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

The youngest dated synvolcanic mafic to ultramafic intrusion in the SAGB in Ontario is the
Montcalm gabbroic complex occurring west of the study area. This peridotitic to gabbroic intrusion hosts
the Montcalm Ni-Cu deposit. A gabbro from this complex has an age of 2702±2 Ma and is cut by a
granodiorite dike with an age of 2700+5/–4 Ma (Barrie and Davis 1990). These ages suggest the
Montcalm gabbroic complex is coeval with Blake River assemblage volcanism in the Kamiskotia area.
SYNTECTONIC INTRUSIONS
Syntectonic plutons are coeval with some of the major deformation episodes in the Abitibi and, later in
this report (see “Structural Framework”), we relate them to the various deformational events. This group
ranges in age from about 2695 to 2670 Ma and occurs throughout the Abitibi greenstone belt (Chown et
al. 1992; Corfu 1993; Mortensen 1993a, 1993b; Heather 1998; Davis et al. 2000). Early syntectonic
intrusions range from about 2695 to 2685 Ma and consist predominantly of tonalite, granodiorite, diorite
and feldspar±quartz porphyries, which are geochemically similar to the coeval Porcupine assemblage
volcanic rocks and have adakitic geochemical affinity (see “Intrusion Subproject”). These intrusions
range from foliated to massive and occur both as stocks within the greenstone belt and as major portions
of the surrounding batholithic complexes such as the Lake Abitibi, Nat River and the northern part of the
Kenogamissi batholiths. A new age of 2686.9±1.2 Ma from monzonite in the Clifford stock and
2688.5±2.3 Ma for an adjacent feldspar porphyritic dike (#34 and # 33: Table 1, Figures 7F and 7E,
respectively), are coeval with an age of 2689±1 Ma for quartz diorite from the Claris Lake stock in
Pontiac Township (Corfu and Noble 1992) and 2686.4±2.8 Ma for granodiorite in the Adams stock
(Frarey and Krogh 1986).
Numerous porphyries have been dated in the Timmins region with most ages ranging from 2691 to
2687 Ma (Corfu et al. 1989; Ayer, Barr et al. 2003). New geochronology on porphyries as a part of this
study include 2689.0±1.4 Ma from the Mount Logano porphyry in northeastern Shaw Township and
2686.2±1.1 Ma from a porphyry dike cutting Tisdale assemblage volcanic rocks in Adams Township (#23
and # 27: Table 1, Figures 6C and 6F), the latter age correlates well with an age of 2686.4±2.8 Ma in the
adjacent Adams stock (Frarey and Krogh 1986). A number of porphyry ages now provide better
constraints on the timing of deformation in the Timmins area (Bateman et al. 2005). These include an age
of 2689.3±4.5 Ma for a syntectonic granodiorite dike folded in D2 within the PDDZ immediately north of
the Kenogamissi batholith (Hall and Smith 2002); an age of 2687.2±2.2 Ma for a strongly foliated,
quartz-phyric sill interpreted to pre- to syn-D2 and 2684.4±1.9 Ma from a crosscutting quartz feldspar
porphyry intrusion, both of which occur at the Hoyle Pond Mine (Dinel and Fowler 2004) (#16 and #17:
Table 1, Figures 5B and 5C); and an age of 2677.5±2.0 Ma from a porphyry intrusion in the vicinity of
the Pamour Mine interpreted to be post-D3 (Bateman et al. 2005) (#19: Table 1, Figure 5E).
Late syntectonic intrusions range in age from about 2680 to 2672 Ma (Corfu 1993; Wilkinson,
Cruden and Krogh 1999; Ropchan et al. 2002) and, thus, are broadly coeval with the Timiskaming
assemblage. These intrusions are relatively small and occur in close proximity to the PDDZ and LLCDZ.
Compositions are typically alkalic, consisting of monzonite, syenite and albitite with the more mafic
phases consisting of diorite, gabbro, clinopyroxenite, hornblendite and lamprophyre. A previously
unreported sample was selected from strongly foliated syenite within the LLCDZ at the southern margin
of the Cairo stock in Cairo Township prior to this project (see Figure 2). The sample was selected in order
to test the age of the intrusion and to provide a maximum age for development of the LLCDZ at this
locality. The youngest zircons in the sample yield a crystallization age of 2676±1.4 Ma, but older
inherited zircons with ages of 2689 and 2720 Ma are also present (J.A. Ayer, OGS, unpublished data,
2005). A new sample of feldspar-phyric syenite cut by the main ore-controlling structure of the Kirkland
Lake fault (the Main Break), was collected from the Discovery Outcrop in Kirkland Lake (see “Kirkland
Lake–Larder Lake Subproject”). This syenite porphyry is the youngest and volumetrically most abundant
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