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Occurrence of the Transvaal Supergroup in northeastern South Africa, showing profiles (traverses) along which stratigraphic observations and measurements were taken (Button 1973). It should be noted that black lines are profile locations, not dykes; also that traverses are of differing lengths reflecting (1) the variable numbers and varying thicknesses of formations covered and (2) the variable steepness of topography along the path of the traverse. For example, the long traverse SE of Belfast (Be) covers five formations (P8P12 in Table 1). Locations: P, Pretoria; Ca, Carolina; Be, Belfast; D, Dullstroom; L, Lydenburg; Bu, Burgersfort; Ch, Chuniespoort; M, Mokopane; S, Sabie. The position of 25 × 25 km grid squares is shown, with each square being identified by an alphabetic character and a numeral.
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Systematic measured profiles on a regional scale are used to document the distribution of noritic and amphibolitic sills (787 in total) in the largely sedimentary latest Archaean–early Proterozoic succession of the Transvaal Supergroup in northeastern South Africa. An aggregate thickness of over 2.2 km of sills intruded this 12 km thick succession....
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... the great thickness of the suc- cession, the results of this investigation represent a unique study of the distribution of intrusions in a sedimentary basin. The general geology of the region studied is shown in Figure 2. The outcrop of the eastern Transvaal Supergroup forms a large arc from Carolina through Burgersfort and swinging NW to Chuniespoort and ending near Mokopane. ...
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... traverses (locations shown in Fig. 2) were selected to provide good exposures of representative sections of the Transvaal Supergroup. Traverses were laid out normal to the regional strike and to the edge of the Transvaal structural basin. Traverses were designed to cover at least a single entire formation, but many extended across several formations. For example, the long ...
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... exposures of representative sections of the Transvaal Supergroup. Traverses were laid out normal to the regional strike and to the edge of the Transvaal structural basin. Traverses were designed to cover at least a single entire formation, but many extended across several formations. For example, the long traverse SE of the town of Belfast (Be in Fig. 2) extended across five for- mations (P8-P12 in Table 1). In this way, data for a total of 440 measured profiles through Transvaal Supergroup strata and included sills were created. In aggregate, stratigraphic thicknesses of 136 km of Transvaal strata and 27.1 km of sill (787 sills) were ...
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... study area was divided into a grid (Fig. 2), each square cover- ing 25 by 25 km or 625 km 2 . The total thickness of sill and sedi- mentary and/or volcanic rock measured on all traverses within each square was calculated, and the sill intensity was computed as a ratio of sill to sill plus host thickness expressed as a percentage (Fig. 4). Figure 4a shows the intensity of sill in ...
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... bodies, which are considered to be related to the marginal zone of the Bushveld Complex ( Sharpe 1981Sharpe , 1984Clarke et al. 2009). Sill intensity is also very much lower in grid squares 4A, 5A and 3B in the north- ern section. Much of this latter region of significantly lower sill intensity corresponds to the position of the Selati Trough (Fig. 2), along which stratigraphic observations and measurements were taken (Button 1973). It should be noted that black lines are profile locations, not dykes; also that traverses are of differing lengths reflecting (1) the variable numbers and varying thicknesses of formations covered and (2) the variable steepness of topography along the ...
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... strata-transgressive nature of the Bushveld Complex (Fig. 12), which cuts through 5 km of the uppermost formations of the Transvaal Supergroup from the Dullstroom basalts to the Lydenburg shale between Dullstroom and Burgersfort, means that the various sedimentary formations lie at variable depths below the base of the Bushveld Complex (Button 1973). A schematic strati- graphic long profile of ...
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... strata-transgressive nature of the Bushveld Complex (Fig. 12), which cuts through 5 km of the uppermost formations of the Transvaal Supergroup from the Dullstroom basalts to the Lydenburg shale between Dullstroom and Burgersfort, means that the various sedimentary formations lie at variable depths below the base of the Bushveld Complex (Button 1973). A schematic strati- graphic long profile of this area showing this relationship is pre- sented in Figure 12. The long section shows that the transgressive relationship varies from mild to sharp. ...
