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The implications of Sr and Nd isotope data on the genesis of the Platreef and associated BMS and PGE mineralisation, Bushveld Igneous Complex, South AfricaMwenze, Tshipeng January 2019 (has links)
Philosophiae Doctor - PhD / The Platreef is a platinum group elements (PGE) deposit located in the Northern limb of the Bushveld Igneous Complex (BIC). It is a series of mafic and ultramafic sills that are overlain by rocks from the Main Zone (MZ) of the BIC. In comparison to PGE deposits (i.e., Merensky Reef and the UG-2 chromitite) occurring in the Critical Zone (CZ) of the Eastern and Western Limbs of the BIC, which are less than 1 m in thickness, the Platreef is 10 to 400 m in thickness and is comprised of a variety of rocks. PGE mineralisation in the Platreef is not confined to a specific rock type, and its distribution and styles also vary with depth and along strike. Despite the numerous researches that have been conducted, the genesis of Platreef is still poorly understood.
New major and trace elements in conjunction with Sr–Nd isotope data, generated from whole-rock analyses of different Platreef rocks, were collected from four drill cores along its strike. The data were examined to determine the source of the magmas and identify the processes involved in its genesis. The study also aimed at establishing whether a genetic link exists between the Platreef magmas and the magmas that formed the Lower Zone (LZ), CZ and MZ in the Rustenburg Layered Suite (RLS) of the BIC.
The petrography revealed that the Platreef in the four drill cores consists of harzburgite, olivine pyroxenite, pyroxenite, feldspathic pyroxenite and norite. Based on the textural and modal mineralogy variations, feldspathic pyroxenite was subdivided into five types (I, II, III, IV and V). The variation in the average contents of MgO, LaN/YbN and ΣREE for the Platreef rocks are consistent with the modal mineralogy from the least to the most differentiated rocks. However, the Sr–Nd isotope data of the Platreef rocks have revealed two distinct groups of samples with decreasing ɛNd2060. Group 1 consists of pyroxenite and feldspathic pyroxenite II, III and V having ɛNd2060 values that range from –8.4 to –2.9, and 87Sr/86Sr2060 values from 0.707281 to 0.712106. The Platreef rocks of group 2 consist of olivine pyroxenite and feldspathic pyroxenite Type I with ɛNd2060 ranging from –12.6 to –10.8, and 87Sr/86Sr2060 ranging from 0.707545 to 0.710042.
In comparison to the LZ, CZ and MZ rocks, which have ɛNd values ranging from –8.5 to –5.1, and 87Sr/86Sr ranging from 0.704400 to 0.709671, Platreef pyroxenite of group 1 have lower negative ɛNd2060 values (from –3.8 to –2.9) and higher 87Sr/86Sr2060 values from 0.709177 to 0.710492, whereas feldspathic pyroxenite of group 1 have overlapping ɛNd2060 values (from –8.4 to –4.9) but also higher 87Sr/86Sr2060 values (from 0.707281 to 0.712106). Instead, the Platreef olivine pyroxenite and feldspathic pyroxenite in group 2 highly negative ɛNd2060 values and overlapping 87Sr/86Sr2060 values.
It is therefore suggested that the Platreef magmas derived from the partial melting of an heterogeneous mantle source comprising depleted mantle melts and both metasomatized slightly unradiogenic Nd enriched melts and highly unradiogenic Nd enriched melts from the subcontinental lithospheric mantle. These magmas ascended via the continental crust using different paths and interacted with rocks of different Sr–Nd isotopic compositions which resulted in the formation the hybrid magmas. The study speculates that sulphide saturation in the Platreef magmas was reached in the staging chambers at depth, and the varying styles of the PGE mineralisation in the Platreef rocks are the result of the varying degree of partial melting of the heterogeneous source for their magmas.
