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RHODESIA GEOLOGICAL SURVEY
SHORT REPORT No. 40
The Karoo· Rocks in the
~Mazunga Area,
Beitbridge District
by
A. 0. THOMPSON, M.Se.
•
ISSUED BY AUTHORITY
--
SALISBURY -1975
3
Pri./t' ", ,be Go""" ...., Pri.,", S.lisbury
The Karoo Rocks in the Mazunga Area,
Beitbridge District
INTRODUCTION
This account of the Karoo rocks in the Mazunga area is an explanation to accompany three geological maps, the Tull, Mazunga and
Gongwe maps, which are published separately. They were compiled
during a geological reconnaisance of the outcrop of the Karoo System
during 1971 and 1972 using air photographs and 1 : 50000 topographic
maps. The mapped area lles between latitudes 21 ° 30' and 22° 12'
south and longtitudes 29° 00' and 30° 36' east and covers an area of
6825 km' of which 2125 km' are in the Tull, 2800 km' in the
Mazunga, and 1 900 km' in the Gongwe map areas. The area is mainly
in the Beitbridge District, but includes parts of the Gwanda and Nuanetsi
Districts. It is subdivided into several large ranches and 'African Tribal
Trust Lands with no large settlements. Mazunga and Tull are the
largest.
The main road from Beitbridge to Bulawayo crosses the Mazunga
map area, and the main road to Fort Victoria and Salisbury crosses
the eastern part of the Gongwe map area. Away from these main roads
there are earth roads and tracks, mainly on the ranches, as well as
several airstrips. The large rivers affect communications, being wide
stretches of sand in the winter and often floods in the summer. The
Pioneer road from Tuli to Fort Victoria, and the old coach road from
Beitbridge to Fort Victoria, now largely overgrown, both cross the area
and, since the survey was made, a rail link from Rutenga to Beitbridge
has been completed.
The area is one of low rainfall with an average of only 355 to 400 mm
per annum falling between October and May. The rainfall is erratic
with frequent drought years. The average temperature ranges from
around lOoe in June to 29°e in October and November. Very cold
nights are experienced in June and July and hot afternoons with
temperatures of 30 e or more in the summer.
In the Tribal Trust Lands, populated mainly by Venda with Kalanga
and Ndebele groups, subsistence economy is practised, though on the
Tuli and Shashi rivers, where there are irrigation schemes, maize and
winter wheat are grown. The European ranches are devoted to cattle
with small irrigated areas along the Limpopo and Umzingwane rivers
producing citrus and vegetables.
0
2
PREVIOUS GEOLOGICAL WORK
The area, which is the northern continuation of King's (1951, 1952)
Transvaal Lowveld, is a flat one sloping southwards to the Limpopo
River with a few hills and east-trending ridges. The highest point is
Gongwe Hill at 2 450 feet (747 m) elevation in the north-east, and the
lowest point is on the Limpopo River in the south at 1 650 feet (493 m).
The area is crossed by four major rivers which meander through
alluvium-bordered valleys to join the Limpopo. The Shashi, Tuli and
Umzingwane flow S.S.E. and the Bubye E.S.E. Their tributaries flow
east or west, and a few of the larger ones southwards. Two probable
examples of river piracy were seen, the Mutshilashokwe from the
Umzingwane and the stream 4,5 km S.S.E. of the Shashi Dam.
The interfluves between the Shashi and Umzingwane rivers and
between the Umzingwane and Mtetengwe rivers slope at about 18 feet
per mile (3,5 m per km), and the interfluve between the Mtetengwe and
Bubye rivers at about 9,6 feet per mile (2,9 m per km) southwards,
showing the flatness of the mapped area.
PREVIOUS GEOLOGICAL WORK
A three-foot seam of coal was discovered outcropping in the east
bank of the Umzingwane River near Morgan's Hill in about 1895 by
De Gruyter, and the area became known as the Tuli Coalfield. De
Gruyter's and other coal claims were acquired by Consolidated Gold
Fields of South Africa Ltd. in 1896 and transferred in 1897 to a
Bulawayo company, Tuli Consolidated Coal Fields Ltd. (Mehliss, 1951).
The exploratory work was reported upon by F. M. Watson in 1896,
R. Sneddon (1896), by W. H. Chandler in 1897 and R. T. Southwood
(1898). The company's holdings were visited in April, 1899, by A. J. C.
Molyneux who reported that the coal occurred in three separate, disconnected basins (a) the Western or Umsingwane basin, (b) the Central
or Mungesi basin and (c) the Eastern or Letitengwe basin (Mehliss,
1951). By 1903 several boreholes and shafts had been sunk, but as the
railway had by then reached Wankie Colliery interest in the Tuli Coalfield waned.
A. J. C. Molyneux (1903) gave the following succession in ascending
order for the strata in the coalfield:
Tuli Lavas
Umsingwani coal-bearing beds
Unconformity
Samkoto veined sands tones
Uncontormity
Metamorphic rocks
Gneiss and granite
PREVIOUS GEOLOGICAL WORK
3
The basaltic lavas, which covered most of the area, extended eastwards from Botswana past Fort Tuli to the Bubye River. Sedimentary
rocks outcropped only in the coalfield area near the Umzingwane River
where they lay unconformably on the metamorphic rocks. All these
rocks were intruded and metamorphosed by dykes. The coalfield
covered an area of several square miles and contained a 3!-foot seam
of semi-bituminous coal. The only fossil found in the whole area
(Molyneux, 1901) came from the coal seams near Morgan's Hill, and
was described by E. A. Arber (Molyneux, 1903, p. 689) as a pith cast
of a calamite resembling Calamites approximaJa, Brongiart.
MelIor (1905) wrote that although glacial beds of the Dwyka Series
had been found in the northern Transvaal, none had been found in
Rhodesia. However, Mennell (1905) identified them among specimens
collected by Molyneux. Later (1906, 1907, 1908 and 1910) he wrote
that the Tuli Coalfield, though not connected with the Karoo rocks
north-west of Bulawayo, resembled them. The coalfield contained basal
Dwyka conglomerates, shales and sandstones, a coal-bearing series,
basalt lavas. and later intrusions which were often glomeroporphyritic,
never ophitic. and sometimes contained olivine.
Zealley (1910) reported that there was a 3!-foot seam of semibituminous coal, and Molyneux (1909 and 1911) included the coalfield
strata in a correlation of the Karoo rocks of Rhodesia, South Africa
and Gondwanaland. Maufe. in generalized accounts (1913, 1919. 1924
and 1929), stated that little fieldwork had been done in the Tuli Coalfield since 1903, but it had been found that discontinuous outcrops of
Karoo rocks extended as far east from it as the Sabi River. Dwyka
beds appeared to be limited to the Tuli Coalfield (1919). He gave
(1913) the following sequence of strata in the Tuli Coalfield. which was
estimated to have reserves of about 45 million tons of coal:
Tuli Basalts
Samkoto Beds=Forest Sandstone
Coal Series
Basal Beds
Anonymous writers (1920 and 1921) gave accounts of the Coalfield
and its resources. Renewed interest in the potential of the coalfield
resulted in Mehliss (1951) examining and reporting to the Gold Fields
of South Africa Ltd. on their Special Grant No. 15 area, and the
company exploring the coalfield under Exclusive Prospecting Order
No. 19 (PelIetier. 1955, and Morrison. 1974). Their work and that of
Messina (Rhodesia) Development Co. Ltd. on E.P.O. No. 393 (Johnson,
4
PRECAMBRIAN ROCKS
1973) provided a great deal of new information on the geology and
coal resources of the area. Swift (1961) had stated that there were two
workable seams in the coalfield with extractable coal reserves of about
40 million tons. and that the coalfield resembled the Malilongwe and
Sabi coalfields (Swift et al .• 1953) to the east.
The geology of the area is referred to in papers on Karoo stratigraphy
by Tyndale-Biscoe (1949) and Bond (1952. 1955 and 1967) and on
palaeontology by Lacey (1961) and Bond (1973). The Karoo igneous
rocks of what is known as the Nuanetsi Igneous Province (mainly
adjacent to the mapped area) have been described and discussed by
Tyndale-Biscoe (1949). Worst (1962). Cox et al. (1965). Cox et al. (1967).
Jamieson (1966) and Macdonald (1967).
Robertson (1967). with a party of schoolboys. conducted a very
successful study of the Karoo rocks along the north bank of the
Limpopo River and the south-west corner of Sentinel Ranch where
they discovered and excavated reptilian fossil remains.
Macgregor (1939) reported upon an abortive search for an alleged
gold occurrence in the Karoo lavas and dykes that form the ridge at
Gong's (Gongwe) Poort.
PRECAMBRIAN ROCKS
The mapped area lies in a portion of the North Marginal Zone of
the Precambrian Limpopo Mobile Belt which consists of intensely
deformed rocks. mainly gneisses that have been raised to the upper
amphibolite and granulite facies of regional metamorphism (Robertson.
1973). The Mesozoic Karoo rocks have been deposited on them with
a major unconformity and subsequently down-faulted in most places.
against the Precambrian rocks. As this reconnaissance survey was only
concerned with the Karoo strata. little attention was paid to the Precambrian rocks which are not differentiated on the three geological maps.
The Precambrian rocks surrounding the Karoo outcrop are predominantly quartzo-feldspathic gneisses. Epidote-rich gneisses abound
in the northern part of the Tuli map area. particularly a few kilometres
south of Hwali Store. Unakite. a colourful pink and green variety used
as a gemstone, has been produced from the Bertie Claims. Banded ironstones form the cores of ridges such as Gwawe. Chamalaya and the
northern extension of Nyongwe. and bodies of serpentinite outcrop in
KAROO SYSTEM
s
the Jopempi and Dijana Hills. In the latter. about 7 km south of Tongwe
Dam, there are occurrences of asbestos and magnesite.
Quartzite forms a ridge in the Precambrian rocks on River Ranch
and Benfer Estate near the Umzingwane River on the south side of the
Karoo rocks. and calc-silicate granulites form hills about 1 km to the
east. Garnets are abundant in the sandy shallow watercourses in this
area and also about 2 km to the west of Gwawe Dam.
The Precambrian rocks around the Towla and Jopempi hills to the
north of the area of the Mazunga map have been described by Robertson
(1973).
KAROO SYSTEM
INTRODUCTION
The rocks of the Karoo System are widely distributed in southern
Africa but in Rhodesia are confined to down-faulted blocks in the
Limpopo and Zambezi valleys. From the Zambezi valley Karoo rocks
extend in tongues across the Rhodesian Craton to near Bulawayo.
Gwelo and Felixburg. Gokwe and Que Que, and the Charter District
around Featherstone, always within the present drainage area of the
Zambezi River. Erosion has been much more extensive in the drainage
areas of Sabi and Limpopo rivers. and has removed all Karoo rocks
from this part of the Craton. Only those outcrops in the Limpopo
Mobile Belt remain.
In the drainage area of the Zambezi River where they have been
extensively studied. the stratigraphy and palaeontology of the Karoo
System are quite well known. and the beds have been correlated with
the standard succession of the Karoo System in South Africa (Bond.
1952. 1955. 1967 and 1973; Lightfoot. 1929; Maufe. 1913. 1919. 1924.
1929; Mennell. 1910; Molyneux. 1901. 1903. 1909. 1911; Swift, 1961;
Worst. 1962). The Karoo System in the Limpopo valley is less well
known and. in the Muzunga area. only in connexion with the search
for coal (Johnson. 1973; Maufe. 1924. 1929; Mehliss. 1951; MenneII.
1905; Molyneux. 1903. 1909; Pelletier. 1955; Robertson. 1967; Zealley.
1910). In this account the stratigraphic nomenclature used is largely that
of Mehliss (1951). During the last quarter of a century more work has
been done to the east between the main road from Beitbridge to Fort
Victoria and the Sabi River (Cox et al. 1965; Cox et al. 1967; Morrison.
1974; Swift et al. 1953; Tyndale-Biscoe. 1949). However. the strati-
6
KAROO SYSTEM
INTRODUCl'ION
graphy and palaeontology are not sufficiently well known to correlate
the strata with the Karoo rocks of the Zambezi basin and South Africa.
form large, intermittent and generally fault-bounded outcrops around the
margins of the Karoo rocks of the Mazunga area. They probably cover
an area of about 160 km long and 40 to 50 km wide. They are essentially an argillaceous series of grey, brown and black carbonaceous
shales and mud stones which tend to become slightly more arenaceous
and reddish or purplish in colour in the upper part. The few sandstones
and rare pebble beds present are discontinuous. The coal horizons
suggest cyclic sedimentation with a cold to temperate climate in a
shallow-water to swampy basin that was subsiding rhythmically. The
source of the sediments was the Precambrian rocks and probably Dwyka
deposits. Fossil plant remains have been identified as Glossopteris,
Phyllotheca, and Calamites which suggest an Ecca or Permain age for
these beds.
The pre-Karoo landscape over much of Rhodesia appears to have
been an extremely flat plain from which isolated hills and ridges, mainly
Precambrian banded ironstones, quartzites and serpentinites, rose
abruptly.
The Karoo basin of the Limpopo Valley was probably bounded on
its northern side by a watershed . that extended from south of the
Matopos Hills, through Bala Bala, south of Selukwe, east of Felixburg
to near Rusape, then eastwards to south of Inyanga and southwards
through the Melsetter and Chipinga Districts to the southern end of
the Umkondo Group. The floor of the basin was metamorphosed
Precambrian rocks belonging to the Basement Schists, cratonic granites
and gneisses, the highly deformed granulite facies gneisses of the
Limpopo Mobile Belt, and a small part of the Great Dyke. Between
the Precambrian rocks and the Karoo rocks there is a major unconformity. The Karoo rocks found in the Mazunga area, which extend in
time from the glacial deposits of the Permian or Carboniferous through
a temperate climate to an arid sand desert climate with volcanic activity
in the early Jurassic period, have been subdivided as follows:
Doleritic dykes and siUs
Intrusive contact
Basalt lavas with intercalated Mbaka Beds
Minor unconformity
"Forest Sandstone"
Red Beds
"Escarpment Grit"
Fulton's Drift Mudstones
Minor unconformity
Basal Beds
Major unconformity
The Basal Beds lie on the deeply eroded Precambrian granulite facies
gneisses and other metamorphic rocks of the Limpopo Mobile Belt. As
they very rarely outcrop little is known about them or their relationship
to the mudstones and shales which everywhere overlie them. They appear
to be discontinuous erosional relics of various types of glacial deposits,
generally ill-sorted conglomerates and sandstones, up to about 25 m
thick, of the Dwyka Series which had covered the whole of Rhodesia,
and served as a source of material for the later sedimentary rocks.
The Fulton's Drift Mudstones are 50 to over 120 m thick and lie
unconformably on either the Basal Beds or the Precambrian rocks. They
7
The Escarpment Grit appears to be present throughout the Mazunga
area and to lie conformably between the Fulton's Drift Mudstones and
the Red Beds. It consists of 1 to 15 m of coarse-grained sandstone
with scattered pebbles up to 30 mm long. and occasionally pebble
layers or beds. Generally the sandstone is white to pale grey in colour,
but may be pink or greenish and contain clayey bands. Often it becomes
finer grained upwards. The sand grains and pebbles in it all appear to
have originated from the Precambrian rocks. No fossil remains have
been found.
The Escarpment Grit of the Zambezi basin marks the end of a period
of extensive and widespread erosion of the Lower Karoo rocks, but
the Escarpment Grit of the Limpopo basin appears to mark only changes
in sedimentation accompanied by uplift of the source area, more rapid
sinking of the basin floor and, as is shown by the introduction of red
colouration, the beginning of a change of climate.
The Red Beds outcrop in fault-bounded areas around the margins
of the Karoo rocks throughout the area and consist of brightly coloured
red, purple. green and white siltstones that contain calcareous nodules
along with some beds of fine-grained sands tones containing scattered
small pebbles, and a very few lenses of siliceous limestone. Cross-bedding
and scour-and-fill structures are common though some beds are structureless. In places there are fragments of desiccated and sun-cracked mudstone. Only some of the larger sand grains are spherical and often there
is an abundance of minute sharp and extremely angular, grains and
splinters of quartz. These and the clay minerals may have come from
Dwyka rocks; the rest came from Precambrian rocks. By this time the
8
lake must have expanded northwards considerably and either had
joined. or was about to join. that of the Zambezi basin.
In these typical semi-arid red beds the remains of the large reptilies
Massospondylus carina/us and Gryponyx africanus have been found.
They are characteristic fossils of the Upper Forest Sandstone of the
Zambezi basin and the Triassic Red Beds of South Africa (Bond. 1973.
page 73).
The Forest Sandstone lies conformably on the Red Beds and probably
covers much the same area. It consists of about 80 to 100 m of fine- to
medium-grained sandstone that is pinkish-white when fresh but develops
a surficial. brownish-red skin. The lower. more calcareous portion. was
probably deposited under water but the upper part shows dune bedding
and was probably formed as large dunes in an arid, hot. sand desert. No
fossils have been found.
The Karoo Basalts lie unconformably on the dune-covered surface of
the Forest Sandstone. They are the most widely exposed Karoo rocks in
the Mazunga area. but their thickness is not known. They were probably
erupted from fissures. though one possible crater. 600 m in diameter.
occurs in the Machuchuta T.T.L. Provisionally they have been subdivided
upwards into (a) olivine-bearing rocks (b) aphanitic basalts (c)
porphyritic basalts containing large feldspars. (d) vesicular basalts and
(e) the more normal basalts. Petrologically they belong to the Nuanetsi
Igneous Province and are different from the more uniform basalts of the
Zambezi basin.
The Mbaka Beds are scattered. comparatively narrow and discontinuous beds of fine-grained to very fine-grained sandstones that vary in
colour from drab or reddish-brown to light red. Occasionally they are
finely bedded or cross-bedded.
BASAL BEDS
The Basal Beds of the Karoo System are poorly exposed and were only
seen in a few scattered and isolated localities. These outcrops are
too small to be shown on the geological maps. The beds. which all appear
to be of glacial origin. lie with marked unconformity on the Precambrian
gneisses. and are probably unconformably overlain or pass into the beds
of the Fulton's Drift Mudstones. Outcrops of tiIlite of the Dwyka Series
seem to be absent in the area.
Mehliss (1951) found three poor exposures of the Basal Beds near the
Umzingwane River in the vicinity of Morgan's Hill and Fulton's Drift.
Here. a coarse conglomerate. about 1.2 m thick. consisted of sub-angular
fragments of Precambrian gneisses. banded ironstone and quartz,
randomly scattered without any traces of sorting or bedding. in a pale
shaly matrix. It lay unconformably on the Precambrian gneisses. but
upwards passed without a break into a dark gritty shale and then the
coaly shales of the Fulton's Drift Mudstones.
Poor exposures of a congIomeratic bed occur on the road 2 km
S.S.W. of Lutope Dip on Jopempi Block (Gongwe map) and in places
it has been indurated by dolerite dykes. The drab-brown coloured rock
shows light grey spotting on fresh surfaces and. though poorly sorted.
a crude bedding structure. It is composed of a heterogeneous mixture of
angular fragments of Precambrian gneisses and quartz in a fine-grained
matrix. the larger fragments. which are under 20 mm long. being subrounded.
Similar rocks. also metamorphosed in places by dykes. outcrop in the
watercourses 1.5 km S.S.E. of Gwawe Hill on Jopempi Block (Gongwe
map) and the following section was measured there:
Thickness
in
metres
Thinly bedded sandstones with 150 mm clay pellet layer
at base.
.
.
.
.
.
.
.
.
.
Conglomerate of pebbles less than 60 mm across in
coarse-grained sandy matrix of gneiss. quartz and
feldspar
.
.
.
.
.
Drab-coloured coarse gritty sandstone
Coarse pebbly conglomerate
Base not seen
A period of dilation followed the extrusion of the basalts. and it was
marked by the last igneous event in the area. the intrusion of numerous.
easterly. sub-ophitic dolerite dykes and fewer sills.
Subsequently there was uplift and extensive erosion along the Limpopo
Mobile Belt before the subsidence which permitted Cretaceous and
possibly Tertiary marine invasions into the Limpopo valIey. Uplift.
erosion and climatic changes followed. resulting in the current landforms
and superficial deposits.
9
BASAL BEDS
KAROO SYSTEM
1.0
0.15
2.0
1.0
Several of the boreholes drilled for coal on Nottingham Ranch.
River Ranch and in the Mtetengwe Tribal Trust Land passed through
2
10
KAROO SYSTEM
l
what are probably Basal Beds lying below the Fulton's Drift Mudstones and on the gneisses. The approximate positions of these boreholes are given on the southern part of the Mazunga map and their
logs, which are not always very clear, are given in Table ill.
In borehole MRDI Basal Beds 24 m thick are recorded (Johnson,
1973) between 432 and 456 m depth. They are a structureless, dirty
greenish-grey sandstone that is poorly sorted and contains scattered
patches of grit, angular pebbles of green to khaki-coloured shale, and
occasionally of quartz. Downwards, the sandstone passes gradationally
into greenish-brown gneiss. A specimen taken at 432,4 m is described
as a structureless, blotchy, light grey rock with 45 to 50 per cent. of
quartz grains, 0,05 to 5,0 mm across, which decreased in size downwards, set in an almost equal amount of clayey matrix. X-rays showed
the clay to be kaolinite and chlorite. Zircon and iron ores are accessory
minerals. Calcite, which formed about 5 to 10 per cent. of the rock,
replaces the clay in areas up to 10 mm diameter.
