Pegmatitas graníticas del campo pegmatítico del río Giraúl (Desierto de Namibe, Suroeste de Angola): clasificación

• Autores: A.O. Gonçalves, Joan Carles Melgarejo i Draper, Andres Paniagua Condado, E. Morais, A.B. Neto
• Localización: Geotemas (Madrid), ISSN 1576-5172, Nº. 6, 1, 2004 (Ejemplar dedicado a: IV Congreso Geológico de España (Zaragoza, 12-15 julio, 2004)), págs. 221-224
• Idioma: español
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• Resumen

  • The pegmatite field of the Giraul river is found at the SW of Angola, 40 km east of the Namibe city, at the Namibe desert. The granite pegmatites are hosted by metapelites, amphibolites, migmatites and granitic rocks of Archean age. The granitic rocks range in composition from diorite to muscovite-biotite leucogranites. The intrusion of both the granites and the pegmatites takes place during the metamorphic climax, between two stages of folding. The next pegmatite types were established on the basis of the mineral structure and mineral composition of pegmatites: a) type I, barren pegmatites; b) type II, beryl-columbite pegmatites, and c) type III, beryl-columbite-phosphate pegmatites, with a complex structure, and rich in phosphates of the purpurite-heterosite series. Type I pegmatites occurs into the leucogranites, as well as into the schists in the vicinity of the granites. Type II and type III pegmatites are distal in relation to the granitic rocks. This arrangement suggests that the pegmatite field has been produced by a fractionation process from the parental leucogranites. The economic minerals occur in the type III pegmatites and comprise K-feldspar of ceramic grade, and minor columbite-tantalite.