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Central Brazil hosts Paleo-Mesoproterozoic A-type granitic suites related to the Goiás Tin Province (GTP) that contain Sn (±W, Nb-Ta, REE) mineralization associated with greisen, veins, and small pegmatite bodies. The Pedra Branca granite massif (1.77-1.74 Ga) is the main representative of GTP, marked by important cassiterite (±wolframite) contents. The cassiterite contains SnO2 = 96-100 wt. %, with the sum FeOtotal, TiO2, WO3, Ta2O5, Nb2O5, In2O3, and UO2 content below 4 wt.%, while wolframite contains WO3 = 71.5-74.5 wt.%, FeOtotal = 14.3-17.4 wt.% and MnO = 6.3-9.9 wt.%, as well as Sn, Ca, Ti, Ta, Nb, Pb, In, and U as trace elements. The δ18O data on the quartz-cassiterite pair (quartz = 9.4-10.4‰, cassiterite = 2.6-2.9 ‰) from greisen reveal a magmatic-hydrothermal signature with calculated crystallization temperatures between 410 and 485°C. However, during the Neoproterozoic Brasiliano/Pan-African Orogeny (800-500 Ma), all lithologies and ore sites were subjected to flattening, fragmentation, and mylonitic deformation. Fluid inclusion data revealed the presence of low-salinity aqueous solutions with homogenization temperatures between 215 and 100°C related to Neoproterozoic deformation. Finally, during the Phanerozoic, prolonged erosive produced Sn (±W)-rich alluvium around the Pedra Branca granitic massif. [ABSTRACT FROM AUTHOR]

The Fazenda Bonfim emerald deposit, State of Rio Grande do Norte, is within the regional geological domain known as Seridó Mobile Belt, Borborema Tectonic Province. It was formed from metasomatic fluids interaction at along lithological contacts between Be-rich albite-granite intrusions and Cr (±V)-rich mafic-ultramafic host-rocks, enclosed in the lens-shaped "hornfels" phlogopite schist. Emerald crystals display relatively high contents of Mg and Na, as well as trace amounts of Ca, K, Cs, Li, P, Sc, Ti, Mn, Co, Ni, Zn, Ga and Rb. Cr is the main chromophore element, followed by Fe and some V. Display also concentric growth zones and randomly-oriented mineral micro-inclusions, indicative for static growth. This zoning is linked to cationic substitution of alkalis accompanied by Cr loss, which favors irregular coloration of crystals. Metasomatic fluids contemporaneous with emerald growth are aqueous (H2O+NaCl), with low to moderate salinity and low density, although trace amounts of CO2 ± CH4 were also observed. These fluids showed a field-trapped between 375-430°C and 200-600 bars, based on combination of fluid inclusions isochores. In addition, oxygen isotope data (d18O = 6.9-7.4‰) suggest an igneous-metasomatic source for fluids and emerald components. [ABSTRACT FROM AUTHOR]