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Western Cape Unit
P.O. Box 572 Bellville 7535 SOUTH AFRICA c/o Oos and Reed Streets Bellville Cape Town
Reception: +27 (0) 21 946 6700 Fax: +27 (0) 21 946 4190
Geochemical hazard mapping
M. Maya and T. Cloete
Council for Geoscience Report number: 2011-0064
© Copyright 2011. Council for Geoscience
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Contents
Contents.................................................................................................................................................. 2
Figures.....................................................................................................................................................2
Tables ...................................................................................................................................................... 3
1 Introduction ....................................................................................................................................4
2 Introduction and background for Geochemical Mapping .............................................................. 5
2.1 Sampling ................................................................................................................................5
2.2 Sample preparation and analytical method.......................................................................... 5
3 Potential geochemical hazards rising from smelters and power stations......................................6
4 Potential geochemical hazardous elements: Arsenic (As) .............................................................. 8
5 Potential geochemical hazardous elements: Lead (Pb) ................................................................10
6 Potential geochemical hazardous elements: Zinc (Zn) .................................................................12
7 Potential geochemical hazardous elements: Copper (Cu)............................................................14
8 Potential geochemical hazardous elements: Nickel (Ni) ..............................................................16
9 Potential geochemical hazardous elements: Chrome (Cr) ...........................................................17
10 Potential geochemical hazardous elements: Vanadium (V) ....................................................19
11 Potential geochemical hazardous elements: Uranium (U) ......................................................21
12 Potential geochemical hazardous elements: Thorium (Th).....................................................23
13 Geochemical distribution of Sb on the 1:100 000 map Tzaneen.............................................25
14 Potential geochemical hazardous elements: Zinc (Zn) ............................................................26
15 Conclusion................................................................................................................................27
Acknowledgements..............................................................................................................................27
References ............................................................................................................................................28
Figures Figure 1: A regional geochemical map of elements associated with power stations and smelters.......8
Figure 2: A regional geochemical map of As distribution ....................................................................... 9
Figure 3: A regional geochemical map of Pb distribution.....................................................................11
Figure 4: A regional geochemical map of Zn distribution.....................................................................13
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Figure 5: A regional geochemical map of Cu distribution.....................................................................15
Figure 6: A regional geochemical map of Ni dsitribution .....................................................................17
Figure 7: A regional geochemical map of Cr distribution. ....................................................................19
Figure 8: A regional geochemical map of V distribution.......................................................................21
Figure 9: A regional geochemical map of U distribution ......................................................................23
Figure 10: A regional geochemical map of Th distribution...................................................................24
Figure 11: Geochemical distribution of Sb on the 1:100 000 map Tzaneen.........................................26
Figure 12: Geochemical distribution of Zn on the 1:100 000 map Tzaneen.........................................27
Tables Table 1: List of known geochemical anomalies ...................................................................................... 4
Table 2: Calibration concentration range of elements in reference materials that were used and the
calculated determination limits (DL)....................................................................................................... 5
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1 Introduction Potentially hazardous geochemical element-anomalies (Table 1) were identified on the existing
geochemical data sets and maps of South Africa, which have been generated over the last three
decades by the Geochemistry Unit of the Council for Geoscience. These anomalous element
accumulations are either natural- or anthropogenic in origin and may or may not be hazardous to man
and animal. Some of these anomalies have been studied due to their known negative health impacts on
the environment.
The natural anomalies of Pb and Zn, for example, are linked to known to pockets of mineralisation
around the Bushveld Complex in the Transvaal Supergroup rocks, which are also known to impact the
quality of drinking water causing high infant mortality rates and also poor fertility of cattle. Typically,
anthropogenic anomalies (Cu, Ni, Cr and V) have been mapped around smelters and some power
stations.
Table 1: List of known geochemical anomalies
Potentially hazardous
elements
Area Comments
Cd, Hg, S, P, Se, Cu, Bi, As Iscor smelter Pretoria
Rustenburg smelters
Rooiwal power station
Anthropogenic
Anthropogenic
Anthropogenic
Radioactive elements
U and Th
Wits goldfields(mine dumps)
Granites (geochemical maps
available)
Karoo basin
Anthropogenic
Natural
Natural
Fe-Mn Asbestos Limpopo and N Cape (Penge and
Griquatown formations)
Natural
Arsenic anomalies Tzaneen-, Polokwane maps
Loeriesfontein
(Geochemical maps available)
Natural
Natural
Cu anomalies Nababeep (Nababeep formation) Anthropogenic
Cr, V anomalies Witbank Anthropogenic
Pb, Zn anomalies Magaliesberg Quartzite Formation
Malmani Subgroup Formation
Natural
Natural
Sb, Zn anomalies Klein Letaba River Anthropogenic
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2 Introduction and background for Geochemical Mapping The Council for Geoscience (CGS) of South Africa has been involved in a regional geochemical mapping
program since 1972. The CGS has collected close to 400 000 stream sediment and soil samples have
been collected since then. SXRF analysis for 23 elements has been done for most of these samples and
nine 1:250 000 scale geochemical wall maps have been produced and are available on open file.
