Hydrothermally altered Beryl-Columbite subtype Pegmatite
Hydrothermal (Au-Te-Bi) + Pegmatite (Rare element, Beryl)
Required Geological Setting
Occurrence
The beryl-columbite subtype rare-element pegmatites subjected to very low temperature hydrothermal alteration. Pegmatites were altered by 100 - 200 degree hydrothermal fluid at 70 MPa (2 km depth). Together with same minerals as the Au-Bi-Te hydrothermal deposit by low temperature hydrothermal fluids, euclase, bertrandite, and chrysoberyl were formed by decomposition of beryl. Euclase was formed at slightly higher 200 degree, and Bertrandite was formed at 100 degree or less.
Mineral Assemblages (Pegmatite residues)
Quartz, Feldspar, Schorl, Columbite-(Fe), Tantalite-(Fe), Beryl
Mineral Assemblages
Gold, Bismuth, Bismuthinite, Kaolinite, Euclase (High temperature), Bertrandite (Low temperature), Chrysoberyl