Transcript Slide 1

Hydrogeology in the
Limpopo Basin
Overview of key hydrogeological
units in the Limpopo basin in
Mozambique, South Africa and
Zimbabwe
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Why Hydrogeological Units
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Insight into groundwater potential for the
basin
In sight of where to apply water conservation
Because water conservation is affected by
hydro geological units’ characteristics such as
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storage capacity ( porosity related)
residence time (underlying units related)
thickness of the weathered overburden (direct
relationship between water yielded to thickness)
Geology of Limpopo basin in Moza
31.5°
32°
32.5°
33°
-21.5°
-22°
Sav
33.5°
ve
e Ri
34°
34.5°
-21.5°
r
-22°
CHICUALACUALA
Machaila
-22.5°
-22.5°
Chigubo
-23°
-23°
Chaila
Dindiza
-23.5°
Lim
-23.5°
pop
iv
o R
er
-24°
MASSINCIR
-24°
GUIJA
-24.5°
-24.5°
CHOKWE
MANJACAZE
-25°
-25°
XAI-XAI
MAGUDE
MANHICA
-25.5°
-25.5°
31.5°
32°
32.5°
33°
33.5°
34°
34.5°
GEOLOGICAL LEGEND
Recent alluvium
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QUATERNARY &
RECENT
Coastal dunes, mobile dunes
Interior dunes, consolidated
dunes including remobilised
& longitudanal
argillites, areanous fluvial sandstones &
mudstones, other superficial deposits
argillites related to marine terrraces
MIOCENE
MAZAMBA
Ferrigenous arid sands
Mozambique Hydrogeology
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mostly sedimentary rocks or unconsolidated
sediments, with minor hard rock lithologies.
primary porosity aquifers with high groundwater
storage capacity.
Coarse grained sediments give abundant
groundwater; fine grained sediments are poor
aquifers.
Coastal regions and areas along the main river
channels are most promising.
Regular recharge is important in terms of ensuring
good fresh water quality.
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The Hydrogeology of the Limpopo Basin in Mozambique.
Period
Rock types
Groundwater
Potential
Holocene
Alluvial
Very good
Pleistocene
Marine / lacustrine alluvials
Very good
Miocene
Ferrigenous arid sands
Very good
Quaternary
Upper
Tertiary
Mixed calcareous sands
Lower
Palaeocene
Very good
Conglomerates + silts + marine sands.
Silts – poor
Sands - good
135-63 my
Conglomerates +
Karoo volcanics
Good
180-135 my
Rhyolite, Basalt,alkaline rocks.
Upper
Cretaceous
Lower
Jurassic
Very poor.
For the unconsolidated sediments:
•Active recharge will be a very significant factor in determining water quality
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•Grain size will determine well yields
Geology of limpopo basin in Zim
28°
28.5°
29°
29.5°
30°
30.5°
31°
31.5°
TABLE OF FORMATIONS
INTERNATIONAL
-20°
-20°
SYSTEM OR
GROUP
PLEISTONE &
RECENT
Alluvium and other superficial deposits
CRETACEOUS
Sandstone, etc.
Rhyolite
JURASSIC
Basalt
KAROO
-20.5°
-20.5°
TRIASSIC
PERMIAN
BEITBRIDGE
EARLY
PRECAMBRIAN
-21°
-21°
Grits, sandstones and siltstones
Glacial beds, mudstones, coal
measures and sandstones
Gniesses of various ages
SHAMVAIAN
Metasediments, felsic metavolcanics
BULAWAYAN
Andestic and dacitic metavolcanics
SEBAKWIAN
Basaltic volcanics with intercalated sediments
Ultramafic lavas and intrusions
Gneisses of various ages
INTRUSIVE IGNEOUS ROCKS
LATE JURASSIC
-21.5°
Granophyre, granite and syenite
-21.5°
Dolerites and Gabbros
GREAT DYKE
VARIOUS AGES
Serpentinite and pyroxenites
Younger granites, granodiorite-adamellite
Older Gneiss Complex
-22°
-22°
28°
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28.5°
29°
29.5°
30°
30.5°
31°
31.5°
Zimbabwe Hydrogeology
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mostly of crystalline basement igneous and
metamorphic rocks. Minor occurrence of sedimentary
rocks in the basin.
secondary porosity features such as fracture zones
and the weathered regolith.
Small scale water supplies available from granitoid
crystalline lithologies; greenstones are more
favourable.
Karoo lithologies can provide moderate and
occasionally large scale groundwater supplies.
Large-scale groundwater supplies restricted to
alluvial aquifers along the major rivers.