2.1 Sampling The study area consist of the three 1:250 000 scale map sheets of Pretoria, Rustenburg and Pietersburg
and some portions of Mafikeng, Thabazimbi, Nylstroom, Tzaneen, Pilgrims Rest, Barberton and Ellisras
sheets. Soil samples for the study area were taken on a grid of one sample/km2
by helicopter supported
transport. However, in the urban environment, soil samples have been taken on foot with 4X4 vehicle
supported transport. Each 5 kg sample was taken from the top 20 cm of the sampling medium. A
sampling density of 1 sample per km2 was adopted from geochemical orientation studies (Labuschagne
et al. 1993). A total number of 126465 samples were taken over a period of 10 years.
2.2 Sample preparation and analytical method The samples were dry sieved and were analysed on the following analytical technique:
• Simultaneous X-Ray Fluorescence Spectrometer (Sim-XRF): TiO2%, MnO%, Fe2O3T%, Sc, V, Cr,
Co, Ni, Cu, Zn, As, Rb, Sr, Y, Zr, Nb, Sn, Sb, Ba, W, Pb, Th and U;
Simultaneous X-Ray Fluorescence analysis
Samples were analysed on a Philips PW 1606 Simultaneous X-Ray Fluorescence Spectrometer (SXRF) for
the following elements: Sc, TiO2%, V, Cr, MnO%, Fe2O3T%, Co, Ni, Cu, Zn, As, Rb, Sr, Y, Zr, Nb, Sn, Sb, Ba,
W, Pb, Th and U. The steps to calibrate the instrument, accuracy and precision obtained and the
reference materials used are described by Elsenbroek (1995 and 1996). The chemical elements analysed
for, with their calibration ranges and determination limits, are displayed in Table 1. A drift correction
was made after every 10th unknown sample, with the aid of an internal glass-disc monitor, to correct
for any instrumental drift. The resulting stability of analyses was checked, per batch of 300 samples
analysed on a daily basis, using in-house powder-briquette monitors of various concentrations. An
example of the results obtained from the in-house monitors is given in Table 2. These monitors
generally have a precision better than 5 % except for MnO%, Sn, Sb, W and U.
Table 2: Calibration concentration range of elements in reference materials that were used
and the calculated determination limits (DL)
Element Range (ppm) Detection Limit ppm)
Sc 1–55 1
TiO2 0.2–3.77 % 100
V 9–526 5
Cr 10–2 900 4
MnO 0,01–0,32 % 100
Fe2O3T 1,40–18,76 % 100
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Co 11–210 10
Ni 10–2 380 10
Cu 19–1 230 9
Zn 10–680 3
As 18–412 10
Rb 9–860 1
Sr 25–1 100 1
Y 5–718 1
Zr 22–1 210 1
Nb 10–960 5
Sn 3–370 2
Sb 10–2 000 5
Ba 114–2 400 10
W 24–490 4
Pb 11–636 4
Th 17–1 000 4
U 9–650 2
3 Potential geochemical hazards rising from smelters and power
stations Rooiwal power station is a coal fired power station situated north of Pretoria. It is well known that fossil
fuel driven stations produces tons of waste and are the biggest sources of CO2, SOx, NOx and other
harmful toxins. Because power generation involves the use of water (cooling towers), power stations
result in huge amounts of water pollution in the surrounding environment.
The Iscor metallurgical plant near Pretoria was the biggest primary producer of iron and steel. This is an
old plant and sections of it (coke ovens and blast furnaces) were closed leading to reduced production
and limiting pollution.
Types of pollutants generated by smelters and power stations
Gaseous emissions
• Carbon monoxide;
• Carbon dioxide;
• Nitrogen oxides;
• Sulphur dioxides;
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• Volatile organic compounds.
Water effluents
• Suspended solids;
• Phenols;
• Cyanides;
• Chlorides;
• Sulphates;
• Heavy metals;
• Thermal pollution in surrounding water bodies.
Solid pollutants
• Dust;
• Slag;
• Sludge.
Environmental impact
• Toxic ashes from power plants and smelters are associated with asthma attacks, cardiac
and respiratory problems;
• Thermal pollution (rising water temperature) increases the decomposition rate of organic
matter which depletes dissolved oxygen. Changes in temperature can kill microorganisms
and also affects the reproductive system of organisms. The impact of such pollution has
been reported by Hohls and Van Niekerk (2000) in the Apies River. They found that
Rooiwal powerstation was the source of nitrates, sulphates, chloride, highly dissolved salts
and high levels of un-ionised ammonia leading to the death of fishes and crabs in the
nearby Apies river;
• CO2 is the main gas linked to global warming;
• Nitrogen oxides and sulphur oxides cause acidic rain.
