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Lithium Pegmatite Exploration in the Omeo Zone (NE Victoria, Australia): Evaluating Prospectivity Using Ta-Nb Oxides

Rosa Didonna1; Tom Andrews2; Zsanett Pinter1; Will Smith1

  • Affiliations: 1Mineral Resources, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Kensington, WA, Australia 2Geological Survey of Victoria (GSV), Department of Energy, Environment and Climate Action, Melbourne, Australia

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 19

  • Programme No: 4.1.10

  • Theme 4 > Session 1

Abstract

Lithium (Li) is a critical metal essential for green technologies, playing a key role in enabling the transition to a low-carbon energy future. It is primarily concentrated in closed-basin brines, volcanic clays, and lithium-caesium-tantalum (LCT) pegmatite deposits. Most Australian LCT pegmatites are located in Western Australia, such as the world-class Greenbushes Li-pegmatite deposit. Despite there is potential for additional pegmatitic deposits across Australia, as demonstrated by Li, Ta, Sn, and Nb exploration activities in Victoria, the exploration workflows for Li deposits remain poorly established due to their complexity of mineral assemblages, coupled with the limitations of geophysical detection techniques. Here, we focus on the Omeo Zone in northeastern Victoria (SE Australia), testing innovative characterisation and exploration workflow. Our investigation goes beyond conventional whole-rock composition methods by integrating microscopic-scale techniques (e.g., automated mineralogy, mass-spectrometry analyses) applied to indicator minerals such as Ta-Nb oxides. We examine mineralogy, textures and fine-scale compositional zoning patterns in Ta-Nb oxides hosted by mineralised and unmineralised pegmatites. Fractionation trends are characterised by an increase in the Ta/(Ta+Nb) ratio with minimal or no changes in Mn/(Mn+Fe), reflecting high Ta solubility in the silicate melt during fractionation. Mineralised pegmatites commonly host Ta-Nb oxides displaying distinct core-to-rim compositional variations (e.g., high Nb-low Ta core, high Ta-low Nb rim), while more complex zonations are recorded among barren pegmatites (e.g., oscillatory and patchy zonings). This research provides insights into the magmatic-hydrothermal history of Li pegmatites, elucidating Ta-Nb oxides fractionation and crystallisation processes to refine exploration workflows and more efficiently target Li resources.