In borehole TI, 9,4 m of unbedded brownish-white mudstone was
found on top of the gneisses. It became coarser grained downwards and
contained much visible chiastolite. In borehole T3 a bed of very finegrained whitish mud stone with a taIcy feel contained boulders of
gneiss and schists. It is 9,4 m thick, lies on the gneisses, and is covered
by a medium- to coarse-grained sandstone. A bed 9,3 m thick in borehole T4, lying on top of the gneisses, was logged as tillite. It consisted
of sub-angular to rounded boulders in a mixed matrix of sand and clay_
In borehole T6 the gneisses were covered by 2 m of very dark greygreen, spotted and sheared mud stones, and on it was 1,4 m of conglomerate composed of shale fragments up to 6 mm long. A bed of
medium-grained grey feldspathic sandstone with marly shale in its
upper part, lay on the gneisses in borehole T8. It was 13,7 m thick and
may belong to the Basal Beds, but has been included in the Fulton's
Drift Mudstones.
Petrography
Slides 21354* and 21355 of the conglomeratic rock from 2 km S.S.W.
of Lutope Dip on Jopempi Block consist mainly of angUlar, often
ragged edged, clasts measuring from less than 0,05 mm in length
scattered through a very fine-grained matrix. Only rarely are the clasts
in contact with each other. The majority are strained grains of
-Numbers refer to slides in the Geological Survey slide collection, Salisbury.
FULTON'S DRIFT MUDSTONES
11
Precambrian quartz containing a few minute inclusions and bubbles;
the rest are a few clouded grains of sericitized feldspar. Some clasts have
a rim, about 0,02 mm thick, where matrix minerals have penetrated
into them. The microcrystalline, brownish matrix is a felt of micaceous
minerals, a small amount of angular quartz grains, and a few porphyroblastic tufts of mica up to 0,Dl mm long. Prof. G. Bond (personal
communication). was of the opinion that the rock was probably a
glacial outwash gravel deposited in a high-energy environment as the
ratio of clasts to matrix was too high for a tillite. The rock had been
slightly metamorphosed, and there had been some reaction between· the
clasts and the matrix. The feldspar grains must have been fresh when
they were deposited, otherwise they would have been comminuted.
FULTON'S DRIFr MUOSTONES
The Fulton's Drift Mudstones are a typical Karoo coal measures
sequence of grey to black argillaceous rocks, coal-bearing horizons and
a few discontinuous lenticular sandstone beds. They outcrop sporadically
around the periphery of the main Karoo area and have been named
after their most important outcrop which is around Fulton's Drift across
the lower Umzingwane River on River Ranch. The beds have a total
thickness of about 50 to over 120 m and rest unconformably on either
the Precambrian gneisses or the Basal Beds of glacial origin. They are
covered by a widespread arenaceous horizon, named the Escarpment
Grit, with a variable degree of unconformity. In them Robertson (1967)
found plant impressions identified as Glossopteris and Phyllotheca and
Mehliss (1951) found Thinnfeldia (Dicroidium) in the upper part only.
The coal horizons are dealt with more fully in the section on
Economic Geology.
lithology
Argillaceous rocks, which have been named mudstones and shales by
different geologists (probably subjectively) in the borehole logs, are
the predominant rocks. Most are light to dark grey or brownish in
colour, but towards the Escarpment Grit at the top of the sequence
they frequently develop a red or purple tint. In places the shales are
black and carbonaceous, and are distinctly fissile, whereas the mudstones
tend to break into rectangular blocks. Laterally the shales, may become
more sandy and pass into grey to brown siltstones. Thin beds of white
to light grey sandstones occur sporadically through the sequence, and
often are either shaly or somewhat pebbly. Conglomerate beds composed of white quartz pebbles are thin and rare.
13
KAROO SYS1EM
FULTON'S DRIFT MUDSTONES
Near the dolerite dykes the argillaceous rocks have been indurated
and metamorphosed, occasionally to hard, chert-like, lydianite.
On Nottingham Ranch, near the confluence of the Gushu and
Limpopo rivers, the following sequence of upper mudstones was
measured below the Escarpment Grit.
12
Distribution and Field Relations
The Fulton's Drift Mudstones form flat, low-lying country with very
few exposures and are best known from the coal exploration and boreholes in the outcrop area around the drift and the nearby Morgan's
Hill. Their soil-covered surfaces are frequently littered with quartz
pebbles from the Escarpment Grit, and fragments of ferricrete, hard
brown ferruginous sandstone, or metamorphosed shale near dolerite
dykes.
The Mudstones occur in fault-bounded, isolated outcrops, generally
of small extent, all around the margins of the Karoo rocks. In the
area of the Mazunga map they outcrop along the southern margin at
(a) on the east side of the Mpandi River where, on Nottingham Ranch,
they lie unconformably on the Precambrian gneisses and in a strip
extending for 6,5 km northwards from the Limpopo River, dipping
flatly westwards under the Escarpment Grit, (b) on both sides of the
Umzingwane River in an area about 6 km long and 1,5 km wide on
River Ranch and the Mtetengwe T.T.L. where they have been prospected
for coal, and (c) small, fault-bounded areas in the Mtetengwe T.T.L.
on both sides of the Mtetengwe River near its confluence with the
Mazunga River.
In the area covered by the Gongwe map the Fulton's Drift Mudstones
outcrop on both the north and east margins of the Karoo rocks. They
outcrop for 16 km west and 9 km east of where the Bubye River bends
from south to east. Their outcrop, which is about 1 km wide, is much
disturbed by faults trending between E.S.E. and north-east. Along much
of its length the beds lie on Precambrian gneisses and dip flatly southwards under the Escarpment Grit. Farther east there is a narrow outcrop, 2 km long, to the north-east of Chimonya Dip (Gongwe map)
and a larger fault-bounded outcrop on Nuanetsi Ranch east of the
Bubye River. Near ,the main road from Beitbridge to Fort Victoria,
and extending from Swanscoe Ranch in the north to the Mtetengwe
T.T.L. in the south, are several outcrops bounded by east-trending
faults. Because of the lack of exposures little is known about these
outcrops. The only area on which there is much information is the
coalfield extending east and west of the Umzingwane River near Fulton's
Drift.
.,
Thicknell
in
melre~
Khaki or buff-coloUIed mudstone
.....
Grey mudstone..
Red siltstone blotched grey. Iron-rich and sandy in
places .
.
.
Light grey flint clay .
Dark grey mudstone
.
.
.
.
.
.
Black, red blotched, iron-stained carbonaceous shale
Dark purple to red, ferruginized siltstone
Grey mudstone .
Base not seen
8,55
0,92
0,05
0,20
12,40
0,92
1,53
Around Fulton's Drift, on River Ranch and in the Mtetengwe T.T.L..
excavations were made to expose the coal seams, and, later. mapping
and diamond drilling were done '(Mehliss, 1951; Pelletier, 1955 and
Johnson, 1973). The approximate positions of the boreholes are shown
on the southern part of the Mazunga map and the generalized logs
are given in Table Ill.
In 1895 F. M. Wilson recorded the following section in the almost
horizontal lower shales on the west side of Morgan's Hill (Mehliss,
1951). Above it was over 21 m of sandstone which was pinkish and
pebbly at the base, white and gritty in the IDiddle and reddish at the
top.
Thickness
in
metres
Soft shale
Ironstone.
Shale
.
Ironstone.
Black shale
Ironstone.
Shale
.
.
Coal and shale
Slate
9,14
0,15
0,61
0,15
1,52
0,30
3,66
1,35
0,91
In 1896 R. Seddon measured a section at the coal outcrop near the
Umzingwane River and gave the following results:
Thicknes$
in mm
Black laminated shale .
Coal of very good quality
Shale
.
.
.
.
Coal of very good quality
Water level
280
125
230
14
KAROO SYSTEM
In a shaft, 11 m deep, sunk about 1,6 km east of this cutting. R.T.
Southwood recorded the following section in 1898:
ThicknU8
in
DIad: shale
Coal
Shale
Coal
Shale
Coal
Shale
Coal
Shale
Coal
Grit
.
.
.
Precambrian gneisses
metres
11,60
0,05
0,10
0,18
0,15
0,30
0,30
0,46
0,92
0,38
0,92
Excavations made by the McDonald brothers in 1971 near the road
crossing the low ground north·east of Morgan's Hill exposed 4,6 m of
Jight to dark grey mudstones. A generalized section down the slopes of
Morgan's Hill is as follows:
Escarpment Grit
Yellowish·buff or khaki-coloured mudstone
Red or maroon mudstone
White shale
Red or dark brown mudstone
Grey flint clay
Dark grey carbonaceous mudstone
Base not seen
A total of seven boreholes, MRDl, T7, TI, T4, T6, T8 and TO, have
been sunk through the FuIton's Drift Mudstones along a strike of
roughly 21 km from Nottingham Ranch in the west to the Mtetengwe
T.T.L. in the east. The full thickness of the beds is 70,6 m in MRDI.
55,3 m in TI, 93,1 m in T6 and 81,7 m in T8. How much of the strata
in the boreholes was affected by faulting is not known, but boreholes
T5, n, Tl and TlO-redrilled were stopped in doleritic rocks, and TlO
passed through several bodies of dolerite which may have marked
fault planes.
The strata recorded in the boreholes suggests cyclic sedimentation
in at least four cycles which are summarized in Table 1. The base of
the first cycle is the Basal Beds or the Precambrian gneisses (TO and T8).
and the earliest sediments are light to dark grey mudstones with thin
beds of gritty sandstones (MRDI, T3 and T8) and conglomerate (T6
and T8). Upwards these pass through grey to black carbonaceous
mud stones into the coal seams with partings of carbonaceous shales.
FULTON'S DRIFT MUDSTONES
15
At the base of the cycle in TO-redrilled, but nowhere else, a coal
horizon, 5,1 m thick, of fractured and pulverized rocks lies almost
directly on the gneisses.
The second cycle is largely dark grey to black mud stone with thin
sandstones under the coal horizon in the west (T3 and T4) and near
the base in the east (TO). The coal horizon is thin in the west, but
around 6 m thick in the east.
The third cycle consists of dark carbonaceous shales in the west and
grey shales in the east. The coal horizon is missing in boreholes MRDl
and T7 where there are thick beds of sandstone, and in borehole T6
where there is a great thickness of grey shale. In boreholes TI and T4
the thick coal horizon contains much shale. In TO and T8 the horizon is
thin, around two metres thick.
The third cycle marks the beginning of a change in sedimentation. The
1,9 m of medium- to coarse-grained sandstone in borehole MRDl has
bedding planes marked by thin black layers (Johnson, 1973). Towards the
TABLE I
GENERALIZED STRATA IN FULTON'S DRIFT MUDSTONES
Thickness
in m
Strata
ESCARPMENT GRIT
15-31
Grey and brown shales becoming red near top. In borehole T8, 4,9 m
of coal and shale on 3,4 m grey shale.
0-7,3
2,7-7,3
Coal and shale horizon .
Light to dark grey or black shales. Absent in boreholes MRDl and T7
where 6,4 to 9,2 m of sandstone with thin conglomerate and in T6
where 4,6 m of sandy mudstone.
1,2-5,8
4,6-10,7
Coal and shale horizon.
Grey and black shales. A thin sandstone underlies the coal horizon in
boreholes T3 and T4 and sandy beds occur in T8 and TO.
1,8-6,4
3,5-18,3
Coal and shale horizon.
Grey, brown, white and black shales with thin conglomerate under coal
horizon in borehole T7. Grit, sandstone and conglomerate beds occur
near the base in boreholes T3, T6 and T8 with a coal horizon 2,1 m
thick in bore hole TO.
Unconformity
or
BASAL BEDS
PRECAMBRIAN G NEISSES
16
ESCARPMENT GRIT
17
KAROO SYSTEM
base, the sandstone becomes gritty and contains rounded granules and
pebbles of quartz up to 40 mm in diameter. Under it is 0,5 m of wellpacked conglomerate composed of sub-rounded to rounded pebbles of
white and grey quartz, and whjte or pink to pale purple quartzite. These
have a dirty yellow sandstone matrix. Towards the base of the conglomerate some of the c1asts are flat and at the base, lying on blue-grey
shaly marl, is a 0,15 m layer of pyrite and pebbles. In borehole T6, which
is about 2 km S.S.E., there is a bed of white sandstone 7,7 m thick with
a gritty layer at its base.
A possible fourth cycle occurs only in borehole T8 where grey shale
passes upwards into a poorly developed coal horizon 5,8 m thick. In the
other boreholes a thick sequence of grey shales, that are almost devoid
of carbonaceous shales, extends upwards to the Escarpment Grit. In the
west their upper part is red and purple mudstones, and in the centre
and east there are sandstone horizons. In borehole T2 there is 5,3 m
of white sandstone and in TI 8,2 m of white sandstone with shale layers.
In TlO there is 10 m of pebbly sandstone and 10 m of pink mudstone
underlying the Escarpment Grit.
Fossils
Fossils in the form of plant impressions were found by Mehliss (1951)
in the upper shales and were thOUght to be Thinnteldia (now Dicroidium)
and possibly Taeniopteris.
Plant impressions were also found by Robertson (1967) in the upper
part of the sequence at two localities on Nottingham Ranch, one 0,6 km
W.N.W. and the other 3,9 km N.N.W. from the confluence of the Gushu
and Limpopo rivers. They occurred in red-brown, ferruginous mud stone,
and there were fragmentary remains in the carbonaceous shales and coal
layers. The better preserved fossils were identified as Glossopteris
indica, G. browniana and possibly Phyllotheca sp. They are figured in
his Plate 5. Remains of Equisitites sp. are recorded (Bond, 1973, page
71) as coming from the Urnzingwane River, Tuli Coalfield (probably from
around Morgan's Hill), and E. A. Arber (Molyneux, 1903, page 689)
identified a pith cast from the coal seams near Morgan's Hills as
resembling Calamites approximata. These fossils suggest an Ecca age
for at least part of the FuIton's Drift Mudstones.
EsCARPMENf GRIT
The extensive bed of sandstone, which separates the grey to red
mudstones forming the upper part of the Fulton's Drift Mudstones from
the overlying Red Beds, was named the Escarpment Grit by Mehliss
(1951) and this name has been retained in this account. Mehliss. largely
on lithological grounds, suggested the correlation with the Escarpment
Grit of the Zambezi Karoo basin, but this correlation cannot be
established with any degree of certainty. The Zambezi Escarpment Grit
consists of beds of white pebbly grits and sandstones which lie with a
markedly transgressive unconformity on the Madumabisa Mudstones and
older rocks, which it separates from the overlying Ripplemarked Flags
and other arenaceous sediments of the Stormberg Series. The Escarpment
Grit bed being described here lies with little or no unconformity on the
Fulton's Drift Mudstones and is overlain, probably conformably, by the
Red Beds. Robertson (1967) found that in the southern part of Nottingham Ranch, west of the Gushu River, the Escarpment Grit bed lay
conformably on the Fulton's Drift Mudstones and that both dipped very
gently westwards. It would seem that the Escarpment Grit marks an
arenaceous interlude in an essentially continuous sedimentation, which
separates the generally grey and often carbonaceous argillaceous beds
of the Fulton's Drift Mudstones from the calcareous red or purple
marls and siItstones of the Red Bed sequence. The top and bottom
of the Escarpment Grit must also mark gradational tectonic and climatic
changes in the area.
Lithology
The Escarpment Grit is a hard sandstone about I to 15 m thick which
forms small hillocks, ridges and scarps that rise above the flat country
of the FuIton's Drift Mudstones. It is easily distinguished from the
sandstones of the Mudstones by its distinctly coarser grain-size and
pebble content. It is usually white or pale grey in colour, but locally
may be tinted red, green or orange-yellow. Generally it is a coarsegrained sandstone containing angular fragments of quartz up to 5 mm
across, though it can pass into fine-grained and sometimes argillaceous
sandstone. Often layers or sheets of small pebbles give a vague bedding
to the otherwise structureless sandstone. These pebbles and the larger
grains stand out on the weathered surfaces and the rock tends to split
along the pebble beds. often producing quite extensive. rough, cobbled
pavements. The sub-angular to rounded pebbles, which are mostly
1 to 3 cm long, are well-packed in a matrix of fine-grained sandstone.
The majority of the pebbles are white to pale grey vein quartz with a
few composed of gneiss, red chert, jasper and banded ironstone, all
Precarnbrian rocks. Intercalated with the sandstone are a few thin beds
3
18
KAROO SYSTEM
RED BEDS
of conglomerate and sometimes beds of greenish-grey shale or mudstone
containing, in places, feldspars (Mehliss, 1951).
At the west end, in borehole MRDI on Nottingham Ranch, the bed
is only 0,6 m thick and consists of 0,2 m of conglomeratic sandstone
with pebbles up to 6 mm long that are closely packed in a matrix of
fine-grained, yellowish-green sandstone (Johnson, 1973). Above it is
green shaly marl and below it 0,2 m of current-bedded mar! which
shows slump structures in its upper part. Under this mar! is a wellpacked conglomerate bed which is 0,2 m thick and consists of pebbles
of fine-grained, yellowish·green sandstone up to 20 mm long in a matrix
of fine-grained sandstone. Between it and the underlying deep purple
mud stone, which contains clay pellets, there is no visible unconformity.
In borehole T3 there is over 7,6 m of fine- to coarse-grained white
sandstone with pebble bands 15 to 20 cm thick, and in T6 there is
13,4 m of red muddy sandstone containing scattered pebbles. The bed
in borehole T5 consists of 6,3 m of well-jointed, fine-grained sandstone
lying between beds of red or purple mar!. It.s colour changes downwards
from purple to greenish and finally cream.
The Escarpment Grit in borehole T2 is broken up into 1,5 m of
fine-grained grit that passes gradationally downwards into O,B m of grey
mud stone underlain by 7,B m of greenish grit containing scattered
pebbles up to 2 cm long. In borehole Tl there is I,B m of coarsegrained grit composed of sub-angular to sub-rounded quartz grains in
a matrix of green mar!' Above, the grit is white and below, grey
mud stone. Borehole TB contains lO,6 m of fine-grained white sandstone
which becomes coarser grained downwards. In it are thin bands of
mud stone. In borehole TlO the total thickness of 1l,9 m is split into
an upper 6,4 m of light green to red pebbly sandstone separated by
3,4 m of green mudstone from a lower 2,1 m of sandstone. In the
redrilled TlO 4,6 m of metamorphosed sandstones with pebbly layers
lies above doleritic rock.
Distribution and Field Relations
The Escarpment Grit has a comparatively small outcrop area. Along
the northern margin of the main Karoo area it is either faulted against
the Precambrian gneisses or lies on the FuIton's Drift Mudstones,
dipping southwards under the Red Beds. In the area of the Gongwe map
it outcrops as a strip extending from 4,5 km west of Gwawe Hill to the
main road from Beitbridge to Fort Victoria. Here, it is broken into
blocks by faults. On the eastern end of the Karoo area it outcrops as
long east-striking strips, bounded by faults, close to the main road on
Safari and Lesanth ranches.
On the southern margin of the Karoo outcrop the flat, westerly
dipping Escarpment Grit forms a strip 2 to 4 km wide which extends on
Nottingham Ranch for 5 km north of the Limpopo River to a major
E.N.E. fault (Robertson, 1967). It lies between the Fulton's Drift
Mudstones and the Red Beds and is traversed by several large easttrending doleritic dykes. Farther east it outcrops and dips northwards
on the Fulton's Drift Mudstones from 2 km east of the Umzingwane
River to near the Mtetengwe River where it is down-faulted against the
Precambrian gneisses by a major east-north-easterly fault. Here, it is
overlain by Red Beds and is intruded by dykes. To the north, there is
a small area of Escarpment Grit near the confluence of the Mtetengwe
and Tongwe rivers.
In the Nottingham Ranch area the Escarpment Grit forms a small
scarp rising above, the flat mudstone country (Robertson, 1967). It is a
coarse-grained, buff-coloured sandstone with interbedded layers of
pebbles up to 30 cm thick. The rounded pebbles are 0,5 to lO mm long
and are mainly of Precambrian vein quartz and quartzites. A few of
the quartzite pebbles contain green fuchsite and hair-like needles of
sillimanite. In the sandy matrix there are occasional layers that are
rich in detrital magnetite, sphene and epidote. The sandstone consists
of sub-rounded grains of quartz and, more rarely, of chert about 0,5 mm
across. They are closely packed in a matrix of fine-grained quartz and
clay minerals.
In the boreholes drilled for coal in the southern part of the Mazunga
map area the bed identified as the Escarpment Grit is of quite variable
composition and its thickness ranges from 0,6 to 17,4 m (Table Ill).
