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Volcanic-hosted rare-metals deposit at Brockman, Western Australia

Mineralogy and geochemistry of the Niobium Tuff

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Rare-metals mineralization at Brockman, Western Australia, is the product of early pyroclastic eruption of trachytic magma enriched in volatiles and incompatible elements such as Zr, Hf, Nb, Ta, Be, Y and REE and Ga. The mineralization is fine-grained (<20 μm) and is the result of alteration and re-mobilization of comparatively simple magmatic precursor minerals such as columbite and zircon by F-rich deuteric solutions that were retained in an ash-flow tuff (the Niobium Tuff) following eruption. Chondrite normalized REE distributions show strong enrichment in HREE. Gel-zircon is the principal residence of the HREE, disseminated bastnaesite (±parisite and synchisite) carries the LREE and bertrandite, in late-stage calcite veins, is the host for Be. Ga occurs in K-mica in the groundmass. Trachytic flows overlying the Niobium Tuff contain many of the same ore minerals, but in trace amounts.

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Ramsden, A.R., French, D.H. & Chalmers, D.I. Volcanic-hosted rare-metals deposit at Brockman, Western Australia. Mineral. Deposita 28, 1–12 (1993). https://doi.org/10.1007/BF00199004

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  • Calcite
  • Niobium
  • Mineral Resource
  • Trace Amount
  • Incompatible Element