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Magmatism and Geodynamics in the Archaean
Published in O.A. Bogatikov, R.F. Fursenko, G.V. Lazareva, E.A. Miloradovskaya, A. Ya, R.E. Sorkina, Magmatism and Geodynamics Terrestrial Magmatism Throughout the Earth’s History, 2020
Did plate tectonics operate during the Archaean? Unfortunately this is not a question that can be answered at present (de Wit and Ashwal, 1997). Many geologists now suggest that plate tectonics were active in the Archaean (Windley, 1992; Condie, 1994; etc.). From that point of view, greenstone belts represent the ancient oceanic spreading zones, and almost all Archaean high-grade terranes can be explained in the context of one or two tectonic settings: deep crustal portions of magmatic arcs or collision orogens (Persival, 1994). However, most of the komatiites in greenstone belts underwent crustal contamination. This suggests that they ascended through continental crust and that the Archaean greenstone belts were not formed in an oceanic environment and could not be defined as ancient oceanic crust, since all the more Archaean ophiolites are absent (Arndt, 1994; Bickle et al., 1994).
Palladiferous placer gold from the Paraíba do Sul River in northern Rio de Janeiro (Brazil) and its geological implications
Published in Applied Earth Science, 2022
Flávio França Nunes da Rocha, Alexandre Raphael Cabral, Stephanie Gertrud Lohmeier, Miguel Tupinambá, Luiz Carlos Bertolino
Before considering a local source, it is instructive to provide some information on the chemical composition of lode gold from orogenic gold deposits in Neoarchaean greenstone-belt rocks of Minas Gerais. At São Bento, gold occurs as electrum inclusions and as lattice-bound Au in arsenopyrite and pyrite (Valadão et al. 2002). The São Bento gold has Ag contents of 20–50% (Márquez et al. 2006). At São Sebastião, gold and Au-bearing silver (77–85% Ag) are spatially associated with bismuth (Brando Soares et al. 2022). The aforementioned deposits are located within, or close to, the Quadrilátero Ferrífero of Minas Gerais – i.e. at least 200 km north-west of Itaocara. In Minas Gerais, it seems that the greenstone-belt-hosted orogenic gold deposits typically have argentiferous gold, not palladiferous gold.
Recent pegmatite-hosted spodumene discoveries in Western Australia: insights for lithium exploration in Australia and globally
Published in Applied Earth Science, 2022
Zoe Phelps-Barber, Allan Trench, David I. Groves
Kathleen Valley is located within the Yilgarn Craton ∼45 km NNW of Leinster, Western Australia (−27.47°, 120.56°). The deposit is hosted in a package of ultramafic and mafic volcanic rocks on the western edge of the Archean Norseman-Wiluna greenstone belt which is spatially associated with Yilgarn granite intrusions (Figure 1; Liontown Resources 2021a). The Kathleen Valley deposit encompasses, as of April 2021, 20 mineralised LCT spodumene pegmatites, trending NE–SW, to a depth of 640 m, and is referenced as two separate locations: Mt Mann and Kathleen’s Corner (dimensions Table 1; location Figure 5). Pegmatites at these locations coalesce at 300–400 m depth, forming a single, 35–75 m thick body, which remains open with the current extent of 600–700 m down dip (Liontown Resources 2021a).
Evaluation of mining and mineral processing methods’ impact on tantalite concentrate in Kenticha open pit mine, southern Ethiopia
Published in Applied Earth Science, 2020
Weldegebrial Haile, Bheemalingeswara Konka, Zerihun Desta
In southern Ethiopia, Adola is one of the regions hosting many gold and Ta mineralizations. Geologically, it consists of two low grade greenstone belts, Megado and Kenticha (Tadesse et al. 2002) (Figures 2 and 3). Megado greenstone belt is hosting Legadembi gold deposit and Kenticha greenstone belt, hosting Kenticha tantalum deposit (Woldai 1989). Post-orogenic granites are considered to be the source for the rare metal pegmatites (Zerihun et al. 1995; Küster et al. 2009). Geological structures like foliations, faults, joints, micro-folds and shear zones are found associated with these rocks (Kozyrev et al. 1985). The granitoids, intruded around 550 to 455 Ma, particularly around 530 Ma as per U-Pb tantalite dating of the Kenticha pegmatite (Yibas et al. 2002; Yihunie 2003; Küster et al. 2009), related to post-orogenic granitoid magmatism, slightly peraluminous I-type and geochemically differentiated form the source for pegmatites and mineralization in Kenticha area (Küster et al. 2009).