ACAP Resources Serule Uranium Mine Water Supply Project
8 REGIONAL HYDROGEOLOGICAL PERSPECTIVE
The geology of the project area is presented in Table 6, whilst Figure 7 presents a regional geology map. The study area
lies on the eastern edge of the "Central Kalahari Sub-Basin" (Smith 1984). The study area is within the Tshimoyapula
Basin, which forms part of the Southeast Central Basin also known as the Morupule Basin.
The oldest rocks are the Archaean aged metamorphic granitic gneisses and migmatites, which belong to the northern
part of the Limpopo Mobile Belt. Unconformably overlying the basement are the sedimentary rocks of the Karoo
Supergroup. The non-conformable relationship between the Karoo Supergroup and the Limpopo belt granitoid gneisses
and metasedimentary rocks is exposed on the margins of the Tshimoyapula Basin. Conformably overlying the Ecca
Group sediments are the non-carbonaceous mudstones of the Tlhabala Formation (Beaufort Group). These are in turn
unconformably overlain by the fluviatile/aeolian deposits of the Lebung Group. To the west Stormberg Lava Group
basalts overlie the Lebung. Throughout the project area there is a thin veneer of Kalahari Group sediments (sand and
duricrusts).
The sedimentary rocks overstep the basement and dip gently westwards, deeper into the basin at an angle of around 1 °
but block faulting overrides any apparent manifestation of the dip beyond the outcrop. The late-post Karoo faulting has
two trends, east south-east (with associated dolerite dykes) and east north-east which is a trend of reactivated basement
faults such as the Letlhakane Fault. Locally horst and graben structures have developed.
Late to post-Karoo dolerite dykes are common in the project area and appear as lineaments on both Landsat TM images
and aeromagnetic maps. The post-Karoo dolerite dykes are part of the WNW-ESE trending Tuli Dyke Swarm, which
cuts across the central part of Botswana.
Table 6 - Project Area Stratigraphy (Main Aquifers in bold adapted from Smith 1984)
AGE
SUPERGROUP
Quaternary to Cretaceous
Jurassic
Karoo
Triassic to Jurassic
Permian to Triassic
GROUP
FORMATION
LITHOLOGICAL DESCRIPTION
Kalahari
Kalahari Beds
Soil, sand, calcrete, silcrete and clay
Tuli Dyke Swarm
Dolerite dyke and sill intrusive event
Stormberg Lava
Serwe Pan
Massive amygdaloidal flood basalt extrusion
Lebung
Ntane Sandstone
Aeolian sandstone. Medium to fine grain with
minor mudstone intercalations becoming fluvial to
base
Mosolotsane
Fluvial red beds. Siltstones and fine grained
sandstone
Beaufort
Tlhabala
Non-carbonaceous mudstones and siltstones with
minor sandstones
Ecca
Tlapana
Carbonaceous shales and dull coal seams with
minor sandstones
Coarse clastic fluvio-deltaic sediments
Mea Arkose
Carboniferous
Archaean
Dwyka
Basement
Limpopo Mobile
Belt
Tswane
Post glacial lacustrine argillaceous mudstones and
siltstones
Dukwi
Base of Karoo sequence tillites, shales, varved
siltstones and mudstones
Quartzo-feldspathic gneiss, metasediments and
meta igneous rocks
The main productive aquifer in the project area is the Ntane Sandstone and this has been the focus of the two Phase II
exploration drilling and test pumping stages.
The geological sections (Figures 8 and 9) show a fault running west to east roughly along the line of the northern
escarpment - which therefore appears to be a fault controlled feature. The basalt is much thicker on the north side of the
fault and the Ntane Sandstone Formation is completely offset over much of its length. The feature produces a sandstone
'cliff buried beneath the basalt, but it is not possible to say whether the fault pre or post-dates the lava eruptions. There
are also insufficient data to plot west to east sections through the northward
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Water Surveys Botswana
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REGIONAL GEOLOGY MAP
400000
450000
400000
425000
425000
450000
475000
500000
525000
475000
500000
525000
SCALE 1 : 750,000
10
в: H H
Projection: UTM Zone 35 South,
WGS 84 Datum
10
20
30
40
50 Kilometers
ACAP Resources Serule Uranium Mine Water Supply Project
limb of the cuesta north of Mmashoro, but the fault is present on the north-west trending limb between Kolokome and
Mmashoro.
The dolerite dykes separate the aquifer into compartments, but appear not to fully displace the Ntane Sandstone
Formation. Thus they may not be considered to act as total barriers to groundwater flow. This is also reflected by the
piezometric surface (Figure 11), which shows a northerly flow across them.
Figure 8 - Schematic north to south sections through the basin (A, B & C)
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Water Surveys Botswana
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ACAP Resources Serule Uranium Mine Water Supply Project
Figure 9 - Schematic north to south section through the basin (D)
The Ntane Sandstone aquifer in the project area is part of a regional system extending northwards to Sowa Pan,
encompassing the Orapa Wellfields and southwards to Serowe. Groundwater levels have been monitored in the BPC
Paje Wellfield and extension area boreholes and in boreholes in wellfields at Serowe, and Orapa. These data allow an
overview of the regional groundwater flow patterns, shown on Figure 10. Broadly they follow the topography and fall
from an elevation of around 1200mamsl on the plateau. to 900mamsl at the margins of the Makgadikgadi Pans.
Water levels fall radially away from the plateau above the escarpment with steep gradients to the north and east (off the
escarpment faces) and shallower gradients to the west. Groundwater divides run north-east to southwest across the
plateau through Serwe Pan; westward more-or less along the Serowe to Orapa road, east towards Serule and northwards
along the edge of the escarpment towards Mmasharo and Sowa Pan. The regional flow is therefore divided into four
main sub-basins.
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Water Surveys Botswana
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ACAP Resources Serule Uranium Mine Water Supply Project
Flow to the west is sub-parallel to the regional horst and graben structures and to the dyke swarms whereas flow to the
north is perpendicular to them. This has significant implications for the flow which will be less restricted east to west
than south to north as the flow in this direction will be impeded by the structures. Moreover, if the escarpment fault
system continues northwards then flow to the west from the proposed wellfield area will be restricted by the offset Ntane.
In the absence of data to the contrary, the northward continuation of the fault system seems a reasonable assumption
because the groundwater divide follows the escarpment. Local groundwater contours (Figure 11) in the study area show
flow northwards off the escarpment towards Sowa Pan and eastwards towards the Ntane Sandstone outcrop.
Final Exploration Drilling & Test Pumping Report June 2010
Water Surveys Botswana
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