A study of titanium-bearing oxides in heavy mineral deposits along the East Coast of South Africa.
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Date
1993
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Abstract
Heavy mineral deposits along the east coast of South Africa represent the world's largest
demonstrated resource of beach placer ilmenite. This mineral occurs as homogeneous,
subrounded grains, with chemical compositions close to pure FeTi03• Concentrates
contain between 48 and 52 per cent Ti02, with minor impurities of MnO, MgO, and
Cr203.
Most coastal ilmenites are unaltered or display only incipient alteration, but the entire
spectrum of alteration products from ilmenite to rutile or anatase, is observed.
Transmission electron microscopy of weathered ilmenites reveals that ilmenite commonly
alters to pseudorutile and then to rutile or anatase, as described by Teufer and Temple
(1966) and Grey and Reid (1975). Ilmenite may also alter directly to rutile (or anatase)
in a single-stage process. In addition, ilmenite altered by high temperature oxidation and
hydrothermal processes is found in the deposits. There is good mineralogical evidence that
the alteration of ilmenites found in the coastal sediments is best described by a multi stage
model, in which some ilmenite grains were altered prior to final deposition.
Other common iron-titanium oxides in the deposits include magnetite, rutile and hematite,
which may occur as discrete grains or as composite grains of two or more oxides.
Ilmenite and magnetite in the coastal sediments are derived from rocks of both the Karoo
Igneous Province and the Natal Basement, while rutile is derived solely from the latter.
Ilmenites from certain rock groups may be distinguished on the basis of their chemical
composition. However, magnetite chemistry is a better indicator of provenance, and
magnetites from the above two sources can be clearly distinguished. The petrography of
the iron-titanium oxides may be used as a provenance indicator, but may be misleading,
as the proportions of the oxide intergrowths change with transport and weathering.
Variations in the proportions and chemical compositions of iron-titanium oxides and other
heavy minerals within the coastal sediments are caused by provenance, selective sorting
during deposition, age of the deposit, weathering, and the recent geological history of the
area. A model is proposed in this study which describes the formation of the heavy
mineral deposits in relationship to the above influences.
Description
Thesis (Ph.D.)-University of Natal, Durban, 1993.
Keywords
Titanium., Theses--Geology., Placer deposits--Indian Coast (South Africa), Heavy minerals--Indian Coast (South Africa), Titanium dioxide.