19
RED BEDS
The Red Beds are a widespread sequence, probably about 300 m
thick, of fine-grained sandstones, marls and mud stones which are usually
red or purple in colour but may be brown, greenish or white. Frequently
they contain small scattered pebbles and calcareous nodules and sometinles they are cross-bedded or contain scour-and-fill structures. Their
contact with the underlying Escarpment Grit is rarely exposed, but is
thought to be more or less conformable, and they seem to be conformably overlain by the Forest Sandstone. The few reptilian fossils
found in them are Massospondylus carinatus and Gryponyx africanus.
20
KAROO SYSTEM
RED BEDS
21
They suggest a correlation with the Forest Sandstone beds of the .
Zambezi Karoo basin.
south side. The beds are displaced by major east-north-east trending
faults and are cut by easterly dykes.
lithology
The Red Beds contain a variety of rocks ranging from mud stones to
fine-grained sandstones with occasional pebbly grits and partly silicified
limestones. The sandstones are very fine-grained to fine-grained red,
purple. green. white or cream-coloured rocks which are massive and
rarely show bedding in their outcrops. The silts tones, marls and mudstones are similarly coloured rocks. which often have small pebbles of
very fine-grained red sandstone scattered through them. and they are
characterized by sparse to abundant calcareous nodules. The rare lenses
of light grey limestones are massive. aphanitic rocks and have siliceous
nodules and veinlets protruding on their weathered surfaces.
In the southern part of Nottingham Ranch between the Tomani and
Mpandi rivers are outcrops of very fine-grained sandstones cut by
calcareous veinlets. and in them are thin lenticular beds. up to 1.2 m
thick. of grey siltstone (Robertson. 1967). Near ,the homestead of
Sentinel Ranch the banks of the Limpopo and Ipayi rivers are very
fine-grained pink siltstones composed of sub-rounded grains of quartz.
a small amount of feldspar and a siliceous cement. Among the siltstones
are beds of pink sandstone with mudstone layers abom 10 cm thick.
The sandstone consists of sub-angular grains of quartz, a small amount
of feldspar. accessory amounts of iron ores and muscovite and a calcareous cement. The mud stone layers are frequently a mass of cracked
and unorientated fragments.
Distribution and Field Relations
The Red Beds outcrop discontinuously almost everywhere around
the margins of the Karoo outcrop. They form low. flat-topped hills. or
country devoid of marked features. They are covered by fine. sandy.
maroon-coloured soil that is fertile and extensively cultivated. Near the
Escarpment Grit outcrops the soil is coarser and stony with numerous
fragments and pebbles from the Grit.
Along the northern margin. in the area of the Tuli map. there are
narrow faulted strips of Red Beds between the basalts and the Precambrian gneisses. They extend eastwards across the Dibilishaba and
Dendele Tribal Trust Lands as far as the Umzingwane River in the area
of the Mazunga map. Farther eastwards they outcrop near the
Umtshabezi River and the main road from Beitbridge to Fort Victoria.
In the area of the Gongwe map area. a wide and much faulted outcrop
stretches from 5 km W.N.W. of Gwawe Hill to the main road. the beds
dipping flatly southwards under ,the Forest Sandstone. Along the east
margin of the Karoo outcrop long. east-north-east. fault-bounded strips
outcrop from Swanscoe Farm in the north to Safari Ranch in the south
with a small area on Lesanth Ranch.
Along the southern margin of the Karoo rocks there are extensive
areas of Red Beds. lying on the Escarpment Grit and passing under
the Forest Sandstone. from the confluence of the Shashi and Limpopo
rivers eastwards across the Umzingwane River to just beyond the
Tongwe River. where they are faulted against the gneisses on their
At the base of the massive cliffs of the Homba Hills on Sentinel
and Nottingham ranches. the top of the Red Beds is a greenish sandstone; in other places it is white sandstone. A fine-grained green sandstone is exposed in a cutting on the main road from Beitbridge to
Bulawayo at 5 km north of Mtetengwe School, and a coarser-grained
sandstone 3 km south-west of Gwawe Hill on Jopempi Block (Gongwe
map).
About 4.5 km E.N.E. of the airstrip at the Tuli Irrigation Scheme
are outcrops of light grey to pinkish-buff. rudaceous rocks which have
a vague bedding. Here. a gritty rock with numerous grains of angular
to sub-angular quartz. 4 to 5 mm long. set in a clayey matrix. contains
fragments of mudstone and Precambrian gneisses up to 30 mm long
and 10 mm wide. as well as large blocks of mudstone up to 3 m long
and 0.6 m thick.
At the base of the Forest Sandstone which forms the Chamtoko
Hills on River Ranch about 3.5 km west of Fulton's Drift. is an
irregular bed of grey siliceous limestone that is 1.5 to 3.0 m thick. In
places it is highly siliceous. Beds of siliceous limestone also outcrop
about 4 km south-west of the homestead on Sentinel Ranch and 1 km
north-west of the Shambekazana reservoir on Jopempi Block (Mazunga
map).
The borehole MRDl on Nottingham Ranch penetrated a total thickness of 289,4 m of Red Beds which. downwards. consisted of 164.2 m
of red sandstone. 12.3 m of red marl. 3.9 m of white sandstone and 9.0 m
22
RED BEDS
KAROO SYSTEM
of green marl lying on Escarpment Grit (Johnson. 1973). The upper
red sandstone contained green to white beds and irregular green patches.
False bedding and scour-and-fill structures were common. and occasionally burrows 3 to 4 cm long were found. The rocks were generally
uniformly fine-grained. but contained scattered pebbles of very finegrained sandstone up to 4 mm long and. occasionally. carbonate veinlets.
There were also thin beds of open-packed pebbles.
The pure white. fine- and even-grained sandstone had narrow false
bedding. scour-and-fill structures. and a greenish-tinted upper surface
that had been eroded. The generally massive and structureless red marl
was sometimes clayey. showed cross-bedding and scour-and-fill structures.
and occasionally contained a few angular pebbles of fine-grained red
sandstone. The basal green mar! was similar. but in it were disturbed
areas of slabs. 1 to 3 cm thick. probably the result of sun cracking.
In borehole T6 the upper 33 m was a fine-grained sandstone which
was mainly red. pink or purple in colour. but had white layers (Mehliss.
1951 and Pelletier. 1955). In it were a few layers of cracked mudstone
or of pebbles up to 20 mm long. The lower 42 m were red or purple
mud stones with occasional grey patches and sandy layers. Calcareous
nodules up to 40 mm long were common.
The Red Beds were represented in borehole T5 by 2 m of greenish
sandstone lying on 49.8 m of purple and red mads with greenish and
white bands and. in places. scattered pebbles. Interbedded with them
were thin sandy layers and beds of pebbly sandstone. Borehole T2
passed through over 134 m of red or purple mar! containing irregular
calcareous nodules. interbedded layers of greenish. white or creamaoloured marls. a few thin beds of red or white sandstone. and some
pebble layers.
In borehole TIO the Red Beds were over 186 m thick. The upper
part consisted of alternating beds of fine-grained sandstones. which
were red. white. or more rarely green in colour. and red mar! containing
calcareous and sandy nodules. Some of the sandstones were structureless and others cross-bedded. In the lower third of the borehole the
rocks were red. purple. or grey mudstones containing calcareous and
sandy nodules. and scattered pebbles up to 50 mm long.
Fossils
Mehliss (1951) records finding reptilian bones. which he did not
remove. in a bed of red mar! about 1.2 km north-east of the BB beacon
23
of Special Grant No. 15. This beacon is on the east bank of the
Umzingwane River and the locality is about 2 km north of Fulton's
Drift.
During the course of the survey bone fragments were found in thin
beds of nodular, fine-grained sandstone lying on pink sandstone and
overlain by grey sandstone at the base of a rock pillar 7 km southwest of the homestead on Sentinel Ranch.
Robertson (1967) found some rather poorly preserved and distorted
bones in the north bank of the Limpopo River east of the Ipayi confluence and 90 m west of the Sentinel Ranch homestead. The bones
were excavated from a friable pink siltstone cut by calcareous veins,
which outcropped for 140 m along the bank at up to 3 m above river
level. The bones, which were partly silicified and had a silt filling in their
interstices, were first photographed in situ (Robertson, 1967, Plates 1 to
4). and later were tentatively identified as Massospondylus carinatus.
They consisted (a) an almost complete post-dorsal vetebra. (b) left
femur articular end including trochanter minor, and an almost complete
right femur from separate individuals. (c) two separate ischia. (d)
fragments of the head of a tibia and (e) various rib and other fragments.
A digit and claw. probably of Gryponyx africanus. are said (Bond.
1973. pages 88-89) to have been found in the same area. These two
reptiles are characteristic fossils of the Forest Sandstone Formation of
the Zambezi Karoo basin. and have not yet been found in the underlying
red beds of the Molteno Stage and Pebbly Arkose Formation.
Petrography
Specimens of fine-grained sandstones were collected at 2 km S.S.E. of
Mangombe Hill on Nottingham Ranch (slide 21356). 2,5 km north-east
of the homestead on Sentinel Ranch (slide 21357). 5 km north of
Mtetengwe School in the Mtetengwe T.T.L. (slide 21358). and 1,5 km
north-west of the airstrip at the Kongoni Irrigation Scheme in the
Shashi T.T.L. (slide 21359).
In slide 21356 a few 0.5 to 1.0 mm sub-angular to rounded grains of
quartz and microline are scattered in a matrix of 0.05 to 0.15 mm
angular to sub-angular. grains of quartz and a very small amount of
feldspar with much red-brown clayey cement.
Slides 21357 and 21358 are well-sorted sandstones composed of 0.1
to 0.3 mm grains with a few as large as 0.3 mm across. They are
24
KAROO SYSTEM
FOREST SANDSTONE
angular grains of quartz with very thin rims of secondary growth. and
rare grains of fresh microline. In slide 21357 the grains are closely
packed with a small amount of siliceous cement containing red and
black ferruginous dust. but in slide 21358 the grains rarely touch and
there is about 30 per cent. of brown siliceous cement containing some
magnetite dust. Slide 21359 has a few scattered 0.5 to 1,0 mm. subangular to rounded grains of quartz and microcline in a matrix of very
angular. almost splintery. to sub-angular grains of quartz, a very little
feldspar, and a fairly large amount of brown. clayey cement. Slide 21359
is less well sorted and has a disrupted structure with a large amount of
brownish siliceous cement containing a little opaque dust. This sandstone consists of angular to sub-angular grains of quartz, 0.05 to 0,30 mm
across, some with a little secondary growth. and a small amount of
stained plagioclase and clear microcline.
clay minerals. A similar rock (slide 21364) was collected in the Dendele
T.T.L. at 4,5 km west of the Machuchuta road gate in the north fence
of Shobi Block. and another nodular rock (slide 21365) was collected
from 3 km N.N.W. of Mtetengwe Store in the Mtetengwe T.TL. The
latter is an aphanitic. light grey. massive rock containing abundant.
rounded to elongated. dark grey nodules about 5 to 15 mm long. They
are composed of dirty carbonate crystals measuring
to 0.05 mm
across. A few. very irregular, 0.5 to 1.0 mm calcite crystals are replacing
the very fine-grained crystals. Between the nodules and separating them.
is a small amount of intergrown carbonate and clay minerals less than
0.01 mm across.
A brownish-grey siltstone (slide 21360) was collected from 4.5 km
south-east of Mangombe Hill on Nottingham Ranch. Less than half the
rock consists of angular to sub-angular grains of quartz and a few of
red-stained plagioclase. the balance being an isotropic clayey matrix
full of black and brown iron ore dust.
A light grey rock with 2 to 5 mm dark grey. angular fragments in
an aphanitic groundmass outcrops 4.5 km E.N.E. of the Kongoni Irrigation Scheme airstrip (slide 21361). About one-third of the rock is
angular. and often irregularly shaped fragments of very fine-grained
Precambrian quartzite and vein quartz. the balance being clayey
material containing a few silt-sized grains of quartz and opaque iron
ores.
Many of the Red Bed rocks contain calcareous nodules. A carbonaterich. fine-grained arkose (slide 21362-3) from the track 6 km south-west
of Chamtoko Hills on River Ranch contains nodules. 0.5 to 10 mm
long of very fine-grained carbonate. which are irregular to rounded in
shape. Some have larger marginal crystals of carbonate which have
partly replaced the adjacent rock. The poorly sorted rock is composed
mainly of quartz. much microcline. a little brown-stained plagioclase.
and a few rounded grains of mud stone and very fine-grained Precambrian quartzite. The grains. which vary from angular to well-rounded.
and from low to high sphericity. have a disrupted framework. the
grains seldom touching each other. The few larger 0.5 to 1.0 mm.
grains are in a matrix of very angular. 0.05 to 0,20 mm. grains of the
same minerals and a dirty brownish-coloured cement of carbonate and
25
om
An impure limestone (slide 21366) from the hill 1 km north-west
of Shabekazana borehole on 10pempi Block is a light grey, aphanitic
rock which contains small cherty veinlets and nodules that stand out on
weathered surfaces. It consists of 0.005 to 0.010 mm, intergrown crystals
of carbonate and a small amount of clay minerals. There are some
minute. incipient porphyroblasts.
The sand grains in these Red Bed rocks are formed of quartz. clear
microcline. stained plagioclase, and very fine-grained quartzites. all of
which have been derived from the Precambrian basement. Most contain
inclusions (sometimes minute needles of sillimanite). which suggest that
they have been subjected to upper amphibolite and possibly granulite
facies regional metamorphism; the quartz is always strained. Accessory
heavy minerals are very scarce and micas appear to be absent. The
carbonate, which has undergone some redistribution, appears to be of
inorganic, concretionary origin. The majority of the sand grains are
sub-angular; very few are well-rounded and possibly of aeolian origin.
Minute sharp-edged chips and splinters of quartz are abundant in
slides 21358 and 213560, numerous in slides 21364 and 21365, and
scarce in slides 21357, 21359 and 21362. Their size. less than 0.1 mm
long, and appearance suggests that they may have come from the finely
ground rock flour of Dwyka-age glacial deposits.
FOREST SANDSTONE
The name Forest Sandstone was given by Mehliss (1951) to the
sandstone lying between the Red Beds and the basalt lavas, and is
retained here without implying any correlation between it and the Forest
Sandstone of the Zambezi Karoo basin. lohnson (1973) called it the
Cave Sandstone.
4
26
KAROO SYSTEM
FOREST SANDSTONE
The Forest Sandstone is a pale-coloured, fine-grained rock, which is
probably around 80 to 100 m thick and lies conformably on the Red
Beds. Its upper surface is irregular and the early basalts filled hollows
and troughs in it. It frequently shows dune bedding and its strike and dip
are variable. The greater part of the sandstone seems to be sub-aerial and
only the lower part sub-aqueous. So far no fossils have been found in it
making correlation with other areas impossible.
which were once occupied by Stone Age people, in the cliffs of the
rugged Chamtoko Hills (Robertson, 1967).
Lithology
The Forest Sandstone is white to pale pinkish-white when fresh
(Johnson, 1973), but when it weathers it develops an outer layer, 1 to
5 mm thick, in which the colour changes from a pale brownish-pink to
a deep brownish-red or brown. This outer layer is soft and friable, and
breaks down to a red-brown sand. The fresh rock is even-grained and
massive with a grain-size ranging from fine to medium. Frequently it
shows dune bedding and is generally well-jointed, the joint planes
sometimes being silicified.
The lower part of the Forest Sandstone is more calcareous than the
upper part and contains a few irregular grey nodules of carbonate
(Johnson, 1973). In it Mehliss (1951) found rare beds of limestone
around one metre thick. At 1 to 2 m below the base of the basaIts
Robertson (1967) records the occurrence of irregular to spherical calcareous nodules up to 20 cm long and a boxwork of silica veinlets.
Coarse-grained, gritty sandstone beds outcrop in the Siyoka T.T.L.
at 4,7 km N.N.E. of Mabafu Store and 7 km north-east of Baemura
School, and in the Dibilishaba T.TL at 1,9 km E.S.E. of the Bertie
Claims.
Over much of the area the Forest Sandstone forms low hills which
rise to heights of 15 to 30 m near the Bubye River. Along the main
road from Beitbridge to Fort Victoria, at about 30 km south-west of
the bridge across the Bubye River, it forms several isolated hills rising
above flat country. North-eastwards from the bridge the Forest Sandstone consists of broken slabs standing on end. They are due to
faulting.
In the south, the Forest Sandstone forms the impressive hills and
cliffs of the Homba Hills on Sentinel and Nottingham ranches, and
numerous rock pillars such as the one about 2,5 km north-east of the
Sentinel Ranch homestead. There are numerous caves and shelters,
27
Alongside the doleritic dykes the Forest Sandstone has been metamorphosed and indurated, often to a quartzite, and on weathering forms
a double line of low ridges with the weathered dyke rock in the trough
between them (Robertson, 1967). In places the metamorphosed sandstone contains hard concretions that stand out like warts on the weathered
surfaces. The larger ones, up to 6 cm diameter, are roughly spherical
and some, lying on the surface about 4,5 km S.S.W. of Rangamano
Hill on Nottingham Ranch, look like cannon balls.
Distribution and Field Relations
Along the northern margin of the Karoo outcrop thin slivers of
Forest Sandstone occur on the north side of the basalt lavas in the
Dibilishaba and Dendele T.T.L. (Tuli map) and near the Umzingwane
and Umtshabezi rivers (Mazunga map). Farther east a wide strip of
Forest Sandstone, lying on the Red Beds and dipping flatly southwards
under the basalts, extends eastwards from 3 km south of Gwawe Hill to
the road from Beitbridge to Fort Victoria (Gongwe map).
Along the southern margin of the Karoo rocks, the Forest Sandstone
lies conformably on the Red Beds and is covered with a more or less
slight unconformity by the basalts. It dips flatly in a northerly direction.
Its frequently faulted outcrops extend along the north side of the
Limpopo River eastwards from the Shashi confluence to the Makawa
Hills. Farther east the sandstone forms Zwibwale Hill, and eastwards,
from Penemene School to the main road from Beitbridge to Fort
Victoria, the sandstone dips gently northwards under the basalts and
is down-faulted against the Precambrian gneisses in the south.
On Sentinel and Nottingham ranches the lower part of the Forest
Sandstone is well exposed in cliffs and rock pillars. It is faintly bedded
and contains occasional calcareous nodules and rare, thin beds of
impure limestone. Here, the sandstone appears to have been deposited
under water. It grades imperceptibly upwards into a slightly coarser
grained and redder, dune-bedded sandstone of aeolian origin. Its upper
surface in contact with the overlying basalt lavas is a distinctly irregular
one which shows deflation. The first lavas appear to have flowed along
the troughs lying between large sand dunes and to have affected the
sandstone down to a depth of 1 to 2 m.
28
KAROO SYSTEM
Dune bedding is fairly common along the southern margin of the
Karoo outcrop and is well displayed near Giraffe Dam in the Mtetengwe
T.T.L. Along the northern margin exposures are poor. The dune bedding
indicates that the dunes were up to 15 m high. Wherever possible the
direction of the dune bedding was measured and Table IT gives the
grid reference of the site, the number of measurements made, and the
average direction of the bedding relative to present-day true north.
The results, which are plotted as a histogram in Figure 1, shows a
predominance of directions between 060 and 180 with a maximum
of 31 readings between 090 0 and 1200 •
0
0
Joint planes, which show no displacement, and often closely spaced
shear planes, which show small displacements, are frequently filled with
veinIets up to 10 mm wide of white or grey silica. These steeply dipping
veinIets protrude for 10 to 15 mm on weathered surfaces, and form an
intersecting pattern on the larger outcrops.
~
In an area, where there are large bare outcrops of Forest Sandstone,
just east of the Umzingwane River and about 1,5 km south-east of the
homestead on Cawood's Mazunga Ranch, numerous pipe-like structures
stand for up to one metre above the ground, and extend for one to two
metres below the surface, sometimes bifurcating like tree roots. Most
are circular in cross-section and have an external diameter of about
40 to 50 cm and an internal diameter of 3 to 20 cm. Their walls consiSt
of about 25 mm of hard silicified sandstone.
TABLE
n
DffiEcrroNS OF DUNE BEDDING IN FOREST SANDSTONE
Grid
reference
72045910
73865962
79126108
19886096
21626078
74485446
75045478
76235509
76355492
76405518
No.
Bearing
Grid
reference
185
176
178
142
039
154
098
345
125
065
76635507
76645519
77055576
77345559
77355590
78475598
78845630
78905625
78775664
79055669
I
I
I
4
1
5
8
I
4
10
-
--
--
No.
6
4
5
6
4
1
2
I
6
2
29
FOREST SANDSTONE
Bearing
Grid
reference
128
088
066
116
180
090
071
211
092
034
79705705
79765710
80535650
80685712
19755724
21005718
21765734
21945817
22545826
Bear-
No.
ing
9
3
3
3
3
1
140
073
100
094
I
5
I
000
091
041
106
180
30
<-;,
~
~
~
~
20
~
10
~
~
~ o1WAW~AW"Az//MlM1
030
060
090
120
150
180
210
240
'
270
,
300
P7Z7lJJ
Bearing in degrees
FIG. I.
