Constant 4He Concentration and 190Pt-4He age of Detrital Pt-Alloy Grains from the Santiago River, Ecuador: Potential as a 4He Mineral Reference Material

Over the last few decades geo- and thermochronological techniques based on the accumulation of radiogenic ⁴He in minerals have gained popularity. Currently there is no mineral-based ⁴He reference material that allows routine screening of gas extraction and measurement procedures. The commonly-used mineral reference material for (U-Th)/He thermochronology have variable U and Th contents which result in variable ⁴He concentrations. Here we demonstrate that native platinum grains (RS-Pt) from placer deposits in the Santiago River, Ecuador, yield constant ⁴He contents and may be used as a reference material. Helium concentrations measured at the Scottish Universities Environmental Research Centre (n = 8) and Institute of Precambrian Geology and Geochronology RAS (n = 9) noble gas laboratories yield mean ⁴He concentrations that overlap at the 95% confidence level. The weighted mean ⁴He concentration is 215 ± 4 × 10¹¹ at g^-1 (2s) and mean ¹⁹⁰Pt-⁴He age is 39.6 ± 0.7 Ma (2s). Samples of the Santiago River Pt concentrate are available on request from the SUERC laboratory.