Dissolving Experimental Research of Re-Os Isotope System for Bitumen Samples

The content of Re-Os in asphalt samples is relatively low, and CO₂ are released in digestion because of large amounts of organic matter. It is important to control the amount of asphalt in the sample and the proportion of oxidant to ensure the Os recovery and stability of the measured signal. The method for the Re-Os isotope was improved because of large amounts of organic matter contained in bitumen samples. The Oxidants was changed to 3 mL HCl, 4 mL HNO₃ and 3mL H₂O₂ from the original 3 mL HCl and 6 mL HNO₃, the improved method making the Os measured signal approximately 2 times larger than before. Changes in oxidants composition increase the amount of the bitumen sample weight greatly from th eoriginal 0.2 g to 0.4 g. Influence of H₂O₂ added with routine reverse aqua regia and direct distillation from a Carius tube on the signal intensity of osmium measured by Inductively Coupled Plasma-Mass Spectrometry(ICP-MS). was studied. Bitumen samples were dissolved and equilibrated with a known amount of ¹⁸⁵Re and ¹⁹⁰Os tracers in 2 mL HCl, 5 mL HNO₃ and 2 mL H₂O₂ by a Carius tube at 200℃ for 12 h and 240℃ for 12 h, with the Os and Re separated using direct distillation or routine distillation and solvent extraction techniques, respectively. ¹⁸⁷Re/¹⁸⁵Re, ¹⁸⁷Os/¹⁹⁰Os and ¹⁹²Os/¹⁹⁰Os were determined by ICP-MS. Bitumen samples in lead-zinc deposits from Yunnan Province were analyzed. The isochron ages was (60±2) Ma (MSWD=2.5, n=7), and the initial ¹⁸⁷Os/¹⁸⁸Os values was 4.36±0.14. The results show that Re-Os isotope is an effective tool to date bitumen samples and the Os in the bitumen originated from the crust. The established method can be used to date and trace the source of bitumen samples.