Industrial mineral deposits of South Africa
Where whole minerals are used, for their physical properties – no metals are
extracted.
• Asbestos
• Aluminosilicates
• Clays
• Phosphates
• Limestone
• Gypsum
• Vermiculite
Recap for each commodity
• Name
• Description
• Properties
• Industrial uses
• Geographic distribution - provinces
• Geological/stratigraphic setting
• Natural process of formation
• Processing (metallurgical) issues
• General about the South African deposits/ore-bodies
Asbestos
• a number of silicate minerals that occur in a finely fibrous form
• Two main groups
- serpentine asbestos, also white (fresh) green (exposed) asbestos,
e. g. chrysotile asbestos – a magnesium aluminosilicate –
hydrated – main resource (95%) globally, rarely > 12 mm
long, as cross-fibre
- amphibole asbestos,
e. g. crocidolite (blue) – after riebeckite (an amphibole) –
complex sodium silicate, also hydrated
- e. g. amosite (brown) – after grunerite (an amphibole) – ironmagnesium silicate, also hydrated
Asbestos
• Quality asbestos fibres are easily separable, soft and flexible, a fairly high
tensile strength
• Properties: incombustibility, resistance to heat, acids and various chemical
solutions.
• May occur in nature as cross, slip or massive
• A product of metamorphism of ultramafic rocks
• Present in Barberton Supergroup ultramafic rocks and Malmani Subgroup
dolomite (Transvaal Supergroup)
Asbestos
Occurrences
• Barberton area of Mpumulanga (Swartkoppies
Formation, part of the Onverwacht Group)
• North-West Province
• Gauteng
• KwaZulu-Natal
• Northern Cape
Aluminosilicates
• Andalusite, sillimanite and kyanite
• Al2O3.SiO2 polymorphs but used interchangeably in industry
• When heated they produce mullite 3Al2O3.SiO2 – a refractory material
• South Africa has largest resource globally – as andalusite
• Derived from thermal metamorphism of Transvaal Supergroup shale in the vicinity of the
Bushveld Complex
• Occur in North West and Limpopo provinces
• Also as alluvial deposits
Aluminosilicates
Sillimanite
• Stable at higher grades – found in gneisses, hornfels and schist
• Around granites in Namaqualand e. g. Swartkoppies near
Pofadder
Kyanite
• Stable at relatively even higher temperature associated with
garnet and corundum e. g. Nkandla – KwaZulu-Natal
Clays
• a group of related minerals - mainly all hydrated aluminium silicates
• mineralogy is complex and accurate identification sophisticated techniques
• large number of different clay species
• two groups considered in this module:
• kaolinite group
• montmorillonite group
• Wide variety of industrial uses: porcelain, earthenware, tiles, paper manufacture,
refractories, white cement, insecticides, fertilisers and edible oils.
Clays – kaolinite group
• e. g. kaolin
• from weathering of granitic rocks
• no exchangeable ions – unreactive
• found in the Western Cape (weathered granite) and Eastern
Cape (weathered shale and tillite of Dwyka and Ecca groups
(Karoo Supergroup))
• weathered under acid conditions
Clays – montmorillonite group
• e. g. bentonite
• from weathering of basic and ultrabasic rocks
• have exchangeable ions – absorbs water, expanding several times
• weathered under alkaline conditions in the presence of Mg and Ca
ions
• At Koppies (Free State), on weathering of volcanic ash (fine
pyroclastic rocks); at Heidelberg (Western Cape) and Dwaalboom
(Limpopo)
Fluorite
• aka fluorspar (CaF2)
• three commercial industrial grades: metallurgical, acid, ceramic
• Metallurgical grade – as flux in iron smelting manufacture, also moves sulphur and
phosphorus, and keeps slag fluid
• ceramic grade – glass manufacture
• acid grade - hydrofluoric acid  fluorocarbon compounds  aerosols
• occurs in Malmani dolomite (North West) and as stratiform or pipe-like
• also in other Transvaal Supergroup rocks and rocks altered by intrusion of Bushveld
Complex granitic rocks (Buffalo Fluorspar Mine) Limpopo and Cullinan (Gauteng)
Gypsum
• calcium sulphate dihydrate (CaO.SO3.2H2O
• tasteless, odourless, fireproof and chemically inert
• used in building and plasters, including POP, also dental applications
• occurs as lumps, aggregates in clay or shale or as powders on/near the surface
• occurs associated with shale thought to be the source of sulphur in turn from
pyrite) and calcareous material, usually in arid, high temperature zones (high
evaporation) and restricted drainage as evaporite material.
• most are found in Northern Cape and Free State provinces
Limestone
• composed mainly of calcite, (CaCO3) with varying MgO, Fe2O3, Al2O3, and
SiO2
• aragonite is also a CaCO3 polymorph in unlithified chemical or biochemical
sediments – not found in rocks
• closely associated with the mineral dolomite (Ca,Mg)CO3, and the rock
dolostone (American); also widely known as the rock dolomite (English)
• one of the most widely used natural products in the world
• 95% quarried is used in cement manufacture; also as a flux in smelting, as
a neutraliser for acid soils and as a building stone (marble)
Limestone
• primary rocks form as lithified chemical precipitates in wide,
open, shallow and warm seas; also biogenically derived as
shells or corals; some are of igneous origin e. g. Phalaborwa.
Marble is a metamorphosed limestone or dolostone
• secondary rocks – evaporite calcrete and dolocrete, cave
limestone (stalactite and stalagmites)
• occur in rocks of all ages Barberton Supergroup to Recent
sediments
Phosphate
• Ca5(PO4).3(F,Cl,OH) general formula as flouroapatite Ca5(PO4)3(F) ,
chloroapatite Ca5(PO4)3(Cl) or hydroxyapatite Ca5(PO4)3(OH)
• common in igneous rocks but in uneconomic quantities
• occur as igneous rocks as carbonatite (e. g. Phalaborwa, Spitzkop,
Glenover) (Limpopo),
• also as biogenic from remains of marine organism skeletons in the
Western Cape’s west and south coasts
• biogenic sands occur at uneconomic levels in the same waters
between 100 m and 1000 m depth
Vermiculite
• hydrated form of the phlogopite
• a hydrated ferro-magnesium-aluminium-silicate
• from weathered ultramafic rocks
• also as part of the carbonatite at Phalaborwa
• expands more than 30 times when heated
Vermiculite
• properties: low mass, incombustibility, chemical inertness,
insolubility, water holding capacity and heat and acoustic
insulation
• commercial/industrial uses: concrete aggregate (plaster,
sealing), thermal insulation, sound deadening, fireproofing and
horticulture
• mined at Phalaborwa carbonatite (parallel to the Cu, Zr, apatite
with REE) and magnetite
• 90% of world supply from SA and USA alone.