online through a thermochemical elemental analyzer (TC/EA); oxygen isotopes were determined from quartz mineral using a Finnigan Mat 252 mass spectrometer. Oxygen and hydrogen isotope results are reported ‰ relative to Vienna-Standard Mean Ocean Water (V-SMOW). The 3-D modeling of alteration volumes was done using Leapfrog® mining, developed by ARANZ Geo Limited. A total of 414 drill holes, including 218 definition drill holes with

Table 2. Isotopic Results for Quartz Veins in the Beattie Deposit Sample no.

Vein type

δO18

δO18 fluid1

6-A 4-B Iso2 Iso4 Iso8 Iso10 1-C Iso1 Iso6 Iso9 4-D Iso3 Iso5 Iso7

ENE-WSW cherty 13.35 8.05 –67 ENE-WSW cherty 13.71 8.42 –74 ENE-WSW cherty 13.20 7.90 –63 ENE-WSW cherty 12.20 6.90 –53 ENE-WSW cherty 16.10 10.8 –83 ENE-WSW cherty 6.90 1.60 –57 ESE-WNW 14.56 9.27 –32 ESE-WNW 14.90 9.60 –36 ESE-WNW 14.80 9.50 –30 ESE-WNW 11.70 6.40 –26 NNW-SSE tension 14.25 8.96 –63 NNW-SSE tension 15.50 10.20 –60 NNW-SSE tension 13.10 7.80 –69 NNW-SSE tension 14.30 9.00 –47

δD

Note: All data are given in ‰; hydrogen isotopes were measured from fluid inclusions within the quartz; oxygen isotopes were determined from quartz mineral 1 Calibration used for δO18 fluid composition at 350°C (see Fig. 7); the relationship for the fractionation factor is A(106/T2) + B, where A and B are constants; A = 3.34; B = –3.31 (Field and Fifarek, 1985)

an average depth of 320 m and spacing between the sections of approximately 100 m, were used for the study (cf. Bigot, 2012). Deposit Geology In the Beattie deposit, mineralization is hosted both inside the Beattie syenite and at its margins along the Beattie and Donchester fault zones and the fracture zone. Several mineralized zones within and adjacent to the Beattie syenite are recognizable (Fig. 3B). The main orebody is located along the Beattie fault, which marks the north contact between the Beattie syenite and the volcanic rocks of the Deguisier Formation with a portion of the sedimentary rocks of the Porcupine Group. The style of mineralization depends on the location in the deposit, either in the fault zones or in the intrusion. Gold mineralization is generally correlated with the fineness of sulfides (pyrite and arsenopyrite) and their abundance. The Beattie gold deposit (including the Beattie mine and the Donchester mine; Fig. 1B) has a past production record from 1931 to 1956 of 1.1 Moz of gold extracted from 10,614,421 tonnes of ore material, at an average grade of 3.92 g/t Au (Bevan, 2009, unpub. report). Recent intensive

Table 1. Main Characteristics of the Three Vein Styles in the Beattie Deposit ENE-WSW ESE-WNW NNW-SSE Location In the fault zones In the vicinity of the fault zones Dip Steep to the south Shallow to the north Structure Massive Flat extension, open space, pseudocolloform Morphology Straight, narrow, irregular Sinuous, occasionally large Composition Cherty quartz, minor sericite Quartz, carbonate (calcite to ankerite), minor sericite Gold occurrence Fine, disseminated in sulfides, None >10 g/t Au Breccia-related Breccia ore spatially related Hydraulic breccia Relative chronology D2-D3 to late D3 D2-D3 to late D3

Widespread in the syenite Medium to steep to the west Tension veins, periodic Thin, occasionally folded and sheared Quartz, carbonate (brown ankerite) None None Late D3