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... Seen in an 80 km long section (Fig. 12), the basal contact of the Bushveld Complex is sharply transgressive across several of the upper units of the Transvaal Supergroup, cutting through some 5 km of stratigraphy, from the level of the Dullstroom basalt to the Lydenburg shale. The contour map of sill intensity (Fig. 4b) shows a pronounced high (in block coordinates 5F and ...
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... collection of our information was made possible owing to the Bushveld Complex having been emplaced near the top of the Transvaal Supergroup and causing the inward dip of the sedimen- tary rocks, and the preservation of a near-complete stratigraphic Button 1973Button , 1976. Place name locations are shown in Figure 2. succession. This resulted in the availability of dip-parallel surface traverses intersecting the entire succession, from Archaean base- ment, through the Transvaal Supergroup to the base of the Bushveld Complex. ...
Citations
... Datings of metamorphic minerals range from 2 177 ± 35 Ma (Ar-Ar on sericite, Timeball Hill Fm, Alexandre et al., 2006) to 2 121 ± 9 Ma (SIMS U-Pb on metamorphic xenotime in the late Archaean Witwatersrand Supergroup, Rasmussen et al., 2007Rasmussen et al., , 2019. The Pretoria Group has been intruded by two suites of mafic sills (Willemse, 1959;Sharpe, 1981;Cawthorn et al., 1981;Button and Cawthorn, 2015). The older suite (the Lydenburg Diabase Suite of Bolhar and Cawthorn, 2022, designated Pre BVC in Figure 2) predates emplacement of the Bushveld Complex and associated mafic sills (Syn BVC in Figure 2). ...
The Palaeoproterozoic sandstones and quartzites of the Pretoria Group (Transvaal Supergroup) in the Transvaal Basin of South Africa are important markers for regional correlations and dating of events of global importance (e.g., the Great Oxidation Event). The succession has few independent age markers, and much of the discussion about the time of deposition and the source of material of these rocks has been based on data from detrital zircon suites.
The clastic sedimentary rocks of the Pretoria Group contain detrital zircon grains ranging from the Mesoarchaean to ages that are near-contemporaneous to, and even younger than the overlying and crosscutting igneous rocks of the Bushveld Complex. We show that the U-Pb age and Lu-Hf isotope distributions of the detrital zircon population in the Pretoria Group are the result of three different types of processes, acting successively: (1) Crystallisation in the igneous or metamorphic protosource rock (i.e., the rock where the zircon originally crystallised), (2) Metamorphic and hydrothermal resetting of the U-Pb chronometer induced by emplacement and crystallisation of the 2 055 Ma Bushveld Complex, and (3) Late, low-temperature processes (e.g., weathering).
Critical age markers of maximum ages of deposition obtained after excluding effects of (2) and (3) are the 2 200 Ma Magaliesberg Formation (outside of the Bushveld aureole) and the 2 080 to 2 100 Ma Lakenvalei Formation. The Leeuwpoort Formation is a worst-case example, containing both young (<2 200 Ma) unmodified detrital zircon and hydrothermally altered zircon in the same age range. The two can only be distinguished from trace element analyses.
Age distributions of Archaean and early Palaeoproterozoic zircon age fractions overlap with detrital zircon age suites in lower (i.e., pre-Timeball Hill Formation) parts of the Transvaal Supergroup, suggesting recycling within the basin or from the basin margin. Overlaps in 2 200 to 2 350 Ma zircon ages with those of volcanogenic zircon in the Timeball Hill Formation again suggest recycling. The origin of 2 080 to 2 150 Ma zircon is uncertain, but neither poorly constrained sources in the Kaapvaal Craton (e.g., Okwa Basement Complex) nor recycling of volcanogenic material from post-Magaliesberg formations can be ruled out.
