2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 114-10
Presentation Time: 11:15 AM


MACKAY, Duncan A.R.1, SIMANDL, George J.2, MA, Wendy3, REDFEARN, Michael3 and GRCIC, Boja3, (1)School of Earth and Ocean Sciences, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2, Canada, (2)BC Ministry of Energy, Mines and Petroleum Resources, BC Geological Survey, PO Box 9333 Stn Prov Govt, Victoria, BC V8W 9N3, Canada, (3)Richmond, BC V7A4V5, Canada

The Aley carbonatite-hosted niobium (Nb) deposit is the most important Nb resource in British Columbia, Canada. The Aley carbonatite intrusion outcrops over an area of 3 to 3.5 km and intruded into sedimentary rocks as a sill prior to deformation and greenschist facies metamorphism. It consists of banded dolomite carbonatite surrounded by calcite carbonatite. The dolomite carbonatite phase consists of apatite, pyrite, calcite, and Nb-bearing minerals such as fersmite, pyrochlore, columbite-(Fe) and rare, fine-grained acicular aggregates of Nb-rich rutile. Lenses of phoscorite (magnetite, apatite, and phlogopite) are found throughout the dolomite carbonatite and contain Nb-bearing minerals, zircon, and interstitial carbonates. Dark blue-green fenite containing abundant richterite, arfvedsonite, and aegirine surrounds the carbonatite intrusion. The deposit has a measured resource of 113 million tonnes at 0.41 % Nb2O5 and an indicated resource of 173 million tonnes at 0.35% Nb2O5 with a cutoff grade of 0.20% Nb2O5 (Taseko Mines Limited, 2013). The 125 to 250 μm size fraction was selected as the optimal size fraction based on a portable XRF study of 12 sediment samples from the Aley carbonatite drainage area. A preliminary QEMSCAN study of two samples, one directly over the deposit and the second 8.8 km downstream, identified fersmite, pyrochlore, columbite-(Fe), monazite-(Ce), REE-bearing fluorocarbonates, magnetite, hematite, ilmenite, amphibole, pyroxene, apatite, rutile, and barite as potential indicator minerals. This presentation will show the results of ongoing research into heavy mineral separation using a Mozley Table (C800 Laboratory Mineral Separator) followed by detailed mineralogical, electron microprobe, and QEMSCAN studies of indicator minerals with an emphasis on the distribution of Nb-bearing minerals (pyrochlore, columbite, and fersmite) downstream of the Aley carbonatite. The results of this study will form a basis for optimization of indicator mineral methodology in exploration for carbonatite-hosted Nb deposits world-wide.