In conlusion, this study suggests that the genesis of the Platreef is much more complex and should be considered very much independent from processes involved in the genesis of the RLS in the Eastern and Western Limbs of BIC in agreement with earlier studies. / NRF
Inkaba ye Africa
Iphakade / 2020-08-31
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Petrographical and mineralogical investigation of the rocks of the Bushveld Igneous complex in the Tauteshoogte-Roossenekal area of the Eastern TransvaalVon Gruenewaldt, G. (Gerhard), 1942- January 1971 (has links)
This study comprises a petrographical and mineralogical investigation of
rocks from an area 850 sq. km in size, situated about 80km northeast of Middelburg.
Roughly half of the area is occupied by rocks of the epicrustal phase of
the Bushveld Complex, and consists largely of Rooiberg Felsite and granophyre
as well as leptite, microgranite and granodiorite. Numerous veins of finegrained
granite traverse the leptite which is considered to be highly metamorphosed
felsite. These veins of fine-grained granite probably owe their origin
to the melting of the leptite. The coalescence of these products of melting gave
rise to the thick sheet of._granophyre between the leptite and the felsite.
Rocks of the Layered Sequence occupy the eastern half of the area and
consist of the Main and Upper Zones which were subdivided into various subzones
on the basis of characteristic rock types and marker horizons. Mineralogical
investigations are restricted to the minerals from rocks of the Layered
Sequence, namely orthopyroxene, plagioclase, apatite and the sulphides of the
Upper Zone.
In Subzone A of the Main Zone, the orthopyroxene is present as cumulus
crystals, but it changes in texture to ophitic in the lower half of Subzone B where
small discrete grains of inverted pigeonite are also developed. Inverted pigeonite
is present in the upper half of Subzone B and in rocks of the Upper Zone, whereas
the orthopyroxene-pigeonite relationships in Subzone C of the Main Zone are
a repetition of those observed in the underlying rocks. The phase-change from
orthopyroxene to pigeonite takes place over a transition zone in which both
phases crystallized from the magma. It is envisaged that the first pigeonite to
have crystallized from the magma at high temperatures had a lower Fe/Mg
ratio than the hypersthene precipitating at slightly lower temperatures, with the
result that the early formed pigeonite was unstable and reacted with the magma
to form hypersthene. This caused the formation of groups of grains of hypersthene
which are optically continuous over large areas and which may contain a
few blebs of augite exsolved from the original pigeonite. A few pigeonite grains
were effectively trapped in other minerals, mostly augite, and consequently
escaped reaction with the liquid. These inverted to hypersthene at the appropriate
temperature and contain numerous exsolution-lamellae of augite. As fractional
crystallization of the magma continued, it moved further into the stability field of pigeonite and out of the stability field of hypersthene with the result that
the formation of hypersthene by the reaction of pigeonite with magma was replaced
by inversion of pigeonite to hypersthene. This inverted pigeonite is also
present as groups of grains optically continuous and contains pre-inversion
exsolution-lamellae of augite orientated at random, and post-inversion exsolution-
lamellae which are orientated parallel to the (100) plane of the orthopyroxene
throughout a unit. The inverted pigeonite is orientated in such a way that its
crystallographic c-axis lies close to or in the plane of layering. This is explained
as being due to the load pressure of the superincumbent crystal mass during
the inversion.
Textural features of the plagioclase revealed interesting information on
the postcumulus changes in the rock. Reversed zoning, interpenetration and
bending of plagioclase crystals as well as the presence of myrmekite are described.
These are considered to be due to increased load pressure prior to
and during crystallization of the intercumulus liquid. It is considered that the
various types of pegmatoids may have originated by an increase in pressure on
the intercumulus liquid which was concentrated to form pipe-like bodies by
lateral secretion or filter pressing.
Cumulus apatite is developed in the olivine diorites of Subzone D of the
Upper Zone. From unit cell dimensions it seems as if it changes in composition
from a fluor-rich hydroxyapatite at the base of this subzone to a relatively pure
hydroxyapatite 70m below the roof. There seems to be a substantial increase in
the fluor content of the apatite in the topmost 70m of the intrusion.
