Hybrid norite and the fate of argillaceous to anhydritic shales assimilated by Bushveld melts

Yudovskaya, Marina A.; Costin, Gelu; Sluzhenikin, Sergey F.; Kinnaird, Judith A.; Ueckermann, Henriëtte; Абрамова, В. Д.; Grobler, D. F.

doi:10.1007/s00126-020-00978-6

Cited by 6 publications

(2 citation statements)

References 44 publications

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“…Below the entire Flatreef sequence, sills of dunite, pyroxenite, and harzburgite may be found intruding the Transvaal Supergroup (Grobler et al, 2019;Yudovskaya et al, 2021). The package of rocks from the lower chromitite seam up to the noritic cyclic units above the Flatreef shows better mineral layering with less contamination than the Platreef, and can be well correlated with the interval from the UG-2 up to the Bastard Reef (above the Merensky Reef) in the western and eastern limbs of the BC (Grobler et al, 2019;Beukes et al, 2021;Mayer et al, 2021).…”

Section: The Flatreefmentioning

confidence: 90%

Geological setting and concentration of scandium in the Flatreef and eastern limb chromitites of the Bushveld Complex

Kotzé

Roelofse

Grobler

et al. 2022

J. S. Afr. Inst. Min. Metall.

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Scandium is an important industrial metal for which demand is projected to increase in the future. Although many Sc deposits are secondary, Sc is scavenged by clinopyroxene during fractional crystallization of primary, mafic-ultramafic magmas. Sc may thus occur in sub-economic concentrations in mafic-ultramafic intrusions. In this work, we present new data on the concentration of Sc in the Bushveld Complex (BC) of South Africa. The eastern and western limbs of the BC are considered to be largely pristine, primary magmatic deposits, whereas the northern limb shows evidence of large-scale, localized crustal contamination. Samples from the primary magmatic cumulates of the eastern limb, from the mineralized Flatreef of the northern limb, and from the crustal-contaminated Footwall Assimilation Zone (FAZ) of the Flatreef were analysed for Sc. Despite the FAZ containing abundant clinopyroxene, interpreted to have recrystallized from the original cumulates in the presence of melted sedimentary rocks, no significant differences are seen in the concentration of Sc compared to other cumulate rocks of the BC containing less-abundant clinopyroxene. The concentration of Sc in the analysed samples is mainly controlled by mineralogy, with anorthosites, chromitites, and harzburgites containing under 20 ppm, and norites and pyroxenites containing 20-40 ppm. The parapyroxenites of the FAZ are less enriched in Sc than expected, suggesting that Sc may have been lost during alteration and recrystallization.

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Section: The Flatreefmentioning

confidence: 90%

Geological setting and concentration of scandium in the Flatreef and eastern limb chromitites of the Bushveld Complex

Kotzé

Roelofse

Grobler

et al. 2022

J. S. Afr. Inst. Min. Metall.

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“…They conclude that whereas semi-massive and disseminated chromitite may have a variable composition due to equilibration with trapped silicate melt, the massive portions of the seams have overlapping compositions. Yudovskaya et al (2020) conducted a detailed petrographic and compositional study of the interaction between the intruding Lower Zone magmas and the anhydrite-rich country rocks in drill core UMT336. The study shows that contact metamorphism and partial melting may result in the formation of hybrid rocks with Sr isotope characteristics similar to those of the pristine magmatic counterparts.…”

Section: Contributions In This Thematic Issuementioning

confidence: 99%

Introduction to the special issue on the Flatreef PGE-Ni-Cu deposit, northern limb of the Bushveld Igneous Complex

2020

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More than 30 years ago, Cox and Singer (1986) suggested that magmatic platinum-group element (PGE)-Ni-Cu deposits are amongst the best understood of ore deposits, yet the origin of PGE mineralization in the Bushveld Igneous Complex (BIC) remains controversial after a century of study. In the northern limb of the BIC, the unravelling of ore formation proved particularly difficult due to relatively poor outcrop, which is typically affected by contamination of the intruding magmas with the host rocks and expressed in the form of abundant xenoliths, footwall rafts and disturbance of magmatic stratigraphy. In this thematic issue, we present contributions on the Flatreef, a recently discovered world-class PGE-Ni-Cu deposit constituting a downdip extension of the mineralized unit of the Platreef of the northern limb. Two deep shafts are currently being sunk, making the Flatreef one of the most significant new mine development on the Bushveld in several decades.

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Controls on Pt/Pd ratios in Bushveld magmas and cumulates: a review complemented by new W isotope data

Maier

Mundl‐Petermeier

2022

Miner Deposita

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The Bushveld Complex of South Africa is underlain by a fine-grained sill complex which most workers interpret to represent the quenched parent magmas to the intrusion. The sills have unusually high Pt contents (up to ~ 25 ppb) and Pt/Pd ratios (average 1.50) exceeding those in most other mantle magmas globally. Unusually high Pt/Pd is also found in many Bushveld cumulates. Understanding the origin of the high Pt/Pd is important for exploration, in view of the contrasting monetary value of the metals, but also for unravelling the petrogenesis of the intrusion. Here, we review existing platinum-group element (PGE) data and present the first radiogenic W isotope data on a Bushveld rock, to evaluate a range of potential models, including PGE fractionation prior to final magma emplacement and within the Bushveld magma chamber, magma derivation from the sub-continental lithospheric mantle (SCLM), contamination of Bushveld magma with Pt-rich continental crust, and a meteoritic component in the mantle source to the magmas or in the crust with which the magmas interacted. We identify three key processes causing fractionation of metals prior to final magma emplacement and within the Bushveld chamber, namely crystallisation of Pt alloys, partial melting of cumulus sulfides triggered by flux of volatiles followed by sulfide melt percolation, and mobilisation of PGE by percolation of volatiles through the cumulate pile. The currently available W and Ru isotope data are inconsistent with derivation of the Bushveld magmas from mantle or crustal sources containing an enhanced meteoritic component relative to normal post-Hadean mantle.

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Hybrid norite and the fate of argillaceous to anhydritic shales assimilated by Bushveld melts

Cited by 6 publications

References 44 publications

Geological setting and concentration of scandium in the Flatreef and eastern limb chromitites of the Bushveld Complex

Geological setting and concentration of scandium in the Flatreef and eastern limb chromitites of the Bushveld Complex

Introduction to the special issue on the Flatreef PGE-Ni-Cu deposit, northern limb of the Bushveld Igneous Complex

Controls on Pt/Pd ratios in Bushveld magmas and cumulates: a review complemented by new W isotope data

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