Patterns of compositional zoning are documented in nine grains of magnesiochromite–chromite (Mgc–Chr), 0.3–0.4 mm in size, subhedral or subrounded, recovered from six placer deposits in British Columbia. Their core zones correspond to Mgc or magnesian Chr, mantled by zones of Chr. A rim of Zn-rich chromite (9.1% ZnO) occurs in one grain. In most of these grains, Fe2+ increases and Mg decreases toward the margin. In contrast, an “anomalous” rim, slightly richer in Mg than the core, is developed in one grain, in which an increase in Mg (=2% MgO) is accompanied by a corresponding increase in Fe3+, Al, minor Ti, and by a decrease in Fe2+ and Cr. In the other zoned grains, contrasting trends are documented for Fe3+ and Cr, which decrease [...]