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Figure 1: A regional geochemical map of elements associated with power stations and
smelters.
The following general anomalies were identified on the map (Figure 1):
1. Iscor plant near Pretoria
2. Pretoria metropole. This anomaly may be influenced by the Iscor plant, industrial activities and
the use of fossil fuel
3. Mabopane
4. Rooiwal power station
5. Buffelsdrift/Wallmanstral anomaly. Close to cultivated areas, this anomaly may also be caused
by the underlying geology
4 Potential geochemical hazardous elements: Arsenic (As)
General background:
Arsenic is a chalcophile element that concentrates in late differentiates and veins forming supra-ore
halos. Ore minerals are arsenopyrite, realgar and orpiment, whilst it substitutes in minerals such as
pyrite, galena, sphalerite, other sulphides and apatite. In soils it is present in clays, limonite and pyrite.
Arsenic is a pathfinder for gold, silver, copper and lead-zinc deposits (Levinson, 1974).
Examples (from Lollar, 2004) of possible earth material sources enriched or depleted in arsenic:
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• Soils and waters are affected by emissions from smelters and power plants;
• Soils and waters affected by mining wastes and by-products;
• Some playa lake sediments;
• Soils and dusts derived from natural As-enriched rocks and sediments;
• Waters that have leached As from As-rich rocks, soils and sediments.
Deficiencies or excess in plants (from Alloway, 1990):
• The intake of Arsenic (III) may give rise to toxic symptoms in anomalous areas;
• Fortunately the species that are most commonly found in soils are not the most toxic;
• The phytotoxic effects of excess As in plants include root plasmolysis and discolouration
followed by red-brown necrosis of the leaf tips and margins.
Health effects associated with excess arsenic in the dominant exposure routes (from Lollar, 2004):
Ingestion, inhalation.
• Acute poisoning can lead to a wide variety of maladies, including: systemic hypotension; GI pain
and bleeding; pulmonary edema; anaemia, destruction of red blood cells; liver necrosis, kidney
failure; encephalopathy and other central and peripheral nervous system disorders;
• Chronic toxicity can lead to: systemic hypotension, skin disorders such as eczema,
hyperkeratosis, melanosis, ulceration, skin cancers, blood leukemia, kidney failure, delirium,
encephalopathy, seizures, and neuropathy.
Figure 2: A regional geochemical map of As distribution
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The following general As anomalies were identified on the map (Figure 2):
As associated with the Malmani Subgroup dolomite and the neighboring Timeball Hill Formation of the
Pretoria Group associated with Pb, Zn and Fluorite mineralization;
1. The Rooiberg Fragment Sediments associated with Sn mineralization;
2. General elevated As on the Makoppa Dome Granite;
3. The Lebombo basalt of the Karoo Supergroup;
4. The Pietersburg Group granite / gneiss;
5. The Goudplaats/Hout River Gneiss;
6. The mafic rocks of the Rustenburg Layered Suite;
7. The Wylliespoort Formation of the Soutpansberg Group;
8. Both the Rooiberg- and Waterberg Group sediments in general.
5 Potential geochemical hazardous elements: Lead (Pb)
General background:
Lead is a chalcophile element and concentrates in felsic igneous rocks and black shales in sediments.
The predominant ore mineral is galena, whilst Pb also substitutes in K-feldspar, plagioclase, mica, zircon
and magnetite. In soil it is present as galena, anglesite and cerussite and it is adsorbed in clays and
organic matter. Lead is a pathfinder for Pb deposits, U deposits and polymetallic vein deposits
(Levinson, 1974).
Examples (from Lollar, 2004) of possible earth material sources enriched or depleted in Lead:
• Soils and waters affected by leaded gas, smelter emissions, mining wastes and by-products;
• Dusts soils and debris containing lead-bearing paint;
• Foods grown in lead-rich soils;
• Soils and dusts derived from naturally lead-enriched rocks;
• Waters that have leached lead from supply pipes.
Deficiencies or excess in plants (from Alloway, 1990):
Although Pb is not especially toxic to plants, high substrate concentrations do result in stunted growth
or death.
Health effects associated with excess lead in the dominant exposure routes (from Lollar, 2004):
Inhalation, ingestion.
• Acute poisoning leads to acute encephalopathy, renal failure and severe GI distress. Chronic
poisoning leads to central nervous system problems, impaired neurobehavioral function,
diminished gross and fine motor development in children, kidney disease, hypertension, anemia
and other hematologic effects;
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• Elsenbroek et al., (2003) found a clear genetic link between the occurrence of severe
haemorrhagic diarrhoea in calves, the reproductive failure of cows and geochemical Pb
anomalies in soils (a selenium-induced copper deficiency was proposed).
