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Igneous Rocks
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
The Skaergaard intrusion is shaped like an inverted cone or funnel, with an area of 50 km2 at the surface, and is exposed on the east coast of Greenland to a vertical depth of some 2500 m; the funnel-shaped mass may continue below this for a similar distance. The lowest part of the exposed gabbro possesses a nearly horizontal layering, consisting of dark bands rich in olivine (formed by the gravity-settling of olivine crystals in the magma) separated by broader bands of olivine-gabbro and hypersthene gabbro. A small scale layering which is repeated many times is called rhythmic banding. The layered rocks pass upwards into gabbros without olivine, succeeded by iron-rich gabbros and finally by quartz-gabbros. The plagioclase in the gabbros ranges from labradorite in the lower rocks to andesine in the upper. At the margins of the mass fine-grained gabbros are present.
Platinum Group Elements Mineralogy, Beneficiation, and Extraction Practices – An Overview
Published in Mineral Processing and Extractive Metallurgy Review, 2021
P. Sahu, M. S. Jena, N. R. Mandre, R. Venugopal
PGE mineralization has taken place in different geological environment and association. Naldrett (2004) has summarized the geological setting of different types of PGE mineralization, which were discussed earlier. Later, Maier (2005) and Mungall and Naldrett (2008) gave exhaustive details of various types of PGE mineralization. These include: (1) peripheral to or within accumulations of sulfide liquid (Norli’sk Talnakh, Russia; Sudbury, Canada) (Farrow et al. 2005; Mungall 2007; Naldrett 2004), (2) layers of very high PGE tenor sulfides within a layered intrusion without chromite (Merensky Reef, S. Africa; J-Mafic reef, Stillwater complex, USA) (Mungall 2002; Naldrett et al. 2008; Naldrett and Wilson 1990) and with chromitite horizons (UG-2, UG-1, MG-3 and MG-2 chromitites of the Bushveld complex) (Scoon and Teigler 1994), (3) development of PGE-rich immiscible sulfides prior to or during emplacement into their present locations (Kola Peninsula of Russia and Ontario, Canada) (Kinnaird et al. 2005; Naldrett 2004), (4) delayed separation of sulfide during the crystallization of a layered intrusion (Platinova reef, Skaergaard intrusion, Rio Jacaré intrusion, Bahia, Brazil, the Volkovsky deposit of the Urals platinum belt and the Stella intrusion of South Africa) (Andersen, Power and Momme 2002; Maier et al. 2003; Naldrett et al. 2008; Sá et al. 2005), (5) chromite crystallization without the development of sulfide immiscibility (ophiolite complexes) (Naldrett et al. 2008), (6) hydrothermal redistribution of PGE (the New Rambler mine in Wyoming, U.S.A., the Waterberg deposit, Transvaal, South Africa and the Coronation Hill deposit, Australia) (Naldrett et al. 2008; Wilde 2005), (7) secondary concentration of PGE associated with chromite schlieren in zoned dunite-pyroxenite intrusions (Nizhny Tagil in the Urals, Koryakia, northeastern Russia and the Kondyor intrusion within the Siberian platform) (Naldrett et al. 2008; Nazimova, Zaitsev and Mochalov 2003), and (8) hydrothermally concentrated PGE (principally Pt) in black shales, often in association with Au (Sukhoi Log deposit in Siberia) (Distler and Yudovskaya 2005; Naldrett et al. 2008).