Chromite chemistry of a massive chromitite seam in the northern limb of the Bushveld Igneous Complex, South Africa: correlation with the UG-2 in the eastern and western limbs and evidence of variable assimilation of footwall rocks

ABSTRACT The UG-2 chromitite layer, with its elevated platinum-group element content, is a key marker horizon in the eastern and western limbs of the Bushveld Igneous Complex and the largest platinum-group element chromite-hosted resource of its kind in the world. In contrast, much less is known about its stratigraphic equivalent in the northern limb, the “UG-2 equivalent” (UG-2E) chromitite. Recent studies on chromite mineral chemistry show similarities between the UG-2 and sections of the UG-2E, but also that the UG-2E was partially contaminated by assimilation of local metasedimentary rocks. Here, we provide a detailed characterization of sulfide minerals and platinum-group minerals in a suite of samples from the UG-2E and compare the results with data obtained from a reference suite of samples from the UG-2. Results from petrographic observations, electron probe microanalysis, laser ablation-inductively coupled plasma-mass spectrometry, quantitative evaluation of materials by scanning electron microscopy, and δ34S isotopes show that: (1) sulfide minerals in the UG-2E and UG-2 consist mainly of pentlandite-chalcopyrite-pyrrhotite, but pyrrhotite is significantly more abundant in the UG-2E and almost absent in the UG-2; (2) iron contents in pentlandite from the UG-2E are significantly higher than in the UG-2; (3) platinum-group element contents within sulfide minerals are different between the two chromitites; (4) UG-2E platinum-group minerals are dominated by arsenides and bismuthotellurides, and by alloys and platinum-group element-sulfide minerals in the UG-2; (5) sulfide mineral chemistry and δ34S values indicate some crustal contamination of the UG-2E; and (6) sulfide mineral and secondary silicate mineral textures in both the UG-2E and UG-2 are indicative of minor, millimeter- to centimeter-scale, hydrothermal alteration. From our observations and results, we consider the UG-2E chromitite in the northern limb to be the equivalent to the UG-2 in the eastern and western limbs that has been contaminated by assimilation of Transvaal Supergroup footwall rocks during emplacement. The contamination resulted in UG-2E sulfide mineral elemental contents and platinum-group mineral types and abundances that are distinct from those of the UG-2 in the rest of the Bushveld.

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Atmospheric trace metals measured at a regional background site (Welgegund) in South Africa

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-4251-2017 ◽

2017 ◽

Vol 17 (6) ◽

pp. 4251-4263 ◽

Cited By ~ 19

Author(s):

Andrew D. Venter ◽

Pieter G. van Zyl ◽

Johan P. Beukes ◽

Micky Josipovic ◽

Johan Hendriks ◽

...

Keyword(s):

South Africa ◽

Trace Metals ◽

Trace Metal ◽

Size Fraction ◽

Abundant Species ◽

Metal Species ◽

Metal Concentrations ◽

Igneous Complex ◽

Size Fractions ◽

Bushveld Igneous Complex

Abstract. Atmospheric trace metals can cause a variety of health-related and environmental problems. Only a few studies on atmospheric trace metal concentrations have been conducted in South Africa. Therefore the aim of this study was to determine trace metal concentrations in aerosols collected at a regional background site, i.e. Welgegund, South Africa. PM1, PM1–2. 5 and PM2. 5–10 samples were collected for 13 months, and 31 atmospheric trace metal species were detected. Atmospheric iron (Fe) had the highest concentrations in all three size fractions, while calcium (Ca) was the second-most-abundant species. Chromium (Cr) and sodium (Na) concentrations were the third- and fourth-most-abundant species, respectively. The concentrations of the trace metal species in all three size ranges were similar, with the exception of Fe, which had higher concentrations in the PM1 size fraction. With the exception of titanium (Ti), aluminium (Al) and manganese (Mg), 70 % or more of the trace metal species detected were in the smaller size fractions, which indicated the influence of industrial activities. However, the large influence of wind-blown dust was reflected by 30 % or more of trace metals being present in the PM2. 5–10 size fraction. Comparison of trace metals determined at Welgegund to those in the western Bushveld Igneous Complex indicated that at both locations similar species were observed, with Fe being the most abundant. However, concentrations of these trace metal species were significantly higher in the western Bushveld Igneous Complex. Fe concentrations at the Vaal Triangle were similar to levels thereof at Welgegund, while concentrations of species associated with pyrometallurgical smelting were lower. Annual average Ni was 4 times higher, and annual average As was marginally higher than their respective European standard values, which could be attributed to regional influence of pyrometallurgical industries in the western Bushveld Igneous Complex. All three size fractions indicated elevated trace metal concentrations coinciding with the end of the dry season, which could partially be attributed to decreased wet removal and increases in wind generation of particulates. Principal component factor analysis (PCFA) revealed four meaningful factors in the PM1 size fraction, i.e. crustal, pyrometallurgical-related and Au slimes dams. No meaningful factors were determined for the PM1–2. 5 and PM2. 5–10 size fractions, which was attributed to the large influence of wind-blown dust on atmospheric trace metals determined at Welgegund. Pollution roses confirmed the influence of wind-blown dust on trace metal concentrations measured at Welgegund, while the impact of industrial activities was also substantiated.