... Parameter testing showed that a sill at least 200 m thick, intruded into a geothermal gradient of at least 100°C/km (four times the normal continental gradient of 25°C/ km) is required in order for any melt to remain in the sill during our period of measurement. A sill this thick is (Button & Cawthorn, 2015), especially given the lack of evidence of a magma reservoir from gravity measurements (Camacho et al., 2019). Our simple modeling assumes that the sill was intruded as a single unit during the Timanfaya eruption, which is not consistent with understanding of how magmatic zones develop from multiple successive episodes of intrusion (Annen, 2017), nor with magnitudes of opening during recent major intrusions (Wright et al., 2006). ...
The 1730–1736 eruption on Lanzarote was one of the most significant volcanic eruptions to occur on the Canary Islands, with lavas covering over 200 km2. Globally, it is volumetrically the third largest known subaerial basaltic fissure eruption in the past 1,100 years. Here we use Sentinel-1 and ENVISAT interferograms on both ascending and descending orbits to construct a time series of line-of-sight surface displacements and calculate linear vertical deformation rates. We resolve a constant subsidence rate of about 6 mm/yr associated with an area of ∼20 km2 within the central and western portion of the Timanfaya lava flows relative to the rest of the island. This is consistent over the 28-year period (1992–2020) covered by the Sentinel-1 and ENVISAT data when combined with the previously published European Remote-Sensing Satellite data. Time series constructed using Sentinel-1 short interval interferograms have previously been shown to suffer systematic biases and we find that by making longer period interferograms these biases can be mitigated (when compared against an averaged stack of 1-year interferograms). Cooling-driven contraction of an intrusion would require improbably large sill thickness to achieve the observed subsidence rates. Our observations are consistent with the cooling of lavas on the order of one hundred meters, twice as thick as previous estimates, which suggests overall lava volume for this eruption may have been underestimated. This is also evidence of the longest duration of lava flow subsidence ever imaged which indicates that these cumulative thick flows can continue to deform significantly even three centuries after emplacement.
... The limbs appear to be (inter)connected at depth based on geophysical evidence, stratigraphic relations, and xenolith studies (Hall, 1932;Cawthorn & Walraven, 1998;Webb et al., 2011). An extensive sequence of basement sills, pyroxenitic to noritic in composition, related to the Bushveld Complex occurs within the Transvaal Supergroup (Cawthorn et al., 1981;Sharpe & Hulbert, 1985;Button & Cawthorn, 2015). Within the Bushveld Complex, the Rustenburg Layered Suite represents an up to 8 km thick sequence of stratified mafic and ultramafic cumulates that hosts world-class deposits of chromium, platinum group elements (PGE) and vanadium (Eales & Cawthorn, 1996;Cawthorn et al., 2006;Maier et al., 2013;Cawthorn, 2015;Prevec, 2019;Scoon & Viljoen, 2019) (Fig. 2). ...
... Phalaborwa, Uitkomst, Molopo Farms, Moshaneng, Mahalapye, Lindeques Drift, Heidelberg) distributed across the northern Kaapvaal craton, at relatively shallow crustal levels was associated with the release of volatiles (dominantly CO 2 ) and toxic metals (Hg) that may have triggered widespread environmental change. The main components of the Bushveld LIP constitute an impressive stack of upper crustal and surficial magmatic products, including thicknesses of 6-8 km of ultramaficmafic cumulates (Rustenburg Layered Suite) (Finn et al., 2015), 3 km of high-level granites (Lebowa Granite Suite) (Kleemann & Twist, 1989), 3-6 km of Rooiberg volcanic rocks dominated by rhyolitic lava flows and intercalated pyroclastic deposits (Lenhardt & Eriksson (2012), and an aggregate thickness of >2 km of basement sills (many noritic in composition) in the Transvaal Supergroup (Button & Cawthorn, 2015). Direct release of gas (CO 2 , SO 2 , halogens) from these magmas, including during high-level granitic magmatism and silicic volcanism, was likely to have been important (e.g. ...