Rocks of the Upper Zone contain considerably more sulphides than those of
the Main Zone. This is ascribed to an increase in the sulphur content of the
magma owing to fractional crystallization. The magma reached the saturation
point of sulphur when rocks of Subzone D of the Upper Zone started to crystallize
with the result that these rocks contain numerous small droplets of sulphide
which constitute on an average about 0, 5 per cent by volume of the rocks. A concentration
of the sulphides in these rocks would not yield a deposit of economic interest because of the unfavourable composition of the sulphide phase, which
consits of more than 90 per cent pyrrhotite. Sulphides in the rocks below this
subzone are intercumulus and a concentration could be of economic importance
because the sulphide phase contains appreciable amounts of chalcopyrite and
pentlandite. Although no economic concentration of sulphides are known from the Upper Zone, this study has revealed the presence of a mineralized anorthosite
below Lower Magnetitite Seam 2 which contains in places up to 1 per cent Cu,
0, 18 per cent Ni and 1, 6g/ton platinum metals.
Continuous, slow convection and bottom crystallization probably gave rise
to the homogeneous rocks of the Main Zone. Injection of a considerable amount
of fresh magma took place at the level of the Pyroxenite Marker which resulted
in a compositional break and gave rise to a repetition in Subzone C of the rocks
of the Main Zone below this marker. The oxygen pressure during crystallization
of the magma was probably low, causing a gradual enrichment in iron in the magma
and gave rise to the appearance of magnetite at the base of the Upper Zone.
Intermittent increase in the oxygen fugacity is considered to be important in the
formation of magnetitite seams.
As a result of fractional crystallization the volatile content of the remaining
magma gradually increased. This is seen firstly, by the appearance of biotite
secondly by the appearance of cumulus apatite and droplets of sulphide and lastly
by hornblende in the rocks of the Upper Zone. Some water-rich residual liquids
apparently also intruded the overlying leptite, causing additional melting of the
latter and the formation of irregularly shaped veins and pockets of granodiorite.
A lateral change in facies of the rocks of the Layered Sequence in a souther
ly direction is described. This is considered to be due to crystallization of the
magma at slightly lower temperatures because of the more effective heat loss
where the magma chamber was thinner.
Two parameters of differentiation for layered intrusions are proposed,
viz. a modified version of the differentiation index and a modified version of the
crystallization index. The former seems more applicable for intrusions such as
the Bushveld Complex, whereas the latter seems to be more applicable for intrusions
in which there is a considerable development of ultramafic rocks. These
two parameters can also be used to indicate the differentiation trend if they are
plotted against height in the intrusion. / Thesis (PhD)--University of Pretoria, 1971. / gm2013 / Geology / unrestricted
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P-T estimates of peak Bushveld metamorphism in the eastern Bushveld complex, Limpopo Province, South Africa : constraints from P-T pseudosectionsRaubenheimer, Denni 19 November 2012 (has links)
The Bushveld Igneous Complex (BIC) is the largest layered mafic intrusion in the world and contains the largest known deposits of vanadium, chromium and Platinum group elements on the planet, as well as large deposits of iron, nickel, copper, tin and fluorite. To aid and improve our understanding of the tectonics that prevailed during the emplacement of the Bushveld Complex relevant data can still be extracted from the metamorphic aureole of the Complex, not the least among which are accurate determinations of pressure conditions during peak metamorphism. A relatively large number of geothermobarometric investigations have been performed on the Bushveld Complex aureole. The summation of all the thermobarometric studies on the Bushveld Complex aureole produces a dataset with largely divergent pressure-estimates, ranging from 1.5 kbar to 5.5 kbar. This study’s main aim was to produce new thermobarometric data for the Eastern Bushveld Complex aureole. To this ends metapelites from the aureole were sampled between Lydenburg and somewhat northwest of Penge. Polished thin-sections were produced for a number of samples and studied under microscope. After XRF analyses were performed on a refined number of samples, pseudosections for these samples were produced using Perplex. Electron microprobe