Geology and Origin of the Vanadiferous Fe-Ti Oxide-rich Kennedy's Vale Discordant Body, Eastern Limb of the Bushveld Complex, South Africa

2017 ◽  
Vol 120 (2) ◽  
pp. 251-270 ◽  
Author(s):  
R.N. Scoon ◽  
G. Costin ◽  
P.J. Gräbe
Keyword(s):  
South Africa ◽  
Bushveld Complex ◽  
Three Dimensional ◽  
Vanadium Content ◽  
Central Core ◽  
Oxide Melt ◽  
Ti Oxides ◽  
Outer Sheath ◽  
Eastern Limb ◽  
Stratigraphic Height

Abstract The 2055 Ma Bushveld Complex, South Africa, is well known for the occurrence of discordant bodies within the Rustenburg Layered Suite (RLS). Many discordant bodies disrupt mining of layered reefs, but a few have been successfully exploited, including the well known platiniferous dunite pipes. The Kennedy's Vale discordant body, situated in the Steelpoort Valley section of the Eastern Limb, has been almost entirely mined out for a central core of vanadium-rich Ti-magnetite. Discordant bodies are particularly abundant in this area which is severely disrupted by syn-Bushveld doming and faulting. The three-dimensional shape of discordant bodies in the RLS is highly variable, most are pipe-like, but Kennedy's Vale is unusual in that it constitutes an elongate, dyke-like body. The Kennedy's Vale occurrence is emplaced within gabbroic-anorthositic wall rocks of the Lower Main Zone, at a stratigraphic height of several thousands of metres below the Ti-magnetite layers. A broad zonation is recognised and the central core of massive Fe-Ti oxides is enclosed by an inner sheath of iron-rich wehrlite pegmatite and an outer sheath of iron-rich clinopyroxenite pegmatite. The sheath contains disseminated Fe-Ti oxides. An irregular and diffuse reaction rim has been identified between the outer sheath and the wall rocks. Kennedy's Vale is part of the iron-rich ultramafic pegmatite (IRUP) group of discordant bodies, highly unusual rocks characterised by the absence of plagioclase and being more differentiated than the wall rocks in which they are emplaced. The composition of the olivine in the outer sheath at Kennedys' Vale (Fo49.6-46.5) is typical of the IRUP at this stratigraphic height, but considerably more differentiated than the pyroxene in the wall rocks. The reaction rim to the dyke includes relic grains of extremely calcic plagioclase and symplectites, indicative of high-temperature reactions. Symplectites formed due to reaction between the primocrysts in the gabbroic wall rocks and Fe-Ti melts. Kennedy's Vale crystallized from dense, immiscible Fe-Ti oxide-rich melts that drained downward within the RLS into the underlying cumulates with which they reacted. The relatively high vanadium content of the Ti-magnetite in the Kennedy's Vale orebody (average of 2.0 to 2.2 weight % V2O5) is consistent with melts sourced from the lowermost group of Ti-magnetite layers in the Upper Zone. The internal zonation of the dyke is ascribed to contamination of melt with distance from the conduit. The core-zone of massive Fe-Ti oxides was the last component to form as it required a persistent supply of Fe-Ti oxide melt. The absence of core parts of massive Fe-Ti oxides from some bodies of IRUP can be explained by their relatively low stratigraphic height or the relative paucity of introduced melt.

A Comparative Study of Sulfur Isotope Variations within the Flatreef and Merensky Reef of the Bushveld Complex, South Africa

2021 ◽  
Vol 59 (6) ◽  
pp. 1363-1380
Author(s):  
Jarlen J. Keet ◽  
Frederick Roelofse ◽  
Christoph D.K. Gauert ◽  
Danie Grobler ◽  
Mike Butler
Keyword(s):  
South Africa ◽  
Bushveld Complex ◽  
Hanging Wall ◽  
Merensky Reef ◽  
Cyclic Unit ◽  
Heterogeneous Nature ◽  
Platinum Mining ◽  
Eastern Limb ◽  
New Perspective ◽  
S Isotope

