Project

My Ph. D. project focusses on the Little Nahanni Pegmatite Group, a rare-element pegmatite swarm which is spectacularly exposed in the Mackenzie Mountains of the Northwest Territories. Geochronological, geochemical, structural, and fluid inclusion studies are being combined with an isotopic study of lithium to look at the formation of a pegmatite dike swarm in the context of the regional geology.

Lithium
Lithium has two naturally occurring stable isotopes, ⁶Li and ⁷Li, with an abundance of 7.6% and 92.4% respectively. The large mass difference between them (~17%) can result in distinctive isotopic signatures in low temperature geological conditions. The measurement of lithium isotopes has been used to study hydrothermal and weathering processes as well as tracing the path of subducted crust through the mantle. While molten basalt is too hot to permit Li isotope fractionation the cooler temperatures of granitic pegmatite crystallisation (400-500°C) lie within the upper temperature limit.

This part of the project will culminate in the analysis of mineral separates from the Little Nahanni pegmatites to determine their lithium isotopic signature and whether isotopic fractionation occurred during the crystallisation of the pegmatites, and if so what that can tell us about their formation.

In conjunction with the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at UBC I am currently working on setting up the procedures required to analyse lithium isotopes on the Nu Plasma MC-ICP-MS. Results fron the initial work on the analytical procedures are good allowing me to focus more on mineral sample dissolution and column chemistry. Lithium fractionates very easily which necessitates a 100% collection of Li in the eluent from the column. If the first fraction of lithium is missed the samples will be deficient in ⁷Li, and if the last fraction is missed ⁶Li is left behind.

Cavell, R. G., Barnes, E. M., Arboleda, P. H., Cavell, P. A., Feng, R., Gordon, R. A., Webb, M. A., 2004. An X-ray and electron microprobe study of Fe, Ni, Ga and Ge distribution and local structure in a section of the Canyon Diablo meteorite. Am. Min. 89, No. 4, p. 519-526.

Barnes, E. M., and Anderson, R. G., 1999. Mineralogy of amygdaloidal, mafic flow rocks of the Endako Group in the Kenney Dam area, northeastern Nechako River map area, central British Columbia. in Current Research 1999-A/B, Geological Survey of Canada, p. 9-20.

Barnes, E. M., and Anderson, R. G., 1999. Bedrock geology of the Uncha Mountain area, northwestern Nechako River area, central British Columbia. in Current Research 1999-A/B, Geological Survey of Canada, p. 129-138.

Anderson, R. G., Snyder, L. D., Resnick, J., and Barnes, E. M., 1998. Geology of the Big Bend area, central British Columbia. in Current Research 1998-A/B, Geological Survey of Canada, p.145-154.