A single-column extraction chemistry for isotope dilution U-Pb dating of carbonate

•Isotope dilution analyses will likely remain the standard for precision and accuracy in carbonate U-Pb studies.•The “stacked resin” chromatography reduces analysis time by factor of two.•Loading samples in dilute HBr did not adversely affect U retention on TRU-resin.•Larger resin beds increased Pb blank (4.5pg Pb to 12pg Pb).•Protocol increases isotope dilution sample throughput while still utilizing acids and resins common to geochemical labs. U-Pb dating can provide age constraints on carbonate minerals from a wide range of geological settings. A major practical limitation, however, is the need for rapid and efficient extraction of Pb and U from large numbers of typically low-Pb (≤10ng/g) calcite samples, while maintaining low blanks (∼10pg Pb) and high Pb-U yields and purity. Here we describe a well-tested ion exchange procedure able to extract Pb and U from large (up to 200mg) calcite samples using a single pass over a mini-column filled with small (∼0.1ml) volumes of AG1-X8 anion exchange and Eichrom TRU-resins. This ‘stacked resin’ technique halves the time spent on elemental extractions and provides MC-ICPMS-ready Pb and U fractions in a single day. The method results in considerable savings in laboratory time and allows higher sample throughput, without negative impacts on data quality. It is ideally suited for high-precision U-Pb dating of speleothems where large numbers of samples need to be processed, but it is equally adaptable to calcites from other settings. While not explored as part of this work, the stacked resin technique should also be applicable to other carbonates (dolomite, ankerite, siderite).