Experiments were conducted to test the hypothesis that carbonatite-hosted Nb deposits owe their origin to the metasomatic alteration of K-feldspar-rich fenite by carbonatitic magma. This involved reacting K-feldspar with a synthetic mixture of CaCO3, MgCO3, Mg(OH)2, CaF2, and Nb2O5. At the experimental conditions, a phlogopite-rich calcite-bearing metasomatic rind containing pyrochlore formed on the K-feldspar. This supports the above hypothesis and also explains the origin of fenite-associated glimmerite, the association of glimmerite with calcite carbonatite, and the genesis of the carbonatite-hosted ores that supply the bulk of the world’s niobium.

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