... For example, erosional structures corroborate sedimentary indicators that microbial mats mostly flourished in current-driven environments, such as palaeoshorelines and periodically restricted basins, whereas variably tufted morphologies can denote either metabolic reactions to nutrient availability and diffusion through the mat or stochastic responses to environmental toxicity. Button and Cawthorn (2015). ...
The Kaapvaal and Zimbabwe cratons host some of the earliest evidence for life. When compared to the contemporaneous East Pilbara craton, cherts and other metasedimentary horizons in southern Africa preserve traces of life with far greater morphological and geochemical fidelity. In spite of this, most fossiliferous horizons of southern Africa have received relatively limited attention. This review summarises current knowledge regarding the nature of early life and its distribution with respect to environments and ecosystems in the Archaean (>2.5 Ga) of the region, correlating stratigraphic, sedimentological, geochemical and palaeontological understanding. There is abundant and compelling evidence for both anoxygenic photosynthetic and chemosynthetic biomes dominating Palaeoarchaean- Mesoarchaean strata dating back to around 3.5 Ga, and the prevalence of each is tied to palaeoenvironmental parameters deducible from the rock record. Well-developed, large stromatolites characteristic of younger Mesoarchaean-Neoarchaean sequences were probably constructed by oxygenic photosynthesisers. Isotopic evidence from the Belingwe greenstone belt and the Transvaal Supergroup indicates that both a full sulphur cycle and complex nitrogen cycling were in operation by the Mesoarchaean-Neoarchaean. The Archaean geological record of southern Africa is thus a rich repository of information regarding the co-evolving geosphere and biosphere in deep time.
... The limbs appear to be (inter)connected at depth based on geophysical evidence, stratigraphic relations, and xenolith studies (Hall, 1932;Cawthorn & Walraven, 1998;Webb et al., 2011). An extensive sequence of basement sills, pyroxenitic to noritic in composition, related to the Bushveld Complex occurs within the Transvaal Supergroup (Cawthorn et al., 1981;Sharpe & Hulbert, 1985;Button & Cawthorn, 2015). Within the Bushveld Complex, the Rustenburg Layered Suite represents an up to 8 km thick sequence of stratified mafic and ultramafic cumulates that hosts world-class deposits of chromium, platinum group elements (PGE) and vanadium (Eales & Cawthorn, 1996;Cawthorn et al., 2006;Maier et al., 2013;Cawthorn, 2015;Prevec, 2019;Scoon & Viljoen, 2019) (Fig. 2). ...
... Phalaborwa, Uitkomst, Molopo Farms, Moshaneng, Mahalapye, Lindeques Drift, Heidelberg) distributed across the northern Kaapvaal craton, at relatively shallow crustal levels was associated with the release of volatiles (dominantly CO 2 ) and toxic metals (Hg) that may have triggered widespread environmental change. The main components of the Bushveld LIP constitute an impressive stack of upper crustal and surficial magmatic products, including thicknesses of 6-8 km of ultramaficmafic cumulates (Rustenburg Layered Suite) (Finn et al., 2015), 3 km of high-level granites (Lebowa Granite Suite) (Kleemann & Twist, 1989), 3-6 km of Rooiberg volcanic rocks dominated by rhyolitic lava flows and intercalated pyroclastic deposits (Lenhardt & Eriksson (2012), and an aggregate thickness of >2 km of basement sills (many noritic in composition) in the Transvaal Supergroup (Button & Cawthorn, 2015). Direct release of gas (CO 2 , SO 2 , halogens) from these magmas, including during high-level granitic magmatism and silicic volcanism, was likely to have been important (e.g. ...
