OVERVIEW OF THE IMPACT OF MINING ON THE ... - IIED pubs

4.18.1.2 Geology
Like the Laphalala sub-catchment, the geological features of the Mogalakwena sub-catchment are relatively
complex and consist of several different formations of widely differing ages. Most of the upper reaches of the
sub-catchment are underlain by a variety of porous consolidated and partially consolidated sedimentary strata,
predominantly sandstones, quartzites and felsites of the Waterberg and Soutpansberg Groups. These have
been variously intruded by acidic and basic granites and lavas of the Bushveld Igneous Complex and the
Transvaal Sequence, which in turn overlie the crystalline rocks of the Basement Complex.
Further downstream, the sub-catchment is underlain by sequences of silicified sandstones and quartzites,
followed by carbon-rich mudstones and shales, and then basalts, of the Karoo Sequence. The sandstones are
highly resistant to weathering and stand well above the surrounding undulating terrain to form local mountains
or ranges of hills (e.g. Wolkberg Mountain). Erosion-resistant rocks of the Waterberg Group show a similar
tendency, standing well clear of the surrounding countryside to form distinctive landscape features.
Large areas of the central parts of the sub-catchment are overlain by recent (Quaternary) deposits of
unconsolidated or poorly consolidated sandy material.
4.18.1.3 Pedology, agriculture and land use
Soils in the sub-catchment can be divided into four main groups:
• Moderate to deep sandy-clay loam soils on the sloping and undulating terrain in the upper reaches of the
sub-catchment;
• Shallow to moderately deep sandy loam soils lining the valley bottoms in the middle reaches of the subcatchment;
• Shallow to moderately deep sandy soils in flat and undulating terrain in the lower reaches of the subcatchment;
and
• Black to mottled, clay-rich, blocky vertisols (often overlying leached sands) in wetland areas subjected to
continuous or seasonal inundation (e.g. Nylsvley).
Most of the clayey loam soils in the upper parts of the sub-catchment are very suitable for irrigation when
sufficient water is available. Large stretches of the upper and lower reaches of the Mogalakwena River are
under the jurisdiction of formal irrigation boards. In addition, the area along the banks of the Limpopo River is
also part of a formal irrigation area, and uses water that is pumped either from the bed of the Limpopo River or
from boreholes sunk next to the riverbed. Further away from the main channel of the Mogalakwena River, land
use consists almost entirely of small-scale livestock farming as well as game farming.
Several towns and numerous small settlements are located in the upper and middle reaches of the subcatchment,
though population densities are much lower as the Limpopo River is approached. The central and
eastern portions of this sub-catchment support very large numbers of small-scale subsistence farmers.
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