Rare Earth and Uranium Minerals Present as Daughter Crystals in Fluid Inclusions, Mary Kathleen U-REE Skarn, Queensland, Australia

T. A. P. Kwak and P. B. Abeysinghe
Department of Geology, La Trobe University, Bundoora, Victoria 3083, Australia
Geological Survey Department, Colombo 2, Sri Lanka

Abstract: At least six separate rare earth and uranium-bearing daughter crystals occur in fluid inclusions hosted by andraditic garnet from the Mary Kathleen REE-U ore skarn, Queensland, Australia. The daughter minerals are particularly high in La, Nd and Ce which reflects the relatively high concentration of these in the bulk ore (La2O3 = 33.5%, Nd2O3 = 9.1% and Ce2O2 = 51.5% of the 2.6 wt. % REE common in the ore). The host garnets themselves contain up to 7600 ppm REE and 5 to 2700 ppm U. The energy-dispersive spectra (EDS) are consistent with the following minerals: a (Y, Ce, U, Ca, Fe, Nb, Ta) mineral; a (Ca, Fe, Ce) carbonate(?) mineral; a (Fe, Ca, Y, Ce, Nb, Ta) mineral; a possible carbonate of La, Mn and Nd; a chlorite of Mn and La as well as a possible chloride or oxychloride of K, Mg, Mn and La. Their occurrence infers that relatively high concentrations of REE and U prevailed in the original, oxidized, concentrated (30–70 wt. % total dissolved salts), high-temperature (550–670°) ore solutions. Their presence as daughter crystals may be due to the fact that CaCl2 is a dominant salt in the solutions and that the latter's solubility was sufficiently high to ‘salt out’ the less soluble REE-U components.

Keywords: fluid inclusions • rare earth minerals • uranium • skarn • Queensland • Australia

Mineralogical Magazine; December 1987 v. 51; no. 363; p. 665-670; DOI: 10.1180/minmag.1987.051.363.05
© 1987, The Mineralogical Society
Mineralogical Society (www.minersoc.org)