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Shrimp U-Pb zircon and opal geochronology, isotope geochemistry, and genesis of the super large Be deposit at Spor Mountain, Utah, USA

December 31, 2018

Ongoing studies of the Spor Mountain beryllium (Be) deposit are focused on (1) characterizing the role of igneous rocks in the genesis of the ore zones, (2) determining the timing and duration of magmatic-hydrothermal events, and (3) establishing processes related to beryllium transport and accumulation. The Spor Mountain Formation (SMF) hosts the deposit, which is the largest known volcanic rock-related Be deposit in the world. Discovery of the Be deposit at Spor Mountain in the 1960s displaced beryl as the main commercial source of beryllium in the global supply chain. Technological advances in mineral processing enabled bertrandite (Be4Si2O7(OH)2) ore of variable grade and composition from Spor Mountain to compete with beryl ore derived from pegmatite. The deposit currently accounts for approximately 85% of the global beryllium mine production.
The Be deposit is in the Basin and Range province of North America, which is characterized by Oligocene and Eocene calderas, extensive alkalic rhyolitic lava and ash flow tuffs, widespread uranium and fluorite occurrences, and Precambrian to Paleozoic sedimentary rocks. The SMF consists of a hydrothermally-altered, fluorite-bearing, lithic-rich (clasts of carbonate, quartzite, and older volcanic rocks) pyroclastic tuff (informal name: Be tuff member) that is overlain by altered, porphyritic, and topaz-rich rhyolite (alkali rhyolite member). The tuff encloses elongate mineralized layers containing numerous nodules that consist of calcite, chalcedony, opal, fluorite, and bertrandite (Be4Si2O7(OH)2, the main ore mineral.