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

KVC are to the east or northeast, except in south-central Jamieson Township where southwest-facing
indicators at outcrop (pillow packing) and in drill core (graded felsic tuff units) suggest the presence of a
possible synclinal axis.
South of the Steep Lake fault (see Figure 20), the KVC consists largely of coherent rhyolite and
associated rhyolitic breccia and lapilli tuff, with lenses of mafic lava in northeast Carscallen and
northwest Bristol townships, and around and to the south of the Genex Mine. Farther north, the lower part
of the KVC consists largely of pillowed and massive mafic lava, whereas the upper part is dominated by
rhyolite (e.g., Ski-Hill and Godfrey Creek units: see Figure 20). A 150 to 200 m thick, northeast-facing
interval of tuffaceous sandstone and conglomerate, with minor graphitic mudstone is present in a series of
drill holes approximately 1 km northeast of the Kam-Kotia Mine. Similar sedimentary strata sectioned by
several drill holes in southern Jamieson Township appear to lie broadly along strike from the sections
northeast of Kam-Kotia and, if the westward facing reported from one Falconbridge core is discounted,
could represent a southeastward extension of that interval. Similar clastic rocks also occur in the Genex
Mine hanging wall (Hocker, Thurston and Gibson 2005a). As with re-deposited volcaniclastic facies
throughout the KVC, these intervals all appear to have been deposited by sediment gravity flows, and
there seems to be no evidence for deposition above storm wave base. The KVC sample set analyzed in the
present study is strongly bimodal, with a compositional gap between 56 and 72 weight % SiO 2 . Rhyolites
in the lower part of the KVC and at the level of the VMS deposits include FII and low-Yb FIIIb types,
with minor high-Yb FIIIb rocks, whereas rhyolites in the upper part of the KVC are uniformly of the
high-Yb FIIIb type.
Hart (1984) divided the KVC mafic volcanic rocks in Godfrey, Jamieson and Robb townships into
primitive and overlying, more evolved types. New geochemical data obtained in this study supports this
division, which is clear on plots of TiO 2 against Zr and P 2 O 5 (see also Hocker, Thurston and Gibson
2005a, p.18, Figure 6). The contact between the two types appears to coincide with the VMS-hosting
interval at the Canadian Jamieson and Kam-Kotia mines. On the Jensen plot, both types fall in the
tholeiitic basalt field, but lavas lying stratigraphically above the VMS deposits are more iron-rich than
those below. Both types have relatively flat chondrite-normalized REE patterns, generally with slight to
moderate negative Eu anomalies, but there is a consistent increase in total REE concentrations
stratigraphically upward from the primitive into the more evolved lavas. The mafic lavas from Carscallen
and Bristol townships fall in the alkali basalt field on the Nb/Y versus Zr/TiO 2 plot (see also Hathway et al.
2005, p.16, Figure 4). Their REE patterns are also unlike those seen in other groups, showing relatively
steep, smoothly S-curved negative slopes in the middle and light REE, and no Eu anomaly. These rocks are
geochemically distinct from the KVC tholeiitic basalts to the northeast. Given their stratigraphic position at
or near the base of the KVC, it is possible that they may represent part of the Kidd–Munro assemblage,
which is present farther to the southwest in Carscallen Township (Ayer, Amelin et al. 2002).
KAMISKOTIA GABBROIC COMPLEX
The Kamiskotia Gabbroic Complex (KGC) has generally been thought to be broadly coeval with the KVC,
which it underlies and intrudes (e.g., Barrie 1992). Barrie (1992) divided the KGC into four zones, of
which only the uppermost two are found in the present study area. Gabbro of the “Upper Zone” is exposed
to the northeast and southwest of Kamiskotia Lake and in a small area to the northeast of Steep Lake.
Remaining KGC rocks in the area are generally of felsic to intermediate composition and were included in
the “granophyre zone”, lying above and along strike with the Upper Zone, by Barrie (1992). A new age of
2704.8±1.4 Ma for a granophyric phase of the Upper Zone gabbro is younger than a previous age of
2707±2 Ma from the stratigraphically lower, Middle Zone gabbro in Turnbull Township (Barrie and Davis
1990). The new age is slightly older than (although within error of) the new age of 2703.1±1.2 Ma from
the lower part of the KVC. However, it is significantly older than the 2700.0±1.1 Ma KVC rhyolite age
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