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Early Proterozoic Magmatism and Geodynamics — Evidence of a Fundamental Change in the Earth’s Evolution
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
The Drusite Complex of small intrusions is one of the most unusual cases of the Early Precambrian magmatic activity. The complex is composed of small (a few hundred metres to 1 km in length), rootless intrusions, basic, ultrabasic and, less commonly, intermediate in composition, which impregnate the high-grade metamorphic rocks of the Belomorian Belt (Shurkin et al., 1962; Sharkov et al., 1994; etc.). The bodies number in the thousands. They are dominated by intrusions of norite and gabbronorite; bodies of ultramafic rocks (plagioclase harzburgite, bronzitite, websterite, and for the most part, plagioclase lherzolite) and anorthosites, marnetite gabbronorite-diorite and pyroxene diorites, are subordinate. As a whole, in their petrographical and geochemical features these rocks are rather close to the cumulates of layered intrusions described above (Monchetundra, Koilismaa, Burakovka, etc). According to estimates made in northern Karelia over an area of about 6,000 km2, ultramafic rocks account for 17%; olivine gabbronorite for 43%; norite and gabbronorite for 30%; gabbronorite–anorthosite for 6%; Mgt gabbro-diorites and diorites for 4% of the intrusions (Malov and Sharkov, 1978). The largest bodies display primary igneous layering, caused by alternation of leucocratic and melanocratic rocks. In some cases, peridotite and pyroxenite occur at the bases of the bodies, and gabbroids with segregations of gabbronorite-pegmatite occur close to the contact with country rocks. However, intrusions composed of only one of the main rock varieties are the most common.
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
The stratigraphy of the Intrusion has been originally established by Goode and Krieg (1967). At the base of the intrusion is a relatively thin (few centimetres), fine-grained, olivine gabbronorite considered to be the only preserved primary magmatic contact among the Giles intrusions (Goode, 2002). The rocks contain thin felsic xenoliths and elevated biotite suggestive of contamination. Plagioclase laths have a composition of An66. The contact rocks are overlain by several 100 m of olivine-orthopyroxenite (the Olivine Bronzitite Zone of Goode & Krieg, 1967), consisting of 20–40 vol% olivine (Fo86–88), 50–70 vol% orthopyroxene (En89), up to ∼5 vol% plagioclase (∼An30) and 5–10 vol% clinopyroxene, as well as traces of spinel and apatite (Goode & Moore, 1975). The proportions of biotite, ilmenite, magnetite and trace sulfides decrease with height, interpreted to reflect decreasing contamination with the floor rocks. The olivine-orthopyroxenite is overlain by orthopyroxenite grading upward into websterite, making up the Pyroxenite Zone (PZ), containing 50–80 vol% orthopyroxenite, 10–40 vol% clinopyroxenite, as well as a few % interstitial plagioclase. At the base of this zone occurs inch-scale layering (Goode, 2002, figure 19).
Subduction erosion: contributions of footwall and hanging wall to serpentinite mélange; field, geochemical and radiochronological evidence from the Eocene HP-LT belt of New Caledonia
Published in Australian Journal of Earth Sciences, 2021
The harzburgites-dunite association is overlain by dunite, pyroxenite, websterite and gabbronorite cumulates (Prinzhoffer, 1981). Cumulate websterite and gabbronorite probably crystallised in equilibrium with depleted melts intermediate between boninite and island-arc tholeiite (IAT) (Cluzel et al., 2016; Marchesi et al., 2009; Pirard et al., 2013; Secchiari et al., 2018), which at present are not preserved. Whole rock and mineral chemical constraints on lherzolites allow a polyphase evolution to be drawn, from oceanic accretion to mantle metasomatism during subduction (Marchesi et al., 2009; Secchiari et al., 2016, 2020; Spandler, Hermann, Arculus, et al., 2004; Ulrich et al., 2010).
Evaluation of mine waste characterization to identify opportunities for optimizing project economics using fragmentation analysis
Published in Mining Technology, 2021
The Kevitsa deposit is hosted within a composite olivine-pyroxenite/websterite complex, an ultramafic cumulate. Two economically significant mineralization patterns have been distinguished within the Kevitsa deposit; regular Ni–Cu mineralization and Ni–PGE mineralization. The predominant mineralization types are Ni–Cu and comprise almost 95% of the deposit. The variability of Cu and Ni is relatively low, but there are distinct precincts of Cu and Ni-rich mineralization. Predictable mineral resources for the Kevitsa mine deposit are believed to be around 240 Mt. The economic metals in the ore are estimated as 0.41% Cu and 0.30% Ni