Directions of dune bedding in the Forest Sandstone.
Petrography
The fine-grained sandstone (slide 21367), which outcrops 3 km northwest of ChandabaIini in the Siyoka T.T.L., is a pale brownish-pink rock
composed of closely packed grains ranging in size from 0,08 to 0,35
mm and averaging about 0,10 to 0,15 mm across. Most are angular
with a fairly high sphericity, and only a few are rounded to wellrounded. The majority are grains of quartz; fresh microcIine and
stained plagioclase grains are rare. The very scarce accessory minerals
are magnetite and rounded sphene. A very thin rim of secondary
growth surrounds the grains and they are separated by a layer, under
0,01 mm wide, of reddish-brown cement. The cement is probably a
mixture of clay, silica and the red-brown iron ores which colour the
rock. Similar fine-grained sandstones were collected from a low rise
2,5 km W.N.W. of Gwawe Hill (Gongwe map) (slide 21368) and from
0,5 km east of the north-west corner of Shobi Block (slide 21369). The
fine-grained, well-sorted sandstone (slide 21370) from River Ranch.
31
KAROO SYS1EM
FOREST SANDSTONE
1,5 km north-west of the Chamtoko Hills is composed of angular to
sub-rounded grains of quartz along with very few grains of feldspar,
quartzite and metasiltstone of medium sphericity. They vary in size from
0,1 to 0,5 mm and average about 0,2 mm. They are very well packed,
and are separated by a thin film of siliceous cement coloured by iron
ore dust. The rock is a pale pinkish-brown colour and weathers through
a zone 30 mm thick from reddish-brown to a brown surface coated with
black.
being clayey cement rich in brown iron ore dust. The grains average
about 0,2 mm across but range from 0,1 mm to a few 4,5 mm pebbles.
The larger sand grains are quartz with some brown-stained plagioclase
and metasiltstone. The smaller grains are quartz and a few of finegrained quartzite and stained plagioclase.
30
The fairly well sorted, fine-grained sandstone (slide 21371) from a
low rise 4,7 km N.N.E. of Mabafu Store in the Siyoka T.T.L. has a fairly
open framework and an average grain-size of about 0,15 mm. The
grains are angular to sub-angular, and only a few of the larger grains
are welI-rounded. Their sphericity varies from Iow to high. Most are
quartz with a few grains of very fine-grained quartzite and rare grains
of microcline and plagioclase. The cement, which forms about IS
per cent. of the rock, seems to be both clayey and siliceous, and is full
of brownish specks of iron ores.
A welI-sorted, fine-grained sandstone with a slightly more open
framework (slide 21372) was collected in the Dendele T.T.L. about two
kilometres east-north-east of the gate on the Machuchuta road in the
north fence of Shobi Block. The grains, which are angular and of low
sphericity, are mainly quartz with a small amount of fresh microcline
and plagioclase, and rare grains of stained plagioclase. They range in
size from 0,05 to 0,30 mm and average about 0,1 mm. The siliceous
cement, which forms about 20 per cent. of the rock, contains some
clay and iron ore dust.
''LA finely bedded sandstone (slide 21373) with alternate medium- and
<T fine-grained layers, was colIected 7 km north-east of Baemura School
in the Siyoka T.T.L. It is a fairly welI sorted rock composed of angular
to sub-angular grains which are tightly packed with very little cement.
The coarser grained beds consist of 0,1 to 0,7 mm (average 0,3 mm)
grains of quartz and small amounts of fine-grained quartzite, microcline
and clear plagioclase set in a very small amount of siliceous cement.
The finer grained beds are tightly packed grains, 0,05 to 0,30 mm
(average 0,15 mm) across, of quartz and very small amounts of stained
plagioclase and fine-grained quartzite with a very little iron-rich cement.
An immature, medium-grained sandstone (slide 21374) outcrops 1,9
km E.S.E. of the Bertie Claims on Dibilishaba T.T.L. It is a poorly
sorted rock in which the sand grains rarely touch, about half of the rock
The bulk of the sand grains in these sandstones has been derived
from the Precambrian rocks with comparatively little wear, most being
angular to sub-angular. Rounded grains are comparatively scarce and
are usually the larger grains. Micas are absent, heavy minerals rare, and
the small quartz chips and splinters seen in the Red Beds are scarce.
The calcareous nodules, abundant in the Red Beds, are also very scarce,
and there seems to be less red-brown dust in the cement of the paler
coloured Forest Sandstone.
TABLE III
BOREHOLES ON E.P.O. No. 19 AND 393
Extracted from final reports. Positions are approximate and collar elevation~ unknown.
To
metre.
Strata
BOREHOLE No. TO. 1,5 km 277° from
Fulton's Drift on the Umzingwane
River, on Lot I, River Ranch. Oct.,
1953.
3,66 Soil
14,33 Grey and yellow shale
15,90 Shaly coal with pyrite
16,59 Grey shale
16,66 Coal and shale
17,37 Grey shale
17,43 Coal and shale
20,27 Grey and black shale
20,37 Coal with pyrite
22,08 Grey and black shale
22,45 Coal
22,50 Shale
22,92 Coal
23,19 Dark grey shale
23,90 Coal
24,38 Black shale, coal streaks
27,58 Carbonaceous shale
27,76 Coal
31,09 Carbonaceous shale
31,20 Coal
31,85 Carbonaceous shale
32,31 Sandstone and black shale
35,97 Black shale, cross-bedded
To
metres
36,32
36,88
41,45
41,66
41,71
41,76
41,78
41,89
Strata
Dark sandy shale
Black shale
No core
Black and grey shale
Carbonaceous shale
Coal
Grey shale
Grey sandstone
BOREHOLE No. TO. Redrilled 17,4 m
north. Jan., 1954.
16,46 No core
17,43 Red-brown mar!
17,54 Yellow shale
19,30 Carbonaceous shale, some coal
23,77 Grey shale
24,23 Carbonaceous shale and coal
24,69 Grey shale
25,30 Carbonaceous shale and coal
28,19 Grey shale
28,29 Carbonaceous shale, some coal
33,05 Grey shale
34,88 Carbonaceous shale and coal
38,99 Grey shale
39,27 Shaly sandstone, cross-bedded
40,00 Grey sandy shale
41,40 Dark grey shale
32
To
metre.
41,15
41,68
44,33
44,81
45,21
45,42
45,57
46,08
46,25
46,43
46,58
48,16
48,36
48,44
48,82
49,00
49,24
49,40
55,78
56,18
58,52
58,53
58,83
60,86
61,06
62,64
KAROO SYSTEM
BOREHOLES
TABLE ill (continued)
TABLE ill (continued)
Strata
Grit with 15 mm pehbles of
quartz and ironstone
Sandstone
Dark grey shale
Carbonaceous shale, some coal
and pyrite
Grey shale
Coal
Carbonaceous shale and coal
Coal
Carbonaceous shale and coal
Coal
Carbonaceous shale and coal
Dark grey shale
Coal
Carbonaceous shale
Dull coal
Carbonaceous shale and coal
Carbonaceous shale
Carbonaceous shale and coal
Fractured dark grey shale
Carbonaceous shale and coal
Fractured dark grey shale
Coal
Fractured dark grey shale
Pulverized coal
Dark grey shale
Gneiss
BOREHOLE No. Tt. 1,4 km 2760 from
Fulton's Drift. On Lot I , River Ranch.
Sept., 1953.
8,53 Red marl
11,28 Sand
28,65 Red marl, calcareous nodules
29,79 Sandy red mar!
31,09 Red marl, calcareous nodules
31,24 Pebble band
32,61 Red mar!, calcareous nodules
32,69 Pebble band
40,54 Red marl
48,77 Red to purple mar!
55,78 Purple marl
64,01 Red and purple mar!
68,28 Purple mar!, calcareous nodules
70,41 White sandy mar!, wavy crossbedding
75,90 Purple and white mar!, cross.
bedding
95,71 Dark grey to purple mar!,
greenish near base. Gritty
nodules
103,02 Dark purple mar!
To
metres
106,68
109,93
112,24
114,07
135,48
137,16
137,46
137,57
137,79
139,60
140,38
143,71
177,39
Strata
Dark grey, purplish marl
Grey marl
White mudstone, cross-bedded
Greenish grit
Dark grey marl, red nodules
White quartzite
Dark grey shale
Sandstone
Dark grey shale
White sandstone and shale bands
Sandstone
Pebbly sandstone
Dolerite
BOREHOLE No. n. 4,2 km 248 0 from
Fulton's Drift. On River Ranch. Sept.,
1953.
25,91 Red marl, calcareous nodules
26,06 Sandy red mar!
39,32 Red-purple marl, calcareous
nodules
46,33 Cream bedded mar!
68,88 Purple mar!, calcareous nodules
69,04 Dolerite
76,10 Purple-red marl, calcareous
nodules
76,76 Porphyritic dolerite
88,70 Purple-red marl
101,80 Greenish-white mudstones,
cross-bedded
106,68 Purple mar!, calcareous nodules
107,52 No core
117,68 Purple marl
117,98 Pale green mar!
118,16 Dolerite
118,36 Pale green marl
128,27 Purple marl
128,63 Pebble band
134,44 Grey sandy marl
135,94 Sandstone
136,19 Grey mudstone
143,97 Pebbly grit, pyrite
149,91 Red-grey mudstone
151,41 Pebbly grit
155,30 Sandstone
172,01 Dolerite
BOREHOLE No. T3. 22,3 km 248 0 Ifrom
Fulton's Drift. On Nottingham Ranch.
Nov., 1953.
4,88 Soil
7,62 Pebbly sandstone
19,81 Shale
To
metres
20,12
20,73
21,03
21,34
21,85
22,86
22,99
23,67
23,80
25,91
26,24
27,74
27,83
28,02
28,52
28,80
29,01
29,34
29,69
36,02
36,58
36,70
37,34
37,74
42,11
42,13
42,25
43,59
43,64
44,63
44,73
45,11
45,58
46,25
46,42
46,48
47,17
47,26
47,54
60,20
61,26
61,47
61,55
61,87
61,95
62,96
65,00
74,68
5
Strata
Carbonaceous shale, coal streaks
Black shale
Coal
Carbonaceous shale
Coal
Black shale
Coal
Black shale
Coal
Black shale
Coal
Black shale
Coal
Black shale
Coal
Carbonaceous shale
Coal
Carbonaceous shale
Coal
Black shale
Coal
Black shale
Coal
Grey sandstone, cross-bedded
Black shale
Grit
Coal
Black shale
Coal
Carbonaceous shale
Coal
Carbonaceous shale
Coal
Carbonaceous shale
Coal
Carbonaceous shale
Coal
Black sbale
Coal
Black shale
Grey-brown mudstone
Quartz porphyry
Carbonaceous shale
Burnt coal
Black shale
Sandstone
Boulder bed
Gncis,
33
To
Strata
metres
BOREHOLE No. T4. 19,6 km 243 0 from
Fulton's Drift. On Nottingham Ranch.
Nov., 1953.
2,44 Soil
7,01 White sandstone
22,19 Grey shale
22,26 Coal
23,87 Black shale
23,95 Coal
24,25 Shale
24,59 Coal
24,80 Dark shale
24,95 Coal
25,21 Black shale
25,66 Coal
32,51 Dark shale
32,84 Coal
33,05 Carbonaceous shale
33,28 Coal
33,50 Shale
33,62 Coal
33,67 Shale
33,82 Sandstone
33,97 Shaly sandstone
34,38 Grey shale
34,43 Sandstone
38,79 Dark shale
38,93 Coal
39,19 Shale, coal streaks
40,26 Coal
44,65 Carbonaceous shale
44,93 Dull coal
45,09 Carbonaceous shale
45,21 Coal, shaly
45,42 Carbonaceous shale
45,67 Dull coal
46,18 Dark shale
46,29 Shaly coal
60,33 Black shale
60,86 Quartz porpbyry
61,37 Boulder bed
70,71 Gneiss
BOREHOLE No. T5. 10,4 km 2420 from
Fulton's Drift. On Nottingham Ranch.
Feb., 1954.
15,24 No core
16,61 Pale green sandstone
17,02 Pebbly grit
20,02 Red-purple marl
26,99 Red marl, sandstone bands
27,58 Dolerite
31,75 Red mar!
34
To
metres
31,80
34,04
34,14
37,09
37,29
46,94
47,55
55,47
58,83
58,90
65,99
77,27
77,42
83,82
85,65
114,91
KAROO SYSTEM
BOREHOLES
TABLE ill (continued)
TABLE ill (continued)
Strata
Sandstone
Red mar1
Pebbly grit
Red mar!
Pebbly grit
Red mar!, pebble bands
Dolerite
Red marl, pebble bands
Red mar!
Pebbly grit
Red-purple marl, sandy bands
Purple-crearn sandstone
Pebbly shale
Grey shale
Purple mudstone
Dolerite
BOREHOLE No. T6. 16,9 km 247 0 from
Fulton's Drift. On Nottingham Ranch.
April, 1954.
4,88 No core
37,19 Pink sandstone
79,25 Red marl, calcareous nodules
83,21
Pebbly red sandstone
84,12 Cavity
96,62 Pebbly red sandstone
119,18 Sandy purple mudstone
128,93 Purple mudstone, calcareous
nodules
154,84 Grey mudstone
159,26 Sandy grey mudstone
160,32 Grey mudstone
167,49 Grey fireclay, coal streaks
172,06 Grey mud stone
176,02 Dark shale and burnt coal
179,22 Dark shale
189,05 Dolerite
189,74 Black mudstone
192,96 Green-grey mudstone
193,40 Conglomerate
195,38 Green-grey mudstone
198,73 Gneiss
BOREHOLE No. T7. 26,3 km 2440 from
Fulton's Drift. On Nottingham Ranch.
June, 1954.
12,19 No core
37,80 Grey and purple mudstone,
weathered
44,35 White sandstone
46,99 Grey mudstone with coal
50,12 Dark mudstone
50,50 Coal
To
metres
52,60
53,36
53,75
54,12
60,22
60,66
60,76
61,99
62,03
62,05
62,20
62,56
64,16
64,34
65,78
75,23
119,79
Strata
Dark mudstone
Coal
Grey mudstone
Coal
Dark mudstone
Coal
Shale
Coal
Grey mudstone
Coal
Carbonaceous shale
Conglomerate
Grey mudstone
Coal
Dark mudstone
Brown-white mudstone
Gneiss
BOREHOLE No. T8. 4,7 km 298 0 from
Fulton's Drift. In Mtetengwe T.T.L.
May, 1954.
7,01
No core
7,32 White sandstone
7,87 Red mudstone
9,85 White sandstone
10,06 Red mudstone
15,95 Red sandstone, cross-bedded
18,36 Sandy red mudstone
18,44 Basalt
19,58 Sandstone, cross-bedded
19,86 Red mudstone
20,02 Basalt
26,49 Red mudstone, calcareous nodules
27,66 Sandstone
53,95 Red mudstone, calcareous nadules, grit bands
54,96 Basalt
70,10 Red mudstone
73,46 White sandy mudstone
75,90 Red mudstone
83,82 White sandy mudstone
84,73 Red mudstone
90,50 White sandy mudstone, bedded
91,82 Purple-grey mudstone
107,59 Grey-purple mudstone, calcareous nodules
107,90 Grey sandy mudstone
108,81
Purple mudstone
136,70 Grey mudstone
147,29 White sandstone
147,98 Grey shale
148,29 Dull coal
•
To
metres
164,74
164,97
165,00
166,45
166,75
167,05
167,31
167,56
167,97
168,40
168,86
169,16
169,94
170,18
173,56
173,91
175,21
175,49
175,69
176,17
176,33
176,61
176,84
177,49
179,83
180,24
180,39
180,47
183,79
184,07
184,25
184,35
184,46
185,01
185,09
185,37
188,57
192,00
193,23
192,30
192,48
193,11
193,30
194,18
194,33
194,46
194,54
194,61
194,74
194,83
195,35
195,66
195,78
35
To
Strata
Grey shale
Coaly shale
Coal
Grey shale
Dull coal
Grey shale
Carbonaceous
Coal
Carbonaceous
Coal
Carbonaceous
Coal
Grey shale
Coal
Grey shale
Coal
Grey shale
Coal
Carbonaceous
Coal
Carbonaceous
Coal
Carbonaceous
Coal
Grey shale
Coal
Grey shale
Coal
Grey shale
Coal
Grey shale
Coal
Grey shale
Coal
Grey shale
Coal
Black shale
Sandy shale
Coal
Shale
Coal
Grey shale
Coal
Grey shale
Coal
Grey shale
Coal
Shale
Coal
Shale
Coal
Shale
Coal
shale
shale
shale
shale
shale
shale
metres
195,89
196,60
196,65
196,75
196,85
197,61
197,89
198,12
211,78
213,21
215,24
228,90
266,09
Strata
Shale
Coal
Shale
Coal
Shale
Coal
Shale
Shaly coal
Dark shale
Shaly conglomerate
Grey shale
Sandstone, feldspathic
Gneiss
BOREHOLE No. T9. 2,5 km 3520 from
Fulton's Drift. In Mtetengwe T.T.L.
May, 1954.
12,50 No core
36,58 Dolerite
BOREHOLE No. TlO. 2,6 km 420 from
Fulton's Drift. In Mtetengwe T.T.L.
July, 1954.
9,75 No core
19,79 Red mudstone
21,11
Sandstone
34,85 Red mudstone
35,61 White sandstone, unbedded
Red sandstone, cross-bedded
51,21
57,07 Red mudstone, calcareous nadules
58,62 Sandstone
59,72 Red mudstone
60,02 Red-white sandstone
63,45 Red mudstone, nodules
65,40 White sandstone
65,99 Red mudstone
66,29 White sandstone
Red mudstone
73,91
75,44 White sandstone, cross-bedded
76,15 Red mudstone, nodules
76,45 Purple sandstone
77,67 Red mudstone
78,33 Purple sandstone
79,71
Red mudstone
87,78 Purple sandstone
98,98 Red mudstone
99,84 Purple-white sandstone
100,07 Red mudstone
103,94 Purple sandstone, cross-bedded
112,42 Red mudstone, nodules
115,52 Purple sandstone, cross-bedded
135,86 Red mudstone, nodules
36
KAROO SYSTEM
BASALTS
TABLE ill (continued)
To
metres
139,35
139,67
139,83
162,76
174,96
176,78
186,54
192,94
196,29
198,42
208,48
218,39
219,00
222,20
226,62
228,00
230,20
231,65
234,19
240,13
247,70
263,55
263,98
268,83
275,39
Strata
Green-red sandstone
Red mudstone
Green sandstone
Red-grey mudstone
Grey mudstone
Pebbly mudstone
Purple mudstone
Pebbly sandstone
Grey mudstone
Sandstone
Pink mudstone
Grey pebbly sandstone
Grey shale
Black shale, coal bands
Grey shale
Dolerite
Grey mudstone
Grey argiIJite
Dolerite
Black shale
Grey shale
Grey-cream argillite
Dolerite
Cream argillite
Cream clay rock
BOREHOLE No. no. Redrilled 91,5 m
SSW.
78,03 Red sandstone, pebble bands
106,38 Red mudstone, pebble bands
106,53 Dyke
132,59 Purple muddy sandstone
133,35 Quartzite
133.81 Dolerite
137,16 Purple muddy sandstone
138,68 Grey mudstone, calcareous nodules
140,21 Dyke
140,67 Sandstone
160,32 Grey mudstone
164,90 Sandstone, pebbly
176,78 Dolerite
179,22 Carbonaceous shale
179,83 Grey shale
179,91 Coal
180,75 Grey shale
To
metres
202,69
217,93
Strata
White siltstone
Dolerite
BOREHOLE MRDl. 26,8 km 250 0 from
Fulton's Drift. On Nottingham Ranch.
1971.
78,00 Amygdaloidal basalt
79,3
Sandstone dyke in lava
79,7
Sandstone
92,3
Lava flows
171,4
White sandstone
195,0
Red and green sandstones
200,0
Red pebbly sandstone
202,5
White sandstone
242,0
Red sandstone
264,0
White sandstone
267,0
Red sandstone
270,0
White sandstone
296,6
Pebbly red sandstone
306,0
Green sandstone
335.6
Pebbly red to green sandstone
336,6
Red mar!
347,9
Red mudstone
351,8
White sandstone
360,8
Green mudstone
361,0
Pebbly grit
361,2
Shaly marl
361,4
Conglomerate
372,0
Purple mudstone
392,9
Brown mudstone
3948
White sandstone
395,3
Conglomerate
410,7
Black shaly mudstone
415,0
Shale and coal
420,4
Black shaly mudstone
422,1
Coal
432,0
Black and brown mudstone
456,0
Basal grits
465,8
Gneiss
BOREHOLE MRD2. About 2,8 km west
of road to Machuchuta and NE. of dam
on upper Shobi River near south
boundary of Dendele T.T.L. (not shown
on Tuli map).