• In humans toxicity may cause mental impairment in young children digesting lead rich soils
(Alloway, 1990);
• Excess Pb can also cause damage to nervous systems.
Figure 3: A regional geochemical map of Pb distribution.
The following general Pb anomalies were identified on the map (Figure 3):
1. Lead anomalies in the Malmani Subgroup dolomite, also associated with As anomaly No.1 in
Figure 2;
2. Lead anomalies associated with the Pilanesberg Complex;
3. Lead anomalies associated with the Pretoria Group sediments (quartzite and shale) and fault
system in the Pretoria area and surroundings;
4. Lead anomaly in the Malmani Subgroup dolomite;
5. Anomalous Pb population in the Rooiberg Group;
6. High level Pb background on the Turfloop Suite and Goudplaats Gneiss;
7. High level Pb background on the Goudplaats- and Hout River Gneiss;
8. Lead anomalies associated with the Schiel Alkaline Complex;
9. High level Pb background on the Nebo Granite, Bushveld Complex;
10. Lead anomalies associated with the Rooiberg- and Waterberg Groups;
11. Lead anomalies associated with the Karoo sediments;
12. High level Pb background on the Rustenburg Layered Suite, Bushveld Complex;
13. High level Pb background on the Vaalwater Formation of the Waterberg Group.
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6 Potential geochemical hazardous elements: Zinc (Zn)
General background:
Zinc is a chalcophile element and concentrates in intermediate igneous rocks as well as shales, and in
particular black shales. The predominant ore mineral is sphalerite. Zinc also substitutes in minerals such
as biotite, amphibole and magnetite. In soils Zn is mainly adsorbed or co-precipitated on Fe-Mn oxides
and adsorbed in organic matter and clays. Zinc is a pathfinder for Pb deposits, Zn-Pb-Ag deposits, some
fluorite deposits, polymetallic sulphide deposits, skarn deposits, porphyry copper deposits and
numerous other deposits (Levinson, 1974).
Examples (from Lollar, 2004) of possible earth material sources enriched or depleted in zinc:
• Zn-rich ore deposits (i.e., massive sulphide, sediment-hosted);
• Soils and waters affected by smelter emissions, mining wastes and by-products;
• Enriched in some rocks, such as black shales, basalts.
Deficiencies or excess in plants:
Zinc deficiency can be a problem in crop and fruit-growing areas causing inter-veinal chlorosis, stunted
growth and violet-red points on leaves (Kabata-Pendias and Pendias, 1984).
Health effects associated with deficiency:
Anorexia, dwarfism, anemia, hypogonadism, hyperkeratosis, acrodermatitis, enteropathica, depressed
immune response, teratogenic effects.
Health effects associated with excess for the dominant exposure routes (from Lollar, 2004):
Ingestion:
• Hyperchronic anemia;
• Inhalation;
• Metal fume fever at high doses.
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Figure 4: A regional geochemical map of Zn distribution.
The following general Zn anomalies were identified on the map (Figure 4):
1. Zn anomalies in the Malmani Subgroup dolomite, also associated with As and Pb anomalies
Numbers 1 in Figure 2 and Figure 3 respectively;
2. Zn anomalies associated with the mafic rocks of the Glenover Complex as well as with the mafic
rocks of the Rustenburg Layered Suite;
3. Anomalous Zn in the Pilanesberg Complex;
4. Anomalous Zn concentrations are present in the Silverton Formation (Pretoria Group) probably
associated with dolerite intrusions within the Silverton shale;
5. Zn anomalies are situated in the Pretoria – Tshwane metropolis, on the Pretoria Group
sediments, probably also associated with the complex fault system in the area;
6. Anomalous Zn associated with the Lebombo basalt of the Karoo Supergroup;
7. Zn anomalies associated with the Rooiberg Group;
8. Moderate Zn anomalies are associated with the diabase intrusions on the 1:50 000 scale
Rooibosbult map sheet;
9. Moderate Zn anomalies are associated with the Bushveld Complex rocks at Villa Nora, with the
Rooiberg Group showing higher Zn concentrations;
10. Moderate Zn concentrations are associated with the Beit Bridge Complex;
11. Moderate Zn anomalies are associated with the Bushveld Complex rocks at the Potgietersrus
Limb;
12. Moderate to high Zn anomalies are associated with the Soutpansberg Group as well as with the
Hout River – and Goudplaats Gneiss;
13. Anomalous Zn concentrations are present in the Silverton Formation (Pretoria Group) on the
eastern side of the Bushveld Complex;
14. Anomalous Zn associated with the Lebombo basalt of the Karoo Supergroup;
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15. Zn anomalies are associated with the Rooiberg Group;
16. Zn anomalies mainly associated with the Rooiberg Group;
17. Zn anomalies are associated with the Bierkraal Magnetite Gabbro of the Rustenburg Layered
Suite;
18. Zn anomalies are associated with the Rooiberg Group, Waterberg Group as well as with the
network of faults trending east-west;
19. Zn anomalies associated with the dolomite in the Assen Formation.
7 Potential geochemical hazardous elements: Copper (Cu) General background:
Copper is chalcophile and concentrates in intermediate igneous rocks and black shales in sediments.
