Development of a leaching procedure for isotopic study of metal/silicate partitioning experiments

Abstract

The ratio of 238U/ 235U has long been assumed to be constant and equal to 137.88. However, recent research has found that uranium fractionation occurs in a variety of environments, especially reducing environments. Fractionation in metal/silicate systems could be a contributor to Earth's geodynamo heating and affect Pb-Pb geochronology. Sixteen experimental iron/silicate samples were separated magnetically into iron and silicate fractions. Each fraction was leached with 2.5 M HCl, 10 M HCl, 10 M HCl at a higher temperature, and HF and the uranium released in each step was measured by mass spectrometry. The depleted nature of the uranium used to create the samples precludes high-precision isotope fractionation assessments. However, the effectiveness of the leaching procedure was examined for potential use on future samples. The U release pattern in silicate fractions was not consistent between all of the samples, and major element concentration measurements will allow identification of the phase being digested in each step. The contamination from silicate and graphite in the metal fractions prevents uranium from being accurately measured.