José Vicente Valarelli

Petrographic and microthermometrical studies of emeralds in the ‘Garimpo’ of Capoeirana, Nova Era, Minas Gerais State, Brazil

Petrographic investigations in the area of the Capoeirana emerald deposit, Minas Gerais State, revealed two main lithostructural units. The first unit is comprised of gneissic rocks of granitic composition belonging to the basement complex, and the second is composed of a highly weathered metasedimentary-metavolcanic sequence represented by metapelitic schists, amphibolites, schists derived from ultramafic rocks, and quartzites. Quartz and pegmatoid veins appear near the contacts between the gneissic rocks and the mineralization metasedimentary-metavolcanic sequence. The emerald mineralization is dominantly concentrated within the intercalations of meta-ultramafic schists near the contact of the pegmatoid veins. Microthermometric studies of the fluid inclusions of the emerald grains indicate that crystallization occurred in the pressure and temperature ranges of 2000 to 2750 bar and 450 to 650 °C, respectively. These data suggest that the mineralizing solutions have had a late hydrothermal-pneumatolytic origin characterized by low pressures, suggestive of the paragenesis talc + tremolite + carbonate + biotite-phlogopite + chlorite of the emerald wall rocks.

Process for production of calcined phosphate in a grate furnace.

Experimental results on bench scale production of calcined phosphate in a grate furnace are presented. Phosphate concentrates were mixed with silica, sodium carbonate and charcoal in varying amounts and granulated (4–6 mm), in some cases with the aid of phosphoric acid. The granules were dried and calcined at 1140–1300°C in a grate furnace. Products with 24.4 to 30.7% total P2O5 were obtained with solubility higher than 70% in 2% citric acid.Other experiments were done employing pelletized (4–6 mm) sugar cane bagasse as fuel instead of coal. In these cases, the raw materials silica, sodium carbonate and phosphate concentrates were granulated and then mixed with the pelletized sugar cane bagasse. Two products with 26.1 and 29.4% total P2O5 containing respectively 18.8 and 24.0% soluble P2O5 (in 2% citric acid solution) were obtained by calcination at temperatures of 930 and 1300°C respectively.The products of both experiments were mainly citric acid-soluble phosphates (rhenanite and andoite) with small amounts of non-reacted apatite.

Ocorrência de fosfato de terras raras na Formação Resende, Paleógeno do Rift Continental do Sudeste do Brasil

Petrographic studies and SEM/EDS and XRD analyses revealed the presence of a phosphate with Ca and REE (La, Nd) in a mudstone deposit of the Resende Formation, located on the northern border of the Resende Basin. The morphological characteristics (prismatic hexagonal habit) and chemical composition of the phosphate allow including this mineral in the rhabdophane group. This phosphate is authigenic and its origin is related to the dissolution of detritic apatite grains, probably by alkaline hydrothermal solutions. These solutions also provided some of the elements involved in the rhabdophane crystalization.