|Résumé||(disponible en anglais seulement)|
Carbonatites, associated fenitization zones, and their weathered equivalents are the most important sources of Nb and some contain significant concentrations of
Ta and rare earth elements (Simandl et al., 2012). They contain important deposits of vermiculite, apatite (phosphate), badelleyite (zirconia), fluorite, U, and magnetite (Mariano 1989a, 1989b, Birket and Simandl, 1999 ).
One of the objectives of
the Specialty Metals component of the Targeted Geoscience Initiative 4 (TGI-4) is to determine if indicator minerals can guide explorationists toward carbonatite-related mineralization. Heavy mineral processing and analysis of indicator minerals are
expensive and time consuming. We measured the concentrations of Nb, Ta, REE, P, Sr, Ba, U, and Th in different grain size fractions of sediments sampled from streams draining three deposits (Fig. 1). Using portable X-ray fluorescence (pXRF) minimizes
the cost, improves output, and optimizes the sampling procedure. Concentrations of these pathfinder elements are expected to correlate with the presence of indicator minerals such as pyrochlore, columbite-tantalite, fersmite, apatite, REE-bearing
fluorocarbonates, monazite, allanite, zircon, xenotime, and minerals of celestite- barite solid solution.
Three carbonatites, Lonnie (Nb prospect), Aley (large Nb deposit), and Wicheeda (high grade REE deposit), are the subject of an indicator
mineral orientation surveys to improve the efficacy of Nb, Ta, and REE exploration techniques (Fig. 1). This study summarizes the methodology used in the above orientation surveys; however, it focusses on the Lonnie Nb prospect.
The results for
key pathfinder elements were precise (most having a mean %RSD less than 6%). In order to acheive the best possible accuracy pXRF results were correlated with results from laboratory techniques for recalibration. Results for eight size fractions
separated by laboratory sieves indicate a systematic distribution of key elements, with the highest abundances found in the finer size fractions. Of these, the +125?m fraction was chosen for further consideration due to its suitability for continued
indicator mineral studies. With the exception of Ba, Sr, and possibly Nb samples upstream from the Lonnie deposit display higher concentrations of carbonatite pathfinder elements than samples downstream of the deposit. This indicates source(s)
farther upstream, probably the Vergil carbonatite and Nb and TREE + Y soil geochemical anomalies. Indicator mineral studies are ongoing.