75,9
Buff to grey sandstone
109,73 Dolerite
37
BASALTS
The Basalts, which are the uppermost member of the Karoo stratigraphic sequence, occupy the greatest part of the mapped area. They
enter it from Botswana at the Shashi River and continue eastwards to
near the main road from Beitbridge to Fort Victoria, a distance of about
160 km. Their width from north to south is around 40 to 45 km, but
their thickness, which must be large, is not known. They lie with
varying degrees of unconformity on the Forest Sandstone and are
traversed by many large faults trending east-north-east to north, and
by easterly dykes which were the last phase of the Karoo igneous
activity.
Formerly the basaIts extended far to the north-west and south-east
of the Limpopo River, but have long since been removed by erosion.
Their former presence is indicated by amygdaloidal agates in the superficial deposits and by the olivine-bearing lavas around Featherstone in the
Charter District (Worst, 1962). In the mapped area they have been
preserved by extensive down-faulting in the Limpopo Mobile Belt.
Similar basalt lavas occur to the east of the main road to Fort Victoria
and continue eastwards into Moc;:ambique. They have been described
by Tyndale-Biscoe (1949), Swift et al. (1953), Cox et al. (1965, 1967),
Jamieson (1966) and Macdonald (1967).
Because of the large-scale faulting and discontinuous exposure, it
was not possible during this reconnaissance survey to map the basalts
in detail or with a high degree of accuracy. However, a provisional
subdivision of the basalts has been made, and from the base upwards
it is (a) the olivine-bearing Mabuli basalts, (b) the hypocrystalline,
aphanitic Marawanerit basalts, (c) the porphyritic Chandabalini basaIts
with their large tabular feldspars, (d) the vesicular basalts and volcanoclastic rocks, and (e) the Tuli basalts which form the top of the Karoo
succession.
lithology
The basalts are hard, well-jointed rocks which vary in colour from
dark brownish-grey to purplish-grey or almost black. Some are soft
and break easily, but most are tough and break with conchoidal to
splintery fractures. They are aphanitic to very fine-grained, and some
contain remarkably large feldspar phenocrysts, 10 to 30 mm across and
1 to 2 mm thick. Many are highly vesicular to scoriaceous and these
are red to purplish-brown in colour. The amygdales and veinlets
38
BASALTS
KAROO SYSTEM
traversing them are filled with green celadonite. and white. grey
cream-coloured agate. quartz. zeolites and calcite.
or
Distribution and Field Relations
The more massive basalts form flat-topped hills, terraces and cliffs,
and in the southern part of the area they frequently form a capping
on the hills and ridges of the Forest Sandstone. The vesicular lavas
form gentler slopes and the olivine basalts tend to weather more rapidly
and form flat country. Exposures are generally good, especially in the
streams and rivers, but there are large areas of basalt covered by black
or grey, clayey soils. In these soils calcrete is common to abundant. In
some places, noticeably the Tuli National Area, the soil is stony, either
with rounded to spheroidal boulders of basalt, or with rough, angular
fragments of the almost indestructible agate.
The basal lavas appear to have flowed across a dune-covered surface
of Forest Sandstone (Robertson, 1967) and produced a more or less
unconformable surface. In the Homba Hills the basalt cappings on the
sandstone hills are several metres higher than the basalt in the flat
country lying to the north of the hills. A basalt capping on top of the
hills, 1,5 km north of the homestead of Sentinel Ranch can be seen to dip
inwards into a hoIlow in the top of the Forest Sandstone. Similar
unconformable relationships can be seen in many places along the
south margin of the Karoo rocks from the Shashi River eastwards to
the Mtetengwe River.
The Mabuli Olivine and Limburgitic Basalts
The Mabuli basalts, which are thought to be the earliest lavas erupted,
are named after the MabuIi borehole on Jopempi Block in the northwest corner of the Gongwe map area (grid reference 19266071).
Generally they lie on the Forest Sandstone and are well exposed in the
southern part of the mapped area. In the northern part of the area they
outcrop on the south side of the Bubye River. Near Chandabalini an
olivine basalt overIies a red vesicular basalt, and near Mabuli horehole
a limburgitic basalt is exposed about 30 m above the Marawanerit
basalts.
The olivine basalts are massive, dark olive-grey, aphanitic rocks. and
the limburgitic basalts are heavy, dark greenish-grey rocks in which
minute black specks of olivine can be seen.
39
Specimens of olivine basalt were collected from 400 m along the
Gilande track from Chamagundawa tank on Jopempi Block (slide
21375), at 2 km east of Mavimba on Jopempi Block (slide 21376), and
4 km north of the Sentinel Ranch headquarters (slide 21377). All are
hypocrystalline with panidiomorphic textures. Slightly ragged calcic
plagioclase laths, 0,2 to 0,8 mm long and 0,05 to 0,15 mm wide, form
most of the rocks. In slide 21376 the laths are slightly altered and have
a dirty appearance. Down their centres are thin zones of inclusions.
Augite occurs as equant, intergranular crystals 0,05 to 0,20 mm across.
It is very slightly chloritized in slide 21377 and forms rare microphenocrysts in slide 21376. In all three slides a few idiomorphic to hypidiomorphic olivine crystals, 0,1 to 0,5 mm long, are outlined with iron
ore dust. The majority are altered to barely pleochroic iddingsite which
ranges in colour from deep brown to a bright orange-red. Dark brown
to orange-brown glass that is almost opaque forms about half the rock
except in slide 21377 which is almost holocrystalline and has a largely
microcrystalline matrix. One of the oHvine basalts (slide 21376) is
vesicular and contains widely scattered amygdales up to 5 mm long
that are completely filled with marginal agate and celadonite, and
coarsely crystalline carbonate cores.
A limburgitic basalt (slide 21378) from 2 km south-east of Lutope
Hill on Jopempi Block contains idiomorphic to hypidiomorphic phenocrysts of oHvine 0,5 to 2,0 mm long. They contain much brownish
glass-like dust and narrow cracks filled with iron ore needles and dust.
Around them a pale orange-brown reaction rim appears to be a mixture
of pyroxene and antigorite. There are also a few allotriomorphic phenocrysts, about 0,3 mm long, of augite and numerous rods of i1menite,
0,3 to 1,5 mm long and 0,01 to 0,10 mm wide, generally near the oHvine
phenocrysts which they sometimes penetrate. Rather less than half the
rock is pale brownish glass that is full of microlites and globules. An
analysis, Lab. No. 73/17, is given in Table N.
Another limburgitic basalt (slide 21379) from 3 km west of Panini in
the Mtetengwe T.T.L. has many allotriomorphic to idiomorphic olivine
phenocrysts, which are 0,2 to 2,0 mm long and average 0,5 to 1,0 mm,
in groups and scattered grains. They have many dusty inclusions and
are cut by numerous narrow cracks filled with chrysotile and antigorite
crystals that have grown perpendicular to their walls. There are a few
pyroxene phenocrysts about 0,5 mm long and abundant long rods and
skeletal crystals of i1menite. Nearly half the rock is a sepia brown glass.
40
41
KAROO SYSTEM
BASALTS
The borehole MRDl on Nottingham Ranch started in olivine basalt
and continued in it to a depth of 78 m (Johnson, 1973). It is described
as a dark grey to black amygdaloidal rock containing small phenocrysts
of augite and altered olivine in a fine-grained matrix. The white and
green amygdales, which were about 10 mm long, were filled with chalcedony, quartz, calcite and chlorite. A specimen taken at 33 m depth
contained about 25 per cent. olivine phenocrysts, 0,5 to 1,5 mm long,
that were partly or completely altered to serpentine, 20 per cent. of
randomly distributed and very slightly chloritized, 0,05 to 0,4 mm
grains of augite, and 15 per cent. of acicular iron ores up to 1 mm long.
These crystals were enclosed in a semi-vitreous matrix of light grey to
colourless grains less than 0,001 mm across. X-ray studies indicated the
presence of nepheline and oligoclase.
0,6 mm across. Patches of very dark brown interstitial glass with almost
black cores and a few microlites, form less than 25 per cent. of the
rock. Iron ores are comparatively scarce and occur as very thin rods,
needles and skeletal growths up to 0,2 mm long. There are also a few
0,02 to 0,03 mm octahedra of magnetite and a very small amount of
orange-red iddingsite or chlorophaeite around or in cracks in the
pyrpxene crystals.
This upper lava was separated from a lower lava at between 78 m and
79,7 m depth by a bed of fine-grained, white sandstone which extended
upwards for 0,4 m into the lava as a baked, dyke-like body. The upper
contact of the sandstone was scoured, grooved and pitted, and the bulk
of it was cross-bedded. The lower half of the bed was greenish and
tuffaceous. From 79,7 m to 80 m depth there was glassy lava and from
80 to 91 m a coarsely amygdaloidal, fine-grained basalt which between
87 and 89 m was veined with white material. Downwards from 91 m
there was basalt riddled with small, calcite-filled amygdales to the chilled
base at 92,3 m which was lying on top of dark coloured, tuffaceous,
very fine-grained Forest Sandstone.
The Marawanerit Basalts
The Marawanerit basaIts, which are named after the Marawanerit
borehole on Jopempi Block in the north-west corner of the Gongwe
map area (Grid reference 20286076), are massive, black, aphanitic rocks
which sometimes contain microphenocrysts of augite. They form a flat
plain around the borehole where they overlie the Mabuli basalts and
are covered, mainly to the west, and south-west, by red to purple,
vesicular lavas. Elsewhere they outcrop in small areas.
A specimen (slide 21380) collected from an aphanitic black basalt
flow about 1,5 km E.N.E. of Lupako Hill on Jopempi Block, is a
hypocrystalline rock with very few microphenocrysts, 0,5 to 1,2 mm
long, of augite. It has an intergranular to interstitial, somewhat tholeiitic
texture, and is composed of fresh idiomorphic laths of calcic plagioclase,
0,1 to 0,4 mm long, and hypidiomorphic to granular pyroxenes, 0,2 to
The ChandabaIini Basalts
The Chandabalini basaIts are aphanitic, reddish-grey, brownish-grey,
or almost black rocks which occasionally contain small amygdales. They
are characterized by large greenish-white feldspar phenocrysts, which
have a roughly sub-parallel flow structure. They measure about 20 to
30 mm by 10 to 15 mm and are 0,5 to 2 mm thick. Viewed one way
they form lustrous patches, and viewed the other way long thin rectangles. They form about 10 to 25 per cent. of the rock.
7(
These basalts are best developed in the north-central portion of the
area of the Mazunga map around Chandabalini borehole (Grid reference
77936042), along the north boundary of Jopempi Block, and in the
adjacent Siyoka Tribal Trust Land. Similar porphyritic basalts outcrop
in the Umzingwane River 2 km south-east of Baemura School, in the
Hwali River in the Dibilishaba T.T.L., and near the road to Tuli in
the north-central part of the Tuli map area. Like the Marawanerit
basalts, they lie on olivine and Iimburgitic basalts and are covered by
red to purple vesicular basalts.
A specimen with abundant feldspar phenocrysts (slide 21381) was
collected from the Umzingwane River in the Siyoka T.T.L. 1,5 km
..j( south-east of Baemura School, and one with slightly fewer phenocrysts
(slide 21382) from 1,5 km south-west of the airstrip at the Kongoni
Irrigation Scheme in the Shashi T.T.L. In slide 21381 the clear, twinned
phenocrysts are slightly cracked and their ends fractured. They are set
in a matrix of twinned, and sometimes zoned, laths of hypidiomorphic
plagioc1ase, 0,1 to 0,3 mm long and 0,05 to 0,10 mm wide, separated
by abundant allotriomorphic grains of augite, 0,05 to 0,10 mm across.
In the matrix are numerous irregular patches, 0,2 to 1,5 mm long, of
brownish to opaque and skeletal iron ores.
In slide 21382 there are fewer phenocrysts with a poorly developed
parallelism. They are well-twinned, cracked and slightly fractured, and
are in a matrix of plagioclase laths, 0,05 to 0,20 mm long, and inter-
4
42
43
KAROO SYSTEM
BASALTS
stitial allotriomorphic augite grains, 0,03 to 0,10 mm across. The
comparatively abundant iron ores are either thin rods and skeletal
crystals 0,1 to 0,2 mm long, or 0,01 to 0,03 mm granules. There is a
very small amount of brownish glass, and a few widely scattered
amygdales up to 1,5 mm long that are completely filled with green
celadonite and sometimes some chalcedony or quartz.
Among the basalts in the Machuchuta T.T.L. at about 4 km northwest of Maramani village is a ring of hills about 15 m high and 600 m
in diameter. The central flat floor is drained by two watercourses
running east and west through gaps in the hills. It is thought tbat the
structure is the remains of a small central volcano (McCall, 1967, page
51). A specimen (slide 21386) from the crater rim is a pale purplish
and white spotted ignimbrite or agglutinate in which heterogeneous
fragments of gneiss up to 15 mm long, and of vesicular basalt up to
40 mm long conform to a faint laminar flow structure. The slide is
largely a dark brown, almost opaque, matrix containing scattered feldspar crystals, minute grains of iron ores and pinpoint-sized vesicles. The
smaller feldspars, about 0,1 mm long, are fairly fresh but the larger
feldspars, up to 2,5 mm long, are irregular and partly resorbed crystals
of much altered and partially uralitized oligoclase. In slide 21387 from
the same locality the laminar texture is not so clear. The groundmass is
opaque and the slightly altered feldspars, which occur singly or in
clusters, are more shattered.
The Vesicular Basalts
The vesicular basalts generally lie on top of all the basalt lavas
except the Tuli basalts, which are younger. They are widely distributed
from one end of the mapped area to the other, but their thickness is
not known. The majority are on the margins or edges of lava flows,
where they were formed by escaping gas. The changes in their appearance and colour from massive to vesicular lava are both distinctive and
abrupt as is shown by specimens from 1 km north-east of Ngulumbi
Hill (slide 21383) and 5 km south-east of Chamagundawa borehole
(slide 21384) on Jopempi Block (Mazunga map). The former is an
aphanitic, red, jasper-like rock in which oxidized and opaque volcanic
glass is traversed by irregular white veinlets up to 1 mm wide. These
veinlets are filled by a film of chalcedony and quartz, or in the wider
parts by dirty white, fibrous zeolite. There are very few minute vesicles.
Slide 21384 is from a deep reddish-brown rock containing patches of
minute vesicles. In it abundant angular fragments of clear feldspar,
0,05 to 0,20 mm across, are scattered along with 0,02 to 0,06 mm grains
and dust of iron ores in a clear isotropic groundmass. Veinlets of black
basaltic glass containing a few laths of feldspar cut across the rock.
An aphanitic, black and highly vesicular or scoriaceous lava (slide
21385) from a hill west of the airstrip on Jopempi Block, 8,5 km south
of Mazunga, has been fractured and penetrated by an irregular network
of veinlets, up to 5 mm wide, that are filled with microcrystalline agate.
quartz and zeolites.
Many of the lava flows contain, along with airborne volcanic bombs
and lava fragments, large pieces of highly vesicular or pumiceous lava,
and reworked blocks of solidified basalt that were picked up and
incorporated into the moving flow. In the Tuli National Area, about
10,5 km north-west of Tuli village, there is an exposure that consists
of lava fragments up to 45 mm long set in a mixture of fragments under
10 mm long cemented with a pink zeolite. Among the vesicular lavas
in a number of places are boulders and lenses of massive lava which
may represent examples of liquid immiscibility (McCall, 1967, p. 51).
The Tuli Basalts
The light grey, brownish-grey to black Tuli basalts are aphanitic to
very fine-grained rocks which occasionally contain individual or clusters
of feldspar phenocrysts up to 20 mm long. They are characterized by
numerous vesicles, 0,5 to 80 mm long, though most are under 10 mm
in length. These vesicles are partly or completely filled with celadonite,
agate, quartz, zeolites or, more rarely, amethyst, calcite and gypsum.
They form warty or knotty protruberances on the weathered surfaces,
which have a dark brown to black skin up to 10 mm thick. Frequently
the stony ground is littered with agate fragments.
The Tuli basalts, which are the youngest of the Karoo Iavas, are very
widely distributed on top of the horizons of vesicular lavas and agglomerates. They form most of the south-western part of the Tuli map area,
including the Tuli National Area, and the tops of all the high hills from
Gongwe westwards to Gongwe Poort, around Ngulumbi Hill and in the
south-west corner of Lot 5 of River Ranch.
A specimen (slide 21388) from Jopempi Block 9 km S.S.W. of
Mazunga has about 25 per cent. of randomly arranged, tabular phenocrysts of plagioclase, that are 5 to 10 mm across and 1 to 2 mm thick,
set in an aphanitic, yellowish-brown matrix. Amygdales, 0,5 to 2 mm
long with a few as large as 12 mm, are abundant. They are completely
\
KAROO SYSTEM
MBAKA BEDS
filled with dark green celadonite, though a few have a thin rim of agate
or cores of calcite. The well-twinned and sometimes zoned feldspar
phenocrysts are slightly fractured and, unlike the clear phenocrysts of
the Chandabalini basalts, they contain small patches clouded with
zoisite, epidote and more sodic plagioclase. The ground mass is chiefly
slightly altered feldspar laths up to 0,5 mm long, most being 0,1 to 0,2
mm, with comparatively few interstitial grains of augite, 0,005 to
0,10 mm across. Minute grains, 0,03 to 0,10 mm across, of allotriomorphic iron ores are abundant, and there are a few small interstitial
patches of brown glass.
TABLE IV
44
A brownish-grey, amygdaloidal basalt (slide 21389) from near the
pumps at the Shashi Irrigation Scheme in the Maramani T.T.L., contains very few twinned feldspar phenocrysts under 5 mm across that are
now brownish and clouded. The small irregular shaped amygdales are
mainly 2 to 5 mm long, and are completely filled inside a thin layer
of brownish chalcedony by coarsely crystalline zeolites. The ground mass
consists of randomly scattered, 0,05 to 0,10 mm feldspar laths enclosed
in mottled brown to black glass.
A microporphyritic amygdaloidal basalt (slide 21390) from a hill on
Jopempi Block, 3,5 km north of Mabina Dip, contains a few hypidiomorphic phenocrysts of augite and plagioclase, about 0,5 mm long, and
a very few, widely scattered and zeolite-filled amygdales up to 2 mm
across in an aphanitic groundmass. Feldspar laths, 0,05 to 0,10 mm
long, with rare needles up to 0,5 mm, a few 0,05 to 0,10 mm grains of
pyroxene, and a little pale coloured glass form the groundmass.
Scattered through it are minute grains of iron ore. An analysis, Lab. No.
75/15, is given in Table IV.
Mbaka Beds
The Mbaka Beds, which are named from the Mbaka Dip on the east
bank of the Mtetengwe River on Jopempi Block, about 11,5 km southeast of Mazunga, are sandstones interbedded at various horizons in the
Karoo basalts of the area. They occur as small, isolated outcrops
scattered throughout the basalt area and one main outcrop, which is
over 27,5 km long and around 200 m wide. It extends from 3,5 km
west of the Mazunga River eastwards past Mbaka Dip, Machokovere
Hill and the Tongwe River to the Pofu borehole on Jopempi Block near
Kuruwalemba Hill. It may continue farther east-north-eastwards under
the alluvium of a small valley.
45
ANALYSES OF KAROO BASALTS
Lab. No ..
73/17
Slide No ..
21378
SiO,
AI,O, .
Fe,O, .
FeO
MgO.
CaO
Na,O.
K.O
H,O+
H,OCO,
TiO, .
P,O, .
MnO.
46,62
7,30
4,07
6,70
20,25
5,35
0,93
1,92
2,77
0,74
0,10
2,46
0,42
0,14
47,74
14,23
2,54
7,04
8,03
10,70
3,27
1,23
2,14
0,36
0,07
1,72
0,45
0,16
47,86
12,56
4,27
6,85
11,30
9,25
1,90
0,85
1,38
0,61
0,07
2,62
0,32
0,15
48,29
18,87
2,69
5,21
2,89
7,28
4,09
3,91
4,27
0,38
0,05
1,21
0,57
0,15
TOTALS
99,77
99,68
99,99
99,86
3,06
2,98
3,04
2,70
S.G.
%
73/18
73/15
73/16
21390
%
%
%
Analyst: B. J. Radclyffe.
NIGGLI MOLECULAR NORMS
Q
Ab
F {or
An
Ne .
Di
r
En .
Fs .
H
Eo.
y Fs .
01 Fo .
Fa .
Mt
Ilm
Ap
Cc
11,55
8,45
10,10
5,40
5,02
0,38
30,86
2,34
15,78
1,20
4,31
3,48
0,91
0,22
7,40
24,95
21,00
2,94
11,94
9,12
2,82
10,29
3,17
2,73
2,50
0,91
0,22
0,16
5,10
17,30
23,73
8,08
32,14
4,24
24,05
22,45
22,48
9,51
4,42
2,80
1,62
4,52
3,74
0,75
0,22
4,17
2,45
2,96
1,74
1,23
0,12
Localities:
Limburgitic basalt. About 2 km soutb-east of Lutope Hill, Jopempi Block,
Beitbridge District (Gongwe map).
73/18 Basalt. About 3 km north-west of Lamulas homestead, Jopempi Block,
Beitbridge District (Gongwe map).
73/15 Basalt. Hill 31- km north of Mabina dip, Jopempi Block, Beitbridge District
(Mazunga map).
