Geology Reference
In-Depth Information
N
Alkaline Intrusions
Granite
Rustenburg Layered Suite
Transvaal and Rooiberg
Bushveld
Complex
24
°
Northern or
Potgietersrus Lobe
100 km
Burgersfort
Eastern
Lobe
25
°
Far Western Lobe
Western
Lobe
Pretoria
26
°
S
Bethal Lobe
(under Karoo cover)
Johannesburg
26
°
27
°
28
°
29
°
30
°
E
Figure 10.4
General geological map of the Bushveld intrusion and associated
rocks, South Africa.
called the 'Merensky reef', which contains iron-nickel-copper sulfides and
important platinum-group minerals. Above the critical zone is the
main zone
which comprises thick, rather uniform, layers of gabbro and norite, whereas the
overlying
upper zone
contains olivine melagabbros, with magnetite-rich gabbros
and anorthosite-magnetite layers near the top. A younger granite suite - thought
to be unrelated, magmatically, to the Bushveld Complex - overlies and conceals
the layered rocks in the centre of the outcrop (Figure 10.4).
10.3 Geotechnical Properties of Igneous Rocks
In this final section we look at the engineering properties of igneous rocks and
review some of the on-site field methods used by practising civil engineers
as part of routine geotechnical assessments. This applied aspect of igneous
petrology has to date received scant attention but we feel it is important for
geologists to understand something about the geotechnical properties of igneous
rocks for the following reasons:
i) Engineers may need to tunnel into a granite pluton or volcanic rock to
build a new road or railway line and the characteristics used to define the
