166-13 Red beryl: Enigmatic gemstone is a U-Pb geochronometer

Session: Mineralogical Characterization of Economic Resources: From Critical Minerals to Gemstones

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Rarer than diamond and more valuable than gold, red beryl is an elusive gemstone found only within vugs or alteration fissures in specific topaz rhyolite layers in the southwestern USA. Red beryl can contain high U (10s to 1000s ppm). This study dates red beryl crystallization with U-Pb by laser-ablation inductively-coupled plasma mass spectrometry at five localities in three ranges, yielding concordant dates at precision comparable to zircon U-Pb and far higher than coeval sanidine K-Ar and zircon fission-track dates. U-Pb dates for the famous gems from the Ruby Violet Claim (20.96 ± 0.23 Ma) of the Wah Wah Mountains, UT and specimens from the Snowflake Claim (24.96 ± 0.29 Ma) of the Black Range, NM are consistent with previous regional geochronology. In contrast, while dates from Searle Canyon (5.41± 0.07 Ma) and Maynard’s Claim (6.75 ± 0.39 Ma) in the Thomas Range are also compatible with expectations, dates from Wildhorse Spring (22.31 ± 0.23 Ma) reassign the red beryl-bearing layer to Spor Mountain volcanism. Red beryl provides direct age constraints on late-stage vapor outgassing, capturing the climax of magmatic system lifecycles, not recorded by conventional geochronometers, which typically crystallize within magma chambers or during eruptions. This research indicates that when beryl or other gem minerals have elevated U they are worth targeting as possible geochronometers and can provide unique insights into magmatic and mineralization histories.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9398

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