Óxidos de Nb-Ta de las pegmatitas graníticas de Giraúl, Angola

Peer ReviewedPostprint (published version

The distribution of rare metals in the LCT pegmatites from the Giraúl field, Angola

The Giraúl granitic pegmatite field, Angola, is composed of five pegmatite types; the most evolved belong to the beryl-columbite, beryl-columbite-phosphate and spodumene types. Pegmatites are concentrically zoned with increased grain size toward a quartz core; the most evolved pegmatites have well-developed replacement units. These pegmatites are rich in Nb-Ta oxide minerals and the field has a moderate interest for critical elements as Ta and Hf. Pegmatites are concentrically zoned with an increased grain size towards a quartz core. Tourmaline, garnet and beryl micas occur as accessory minerals. The abundance of Zr and Nb-Ta minerals increases with the evolution of the pegmatites, as well as the proportions of beryl and Li-rich minerals. The ; the Ta/(Ta+Nb) ratios in Nb-Ta oxide minerals and the Hf/(Hf+Zr) ratios in zircon also increase with the grade of evolution of the pegmatites and inside within each pegmatite body from border to inner zones, and especially in the late veins and subsolidus replacements. Textural patterns and occurrence of late veins with Ta-rich minerals suggest that Nb and especially Ta can be enriched in late hydrothermal exsolved fluids exsolved from the magma, along with Hf and other incompatible elements as Sn, U, Pb, Sb and Bi.Peer ReviewedPostprint (published version

Óxidos de Nb-Ta de las pegmatitas graníticas de Giraúl, Angola

Peer Reviewe

The distribution of rare metals in the LCT pegmatites from the Giraúl field, Angola

The Giraúl granitic pegmatite field, Angola, is composed of five pegmatite types; the most evolved belong to the beryl-columbite, beryl-columbite-phosphate and spodumene types. Pegmatites are concentrically zoned with increased grain size toward a quartz core; the most evolved pegmatites have well-developed replacement units. These pegmatites are rich in Nb-Ta oxide minerals and the field has a moderate interest for critical elements as Ta and Hf. Pegmatites are concentrically zoned with an increased grain size towards a quartz core. Tourmaline, garnet and beryl micas occur as accessory minerals. The abundance of Zr and Nb-Ta minerals increases with the evolution of the pegmatites, as well as the proportions of beryl and Li-rich minerals. The ; the Ta/(Ta+Nb) ratios in Nb-Ta oxide minerals and the Hf/(Hf+Zr) ratios in zircon also increase with the grade of evolution of the pegmatites and inside within each pegmatite body from border to inner zones, and especially in the late veins and subsolidus replacements. Textural patterns and occurrence of late veins with Ta-rich minerals suggest that Nb and especially Ta can be enriched in late hydrothermal exsolved fluids exsolved from the magma, along with Hf and other incompatible elements as Sn, U, Pb, Sb and Bi.Peer Reviewe