Further measurements on isotopic anomalies of ¹⁹⁶Hg/²⁰²Hg ratio in some of acid insoluble residues of Sikhote Alin and other iron meteorites

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In residues of several iron meteorites, obtained by dissolution of a metal piece in 2M H₂ SO₄, isotopic ratio of ¹⁹⁶Hg/²⁰²Hg has been measured by radiochemical neutron activation analysis in Hg fractions, released by stepwise heating. Both positive and negative deviations relative to terrestrial composition, have been found. Anomalies are more frequently observed in the high temperature fractions (200 < T < 600°C) as compared to the low temperature distillates (T ≤ 200°C). The largest deviations so far seen are, respectively, enrichment of ¹⁹⁶Hg by 67% in a 400°C fraction of Carlton and depletion of the same isotope by 86% in a 300°C fraction of Sikhote Alin residue (magnetic) of <38 μm grain size. The anomalous components appear to be sporadic and heterogeneously distributed. A lack of homogenisation of the two isotopes that are produced in different nucleosynthetic processes suggests that iron meteorites have been formed in a non-magmatic process, entrapping presolar grains. Alternatively, some foreign materials presumably of different isotopic compositions might have been introduced in meteorite parent bodies during their collisions with other cosmic objects and or dense cloud of interstellar dust.