Abstract
An Os isotope stratigraphy is one of the most powerful tools to determine the sedimentation age of Fe-Mn crusts. Since a typical growth rate of Fe-Mn crust is very slow such as several mm/Myr, the Re-Os isotope analysis with a high-resolution sampling is required for precise age determination. Fine-scale sampling with a metallic drill is a common technique, but such sampling decreases the amount of sample powders, which in turn arises a necessity for a low-level Re and Os blank analysis to obtain an accurate isotope composition. Thus, in the present study, our main goals are (1) evaluation of Re and Os contamination amounts through drill sampling using three types of metallic drills, (2) measuring Os amounts in acid reagents that we use for sample digestion, and (3) investigating Os blank during a Carius tube digestion method under various heating temperature and time conditions. The Re contamination amounts through drill sampling reached ca. 50 pg despite of the drill material. On the other hand, the Os contamination amount through drill sampling can be negligible only when a tungsten carbide (WC) drill was used for sample preparation. The Os amount and 187Os/188Os ratio of TAMAPURE AA-10 HNO3 solution were much higher than those of electric industrial grade (EL) and special grade HNO3 solutions. It has been also turned out that the Os blank did not depend on the heating temperature and time conditions in the Carius tube. Consequently, drill sampling using a WC drill combined with low Os blank acid digestion by EL inverse aqua regia in a Carius tube allows us an accurate Os isotope analysis of Fe-Mn crusts.
