Title: Rare element enrichment processes in LCT pegmatites and implications for geochemical exploration
Researchers: David Kaeter, Dr Julian Menuge
An increasing demand for consumer electronics and alternative energy sources lead to an increasing demand for high-technology elements. Important examples include Li and Ta: Lithium-ion batteries are used widely, from smartphones to electric vehicles; while Ta capacitors were vital for the size reduction of mobile phones. Both elements as well as Cs, which is an important component of drilling fluids, are enriched in rare-element pegmatites of the Li-Cs-Ta (LCT) family. Most pegmatites are simple consisting only of quartz, feldspar and mica and less than 1% of all pegmatites bear rare-element mineralisation. Processes leading to this exceptional enrichment of incompatible elements are not well understood. Crystallisation processes, pegmatite magma sources, pegmatite – wall-rock interactions and tectonic environments are all likely to play important roles.The increasing demand for Li resulted in current exploration by Blackstairs Lithium Ltd. (BLL), an Irish joint venture subsidiary of Ganfeng Lithium Corp. and International Lithium Corp., in a highly prospective area with known LCT pegmatite occurrences in the East Carlow Deformation Zone (ECDZ) at the eastern margin of the Caledonian S-type Leinster Granite.
Minerals in the Leinster LCT pegmatite suite (LPS) will be characterised regarding their microtextures and geochemical compositions, especially those enriched in strategic, rarer metals like Cs, Rb, Ta, Nb, and Sn, as well as variables such as Mn/Fe ratio. Geochemical variations within zoned crystals, or between different crystals of the same mineral, will be utilised to test different petrogenetic models for rare-element enrichment processes and pegmatite crystallisation, like Rayleigh fractionation, constitutional zone refining and immiscibility, and to characterise metasomatism and alteration. Sr, Nd, and O isotopic variations will be used to distinguish magma sources, test for possible assimilation of country rock and evaluate the effect and onset of hydrothermal activity and alteration processes. The timing of pegmatite emplacement relative to deformation in the ECDZ will be examined to assess its significance in rare-element mineralisation. Petrogenetic models derived from the LPS samples will be tested on LCT pegmatite samples from Brazil Lake, Nova Scotia, Canada, and refined if necessary.
The results will help in understanding the structural and geochemical relationships of spodumene-bearing and simple pegmatites and improve mineral exploration strategies for LCT pegmatites and specifically for rocks economically enriched in Cs, Ta and other rarer metals. In addition, a standard protocol for the analysis of rare-element minerals in pegmatites will be established within NCIG and iCRAG as a useful tool for mineral exploration.