An improved Carius tube technique for determination of low concentrations of Re and Os in pyrites

Abstract

A simple and highly selective analytical method is developed for Re–Os dating in hydrothermal pyrites. Pyrites were first digested with HNO₃ in a 120 ml Carius tube. The released additional gas and a small portion of volatile Os (∼6% of total Os) were collected by 10 mol l⁻¹ of HCl in an ice-water bath. After the sulfides were totally reacted with HNO₃, the HCl solution containing all the released Os was transferred back to the Carius tube. The sample was further digested in aqua regia at 200 °C for about 10 h in a sealed Carius tube. Because prior digestion in an open Carius tube removed the additional gas, this improved technique allows increasing the sample mass to about 3 g, which is vital for Re–Os dating in Re and Os poor hydrothermal pyrites. Os was separated from the matrix by distillation and Re by anion exchange resin. The results obtained for molybdenite reference materials, JDC and HLP mixed with 3 g pyrite are in good agreement with certified values. Despite very low concentrations of Re and Os, the pyrite yields excellent repeatability and can be used for Re and Os poor hydrothermal pyrites.