The Geochemical and Mineralogical Characterisation of Lithium-bearing Pegmatites of Southeast Brazil |Chapter 1 | Current Research on Geography, Earth Science and Environment Vol. 1

The Doce River region is located in the central northern part of the Mantiqueira Structural Province, east of the São Francisco carton in the eastern Minas Gerais and northwestern Espírito Santo states. The P-Li-Nb pegmatites are located in the south of Brazil, in the states of Minas Gerais and Espírito Santo. They represent the largest pegmatite fields of Brazil and the richest in precious stones. Two types of pegmatites are characterised by their mineralogical characteristics and tectonic and magmatic relations. The first group occurred during a compressive deformation phase D1 about 582 Ma and 550°C - 700°C and 4 - 5 kb. The second pegmatite group was formed during the decompression phase D2 (520 - 500 Ma) of the Brasiliano metamorphic rock fusion. The geochemical parameters of the P-Li-Be bearing pegmatites of the first group show the same trend of fractionation, as suggested by the mineralogical composition. The variation of tourmaline and columbite-tantalite composition of the first group game again applies a change of melt composition during the regional development of the pegmatites. A systematic compositional trend seems to suggest a petrogenetic link between the pegmatites of the region. The Fe/Mn ratio of tourmaline in samples of the first group shows the same behaviour as in columbite-tantalite and garnets. The simple pegmatites are transitioning north into the gem-rich pegmatites. The Fe/Mn ratio not only shows qualitatively the fractionation index, the degree of regional development, but also the internal development of the body. The ratio shows a negative correlation with lithium. The Co, Zn and Nb contents are rising in the first group, but falling when starting crystallisation of garnet, columbite-tantalite, and Behierit. The geochemical parameters of the P-Li-Be bearing pegmatites of the first group show the same trend of fractionation, as suggested by the mineralogical composition.

 

Author (s) Details

Essaid Bilal
Ecole Nationale Supérieure des Mines de Saint-Étienne, CNRS-UMR6425, Saint-Étienne, France.

 

Adolf Heinrich Horn
IGC-UFMG, Belo Horizonte, Brazil.

 

Fernando Machado de Mello
IA-Departamento de Geociências da UFRRJ, Rio de Janeiro, Brazil.

 

Helena Saraiva Koenow Pinheiro
IA-Departamento de Geociências da UFRRJ, Rio de Janeiro, Brazil.

 

Please see the book here:- https://doi.org/10.9734/bpi/crgese/v1/3969