Ore minerals are native copper, chalcopyrite, bornite and other sulphides (Levinson, 1974). Copper also
substitutes in minerals such as pyroxene, amphibole, magnetite and biotite. In soils it is present in clays,
Fe-Mn oxides and organic matter. Copper is a pathfinder for several kinds of deposits including VMS,
SEDEX, MVT, porphyry copper and Cu shale deposits.
Examples (from Lollar, 2004) of possible earth material sources enriched or depleted in copper:
• Cu-rich ore deposits (i.e., porphyry, massive sulphide, sediment-hosted);
• Soils and waters affected by smelter emissions, mining wastes and by-products;
• Cu locally enriched in some rocks (continental red bed sediments, basalts).
Deficiencies or excess in plants:
• Copper deficiencies are common in crops and affect the size, shape, nutritional value and colour
of fruits and vegetables (Alloway, 1990);
• Copper deficiency in soils in low background areas may result in wilting, melanism, white
twisted tips, ‘blind ear’, ‘wither-tip’ and blackening in cereals, sunflowers, spinach, lucerne and
also a reduction in crop yield (Davies, 1980).
Health effects associated with deficiency:
• Copper deficiency leads to Anaemia, Menke’s syndrome;
• Copper deficiency in diets for cattle may give rise to hypocupraemia (also see Mo) which
symptoms include scouring, unthriftiness, stunted growth, immaturity and loss of coat colour;
• and in sheep to paralysis and a demyelinating disease called swayback (Davies, 1980).
Health effects associated with excess copper in the dominant exposure routes (from Lollar, 2004):
Ingestion, inhalation:
• Wilson’s disease (associated with Cu buildup in organs), intestinal and liver inflammation,
hemolysis (destruction of red blood cells, with diffusion of hemoglobin into surrounding fluids),
hyperglycemia;
• Copper sulphate poisoning may occur in anomalous areas when high amounts of copper (II) is
digested;
• Hereditary Cu toxicosis is known as Wilson’s disease.
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Figure 5: A regional geochemical map of Cu distribution
The following general Cu anomalies were identified on the map (Figure 5):
1. Cu anomalies in the Malmani Subgroup dolomite, also associated with As, Pb and Zn anomalies.
Numbers 1 in Figure 2, Figure 3 and Figure 4respectively;
2. The Ventersdorp Supergroup lavas show elevated Cu;
3. Mafic rocks of the Rustenburg Layered Suite show medium to high Cu anomalies;
4. Cu anomalous trend follow the shale of the Silverton Formation, could also probably be dolerite
intrusions in the shale;
5. Cu contamination at the Rustenburg mines;
6. High Cu concentrations follow the magnetite gabbro of the Rustenburg Layered Suite, in both
the eastern and western lobes of the Bushveld Complex;
7. Moderate Cu anomalies are associated with the diabase intrusions on the 1:50 000 scale
Rooibosbult map sheet;
8. Mafic rocks of the Rustenburg Layered Suite show medium to high Cu anomalies at the Villa
Nora outcrop;
9. An anomalous Cu concentration trend follows the Soutpansberg Group;
10. Mafic rocks of the Rustenburg Layered Suite show medium to high Cu anomalies at the
Potgietersrus Limb;
11. Anomalous Cu is associated with the Lebombo basalt of the Karoo Supergroup;
12. The Cu anomalies in the Pretoria Group sediments are probably associated with the diabase
intrusions.
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8 Potential geochemical hazardous elements: Nickel (Ni)
General background:
Nickel is both siderophile and chalcophile and concentrates in mafic-ultramafic igneous rocks and black
shales in sediments. Ore minerals are pentlandite, nickeliferous pyrrhotite, niccolite, nickeliferous
laterite and Mn nodules. It also substitutes in olivine, Mg-pyroxenes, amphiboles, micas, pyrite,
chalcopyrite and other sulphides. In soils it is present in Fe and Mn oxides (eg. limonite and laterite),
clays and adsorbed by organic matter. Nickel is a pathfinder for massive sulphide, Pt metal and certain
U deposits (Levinson, 1974).
Examples (from Lollar, 2004) of possible earth material sources enriched or depleted in nickel:
• Enriched in ultramafic rocks and their associated mineral deposits;
• Enriched in many black shales, some phosphatic shales;
• Soils, sediments and waters affected by mining waste, smelter emissions, power plants,
industrial waste and by-products.
