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

and the North Timmins–Crawchest regional lines cross the Porcupine assemblage. On both profiles,
several prominent reflective bands define an antiformal structure 3 to 6 km beneath the Porcupine
assemblage. These features may represent the base of the Porcupine assemblage metasediments underlain
by, and folded with mafic volcanic rocks of the Tisdale assemblage during regional shortening.
South of Timmins, the South Timmins regional line images the Adams stock as a shallow, pancakeshaped
body. To the east, the South Porcupine regional line crosses the Shaw Dome. This profile displays
a prominent band of reflections at 1 to 5 km depth within the Deloro assemblage in core of the Shaw
structure. The dip of these reflectors change from shallowly northward to shallowly southward at an apex
in the central part of Shaw Township and, thus, correlate well with a “Dome” structure (Reed, Snyder and
Salisbury 2005). This band of reflection is underlain by a less reflective zone to a depth of about 7 km
that may coincide with homogeneous crust typical of a granitic pluton (i.e., similar to the area underlain
by the Adams stock).
The PDDZ is imaged by the Kettle Lakes line in German and Macklem townships, and the
Shillington line in Taylor and Currie townships. Reed, Snyder and Salisbury (2005) report that both
profiles show south-dipping reflectors underlying the lower Tisdale assemblage with their northernmost
extent marked by the surface trace of the PDDZ. A marked transition to north-dipping reflectors occurs
north of the PDDZ near the surface and this transition zone dips moderately southward beneath the
Tisdale assemblage on both lines. Seismic lines crossing the PDDZ further to the west are less
informative about the possible dip of this structure which may reflect a steeper orientation and/or less
distinctive impedance contrast across the PDDZ in the Timmins area.
Potential Field Inversions
Computer-based interpretations of the geophysical data including magnetic and gravity inversions have
also been done for each of the detailed mapping areas as part of this project. This has better constrained
the distribution of rock units and structures for the mapping-based subprojects and has helped to visualize
the dip and/or plunge of lithological units, folds and faults at depth. An example of the utility of the
inversions can be seen for the southern Currie Township area (see “Geophysics Subproject”) where
inversions of the magnetic data suggest a syncline in the highly magnetic lower Blake River volcanic
rocks (see Figure 2) and an overall southerly dip to this part of the assemblage in the gravity inversions.
In Tully Township, the area underlain by ultramafic volcanic rocks in the southern part of the Kidd–
Munro assemblage is associated with magnetic highs and gravity lows. This may be of economic
significance as this might reflect extensive serpentinization related to the Pipestone deformation zone.
This area is known to host a number of gold deposits (Berger 2002). In addition, Thompson (2005)
identified this area as one which has a favourable metamorphic signature for hosting gold deposits. The
inversions also indicate the ultramafic rocks are synformally folded with an overall dip to the north, a
feature also suggested by north-dipping seismic reflectors on the South Timmins seismic profile in this
general area.
Inversions in the Tisdale and Deloro township areas of the Timmins camp identify the PDDZ as a
steeply north-dipping structure (Reed 2005a) in an area where the seismic profiles do not provide much
information on the inclination of this structure. In addition, the magnetic inversion in the Teck Township
area indicates a steep northerly dip to the LLCDZ.
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