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

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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 γ-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 nonmagnetic 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.