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Hydrogeological Units – Limpopo Basin Zimbabwe
Hydrogeologic
al unit
Main lithologies
Groundwater occurrence
Average range of
borehole
depth
(m)
Average
range
of
sustainable borehole
yield (m3/d)
1
Achaean Granite and
Gneissose rocks
Principally in weathered and fractured zones.
10-35m thick
40-50 in African
surface.
30-40 on postAfrican surface
50-100
in
African
surface.
10-50
in post African surface
2
Greenstone Belts Bulawayan metalavas
and
Shamvaian
metasediments
Associated with weathering of Bulawayan
strata to 50m and fracturing in Shamvaian
strata
30-50 in Bulawayan
40-60
in
Shamvaian
100-250 or more in
Bulawayan
10-25 in Shamvaian
Karoo Sequence has
been divided into 5
sub-units.
Batoka Basalt
Controlled by weathering and fracturing from
30-70m below surface
40-60
20-100
3b
The Forest Sandstone
Saturated
aquifer
generally
confined
50-100
50-300
3c
The Escarpment Grit
Saturated sandstone and grit.
confined except in Zambezi Valley
Generally
50-70
100-300
3d
The
Madumabisa
Mudstone
Associated with shallow weathering or sandy
intercalations which water strike between 4070m occur
50-70
10-25
3e
The Upper and Lower
Wankie Sandstone
Saturated sandstone confined aquifer
100-150
100-500
4
The
Cretaceous
Sandstones
Deep zones of primary features possibly
shallow weathering along drainage lines
70-100
10-50
5
Kalahari sands
Saturated
unconsolidated
consolidated pipe sandstone
70-100
100-1000
6
Alluvial Deposits
Primary porosity and permeability in gravel
lenses, sand layers
20-70
100-5000
3a
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sandstone
sands
and
Geology of limpopo basin in S.A
26°
27°
28°
29°
30°
31°
GEOLOGICAL LEGEND
TERTIARY &
RECENT
Unconsolidated superficial deposits, limestone,
conglomerate, sandstones
CRETACEOUS
Sandstone, shale, limestone
Rhyolite, dacite, pyroclastics
JURASSIC
-23°
-23°
STORMBERG
TRIASSIC
KAROO
PERMIAN
CARBONIFEROUS
Sandstones, shale, mudstone, coal
ECCA
Shale, sandstone, gritstone, coal
DWYKA
Tillite, sandstone, shale
PILANSBERG INTRUSIVE
COMPLEX
WATERBERG
-24°
Basalt, pyroclastics intercalated with sandstones
Alkalis, basic to ultrbasic intrusives, carbonatite
KRANSBERG
Sandstone, conglomerate, siltstone
NYLSTROOM
Lava, sandstone, conglomerate, siltstone, greywacke
Granites, felsite, tuffaceous & shaly sediments,
agglomerate
-24°
Granophyre
BUSHVELD
INTRUSIVE
COMPLEX
Gabbro, norite, chromitite, magnetite
-25°
-25°
PRECAMBRIAN
Pyroclastic felsite
LIMPOPO BELT
PRETORIA
Migmatite, gniess, high grade metamorphic rocks
Quartzite, shale, hornfels, andesite, chert, tuff,
limetsone, conglomerate
Quartzite, shale, hornfels, lavas, pyroclasts, chert,
jaspilite, limetsone
Quartzite, shale, tillite, andesite, chert, jaspilite, limetsone
Quartzite, shale, conglomerate
Dolomite, chert, conglomerate, quartzite, shale, tillite
MALIMANI
Quartzite, shale, conglomerate, andesite
Granite
DOMINIAN
Conglomerate, quartzite, shale, phylite, tillite, lavas
Migmatite, gniess
-26°
-26°
Ultrabasic to basic intrusives
Conglomerate, quartzite, shale, limestone, lavas
ARCHAEAN
GREENSTONES
26°
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27°
28°
29°
30°
31°
Metasediments
South Africa Hydrogeology
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Geology quite complex.
Quartzites / basal conglomerates (Dominion group)
and Karst limestones (Malimani & Pretoria group) at
the base of the sequence have high to very high
potential.
Crystalline basement complex rocks have low to very
low groundwater potential, except Archean
greenstones, which have medium potential.
Indurated and metamorphosed sedimentary rock also
have low potential. Karoo has generally low potential.
Recent unconsolidated sediments and alluvial
material have high potential.
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Hydrogeological units of S.A.
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Conclusions
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Very varied hydrogeological units
Different GW potential
Implication = Different conservations potential
Need to expand this to assess potential for
conserving water
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Thank you
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