A Rapid Method to Determine the Re-Os Age and Re Content of Molybdenite by Inductively Coupled Plasma-Mass Spectrometry

Re-Os isotope method is a powerful tool for dating ore deposits, but digesting samples with the Carius tube is complicated and dangerous.A simple and quick method to determine the age of molybdenite Re-Os and Re content has been established.5-15 mg of molybdenite samples were digested with 3 mL HNO₃ in a 10 mL colorimetric cylinder.Molybdic acid in solution was removed by a centrifuge, the supernatant of the solution was then diluted to an appropriate volume.M187/M185 ratio of the resulting solution was determined directly by Inductively Coupled Plasma-Mass Spectrometry(ICP-MS).According to the principle of radioactive decay, it can be inferred that the mass ratio is positively correlated with the age.The Re-Os age of the sample can be calculated by comparing with the M187/M185 ratio of the molybdenite standard material(JDC and HLP).The Re content in the sample can be calculated on the basis of ¹⁸⁵Re counting using the relative method.In order to test the reliability of this method, a series of molybdenite samples, whose ages vary from 13.26 Ma to 2130 Ma, were analyzed.The resulting ages were generally identical to the reference ages within 0.36%-7.42% deviations.The samples with older ages yield better results because the ¹⁸⁷Os is more radiogenic.This method, without spike addition, can avoid the trouble of sealing and opening the Carius tube and the process of separating and purifying Re and Os, which significantly improves the experimental efficiency.This simple and quick method is highly suitable for the preliminary analysis of molybdenite Re-Os ageing.