Abstract-High-precision Cu isotopic compositions have been measured for the metal phase of 29 iron meteorites from various groups and for four terrestrial standards. Cu. This correlation between nonmass-dependent and mass-dependent parameters suggests that the Cu isotopic composition of iron meteorites has not been modified by planetary differentiation to a large extent. Therefore, Cu isotopic ratios can be used to confirm genetic links. Cu isotopes thus confirm genetic relationships between groups of iron meteorites (e.g., IAB and IIICD; IIIE and IIIAB); and between iron meteorites and chondrites (e.g., IIE and H chondrites). Several genetic connections between iron meteorites groups are confirmed by Cu isotopes, (e.g., IAB and IIICD; IIIE and IIIAB); and between iron meteorites and chondrites (e.g., IIE and H chondrites).

We measured Cu isotope compositions of 12 out of the 14 known IVB iron meteorites. Our results show that IVB iron meteorites display a very large range of δ 65 Cu values (-5.84 ‰ < δ 65 Cu < -0.24 ‰; defined as per mil deviation of the 65 Cu/ 63 Cu ratio from the NIST-976 standard). These Cu isotopic data display clear correlations with W, Pt, and Os isotope ratios, which are very sensitive to secondary neutron capture due to galactic cosmic ray (GCR) irradiation. This demonstrates that δ 65 Cu in IVB irons is majorly modified by neutron capture by the reaction 62 Ni(n,γ) 63 Ni followed by beta decay to 63 Cu. Using correlations with Pt and Os neutron dosimeters, we calculated a pre-exposure δ 65 Cu of -0.3 ± 0.8 ‰ (95% conf.) of IVB irons that agrees well with the Cu isotopic compositions of other iron meteorite groups and falls within the range of chondrites. This shows that the volatile depletion of the IVB parent body is not due to evaporation that should have enriched IVB irons in the heavy Cu isotopes.

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