C. V. Dutra da Costa J.J.R. Branco K. J. Murata 1959 <p>Two zoned pegmatites in south-eastern Minas Gerais were sampled in detail for their content of monazite and xenotime and the monazite was analysed for certain of the rare-earth elements and thorium.</p><p>The ratio of xenotime to monazite increases in both pegmatites from the wall toward the quartz core. The content of the less basic rare-earth elements and of thorium in monazite rises in the same direction. These variation trends suggest that during the crystallization of these pegmatites there was a fractionation of the elements leading to a more or less steady enrichment of the less basic rare-earth elements and of thorium in the residual fluids. One mode of explaining these observed effects postulates that the rare-earth elements and thorium were present in pegmatitic fluids as co-ordination complexes rather than as simple cations.</p> application/pdf 10.1016/0016-7037(59)90043-2 en Elsevier Composition of monazites from pegmatites in eastern Minas Gerais, Brazil article