Part 2 - Eskom

ENVIRONMENTAL SCOPING REPORT FOR THE PROPOSED 40MW OPEN CYCLE GAS TURBINE POWER
PLANT IN THE AMERSFOORT AREA, MPUMALANGA
7.1.5. Geology
7.1.5.1. Regional Geology
Bohlweki-SSI Environmental
The majority of the study area is underlain by Karoo Supergroup sedimentary rocks
of the Vryheid and Volksrust Formations of the Ecca Group. These are largely
comprised of sandstone, mudstone, shale, siltstone, and coal seams.
The available geological maps covering the study area did not indicate any major
structural features such as faults or fractures. Limited tectonic activity is recognised
within the study area, and the only evidence of secondary processes is outcrops of
intrusive younger dolerite sills mapped in the Karoo sediments.
Four generations of dolerite intrusions are recognised within the study area, based
on olivine or plagioclase content, alteration, and texture. The intrusive dolerite has
produced large-scale devolatilisation and structural displacement of the coal. These
adverse geological conditions caused the closure of the Majuba Colliery in 1993. The
lithostratigraphy of the study area is presented in Table 7.2 below.
Table 7.2: Lithostratigraphy of the study area
Age Supergroup Group Subgroup Formation Lithology
Jurassic Dolerite
Permian Karoo Ecca Volksrust Mudstone,
siltstone,
shale
Permian Karoo Ecca Vryheid Sandstone,
siltstone,
shale, coal
7.1.5.2. Geology of the farm Roodekopjes 67HS
The general geology of the farm Roodekopjes 67HS from surface downwards is
illustrated in Figure 7.8. The B8 dolerite sill outcrops at surface on the site and
averages in the order of 30m thick. A sandstone and siltstone interval of between 5
and 25m is followed by two to three stages of sill intrusion of the B4 dolerite totalling
approximately 120m in thickness. Below this composite dolerite sill are sequences of
sandstones, siltstones and mudstones containing minor coal seams. The main coal
seams namely the Alfred and Gus seams are at an average depth of 280m below
surface. They total about 5m in thickness with a small parting between them that
thickens and becomes more prominent towards the east.
Below this is a sequence of bioturbated siltstones, sandstone and mudstone with
minor coal seams. The B6 dolerite sill underlies the whole farm. This dolerite has
indurated the coal and the coal seams volatile content is well below the required
average for Majuba. The seam elevation and attitude for farm Roodekopjes is flat
and consistent.
E02.JNB.000308
ESKOM HOLDINGS LIMITED
01
45
08/10/2009