Abstract

The determination of trace-element and rare-earth-element abundances in tourmaline and other B-rich minerals by inaa analysis is hampered by the problem of incident neutron-flux suppression in the sample, arising from the intrinsically large neutron-capture cross section of B. Using a novel wet-chemical technique involving pretreatment by B volatilization, trace-element and REE abundances in tourmalines from gold-bearing vein deposits of the Superior province are reported. Abundances of REEs in tourmaline determined only by instrumental neutron-activation analysis are on average lower by a factor of 60%, as a consequence of the neutron-capture effect, compared to inaa results obtained on samples that have undergone the wet-chemical pretreatment. Total abundances after pretreatment range from less than detection to in excess of ΣREE = 167 ppm. The REE contents do not correlate with the levels anticipated in contiguous host rocks. This result indicates that the REE are only partially indigenous to wall rocks and suggests some transport of the REE in hydrothermal solutions.

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