Deficiencies or excess in plants:
• Nickel is toxic to plants and animals under conditions of above average exposure (Alloway,
1990);
• Nickel toxicity, causing poor growth in crops, can be found on poorly drained soils derived from
ultra basic rocks (Davies, 1980).
Health effects associated with deficiency:
None recognized
Health effects associated with excess nickel in the dominant exposure routes (from Lollar, 2004):
• Inhalation: Chronic bronchitis, emphysema, reduced lung capacity and cancers of the lungs and
nasal sinus;
• Ingestion: Death (due to cardiac arrest), gastrointestinal effects (nausea, cramps, diarrhoea,
vomiting), effects on blood, liver, kidneys. Also neurological effects (giddiness, weariness).
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Figure 6: A regional geochemical map of Ni dsitribution
The following general Ni anomalies were identified on the map (Figure 6):
1. Most of the mafic rocks in the Rustenburg Layered Suite contain anomalous Ni concentrations,
in the eastern and western lobes, at Villa Nora, as well as the Potgietersrus Limb;
2. The Makoppa Dome show elevated concentration of Ni probably because of the river flood
flows over the dome coming from the Rustenburg Layered Suite;
3. Moderate Ni anomalies are associated with the diabase intrusions on the 1:50 000 scale
Rooibosbult map sheet;
4. The Pietersburg Group mafic rocks show a strong north-east, south-west anomalous Ni trend;
5. The Bandelierskop Complex as well as the Pietersburg Group show anomalous Ni
concentrations in the Hout River- and Goudplaats gneiss;
6. Rocks in the Marble Hall Fragment show anomalous Ni concentrations;
7. Rocks in the Assen Formation and Crocodile Fragment show anomalous Ni concentrations;
8. Moderate anomalous Ni concentrations are associated with the Lebombo basalt of the Karoo
Supergroup.
9 Potential geochemical hazardous elements: Chrome (Cr)
General background:
Chromium is siderophile and concentrates in ultra basic rocks. The ore mineral is chromite but it also
substitutes in micas, garnets, pyroxene and magnetite. In soils it is present in chromite, limonite,
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magnetite and clays. It is a pathfinder for chromite, platinum and other ultramafic deposits (Levinson,
1974).
Examples (from Lollar, 2004) of possible earth material sources enriched or depleted in chrome:
• Commonly enriched in ultramafic rocks and their associated ore deposits;
• Much naturally occurring Cr is relatively insoluble chromite;
• Soluble Cr may occur naturally in evaporative lake sediments or other evaporative
environments, as a trace element within other soluble salts;
• Anthropogenic Cr can occur in soils, sediments, and waters affected by industrial wastes and
by-products.
Deficiencies or excess in plants:
• Chromium is toxic to plants and animals under conditions of above average exposure (Alloway,
1990);
• Excess Cr in soils may cause chlorosis of new leaves and injured root growth in crop plants
(Kabata-Pendias and Pendias, 1984).
Health effects associated with deficiency:
Cr (III) is essential –deficiencies result in defective glucose metabolism, hyperlipidemia, corneal opacity.
Health effects associated with excess chrome in the dominant exposure routes (from Lollar, 2004):
Ingestion, inhalation, percutaneous absorption:
• Irritation of and generation of lesions in skin, respiratory tract, and gastric and intestinal
mucosa; contact dermatitis; pulmonary edema;
• Acute kidney failure;
• Long-term risk for lung cancers;
• Pneumoconiosis from exposure to chromite ore dust.
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Figure 7: A regional geochemical map of Cr distribution.
The following general Cr anomalies were identified on the map (Figure 7):
1. Most of the mafic rocks in the Rustenburg Layered Suite contain anomalous Cr concentrations,
in the eastern and western lobes, at Villa Nora, as well as the Potgietersrus Limb;
2. The Makoppa Dome shows elevated concentration of Cr probably because of the river flood
flows over the dome coming from the Rustenburg Layered Suite;
3. Moderate anomalous Cr concentrations are associated with the Lebombo basalt of the Karoo
Supergroup;
4. The Pietersburg Group mafic rocks show a strong north-east, south-west anomalous Cr trend;
5. The Bandelierskop Complex as well as the Pietersburg Group show anomalous Cr
concentrations in the Hout River- and Goudplaats gneiss;
6. Cr contamination at the Middelburg mines (reference of report);
7. Cr contamination at the Witbank mines (reference of report);
10 Potential geochemical hazardous elements: Vanadium (V)
General background:
Vanadium is both sidérophile and lithophile, and is associated with Ti, Fe and P in vanadiferous
magnetites and with Cu, Pb, Zn, Mo, Ag, Au and As in polymetallic sulphide deposits. It is also associated
with U, Se, Mo, Cu, K, Ca and C in sandstone-type uranium ores and is also associated with P, U, F, Se,
As in phosphorites and black shales. Vanadium is also associated with Fe, Mn and P in certain V-rich
sedimentary iron ores. The principal ore minerals are vanadiferous magnetite and V-containing uranium
20
minerals. In soil V occurs within resistates (e.g. magnetite, sphene) or in decomposing mafic minerals. It
is also present in Fe-Mn oxides. It is absorbed or coprecipitated with clays (e.g. laterites). Vanadium is a
pathfinder for sandstone, classical vein, and unconformity vein types of uranium deposits. Vanadium is
a good indicator of its own deposits and vanadiferous magnetite deposits (Levinson, 1974).
