Thallium: A potential guide to mineral deposits

Abstract

ABSTRACT Ikramuddin, M., Asmeron, Y. Nordstrom, P.M., Kinart, K.P., Martin, W.M., Digby, S.J.M., Elder, D.D., Nijak, W.F. and Afemari, A.A., 1983. Thallium: a potential guide to mineral deposits. In: G.R. Parslow (Editor), Geochemical Exploration 1982. J. Geochem. Explor., 19: 465–490. Several recent studies have suggested that rocks associated with mineral deposits of hydrothermal origin are generally enriched in Rb. Tl is similar in its geochemical characteristics to Rb, but its use as a potential guide to ore deposits has not been suggested. Although Tl has the same size and valency as Rb, it is concentrated more in residual melts than Rb and K because the Tl-O bond is more covalent and weaker than either the Rb-O or K-O bonds. A new method which is rapid and precise has been developed by one of the authors for the determination of Tl in geological materials at the ppb level. About 350 rocks from 4 mineralized areas in northeastern Washington and central Montana were analyzed for Tl by this method. Most of these rocks were also analyzed for SiO 2 , Al 2 O 3 , Fe 2 O 3 , MgO, CaO, Na 2 O, K 2 O, TiO 2 , P 2 O 5 , MnO, Ag, As, Au, Ba, Co, Cu, F, Li, Mo, Ni, Pb, Sr, Sb, Sn, Sr, Te, U, W, and Zn. The ore deposits of the areas studied include the gold-silver deposits of the Republic district, the uranium deposit of the Midnite mine, the copper-molybdenum deposit of Mount Tolman, and the gold deposits of the North Moccasin mining district. In all the mineralized areas there is significantly more Tl in hydrothermally altered rocks than in unaltered rocks. The very high abundance of Tl in the altered rocks of the North Moccasin gold district, and the significant positive correlations of Tl and K and Tl and Rb in the mineralized rocks of the other three areas suggest that Tl was concentrated in hydrothermal fluids. In altered rocks the average K/Rb and K/Tl ratios are lower, and the Rb/Sr and Tl/Sr ratios are higher. Often the abundance of Tl and the K/Tl and Tl/Sr ratios are more useful in delineating mineralized areas than the abundance of Rb and the K/Rb and Rb/Sr ratios. The ternary relationships between Tl and several other elements, especially Rb, K, Ba, and Sr, show mineralized rocks to fall near the Tl apices or near the Tl-Rb or Tl-K boundaries.