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

The revised age of 2672.8±1.1 Ma for the albitite dike provides a more robust maximum age
estimate for crosscutting gold mineralization at the McIntyre Mine. The dike age is also considered to be
identical within error to that of an intermineral dike (interpreted to represent a heavily altered
lamprophyre) cutting Timiskaming assemblage units at the Holloway Mine (Ropchan et al. 2002). Also,
the emplacement age for SM85-60 appears to be slightly younger than that determined for the
compositionally similar albitite dike intruding Tisdale assemblage ultramafic volcanic rocks from
Whitney Township (2676.5±1.6 Ma; see 04JAA-0010 below).
04JAA-0009 Heterolithic breccia, north Tisdale syncline, western Tisdale
Township
This sample was collected to test for the possible presence of Krist formation at the contact between
Porcupine assemblage sediments and underlying Tisdale assemblage volcanic rocks in the north Tisdale
syncline, western Tisdale Township. Although a heavy mineral separate was recovered from this sample,
no datable minerals were observed.
KCR.52 Porcupine greywacke, central Tisdale syncline, Tisdale Township
(NAD83, Zone 17 UTM 479026E, 5372271N; #14 on Figure 2 and Table 1)
A representative band of Porcupine Group greywacke was sampled across the central Tisdale syncline by
W. Bleeker (GSC) from Pamour Exploration drill hole NK90-04, over an interval between 320 and 400
feet depth. Here, steeply bedded greywackes overlie mafic volcanic rocks with an intervening transition
zone of black argillite (W. Bleeker, GSC, personal communication, 2004). An abundant and varied
assortment of zircon was recovered from this sample. Least paramagnetic and best quality populations
included large, slightly elongate, colourless to very pale brown prisms with minor rod inclusions, smaller,
well-faceted short prisms, medium-brown, euhedral to slightly rounded, short prisms, and elongate (~4:1)
square or four-sided clear, colourless prismatic grains.
Six air-abraded single detrital grains yield 207 Pb/ 206 Pb ages that range narrowly from approximately
2691 to 2700 Ma, although two fractions (A3, C1) are slightly discordant, and one of these is relatively
imprecise due to elevated common Pb (A3: Figure 4F; Table A1). The U/Pb geochronological results are
consistent with detritus having been sourced in uplifted, older Abitibi assemblages, which, in this sample,
appear limited to Blake River assemblage rocks (ca. 2696-2703 Ma), some of the older regional porphyry
suite intrusive rocks (ca. 2690–2691 Ma), or even recycled components of Krist formation fragmental
volcanic rocks (lower Porcupine assemblage; ca. 2687–2692 Ma). The most robust constraint on the
maximum age of deposition for this Porcupine unit is provided by single-grain fraction A1, which is
concordant at 2690.9±2.5 Ma (2σ).
04JAA-0003 Fine-grained wacke, Porcupine assemblage, eastern Tisdale
Township
(NAD83, Zone 17 UTM 484309E, 5371290N; #15 on Figure 2 and Table 1)
This sample represents a fine-grained greywacke within Beatty formation sandstones of the Porcupine
sequence directly underlying the Timiskaming angular unconformity in eastern Tisdale Township.
Sample 04JAA-0003 contained an abundant and diverse supply of nonmagnetic zircon, ranging from
clear and colourless narrow elongate prisms to large, medium-brown larger grains with or without
inclusions. Most grains show some evidence for sedimentary abrasion such as slight rounding of grain
edges or pitted surfaces. A selection of high-quality, clear single grains were chosen for air-abrasion and
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