Red beryl gemstone is a U-Pb geochronometer with implications for Be exploration

Abstract

Red beryl is a rare gem found in vugs or fissures in specific topaz rhyolite layers in the southwestern United States. Unlike other beryl, it contains high U (tens to thousands of parts per million). This study provides U-Pb dates for red beryl crystallization from five localities in three ranges, yielding robust laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) dates at higher precision than coeval sanidine K-Ar and zircon fission-track dates. U-Pb dates for specimens from the Ruby Violet Claim (20.96 ± 0.23 Ma) of the Wah Wah Mountains, Utah, Snowflake Claim (24.96 ± 0.3 Ma) of the Black Range, New Mexico, and Searle Canyon (6.69 ± 0.12 Ma) and Maynard’s Claim (6.87 ± 0.11 Ma) in the Thomas Range, Utah, are compatible with prior regional age constraints. However, red beryl dates from Wildhorse Spring, Utah (22.34 ± 0.20 Ma), are older than the expected age of ca. 6 Ma. These data reassign the red beryl−bearing layer to Spor Mountain volcanism, the host to the world’s largest Be deposit, indicating that a wider region should be explored for Be mineralization. Red beryl provides direct age limits on outgassing, capturing very late-stage volcanic processes not recorded by common geochronometers, which typically form within magma chambers or during eruptions. Our results show that if red beryl, a gem, or other unusual minerals have elevated U, they should be targeted as possible geochronometers.