Stewart R. Wallace — 1919–2009 - Society of Economic Geologists

JULY 2009 No 78 SEG NEWSLETTER 13
Discovery and Geology of the Platinum Group Element
Deposits of the Bushveld Complex, South Africa
ROGER N. SCOON (SEG 1985 F), † Postnet Suite 291, Private Bag X31, Knysna 6570, South Africa, and ANDREW A. MITCHELL
(SEG 2001 F), Department of Geology, University of KwaZulu-Natal, Private Bag X54001, Durban 4000, South Africa
INTRODUCTION
The Bushveld Complex, which
includes the largest known
mafic intrusion in the world,
reveals some spectacular geology,
including the classic layering
of dark ultramafics and
light-colored anorthositic rocks
(Fig. 1). Three distinct groups of
rocks make up the complex
(Tankard et al., 1982), the oldest
of which is the Rooiberg
Group (dominated by rhyolite)
and the youngest, the Lebowa
Granite Suite (including a suite
of granophyres). The majority
of the ore deposits are, however,
restricted to the intervening
group of ultramafic-mafic
rocks, or Rustenburg Layered
Suite. The Rustenburg Layered
Suite is intrusive into the sedimentary
rocks and subordinate
volcanic rocks of the Transvaal
Supergroup (ca. 2.5–2.1 Ga) and has
been dated at 2.055 Ga (Scoates and
Friedman, 2008). The Bushveld contains
the greatest concentration of mineral
wealth on the planet and includes, in
addition to the platinum group element
(PGE) ores, base metals (e.g., chromium,
iron, tin, titanium, and vanadium) and
industrial minerals (e.g., andalusite,
dimension stone, and magnesite), as
described by Willemse (1969) and
Wilson and Anhaeusser (1988). Mining
operations have spawned extensive
towns and associated industrial complexes,
including downstream processing
plants with smelters and precious
metal refineries, many of which use
technology specifically designed for the
Bushveld ores.
THE RUSTENBURG
LAYERED SUITE
The Rustenburg Layered Suite forms
three principal limbs (Fig. 2) together
† Corresponding author:
e-mail, rnscoon@iafrica.com
FIGURE 1. Classic layering at the contact between the Lower Critical
and Upper Critical zones in the Olifants River section, Eastern limb.
Dark-colored layers of feldspathic orthopyroxenite and chromitite are
intercalated with light-colored layers of anorthosite.
with a number of smaller satellite bodies.
The eastern limb is particularly well
known owing to the excellent exposures
(Hall, 1932). Here, the
Transvaal Supergroup
has been tilted and
uplifted in response to
vertical tectonics
induced by intrusion of
the mafic rocks (Daly,
1926) to form a 2,000m-high
range, whereas
the Rustenburg Layered
Suite crops out in wide
valleys associated with
the Olifants River system,
and also forms a
rugged, 250-km-long
escarpment. This area
influenced development
of the Great Escarpment,
which in turn formed by
uplift during the
Cenozoic era (Du Toit,
1933) and has resulted
in a discrete geographicbotanic
system known as the
Middleveld (located
between the central
to page 14 ...
FIGURE 2. Schematic map of the Bushveld Complex depicting the three main limbs of the
intrusion with mines and other localities referred to in the text: 1 = Winnaarshoek, 2 =
Maandagshoek, Mooihoek and Driekop, 3 = Onverwacht, 4 = Brits, 5 = Kroondal, 6 =
Union, 7 = Amandelbult, 8 = Sandsloot. Outliers and satellites not shown.