The concentration and isotopic composition of lead in Toluca iron meteorite

Introduction. Lead extracted from several iron meteorites has been found to be far more radiogenic than can be accounted for by the amount of uranium and thorium present in these same meteorites [Patterson, 1955; Starik et al., 1959, 1960; Marshall and Hess, 1961; Murthy, 1964]. This is similar in many respects to the excess radiogenic lead reported in some stone meteorites [Bate et al., 1957; Hamaguchi et al., 1957; Hess and Marshall, 1960]. The lead from one such iron meteorite, Toluca, has been studied in several laboratories, and the data from these former investigations are given in Table 1. Starik et al. [1959, 1960] analyzed lead from the metal phase and found its isotopic composition to be similar to that measured by them for lead in Canyon Diablo, Burgavli, and Aroos troilites. The latter analyses were considered by Murthy and Patterson [1962] to be of primordial lead and were included by them in their determination of an average value for the isotopic composition of primordial lead. Reed et al. [1960], by means of activation analyses on Toluca troilite, were able to obtain a value for the Pb208/Pb204 ratio in agreement with Starik's metal phase determination.