Anne Belanger

2008 - Michael Keen Memorial Awards

A suite of metamorphosed and hydrothermally altered sedimentary and chemogenic rocks were sampled from an area on the northern flank of Barrow River, Melville Peninsula (N 67^o24'08.44", W 82^o35'43.23"), Nunavut. The study area is in the Proterozoic Penryhn Group which lies within the Foxe Fold Belt of the Trans-Hudson orogen. On a regional scale, the Penryhn Group consists of interlayered politic and psammitic gneisses, amphibolites, marbles and calc-silicates, all intruded by continental arc and syn-collisonal plutons and pegmatites.

In order to identify the nature and extent of superimposed hydrothermal and metamorphic processes, samples were collected from 19 outcrops spanning an area of about 400 x 100 m. Sampled lithologies include amphibolites, granites, tourmalinites, greywackes and sulphide-rich rocks, typically with abundant fine-grained, euhedral tourmaline crystals. The presence of matrix K-feldspar and fibrolitic silimanite within tourmaline cores suggests upper amphibolite facies metamorphism. Sulphide-rich layers contain pyrrhotite and pyrite, however their abundance is highly variable throughout the sampling area.

The study area has been the focus of several mineral exploration projects, including those by Aquataine (1970) Borealis Exploration Limited (BEL; 1985-87), and BEL-BHP (1994-1996). Assays indicated concentrations of 2000-7000 ppb Au, with Zn contents locally over 9%. The area was classified as a "black shale" environment.

This report focuses on the petrography, composition, origin of tourmaline and evaluation of sedimentary-exhalative type deposit potential. At least two generations of tourmaline have been documented from petrographic and electron microprobe work; early tourmaline may be detrital while other crystals were generated in two stages of hydrothermal metamorphism and mineralization. Tourmalines range in colour from clear to light-brown; locally with darker cores that may have been inherited from originally detrital grains. Distinctive diamond-shaped oikocrysts, interpreted as pseudomorphs after tremolite, consist of medium-grained muscovite + tourmaline + silmanite cores with finer-grained albite + quartz + orthoclase + tourmaline rims. Torumaline compositions are Mg-rich (dravite) with variable Mg/(Mg+Fe) from 0.57 in cores but mostly 0.94-0.98 in rims. Boron and magnesium are believed to be derived from pre-metamorphic sediments. Dravite tourmaline, tourmalinites and diabase intrusive, within an intercontinental basin and a possibility for local rifting and minor concentrations of Zn, Pb and Au all suggest the study area could have been deposited with a sedimentary-exhalative environment.

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Pages: 100
Supervisors: David Corrigan / Rebecca Jamieson