The Paleoproterozoic Bushveld Complex, including the world’s largest layered intrusion and host to world-class stratiform chromium, platinum group element, and vanadium deposits, is a remarkable natural laboratory for investigating the timescales of magmatic processes in the Earth’s crust. A framework for the emplacement, crystallization, and cooling of the Bushveld Complex based on integrated U-Pb zircon-baddeleyite-titanite-rutile geochronology is presented for samples of different rock types from the Bushveld Complex, including ultramafic and mafic cumulates, mineralized horizons, granitic rocks from the roof, and a carbonatite from the nearby alkaline Phalaborwa Complex. The results indicate that (1) the Bushveld Complex was built incrementally over a ∼5 million-year interval from 2060 Ma to 2055 Ma with a peak in magma flux at c.2055–2056 Ma, (2) U-Pb zircon crystallization ages do not decrease in an uninterrupted systematic manner from the base to the top of the intrusion indicating that the Bushveld Complex does not represent the crystallized products of a single progressively filled and cooled magma chamber, and (3) U-Pb rutile dates constrain cooling of the intrusion at the level of the Critical Zone through ∼500 °C by 2053 Ma. The c.2060 Ma Phalaborwa Complex (pyroxenite, syenite, carbonatite + Cu-Fe-phosphate-vermiculite deposits) represents one of the earliest manifestations of widespread Bushveld-related magmatism in the northern Kaapvaal craton. The extended range and out-of-sequence U-Pb zircon dates determined for a harzburgite from the Lower Zone (c.2056 Ma), an orthopyroxenite from the Lower Critical Zone (c.2057 Ma), and orthopyroxenites from the Upper Critical Zone (c.2057–2060 Ma) are interpreted to indicate that the lower part of the Bushveld Complex developed through successive intrusions and accretion of sheet-like intrusions (sills), some intruded at different stratigraphic levels. Crystallization of the main volume of the Bushveld Complex, as represented by the thick gabbroic sequences of the Main Zone and Upper Zone, is constrained to a relatively narrow interval of time (∼1 million years) at c.2055–2056 Ma. Granites and granophyres in the roof, and a diorite in the uppermost Upper Zone, constitute the youngest igneous activity in the Bushveld Complex at c.2055 Ma. Collectively, these results contribute to an emerging paradigm shift for the assembly of some ultramafic-mafic magmatic systems from the conventional “big tank” model to an “amalgamated sill” model. The volume-duration relationship determined for magmatism in the Bushveld Complex, when compared to timescales established for the assembly of other layered intrusions and more silica-rich plutonic-volcanic systems worldwide, is distinct and equivalent to those determined for Phanerozoic continental and oceanic flood basalts that constitute large igneous provinces. Emplacement of the 2055–2060 Ma Bushveld Complex corresponds to the end of the Lomagundi-Jatuli Event, the largest magnitude positive carbon isotope excursion in Earth history, and this temporal correlation suggests that there may have been a contribution from voluminous Bushveld ultramafic-mafic-silicic magmatism to disruptions in the global paleoenvironment.
... Igneous sills have been widely found in sedimentary basins around the world as observed in outcrops (Burchardt, 2008;Galerne et al., 2011;Muirhead et al., 2012;Senger et al., 2014;Button and Cawthorn, 2015;Schofield et al., 2015;Eide et al., 2017) and seismic-reflection data (Cartwright and Huuse, 2005;Planke et al., 2005;Hansen and Cartwright, 2006;Magee et al., 2016a;Mark et al., 2017;McLean et al., 2017;da Costa Correia et al., 2019;Kumar et al., 2019). The emplacement of sills can play constructive and destructive roles in the formation and evolution of the whole petroleum system (Galushkin, 1997;Chevallier and Woodford, 1999;Planke et al., 2000;Monreal et al., 2009;Rateau et al., 2013;Schofield et al., 2015;Spacapan et al., 2018;da Costa Correia et al., 2019); therefore, the timing and spatial distribution of igneous sill emplacement have been widely analyzed (Trude et al., 2003;Malthe-Sørenssen et al., 2004;Svensen et al., 2004;Planke et al., 2005;Hansen, 2006;Hansen et al., 2008;Sydnes et al., 2018;Wu et al., 2018). ...