analyses were used to analyze mineral chemistries of five samples and the resultant data used to construct isopleths for these samples in Perplex. The isopleth data was then used to scrutinize and, where possible, refine PT-estimates. The principal results obtained from mineral equilibrium modeling were the pseudosections and isopleths of samples DY09-54 and DY09-56. These samples’ cumulate results suggest that the metapelites of their sampling locality, which lies roughly ~36 km northwest of Penge, reached 530-565 ºC and 2230-2960 bar during peak metamorphism. Modelled isopleths of MnO/(MnO+CaO+FeO+MgO) suggest that these estimates be refined to 550 ± 5 ºC and 2650 ± 20 bar. These pressure estimates agree well with the majority of barometric studies in the literature that post-date the nineteen-eighties. The pressure estimates of 2230-2960 bar suggest that DY09-54 and DY09-56 were at a crustal depth of 7.9-10.4 km during peak metamorphism, assuming that a roughly 1.5 km thick load of rock, mainly of the Rooiberg Group and/or the Lebowa Granite Suite, were situated above the Rustenburg Layered Suite and at the top of the pile that overlay the samples. In such a case the Rustenburg Layered Suite’s contribution to the load would have represented a 4.2-6.7 km thick pile of these mafic rocks and, assuming that the load of Pretoria Group strata in the floor to the Complex had a thickness of 2350 m, the base of the Rustenburg Layered Suite would have been at a crustal depth of 5.6-8.0 km during peak metamorphism and directly above samples DY09-54 and DY09-56. Modelled palaeogeotherms together with the peak-metamorphic crustal depths estimated for samples DY09-54 and DY09-56 suggest that at peak metamorphism the samples’ temperatures had been elevated by no less than 320-355 °C, assuming that no thermal metamorphic effect was active on the samples just prior to the intrusion of the Bushveld Complex. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Geology / unrestricted
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Temporal assessment of atmospheric trace metals in the industrialised western Bushveld Complex / van Wyngaardt G.Van Wyngaardt, Grizelda January 2011 (has links)
The presence of trace transition metal species in the atmosphere can be attributed to
the emission of particulate matter into the atmosphere by anthropogenic activities, as
well as from natural sources. Trace metals emitted into the atmosphere can cause
adverse health–related and environmental problems. At present, limited data exists
for trace metal concentrations in South Africa. In this investigation, the general aim
was to determine the concentrations of trace metals in atmospheric aerosols in the
industrialised western Bushveld Igneous Complex, as well as to link the presence of
these species in the atmosphere to possible sources in the region.
The measurement site was placed in Marikana, a small rural town situated 35 km
east from Rustenburg in the North West Province of South Africa. It is surrounded
by numerous industrial and metallurgical operations. MiniVolumeTM samplers and
Teflon® filters (2 ;m pores) were utilised to collect PM2.5 and PM10 particulate
samples. The MiniVolumeTM samplers were programmed to filter 5 litres of air per
minute for 12 hours per day, over a six–day period. The starting time for sampling
was altered every six days, in order to obtain both day and night samples. Sampling
was performed for a period of one year.
The collected samples were chemically analysed with inductively coupled plasma
mass spectroscopy (ICP–MS). Surface analysis of the sampled filters was performed
with a scanning electron microscope (SEM) in conjunction with energy–dispersive
spectroscopy (EDS). The dataset was also subjected to factor analysis in an attempt
to identify possible sources of trace metal species in the atmosphere.
The concentrations of 27 trace metals (Be, B, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe,
Co, Ni, Cu, Zn, As, Se, Pd, Cd, Ba, Pt, Au, Hg, Tl, Pb, U) were determined. Pd, Hg,
Tl, U, Ca, Co, As, Cd, Ba and Au were above the detection limit 25% or less of the
time during the sampling period. With the exception of Ni, none of the trace metals
measured at Marikana during the sampling period exceeded local and international
standards. Higher Ni levels were possibly due to base metal refining in the region.
Pb, which is the only metal species that has a standard prescribed by the South
African Department of Environmental Affairs (DEA), did not exceed any of the standards. It is also significant to refer to Hg that was below the detection limit of the
analytical instrument for the entire sampling period.
