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Title: Emerald from the Fazenda Bonfim Deposit, northeastern Brazil: chemical, fluid inclusions and oxygen isotope data
Authors: Santiago, Judiron Santos
Souza, Valmir da Silva
Filgueiras, Bernardo de Carvalho
Cuadros Jiménez, Federico Alberto
Assunto:: Geologia - Rio Grande do Norte
Gemas (Mineralogia)
Isótopos de oxigênio
Issue Date: 2018
Publisher: Sociedade Brasileira de Geologia
Citation: SANTIAGO, Judiron Santos et al. Emerald from the Fazenda Bonfim Deposit, northeastern Brazil: chemical, fluid inclusions and oxygen isotope data. Brazilian Journal of Geology, São Paulo, v. 48, n. 3, p. 457-472, jul./set. 2018. DOI: http://dx.doi.org/10.1590/2317-4889201820170130. Disponível em: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2317-48892018000300457&lng=en&nrm=iso. Acesso em: 29 mar. 2019. Epub Aug 20, 2018.
Abstract: 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 (H 2 O+NaCl), with low to moderate salinity and low density, although trace amounts of CO 2 ± CH 4 were also observed. These fluids showed a field-trapped between 375-430ºC and 200-600 bars, based on combination of fluid inclusions isochores. In addition, oxygen isotope data (δ 18 O = 6.9-7.4‰) suggest an igneous-metasomatic source for fluids and emerald components.
Licença:: © 2018 Sociedade Brasileira de Geologia. This is an open access article distributed under the terms of the Creative Commons license. (CC BY).
DOI: http://dx.doi.org/10.1590/2317-4889201820170130
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