Examples (from Lollar, 2004) of possible earth material sources enriched or depleted in vanadium:
• Vanadium-bearing magnetite found in the ultramafic gabbro bodies;
• Bauxite;
• Fossil fuel deposits such as crude oil, coal, oil shale and tar sands;
• Vanadium is sometimes associated with uranium in sandstones.
Deficiencies or excess in plants:
Excess of Vanadium in plants causes reduced growth, chlorosis and reduction and inhibition of rhizoid
development.
Health effects associated with deficiency:
None recognised.
Health effects associated with excess vanadium in the dominant exposure routes (from Lollar, 2004):
When vanadium uptake takes place through the air (exposure to vanadium peroxide)it can cause severe
eye, nose and throat irritation, bronchitis and pneumonia. Other effects include inflammation of
stomach and intestines, damage to the nervous system and bleeding of liver and kidneys.
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Figure 8: A regional geochemical map of V distribution
The following general V anomalies were identified on the map (Figure 8):
1. High V concentrations follow the magnetite gabbro of the Rustenburg Layered Suite, in both the
eastern and western lobes of the Bushveld Complex;
2. An anomalous V concentration trend follows the Soutpansberg Group;
3. V contamination at the Witbank mines / factories(reference of report);
4. V contamination at the Middleburg mines / factories (reference of report);
5. Moderate to anomalous V concentrations are associated with the Lebombo basalt of the Karoo
Supergroup;
6. Moderate V anomalies are associated with the diabase intrusions on the 1:50 000 scale
Rooibosbult map sheet;
7. Some formations in the Waterberg Group contain moderate to anomalous V concentrations.
11 Potential geochemical hazardous elements: Uranium (U)
General background:
Uranium is lithophile and enriched in pegmatite and carbonatite in igneous rocks. In sediments it is
enriched in sandstone and placers. Uranium is strongly associated with the rare-earth elements. The
predominant ore minerals are uraninite, brannerite and carnotite. Uranium also substitutes in zircon,
apatite, allanite, niobate-tantalates and monazite. In soils it is present in resistate minerals and
22
adsorbed on organic matter, clays and iron oxides. Uranium is a pathfinder for uranium deposits, Au-U
placers, Ag-Au veins and carbonatites (Levinson, 1974).
Examples (from Lollar, 2004) of possible earth material sources enriched or depleted in Uranium:
• A variety of rocks, soils, sediments, dusts, Tores and other solids are enriched in uranium (U)
and thorium (Th), which can decay to radon, radium and other daughter products;
• Ground waters that have travelled through U-rich rocks, soils and sediments.
Deficiencies or excess in plants:
Effects due to excess amounts of U in plants include abnormal numbers of chromosomes and unusually
shaped fruits (Alloway, 1990).
Health effects associated with deficiency:
None recognized
Health effects associated with excess uranium in the dominant exposure routes (from Lollar, 2004):
• Ingestion: Common exposure route for uranium, which can trigger acute renal damage and
failure;
• Inhalation: Primarily is exposure route for fine radionuclide particles, radon, gas, which can
decay to other radioactive daughter products and lead to lung cancer.
23
Figure 9: A regional geochemical map of U distribution
The following general U anomalies were identified on the map (Figure 9):
1. Anomalous U in the Pilanesberg Complex;
2. Moderate to high concentrations of U on the Lebowa Granite Suite, Bushveld Complex;
3. Moderate U concentrations on the Vaalwater Formation of the Waterberg Group;
4. Moderate U concentrations on parts of the Mashashane Suite granite;
5. Moderate U concentrations on parts of the Meinhardtskraal granite;
6. U anomalies associated with the Schiel Alkaline Complex.
12 Potential geochemical hazardous elements: Thorium (Th)
General background:
Thorium is lithophile and concentrates in late stage granites and pegmatites as well as carbonatites. Ore
minerals are monazite, thorite, huttonite and thorianite. Thorium also substitutes in minerals such as
zircon, sphene, allanite, xenotime and uraninite. In soils it is normally present as clastic and detrital
mineral phases such as monazite, zircon, sphene, xenotime as well as a substitution in clays. Thorium is
a pathfinder for rare-earths (eg. Ce); Nb and Ta; some uranium deposits and U, Au, Th, and RE in placers
(Levinson, 1974).
