Cristiane Castañeda

Late Neoproterozoic–Cambrian granitic magmatism in the Araçuaí orogen (Brazil), the eastern brazilian pegmatite province and related mineral resources.

Abstract The Araçuaí orogen extends from the eastern edge of the São Francisco craton to the Atlantic margin, in southeastern Brazil. Orogenic igneous rocks, formed from c. 630 to c. 480 Ma, cover one third of this huge area, building up the Eastern Brazilian Pegmatite Province and the most important dimension stone province of Brazil. G1 supersuite (630–585 Ma) mainly consists of tonalite to granodiorite, with mafic to dioritic facies and enclaves, representing a continental calc-alkaline magmatic arc. G2 supersuite mostly includes S-type granites formed during the syn-collisional stage (585–560 Ma), from relatively shallow two-mica granites and related gem-rich pegmatites to deep garnet-biotite granites that are the site of yellow dimension stone deposits. The typical G3 rocks (545–525 Ma) are non-foliated garnet-cordierite leucogranites, making up autochthonous patches and veins. At the post-collisional stage (530–480 Ma), G4 and G5 supersuites were generated. The S-type G4 supersuite mostly consists of garnet-bearing two-mica leucogranites that are the source of many pegmatites mined for tourmalines and many other gems, lithium (spodumene) ore and industrial feldspar. G5 supersuite, consisting of high-K–Fe calc-alkaline to alkaline granitic and/or charnockitic to dioritic/noritic intrusions, is the source of aquamarine-topaz-rich pegmatites but mainly of a large dimension stone production.

Radiation-induced centers in Cs-rich beryl studied by magnetic resonance, infrared and optical spectroscopy

Abstract Natural and γ-irradiated pink and colorless beryl from Brazil has been investigated by electron paramagnetic resonance (EPR), optical absorption and infrared absorption. Beryl has the chemical formula Be 3 Al 2 Si 6 O 18 and is hexagonal with space group P6/mcc. Electron microprobe analysis of the different samples shows that the beryl samples are rich in Cs (3.30 wt.%) and contain low concentrations of transition-metal ions, in total ∼0.03 wt.% Fe and ∼0.05 wt.% Mn. In addition to the transition-metal ions, beryl accommodates many molecules and alkalis in its channels, which lie parallel to the c -axis and which have large diameters with a maximum of 5.1 A. Infrared absorption measurements in the different samples indicate the presence of type-I and type-II water together with OH − . Other molecules in the channels with not yet associated infrared absorptions are NO 3 0 and CO 3 − which have been observed by EPR. In this work we focus on the EPR identification of the different molecules and discuss their relation to color.