Chemical Classification of Iron Meteorites: XII. New Members of the Magmatic Groups

Abstract

Data are reported for thirty iron meteorites that are members of the magmatic groups, for three main group pallasites, one anomalous mesosiderite, and for three ungrouped irons and an ungrouped pallasite that are similar to IIIAB irons in their Ni, Ga, and Ge contents. The set includes four observed falls (11% of iron falls) Ban Rong Du, Chisenga, Nyaung and Sterlitamak, and Zaisho, one of two known pallasite falls. Two of the ungrouped irons (Ban Rong Du and Mount Howe 88403) and the ungrouped pallasite Yamato 8451, although having Ni, Ga, and Ge contents in the same general range as IIIAB, have very different contents of Co and exhibit significant differences for several other elements; they are clearly not related to IIIAB or to its little sister, group IIIE. A fourth ungrouped iron, Tres Castillos, chiefly differs from IIIAB in terms of its low Ga and high Ge contents; its Ga/Ge ratio is 35% higher than that of any other IIIAB iron. We report data on four new IIAB irons, all falling within established fields; the Bilibino iron is somewhat unusual, having a low Ir content (0.12 μg/g) and a structure altered by reheating. The IVA irons are also typical. One, Albion, may be a mislabeled specimen of Gibeon; another, Page City, exhibits large cracks (up to 3 cm). The Chaunskij anomalous mesosiderite has exceptionally high Ni and very low Ir concentrations. Two of three new main group pallasites are anomalous; Pecora Escarpment 91004 has an Ir content above the normal range, and Zaisho has an exceptionally high Fa content in the olivine.