Page 33 - SAICE book proof 2 LATEST JULY 2014

s a i c e

A lopolith is a large igneous intrusion which is len-
CHAPTER 3: Gauteng Province
ticular in shape with a depressed central region. Lopo-
liths are generally concordant with the intruded strata
with dike or funnel-shaped feeder bodies below the body.
Introduction The term was first defined and used by Frank Fitch Grout
during the early 1900s in describing the Duluth gabbro
In a certain sense Gauteng is a unique place and takes complex in northern Minnesota and adjacent Ontario.
its place in the world as an area within which many
interesting items can be found. It is a small province of Lopoliths typically consist of large layered intrusions that
roughly 80 km from south to north and 120 km from range in age from Archean to Eocene. Examples include
east to west or about 18 178 km². the Duluth gabbro, the Sudbury Igneous Complex of
Ontario, the Bushveld igneous complex of South Africa,
Within its boundaries or just outside, the following are the Great Dyke in Zimbabwe, the Skaergaard complex
facts that contribute to its uniqueness: of Greenland and the Humboldt lopolith of Nevada. The
Sudbury occurrence has been attributed to an impact
The Cradle of Humankind at Maropeng to the west event and associated crystal melting.
of Johannesburg is believed to have yielded many
fossils and some of the earliest hominid remains on
earth. The dolomitic caves beneath the hills still hold not uncommon that it could be freezing point in the
many secrets. early morning and peaking at 18°C at midday. Snow
is rare.
Along a roughly east-west ridge of about 70 km, now
transecting Johannesburg, the world’s richest gold At between 1 500 m and 1 700 m above sea level
reefs of its time were discovered and mined since this is one of the biggest cities in the world at this
1886. At first, gold was discovered in the Blaauwbank elevation. Add to this fact, it is a city without a major
Spruit flowing to the north and it was only when the river running through it or next to it. This means that
gold seekers moved upstream that they discovered almost all the water that is required by the cities of
the origin of the alluvial gold in the waters flowing Johannesburg and Pretoria is pumped from the Vaal
from the Witwatersrand ridges. River system 300 m lower than the Witwatersrand.

The Witwatersrand with its gold reef ridge along To the south, Gauteng borders the site of the world’s
which the gold reef sits at the northern edge of the largest known meteor hit known as the Vredefort
huge ancient lake, dominated the South African inte- Dome (detailed in Earth and life. A southern African
rior in ancient times. perspective on a 4.6 billion-year journey by Terrence
McCarthy and Bruce Rubidge).
Just to the north of Pretoria, the Magaliesberg ridge
constitutes the southern edge of the world’s biggest All this and much more has shaped the way in which
lopolith or volcanic pipe and the source of many types Gauteng developed and how civil engineering services
of minerals. This lopolith is now the home of the rich- and infrastructure was created to transform the
est platinum mines in the world. environment and serve the activities of the human
settlements which flocked to the promises of the
Gauteng straddles the east-west watershed of South gold deposits. It is also the first home to the mining,
Africa. At this point and at an elevation approximately metallurgy and other related engineering professions.
1 500 m above sea level, the water to the north of
the province flows into the Indian Ocean and to the Gauteng Province is home to 12 million people and
south water from the marshes, and fountains south of many immigrants from all over Africa. It is also a popu-
Johannesburg end up in the Atlantic Ocean. lar destination for shopping tourism from neighbour-
ing countries. Johannesburg is still known as the city
The Gauteng climate is Highveld or high savannah of gold and Pretoria (Tshwane) is the administrative
bases. Summers are mild to hot with summer rains capital of South Africa and has a musical line saying
accompanied by severe thunderstorms and one of the “Pretoria rules the waves”.
highest lightning strike incidences in the world. Win-
ters are mild but some frost occurs in winter, and it is Civil engineering structures are often named after a

1