73/16 Basalt. About 5 km north-west of Gongwe Poort, Jopempi Block, Beitbridge
District (Gongwe map).
73/17
47
KAROO SYSTEM
DOLERITIC INTRUSIVE ROCKS
At Pofu borehole and Machokovere Hill a bed of drab-coloured
sandstone lies on a thinly bedded, light red-coloured sandstone, and at
Pofu the following incomplete stratigraphic section was measured.
iron ores covers all the grains and gives the rocks their body colour.
The grains are generally angular to sub-angular. Only in slide 21392
are they rounded to well-rounded. In slide 21394 some grains arc
rounded. In the fine-grained beds in slide 21395 some of the grains are
very angular and in slides 21396, 21399 and 21400 there are small
splinters of quartz. Sphericity is Iow to medium except in slide 21397
where it is high, and the packing and sorting varies from poor in slides
21396, 21398 and 21400 to good in slides 21394 and 21397 (both
aeolian) and 21399. The grains range in size from 0,02 to 0,35 mm, but
most are less than 0,15 mm across. The cement, which is always
densely stained to almost opaque with iron ore minerals, varies quite
widely in amount from rock to rock. In slides 21398 and 21399 it is
siliceous.
46
Reddish-purple, compact, cross-bedded sandy siltstone
Drab, shaly sandstone
.
.
.
.
.
.
.
Red, compact, thinly cross-bedded, fine-grained sandstone
Soft, poorly exposed greyish-drab, siltstone
Thickness
in
metres
1S,2
12,2
4,0
9,2
In the area of the Tuli map a small outcrop of fine-grained reddishbrown sandstone occurs in the south-west of the Maramani T.T.L. at
1 km north of Limpopo Store, and in the area of the Mazunga map
there are small patches at (a) 3,5 km south-west of Zebra Dam, (b) on
the east side of the Mapandi River at about 4,5 km S.S.E. of Mapandi
Dam, (c) on Gem Ranch west of the Umzingwane River and 3,5 km
west of the homestead on Cawood's Mazunga Ranch, (d) on the fence
3 km W.N.W. of Chamunyu tank, and (e) on a hill 1,3 km west of the
confluence of the Mazunga and Manange rivers.
The Mbaka Beds are fine- to very fine-grained sandstones that range
in colour from red-brown or drab to mouse-grey. Sometimes they have
surface calcareous encrustations. Generally they are hard, massive and
structureless rocks which break with a conchoidal fracture, but in the
main outcrop around Pofu and Machokovere Hill, some are very finely
bedded or cross-bedded. They appear to be mainly sedimentary rocks,
and only the rocks near Pofu and north of Limpopo Store are probably
of aeolian origin.
Petrography
A number of specimens were collected for detailed study from near
Pofu borehole (slides 21393-4), Machokovere Hill (slide 21395) and
Mbaka Dip (slide 21396) on J opempi Block. Other specimens were
collected from 1 km north of Limpopo Store in the Maramani T.T.L.
(slide 21397), on Gem Ranch at 3,5 W.S.W. of the homestead on
Cawood's Mazunga Ranch (slide 21398), 4 km south-west of Zebra
Dam on Jopempi Block (slide 21399), and 3 km W.N.W. of Chamunyu
tank on J ope.rnpi Block (slide 21400). The main constituent in all of
them is strained quartz with many minute inclusions, that came from
the Precambrian rocks. With it are rare grains of twinned plagioclase,
muscovite, augite, basaltic lavas, and partly devitrified volcanic glass.
A thin pellicle of densely coloured, red-brown or occasionally black,
DOLERITIC INTRUSIVE ROCKS
A large number of dykes, which generally trend between E.S.E. and
E.N.E. and dip at high angles, along with a few sheets and sills, intrude
all the rocks in the mapped area from the oldest Precambrian gneisses
to the youngest Karoo lavas. They mark the last phase of Karoo igneous
activity in the area, and where probably intruded along existing fault
planes during a period of N.N.W. to E.S.E. regional dilation soon after
the extrusion of the lavas to which they bear a close resemblance,
especially the olivine-bearing and feldspar phenocryst types. Virtually
all contain some basaltic glass but few are holocrystaIline, ophitic
dolerites; most of the coarse-grained rocks are sub-ophitic. The holohyaline types consist of glass containing microlites and all appear to
have been intruded at a comparatively shallow depth into cool wallrocks.
The majority of these intrusive rocks are dykes. Sills and sheets are
remarkably rare and probably most of the sills recorded in the boreholes are steeply dipping dykes. Only one sill-like body, 1,5 km northwest of Mtetengwe Store, was seen during the mapping of the area.
and MehIiss (1951) records only three sills of olivine dolerite, which
were less than 430 m long. in Special Grant No. 15.
Doleritic dykes are widely distributed throughout the whole of the
Limpopo Valley (Tyndale-Biscoe. 1949; Cox et al. 1967; Robertson.
1967. 1973) and the mapped area. where they appear to be more
abundant in the south than in the north. but this may be due to thicker
covers of soil and vegetation in the north. Some of the dykes have
48
KAROO SYSTEM
DOLERITIC INTRUSIVE ROCKS
weathered into low walls and others into soil-filled troughs which run
straight for considerable distances across country. Those dykes with
chilled, fine-grained or glassy margins, or with walls or hard metamorphosed or silicified rocks weather into V-shaped structures with low
side walls and a central depression. The dykes with large feldspar
phenocrysts are always deeply weathered, and many of the east-trending
lineaments seen on the air photographs probably mark dykes with a
good cover of soil and denser vegetation.
Two specimens of fractured dolerites were collected from 0,5 km
south of Shashi Store (slide 21403) and from 8,5 km north-west of the
homestead on Sentinel Ranch (slide 21404). Both are medium-grained
rocks composed of 1 to 3 mm crystals of plagioclase and augite which
have been cracked, disrupted and slightly corroded by the intrusion of
a small amount of very dark brown basaltic glass. Most of the larger
crystals are idiomorphic, 1,5 to 2,0 mm crystals of greenish augite that
have been locally cracked internally and are surrounded by thin reaction
rim. The 1 to 3 mm, hypidiomorphic and interstitial feldspar laths are
twinned and poorly zoned. They have been cracked and marginally
corroded. Isolated fragments in the glass have been reduced to a vermiform mass that in places is stained greenish.
Generally the dykes are composed of dark coloured rocks. Only the
porphyritic dykes are light to dark grey, and the contaminated dykes
are spotted a pale greenish-grey. Those dykes that are less than one
metre wide, and the margins of some of the wider dykes, consist of
black glassy rocks which are brittle and break with a conchoidal
fracture. One dyke, on the road 1 km south of the Bill Irrigation
Scheme, has a 60 m-wide core of fine-grained porphyritic basalt and
chilled margins about 9 m thick on both sides.
The somewhat variable soils formed from the dykes are generally
stony and are full of fragments 50 to 100 mm long. Spheroidal weathering and large boulders are rare.
Petrography
A holocrystalline olivine basalt (slide 21401) was collected from a
dyke at the airstrip 7 km south-west of Tshibilengwe Hill on Sentinel
Ranch. It is a fine-grained rock composed essentially of hypidiomorphic
to idiomorphic laths of plagioc1ase feldspar, 0,2 to 0,4 mm long with
a few up to 1,5 mm long, and two varieties of augite, one in purplish,
very weakly pleochroic, hypidiomorphic crystals 0,4 to 0,6 mm long,
and the other a pale greenish augite in 0,2 to 0,7 mm interstitial grains
which produce a sub-ophitic texture. A small amount of fresh olivine
in idiomorphic crystals 0,1 to 0,2 mm long is scattered through the rock
and the accessory minerals are iron ores, frequently in 0,1 to 0,2 mm
octahedra, and rare brownish-red biotite.
An altered olivine basalt (slide 21402) from 8,5 km south-east of
Marimani School in the Marimani T.T.L. contains olivine phenocrysts,
0,5 to 1,0 mm long, that are now almost completely altered to serpentine
minerals and are outlined by a rim of iron ores. The groundmass is 0,2
to 0,8 mm long feldspar laths which show flow structure, a little inter-.
stitial augite, some light coloured glass and accessory iron ores that
are 0,2 to 0,3 mm long and only 0,01 to 0,03 mm wide.
49
Specimens of fine-grained, sub-ophitic dolerite came from 7,5 km
E.S.E. (slide 21405) and 9 km south-west (slide 21406) of Tshibilingwe
Hill on Sentinel Ranch. In them a few feldspar crystals up to 3,5 mm
long and very few, 0,1 to 1,5 mm, crystals of purplish augite occur in
a holocrystalline ground mass of 0,5 to 1,0 mm laths of plagioclase and
granular augite.
Skeletal crystals of iron ores in slide 21405 and tabular crystals
measuring 0,5 to 1,0 mm by 0,1 to 0,2 mm in slide 21405, are abundant,
and there are small patches of bright orange-brown glass, possibly
chlorophaeite, in slide 21406.
*'
Samples of the feldspar porphyry type were collected on Cawood's
Mazunga Ranch about 3 km north of Giraffe Dam in the Mtetengwe
T.T.L. (slide 21407), 7 km south-east of Limpopo Store (slide 21408) in
the Maramani T.T.L., and from 300 m east of Fly Dam (slide 21409)
on Jopempi Block (Mazunga map). All contain tabular plagioc1ase
phenocrysts, 3 to 10 mm wide and 1 to 2 mm thick, set in a groundmass
of feldspar laths 0,1 to 1,0 mm long and smaller interstitial grains of
augite, and, in slide 21407 and 21408, less than 20 per cent. of brown
glass containing microlites and orange-brown patches resembling chlorophaeite. Grains, needles and skeletal crystals are accessory in all.
Similar, but altered rocks, were found at 2,5 km N.N.W. of Gwawe
Hill on Jopempi Block (slide 21410) and 1 km north-east of Mangombe
on Nottingham Ranch (slide 21411). In them the large tabular feldspars,
and the few augite phenocrysts in slide 21410, are corroded, cracked
and clouded with alteration products. Their groundmass consists of
0,5 to 1,0 mm crystals of plagioclase and augite, skeletal iron ores up
so
SI
KAROO SYSTEM
STRUCI'UIm
to 0,5 mm long, and small patches of brown glass. In slide 21411 the
groundmass feldspars are clouded and the augite cracked.
one to possibly three kilometres of Karoo and younger deposits have
been removed.
Contaminated basalt specimens were collected from dykes 1,5 km
S.S.E. of Gawe Hill (slides 21412-3) on Jopempi Block, 2,5 km northwest of the homestead on Safari Ranch (slide 21414), and 3,5 km east of
Penemene Store in the Mtetengwe T.T.L. (slide 21415). All consist of
dirty brownish plagioclase laths enclosed in brownish glass containing
microlites. In the glass are a few scattered fragments, about 0,5 to 3,0
mm across, of strained quartz and also in slide 21414 rare fragments
of dirty brown feldspar from the Precambrian rocks. These fragments
have been much corroded and have smooth, rounded outlines.
FAULTS
Fresh basalt specimens were collected from dykes at 9 km south-east
of Limpopo Store in the Maramani T.T.L. (slide 21416) and 2,5 km
south-west of Penemene Store in the Mtetengwe T.T.L. (slide 21417).
In them small allotriomorphic laths of plagioc1ase and some greenish
augite grains, less than 0,05 mm across, occur in a small amount of a
pale glass in slide 21417 and much black glass in slide 21416. Altered
basalt containing clouded and partly altered feldspars and augite in
small amounts of brownish glass were collected from dykes at 7 km
N.N.E. of Gilande borehole on Jopempi Block in the area of the
Mazunga map (slide 21419) and 2 km north of Lupako Hill on Jopempi
Block in the area of the Gongwe map (slide 21418).
STRUCTURE
In the mapped area the highly complex structures in the Precambrian
rocks have not been studied, only those of the flat-dipping Karoo rocks.
The Karoo rocks of the Limpopo basin once covered a very large area
but the present outcrops are comparatively small erosional relics that
have been preserved by the trough faulting that followed the outpouring
of the Basalts.
The Karoo sedimentary rocks were deposited in a flat shallow basin
with a floor of gneisses and metamorphic rocks of the Limpopo Mobile
Belt. From Dwyka (Permian) to Stormberg (early Jurassic) times the
floor subsided gently under a growing cover of sedimentary and, at
the end, volcanic rocks. Then regional dilation produced fissures occupied by dykes and major normal faults. Subsequent vertical movements
have resulted in one and perhaps two marine invasions, but mainly
uplift and very extensive erosion in the mapped area. Over much of it
The Karoo rocks have been affected by a system of large faults which
trend in a general east-north-easterly direction and dip at over 50
degrees except in the east where, in places, dips as flat as 20 degrees
were observed. Their displacement of the Karoo rocks is very variable
and, in some, may be of the order of hundred and perhaps thousands of
metres. The fewer northerly striking faults have much shorter strikelengths and smaller displacements.
These major faults post-date the youngest basalts and generally
bound the Karroo outcrop with down-throws inwards towards the
centre. They and the doleritic dykes were probably formed during a
period of regional N.N.W. and E.S.E. dilation with a vertical maximum
pressure. This dilation may have been due to a readjustment of the
crust under a load of about one kilometre of sedimentary rocks and at
least 1,5 km of basalt lavas, and the emptying of the deep-seated magma
chambers which supplied the extrusive and intrusive igneous rocks.
In the area covered by the Tuli and Mazunga maps the Karoo
boundary faults bring the basalts into contact with the gneiss along much
of their length. Along the northern margin of the Karoo rocks there are
only comparatively few short slices of sedimentary rocks on the south
side of the faults. Near the Umtshabezi River northerly faults displace
the boundary fault 1,5 km south on the east side, and for a short distance
there are outcrops of up to 3 km of sedimentary rocks on the south
side. In the area of the Gongwe map the fault forming the north
boundary of the Karoo rocks passes into the gneisses W.N.W. of Gwawe
Hill and Karoo sediments either lie unconformably on the gneisses or are
displaced in a complex manner by easterly or northerly faults. Among
the Karoo rocks there are small outcrops of gneisses in an area of poor
exposure.
The southern boundary of the Karoo rocks enters the area of the
Mazunga map near the confluence of the Gushu and Limpopo rivers.
Here sedimentary rocks rest on the gneiss for about 7 km north of the
confluence to where they are faulted against the gneisses as far as the
Umzingwane River. Another fault to the south of it starts east of the
Umzingwane and becomes the boundary fault. Its displacement increases
eastwards until the basalts are in contact with the gneisses, and then
52
STRUCfURE
53
KAROO SYSTEM
MICRO-SHEARS
decreases until, east of the main road to Beitbridge, it passes into the
gneisses. At the eastern end of the Karoo outcrop in the vicinity of the
main road, several large easterly faults and smaller northerly faults
produce a ragged termination to the Karoo rocks.
While it is easy to recognize the large easterly faults along the margins
of the Karoo outcrop they could not be detected, although probably
present, in the extensive central outcrop of basalts.
DYKES
The whole area is traversed by dykes of doleritic rocks and remarkably
few sills which intrude all the Karoo rocks and adjacent gneisses. Their
composition and textures show that they are related to the basalts (some
possibly having been feeders to fissure eruptions) and were intruded
into cool or cold wall-rocks at no great depth. That they came from
a deep magma chamber is shown by the largely digested inclusions
of Precambrian gneisses seen in the dykes at 7 km north of Massabie's
Drift and on the road 3 km south-east of Maribeha Hill (Tuli map).
Only a few of the dykes have been displaced by the northerly faults.
Along the southern part of the mapped area from the Shashi River
to about 30 km east of the main road from Beitbridge to Fort Victoria,
there is a swarm of branching dykes which generally have gently curved
strikes trending a little to the north or south of east and nearly vertical
dips to both north and south. Their length varies from a few metres
to over 20 km; most are long. Northerly dykes are rare but one, over
20 km long, extends north-eastwards from the south-west corner of
Sentinel Ranch to just south of Gawana Dam (Mazunga map).
LINEAMENTS
A remarkable number of lineaments that are visible on the air photographs could not be identified on the ground. Like the dolerite dykes
and the faults, the majority trend nearly eastwards and only a few in
directions between north-east and north-west. They probably represent
faults, dykes and, particularly in the Tuli National Area joints which
are not exposed but are marked by a change in soil or vegetation. The
breccia on the hillock 4,5 km north-east of Massabie's Drift may be a
diatreme on a lineament which extends north-westwards from the
Limpopo River.
Micro-shears are abundant in some of the Karoo sedimentary rocks
(Fig. 2), particularly the Forest Sandstone, and often secondary silicification has produced veinlets in them so that on some weathered outcrops they form prominences over 300 mm high though most are only
a few millimetres high. The micro-shears are usually 2 to 5 mm wide
with some over 100 mm across. Their slickensided surfaces show both
horizontal and vertical displacements of a few centimetres. In an outcrop
there is usually a dominant trend with a divergence of under 30 degrees.
The majority have an easterly strike similar to that of the dolerite dykes
and lineaments, though some have a northerly strike. Where displacements occur the offsets are mainly in an easterly direction.
In an exposure of the Forest Sandstone 4,5 km south of the homestead
\ on Joco Ranch (Gongwe map) a micro-shear cuts nodules which are
considered to have been formed during the eruption of the basalt lavas.
The micro-shears therefore appear to have been formed after the
extrusion of the basalts.
o
5 0 mm (approx .)
I
FIG. 2. Micra-tau Its in silty sandstone trom the Forest Sandstone 2 km northeast ot Lupako Hill, Jopempi Block. Beitbridge District.
JOINTS
The frequency of occurrence of joints in the mapped area is shown
on figure 3 with those in the Karoo sedimentary rocks nearest the
centre and those in the basalts on the outside. By far the majority of
joints strike between 000° and 030· and fewest between 330° and
000°. However, in the sedimentary rocks the joints show a maximum
between 300° and 330· and minimum between 330° and 000· and in
SUPERFICIAL DEPOSITS
54
SUPERFICIAL DEPOSITS
the basaltic rocks a maximum between 000· and 030 with none between
330· and 000 Because only a small number of readings were taken
over a very large area it is unsafe to draw conclusions from these
figures.
0
0
•
N.
1--.
W.'
I
1····· ······· ·······...........-· ··;···-·:· ,
... '........ ... __ .1
E.
FIG. 3. Joint directions in the Karoo rocks of the Mozunga area.
SUPERFICIAL DEPOSITS
An extension of the banded ironstone rubble, described by Robertson
(1973, p. 152) as littering the slopes of Mount Towla, .the Jopempi ridge
and the surrounding country to the north of the Mazunga map area,
continues southwards as far as Mazunga and the access road to
Cawood's Mazunga Ranch at about 9 km from the main road. A similar
deposit was found on a hillock 100 m south of the airstrip on Bishopstone Estates, some 40 km south of its nearest possible source.
The unconsolidated rubble bed, which is under one metre thick. is
composed of rounded fragments of banded ironstone and much vein
quartz partly cemented with carbonate. Most fragments are 100 to 150
mm long and the largest 250 mm long. The deposit on the access road
is about 220 feet (67 m) and that on the hillock 100 feet (30 m) above
the level of the Umzingwane River.
Alluvium occurs along the banks of all the main rivers and their
larger tributaries, and is best developed in the valleys of the Umzingwane
55
and Bubye rivers. Only a narrow strip of alluvium extends along the
north bank of the Shashi River until below the Tuli confiuence. Here
there are the Bili, Jalunganga and Shashi Irrigation Schemes extending
up the valleys of minor tributaries. Only narrow discontinuous strips
of alluvium occur along the Hwali and Tuli rivers. though near the
confluence of the Tuli and the Shashi, the Kongoni and Sebasa
Irrigation Schemes are on localized wider patches. To the east the
Hwali and Pazhi rivers, tributaries of the Limpopo, have discontinuous
strips of alluvium up to about 1 km wide. In contrast to this there
is continuous alluvium up to 1,5 km wide along both the Urnzingwane
and Bubye rivers and their main tributaries. Large cut-off meanders
filled with alluvium were seen in the Umtshabezi River near its confluence with the Umzingwane, and around basalt islands in the
Umzingwane itself. About 2,5 km south-east of Baemura School, at the
confluence of the Malukula and Umzingwane rivers, there are exposures'
of alluvium 9 to 12 m thick. The sand and gravel in the beds of the
major rivers probably reaches great thicknesses, and in the Umzingwane
may be as much as 20 m thick.
I
Earth movements, some of them comparatively recent, are thought
to be partly responsible for the formation of alluvium, as for example
in the upper Tongwe River north of Gongwe Poort and 7,5 km west
of Van der Merwe's Pool in the Tuli National Area.
Alongside the major rivers the alluvium is composed of gravel and
sands, but along the smaller rivers it is finer grained sand which is
better sorted and darker in colour. Sometimes the alluvium is dirty white
and calcareous, as for example that north of Gongwe Poort which is
light grey and very dusty when dry.
