Christopher S. Holm-Denoma Richard J. Moscati Leonid A. Neymark 2018 <p id="sp0075"><span>Cassiterite (SnO</span>₂<span>), a main ore mineral in tin deposits, is suitable for U–Pb isotopic dating because of its relatively high U/Pb ratios and typically low common Pb. We report a LA-ICPMS analytical procedure for U–Pb dating of this mineral with no need for an independently dated matrix-matched cassiterite standard. LA-ICPMS U-Th-Pb data were acquired while using NIST 612 glass as a primary non-matrix-matched standard. Raw data are reduced using a combination of Iolite™ and other off-line data reduction methods. Cassiterite is extremely difficult to digest, so traditional approaches in LA-ICPMS U-Pb geochronology&nbsp;that utilize well-characterized matrix-matched reference materials&nbsp;(e.g., age values determined by ID-TIMS) cannot be easily implemented. We propose a new approach for in situ LA-ICPMS dating of cassiterite, which benefits from the unique chemistry of cassiterite with extremely low Th concentrations (Th/U ratio of 10</span>⁻⁴<span>&nbsp;</span>or lower) in some cassiterite samples. Accordingly, it is assumed that<span>&nbsp;</span>²⁰⁸Pb measured in cassiterite is mostly of non-radiogenic origin—it was initially incorporated in cassiterite during mineral formation, and can be used as a proxy for common Pb. Using<span>&nbsp;</span>²⁰⁸Pb as a common Pb proxy instead of<span>&nbsp;</span>²⁰⁴Pb is preferred as<span>&nbsp;</span>²⁰⁴Pb is much less abundant and is also compromised by<span>&nbsp;</span>²⁰⁴Hg interference during the LA-ICPMS analyses.</p><p id="sp0080">Our procedure relies on<span>&nbsp;</span>²⁰⁸Pb/²⁰⁶Pb vs<span>&nbsp;</span>²⁰⁷Pb/²⁰⁶Pb (Pb-Pb) and Tera-Wasserburg<span>&nbsp;</span>²⁰⁷Pb/²⁰⁶Pb vs<span>&nbsp;</span>²³⁸U/²⁰⁶<span>Pb (U-Pb) isochron dates that are calculated for a ~1.54 Ga low-Th cassiterite reference material with varying amounts of common Pb that we assume remained a closed U-Pb system. The difference between the NIST 612 glass normalized biased U-Pb date and the Pb-Pb age of the reference material is used to calculate a correction factor (F) for instrumental U-Pb&nbsp;fractionation. <span>The correction factor (F) is then applied to measured U/Pb ratios and Tera-Wasserburg isochron dates are obtained for the unknown cassiterite analyzed in the same analytical session. This allows for U-Pb dating of cassiterite of any age with no need for an independently dated matrix-matched reference material, nor assumptions about the<span> isotopic composition o</span>f common Pb.</span></span></p><p id="sp0085">Results for cassiterite from tin deposits in Bolivia, Brazil, China, Russia, Saudi Arabia, South Africa, Spain, and the United Kingdom, with ages ranging from ~20 Ma to ~2060 Ma, demonstrate the applicability of this approach across a broad range of geologic time. These ages are in good agreement with published geochronology of the&nbsp;host rocks assoc<span>iated with the tin deposits and with previously published U-Pb ages of some cassiterites from the same deposits. Thus, our in situ LA-ICPMS methodology verifies the use of cassiterite as a reliable U-Pb mineral-geochronometer with the advantages of fast and relatively low cost in situ analyses with moderate spatial resolution.</span></p> application/pdf 10.1016/j.chemgeo.2018.03.008 en Elsevier In situ LA-ICPMS U–Pb dating of cassiterite without a known-age matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary article