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

Porcupine assemblage (Ayer, Amelin et al. 2002). The southern margin of this unit occurs in Wesley and
Moody townships within the study area. The youngest detrital zircons from sandstone in Purvis Township
(just north of the study area) yielded a maximum age of deposition of 2698±2.4 Ma. Older detrital zircons
from this sample yield ages of 2745 Ma, 2725 Ma and 2715 Ma suggesting provenance from the Pacaud,
Deloro and Kidd–Munro assemblages, respectively. A significantly older detrital zircon with an age of
2825 Ma may have been derived from pre-Abitibi rocks of the Opatica Subprovince. All three of these
sedimentary units are included within the Porcupine assemblage and are interpreted to have had
unconformable basal contacts with older volcanic assemblages, but the contacts have been modified by
subsequent deformation and many are now the locus of regional deformation zones (see “Structural
Framework”).
Larder Lake South Area
A unit interpreted to be part of the Porcupine assemblage occurs in the southeast corner of the study area.
It was previously identified as part of the Hearst assemblage (Jackson, Fyon and Corfu 1994) and consists
of turbidites and heterolithic conglomerate. It unconformably overlies, and is complexly infolded with the
Larder Lake group volcanic rocks of the Tisdale assemblage. Two samples (a turbidite and a
conglomerate) were analyzed from northern Skead Township (see Figure 2) and the youngest detrital
zircon age detected was 2695.6±3.0 Ma with older detrital zircons at 2703 Ma, 2708 Ma, 2715 Ma and
2718 Ma (Ayer, Barr et al. 2003). Thus, the unit was deposited sometime after 2695.6±3.0 Ma. It is,
therefore, interpreted to be part of Porcupine assemblage, but, unlike the samples from the Timmins area,
the unit was lacking in a source for detrital zircons closer to the actual age of deposition (i.e.,