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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
Statistical studies showed that, against the general pattern of NW–SE-, E–W-and NE–SW-trending bodies, one cluster of intrusions has a markedly different areal distribution. The NW–SE-trending zone is the main zone, i.e. most satured with drusites (5–30% of the area). It is also characterized by ultrabasic igneous rocks, dominated by peridotite and pyroxenite (Fig. 5.8). Transverse E–W-and NW–SE-trending zones are connected with the main NW–SE-trending zone to the east and, to a lesser degree, to the west. Unlike the main zone, the transverse zones are dominated by gabbroids, with ultrabasic varieties subordinate. However, we should note that all types of intrusions are observed inside all zones.
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).
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
The ultramafic rocks observed within the COC are comparable with the bedrock lithologies that have been described from the Greenvale Ni–Co–Sc–Cr laterite deposits (Zeissink, 1969). Sc in ultramafic rocks is primarily hosted within clinopyroxene (Williams-Jones & Vasyukova, 2018). Consequently, pyroxenite has been recognised as a favourable host rock to primary, magmatic Sc mineralisation and secondary, laterite-hosted Sc mineralisation (Wang et al., 2021). Ni laterite deposits are developed best on top of harzburgite and dunite. Ni preferentially partitions into olivine during the fractionation of ferro-magnesian magmas (Herzberg et al., 2016); thus, olivine-rich peridotite generally contains greater concentrations of Ni. We have interpreted that, prior to alteration, the COC comprised differentiated peridotite, including pyroxenite and dunite. The COC contained bedrock lithologies that were favourable to the formation of lateritic Ni–Co–Sc–Cr deposits; however, we have not observed evidence for the development of a thick laterite profile in which leached metals could be concentrated into economically viable lodes.
Genetic and ore-forming ages of the Fe–P–(Ti) oxide deposits associated with mafic–ultramafic–carbonatite complexes in the Kuluketage block, NW China
Published in Australian Journal of Earth Sciences, 2019
W. Chen, X. B. Lü, X. F. Cao, Q. Yuan, X. D. Wang
The pyroxenite phase is grey to grey-green in colour and consists of diopside (70–95 vol%), minor biotite, hornblende, magnetite, and apatite (Figure 7c-1,c-2). The biotite pyroxenite is grey in colour, and it is made up of biotite (70–85 vol%), diopside (15–20 vol%), minor magnetite, and apatite (Figure 7f-1,f-2). The hornblendite is grey-green in colour and is composed of hornblende (60–80 vol%), plagioclase (10–15 vol%), minor diopside, biotite, magnetite, and apatite (Figure 7a-1,a-2). The pink-white diorite consists of 50–60 vol% plagioclase, 10–15 vol% hornblende, 10–15 vol% biotite, minor diopside, magnetite, and apatite (Figure 7d-1, d-2). The pink-yellow monzogranite is composed of plagioclase (30–40 vol%), K-feldspar (20–30 vol%), quartz (10–15 vol%), minor biotite, hornblende, magnetite, and apatite (Figure 7b-1, b-2).