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