ABSTRACT The Flatreef, a down-dip, sub-horizontal extension of the Platreef, which underlies the Turfspruit and Macalacaskop farms, represents the future of platinum mining in South Africa. The stratigraphic connection between the Platreef, located at the base of the northern limb of the Bushveld Complex, and the Merensky Reef in the western and eastern limbs of the complex, was disputed for many years due to the heterogeneous nature of the Platreef along strike. However, the discovery of the Flatreef led to a new perspective on the Platreef as the former allowed for the study of a magmatic stratigraphy less affected by footwall interaction. Here, we report whole-rock S isotope (δ34S) compositions across the stratigraphic units of the Flatreef and its footwall and hanging wall as intersected by boreholes UMT-276 and UMT-393, as well as stratigraphic units of the Merensky Reef at Two Rivers Platinum mine in the eastern limb. The units of the Flatreef containing platinum group element mineralization, namely the Main Reef and Upper Reef, have δ34S values that overlap with the range recorded for the Merensky Reef in the western and eastern limbs. In UMT-393, Main Reef δ34S values range between 0.2 and 1.5‰ (with the exception of three outliers, 9.7‰, 11.1‰, and 7.9‰), and 0.52‰ and 11.2‰ for two Upper Reef samples. However, in UMT-276, Main Reef δ34S values range between –0.96 and 2.24‰ and 3.19‰ was recorded for an Upper Reef sample. The S isotope compositions recorded for the Merensky Reef pyroxenite at Two Rivers Platinum mine are relatively higher with δ34S values ranging between 1.24 and 4.83‰. The top unit of the Flatreef, which is a transition zone below the Main Zone, as well as the Footwall Cyclic Unit have heavier S isotope compositions with δ34S values ranging between 6 and 17‰ for the former and 0.7 and 18.6‰ for the latter. At Two Rivers Platinum mine, the hanging-wall anorthosite has a δ34S value of 2.9‰ in contrast to the 5.7‰ measured for the footwall anorthosite and 3.27‰ for the footwall feldspathic pyroxenite. The consistent near-mantle S isotope signature and accompanying metal enrichment in the Main Reef of the Flatreef may be explained by extensive interaction of sulfide minerals in a Lower Zone conduit/pre-Platreef staging chamber with large volumes of uncontaminated magma. The δ34S values of the Merensky Reef at Two Rivers Platinum mine are slightly higher compared to that of the Main Reef at Turfspruit and Macalacaskop possibly due to interaction with underlying carbonate rocks.

Unusual Fe-Ti-Cr spinels from discordant bodies of iron-rich ultramafic pegmatite at the Amandelbult Platinum mine, northwestern Bushveld Complex

2002 ◽  
Vol 66 (6) ◽  
pp. 857-879 ◽  
Author(s):  
R. N. Scoon ◽  
H. V. Eales
Keyword(s):  
Bushveld Complex ◽  
Analytical Data ◽  
Critical Zone ◽  
Northwestern Part ◽  
Main Zone ◽  
Spinel Type ◽  
Oxide Melt ◽  
Complex Process ◽  
Compositional Gradients ◽  
Stratigraphic Height

Abstract Spinels associated with discordant bodies of iron-rich ultramafic pegmatite are described from the Amandelbult Platinum mine in the northwestern part of the Bushveld Complex. The spinels are divided into three groups, disseminated Ti-magnetite, disseminated Fe-Ti-Cr spinel and massive Fe-Ti-Cr spinel. The Fe-Ti-Cr spinels show a range of unusual compositions intermediate between chromite and Ti-magnetite. A relationship was found between stratigraphic height and spinel-type, with the Fe-Ti-Cr spinels restricted to pegmatites from the Upper Critical zone and Ti-magnetite to pegmatites from the Lower Main zone. Ilmenite is a ubiquitous component of all of the pegmatites examined here. The massive Fe-Ti-Cr oxide pegmatites are found only where earlier-formed chromitite layers are juxtaposed with sheet-like bodies of olivine-clinopyroxene pegmatite. A distinct thickening of the original chromitite layers in this situation, and compositional gradients within them, points to accretion of Fe-Ti-Cr spinels onto them prior to partial sub-solidus re-equilibration. Analytical data are presented for these spinels and for the Ti-magnetite. The composition of the Fe-Ti-Cr spinels is not duplicated by cumulus spinels in the Bushveld Complex, but the compositions and microtextures of the disseminated Ti-magnetite are very similar to cumulus Ti-magnetite from the Upper zone. Accordingly, it is deduced that the Ti-magnetite in the pegmatites from the Lower Main zone, together with the ilmenite, crystallized at magmatic temperatures from a suitable Fe-Ti-rich silicate-oxide melt. No evidence has been found to link the pegmatites to hydrothermal fluids. The Cr-rich nature of the disseminated spinels in pegmatites from the Upper Critical zone suggests that the pegmatite melt was richer in chromium at this stratigraphic height, although re-equilibration with earlier-formed cumulus chromite also occurred. Formation of the Fe-Ti-Cr oxide pegmatites reflects a complex process that is incompletely understood and why new oxides plate onto pre-existing chromitite layers that are juxtaposed with Fe-rich ultramafic pegmatites is a matter of conjecture.

