William M. Lucko HBSc thesis abstract

Thesis Title: 
The Pegmatites of the Quetico Gneiss Belt, Northwestern Ontario and their Uranium Potential
William M.

Reconnaissance studies along a roughly north-south traverse across the Quetico gneiss belt, utilizing roadcuts in Ontario Highway 527, have been made in order to characterize uranium-bearing pegmatites I and adjacent to the Gneiss Belt.  Analyses of samples by the Geological Survey of Canada revealed uranium contents ranging from less than 10 ppm U to 36.3 ppm in the pegmatites.

The pegmatites are of three distinct types: a granitic pegmatite showing intrusive relationships to all other rocks in the area, a migmatitic pegmatite intimately related to the gneisses of the Quetico Belt, and, a pink syenitic pegmatite emplaced in the high grade gneiss.  The granitic pegmatites are located near the north and south margins of the Gneiss Belt and extend into the adjacent Wabigoon and Shebandowan Wawa Greenstone Belts.  The pegmatites occur as dykes or lensoidal bodies of plagioclase-perthite-quartz with varying amounts of biotite and muscovite.  Accessory minerals include zircon, garnet, tourmaline, and rare hematite.  Apatite occurs in the most uranium-rich sample.

The syenitic pegmatite occurs as a dyke in the middle of the Quetico belt and is bordered by the migmatitic pegmatites.  Feldspars constitute 75% of the rock, and quartz 20%, with biotite and zircons as the accessories.  Uranium in the syenitic pegmatites is the lowest at 2.3 ppm.

The migmatitic pegmatites occur as lenses and migmatite bands most strongly in the centre of the Quetico Belt.  The pegmatites are feldspar-rick (ca. 75%) consisting of oligoclase with microcline exsolutions, quartz, muscovite, and minor corroded biotite.  Accessories include zircon, cordierite, sillimanite, garnet, and chorite.  The latter suggest that these pegmatites have been metamorphosed.  Boudinage and ptygmatic folding of small dykes is also observed.

Uranium in the migmatitic pegmatites was fairly uniformly distributed in the range of 2-7 ppm, but ranges to highs of 36.3 ppm in the granitic pegmatites.  No uranium mineralization was identified, but zircon is the probable host in most rocks.  The high value was found in an apatite-bearing rock, and this mineral is a likely host for uranium, as well.  The pegmatites do not seem likely prospects for economic deposits of uranium, owing to a lack of identifiably mineralization and low concentrations.  They may, however, be the ultimate source of disseminated uranium in the Sibley Group sandstones and unconformity-vein type uranium deposits in the Greenwich Lake area.