Geochemical exploration for platinum-group elements in the Bushveld Complex, South Africa

Wilhelm, Heike; Zhang, H.; Chen, F. L.; Elsenbroek, J. H.; Lombard, Melissa A.; Bruin, D. de

doi:10.1007/s001260050101

Cited by 24 publications

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“…At that time, little information was available on the mineralogy of the PGM. Wilhelm et al (1997) detected one detrital Pt-Fe alloy grain intergrown with laurite in their geochemical exploration campaign in the western Bushveld (Karee Spruit close to Brits). Oberthür et al (2004) and Melcher et al (2005) studied the placer accumulations on the farm Maandagshoek in the eastern Bushveld and identified a complex PGM assemblage originating from multiple sources (Merensky Reef,and platiniferous pipes).…”

Section: Previous Workmentioning

confidence: 97%

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Alluvial and Eluvial Platinum-Group Minerals From the Bushveld Complex, South Africa

Oberthür

Weiser

Melcher

2014

South African Journal of Geology

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The present work provides an initial description of detrital platinum-group minerals (PGM) collected from alluvial sediments of rivers draining the Bushveld Complex, and from eluvial concentrations at the Onverwacht platiniferous pipe. During a field campaign, sediments were sampled at nine localities around the Bushveld Complex, and heavy mineral assemblages were investigated using optical and scanning electron microscopy (SEM) as well as microprobe analysis (EPMA) of PGM. All concentrates from the alluvial samples contain discrete PGM grains with grain sizes in the range from ~50 to 150 µm (maximum 600 µm). The overall PGM proportions are: native Pt, Pt-Pd and Pt-Fe alloys (together 54%), sperrylite (33%), cooperite/braggite (11%), and stibiopalladinite (2%). This PGM assemblage distinctly contrasts to the suite of PGM in the pristine, sulfide-bearing mineralization in the Merensky, UG-2 and Platreef, the assumed sources of the detrital PGM. Specifically, PGE-bismuthotellurides and -sulfarsenides, common in the primary ores, are missing in the assemblage of detrital PGM in the fluvial environment. Nearly all detrital PGM (98%) are Pt minerals, corroborating earlier findings that Pd-dominated PGM are unstable and are dissolved in the supergene environment, and that PGE-bismuthotellurides and -sulfarsenides, common in the PGM assemblages of the pristine ores are unstable during weathering and mechanical transport.The eluvial material collected at Onverwacht contained ca. 150 PGM grains with sizes mainly in the range 100 to 300 µm range (maximum 1.87 mm). The PGM assemblage comprises grains of Pt-Fe alloys (66%), sperrylite (14%), and many rarer PGM including stibiopalladinite, hollingworthite, laurite, PGE arsenides and PGE sulfides. The suite of eluvial PGM observed is similar to the PGM assemblage described previously from the Onverwacht pipe proper, including the type locality minerals genkinite, irarsite and platarsite, as well as some additional and possibly new PGM. Most of the relatively rare PGM detected in the suite of eluvial grains from Onverwacht were also reported in the detrital PGM assemblage from the Moopetsi river, farm Maandagshoek (Oberthür et al., 2004), indicating that many of the latter grains originate from platiniferous pipes and not from the Merensky or UG-2 reefs.Detrital PGM can be expected to be present in rivers draining PGE-bearing layered intrusions, and economic placers may form under particular sedimentological conditions. Therefore, this work also highlights the fact that the nowadays somewhat neglected field methods and basic techniques have their merits and value in mineral exploration, especially if they are combined with modern micro-analytical methods. The systematic recovery of PGM from stream sediments, soils and till should regain wider application in mineral exploration as these tools can provide useful indicators of platinum mineralization.

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Section: Previous Workmentioning

confidence: 97%

“…Site not sampled by us; sample taken and described by Wilhelm et al (1997), close to Brits prison where one detrital PGM (one grain of Pt-Pd-Fe alloy intergrown with laurite) was found.…”

Section: Localitymentioning

confidence: 99%

Alluvial and Eluvial Platinum-Group Minerals From the Bushveld Complex, South Africa

Oberthür

Weiser

Melcher

2014

South African Journal of Geology

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“…This paper focuses on physical and hydrologic aspects of the CZ, using hydropedology as an example (among many other disciplines involved in CZ studies) to illustrate the opportunity and the need for integrated, multiscale, and synergistic efforts. Coupling physical/hydrologic and biogeochemical/ecological processes in the CZ is an emerging topic, which has been recently reviewed by McClain et al (2003), Lohse et al (2009) have used the term "critical zone" to refer to wide-ranging things: from geological formation where precious metals (such as platinum and gold) can be mined (Wilhelm et al, 1997) to pipe corrosion in soil within ground water fluctuation zone (Decker et al, 2008); from the rhizosphere where soil and roots have close interaction (Ryan et al, 2001) to transitional zones in alluvial coastal plain rivers important for water resource management (Phillips and Slattery, 2008); from body ventricular slow conduction area with electrophysiological limitations (Elsherif et al, 1990) to local cold regions of ice-structure interaction where intense pressures occur over short time leading to ice failure (Johnston et al, 1998). The majority of these 314 papers were in the subject areas of geosciences (46%) and minerals/energy (41%).…”

Section: Introductionmentioning

confidence: 99%

Earth's Critical Zone and hydropedology: concepts, characteristics, and advances

Lin

2010

Hydrol. Earth Syst. Sci.