Lithostratigraphy of the Palaeoproterozoic Hekpoort Formation (Pretoria Group, Transvaal Supergroup), South Africa

2020 ◽  
Vol 123 (4) ◽  
pp. 655-668
Author(s):  
N. Lenhardt ◽  
W. Altermann ◽  
F. Humbert ◽  
M. de Kock
Keyword(s):  
South Africa ◽  
Bushveld Complex ◽  
Sedimentary Rocks ◽  
Type Locality ◽  
Large Igneous Province ◽  
Braided River ◽  
River Systems ◽  
The West ◽  
Igneous Province ◽  
Transvaal Supergroup

Abstract The Palaeoproterozoic Hekpoort Formation of the Pretoria Group is a lava-dominated unit that has a basin-wide extent throughout the Transvaal sub-basin of South Africa. Additional correlative units may be present in the Kanye sub-basin of Botswana. The key characteristic of the formation is its general geochemical uniformity. Volcaniclastic and other sedimentary rocks are relatively rare throughout the succession but may be dominant in some locations. Hekpoort Formation outcrops are sporadic throughout the basin and mostly occur in the form of gentle hills and valleys, mainly encircling Archaean domes and the Palaeoproterozoic Bushveld Complex (BC). The unit is exposed in the western Pretoria Group basin, sitting unconformably either on the Timeball Hill Formation or Boshoek Formation, which is lenticular there, and on top of the Boshoek Formation in the east of the basin. The unit is unconformably overlain by the Dwaalheuwel Formation. The type-locality for the Hekpoort Formation is the Hekpoort farm (504 IQ Hekpoort), ca. 60 km to the west-southwest of Pretoria. However, no stratotype has ever been proposed. A lectostratotype, i.e., the Mooikloof area in Pretoria East, that can be enhanced by two reference stratotypes are proposed herein. The Hekpoort Formation was deposited in a cratonic subaerial setting, forming a large igneous province (LIP) in which short-termed localised ponds and small braided river systems existed. It therefore forms one of the major Palaeoproterozoic magmatic events on the Kaapvaal Craton.

Variations in Composition, Texture, and Platinum Group Element Mineralization in the Lower Group and Middle Group Chromitites of the Northwestern Bushveld Complex, South Africa

2019 ◽  
Vol 114 (3) ◽  
pp. 569-590 ◽  
Author(s):  
Felix E.D. Kaufmann ◽  
Marie C. Hoffmann ◽  
Kai Bachmann ◽  
Ilya V. Veksler ◽  
Robert B. Trumbull ◽  
...  
Keyword(s):  
South Africa ◽  
Platinum Group Element ◽  
Bushveld Complex ◽  
Group Element ◽  
Middle Group ◽  
Platinum Group ◽  
Lower Group

DETRITAL PLATINUM-GROUP MINERALS IN RIVERS DRAINING THE EASTERN BUSHVELD COMPLEX, SOUTH AFRICA

2004 ◽  
Vol 42 (2) ◽  
pp. 563-582 ◽  
Author(s):  
T. Oberthur ◽  
F. Melcher ◽  
L. Gast ◽  
C. Wohrl ◽  
J. Lodziak
Keyword(s):  
South Africa ◽  
Bushveld Complex ◽  
Platinum Group Minerals ◽  
Platinum Group
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