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

04MGH-0523 Intermediate volcaniclastic, south-central Langmuir Township
Sample 04MGH-0523 was collected from a sequence of intermediate epiclastic rocks found within
“Supracrustal Package B” or “Supracrustal Package C”, located in the south-central part of Langmuir
Township. Although dating was targeted to resolve Tisdale versus Deloro assemblage ages southeast of
the Shaw Dome, no accessory phases were found in the heavy mineral concentrate from this sample that
were amenable to U/Pb geochronology.
96TB-099 Fragmental felsic volcanic, southern Langmuir Township
(NAD83, Zone 17 UTM 499477E, 5352378N; #26 on Figure 2 and Table 1)
Because of the same issues related to the occurrence of previously dated Deloro-age rocks—outside of the
core of the Shaw Dome and apparently within the adjacent Tisdale stratigraphy—the same approach used
with sample C88-17 (see above) was applied here. Namely, the purpose was to test for the possible
influence of inherited or xenocrystic zircon grains on the determined age of 2723.4±1.5 Ma (Barrie 1999;
Barrie and Corfu 1999) for the fragmental felsic volcanic (“dacite”) unit from Langmuir Township
(sample 96TB-099).
Three additional clear and colourless single zircon fractions were prepared for this sample, two of
which represent euhedral short prisms, while a third is a euhedral, equant grain. The new U and Pb
isotopic data for all three analyses cluster tightly on concordia (Table A1; Figure 6E, unshaded ellipses).
This cluster overlaps directly with the most concordant three data points of Barrie (1999) and Barrie and
Corfu (1999). With the exception of new fraction Z-C, which appears to be marginally older
(xenocrystic?), a regression of all 4 points from Barrie and Corfu (1999; shaded ellipses in Fig. 6E) and
new analyses Z-G and Z-H yields an upper intercept age of 2723.1±1.3 Ma (69% probability of fit;
MSWD = 0.56; lower intercept = 207 Ma). This age is identical to, but slightly more precise than, the
previous age of Barrie (1999) and Barrie and Corfu (1999), and confirms that the felsic volcanic at this
locality belongs to the Deloro assemblage.
04MGH-0523 Intermediate volcaniclastic, south-central Langmuir Township
Sample 04MGH-0523 was collected from a sequence of intermediate epiclastic rocks found within
“Supracrustal Package B” or “Supracrustal Package C”, located in the south-central part of Langmuir
Township. Although dating was targeted to resolve Tisdale versus Deloro assemblage ages southeast of
the Shaw Dome, no accessory phases were found in the heavy mineral concentrate from this sample that
were amenable to U/Pb geochronology.
04MGH-0283 Intrusive porphyry, Eldorado Township
(NAD83, Zone 17 UTM 487699E, 5351167N; #27 on Figure 2 and Table 1)
Sample 04MGH-0283 represents a quartz-feldspar porphyry intrusive unit, intersected in drill core (Inco
DDH-87615; Box 86, 1574.6–1582.8 feet interval) on the Redstone property in Eldorado Township. The
unit is interpreted to occur within Tisdale assemblage stratigraphy in the footwall to the main Redstone
property mineralized horizon. Zircons recovered from this sample are abundant and of generally good
quality, mostly occurring as slender, elongate prisms up to about 4-5:1 (length:width). Generally, these
grains are clear and either colourless or pale-medium brown, and have square, or, more rarely, flat crosssections.
High-quality representative grains were selected for air abrasion and isotopic analysis.
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