K, Rb and Cs in carbonatites and associated rocks from central Sweden

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Abstract
Forty-five samples of rocks and minerals from the Alnö alkaline district have been analysed for rubidium and cesium by neutron-activation analysis (NAA). The contents of both elements vary within wide limits. Alnöites contain 53–161 ppm Rb and 0.2–38 ppm Cs, and carbonatites <1–107 ppm Rb and 0.1–6.5 ppm Cs. Rubidium is substituted for potassium, mainly in phlogopite (K/Rb about 200) and K-feldspar (K/Rb about 400–600). Cesium, on the other hand, is not correlated to rubidium or potassium and most likely occurs in discrete cesium minerals. This seems to be in agreement with reports on the geochemistry of cesium in kimberlites.