321


exploration work conducted by Clifton Star Resources Inc. and Osisko Mining Corporation established measured and indicated resources of 3.11 Moz gold from 60.9 Mt grading 1.59 g/t Au, and inferred resources of 1.44 Moz gold from 29.7 Mt grading 1.51 g/t Au (Williamson et al., 2013, unpub. report). Mineralization styles Mineralization styles in the Beattie deposit are twofold: (1) lithology controlled, limited to the syenite, and (2) structure controlled, associated with the Beattie and Donchester fault zones and the fracture zone (Table 3; Fig. 4). Disseminated ore is widespread in the deposit and occurs both in the lithology-controlled style and in the structure-controlled style. However, gold content, mineralogy, alteration, and volume of ore are different depending on the style. Ore in the lithologycontrolled style is almost the same everywhere in the Beattie syenite; ore in the structure-controlled style displays several types of mineralization including breccia, replacement, and vein. Lithology-controlled style: The lithology-controlled gold mineralization occurs exclusively within the porphyritic Beattie syenite unit and the lath syenite unit (Fig. 4). Ore minerals consist of gold-bearing arsenian pyrite and minor arsenopyrite that are finely disseminated in a moderately to strongly iron carbonate and sericite altered syenite (Fig. 2A, B, F). Mineralization generally grades from 0.3 to 3 g/t Au with an average value of about 2 g/t Au (Table 4); the sulfide concentration is about 5% to 8%. This style of mineralization represents lowgrade material with some mineralized zones continuous over 100 m in the western part of the deposit. Structure-controlled style: The structure-controlled gold mineralization occurs in the fault zones at the borders of the Beattie syenite, along the Beattie and Donchester faults, and in the shear zone within the Beattie syenite—the fracture zone. Ore minerals consist mostly of pyrite, with minor arsenopyrite, tellurides, and chalcopyrite in strongly silicified fault zones. Mineralization grades above 3 g/t Au, with average values of about 5 g/t Au, and regular anomalous zones above 10 g/t Au occur (Table 4); the sulfide content ranges from 10% to 20%, and high silica values are typical. In the deposit, there are three subtypes of mineralization that belong to the

%Au

N

Mag

S

Section 630200 E

+300

+200

+100

0

Lithology-controlled Structure-controlled E-W fault zones Margin of the syenite

-100

100 m

Fig. 4. Cross section in the Beattie deposit (630200E; see Fig. 3). Lithology-controlled gold mineralization style is located within the Beattie syenite, whereas structure-controlled mineralization is concentrated along the faulted margins of the Beattie syenite. Gold concentration is higher in the latter type. There is an inverse correlation between gold and magnetism in both styles. Modified after Davidson and Banfield (1944) and Graham (1954).

structure-controlled style: breccia, cherty quartz vein, and polymetallic vein. Breccia ore constitutes the majority of the historically mined ore in the Beattie deposit (Davidson and Banfield, 1944). Rock consists of a grayish blue- to yellowish-colored breccia of angular to subangular fragments of silicified syenite, basalt, and sedimentary rocks, cemented in an abundant silicified

Table 3. Main Characteristics of the Two Mineralization Styles in the Beattie Deposit

Lithology-controlled style

Structure-controlled style

Nature of the mineralization Disseminated sulfides Disseminated sulfides, small clusters of sulfides Texture Porphyritic, stockwork Replacement, breccia, vein Setting of the mineralization Limited to the porphyritic Beattie syenite unit In second-order breaks and shear zones adjacent to and lath syenite unit and within the Beattie syenite Alteration Iron carbonate and sericite Quartz, minor sericite Metallic mineralogy Py, Apy, Gl, Sp Py, Apy, Gl, Sp, Cp, En, Tt, Cl, Hs, El Elemental association (+Au) As, Ag, Pb, Zn Te, Hg, Mo, As, Se, Ag, Sb, Cu, Zn, Pb Gold occurrence Invisible gold in lattice of arsenian pyrite and Electrum in microfractures and porosity of brecciated arsenopyrite pyrite Au grades 3 g/t Au ; average 5 g/t Au Sulfide content 5% to 8% 10% to 20% Au/Ag 1.2 0.9 Paragenesis stage Sulfide stage Breccia stage Abbreviations: Apy = arsenopyrite, Cl = coloradoite, Cp = chalcopyrite, El = electrum, En = enargite, Gl = galena, Hs = hessite, Py = pyrite, Sp = sphalerite, Tt = tennantite-tetrahedrite

Avg. (n = 5) Std. dev.

Avg. (n = 10*)


Syenite—hematite alteration

Syenite—sericite alteration



Lithology-controlled style

Syenite—iron carbonate alteration


Breccia ore— quartz alteration

One sample

One sample

Structure-controlled style

Cherty Polymetallic vein vein

Avg. (n = 6)

Std. dev.

