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

north of the Warden Hill fault. Thus, the Potter and Potterdoal mines are interpreted to be time-stratigraphic
equivalents (Arndt, Naldrett and Pyke 1977; Coad 1976; Epp 1997; Péloquin, Houlé and Gibson 2005). In
both cases, the massive sulphides are related to volcanic fragmental rocks occurring at the contact between
the tholeiitic and komatiitic units (Gamble 2000; Gibson and Gamble 2000; Epp 1997). The presence of
interflow sedimentary and volcaniclastic units at the mafic–ultramafic contact along strike from the
Potterdoal deposit, and between Theo’s and Fred’s flows on the north limb of the McCool syncline (south of
the Warden Hill fault), as well as the extension of the mafic–ultramafic contact under the overburden to the
east, indicates further potential for volcanogenic massive sulphide mineralization.
CURRIE TOWNSHIP
Currie Township is dominated by the basaltic rocks of the lower Tisdale and lower Blake River
assemblages (Figure 24). Although, the intermediate to felsic volcaniclastic rocks, argillites and
greywackes of the upper Tisdale assemblage are a lesser component of the geology of the township and
very rarely crop out, they are important in that they host the Currie (Tillex) base metal showing. The
assemblage boundaries are interpreted from the magnetic signature of the units and from drill core.
The stratigraphic succession in Currie Township is generally east-west striking, vertical to southward
dipping and southward younging where facing directions were observed. The stratigraphic sequence from
north to south is lower Tisdale, upper Tisdale and lower Blake River assemblages. The lower Tisdale and
the lower Blake River assemblages are dominated by mafic flows. The upper Tisdale assemblage
(including the “Marker Horizon”) is dominated by felsic tuffs (including feldspar crystal tuffs), mafic to
intermediate tuffs and sediments (argillites and greywackes). Proterozoic diabase dikes and Archean
porphyry dikes crosscut the volcanic assemblages. The porphyry dikes resemble the feldspar crystal tuffs
of the upper Tisdale assemblage.
Based on limited geochemistry, the basalts in the lower Tisdale and lower Blake River assemblages
are dominantly tholeiitic. However, one sample from a porphyritic pillowed flow in the lower Blake River
assemblage is geochemically similar to the upper Tisdale assemblage intermediate volcanic rocks. The
geochemistry of the upper Tisdale assemblage tuffs shows them to be calc-alkalic in affinity. Multiple
geochemical populations are recognized in the upper Tisdale assemblage, possibly due to variations at the
source and/or in subsequent crustal contamination.
The volcanic rocks of Currie Township are deformed. In general, the rocks in all of the assemblages
exhibit well-developed east-west subvertical schistosity. A large-scale fold is recognized in the magnetic
signature of the lower Blake River assemblage. In drill core of the upper Tisdale assemblage, the
schistosity is seen to be bedding parallel, and zones of strong deformation and fault gouges, also bedding
parallel, were observed. In general, the upper Tisdale assemblage is more deformed than the lower
Tisdale and lower Blake River assemblages. The upper Tisdale assemblage tuffs and sediments may have
been more susceptible to deformation and acted as a corridor where higher strain was focussed; the
existence of a strata-parallel fault occurring at or near the upper Tisdale–lower Blake River assemblages
contact should not be ruled out.
In the upper Tisdale assemblage, the porphyritic dikes form 2 main geochemical populations
equivalent to populations observed in the volcanic rocks of that assemblage. The porphyritic dikes from
the lower Tisdale and lower Blake River assemblages are geochemically similar to the volcanic rocks and
porphyry dikes of the upper Tisdale assemblage. This similarity between the porphyry dikes in all the
assemblages and to the upper Tisdale assemblage volcanic rocks suggests that they are co-magmatic. The
magmatic event responsible for the upper Tisdale assemblage volcanic rocks, therefore, has an intrusive
expression, and the event continued during the deposition of the lower Blake River assemblage.
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