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

Abstract

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.