This study characterizes natural black, blue, dark green, light green and pink tourmalines from granitic pegmatites of the Mata Azul Pegmatitic Field in central Brazil. The differences were assessed by applying electron-microprobe analysis as well as Mössbauer and optical spectroscopies. Mineral chemistry data show an increasing Mn/(Mn + Fe) atomic ratio as follows: black (0.01-0.02), blue (0.04-0.05), dark green (0.09-0.21), light green (0.33-0.42) and pink (0.68-1.00). The Mössbauer spectroscopy results show the presence of Fe 2+ (doublets with isomer shift (δ): 1.04-1.15 mm/s) for the black, blue, light green and dark green tourmalines. Fe 2+ is found in three different environments that are identified by quadrupole splitting (Δ) of 2.38-2.49 mm/s for the first, Δ = 2.13-2.34 mm/s for the second, and Δ = 1.54-1.71 mm/s for the third. The black sample spectrum has an additional fourth doublet (δ = 0.78 mm/s, Δ = 1.22 mm/s) that is assigned to an electron delocalization between Fe 2+ and Fe 3+. In the studied samples, the black color results most likely from high absorbance in all the visible spectra caused by Fe

Disponível on-line no endereço www.igc.usp.br/geologiausp -159 - ResumoNo sul do Estado do Tocantins e norte do Estado de Goiás, pegmatitos graníticos estéreis e mineralizados são conhecidos e explorados há muito tempo, mas só recentemente foram caracterizados quanto aos aspectos mineralógicos, composicionais e genéticos e agrupados sob a denominação de Campo Pegmatítico Mata Azul. Em três desses corpos localizados no município de Jaú do Tocantins, com mineralização de berilo, fosfatos de Fe e Mn ocorrem sob a forma de nódulos ou massas centimétricas. Duas associações de fosfatos são diferenciadas. Na primeira delas, hospedada nos pegmatitos São Júlio e Pichorra, foram descritas três fases primárias, identificadas como zwieselita, sarcopsídio e fluorapatita. Processos hidrotermais alteram essas fases, formando rockbridgeíta, uma fase do subgrupo da alluaudita e heterosita. Na segunda associação, presente no pegmatito Fazenda Mesquita, não há sinal de fosfato primário e todas as fases presentes são secundárias. Rockbridgeíta, de cor verde a alaranjada, compõe boa parte do volume das amostras. Fosfosiderita e strengita aparecem como alterações da rockbridgeíta, às vezes preenchendo cavidades nas massas de fosfato. Nas duas associações, óxidos e hidróxidos de Fe e Mn, oriundos da oxidação intempérica, correspondem às últimas fases formadas, podendo constituir crostas que recobrem boa parte dos nódulos e das massas de fosfatos. Em algumas amostras das associações de fosfatos, cristais de uraninita, gahnita, almandina e columbita-(Fe) foram identificados.Palavras-chave: Fosfatos de Fe-Mn; Pegmatitos; Mata Azul. AbstractIn central Brazil, in the southern Tocantins and in the northern Goiás States, barren and mineralized granitic pegmatites are known and explored for a long time, but only in recent years they were properly characterized and grouped in the so called Mata Azul Pegmatitic Field. In Jaú do Tocantins, three of the pegmatite bodies explored for beryl, a Fe-Mn phosphate associations occur as centimetric nodules and aggregates. Two phosphate associations were characterized: the first, hosted in Pichorra and São Júlio pegmatites present three primary phases, identified as zwieselite, sarcopside and fluorapatite. Hydrothermal processes transform the primary phosphates in rockbridgeite, heterosite and a phase of the alluaudite subgroup. The second association was observed in the Fazenda Mesquita pegmatite, where primary phosphates are absent and orange to green rockbridgeite is the main phase, followed by phosphosiderite and strengite formed by the weathering of rockbridgeite. In both associations, the weathering of the Fe-Mn phosphates give rise to Fe and Mn oxides. Minor phases as uraninite, gahnite, almandine and columbite-(Fe) were identified as inclusions in the phosphate phases.

Agradeço a orientação do professor Nilson, sempre disposto a dedicar parte do seu tempo para discutir e sanar dúvidas.A minha família pelo apoio a esta escolha profissional.Ao instituto de Geociências da UnB pela utilização dos laboratórios e auxílio dos técnicos dos laboratórios de microssonda, laminação e geocronologia. Aos colegas de pós-graduação pela idéias e discussões, assim como os professores José Oswaldo, Catarina, Valmir, Edí, Claudinei e Elton.A CAPES pelo auxílio da bolsa de doutorado.A professora Rúbia Viana por ter me introduzido aos pegmatitos de Tocantins.Aos garimpeiros e ex-garimpeiros "João Preto", Domingos, Vivaldo e Cláudio pelo auxílio nos trabalhos de campo, sem o qual não seria possível conhecer todas as ocorrências estudadas nesta tese.

In Goiás and Tocantins States, Central Brazil, several granitic pegmatites were characterized and grouped for the first time. These pegmatites had been intensely explored by hand in the past, producing mainly gemstone varieties of tourmaline and beryl. Barren, beryl-and tourmaline-bearing pegmatites occur across an area of 2,000 km 2 where they intrude regional metasedimentary rocks and peraluminous granites. K-feldspar (mostly altered to kaolin), quartz and mica (mainly muscovite) are the major minerals. The main accessory minerals are beryl, tourmaline, garnet, albite, Fe-Mn phosphate aggregates, and trilithionite. The paragneiss surrounding the barren pegmatites was affected by thermal metamorphism and later hydrothermal alteration, producing Ca-silicates, Ti-Nb-Y oxides and sulfides. Leucogranites of the Mata Azul Suite are peraluminous and syn-to post-orogenic with geochemical characteristics of the LCT granite-pegmatite group. LA-ICP-MS U-Pb geochronology in monazite yields an age of 519 ± 2.8 Ma. Additionally, U-Th-Pb chemical dating of uraninite reveals a maximum age between 500 and 560 Ma. These ages, the field relationships, the mineralogy and the geochemical data suggest that the granites of the Mata Azul Suite are the probable sources of the studied pegmatites. The mineral associations and the mineral chemistry are used to define the degree of fractionation of the pegmatites. We propose that the group of studied pegmatites represents a pegmatitic field, called the Mata Azul Suite Pegmatitic Field.