Two new cassiterite reference materials for in-situ U-Pb dating from the European Variscan metallogenic belt
- 1ETH Zürich, IGP, ERDW, Zurich, Switzerland (lorenzo.tavazzani@erdw.ethz.ch)
- 2GeoRessources, Université de Lorraine, CNRS, Nancy, France
- 3Natural History Museum, Imaging and Analysis Centre, London, UK
Cassiterite (SnO2) is one of the dominant ore phases in tin-tungsten bearing magmatic-hydrothermal deposits. It can contain high uranium contents and usually hosts low levels of common Pb, making it one of the best U-Pb geochronometers among ore minerals [1]. The widespread use of in-situ techniques to obtain crystallization ages for cassiterite, however, is limited by a paucity of accurately characterized reference materials (RMs). Such shortage is mostly caused by the difficulty of achieving closed-system acid decomposition of this mineral, which represents the foundation of isotope dilution techniques, necessary for accurate and precise determination of U-Pb isotopic composition using thermal ionization mass spectrometry (TIMS) techniques.
In this contribution, we present a new set of U-Pb isotopic compositions of two cassiterite samples from the archetypal Variscan Sn-W greisen deposits of Panasqueira (Portugal) and Krasno (Czechia) obtained with an updated protocol of complete HBr decomposition of cassiterite in the presence of a U-Pb tracer, followed by U and Pb purification, and TIMS analyses. Previous to dissolution, the U-Pb isotopic compositions of the same cassiterite aliquots are characterized via laser-ablation-inductively coupled-mass spectrometry (LA-ICP-MS) and each cassiterite fragment is imaged with an ultra-fast washout laser ablation system to obtain high-resolution maps of the content and distribution of key trace elements (e.g. U, Pb, Fe, REE).
These two samples show variable but high U concentrations (2-20 ppm) and produce U-Pb isochron ages with 1% precision and low dispersion. We compare these new materials with established RMs (Yankee [2]; AY-4 [3]) and discuss their usability as primary reference materials for microbeam applications.
[1] Neymark, L. A., et al., Chemical Geology. 2018, 483, 410-425.
[2] Carr, P.A., et al., Chemical Geology. 2020, 539, 119539.
[3] Yuan, S., et al., Ore Geology Reviews. 2011, 43, 235–242.
How to cite: Tavazzani, L., Szymanowski, D., Carr, P., Guillong, M., Buret, Y., Cortes-Calderon, E. A., Mercadier, J., and Chelle-Michou, C.: Two new cassiterite reference materials for in-situ U-Pb dating from the European Variscan metallogenic belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16536, https://doi.org/10.5194/egusphere-egu24-16536, 2024.
