Deformational processes in formation of the Bellechasse-Timmins gold deposit, southern Québec Appalachians, Canada

1 1 2VALETTE, M. , TREMBLAY, A. , AND BOILARD, D.1. Département des sciences de la Terre et de l’Atmosphère, Université du Québec à Montréal

2. Dany Boilard Inc. Exploration, Sainte-Justine, Québec

Figure 6: Schematic interpretation of the geometryof the BT gold deposit, as the result of fold-relatedsaddle reef structural trap (3D).

Neck reef

Leg reef

Saddle reef

A B

Figure 5: Schematic evolution for formation anddeformation of the dioritic intrusions hostingthe Au mineralization.

Sedimentsformation

Diorite sillintroduction

Regionaldeformation

Figure 4c: Stereographic plots for veins.

N

S

W E

Equal-areaLower hemisphere n = 170

Poles to veins

Intersection of veins

6.75

6.00

5.25

4.50

3.75

3.00

2.25

1.50

0.75

0.00

Density

Maximum density: 6.7%at 132.9/7.4 (pole)312.9/82.9 (plane)

Counting method:Fisher distribution

c

1

1

2

2

3

Figures 4a and 4b: Stereographic plots for S and fold axes.1

N

S

W E

Equal-areaLower hemisphere n = 29

Calculed fold axes (veins) (9)Calculed fold axes (S /S ) (10)1 0

Mesured fold axes (9)

b

N

S

W E

Equal-areaLower hemisphere n = 159

Poles to S1

21.94

19.50

17.06

14.63

12.19

9.75

7.31

4.88

2.44

0.00

Density

Maximum density: 21.9%at 312.0/0.0 (pole)132.0/90.0 (plane)

Counting method:Fisher distribution

a

Figure 3: Geological detailed map of the BT gold deposit and schematic section of the #1 Timmins zone.

Shear zone

Schistosity

Vein

Stretching lineation ( Lm )

Intersecting lineation ( )0 L1

STRUCTURAL FEATURES

Anticlinal

Diorite/gabbro intrusions

PLUTONIC ROCKS

Volcaniclastic - purple and green

Volcaniclastic - medium to light grey

Volcaniclastic - dark to medium grey

Graphitic volcaniclastic - dark grey

ETCHEMIN FORMATION

SEDIMENTARY AND VOLCANIC ROCKS

Road

Grid

Water

Drilling

Sample

OTHERS

NW SE

A B

ZT1-02 ZT1-035m

85

75

75

18

58

4

88

81

18

75

7

20

82

75

66

12

C D

A MV-01

A B

D

JF-1

MV-07

MV-04

5156450mN

5156500mN

5156400mN

40

57

00

mE

40

57

50

mE

40

58

00

mE

78

77

83

77

83

64

BD2011-157

BD2011-164

BD2011-159

BD2011-174

BD2011-177

BD2011-158

BD2011-163

BD2012-192

BD2012-190BD2011-171

BD2011-170

BD2007-51

BD2007-52

BD2007-53

BD2007-54

BD2007-55

BD2007-56

BD2007-57

BD2007-58

BD2007-59

BD2007-60

BD2007-61

BD2007-62

BD2007-63

BD2007-64

BD2007-65

BD2007-69

#1 Timmins Zone

ZT1-05

ZT1-02

ZT1-03

ZT1-04

ZT1-01

Ran

g St J

oseph

?

S.Z

. Pro

long

atio

n

?

Rico

10 m B

A

Figure 2: Geological map of the Beauce area showing the location of the Bellechasse-Timmins gold deposit (De Souza, 2012).

CALDWELL GROUPSlate and sandstone / basalt

Slate and orthoquartzite

ROSAIRE GROUP

CONTINENTAL ROCKS - HUMBER ZONE

Serpentinite

Peridotite, serpentinite, granitoid

RIVIÈRE-DES-PLANTESULTRAMAFIC COMPLEX

Mafic and felsic volcanic rocks

ASCOT COMPLEX

Caldwell-type metasandstone

Pebbly mudstone, slate and conglomerate

Ware volcanics

SAINT-DANIEL MÉLANGE

Volcaniclastic sandstone

FRONTIÈRE FORMATION

Volcanogenic cherty mudrock

ETCHEMIN FORMATION

Graphitic slate and volcaniclastic rocks

BEAUCEVILLE FORMATION

Turbiditic slate and sandstone

MAGOG GROUPST-VICTOR FORMATION

OCEANIC ROCKS - DUNNAGE ZONE

Gaspé Belt

Normal fault

Taconian reverse fault

Late-Taconian reverse fault

Acadian reverse fault

Undetermined fault

Anticline, syncline

AUnconformities: B

10 km

70°30’

46°15’

72°30’

46°30’

70°00’

46°15’

La Guadeloupe Fault

tluaF hpesoJ-tS

Fig. 3

Figure 1: Geological map of the southern Québec Appalachians (De Souza, 2012).

Thrust / Reverse

Backthrust

Normal fault

Anticline

STRUCTURAL FEATURES

Ordovician

Silurian

Devonian

Cretaceous

PLUTONIC ROCKS

Chain Lakes massifSInternal (Sutton-Bennett Schist)

External

Humber Zone(Neoproterozoic - Ordovician)

Boil Mountain Complex

Jim Pond Formation

Hurricane Mountain Formation

Dead River Formation

Ammonoosuc Volcanics

Ophiolite

St. Daniel Mélange

Ascot Complex

Magog Group

Dunnage Zone (U. Cambrian - U. Ordovician)

WESTERN MAINE (BMA)SOUTHERN QUEBEC

Post-Ordovician

SEDIMENTARY AND VOLCANIC ROCKS

External

70°W

45°N

71°W

72°W

46°N

47°N

ND

MA

NDMA

SM

A

BMA

VERMONT

NEWHAMPSHIRE

MAINEQUÉBEC

.F epuoledauG aL

.F ttenneB

.F hpesoJ-tS

.F e

morB

eniL s’nagoL

Riv.

Chaudière

Riv. S

t-François

.F

hp

esoJ-t

S

tluaF ehcuteP eiraM-reviR airotciV

S

S

S

25 km

.F skaeP rehsarT

QUEBECCITY

Fig. 2

Photograph 9: Field example ofdilatation jog, grid #4, Timminszone #1.

EW

Photograph 8: Foldedextension veins, grid #2,Timmins zone #1.

40 cm

SSENNW

Photograph 7: Field exampleof slickenside showing strike-slip motion, grid #1, Timminszone #1.

Photograph 6: Field example of subhorizontal lineations in shear zone, grid #1, Timmins zone #1.

12°N358

10 cm

N S

Photograph 5: Field exampleof slickenside showing reversemotion, grid #1, Timminszone #1.

ESE WNW

Photograph 4: Field exampleof steeply-plunging lineationsin shear zone, grid #1,Timmins zone #1.

66°N172

10 cm

N S

500 µm

Chl

Pla

Ox

Pla

Cal

Ser

Chl

Qz

Photograph 2: Drill core of#1 Timmins zone showingquartz vein with native gold.

5 cm

Qz

Chl

D

Chl

DQz

Photograph 3: Thin section of a diorite showing thetypical mineral assemblage of the regional greenschist-facies metamorphism (LPAx10).

The occurrence of down-dip lineations indicates the predominance of reverse faulting during mineralization. Ductile-brittle shears related to the mineralization are mainly due to flattening and «locking up» of fold hinges, which have been sheared out by high-angle reverse faults (Fig. 6). The overall geometry of the ore zones is therefore controlled by and coeval with the regional folding event, and basically represents the product of hydrothermal circulation and fracturing related to regional metamorphism and folding affecting the diorite sills/dykes and hosting sedimentary rocks. Fluids migrated along faults/shear zones and other weakness planes (such as bedding and S ) during folding and 1

precipated in favourable low-pressure dilation zones (e.g. faults, S planes, fold 1

axes) created when the hydraulic pressure of trapped fluids exceeded the lithostatic pressure (Cox et al., 1991; Windh J., 1995).

VI. DISCUSSION & CONCLUSION

There are 3 principal orientations of quartz veins, almost perpendicular to each other, and their intersection is subparallel to the fold axis developed in the diorite intrusions. These 3 orientations likely represent different stages of deformation and veins formation (Fig. 4c). The first one, subparallel to S , was formed during the development of 1

the schistosity. The second family, represented by flat-lying extension veins, is attributed to folding, when intrusions start to be fractured due to high competency contrast and during variations of hydrothermal fluid pressure. These veins are locally folded, which indicates that they were formed before the end of folding (Photos #8 and #9). Finally, the third type of veins is the result of fracturation during NE-SW extension and/or late-stage compressional strike-slip faulting coeval with the NW-directed compression that generated the auriferous shear zones.

