The use of phosphorus contents in yielding estimates of the proportion of trapped liquid in cumulates of the Upper Zone of the Bushveld Complex

1988 ◽  
Vol 52 (364) ◽  
pp. 81-89 ◽  
Author(s):  
R. Grant Cawthorn ◽  
Kevin L. Walsh
Keyword(s):  
South Africa ◽  
Phosphorus Content ◽  
Bushveld Complex ◽  
Experimental Studies ◽  
Liquid Composition ◽  
Major Influence ◽  
Mafic Rocks ◽  
Interstitial Component ◽  
Basic Rocks

AbstractPhosphorus contents in cumulus rocks occurring close to the level of apatite appearance in the basic rocks of the Bushveld Complex, South Africa, provide a method of calculating the proportion of intercumulus component in these rocks. Previous experimental studies have accurately constrained the phosphorus content of magmas when apatite becomes stable. The ratio of the phosphorus content in the cumulates immediately below the appearance of apatite to this liquid composition defines the proportion of trapped liquid.Application of this method to rocks from the uppermost mafic rocks of the Bushveld Complex leads to the conclusion that there is from 1 to 6 per cent intercumulus component. Many of these rocks are multiphase cumulates and in such rocks estimation of intercumulus component from textural criteria is difficult.If crystals grow In situ on the floor of the magma chamber such small proportions of interstitial component can be produced without appealing to excessive diffusion and circulation of magma through an unconsolidated crystal pile. The geometry of the intrusion as well as its size might have a major influence on the proportion of the liquid ultimately solidifying within a cumulus rock.

scholarly journals In situ Sr Isotope Compositions of Plagioclase from a Complete Stratigraphic Profile of the Bushveld Complex, South Africa: Evidence for Extensive Magma Mixing and Percolation

2017 ◽  
Vol 58 (11) ◽  
pp. 2285-2308 ◽  
Author(s):  
Bartosz T Karykowski ◽  
Sheng-Hong Yang ◽  
Wolfgang D Maier ◽  
Yann Lahaye ◽  
C Johan Lissenberg ◽  
...  
Keyword(s):  
South Africa ◽  
Bushveld Complex ◽  
Magma Mixing ◽  
Sr Isotope

scholarly journals Magnetite layer formation in the Bushveld Complex of South Africa

2021 ◽  
Author(s):  
Zhuo-Sen Yao ◽  
James Mungall
Keyword(s):  
South Africa ◽  
Alternative Model ◽  
Ad Hoc ◽  
Bushveld Complex ◽  
Layer Formation ◽  
Layered Intrusions ◽  
Economic Significance ◽  
Magnetite Layer ◽  
Compositional Convection

Abstract The great economic significance of layered mafic-ultramafic intrusions like the Bushveld Complex of South Africa results from the existence within them of some layers highly concentrated in valuable elements. Here we address the origins of the Main Magnetite Layer, a globally important resource of Fe-Ti-V-rich magnetite. Previous models of in situ fractional magnetite crystallization require frequent ad hoc adjustments to the boundary conditions. An alternative model of rapid deposition of loose piles of magnetite crystals followed by compositional convection near the top of the pile and infiltration of the pile from beneath by migrating intercumulus melt fits observations without any adjustments. The data admit both explanations, but the latter model, with the fewest unconstrained interventions, is preferable. The choice of models has pivotal ramifications for understanding of the fundamental processes by which crystals accumulate and layers form in layered intrusions.

Caveats in defining the magmas parental to the mafic rocks of the Bushveld Complex, and the manner of their emplacement: review and commentary

2002 ◽  
Vol 66 (6) ◽  
pp. 815-832 ◽  
Author(s):  
H. V. Eales
Keyword(s):  
South Africa ◽  
Trace Element ◽  
Bushveld Complex ◽  
Bulk Composition ◽  
Trace Element Data ◽  
Mafic Rocks ◽  
Critical Zones ◽  
Derivatives Of ◽  
Western Limb ◽  
Northern Sector

Abstract The composition of magmas proposed as parental to the layered suite of the Bushveld Complex, and some models for the manner of their emplacement, are reviewed briefly. Included are some contributions published in South Africa, with which overseas readers might be less familiar. Emphasis is given to the broader features of the cumulates, and the contradictions raised by whole-rock compositional, Sr-isotopic, and trace-element data that cloud their correlation with proposed parental magmas. It is concluded that the Lower, Critical and Main Zones are the derivatives of only two primary magmatic lineages, while a third was added to residual liquids from which the layered rocks above the Pyroxenite Marker were formed. Excessive amounts of olivine and chromium in the cumulates of the Lower and Lower Critical Zones in the northern sector of the Western Limb can seemingly not be accounted for by the composition and volume of the putative magmas. This is attributed to (1) this sector being a proximal facies located close to the original feeder, and/or (2) crystal-charged magma batches, expelled from a lower magma chamber, being periodically injected into and dispersed within the liquids already in place in the Bushveld chamber. Thus, ongoing changes in the bulk composition of the liquids within the chamber would not be reflected in the rinds of earlier, chilled-facies rocks. The expulsion of significant volumes of liquid residua from the chamber during cumulate deposition is not ruled out.