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The statistical and wavelet analysis of density and susceptibility measurements of the Bellevue drillcore, Northern Lobe, Bushveld Igneous Complex, South Africa

10.3997/2214-4609-pdb.143.p5 ◽

2001 ◽

Author(s):

S.J. Webb ◽

G.R.J. Cooper ◽

L.D. Ashwal ◽

M.W. Knoper

Keyword(s):

South Africa ◽

Wavelet Analysis ◽

Igneous Complex ◽

Bushveld Igneous Complex

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High K/Rb ratios in rocks from the Bushveld Igneous Complex, South Africa

Earth and Planetary Science Letters ◽

10.1016/0012-821x(68)90048-4 ◽

1968 ◽

Vol 4 (1) ◽

pp. 22-29 ◽

Cited By ~ 10

Author(s):

A.J. Erlank ◽

R.V. Danchin ◽

C.C. Fullard

Keyword(s):

South Africa ◽

Igneous Complex ◽

High K ◽

Bushveld Igneous Complex

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Assessing the extent of local crust assimilation within the Flatreef, northern limb of the Bushveld Igneous Complex, using sulfur isotopes and trace element geochemistry

Mineralium Deposita ◽

10.1007/s00126-020-01024-1 ◽

2020 ◽

Cited By ~ 1

Author(s):

Evan Keir-Sage ◽

Matthew I. Leybourne ◽

Pedro J. Jugo ◽

Danie F. Grobler ◽

Cédric C. Mayer

Keyword(s):

Trace Element ◽

Primitive Mantle ◽

Trace Element Geochemistry ◽

Isotopic Data ◽

Igneous Complex ◽

Merensky Reef ◽

Northern Limb ◽

Geochemical Parameters ◽

Pge Mineralization ◽

Bushveld Igneous Complex

Abstract The proximity to metasedimentary footwall rocks relative to platinum group element (PGE) mineralized intrusive rocks in the northern limb of the Bushveld Igneous Complex (BIC) has resulted in complex local contamination in the intrusions. To assess the extent of incorporation of non-magmatic material and its effects on PGE mineralization, major element, trace element, and S isotopic data were collected from drill core UMT094 on the Turfspruit farm, where core logging has shown that the mineralized Platreef, forming the Flatreef deposit, is located stratigraphically well above local sedimentary footwall rocks. The S isotopic data combined with whole rock geochemistry data (including CaO/Al2O3, (V/Ti)PM, (Ni/Cr)PM, S/Se, loss on ignition) were used to assess incorporation of a range of local footwall material. The δ34S data show a steady decrease from the footwall assimilation zone (δ34S typically + 8 to + 9‰, maximum 12‰) to near constant δ34S values (δ34S < + 4‰) below the main PGE reef. Similar values have been documented for the Merensky Reef in the eastern and western limbs of the BIC (δ34S ~ 0 to + 3.5‰). Other geochemical parameters, such as S/Se and CaO/Al2O3, also match the ranges documented for the Merensky Reef elsewhere in the BIC. In addition, parameters such as whole rock V/Ti, normalized to primitive mantle (V/Ti)PM, are shown to be useful indicators of contamination and the type of contaminant with 1 < (V/Ti)PM < 2 for uncontaminated magmatic units; [V/Ti]pm > 2 for shale assimilation; and [V/Ti]pm < 1 for carbonate assimilation. The results suggest that the main PGE mineralization in the Flatreef deposit formed without significant in situ contamination and that the primary mechanism of PGE mineralization in the Platreef at Turfspruit was no different than the mechanism that generated the Merensky Reef in the eastern and western limbs of the BIC.

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

Mineralium Deposita ◽

10.1007/s00126-020-01027-y ◽

2020 ◽

Author(s):

Wolfgang D. Maier ◽

Marina Yudovskaya ◽

Pedro Jugo

Keyword(s):

Ore Deposits ◽

Special Issue ◽

Ore Formation ◽

Igneous Complex ◽

Northern Limb ◽

Pge Mineralization ◽

World Class ◽

Bushveld Igneous Complex ◽

Mine Development ◽

Host Rocks

AbstractMore 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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