Minor elements in perovskite from kimberlites and distribution of the rare earth elements: An electron probe study

Abstract

We report REE and minor element distributions for perovskites from seven kimberlites (South Africa and U.S.A.). The REE (1.6–6.3 oxides wt.%) are always strongly light REE enriched, often with Ce > La (chondrite-normalized), and show an expected close correlation with whole-rock analyses. Where examined, perovskite contains far more REE than coexisting apatite, by about an order of magnitude. Calculations indicate that iron is mostly present as Fe 3+ and is low (1.0–2.9 wt.% Fe 2O 3) compared with perovskite from carbonatite complexes such as Oka (4.4 wt.% FeO [3]). In addition to established Nb (0.3–1.7 oxide wt.%), geochemically interesting elements encountered include Zr (up to 1.5 oxide wt.%), Ba and Sr (up to 0.2, 0.4 oxide wt.% respectively). Specific geological applications suggest a possible genetic link between Wesselton pipe and Benfontein Sills kimberlites, and that carbonate-rich dikes in the Premier mine were derived from kimberlites. The overall similarities with incompatible element-rich titanates in veined mantle peridotites suggest a more direct link between kimberlite magmatism and mantle metasomatism.