Overview of Results from the Greenstone ... - Geology Ontario

S2 is the earliest regional fabric and the main foliation of the Larder Lake and Upper Canada
deformation zones. It is defined by flattened clasts in conglomerates and tuffs, and by penetrative
schistosity and compositional banding of secondary chlorite, talc, white mica, fuchsite and carbonate in
hydrothermally altered mafic, ultramafic and alkalic metavolcanic rocks. In Teck Township, S2 occurs
within the 400 to 500 m wide Larder Lake–Cadillac deformation zone. In Gauthier Township, the fabric
occurs within a broader (~1300–2100 m wide) halo that extends from the southern flank of the Larder
Lake–Cadillac deformation zone to the Upper Canada deformation zone and about 400 to 500 m further
north. S2 is a steeply dipping fabric, orientation of which varies broadly from northeast (~060–070°, e.g.,
Upper Canada deformation zone) to east (e.g., at the Teck–Lebel townships border) and to southeast
(~110–150°, e.g., eastern part of Gauthier Township transect). Within the LLCDZ, S2 appears to
generally follow the orientation of the deformation zone. Stretching lineation (L2), associated with S2, is
defined by stretched clasts in conglomerates and tuffs, varioles in mafic metavolcanic rocks, and rod-like
secondary mineral aggregates in hydrothermally altered rocks. Lineation L2 is particularly well developed
in Gauthier Township where it plunges moderately (35–60°) to the east.
S3 is a north-trending (~340–020°) steeply dipping crenulation cleavage. It is best documented in the
Upper Canada deformation zone and also identified in several other locations in Gauthier Township.
Structural timing of the cleavage is constrained by relationships with S2 and S4: S3 crenulates S2, is axial
planar to symmetric and S-asymmetric folds of S2, and is overprinted by S4. Similarly oriented, northtrending
cleavage axial planar to symmetric and Z-asymmetric folds of S2 was mapped in Teck
Township, in carbonate-fuchsite-altered ultramafic rocks within the LLCDZ. No unequivocal overprinting
by S4 was documented there, and the north-trending fabric was assigned to S3 based on similarity in
orientation with the S3 foliation of the Gauthier Township transect.
Foliation S4 trends northeast in the Gauthier Township (060–080°) and the Teck Township (040–060°)
transects. It is a steeply dipping regional foliation axial planar to outcrop-scale Z-asymmetric and, more
rarely, symmetric F4 folds. Locally, foliation changes orientation to east and even east-southeast, due to
deflection along narrow high strain zones. However, on a regional scale, the orientation of S4 is relatively
constant, and there is no systematic change in the S4 trend with increasing or decreasing distance to the
LLCDZ. Most commonly, S4 is a discrete crenulation cleavage axial planar to microfolded bedding and S2
fabric; in Timiskaming assemblage conglomerates in Teck Township, S4 is defined by pebble flattening.
A late crenulation cleavage, S5, was observed in the Larder Lake–Cadillac deformation zone, in the
eastern part of the Gauthier Township transect. It strikes 130 to 170°, dips 30 to 80°W, overprints S2 and S4
and is commonly axial planar to S-shaped folds of S2. No map-scale structure is associated with this fabric.
KINEMATIC INDICATORS IN THE LARDER LAKE–CADILLAC DEFORMATION ZONE
Asymmetric shear sense indicators were mapped at two locations along the Larder Lake–Cadillac
deformation zone in Gauthier Township. In the northern wall of the flooded McBean open pit, where
highly strained Timiskaming assemblage conglomerates with well-developed stretching lineation (L2) are
exposed. On the surface that is parallel to L2 and perpendicular to S2, some of the least strained pebbles
show asymmetric pressure shadows indicating oblique reverse-dextral slip (south side over north and to
the west) along the direction of stretching lineation.
The other location is the stripped outcrop at the Princeton property, eastern part of the Gauthier
Township transect. Here, shear sense is indicated by a combination of dextral Z-shaped drag folds,
asymmetrical recrystallized tails around pebbles, the clockwise orientation of extensional quartzcarbonate
veins with respect to foliation (S2), and offsets of these veins along S2. The interpreted
movement direction is similar to that documented at the McBean pit, that is, oblique reverse-dextral slip
parallel to the L2 stretching lineation.
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