Geochemistry of the granites and pegmatites of the Araçuaí Pegmatite district, Minas Gerais (Brazil)

The Arau̧aí pegmatite district (APD, Minas Gerais) belongs to the eastern Brazilian pegmatite province. Major and trace element studies, including REE, demonstrate a continuous evolution of the APD through differentiation from biotite granites, to two-mica granites, pegmatitic granites and finally to increasingly differentiated pegmatites. Some of the pegmatites show an internal differentiation covering almost the entire range of the regional variation in the APD. The evolution from silicate-dominated melt to water-dominated fluids is documented in the pegmatitic granites by non chondritic Y/Ho and Zr/Hf ratios and the lanthanide tetrad effect in the REE distribution patterns. Element plots, such as K/Rb vs. Cs for K-feldspar and muscovite classify the most evolved pegmatites as Be-, Li-Be-, and Li-Cs-Be-Ta types and turned out to be reliable prospection aids for Ta and Nb. Gem tourmaline and beryl mineralisation are bound to zones of albitisation in Be- and Li-Be type pegmatites. The most differentiated Li-Cs-Be-Ta pegmatites are poor candidates for gem tourmaline and beryl prospection.