Sill emplacement mechanisms are very complex, diverse and regional, and insights from sill reflections are helpful for understanding the emplacement process of magma in the Tarim Basin. This study takes advantage of high-quality two-dimensional seismic data, which is rarely used to study sills in the Tarim Basin, to analyze the sills’ geometric characteristics, plan-view distributions, emplacement timing, and emplacement mechanisms with unconformity surfaces. In the seismic reflection profiles of the Middle-Upper Ordovician in the North Depression and the southern part of the Tabei Uplift in the Tarim Basin, sills with strong positive polarity reflections appear, and they are closely distributed near the Tg52 unconformity surface, which represents the interface between Middle Ordovician limestone and Upper Ordovician mudstone. According to the vertical position of the sills relative to the unconformity, we can divide the sills into saucer-shaped or quasi-saucer-shaped sills above the unconformity surface, sill complexes and saucer-shaped sills on the unconformity surface, and saucer-shaped sills below the unconformity surface. Potential hydrothermal vents and peripheral faults associated with sill intrusion terminate upwards in the middle Permian strata, suggesting that these sills formed in the middle Permian. Sills with inner flat sheets on the Tg52 unconformity surface formed when the magma ascended and encountered an abrupt change in the fracture toughness and tensile strength between the two adjacent host rock layers. The sills above and on the Tg52 unconformity surface overlap or are vertically linked; therefore, the sills above the Tg52 unconformity surface are the result of the continuous upward expansion of the sills on the unconformity surface, forming sill complexes. Our findings further confirm that unconformities are important interfaces that affect the emplacement of sills.
... well and field data, approximately 60% of intrusions fall less than 10 m (<35 ft) in thickness within sedimentary basins globally (Button andCawthorn, 2015, Schofield et al., 2015;Mark et al., 2017;Eide et al., 2018;Svensen et al., 2014Svensen et al., , 2016. This aspect on its own may not appear significant, but when it is considered in the context of the limitations of imaging of seismic reflection data, this can become an issue. ...
... well and field data, approximately 60% of intrusions fall less than 10 m (<35 ft) in thickness within sedimentary basins globally (Button andCawthorn, 2015, Schofield et al., 2015;Mark et al., 2017;Eide et al., 2018;Svensen et al., 2014Svensen et al., , 2016. This aspect on its own may not appear significant, but when it is considered in the context of the limitations of imaging of seismic reflection data, this can become an issue. ...
In situ overpressures in sedimentary basins are commonly attributed to disequilibrium compaction or fluid expansion mechanisms, though overpressures in shallow sedimentary sequences may also develop by vertical transfer of pressure from deeper basin levels, for example via faults. Mafic sill complexes are common features of sedimentary basins at rifted continental margins, often comprising networks of interconnected sills and dikes that facilitate the transfer of magma over considerable vertical distances to shallow basinal depths. Here we document evidence for deep sills (depths >5 km (16,000 ft)) hosting permeable, open fracture systems that may have allowed transmission of overpressure from ultra-deep basinal (>7 km (23,000 ft)) levels. Most notably, well 214/28-1 encountered overpressured, thin (<8 m (26 ft)) and fractured gas-charged intrusions, which resulted in temporary loss of well control. While the overpressure could reflect local gas generation related to thermal maturation of Cretaceous shales into which the sills were emplaced, this would require the overpressures to have been sustained for unfeasibly long timescales (>58 Myr). We instead suggest that transgressive, interconnected sill complexes, such as those penetrated by well 214/28-1, may represent a previously unrecognized mechanism of transferring overpressures (and indeed hydrocarbons) laterally and vertically from deep to shallow levels in sedimentary basins, and that they represent a potentially under-recognized hazard to both scientific and petroleum drilling in the vicinity of subsurface igneous complexes.
... Due to paucity of outcrop, we could not yet identify large potholes at Turfspruit, but cm-sized potholes are abundant in drill core and in Shaft #1 exposures (Online resource 2). Synmagmatic doming of the floor rocks to the Bushveld is equally to be expected, in view of the abundant Bushveld aged sills below the complex (Sharpe 1981;Button and Cawthorn 2015) that likely caused localised partial melting of the sedimentary rocks. Examples of such domes have been documented by Sharpe and Chadwick (1982), Uken and Watkeys (1997) and Scoon (2002). ...