265

104

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Abstract. The Critical Zone (CZ) is a holistic framework for integrated studies of water with soil, rock, air, and biotic resources in the near-surface terrestrial environment. This most heterogeneous and complex region of the Earth ranges from the vegetation top to the aquifer bottom, with a highly variable thickness globally and a yet-to-be clearly defined lower boundary of active water cycle. Interfaces among different compartments in the CZ are critical, which provide fertile ground for interdisciplinary research. The reconciliation of coupled geological and biological cycles (vastly different in space and time scales) is essential to understanding the complexity and evolution of the CZ. Irreversible evolution, coupled cycling, interactive layers, and hierarchical heterogeneity are the characteristics of the CZ, suggesting that forcing, coupling, interfacing, and scaling are grand challenges for advancing CZ science. Hydropedology -the science of the behaviour and distribution of soil-water interactions in contact with mineral and biological materials in the CZis an important contributor to CZ study. The pedosphere is the foundation of the CZ, which represents a geomembrance across which water and solutes, as well as energy, gases, solids, and organisms are actively exchanged with the atmosphere, biosphere, hydrosphere, and lithosphere, thereby creating a life-sustaining environment. Hydropedology emphasizes in situ soils in the landscape setting, where distinct pedogenic features and soil-landscape relationships are essential to understanding interactive pedologic and hydrologic processes. Both CZ science and hydropedology embrace an evolutionary and holistic worldview, which offers stimulating opportunities through steps such as integrated systems approach, evolutionary mapping-monitoring-modeling framework, and fostering a global alliance. Our capability toCorrespondence to: H. Lin (henrylin@psu.edu) predict the behaviour and evolution of the CZ in response to changing environment can be significantly improved if crosssite scientific comparisons, evolutionary treatment of organized complex systems, and deeper insights into the CZ can be made.

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“…The combined data presented here and in Harney et al (1990) suggest that the potential of the Pyroxenite Marker as an ore deposit, raised by Wilhelm et al (1997), is exceedingly low. The PGE and sulphide contents of our samples are, however, relatively variable, in accord with the general lithological heterogeneity of the Pyroxenite Marker.…”

Section: Implications For Explorationmentioning

confidence: 65%

“…It is commonly interpreted as a major replenishment to a relatively evolved Bushveld chamber with less differentiated magma (von Gruenewaldt, 1973;Molyneux, 1974;Mitchell, 1990;Kruger, 1994). Based on a laterally continuous PGE anomaly in a regional soil and stream sampling survey (Wilhelm et al, 1997), there has been some speculation about the presence of a PGE-enriched layer in the upper Main Zone particularly in view of the recent discovery of a PGE-and Au-rich horizon in the upper portion of the Skaergaard (Andersen et al, 1998) and Rincon del Tigre (Prendergast, 2000) intrusions. Visible sulphides in some samples from the Pyroxenite Marker suggest that the latter may be a potential target for such a PGE-enriched horizon.…”

Section: Introductionmentioning

confidence: 99%

Platinum-group elements in the Pyroxenite Marker, Bushveld Complex: implications for the formation of the Main Zone

Maier

Barnes

Merwe

2001

South African Journal of Geology

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Concentrations of platinum-group elements and sulphides in the Pyroxenite Marker of the upper Main Zone are variable, but generally low (up to 100 ppb PGE and 0.2 weight % S). The metal patterns may mostly be explained by sulphide segregation from PGE depleted residual Upper Critical Zone magma, but they are inconsistent with sulphide segregation from a replenishing influx of undepleted Critical Zone magma. Instead, we favour a model whereby a relatively cool and dense Main Zone crystal mush intruded the Bushveld chamber during the later stages of the deposition of the Upper Critical Zone and displaced warmer and lighter residual magma depleted in chalcophile metals (Sharpe, 1985). Based on the metal contents and textural evidence such as the occurrence of ophitic textures, we hypothesize that the Pyroxenite Marker formed in response to localized supercooling and the suppression of plagioclase crystallization. The model implies that the layer represents a poor target for PGE mineralization in the upper portions of the Bushveld Complex.

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Geochemical exploration for platinum-group elements in the Bushveld Complex, South Africa

Cited by 24 publications

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Alluvial and Eluvial Platinum-Group Minerals From the Bushveld Complex, South Africa

Alluvial and Eluvial Platinum-Group Minerals From the Bushveld Complex, South Africa

Earth's Critical Zone and hydropedology: concepts, characteristics, and advances

Platinum-group elements in the Pyroxenite Marker, Bushveld Complex: implications for the formation of the Main Zone

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