Origin of emerald deposits of Brazil |
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Authors: | G Giuliani L J H D Silva P Couto |
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Institution: | 1. ORSTOM, Universidade de Brasilia, Brazil 2. C.R.P.G., 15 Rue N.D. des Pauvres, BP 20, 54501, Vandoeuvre-les Nancy, France 3. Minera?? Caraiba Metais Ltda, Bahia, Brazil 4. Secretaria das Minas e Energia, C.P.R.M./SGM, Bahia, Brazil
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Abstract: | Precambrian emerald deposits of Brazil are found in a typical geologic setting with Archean basement and supracrustal, ultramafic, granitoid and rocks. Volcano-sedimentary series occur as imbricated structures or as bodies affected by complex folding and deformation. Emerald mineralization belongs to the classic biotite-schist deposit, which formed by the reaction of pegmatitic veins within ultrabasic rocks. At the same time, pegmatite-free emerald deposits linked to ductile shear zones are also known. Emerald formation is attributed to infiltrational metasomatic processes provoking a K-metasomatism of the ultrabasic rocks and also a desilication of the pegmatites. A new classification based on the geological setting, structural features, and ore paragenesis is proposed. |
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