The original version of this article contained several mistakes. Due to technical problems at the typesetter, author corrections were not carried out correctly. The original article has been corrected.
... Due to paucity of outcrop, we could not yet identify large potholes at Turfspruit, but cm-sized potholes are abundant in drill core and in Shaft #1 exposures (Online resource 2). Synmagmatic doming of the floor rocks to the Bushveld is equally to be expected, in view of the abundant Bushveld aged sills below the complex (Sharpe 1981;Button and Cawthorn 2015) that likely caused localised partial melting of the sedimentary rocks. Examples of such domes have been documented by Sharpe and Chadwick (1982), Uken and Watkeys (1997) and Scoon (2002). ...
The Flatreef is a world-class platinum-group element (PGE) deposit recently discovered down-dip from existing mining and exploration operations on the northern limb of the Bushveld Complex. Current indicated resources stand at 42 Moz PGE (346 Mt with 3.8 g/t Pt+Pd+Rh+Au, 0.32% Ni and 0.16% Cu) which, in the case of Pt, is equivalent to ~ 10 years global annual production, making it one of the largest PGE deposits on earth. The grade and thickness of the Flatreef mineralised interval is highly unusual, with some drill core intersections containing up to 4.5 g/t Pt+Pd+Rh+Au over 90 m in drill core. Here, we document the down-dip and along-strike litho- and chemostratigraphy of the Flatreef and its footwall and hanging wall rocks, based on a diamond drill core database totalling > 720 km. At the base of the sequence intersected in the drill cores are up to 700-m-thick sills of ultramafic rocks (dunite, harzburgite, pyroxenite) emplaced into pelitic, dolomitic, and locally quartzitic and evaporitic rocks belonging to the Duitschland Formation of the Transvaal Supergroup. Next is an approximately 100–200-m sequence of low-grade-sulphide-mineralised, layered mafic-ultramafic rocks containing abundant sedimentary xenoliths and, in places, several chromite seams or stringers. This is overlain by a ~ 100-m-thick sequence of well-mineralised mafic-ultramafic rocks (the Flatreef sensu strictu), overlain by a laterally persistent mottled compositional analogies at the base of > 1 km of homogenous Main Zone gabbronorite. Based on stratigraphic, lithological and compositional alanalogies to the layered rocks in the eastern and western Bushveld Complex, we correlate the Flatreef and its chromite bearing footwall rocks with the Upper Critical Zone, notably the interval between the UG2 chromitite and the Bastard Reef as found elsewhere in the Bushveld Complex. This includes recognition of a Merensky Reef correlative. The ultramafic rocks below the main chromitite seam (UG2 correlative) in the Flatreef footwall are correlated with the Lower Critical and Lower zones. However, compared to the western and eastern Bushveld limbs, the studied sequence is strongly enriched in sulphide and PGE, many of the rocks show elevated CaO, K2O, Rb and Zr contents, and lateral continuity of layers between drill cores is less pronounced than elsewhere in the Bushveld, whereas ultramafic units are locally considerably thickened. These compositional and lithological traits are interpreted to result from a range of processes which include contamination with calcsilicate and hornfels, intrusion of granitic magmas, and the influence of multiple structural events such as pre- to syn-emplacement regional-scale open folding and growth faults. Evidence for the existence of potholes also exists. In the shallow, up-dip portions of the project area, the entire magmatic sequence below the Main Zone becomes increasingly contaminated to the extent that individual units are somewhat more difficult to correlate between drill cores. This package represents the Platreef as exposed in outcrop and shallow bore holes across much of the northern limb of the Bushveld Complex. The new data presented here thus indicate that the Platreef is a relatively more contaminated up-dip extension of parts of the Critical and Lower zones.