Basalt—quartz alteration

SiO2 (%) 57.76 1.32 52.23 60.73 1.24 55.67 2.04 55.10 2.45 75.43 8.02 92.20 65.50 57.78 4.04 Al2O3 16.40 1.20 14.22 17.93 0.50 14.86 0.69 14.80 2.06 8.13 3.67 2.00 3.08 12.07 1.04 Fe2O3 5.22 0.30 14.13 4.90 0.46 4.73 0.39 4.29 0.83 3.01 1.41 1.78 2.03 8.80 2.51 CaO 3.80 1.45 8.35 1.13 0.82 7.63 1.72 4.26 1.07 2.12 1.55 0.14 1.16 4.05 2.04 MgO 1.40 0.52 5.86 0.54 0.17 0.97 0.31 1.63 0.18 0.40 0.44 0.09 0.19 1.37 0.82 Na2O 5.47 0.17 3.09 4.67 0.47 1.01 0.95 1.70 0.53 0.30 0.21 0.02 0.05 0.56 0.43 K2O 4.55 0.66 0.27 6.25 1.20 10.45 2.04 8.84 1.55 6.55 3.26 0.89 2.16 5.86 2.13 Cr2O3 0.00 0.00 0.01 0.00 0.01 0.00 0.01 0.00 0.01 0.00 0.01 0.01 0.01 0.00 TiO2 0.57 0.02 1.52 0.56 0.05 0.48 0.03 0.49 0.27 0.40 0.25 0.08 0.09 1.19 0.25 MnO 0.11 0.03 0.21 0.06 0.02 0.16 0.03 0.13 0.03 0.06 0.05 0.01 0.03 0.15 0.09 P2O5 0.32 0.07 0.12 0.26 0.11 0.28 0.01 0.27 0.04 0.20 0.11 0.06 0.07 0.46 0.34 SrO 0.18 0.05 0.06 0.01 0.08 0.03 0.10 0.02 0.03 0.01 0.01 0.01 0.02 0.01 BaO 0.33 0.07 0.23 0.01 0.25 0.05 0.32 0.08 0.14 0.09 0.01 0.03 0.04 0.01 C 0.94 0.48 0.44 0.11 1.45 0.25 1.66 0.19 0.95 0.46 0.05 0.31 1.23 0.63 S 0.04 0.01 0.15 0.07 0.05 1.12 0.50 1.42 0.70 1.67 0.97 0.56 1.59 2.26 0.90 LOI 2.99 1.62 2.84 2.05 0.91 4.25 0.85 6.18 0.55 2.84 1.33 1.09 17.00 6.15 1.96 Total 98.40 0.91 99.10 2.42 98.30 1.96 98.10 0.94 99.85 1.06 98.40 91.40 98.46 1.81 Ba (ppm) 2,964.50 667.56 86.00 2,099.50 250.12 2,072.00 429.45 2,720.00 691.71 978.00 198.18 124.00 236.00 302.30 84.15 Ce 242.50 6.05 21.83 251.60 17.66 221.00 14.91 220.00 58.17 118.77 22.11 49.40 43.10 45.62 17.03 Cr 10.00 0.00 173.25 10.00 0.00 10.00 0.00 10.00 0.00 12.24 16.89 30.00 10.00 8.00 2.31 Cs 5.15 1.78 3.59 1.49 3.57 0.62 2.96 0.69 2.11 0.54 0.33 0.83 3.24 1.78 Dy 6.73 0.52 6.29 0.66 5.90 0.24 5.73 1.03 3.51 0.70 1.60 1.42 6.55 2.07 Er 3.10 0.29 3.03 0.39 2.98 0.13 2.92 0.82 1.74 0.28 0.59 0.71 4.05 1.26 Eu 4.20 0.17 4.17 0.29 3.89 0.15 3.69 0.67 2.22 0.50 1.23 