Calcrete is widely distributed throughout the mapped area and is
usually less than one or two metres thick. It occurs as light grey,
rounded concretions that are best developed in the black clayey soil
overlying some basalts, particularly the more mafic varieties such as
the Mabuli limburgitic basalts. Along the watercourses in these areas it
is often seen to contain fragments of basalt and ferricrete. A large
patch of calcrete occurs 3 km W.S.W. of the Lamulas homestead on
Jopempi Block (Gongwe map).
Ferricrete grains up to 10 mm across occur mainly in the sandy soils.
They are quite widely distributed, but never form large deposits.
56
ECONOMIC GEOLOGY
COAL
ECONOMIC GEOLOGY
CoAL
CLAYS
Probably the only outcrop of coal in the mapped area was discovered
in the east bank of the Umzingwane River near Morgan's Hill in about
1895 by De Gruyter. His and other interests in the area were acquired
in 1896 by Consolidated Gold Fields of South Africa Ltd. and transferred to a subsidiary Bulawayo company, Tuli Consolidated Coal
Fields Ltd., the following year. F. M. Watson had visited the Umzingwane area in 1895 and near Morgan's Hill measured the section already
given under the Fulton's Drift Mudstones. In mid-1896 R. Sneddon
(1896) collected a sample of coal (Table VI) which had a S.G. of 1,36.
He records that about 1,6 km east of the outcrop in the river, a shaft
had been sunk to 11 m in what became known as the Umzingwane
Coalfield (Fig. 4).
Although poorly exposed the Fulton's Drift Mudstones have a large
outcrop area and could contain clays of value to the refractory and
ceramic industries. Four samples were collected and the partial analyses
given in Table V are similar to clays being investigated in the Karoo
rocks to the east, around Chivumbura and Chiredzi, but no physical or
firing tests have been done on them.
In 1970 samples of a pale grey clay from the Mtetengwe T.T.L.
about 1 km south-east of Fulton's Drift were analysed for Mr. W. A.
Ferguson of Benfer Estate, and the Mac Nic Syndicate was formed to
produce flint clay for refractory bricks. However, title to the deposit
could not be obtained.
Five samples from excavations in an area 1,5 km east of Mtetengwe
Store, near the bridge over the Mtetengwe River on the Bulawayo
road, had alumina contents of 26,9 to 37,2 per cent. and silica contents
of between 49,0 and 59,5 per cent.
TABLE V
PARTIAL ANALYSES OF FULTON'S DRIFT MUDSTONES
Lab. No, .
73 /11
%
73 /12
%
73 /13
%
73 /14
%
Na,O.
K,O
14,6
48,0
33,8
1,3
0,3
0,5
0,2
0,7
18,4
46,8
32,0
1,1
0,2
0,3
0,1
0,5
10,3
53,8
32,8
0,8
0,3
0,5
0,3
0,7
12,3
53,8
32,0
0,8
0,2
0,3
0,1
0,7
TOTALS
99,4
99,4
99,5
100,2
Ign. loss
SiO,
AI,O, .
Fe,O"
MgO .
Cao
Analyst: B. J. Radc1yffe.
Localities:
73/11 About 2 km south-east of Gwawe Dam, Jopempi Block, Beitbridge District
(Gongwe map).
73/12 Old shaft, 4 km north of the confluence of the Gushu and Limpopo rivers,
Nottingham Ranch, Beitbridge District (Mazunga map).
73 / 13 Pit, 1 km north of Lupako Dip on track to the Bubye River, Jopempi Block.
Beitbridge District (Gongwe map).
73/14 Northern slope of hill, 300 m west of Lupako Dip, Jopempi Block, Beitbridge
District (Gongwe map).
57
The railway line from Cape Town reached Bulawayo in 1897 and it
was proposed to extend it northwards to Salisbury with a line going
from near Gwelo down the Sanyati valley and across the Zambezi River
near Kariba to the Congo. Another line from Bulawayo was to serve
the rapidly developing and promising gold mines between Gwanda and
West Nicholson, continue down the east bank of the Umzingwane River.
and cross the Limpopo River to join the South African railway system
in the northern Transvaal. This line would cross the Umzingwane Coalfield which could not only supply the locomotives but also the Gwanda
mines and Matabeleland.
The Tuli Consolidated Coal Fields Ltd. had a capital of £15 000 and
held the rights to 24697 ha (55 630 acres) in the Umzingwane and
Singwesi coalfields (RS.A. Co. 1900, p. 364 and 1902, pp. 413-4). The
principal shareholders included the Matabeleland Gold Reefs and
Estates Co. Ltd. (RSA Co. 1899, pp. 81-9; 1900, pp. 218-9 and 1902.
pp. 231-9), Rhodesia Ltd. (RSA Co. 1899, pp. 133-6. and 1902, p. 331)
and Rhodesia Exploration and Development Co. Ltd. (RS.A. Co. 1900.
pp. 265-88 and 1902, pp. 311-21). The consulting engineer to it. the
Gwanda Railway Syndicate and several other coal exploration companies was A. I. C. Molyneux.
Work began in 1896, and by 1897 the outcrop in the Umzingwane
River had been trenched and No. 1 shaft sunk 1,6 km east of it. During
1898 five shafts measuring 4 feet by 6 feet had been sunk, and, on
account of water problems, hand drilling was started in April, 1899.
No. 1 hole had just been completed when, because of the outbreak of
war in South Africa, the company had to withdraw from the area and
ECONOMIC GEOLOGY
COAL
its wagons, animals, etc., were requisitioned by the Imperial Forces at
Fort Tull. Work was not resumed until April, 1901. Three holes were
drilled and by the end of the year it was stated that a 96,5 cm seam of
good bituminous coal extending over 450 ha (1 000 acres) of the
Urnzingwane Coalfield would yield 9241 tonnes per hectare (3800 tons
per acre).
Borehole 1, 2 and 3 were on the west side of the Urnzingwane River
and borehole 4 on the east side (Fig. 4). Borehole 1 is said to have
found 107 cm coal at 12,2 m and 12 cm coal at 22,9 m, and borehole
2 found 122 cm coal at 17,1 m and 122 cm coal at 22 m (D in
Table VI). Borehole 3 passed through 91 cm coal at 16,8 m (E in
Table VI) and five seams 18 to 30 cm thick between it and 34,5 m
depth. Borehole 4 found a seam 91 cm thick.
58
~ ~)jc"t.
C 6ord'lOI,
....E.
~L
., - . .
""
.~
FIG. 4.
Sketch map of the Umzingwane, Singwesi and Letengwe Coalfields (1904).
A considerable amount of work was done on the Umzingwane Coalfield between 1896 and 1904 (Fig. 4). The outcrop in the east bank of
the Umzingwane River was exposed in a trench 6,1 m long, 1,2 m wide
and 0,6 m deep and was sampled (Table VI). To the east of it five shafts
were sunk. No. 1 shaft was sunk to 22,1 m depth without encountering
much water. It passed through 13,5 m of dark shale, 46 cm coal, 46 cm
shale, 91 cm good bituminous coal and 150 cm shale and sandstone to
the top of the gneisses. Drives were made in the coal for 30,5 north-east,
30,5 m east and 4,6 m south-west of the shaft. No. 2 shaft was sunk to
the north-east and after going through 16,3 m of brown shale was
stopped in hard sandstone at 19,5 m depth. No. 3 shaft also went to
32 m depth without finding coal. No. 4 shaft reached a depth of 21,3 m
in the gneisses. It passed through 16,7 m of dark shale, 46 cm coal,
56 cm shale and 112 cm coal (sample F in Table VI) which was driven
on for 9,8 m north-east and 7,9 m north-west. No. 5 or C shaft was
sunk in the east of the area to 22,9 m depth and passed through 2,4 m
clay, 2,1 m sandstone, 0,3 m shale, a 2,7 m sheet of dolerite and 15,4 m
of drab shale. It is said that a borehole found a 107 cm coal seam at
34,4 m below the floor of No. 5 shaft.
59
The Singwesi Coalfield (Fig. 4) lies to the east of the Umzingwane
Coalfield on both sides of the Mazunga River, which was also called the
Singwesi, Imgwesi and Palm River. By 1902 coal had been proved over
120 ha (300 acres) and it was thought to connect under the overlying
Red Beds with the Urnzingwane Coalfield (B.S.A. Co., 1902, p. 416).
Later, in 1903, Molyneux reported that a seam 110 cm thick, which had
been metamorphosed by dolerite to a semi-anthracite, extended over
1.3 km'.
Five shafts and three boreholes were completed on the Singwesi Coalfield. One shaft was sunk for 11 m in grey shale. Boreholes 18 and 28
were sunk to 23,8 and 31,7 m in dark clay with no coal. In another
borehole, a seam 107 cm thick was found at 25,6 m and a thinner seam
at 44,5 m depth. Two analyses (G and H in Table VI), which are
identical, are said to have come from separate localities in a shaft and
a borehole.
The Massabi Coalfield on Nottingham Ranch lies to the north of the
Limpopo River and to the west of the Gushu River (Fig. 5). An area
of 405 ha (1 000 acres), Special Grant No. 23, was acquired by the
Gwanda Railway Syndicate in which the Matabeleland Gold Reefs and
Estates Co. Ltd. was a large shareholder (B.S.A. Co. 1899, pages
81-89; 1900, pages 218-219; 1902, pages 231-239 and 311-321). Shaft
sinking began in 1899 but, because of the South African war, all work
ceased between November, 1899, and April, 1901. Five shafts were sunk
.and in No. 2 shaft four seams, 51, 132, 38 and 122 cm thick were
found. The coal (I in Table VI) was said to be a good quality bituminous
coal which caked well and formed an ash which did not clinker.
Molyneux (1903) estimated that two seams of good coal, 120 and 180
cm thick, had been proved over an area of 40 km' .
Little is known about the Letengwe or Mashanga Coalfield around the
confluence of the Mtetengwe and Tongwe rivers, which earlier were
called the Letetengwe and Letombwe rivers (Fig. 4). This area of 40 ha
(100 acres) to the east of the Singwesi Coalfield was acquired in 1900
60
COAL
ECONOMIC GEOLOGY
61
TABLE VI
PROXIMATE ANALYSES OF COALS, 1896-1902
A
Sample
~
.,..
eI
A
B
C
No.3
...",
~No.5
D
......~
}t'
E
F
G
0;..-
I
........
H
.......
,~,.,.,,~
A
~ ..~~~NO.2'
~~,
~
",." .
~C
~o.1 ~No.4
--
o
1 MILE
I
I
FIG. 5. Sketch map of the Massabi Coalfield (1904) showing shafts.
by the Gwanda Railway Syndicate on the advice of A. J. C. Molyneux
who said that it was on the line of the proposed Gwanda railway. At
least two shafts and two boreholes were sunk. Shaft No. 1 is said
to have found 30 cm of shaly coal, probably at 7,2 m, and No. 2
shaft which was over 9 m deep found no coal; nor did the two boreholes. Later the area was included in Special Grant No. 15.
By 1902 the colliery at Wankie was being rapidly developed and the
line of the northern railway was changed from Gwelo to Kariba, to
BuIawayo to Victoria Falls. When the railway reached Wankie in 1903
the colliery was ready to produce. The Gwanda and West Nicholson
gold mines did not reach expectations and the railway line to them from
Bulawayo was not completed until 1905. It still has not been extended
beyond West Nicholson. In this changed situation, interest in the Tuli
Coalfield died, and the holding companies were liquidated.
M
V.M.
F.C.
Ash
%
%
%
%
C.V.
MJlkg
2,32
2,07
1,77
0,68
1,49
1,02
0,96
0,96
1,17
38,36
23,27
21,31
19,98
23,38
22,55
9,33
9,33
35,58
54,06
57,95
61,86
53,48
56,57
52,37
70,56
70,56
54,54
15,26
16,71
15,06
25,86
18,56
24,01
19,15
19,15
8,71
27,68
29,54
24,42
28,14
23,49
23,96
23,96
31,40
Analyst: Samples B-1, G. A. Pingstone, Bulawayo.
Localities:
A Outcrop in the Umzingwane River (Sneddon, 1896).
B Urnzingwane Coalfield, 107 cm (42 inches) seam, April, 1899.
D Urnzingwane Coalfield, 122 cm (48 inches) seam in Borehole No. 2, January, 1902.
E Urnzingwane Coalfield, Borehole No. 3, January, 1902.
F Urnzingwane Coalfield, Shaft No. 4, January, 1902.
G Singwesi Coalfield, 107 cm (42 inches) seam affected by dolerite sheet. From
25,6 m down shaft.
H Singwesi Coalfield, 107 cm (42 inches) seam at 24,4 m in Borehole No. 3, January
1902.
I Massabi Coalfield, two 122 cm (48 inches) seams, November, 1901.
The rights of the Tuli Consolidated Coal Fields Ltd. to the two parts
of Special Grant No. 15, the Umzingwane and Singwesi Coalfields, and
the Letengwe Coalfield were transferred on 16th April, 1924, to the Gold
Fields Rhodesian Development Co. Ltd. and are still held. Special Grant
No. 23 over the Massabi Coalfield, held by the Gwanda Railway Syndicate since 1901, was changed to Special Grant No. 30 on 24th November,
1903. It was transferred to CopthaU's Stores Ltd. on 27th April, 1914,
and was terminated on 31st December, 1972. The greater part of the
Tuli Coalfield which consisted of the Massabi, Umzingwane, Singwesi
and Letengwe coalfields, is now covered by reserved areas.
In 1950 consideration was being given to a possible future shortage
of coal in Rhodesia and the extension of the railway line from West
Nicholson to Beitbridge, past Special Grant No. 15 in which Gold
Fields Rhod. Dev. Co. Ltd. had a 33t per cent. interest, Charter Trust
and Agency Ltd. 31 per cent., Willoughbys Conso!. Co. Ltd. 25 per
cent. and the London and Rhodesian Mining and Land Co. Ltd. an 11
62
ECONOMIC GEOLOGY
per cent. interest. In 1951 an area of 184 km 2 (71 square miles) of the
grant was mapped geologically, on a scale of 1 : 20000 (Mehliss, 1951)
and, as it was discovered that the potentially coal-bearing ground
extended well to the west and that Molyneux's idea of localized coal
basins possibly was wrong. Gold Fields Rhod. Dev. Co. Ltd. applied
for and was granted Exclusive Prospecting Order No. 19 from May,
1953 to December, 1961, over an area of 259 km 2 (100 square miles)
(Morrison, 1974). A total of $29 540 was spent on road making, mapping
on a scale of 1 : 50000 and 1 800 m of diamond drilling in 11 boreholes
(Pelletier, 1955). After the expiry of the order the company was allowed
to retain rights over part of the coalfields area.
Messina (Rhodesia) Development Co. Ltd. was granted Exclusive
Prospecting Order No. 393 from 24th January, 1971, to 11th January,
1973, over 1 295 km 2 (500 square miles) from near the Limpopo River
on Sentinel Ranch N.N.W. to the Dendele T.T.L. During the period
of tenure, the company spent $14558 and sank two boreholes, MRDl
and 2 (Johnson, 1973; Morrison, 1975). The information, particularly
the drilling logs and coal analyses, given in various reports supplied by
the two companies, has been extensively used in this Short Report.
The Karoo strata in the mapped area is a synclinal structure which
dips inwards at less than 10 degrees and plunges very flatly west-southwestwards from east of the main road from Beitbridge to Fort Victoria
for 165 km to the Shashi River. It continues beyond into South Africa
and Botswana. It is 50 to 55 km wide northwards. The structure is
dominated by numerous long east-north-easterly faults which rapidly
displace the Karoo rocks downwards towards the centre as a trough-like
structure. As a result, the basalts outcrop over practically the whole of
the mapped area and the sedimentary rocks lying under them form small
discontinuous outcrops, never more than 10 km wide, along the margins
of the Karoo outcrop, mainly near the eastern end where they outcrop
for 50 km along the Bubye River and for around 30 km south-west
of the road to Fort Victoria. Along much of the northern and southern
margins, the basalts or upper sediments are down-faulted against the
Precambrian gneisses. The lower sediments, including the coal-bearing
Fulton's Drift Mudstones, are exposed in a strip on the southern margin
for about 30 km west and 15 km east of where the Umzingwane River
crosses it. This strip, the Tuli Coalfield, is the only portion of the mapped
area that has been partly explored for coal. Here, the downward
sequence of Karoo sedimentary rocks under the basalts appears to be 80
to 100 m of Forest Sandstone, 300 m of Red Beds,S to 10 m Escarpment
COAL
63
Grit, around 100 m of Fulton's Drift Mudstones, with under 10 m of
Basal Beds lying unconformably on gneisses. The total thickness of sedimentary rocks is of the order of 500 m, but the thickness of the basalts
is not known.
Although the Fulton's Drift Mudstones probably occur throughout
the area of Karoo rocks, the extent, number, quality and behaviour
of their coal horizons are quite unknown. The coal horizons probably
lie at depths in excess of 500 m, and possibly even of 1 000 m, over
the greater part of the Karoo area so are beyond economic mining
depths. Mining in the shallower parts will be complicated by the
comparatively intense faulting and the presence of very large dykes
and sheets of late-Karoo dolerites. The temperature gradient will
probably be high in the Karoo shales which have a thermal conductivity
of around 5,7 x 10.3 cal/cm/secrC (Mossop and Gafner, 1951). At
Messina, about 50 km S.E., the thermal gradient is fairly high at 0,269 x
1O-3 °C/cm in Precambrian gneissic rocks which have an average thermal
conductivity of 5,1 x 10-3 cal/cm/sec/oC (Diment and Weaver, 1964).
The permanent water level appears to be at 9 to 18 m. The rocks of
the Fulton's Drift Mudstones are almost entirely impervious shales
with hardly any porous sandstones, so that large quantities of underground water are likely to be encountered only in the vicinity of faults
and bodies of dolerite. Methane is probably present and, like the water,
may be trapped in large volumes under pressure near the faults and
dolerites. There is probably much burnt coal alongside the igneous
intrusions, but there is no information on the quantities to be expected.
The coal seams are probably weathered to a depth of 3 to 10 m and
recognizable outcrops are extremely rare, even in the riverbeds. In the
Tuli Coalfield the roof and floor of the coal seams is almost invariably
shale which, in the early tunnelling at a depth of about 12 m, seems
to have stood well.
In the early exploration of the Umzingwane Coalfield (Fig. 4), a lower
46 cm of coal not far above the gneisses, was found separated by
around 50 cm of shale from an upper 90 to 100 cm of coal. Analyses,
probably of picked or cleaned samples, are given in Table VI. In the
adjacent Singwesi Coalfield (Fig. 4) coal thicknesses of 41 to 107 cm
were recorded and in the Massabi Coalfield to the west (Fig. 5) four
seams of 51, 132, 38 and 122 cm, again not far above the gneisses, were
found in shafts. The compositions of two of the seams is given in
Table VI.
64
ECONOMIC GEOLOGY
COAL
Twelve boreholes were sunk in the area of Exclusive Prospecting
Order No. 19 and two in the area of E.P.O. No. 393, but five (T5, T2,
TI, TIO and MRD2) were stopped in dolerite before reaching coal and
TO and TO redriIIed may be in a fault zone. The approximate positions
of these boreholes in the Tuli Coalfield are shown on the Mazunga
area map, their generalized logs are given in Table ITI, and analyses
of the coals in Tables VII and VIII. It should be noted that there are
minor differences in the depths given in Tables ITI and in Tables vn
and VIII for what are obviously the same occurences'
Five boreholes (from west to east MRDI. 1'7, TI, T4 and T6) were
all drilled on Nottingham Ranch, the western section of Pelletier (1955).
Here the Fulton's Drift Mudstones of the Massabi Coalfield strike
northwards from the Limpopo River for 6 km to a large E.N.E. fault
which downthrows to the north. Boreholes 1'7, TI and T4 started in
the Escarpment Grit on the south side of the fault. On the north side
of the fault borehole MRDl started in the basaIts and T6 in the Red
Beds at 361 and 97 m respectively above the top of the Fulton's Drift
Mudstones.
In borehole MRDl the base of the bottom coal is at 422,1 m about
34 m above the gneisses. The sequence upwards is 170 cm coal
TABLE VD
PROXIMATE ANALYSES OF COALS FROM E.P.O. No. 19 AND
E.P.O. No. 393
BOREHOLE
TO
REDRILLED
From
metres
Width
To
metres mm
19,05
23,27
24,69
33,58
34,42
44,45
44,91
45,24
45,62
46,25
48,44
55,78
58,52
58,95
59,63
60,22
19,30
24,23
25,30
33,96
34,70
44,88
45,24
45,62
46,08
46,58
48,82
56,18
58,95
59,63
60,22
60,86
254
450
609
382
279
432
330
381
465
330
382
407
431
680
590
635
M
V.M.
F.C.
Ash
S
%
%
%
%
%
C.V.