24
Examples (from Lollar, 2004) of possible earth material sources enriched or depleted in Thorium:
• A variety of rocks, soils, sediments, dusts, Tores and other solids are enriched in uranium (U)
and thorium (Th), which can decay to radon, radium and other daughter products;
• Ground waters that have travelled through Th-rich rocks, soils and sediments.
Deficiencies or excess in plants:
Effects due to excess amounts of Th in plants include abnormal numbers of chromosomes and
unusually shaped fruits (Alloway, 1990).
Health effects associated with deficiency:
None recognized
Health effects associated with excess thorium in the dominant exposure routes (from Lollar, 2004):
• Ingestion: Common exposure route for Thorium, which can trigger acute renal damage and
failure;
• Inhalation: Primarily is exposure route for fine radionuclide particles, radon, gas, which can
decay to other radioactive daughter products and lead to lung cancer.
Figure 10: A regional geochemical map of Th distribution.
25
The following general Th anomalies were identified on the map (Figure 10):
1. Anomalous Th in the Pilanesberg Complex;
2. Moderate to high concentrations of Th on the Lebowa Granite Suite, Bushveld Complex;
3. Moderate Th concentrations in the sediments of the Waterberg Group;
4. Moderate Th concentrations on parts of the Meinhardtskraal Granite;
5. Th anomalies associated with the Schiel Alkaline Complex;
6. Moderate Th concentrations associated with the Beit Bridge Complex.
13 Geochemical distribution of Sb on the 1:100 000 map Tzaneen General:
Antimony is chalcophile and concentrates in late differentiates and veins forming supra-ore halos. The
ore minerals are stibnite, native antimony and sulphosalts, whilst it substitutes in minerals such as
galena, sphalerite, pyrite and other sulphides, ilmenite and olivine. In soils Sb is mainly present in Fe-
Mn oxides and clays. Antimony is a pathfinder for epithermal type gold and silver deposits. It is also
enriched in Pb-Zn-Ag deposits (Levinson, 1974).
Distribution Pattern:
Most of the Sb anomalies are situated on the Groot Letaba Gneiss and straddle the Letaba River valley
in a NW-SW and a NE-SW direction (Figure 11). The anomaly Sb1 is interpreted as of agricultural origin,
since it corresponds to a large degree with agricultural land along the banks of the Letaba River. It is
however not clear at this stage if it resulted from the spraying of pesticides or the application of
fertiliser. Sparse anomalies of Sb are widely scattered on the Biotite Granite and also on the Novengilla
Suite.
26
Figure 11: Geochemical distribution of Sb on the 1:100 000 map Tzaneen.
14 Potential geochemical hazardous elements: Zinc (Zn) General:
Zinc is chalcophile and concentrates in intermediate igneous rocks as well as shales and in particular
black shales. The predominant ore mineral is sphalerite. Zinc also substitutes in minerals such as biotite,
amphibole and magnetite. In soils Zn is mainly adsorbed or co-precipitated on Fe-Mn oxides and
adsorbed in organic matter and clays. Zinc is a pathfinder for Pb deposits, Zn-Pb-Ag deposits, some
fluorite deposits, polymetallic sulphide deposits, skarn deposits, porphyry copper deposits and
numerous other deposits (Levinson, 1974).
Distribution Pattern:
The Zn anomaly Zn1 (Figure 12) which is situated on the Groot Letaba Gneiss follow the Letaba River in
a NW-SW and a NE-SW direction as is the case with Sb on the Sb geochemical map (Figure 11). The Zn
anomaly is probably of anthropomorphic origin, and correlates well with agricultural activity along the
banks of the Letaba River. Sparse anomalies of Zn are also widely scattered on the Biotite Granite, the
Novengilla Suite, the Rubbervale Formation and on the Goudplaats Hout River Gneiss of which anomaly
Zn2 is regarded the most important. Anomaly Zn2 also happened to correspond with a Cu anomaly
which may be significant from an exploration point of view.
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Figure 12: Geochemical distribution of Zn on the 1:100 000 map Tzaneen.
15 Conclusion Geo-environmental anomalies shown in this report are mainly due to the natural concentration of
elements in rock formations. Anomalies resulting from human activities are mostly restricted to mining,
urban and agricultural areas. One of the main hazards related to these anomalies is the pollution of
waters (surface and ground waters) and soils. In waters, prevailing pH conditions may keep these
metals in solution and it will be transported further downstream into dams and aquifers. In soils, these
metals can be taken up by plants and organisms, thereby affecting humans and animals too.
A proper evaluation of the nature of these geochemically hazardous areas is needed and such
evaluation should be site specific. The evaluation should include the relationships between primary
parameters such as rocks, minerals, ore, soils, sediments, dust and water and secondary parameters
such as climate, topography and population.
16 Acknowledgements The staff of Geochemistry Unit is hereby acknowledged for all the years of working on the sampling and
accumulation of data and the compilation of maps to where it is today.
28
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