VCMSM Report 8 - An evaluation of zirconium, niobium and rare earth elements in alkaline silicate igneous rocks in Victoria.
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Product description:Executive Summary:As part of the Developing Victoria's Critical Minerals Initiative, new geochemical, mineralogical and geochronological data were acquired to understand the presence and distribution of zirconium, niobium and rare earth elements in alkaline silicate igneous rocks of Victoria. This study includes a summary of Victorian alkaline magmatic events and related tectonism spanning the Ordovician-recent, from which four alkaline igneous complexes were analysed for critical minerals for the first time. Reconnaissance sampling found elevated concentrations in three of the four complexes, with values up to 2,630 ppm zirconium, 690 ppm niobium and 3,565 ppm total rare earth oxide. Concentrations vary between complexes, with: • Zirconium highest in the Den Hills Formation. • Niobium highest in the Barwite Igneous Complex; and • Rare earth elements highest in the Mount Leinster Igneous Complex. Although present in low volumes in the samples collected, minerals of economic interest including bastnäsite, monazite and xenotime occur throughout the complexes. Combining paragenetic observations with mass balance geochemical analysis reveals the source and controls on mineralisation, which vary between the complexes. This provides insights into the prospectivity of each complex and mineral exploration targeting. • At the Mount Leinster Igneous Complex, zirconium and niobium are elevated in late dykes. Rare earth elements are elevated in altered rocks and were introduced by a structurally controlled hydrothermal fluid. • At the Den Hills Formation, zirconium and niobium are elevated in altered rocks, introduced by a deuteric hydrothermal fluid. This fluid did not introduce rare earth elements, which were locally remobilised during alteration. • At the Gallows Hill Phonolite, zirconium, niobium and rare earth elements precipitated directly from the silicate magma. Deuteric alteration affected the mineralogy but did not remobilise zirconium, niobium or rare earth elements. • At the Gonzaga Monzonite, zirconium and light rare earth elements are enriched in altered rocks. Niobium and heavy rare earth elements are depleted in altered rocks. The source and mobility of these elements during alteration remains uncertain. New geochronology data collected from three of the complexes shows that they were emplaced in the Triassic and Jurassic periods. Triassic magmatism was initiated by distal plate boundary extensional mode switch events in the New England Orogen, and Jurassic magmatism was initiated by the breakup of Gondwana. The Mount Leinster and Barwite igneous complexes are both Triassic and coeval with the Toongi Alkaline Magmatic Field near Dubbo in New South Wales. Of all the units sampled in the study, the Gallows Hill Phonolite most closely resembles the Toongi zirconium, hafnium, niobium, tantalum and rare earth element deposit. The combined results of this study indicate that the mineralisation in each complex is likely to be heterogeneous. Further sampling is required to determine the extent of mineralisation in each of the complexes. Bibliographic Reference: Andrews, T.M., Pintér, Z, Cayley, R.A. & Boger, S.D. 2025. An evaluation of zirconium, niobium and rare earth elements in alkaline silicate igneous rocks in Victoria. Victoria’s Critical Minerals and Strategic Materials, Report 8. Geological Survey of Victoria. Department of Energy, Environment and Climate Action, Melbourne. 102 pp. Download: The downloadable version of this report is supplied as (PDF 95 MB), Attachment A1 (XLSX/ODF 64 KB), Attachment A2 (XLSX/ODF 64 KB) & Attachment A3 (XLSX/ODF 30 KB). | ||||||