The impact of meteorological conditions revealed that wet removal of atmospheric
PM10 trace metals was more significant than the wind generation thereof. During the
dry months, the total trace metal concentrations in the PM10 fraction peaked, while
PM10 particles were mostly washed out during the wet season. Wind speed showed
an unexpected inverse pattern compared to wet deposition. A less significant
seasonal trend was observed for the trace metal concentrations in the PM2.5 fraction,
which was attributed to a faster replenishment of smaller particles into the
atmosphere after rain events.
Separation of trace metal concentrations into PM10–2.5 and PM2.5 fractions indicated
that 79% of the total trace metal levels that were measured were in the PM2.5
fraction, which indicated a strong influence of industrial and/or combustion sources.
Fractionalisation of each of the trace metal species detected showed that for each
metal species, 40% and more of a specific metal was in the PM2.5 fraction, with Cr,
V, Ni, Zn and Mn occurring almost completely in the PM2.5 fraction.
Surface analysis with SEM supported results from the chemical analysis, which
indicated that a large fraction of the particles was likely to originate from
anthropogenic activities and from wind–blown dust. SEM–EDS also detected nonmetallic
S that is usually associated with the Pt pyrometallurgical industry that is
present in the western Bushveld Igneous Complex.
Correlations between Cr, V, Ni, Zn and Mn revealed that the main sources of these
species were pyrometallurgical industries. Explorative factor analysis of the
unprocessed and Box–Cox transformed data for all 27 metals detected, resolved four
meaningful emission sources, i.e. crustal, vanadium related, base metal related and
chromium related. Comparison of trace metal species to other parameters measured
(e.g. CO, BC) also indicated pyrometallurgical activities and wind–blown dust to be
the main sources of trace metals in this region. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2011.
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Temporal assessment of atmospheric trace metals in the industrialised western Bushveld Complex / van Wyngaardt G.Van Wyngaardt, Grizelda January 2011 (has links)
The presence of trace transition metal species in the atmosphere can be attributed to
the emission of particulate matter into the atmosphere by anthropogenic activities, as
well as from natural sources. Trace metals emitted into the atmosphere can cause
adverse health–related and environmental problems. At present, limited data exists
for trace metal concentrations in South Africa. In this investigation, the general aim
was to determine the concentrations of trace metals in atmospheric aerosols in the
industrialised western Bushveld Igneous Complex, as well as to link the presence of
these species in the atmosphere to possible sources in the region.
The measurement site was placed in Marikana, a small rural town situated 35 km
east from Rustenburg in the North West Province of South Africa. It is surrounded
by numerous industrial and metallurgical operations. MiniVolumeTM samplers and
Teflon® filters (2 ;m pores) were utilised to collect PM2.5 and PM10 particulate
samples. The MiniVolumeTM samplers were programmed to filter 5 litres of air per
minute for 12 hours per day, over a six–day period. The starting time for sampling
was altered every six days, in order to obtain both day and night samples. Sampling
was performed for a period of one year.
The collected samples were chemically analysed with inductively coupled plasma
mass spectroscopy (ICP–MS). Surface analysis of the sampled filters was performed
with a scanning electron microscope (SEM) in conjunction with energy–dispersive
spectroscopy (EDS). The dataset was also subjected to factor analysis in an attempt
to identify possible sources of trace metal species in the atmosphere.
The concentrations of 27 trace metals (Be, B, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Fe,
Co, Ni, Cu, Zn, As, Se, Pd, Cd, Ba, Pt, Au, Hg, Tl, Pb, U) were determined. Pd, Hg,
Tl, U, Ca, Co, As, Cd, Ba and Au were above the detection limit 25% or less of the
time during the sampling period. With the exception of Ni, none of the trace metals
measured at Marikana during the sampling period exceeded local and international
standards. Higher Ni levels were possibly due to base metal refining in the region.
