Structural Analysis and Pegmatite Differentiation in the Ancient Claim, Giraúl IV, Namibe Pegmatite District, Angola

• Autorzy: Leal Gomes Carlos

Identyfikatory

DOI

10.29227/IM-2024-01-05

Warianty tytułu

PL

Analiza strukturalna i zróżnicowanie pegmatytów w starożytnym twierdzeniu, Giraúl IV, dystrykt pegmatytów Namibe, Angola

• Języki publikacji: EN

Abstrakty

EN

Since the early 60´s, in the past XX century, the Giraúl pegmatites have been known for their resources of beryl, mica and feldspars, which were exploited in a regular basis from Giraúl claims I to IV till 1974, during the Portuguese administration of Angolan territory. A broader exploration of this pegmatite field was performed by the ancient Lobito Mining Company (LMC) engaged in detailed geological mapping of the granitic pegmatites and the structural constraints of their location. A structural map of the region was than elaborated, combining the interpretation of aerial photographs with field work performed by the LMC geologists. Recently, a growing economic interest is attributed to these claims, in the region of Bulamucolocai, Pitau and Muvero desert-dry rivers (locally known as “Mulolas”), considering the Li, Cs, and Ta (LCT) metallic specialization of some pegmatite bodies and the occurrence of beryl and tourmaline gemstones, mainly, morganite (Cs-beryl), aquamarine and also elbaite-liddicoatite. Giant crystals of spodumene, up to 6 m in length, define individualized quartz + spodumene units inside some of the more typical LCT pegmatite bodies. Pollucite was identified in the main pegmatites of Giraúl IV claim and not in the adjacent igneous leucocratic breccias. These, in turn, correspond to a complex pegmatite assemblage, very peculiar in what concerns its selective metasomatic effect over some surrounding rocks, with the formation of rims of holmquistite amphibole in contact with gabbro and norite and schorl-dravite tourmaline in contact with gneissic to metapelitic hosts. The breccia-like granitic rock combines clasts of spodumene an K-feldspar with a matrix mainly composed of some quartz, albite and mica including tourmaline, garnet and F-apatite, as accessory minerals. In the same area, huge potassic pegmatites hold giant crystals of microcline and orthoclase and very little quartz, being unusual due to its high content of triplite – zwieselite and triphylite – lithiophilite primary phosphates. The overall composition of these pegmatites is more likely syenitic (low quartz content) than truly granitic. A high-resolution structural analysis of the LCT ensemble (pegmatite plus related lithotypes) is now proposed enhancing the unusual relations between granite breccia plugs, sill-like more typical pegmatites, irregular shaped isodiametric bodies and products of metasomatism. This approach will lead to the understanding of the true dimension, anatomy and inner fraccionation of the different LCT facies and rare-metal deposits with obvious consequences regarding mineral detection and resource – reserve estimation, through the proposal of a more suitable conceptual model to rule its exploration.

Słowa kluczowe

EN

structural analysis; pegmatite; mineral; Angola

PL

analiza strukturalna; pegmatyt; minerały; Angola

• Wydawca: Polskie Towarzystwo Przeróbki Kopalin
• Czasopismo: Inżynieria Mineralna
• Rocznik: 2024
• Tom: Vol. 1, no. 1
• Strony: 33--42
• Opis fizyczny: Bibliogr. 8 poz., rys., tab., zdj.

Twórcy

autor

Leal Gomes Carlos

• Lab2PT – University of Minho, Gualtar, 4710-057 Braga, Portugal

• https://orcid.org/0000-0001-6854-5398

Bibliografia

• 1. A. Silva, A geologia da república de Angola desde o Paleoarcaico ao Paleozóico inferior. Instituto Nacional de Engenharia, Tecnologia e Inovação, IP, 45p., 2005.
• 2. A. Silva, C. Macedo, and J. Ferreira, Interpretação das determinações de idades K/Ar de algumas rochas do Precâmbrico das regiões de Vila Paiva Couceiro, Quilengues, Chicomba e Caluquembe (Angola), Mem. Serv. Geol. Min. Angola, Luanda, 15, 15 pp., 1975.
• 3. J. Torquato, and H.L. Allsopp, Rubidium-strontium geochronology of granitic rocks from the Morro Vermelho area (Tiger Bay, Angola), Geol. Rdsch., 62, pp. 172-179, 1973.
• 4. J. Torquato, and M.A.A. Salgueiro, Sobre a idade de algumas rochas da região da Cahama (Carta Geológica no 399), Angola, Bol. Inst. Geoc. Univ. São Paulo, São Paulo, 8, pp.97-106, 1977.
• 5. O. Von Knorring, Mineralogical and geochemical aspects of pegmatites from orogenic belts of equatorial and southern Africa. African. Magm. and Tectonics, Kennedy vol., 157-184, 1970.
• 6. J. Torquato, and H.L. Allsopp, Rubidium-strontium geochronology of granitic rocks from the Morro Vermelho area (Tiger Bay, Angola), Geol. Rdsch., 62, pp. 172-179, 1973.
• 7. W. Q. Kennedy, The structural differentiation of Africa in the Pan-African (~500m.y.) tectonic episode. Res. Indt. Afr. Geological Leeds, 8th Ann. Rept. 48- 49, 1964.
• 8. C. Leal Gomes, Panorâmica sobre os Recursos de Lítio em Países Africanos de Língua Portuguesa Boletim de Minas, 52 - Edição Especial – Lítio, pp. 49-71, 2018.

Uwagi

Opracowanie rekordu ze środków MNiSW, umowa nr SONP/SP/546092/2022 w ramach programu "Społeczna odpowiedzialność nauki" - moduł: Popularyzacja nauki i promocja sportu (2024).