¹⁹⁶Hg/²⁰²Hg ratio and Hg content in meteorites and terrestrial standard rocks: a RNAA study

Abstract

Radiochemical neutron activation was applied for the determination of mercury isotopic ratios (¹⁹⁶Hg/²⁰²Hg) for standard rock samples and meteorite samples. After neutron activation, Hg was released upon heating from 100°C to 500°C at 100°C steps and the activity ratio of ¹⁹⁷Hg/²⁰³Hg was measured for each released fraction. After the correction for the interfering g-rays of ⁷⁵Se to ²⁰³Hg, the ratios obtained from the Dhajala meteorite (bulk and magnetically separated samples) were identical to those of the Hg monitor as well as standard rock samples (JB-1, basalt, and JG-1, granodiorite). An apparently low ratio of ¹⁹⁶Hg/²⁰²Hg was observed at high temperature (500°C) for the Allende meteorite reference sample. As such a low value was not reproduced in another run, the presence of isotopically anomalous Hg in the Allende reference sample can not be concluded. Hg/Se ratio was observed to be very high in the non-magnetic fraction of Dhajala compared with that in the magnetic fraction, suggesting that Hg is less chalcophile than Se. Yamato 82050 (CO3) has an anomalously high content of Hg with a normal ¹⁹⁶Hg/²⁰²Hg ratio, being at least an order of magnitude higher than the expected value. This meteorite must have been contaminated with Hg, presumably on Antarctica.