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

previously identified as the Coulson–Rand assemblage (Jackson and Fyon 1991). Here the lack of an age
gap and the presence of xenocrystic zircons with an age of 2723 Ma indicates that it conformably overlies
the Stoughton–Roquemaure assemblage located to the north, despite the presence of the North Branch
Porcupine–Destor deformation zone at this contact. 2) In the north-central area, where it is complexly
infolded with the upper Kidd–Munro assemblage rocks in Dundonald and Clergue townships; and 3) west
of the Mattagami River fault in the northwest where a thick sequence of calc-alkalic volcanic rocks have
an age of 2719.5±1.7 Ma (Ayer, Amelin et al. 2002). In the latter area, it lies in faulted contact with a
northeast-facing unit of the upper part of the Kidd–Munro assemblage to the south, and has unknown
contact relationships with rocks assumed to be part of the Blake River assemblage to the north.
Upper Part
The 2717 to 2711 Ma upper part of the Kidd–Munro assemblage is the traditionally known part of the
Kidd–Munro assemblage as identified by Jackson and Fyon (1991). It extends across the northern part of
the study area (see Figure 2) and is dominated by tholeiitic mafic and komatiitic rocks with localized
accumulations of tholeiitic felsic volcanic rocks and graphitic sedimentary units. In the east, the basal
contact is interpreted to be conformable with underlying calc-alkaline volcanic rocks of the lower Kidd–
Munro assemblage to the north. To the west, the northern margin is in faulted contact with the Porcupine
assemblage. The southern margin lies in faulted contact with sedimentary rocks of the Timiskaming
assemblage along the Porcupine–Destor deformation zone (PDDZ) in the east, and the Porcupine
assemblage (Pipestone fault) to the west. West of the Mattagami River fault, the assemblage has been
sinistrally offset to the south by about 8 km. Here, both the northern and southern contacts are marked by
faults. New geochronologic samples with crystallization ages of 2712.3±2.8 Ma and 2714.6±1.2 Ma from
central Loveland and southern Thorburn townships (#1 and #2: Table 1, Figures 3A and 3B) confirm the
mapping-based interpretation of a northeast-facing package in faulted contact with the lower Kidd–Munro
assemblage in Thorburn Township to the north (see “Kamiskotia Area Subprojects”). In addition, one of
these samples was found to contain a pre-Abitibi-age xenocryst with an age of 2861.4±1.7 Ma (#2: Table
1, Figure 3A).
A less extensive part of the upper Kidd–Munro assemblage also occurs south of the Kamiskotia area.
Here, the assemblage faces to the northeast and unconformably overlies iron formations at the top of the
Deloro assemblage to the south (see above). Newly extracted zircons from a previously sampled
overlying felsic tuff in Carscallen Township (Ayer, Amelin et al. 2002) yielded a more precise
crystallization age of 2712.2±0.9 Ma (#8: Table 1, Figure 4B). This indicates an age gap of approximately
12 my exists between the unconformably underlying Deloro and the upper Kidd–Munro assemblages at
this locality. The newly analyzed zircons from this sample also revealed the presence of a discordant pre-
Abitibi xenocryst with an age of 2853.6±1.4 Ma (see Figure 4B).
TISDALE ASSEMBLAGE
Lower Part
The lowermost part of the Tisdale assemblage ranges in age from 2710 to 2706 Ma. It consists
predominantly of tholeiitic mafic volcanic rocks with localized accumulations of komatiite, intermediate
to felsic calc-alkaline volcanic rocks and iron formation. It is widespread in the central part of the map
area where it forms the nose and limbs of a broad west-closing synclinorium cored by the Blake River
assemblage (see Figure 2). The basal contact of Tisdale assemblage is marked by iron formation and chert
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