150 Geochronology of Critical Mineral Deposits with Special Reference to U-Th-Pb Dating of Common-Pb-Rich Minerals (Posters)

Radiometric dating of ore deposits containing critical minerals. Studies discussing analytical aspects of methods such as U-Th-Pb, Ar-Ar, Rb-Sr, Sm-Nd, Re-Os and/or using radiometric ages for ore genesis research or critical mineral resource evaluation.

Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

U-Pb dating of dolostone: am I projecting?

Paper number: 150-1
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

U-Pb dating of dolostone via LA-ICPMS is an emerging technique, which is potentially attractive due to dolostone’s relatively strong weathering-resistance and relatively high U concentrations.  This study seeks to: 1) test the viability of U-Pb dating of dolostone on samples of known age, 2) identify a matrix-matched reference material for LA-ICPMS dating, and 3) assess differences in matrix-induced fractionation for calcite vs. dolomite.  To that end we have analyzed hundreds of dolomite and dolostone samples, including:  1) roughly thirty ‘gemmy’ hydrothermal dolomite specimens from around the world, 2) Paleozoic dolostones from the Champlain Valley of Vermont, and 3) late Proterozoic and Paleozoic dolostones from the Kingston Peak Range of Nevada.  Initial results suggest that hydrothermal dolomite tends to be enriched in common-Pb and generally unsuitable for isochron dating.  In contrast Proterozoic and Paleozoic sedimentary dolostone often has measurable 238U/206Pb ratios that define an isochron, but ratios are rarely above ~5.  Curiously, isochrons constructed from these lower 238U/206Pb ratio shots tend to consistently underestimate the true age of the dolostone, rather than scatter randomly.  In contrast, we obtain relatively accurate isochron ages from dark-colored, presumably organic-rich, dolostones that produce the highest 238U/206Pb ratios with the most accurate isochron ages. Efforts to identify a suitable dolostone reference material have so far failed given the typically low 238U/206Pb ratios of dolostone.  However, experiments using a TIMS-dated dolomite specimen as a primary reference material demonstrate up to 20% differences in 238U/206Pb fractionation between calcite and dolomite analyzed in the same analytical session.  These differences are magnified at low laser energies and underscore the potential pitfalls of U-Pb dating of dolostone relative to a calcite reference material.

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

doi: 10.1130/abs/2025AM-414363

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