V. QUARTZ VEINS GEOMETRY

Our structural analysis shows that both the intrusions and hosting sedimentary rocks are crosscut by a steeply-dipping NE-trending axial-planar schistosity (Fig. 4a) and by 50 cm- to 5 metres-wide shear zones subparallel to that S schistosity. The shear zones host steeply-plunging 1

slickenlines/lineations and preserved structural evidence for NW-verging reverse faulting (Photos #4 and #5). Subhorizontal lineations/fault striae are also locally found, suggesting late-stage strike-slip motion (Photos #6 and #7). Structural relationships between the bedding (S ) and 0

S in the sedimentary rocks indicate that the sedimentary 1

strata hosting the diorite are tightly folded, with fold axes plunging moderately to steeply (ca. 60°) toward the NE or the SW (Fig. 4b). As a result of rheological contrast between the two rock types, similar folds are found in the sedimentary rock sequence whereas the diorite intrusions are characterized by concentric folds (Fig. 5).

IV. STRUCTURAL CHARACTERISTICS

The Au mineralization consists of quartz veins and quartz-filled breccias (Photo #1), essentially developed in the diorite intrusions (Fig. 3), and which locally form well-developed stockwork structures. The veins are made up of quartz ± carbonates, minor sulphide minerals (mostly pyrite and pyrrhotite), and native gold occurences (Photo #2). Various types of mineral alteration are visible in the diorite, for instance, albitization, silicification, chloritization and carbonatization, all types being related to regional metamorphism (Photo #3).

III. AU MINERALIZATION & HYDROTHERMAL ALTERATION

The BT gold deposit is hosted by the Magog Group, an Ordovician synorogenic forearc basin sequence belonging to the Dunnage Zone of the southern Québec Appalachians (Fig. 2). The Dunnage Zone is made up of ophiolites, island-arc volcanic rocks and synorogenic clastic and volcaniclastic sedimentary rocks related to the obduction of Iapetan oceanic crust (Pinet et Tremblay, 1995; Tremblay et al., 2011). The Au mineralization is developed in diorite sills (and dykes) crosscutting the Upper Ordovician (Caradocian) Etchemin Formation, which has been deformed and metamorphosed at greenschist facies during the Middle Devonian Acadian orogeny (Tremblay et al., 2000).

II. REGIONAL GEOLOGY

The Bellechasse-Timmins (BT) gold deposit is located approximately 110 km southeast of Québec city, more precisely 7 km from the town of Saint-Magloire in the Bellechasse County, Québec (Fig. 1), and is part of the Bellechasse gold belt of the southern Québec Appalachians (Gauthier et al., 1987). It is the result of fractures filling and the formation of saddle reef and related structures dur ing orogenic d e f o r m a t i o n c o e v a l w i t h hydrothermal fluids circualtion and mineralization, such as typified, for instance, by the Lachlan Fold Belt of Central Victoria in Australia (Cox et al., 1991; Windh J., 1995).

I. INTRODUCTION

Mr. Frank Candido (President and Director of Golden Hope Mines Ltd) is thanked for giving us the opportunity to develop the project, and facilitate the access to the BT property, and all the available information. Many thanks to Michelle Laithier for her artistic talent and her essential contribution to this poster.

ACKNOWLEDGMENTS

Cox S.F., V.J. Wall, M.A. Etheridge and T.F. Potter, 1991. Deformational and metamorphic processes in the formation of mesothermal vein-hosted gold deposits - Examples from the Lachlan Fold Belt in central Victoria, Australia. Ore Geology Reviews 6: 391-423.

De Souza S., 2012. Evolution tectonostratigraphique du domaine océanique des Appalaches du sud du Québec dans son contexte péri-Laurentien. Thèse de doctorat en Sciences de la Terre, Université du Québec à Montréal, Qc, Canada.

Gauthier M., M. Auclair and M. Durocher, 1987. Synthèse métallogénique de l ’Estrie et de la Beauce - Section nord. Ministère de l ’Energie et des Ressources Naturelles, Québec, Canada. MB87-38.

Pinet N., and A. Tremblay, 1995. Tectonic evolution of the Québec-Maine Appalachians : from oceanic spreading to obduction and collision in the northern Appalachians. American Journal of Science 295: 173-200.

Tremblay A., G. Ruffet and S. Castonguay, 2000. Acadian metamorphism in the Dunnage Zone of southern Québec Appalachians: 40Ar/39Ar evidence for collision diachronism. Geological Society of America Bulletin 112: 136-146.

Tremblay A., G. Ruffet and J.H. Bédard, 2011. Obduction of Tethyan-type ophiolites - A case-study from Thetford-Mines ophiolitic complex, Québec Appalachians, Canada. Lithos 125: 10-26.

Windh J., 1995. Saddle Reef and Related Gold Mineralization, Hill End Gold Field, Australia: Evolution of an Auriferous Vein System during Progressive Deformation. Economic Geology 90: 1764-1775.

REFERENCES