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

In northwest Cleaver Township, a felsic to intermediate tuff of the upper Tisdale assemblage has an
age of 2702±3 Ma, while a single grain yielded a concordant (inherited) age of approximately 2723 Ma
(98JAA-0011; Ayer, Amelin et al. 2002). SHRIMP analyses of sector and oscillatory-zoned domains
within these grains confirm a primary magmatic age at ca. 2700 Ma, but uranium concentrations in most
grains were too low to yield sufficient age resolution for a more precise conclusion using this method.
Despite this uncertainty, the presence of a significant population of zircon cores with ages in excess of the
primary, magmatic age is likely confirmed, and have 207 Pb/ 206 Pb ages ranging from approximately 2720 to
2735 Ma (Figure 9C; Appendix 2).
In northwestern Holloway Township, a heterolithic volcanic tuff breccia or debris flow unit within
the Porcupine–Destor deformation zone is a local host to the Lightning Zone gold mineralization at the
Holloway Mine. A sample of this unit (3D-CG) has been shown by Ropchan et al. (2002), on the basis of
the youngest analyzed zircon present, to be as young as 2686.8±1.8 Ma, or younger if the zircons are
recycled, while the presence of older zircon populations at ca. 2694 Ma and 2712 Ma attests to the
possible involvement of Porcupine (2685–2690 Ma) and Kidd–Munro (2712–2718 Ma) assemblage
components as xenocrysts or detritus. Spot age determinations carried out using the SHRIMP on
approximately 20 zircon grains from this sample confirm the presence of young, concordant age domains
near 2680 Ma and reinforce earlier conclusions that this sample was likely deposited as a component of
Timiskaming assemblage sedimentation (Figure 10A; Appendix 2). The cumulative probability plot
Figure 12. U/Pb SHRIMP results from Timiskaming assemblage sedimentary rocks in the Timmins area.
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