Zircon geochronology and geochemistry of pre-Bushveld sills in the eastern Transvaal Supergroup, South Africa

2021 ◽  
Author(s):  
R. Bolhar ◽  
R.G. Cawthorn
Keyword(s):  
South Africa ◽  
Thermal Effects ◽  
Isotope Ratio ◽  
Bushveld Complex ◽  
The Other ◽  
Zircon Geochronology ◽  
Geographic Proximity ◽  
Mafic Rocks ◽  
Different Types ◽  
Transvaal Supergroup

Abstract An extensive suite of sills occurring in the eastern and western Transvaal Supergroup has been termed the Marico Diabase Suite. As a result of their overall geographic proximity to the Bushveld Complex and occurrence in the Transvaal Supergroup they have been assumed to be related to the Bushveld Complex. Previous studies have identified two different types of rocks within this suite, namely the Maruleng and Lydenburg types, based on geochemical and metamorphic characteristics. The Maruleng type has mineralogical (orthopyroxene-bearing) and geochemical affinities with the mafic rocks of the Bushveld Complex, and rocks belonging to this type are much more closely spatially related to the Bushveld Complex. The Lydenburg type, on the other hand, is much more extensive spatially and was emplaced at variable depths within the Transvaal Supergroup. The latter type of rock is variably metamorphosed, far beyond the likely thermal effects arising from emplacement of the Bushveld Complex. Using LA-SF-ICPMS and LA-MC-ICMS for U-Pb-Hf isotope ratio and REE+Ti concentration analysis, we demonstrate that zircon grains from this latter type were subjected to hydrothermal alteration, which caused the introduction of common lead. Despite compositional and isotopic overprinting, an age of 2 083 ± 18 Ma (MSWD = 12, n = 16) is obtained, suggesting a pre-Bushveld in age. We suggest that the original term Marico Diabase Suite encompasses two different events. The Maruleng Suite should be grouped as part of the Bushveld Complex, whereas the Lydenburg Suite should be given a status that is independent from the Bushveld event.

The extension of the western limb, Bushveld Complex (South Africa), at Cullinan Diamond Mine

2006 ◽  
Vol 70 (3) ◽  
pp. 241-256 ◽  
Author(s):  
R.G. Cawthorn ◽  
N. McKenna
Keyword(s):  
Bushveld Complex ◽  
Incompatible Trace Element ◽  
Critical Zone ◽  
Alkaline Complex ◽  
Rock Composition ◽  
Mafic Rocks ◽  
Element Abundances ◽  
Metasedimentary Rocks ◽  
Interstitial Component ◽  
Western Limb

AbstractMafic rocks of the Bushveld Complex at the southeastern end of the western limb, intersected in bore core from the Cullinan Diamond Mine, are described. A 260 m thick ultramafic body of orthopyroxene and chromite cumulate rocks, with mg# – 100*Mg/(Mg+Fe) – values from 77 to 84 and 0.25 to 0.5% Cr2O3 in the pyroxene, is considered to have affinity to the Critical Zone. Such an interpretation considerably extends the eastern limit of Critical Zone rocks of the western limb of the Bushveld Complex. The whole-rock composition of the lower, chilled basal contact of this body has 10% MgO and 500 ppm Cr, and is comparable to magmas considered parental to the Bushveld Complex. Due to intrusion of a younger sill, the upper contact is not preserved in the bore core. The cumulate rocks have higher interstitial component, inferred from incompatible trace element abundances (Zr, Ti and K), than normal Critical Zone rocks, interpreted to be a result of more rapid cooling due to proximity to the basal contact. The near-constancy of mg# in the pyroxene in the entire succession suggests that large volumes of magma flowed through this conduit, with only the liquidus phases of orthopyroxene and chromite being precipitated.Five generations of sills, intruded into the underlying metasedimentary rocks, are identified. The oldest is tholeiitic, and was metamorphosed prior to the emplacement of the Bushveld Complex. The second equates to the magma proposed as being parental to the Bushveld Complex (2060 Ma). The third represents the products of differentiation of that magma. The fourth is syenitic, and related to the Pienaars River Alkaline Complex (1430–1300 Ma). The fifth is tholeiitic (1150 Ma), and cuts the Cullinan kimberlite.

