119 Recent Advances in Economic Geology (Posters)

Monday, 20 October 2014
9:00 AM - 6:30 PM
Exhibition Hall C

INDICATOR MINERALS AND STREAM SEDIMENTS IN EXPLORATION FOR CARBONATITE-HOSTED NB DEPOSITS, ALEY CARBONATITE, BRITISH COLUMBIA, CANADA

Paper number: 119-10
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

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.