Pb, which is the only metal species that has a standard prescribed by the South
African Department of Environmental Affairs (DEA), did not exceed any of the standards. It is also significant to refer to Hg that was below the detection limit of the
analytical instrument for the entire sampling period.
The impact of meteorological conditions revealed that wet removal of atmospheric
PM10 trace metals was more significant than the wind generation thereof. During the
dry months, the total trace metal concentrations in the PM10 fraction peaked, while
PM10 particles were mostly washed out during the wet season. Wind speed showed
an unexpected inverse pattern compared to wet deposition. A less significant
seasonal trend was observed for the trace metal concentrations in the PM2.5 fraction,
which was attributed to a faster replenishment of smaller particles into the
atmosphere after rain events.
Separation of trace metal concentrations into PM10–2.5 and PM2.5 fractions indicated
that 79% of the total trace metal levels that were measured were in the PM2.5
fraction, which indicated a strong influence of industrial and/or combustion sources.
Fractionalisation of each of the trace metal species detected showed that for each
metal species, 40% and more of a specific metal was in the PM2.5 fraction, with Cr,
V, Ni, Zn and Mn occurring almost completely in the PM2.5 fraction.
Surface analysis with SEM supported results from the chemical analysis, which
indicated that a large fraction of the particles was likely to originate from
anthropogenic activities and from wind–blown dust. SEM–EDS also detected nonmetallic
S that is usually associated with the Pt pyrometallurgical industry that is
present in the western Bushveld Igneous Complex.
Correlations between Cr, V, Ni, Zn and Mn revealed that the main sources of these
species were pyrometallurgical industries. Explorative factor analysis of the
unprocessed and Box–Cox transformed data for all 27 metals detected, resolved four
meaningful emission sources, i.e. crustal, vanadium related, base metal related and
chromium related. Comparison of trace metal species to other parameters measured
(e.g. CO, BC) also indicated pyrometallurgical activities and wind–blown dust to be
the main sources of trace metals in this region. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2011.
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Evaluation of environmental compliance with solid waste management practices from mining activities : a case study of Marula Platinum MineManyekwane, Dikeledi, Lethabo January 2019 (has links)
Thesis (M. Sc.(Geography)) -- University of Limpopo, 2019 / Global production of Platinum Group Metals (PGMs) is dominated by South Africa due to
its large economic resources base in the Bushveld Igneous Complex (BIC). PGMs are
used in a wide range of high technology applications worldwide including medicinal,
industrial and commercial purposes, and its contribution to the Gross Domestic Product
(GDP) and creating jobs for many. In an area where mining activities dominate, there are
likely to be problems that need effective environmental management approaches, which
can be facilitated through legislations. Marula Platinum Mine (MPM) is located in Limpopo
province BIC which has the second largest number of mining productivity in South Africa.
Environmental legislations have been put in place by the South African government in
order to avoid or minimise the footprints caused by PGM mining.
This study looked at environmental compliance with solid waste management practices
by Marula Platinum Mine (MPM) as guided by Mineral and Petroleum and Resource
Development Act (MPRDA) and National Environmental Management Act (NEMA) as
well as the environmental impacts of MPM in the surrounding communities. Both primary
(questionnaires, field observations and key informant interviews) and secondary (NEMA,
MPRDA, journals, reports, pamphlets, internet and books) data was used to address the
objectives of the study. Descriptive method and Statistical Package for Social Sciences
(SPSS) version 25 were used for the analysis of data. The key research results revealed
that MPM was compliant with 65% and 21% partially compliant with solid waste
management practices. Only 14% of information on solid waste management practices
could not be accessed because MPM is still operational. MPM had also had negative
footprints on the surrounding villages such as dust generation and cracks on walls and
floors on houses of community members, strikes and increase in the usage of substance
abuse.
Recommendations of the study are that MPM should address challenges that hinder
environmental compliance so as to be 100% compliant with MPRDA and NEMA
regulations. MPM should also provide other mitigation measures for blasting of explosives
to reduce dust generation and problems of cracks on houses of surrounding village
members.
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