0.91 1.85 0.62 Ga 24.50 2.45 19.69 28.13 1.53 22.60 1.42 24.00 2.18 14.90 4.54 10.70 6.10 18.82 2.35 Gd 13.33 1.96 14.16 2.28 13.86 0.69 13.60 2.01 7.39 2.60 3.94 3.05 7.10 2.51 Hf 9.25 0.38 9.70 0.44 8.27 0.38 8.40 1.04 4.57 1.37 0.90 2.80 5.50 1.60 Ho 1.18 0.12 1.08 0.16 1.02 0.06 1.01 0.30 0.67 0.05 0.23 0.23 1.36 0.45 La 115.05 4.10 7.09 122.98 6.03 105.40 6.08 107.00 28.74 58.17 12.91 22.80 21.40 19.62 6.99 Lu 0.42 0.05 0.37 0.06 0.38 0.04 0.39 0.14 0.25 0.02 0.06 0.08 0.57 0.18 Nb 12.45 0.53 5.54 12.25 1.13 10.40 0.58 10.80 2.14 6.23 2.18 1.10 2.10 10.86 4.07 Nd 103.15 3.83 103.23 9.88 89.60 5.09 90.20 21.93 51.37 7.90 24.70 19.00 25.54 9.25 Pr 28.70 1.36 29.66 2.42 25.50 1.77 26.50 6.42 14.35 2.91 6.36 5.28 6.28 2.41 Rb 118.45 21.07 8.46 151.88 14.80 185.90 21.38 195.50 29.64 106.83 38.00 23.70 42.70 116.42 27.37 Sm 17.74 1.10 17.32 1.91 15.45 1.07 16.10 2.98 8.96 2.06 5.16 3.42 6.22 2.27 Sn 2.00 0.00 2.00 0.00 1.29 0.66 1.00 0.35 0.87 0.23 1.00 3.00 1.60 0.80 Sr 1,959.00 638.32 118.46 544.30 45.89 745.00 215.44 947.00 210.74 147.99 130.26 36.50 82.00 151.54 85.03 Ta 0.50 0.04 0.48 0.05 0.44 0.05 0.40 0.20 0.33 0.06 0.10 0.10 0.76 0.29 Tb 1.55 0.11 1.53 0.14 1.43 0.06 1.41 0.14 0.82 0.22 0.45 0.33 1.10 0.37 Th 25.15 2.07 24.55 4.09 22.20 1.51 22.80 7.73 19.33 2.34 1.81 4.28 1.79 0.68 Tl 0.65 0.09 0.88 0.53 1.70 0.45 1.50 0.51 1.13 0.81 0.60 0.50 2.00 0.72 Tm 0.44 0.06 0.38 0.06 0.36 0.04 0.39 0.13 0.23 0.01 0.07 0.08 0.56 0.19 U 6.76 0.77 5.98 1.28 6.05 0.88 6.78 1.03 9.49 1.70 3.64 1.26 1.26 1.10 V 133.00 29.62 396.62 123.25 27.35 125.70 43.76 144.00 40.90 34.26 15.24 260.00 51.00 236.60 133.80 W 1.45 0.74 6.75 4.65 11.10 3.28 12.00 4.23 9.79 0.72 3.00 2.00 25.80 17.99 Y 34.55 3.00 37.08 32.00 3.65 29.39 1.82 29.90 7.21 19.13 1.46 6.70 6.70 36.72 12.95 Yb 2.74 0.28 2.49 0.38 2.51 0.19 2.44 0.86 1.57 0.07 0.43 0.58 3.75 1.14 Zr 356.75 29.61 114.46 386.68 18.45 327.30 12.92 317.00 47.65 181.43 54.99 30.00 110.00 202.80 56.98

