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Geology of Chromite deposits in the Arabian Shield, Saudi Arabia
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
O. R. El-Mahdy, A. M. Al-Shanti
Chromite mineralisation also occurs as chromitite layers, where chromite is disseminated either as individual grains or in aggregates or clusters in serpentine matrix. The layers are generally of high length to width ratio and are commonly 40-60 meters long and 10-50 cms thick. They are conformable with the host rocks and commonly form prominent outcrops. They may occur as a single layer, or more frequently are dissected and dismembered into a series of aligned small bodies by tectonic disturbances. They generally show effects of faulting and folding.
Petrogenesis of the Kalka, Ewarara and Gosse Pile layered intrusions, Musgrave Province, South Australia, and implications for magmatic sulfide prospectivity
Published in Australian Journal of Earth Sciences, 2023
W. D. Maier, B. Wade, Sarah-Jane Barnes, R. Dutch
Wingellina Hills is the only Giles intrusion that contains schlieren and lenses of chromitite within peridotite (Ballhaus & Glikson, 1989). This is expressed by markedly higher Cr/V than in all other Giles intrusions (Figure 13). The only other Giles intrusion where chromite is relatively common (although only in disseminated form) is Pirntirri Mullari. Ballhaus and Glikson (1995) suggested that the Giles intrusions have low chromite because they crystallised from a relatively Cr-poor parent magma, with local chromite crystallisation triggered by supercooling, but the data of Godel et al. (2011) indicate Cr levels in NB1-2 comparable with, for example, Bushveld magnesian basalt, a likely parental magma to many of the Bushveld massive chromitites. Alternatively, the low chromite content in the Giles intrusions could reflect the fact that in most bodies relatively Cr-rich clinopyroxene preceded relatively Cr-poor orthopyroxene on the liquidus that could result in early depletion of Cr and suppression of chromite stability. The model is consistent with the observation that Wingellina Hills appears to be one of few Giles intrusions having a thick harzburgitic interval at its base (Maier et al., 2015).
Tectonic setting and mineralisation potential of the Cowley Ophiolite Complex, north Queensland
Published in Australian Journal of Earth Sciences, 2022
A. Edgar, I. V. Sanislav, P. H. G. M. Dirks
Ophiolite complexes have the potential to host resources of critical metals, typically formed by magmatic (Shi et al., 2012) or lateritic processes (Elias, 2002). The magmatic processes governing the formation of podiform chromite deposits have been widely debated (Lago et al., 1982; Rollinson, 2005; Xiong et al., 2015). Most models for podiform chromite deposits within supra-subduction zone, ophiolite complexes describe slab-derived, magmatic fluids interacting with the overriding mantle wedge. This process involved the melting of chrome-rich clinopyroxene and orthopyroxene, thus enriching the slab-derived melt in chromium, and results in the subsequent precipitation of chromitite during dunite crystallisation (Rollinson & Adetunji, 2013; Zhou & Robinson, 1997). However, these models cannot account for podiform chromite deposits with UHP mineral inclusions and exsolution (Xiong et al., 2015), so additional processes are at play in some cases. We interpret that the COC developed within a supra-subduction zone environment, which is favourable for the formation of ophiolite-hosted, podiform chromite deposits. However, no podiform chromite or chromitite lenses have been observed within the COC. The Cr grades in the whole-rock geochemistry of the ultramafic rocks that we have described do not exceed 3600 ppm and are sub-economic.
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).