Alkaline rock provinces are favorable areas for prospecting for niobium-bearing carbonatites. In areas of extensive tropical weathering, geochemical criteria serve to distinguish carbonatites from other carbonate rocks, since the former tend to be enriched not only in Nb and Sr, but also in rare earths, Zr, Ti, Ba, and P, and are characterized by high Nb/Ta ratios and commonly by the presence of U or Th. X-ray fluorescence spectrometry is considered the most satisfactory of the quantitative analytic techniques; two direct methods, here described, were found to be rapid and sufficiently accurate for use in prospecting and in evaluation of niobium-bearing occurrences.

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