IN SITU AND PILOT ORGAN PERFUSION TECHNIQUES FOR THE STUDY OF METABOLIC DYNAMICS

1972 ◽  
Vol 68 (2_Supplb) ◽  
pp. S9-S25 ◽  
Author(s):  
John Urquhart ◽  
Nancy Keller
Keyword(s):  
Cardiac Output ◽  
Large Fraction ◽  
Experimental Studies ◽  
Test Substance ◽  
Organ Perfusion ◽  
Systemic Blood ◽  
Experimental Control ◽  
Arterial Blood ◽  
Vascular Connections

ABSTRACT Two techniques for organ perfusion with blood are described which provide a basis for exploring metabolic or endocrine dynamics. The technique of in situ perfusion with autogenous arterial blood is suitable for glands or small organs which receive a small fraction of the animal's cardiac output; thus, test stimulatory or inhibitory substances can be added to the perfusing blood and undergo sufficient dilution in systemic blood after passage through the perfused organ so that recirculation does not compromise experimental control over test substance concentration in the perfusate. Experimental studies with the in situ perfused adrenal are described. The second technique, termed the pilot organ method, is suitable for organs which receive a large fraction of the cardiac output, such as the liver. Vascular connections are made between the circulation of an intact, anaesthetized large (> 30 kg) dog and the liver of a small (< 3 kg) dog. The small dog's liver (pilot liver) is excised and floated in a bath of canine ascites, and its venous effluent is continuously returned to the large dog. Test substances are infused into either the hepatic artery or portal vein of the pilot liver, but the small size of the pilot liver and its blood flow in relation to the large dog minimize recirculation effects. A number of functional parameters of the pilot liver are described.

A geometallurgical characterization study of the Crystalkop Reef at the Great Noligwa Mine, Klerksdorp Goldfield, South Africa

2017 ◽  
Vol 120 (3) ◽  
pp. 303-322
Author(s):  
D. Pienaar ◽  
B.M. Guy ◽  
C. Pienaar ◽  
K.S. Viljoen
Keyword(s):  
South Africa ◽  
Treatment Plant ◽  
Processing Parameters ◽  
Processing Plant ◽  
Small Contribution ◽  
Gold Cyanide ◽  
Three Samples ◽  
Characterization Study ◽  
Different Sources

Abstract Mineralogical and textural variability of ores from different sources commonly leads to processing inefficiencies, particularly when a processing plant is designed to treat ore from a single source (i.e. ore of a relatively uniform composition). The bulk of the Witwatersrand ore in the Klerksdorp goldfield, processed at the AngloGold Ashanti Great Noligwa treatment plant, is derived from the Vaal Reef (>90%), with a comparatively small contribution obtained from the Crystalkop Reef (or C-Reef). Despite the uneven contribution, it is of critical importance to ensure that the processing parameters are optimized for the treatment of both the Vaal and C-Reefs. This paper serves to document the results of a geometallurgical study of the C-Reef at the Great Noligwa gold mine in the Klerksdorp goldfield of South Africa, with the primary aim of assessing the suitability of the processing parameters that are in use at the Great Noligwa plant. The paper also draws comparisons between the C-Reef and the Vaal Reef A-facies (Vaal Reef) and attempts to explain minor differences in the recovery of gold and uranium from these two sources. Three samples of the C-Reef were collected in-situ from the underground operations at Great Noligwa mine for mineralogical analyses and metallurgical tests. Laboratory-scale leach tests for gold (cyanide) and uranium (sulphuric acid) were carried out using dissolution conditions similar to that in use at the Great Noligwa plant, followed by further diagnostic leaching in the case of gold. The gold in the ore was found to be readily leachable with recoveries ranging from 95% to 97% (as opposed to 89% to 93% for the Vaal Reef). Additional recoveries were achieved in the presence of excess cyanide (96% to 98%). The recovery of uranium varied between 72% and 76% (as opposed to 30% to 64% for the Vaal Reef), which is substantially higher than predicted, given the amount of brannerite in the ore, which is generally regarded as refractory. Thus, the higher uranium recoveries from the C-Reef imply that a proportion of the uranium was recovered by the partial dissolution of brannerite. As the Vaal Reef contain high amounts of chlorite (3% to 8%), which is an important acid consumer, it is considered likely that this could have reduced the effectiveness of the H2SO4 leach in the case of the ore of the Vaal Reef. Since the gold and uranium recoveries from the C-Reef were higher than the recoveries from the Vaal Reef, the results demonstrate that the processing parameters used for treatment of the Vaal Reef are equally suited to the treatment of the C-Reef. Moreover, small processing modifications, such as increased milling and leach retention times, may well increase the recovery of gold (particularly when e.g. coarse gold, or unexposed gold, is present).

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