Element

Ore control

Facies Fresh syenite Fresh basalt

Table 4. Chemical Composition of the Different Facies in the Beattie Deposit

322 BIGOT AND JÉBRAK

Notes: All analyses performed at both ACME Lab, Vancouver, and ALS Chemex, Val d’Or; basalt belongs to the Deguisier Formation to the north of the syenite; data from Goutier and Lacroix (1992), MB 92-06; for the polymetallic vein, Osisko reported 341 g/t Au: http://www.osisko.com/2010/11/osisko-and-clifton-star-intersect-70-metres-averaging-1-94-gt-au-at-duparquet/ Abbreviations: avg. = average, std. dev. = standard deviation

Avg. (n = 10*) Avg. (n = 5) Std. dev. Element

Ore control

Au (ppm) 0.01 0.01 0.00 0.01 0.01 2.14 0.53 1.38 0.09 6.90 3.50 10.60 120.00 4.46 2.41 As 9.10 2.82 3.56 15.33 6.62 290.40 124.01 226.12 175.00 812.00 307.08 223.00 >250 4,420.00 2,189.79 Bi 0.42 0.10 0.60 0.20 1.16 0.25 0.68 0.24 0.85 0.31 0.30 1.29 0.07 0.04 Hg 0.05 2.08 0.45 0.47 2.35 1.89 1.75 0.38 21.15 12.41 170.00 >25.0 15.79 17.80 Sb 1.30 0.35 1.64 0.88 2.95 0.93 7.50 3.90 8.70 4.36 41.10 >250 12.93 7.06 Se 0.45 0.13 0.55 0.19 1.59 0.33 1.80 0.79 3.70 1.18 2.70 107.00 3.98 1.59 Te 0.01 0.11 0.01 0.01 0.95 0.51 1.43 0.51 133.00 117.50 >250 6.54 3.36 Ag 1.03 0.77 0.69 0.68 0.25 1.79 1.08 2.86 1.66 7.58 2.74 44.60 3,580.00 2.58 1.06 Cd 0.18 0.11 0.28 0.05 0.30 0.00 0.30 0.07 0.48 0.09 0.30 7.60 0.30 0.00 Co 9.00 1.41 45.85 7.00 2.65 10.00 1.17 9.00 2.31 13.70 4.47 7.00 2.00 22.00 4.69 Cu 18.90 4.45 96.46 24.95 4.93 29.20 5.61 36.79 13.78 71.57 29.33 125.00 7,920.00 77.60 28.36 Mo 1.10 0.44 0.83 0.45 11.90 10.30 58.30 11.72 177.41 161.56 175.00 29.00 23.00 29.31 Ni 5.20 1.76 57.73 5.10 0.84 5.60 1.41 4.00 1.31 4.54 3.91 6.00 3.00 14.00 17.17 Pb 34.15 6.70 9.90 34.30 7.71 36.40 4.34 62.00 29.14 36.40 19.74 35.00 22.00 29.00 26.04 Zn 75.50 17.02 111.08 73.75 28.70 59.70 17.80 92.00 13.94 58.67 34.52 38.00 1,040.00 96.80 58.20

Avg. (n = 6) One sample One sample Avg. (n = 4) Std. dev.




Structure-controlled style Lithology-controlled style

Syenite—sericite alteration Syenite—iron carbonate alteration Syenite—hematite alteration Facies Fresh syenite Fresh basalt

Table 4. (Cont.)

Breccia ore— quartz alteration

Cherty Polymetallic vein vein

Basalt—quartz alteration

Std. dev.


323

groundmass and cut by a network of tiny quartz stringers (Fig. 2C, D). The orebodies are similar to dikes. They form subvertical narrow volumes extended E-W along the fault zones, the Beattie fault to the north, the Donchester fault to the south, and the central fracture zone (Fig. 4). The mineralization of the breccia ore type consists mainly of fine disseminated pyrite with small clusters of pyrite; grade is about 7 g/t Au (Table 4). Cherty quartz veins (Fig. 2E) have been observed only within the fracture zone among foliated syenite. They are irregular gray-blue cherty veins about 10 to 20 cm wide. Pyrite grains are very fine and disseminated. Minor sericite is present in the veins. The mineralization of cherty quartz veins usually grades about 10 g/t Au (Table 4). Polymetallic veins occur along the Beattie fault and the fracture zone, but are rare. They consist of Cu-Ag-Te-Hg-SbAs-Au-Se–rich veins related to intense silicification (Table 4). The mineralogical assemblage contains pyrite, enargite, tennantite-tetrahedrite, and coloradoite. These narrow veins comprise the highest gold values in the deposit, including results up to 119.5 and 341 g/t Au. Mineralogy and paragenesis The paragenetic sequence in the Beattie deposit is divided into four main stages (Fig. 5): (1) Fe-Ti assemblage, (2) hematite stage, (3) sulfide stage, and (4) breccia stage. The mineral paragenesis presents an evolution from initial magmatic phase to hydrothermal event. The Fe-Ti assemblage is the igneous phase. It consists of widespread subhedral titaniferous magnetite (0.1–0.25 mm; Fig. 6A; up to 2% Ti in magnetite) associated with twinned euhedral titanite (0.15–0.35 mm). Very fine inclusions of apatite (0.005 mm) with submicron barite crystals locally occur in titanite crystals (Fig. 6B). Anhedral ilmenite (