1,80
1,92
1,92
1,93
1,58
1,37
1,40
1,37
1,79
1,38
0,90
1,35
1,63
1,91
1,97
1,68
22,80
20,38
24,68
18,03
25,58
22,31
27,64
23,63
26,89
26,52
29,50
23,94
18,57
16,19
15,99
13,02
36,90
35,10
46,40
30,74
38,33
30,62
47,35
43,78
44,90
40,06
16,36
30,86
17,76
29,77
34,37
25,20
38,42
42,60
27,00
49,30
34,51
45,70
23,61
31,22
26,42
32,04
53,24
43,85
62,04
52,13
47,67
60,10
3,82
2,97
1,73
1,84
2,47
2,90
1,49
1,26
1,71
4,60
5,30
0,88
0,27
0,29
0,35
0,34
20,0
18,4
24,1
15,8
21,5
16,9
25,3
22,0
23,2
21,3
11,5
15,7
7,7
12,8
13,6
8,5
S.T.
TABLE VII (continued)
BOREHOLE
From
metres
28,04
28,45
28,93
29,54
35,86
36,14
36,73
37,01
45,11
45,47
46,28
46,51
46,84
47,52
I
BOREHOLE
3t
It
It
2
T3
To
Width
metres mm
28,29
28,70
29,16
29,95
36,14
36,60
37,01
37,34
45,47
45,59
46,43
46,84
47,42
47,80
M
V.M.
F.e.
Ash
%
%
%
S
%
%
e.V.
S.T.
253
254
229
407
279
457
280
330
356
127
152
330
585
280
1,98
2,11
1,65
1,99
1,71
1,82
1,87
1,81
1,34
1,36
1,64
1,44
1,23
1,07
28,54
30,04
31,04
29,86
29,96
34,02
34,34
27,93
30,69
33,64
33,84
32,32
36,18
28,02
35,94
40,95
41,97
39,95
37,75
46,30
47,09
37,84
28,91
35,90
48,02
41,62
33,71
24,63
33,54
26,90
25,34
28,20
30,58
17,86
16,70
32,42
39,06
29,10
16,50
24,62
28,88
46,28
1,06
0,84
7,02
1,37
4,02
0,93
2,87
2,85
1,24
2,69
2,57
0,68
0,80
2,63
21,9
24,2
25,1
23,9
22,8
27,6
28,0
22,3
18,2
22,0
28,0
24,7
22,4
15,1
1
It
2t
1
It
2t
3
It
S.T.
2t
3t
3
2
T4
From
metres
To
metres
Width
mm
M
V.M.
F.e.
Ash
S
%
%
%
%
%
C.V.
22,17
24,26
24,84
25,73
25,88
32,41
32,89
33,40
38,61
39,24
39,47
39,90
40,26
45,44
22,48
24,61
25,30
25,88
26,09
32,74
33,20
33,53
38,91
39,47
39,83
40,26
40,39
45,57
304
350
457
152
204
330
305
127
305
229
355
356
127
128
2,45
2,25
1,76
2,09
2,09
1,93
1,69
1,92
1,27
1,29
1,30
1,13
1,31
0,77
29,02
26,06
24,52
21,85
27,80
26,36
29,04
25,20
25,43
20,14
23,93
23,45
15,49
31,46
39,63
39,33
38,19
32,30
39,17
47,ll
51,41
43,88
51,22
42,22
51,79
51,04
24,52
20,15
28,90
32,36
35,53
43,76
30,94
24,60
17,86
29,00
22,08
36,35
22,98
24,38
58,68
47,62
1,84
1,95
7,76
5,82
2,03
1,68
1,95
1,61
1,70
0,67
0,77
0,66
0,51
0,36
22,S
21,4
21,0
17,7
21,9
24,9
27,7
23,2
26,1
20,7
25,2
25,2
12,0
13,1
BOREHOLE
1
65
T7
From
metres
To
metres
Width
mm
M
V.M.
F.e.
Ash
S
%
%
%
%
%
e.V.
S.T.
50,11
52,60
53,03
53,75
60,22
60,78
61,19
61,49
62,03
50,50
53,03
53,44
54,13
60,68
61,19
61,49
61,70
62,20
381
432
406
381
457
407
304
203
177
1,61
1,55
1,47
1,61
1,46
1,45
1,43
1,56
1,04
32,19
27,09
32,35
27,43
32,31
31,69
34,70
27,30
26,86
42,38
35,40
40,95
35,12
42,81
44,31
46,54
38,14
32,90
23,82
35,96
25,23
35,84
23,42
22,55
17,33
33,00
39,20
1,73
1,28
2,31
2,63
1,28
1,66
1,26
1,76
8,04
25,6
21,1
25,1
21,0
25,6
25,8
27,9
22,0
19,7
3
3
3
It
3t
4
3t
2t
3
COAL
ECONOMIC GEOLOGY
66
TABLE VII (continued)
~
<Ii
BoREHOLE T8
To
metres
Width
mm
M
V.M.
F.e.
Ash
S
%
%
%
%
%
C.V.
168,86
170,00
173,21
175,21
175,69
176,33
176,91
179,83
180,42
183,79
184,50
185,09
192,00
194,18
194,46
194,89
195,60
196,24
196,70
197,41
169,19
170,20
173,91
175,44
176,17
176,61
177,55
180,24
180,52
184,07
184,89
185,37
192,48
194,31
194,66
195,35
196,14
196,57
197,18
198,12
330
210
700
229
480
280
635
406
102
280
381
279
483
127
202
457
554
330
483
7\0
1,23
I,ll
0,84
1,23
1,33
1,02
1,13
1,02
0,84
1,02
0,87
1,00
0,69
0,65
0,69
0,64
0,92
0,70
0,68
0,63
17,22
20,75
22,17
19,03
19,98
23,70
23,84
23,24
24,66
24,46
23,27
22,70
21,79
23,57
20,53
25,00
16,39
24,57
19,99
19,77
31,39
37,50
38,39
35,24
33,23
40,44
43,45
44,56
40,80
51,74
46,10
45,04
43,28
50,34
42,60
52,66
42,57
46,27
39,09
35,26
50,16
40,64
38,60
44,50
45,46
34,84
31,58
31,18
33,70
22,78
29,76
31,26
34,24
25,44
36,18
21,70
40,12
28,46
40,24
44,34
8,28
2,27
9,95
3,72
2,02
2,10
2,29
5,35
8,55
1,09
1,52
1,15
1,42
1,28
0,72
4,60
0,82
0,84
2,26
2,89
15,9
20,0
20,5
18,3
17,9
21,9
23,3
24,0
23,1
27,2
24,6
23,7
22,5
25,8
21,4
17,1
19,3
23,7
19,4
17,0
>
U
S.T.
00
"1-
<Ii
.c~
to .(.
~
0
Z
0g.;
4t
It
5
1
It
It
~
::E
Width
mm
M
%
V.M.
%
F.C.
%
Ash
%
~
~
~ '"..l
w «
0
U
e.V.
S.G.
406,1
406,7
408,1
411,2
413,0
413,9
414,7
422,1
425,5
1000
600
400
400
600
900
500
1 700
900
1,74
1,89
2,13
1,40
2,13
1,86
2,04
1,60
1,23
26,06
20,33
16,73
27,71
14,49
20,13
15,32
23,48
20,57
18,07
33,87
47,19
8,14
54,20
30,42
52,53
13,98
17,71
54,13
43,91
33,95
62,75
29,18
47,59
30,11
60,94
60,49
1,32
0,96
1,30
4,40
2,26
4,94
0,72
3,74
0,54
33,0
27,0
2,33
2,23
1,97
2,68
1,93
2,23
1,96
2,58
2,55
Analysts: Research Centre, Messina (Transvaal) Development Co. Ltd., S. Africa.
V.M. = Volatile maller; loss in 7 minutes at 925 0 C
M = Moisture loss at 105 0 C
F.e. = Fixed carbon [lOO-(M+V.M.+ash»)
Ash = Incombustible residue at 200 0 C
1 MJ /kg = 430 B.Th. U./lb.
S = Sulphur
e. V. = Calorific value in MJ /kg
S.G. = Specific gravity
S.T. = Swelling test
= 239 k ca1/kg = 0,443 1b./lb.
0::
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410,8
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Analysts: Gold Fields Laboratory, Johannesburg.
From
metres
;::.,...,..r!;I~~~'j;
-",
From
metres
BoREHOLE
67
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o
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68
ECONOMIC GEOLOGY
(49.9 per cent. ash). 540 cm black mudstone. 430 cm coal and shale.
250 cm black shale. and 620 cm coal and shale. the top being at 402.0 m
depth. The upper coal and shale horizons consist of thin seams and
lenses of coal. cut by perpendicular needles of aragonite. in carbonaceous
shales with blebs of pyrite.
The base of the coal in borehole T7 is at 61.59 m. about 11.3 m
above the gneisses. and the sequence upwards is 83 cm coal (ash 33.0.
17.3 and 22.6 per cent.). 10 cm shale. 44 cm coal (ash 23,4 per cent.).
609 cm dark mudstone. 38 cm coal (ash 35.8 and 25.2 per cent.). 39
cm mudstone. 76 cm coal (ash 36.0 per cent). 210 cm mudstone. and
38 cm coal (ash 23.8 per cent.). the top being at 50.12 m depth.
In borehole T3 the bottom of the coal is at 47.83 m and 17.17 m
above the gneiss. Upwards the sequence is 59 cm coal (46.3 per cent.
ash). 10 cm shale. 66 cm coal (ash 28.9 and 24.6 per cent.). 7 cm
carbonaceous shale. 16 cm coal (ash 16.5 per cent). 68 cm carbonaceous
shale. 46 cm coal (ash 29.1 and 39,1 per cent.). 38 cm black shale with
coal streaks. 10 cm coal. 99 cm carbonaceous shale. 5 cm coal. 135 cm
black shale. 10 cm coal, 3 cm grit. 437 cm black shale. 40 cm sandstone.
64 cm coal (ash 32,4 and 16.7 per cent.). 12 cm black shale. 46 cm coal
(ash 17.9 and 30.6 per cent.). 633 cm black shale. 35 cm coal (ash 28.2
per cent.). 33 cm shale. 21 cm coal (ash 25.3 per cent.). 28 cm shale.
50 cm coal (ash 27.0 and 33.5 per cent.). 21 cm shale. and 7 cm coal.
the top being at 27.74 m depth.
In borehole T4 the floor of the bottom coal is at 46.28 m and 15.09
m above the gneisses. The sequence upwards is 10 cm coal. 51 cm
black shale. 25 cm coal (ash 47.6 per cent.). 21 cm carbonaceous shale.
12 cm coal. 16 cm carbonaceous shale. and 28 cm coal. All this coal
is dull and shaly. Above it is 439 cm shale. 107 cm coal (ash 24,4. 23.0
and 36,4 per cent.). 28 cm shale with coal. 10 cm coal (ash 22.1 per
cent.). 521 cm shale and sandstone. 10 cm coal (ash 29 per cent.). 22 cm
shale. 23 cm coal (ash 17.9 per cent.). 21 cm carbonaceous shale. 33
cm coal (ash 24.6 per cent.). 685 cm shale. 29 cm coal (ash 30.9 per
cent). 17 cm dull coal (ash 43.7 per cent.). 26 cm black shale. 17 cm
coal (ash 35.5 per cent.). 18 cm shale. 33 cm bright and dull coal (ash
32,4 per cent.). 31 cm shale. 8 cm coal. 144 cm shale. 16 cm coal (ash
28.9 per cent). 2 cm carbonaceous shale. 8 cm coal (ash 28.9 per cent).
the top being at 22.17 m depth.
In borehole T6 the coal between 170.06 and 176.02 m is recorded as
burnt coal and the coal above 167,49 m as shaly coal; none was
COAL
69
analysed. Starting at 176.02 m depth and 19.36 m above the gneisses.
the upward sequence was 46 cm coal, 40 cm shale. 15 cm coal. 16 cm
shale. 35 cm coal. 122 cm shale. 15 cm coal. 77 cm shale. 30 cm coal.
475 cm shale (167,49 m depth). 10 cm coal. 66 cm fireclay. 8 cm coal.
102 cm fireclay. 38 cm coal. 10 cm fireclay. 79 cm coal. 38 cm fireclay.
30 cm coal, 23 cm fireclay. 8 cm coal. 63 cm fireclay. and 15 cm coal
with the top at 162.59 m depth.
Borehole T8. which lies on the east bank of the Umzingwane River.
14t km E.N.E. of borehole T6 and north of the Umzingwane Coalfield workings. gives quite a different succession. The floor of the bottom
coal is at 198,12 m depth and 30,78 m above the gneisses. The lowermost
coal horizon of the other boreholes appears to have been replaced by
sandstone. The sequence up from 198,12 m is 23 cm of dull shaly coal.
28 cm shale. 28 cm dull shaly coal. 48 cm bright coal. 10 cm shale.
10 cm coal. 18 cm shale. 28 cm coal (ash 22.8 per cent.). 332 cm shale,
15 cm coal. 28 cm shale. 53 cm coal (ash 21.7 per cent.). 8 cm shale.
13 cm coal, 7 cm shale. 8 cm coal, 13 cm shale. 15 cm coal, 88 cm
shale. 18 cm coal. 64 cm shale. 18 cm coal (ash 34.2 per cent.). 7 cm
shale. 23 cm coal (ash 34.2 per cent.). 663 cm shale. 28 cm coal (ash
31.3 per cent.). 8 cm shale. 55 cm coal (ash 29.8 per cent.). 11 cm shale.
10 cm coal. 18 cm shale. 28 cm coal (ash 22.8 per cent.). 332 cm shale.
8 cm coal (ash 33.7 per cent.). 15 cm shale. 41 cm coal (ash 31,2 per
cent.). 234 cm shale. 65 cm coal and calcite (ash 31,6 per cent.). 23 cm
carbonaceous shale, 28 cm coal and calcite (ash· 34.8 per cent.). 16 cm
carbonaceous shale. 48 cm coal and calcite (ash 45, 5 per cent.). 20 cm
carbonaceous shale. 29 cm coal and calcite (ash 35,2 and 38,4 per cent.).
129 cm shale. 35 cm coal and calcite. 338 cm fireclay. 15 cm coal (ash
40,6 per cent.). 87 cm shale. 30 cm coal (ash 50.2 per cent.). 46 cm
shale. 43 cm coal, 41 cm shale, 25 cm coal, 56 cm shale. 30 cm dull
coal, 92 cm shale. 2 cm coal. 51 cm fireclay. and 3 cm coal at 165 m
depth.
After the deposition of some 15 to 30 m of shale on either the Basal
Beds or the gneisses. the first coal horizon was deposited in the Fulton's
Drift Mudstones and the succeeding 15 to 20 m of strata consists of
grey to carbonaceous shales and mudstones containing two to four coal
horizons and very localized sheets of sandstone. The coal layers vary
from a few centimetres to around a metre in thickness. and are separated
by varying amounts of shale. The absence of roots and stems of large
plants. the absence of true fireclays or seat-earths. and the high and
variable ash contents within the coal seams suggests that the coals were
ECONOMIC GEOLOGY
DIASPORE
formed from the debris of small plants mixed with contemporaneous
detrital clay or silt. Argillaceous sedimentation appears to have been
continuous to form the shales and mud stones. With the addition of
organic debris the shales passed gradationally through black and
carbonaceous shales to become coals when the amount of organic matter
was very large. This appears to have been caused by rhythmical subsidence which controlled the position of the shoreline, the depth of the
water, and the amount of organic matter added. Neither macroscopic
nor microscopic studies of the coals have been made.
failure if their properties are not taken into account in design life and
structure of tbe road. According to Weinnert (1963) rocks rich in
plagioc1ase and ferromagnesian minerals, if incipiently weathered, are
suspect, particularly in areas of high rainfall. This is very much a
generalization because there is probably no better road or building
aggregate than a fine-grained dolerite from the point of view of strength,
durability and resistance to weathering. This rock is composed entirely
of calcic plagioclase and pyroxene, but its texture is the controlling
factor. However, in the area in question the Tuli basalts would probably
be superior to the Mabuli limburgites and the Chandabalini porphyritic
varieties.
70
From the meagre amount of information available it would be rash at
this stage to draw conclusions about the quality, quantity or potential
of the coal in the area; much more information is needed.
CoNSTRUCfION MATERIALS
The channels of the larger rivers in Mazunga area have deep
pockets of sand suitable for most building and construction purposes.
Generally the sands are quite coarse and contain very little mica or
few basalt fragments. The sands are composed of quartz and lesser
amounts of feldspar. The degree of rounding varies considerably, but
the quartz sands are always more angular than the basalt-derived sands,
despite shorter distance of transport of the latter. These contain
weathered and rounded particles of basalt, often coated with a film of
clay which renders them quite unsuitable as building material. Riverbank sands are much finer grained and contain more mica and organic
matter than the channel sands.
Sand.
Road Metal. The Karoo sedimentary rocks are too soft and friable to
provide a source of road metal except where they have been thermally
indurated by overlying basalt flows and adjacent dolerite intrusions, or
where they have been subjected to silicification in fault and shear-zones.
A large quarry has been established in metamorphosed Forest Sandstone, 3 km for the main road along the access road to J oco Ranch.
This is one of the very few suitable localities in the area as outcrops
of silicified, so-called "quartzitic rock", are rare. In its normal state
the Forest Sandstone is a very soft and friable rock with a low crushing
strength.
Of the Karoo rocks, the basalts and dolerites afford the most suitable
materials, and deposits are numerous and extensive. The vesicular
basalts and those containing an appreciable quantity of olivine are less
reliable than others and are more likely to result in base and sub-base
71
Building Stone. Supplies of stone for building purposes are not a matter
of importance in an area of such low population density and development potential. Practically any variety of rock of pleasing appearance,
not excessively weathered, and more importantly with rectangular jointing structure for ease of quarrying, could be utilized. Quarries could be
established at some of the outcrops of indurated and silicified Forest
Sandstone and small blocks of fine-grained reddish sandstone could be
won from the exposures of the Red Beds Formation on Nottingham
and Sentinel Ranches.
DIASPORE
During construction of the new main road from Beitbridge to Fort
Victoria, two most unusual occurrences of diaspore, predominantly in
the form of almost perfectly spherical nodules, were discovered on
surface and in gravel excavations at points approximately 20 and 30
kilometres respectively south-west of the Bubye River bridge. The
general profile revealed in the pits is a 45 cm cover of red-brown sandy
loam with quartz fragments and rare diaspore balls, followed by 30 cm
of diaspore-bearing gravel composed of sub-rounded fragments of
indurated Karoo fireclay together with dolerite, quartz and granitic
gneiss and lumps of calcrete. Primitive artefacts also occur in this gravel
bed suggesting a PIeistocene age for its deposition. Below this level the
calcrete content increases rapidly to bedrock of decomposed dolerite,
granitic gneiss and amphibolite at a depth of 1,5 m. The diaspore content
of the gravel layer was visually estimated to vary between one and 10
per cent. (Morrison, 1970).
The source, and mode of formation particularly, of the diaspore was
puzzling although it seemed reasonable to assume that the nodules were
in some way associated with the alumina-rich Karoo shales of the
ECONOMIC GEOLOGY
GOLD
area and had either grown as concretions in these shales or were the
result of some metamorphic effect on them. Confirmation of this view
is provided by Morrison (1973) who was afforded the opportunity, at
Messina Mine, of examining specimens of Karoo shale from eastern
Botswana which contain casts and diaspore nodules paler in colour but
otherwise identical in all respects to those in the gravels near the Bubye
River. During the course of the present survey it was further substantiated by the discovery of diaspore balls in situ in borrow pits alongside the old road some 5 km north of Bubye River bridge. Here there is
a tendency to latitudinal parting in the balls which presumably
reflects original bedding in the Karoo-age, Fulton's Drift Mudstones, in
which they occur. At this locality there is a flat-dipping dolerite intrusion
which has metamorphosed the mudstones and apparently by some
obscure process, patchily raised the alumina content from some 40 per
cent., which is the average for the mud stones, to as much as 80 per
cent. in the nodules themselves.
Most nodules in the gravel deposits are almost perfectly spherical in
shape and range from 1 to 5 cm in diameter. The irregular ones may be
grotesquely formed or have a muffin or sausage shape, and a type of
dumb-bell form with two spheroids joined by a bar of similar diameter
to the spheroids themselves has been noted. At the locality north of the
river biscuit -like discs up to 7 cm in diameter are present. All are
characteristically heavy (S.G. 3,11-3,26), very hard, tough, extremely finegrained and with a greasy lustre. They have a patina less than 1 mm
deep, in various shades of drab-brown and internally are somewhat
paler in colour. The brown patina seems to have been acquired during
transport as the nodules in situ are pale grey, even paler than the
encompassing mudstones. A cut surface sometimes exhibits faint irregular
veining but no suggestion of radial or concentric texture is discernible.
TABLE IX
72
A microscope slide (slide 21420) is not very revealing. It consists
essentially of slender diaspore prisms averaging 0,015 mm in length.
These usually occur clustered and with a completely random orientation.
The matrix is too fine-grained for positive determination. It is sensibly
isotropic and lowly refracting; in parts it resembles chalcedony but
usually merges imperceptibly into the several lenticular voids in the
slide and the mounting medium at the edges. Judging by chemical
analyses that have been made, this matrix must consist of some other
form of hydrated aluminium oxide. In addition, a small amount of
opaque ore minerals is scattered throughout the slide and there are
patches in which calcite may be recognized.
73
ANALYSES OF DIASPORE NODULES
Sample
2
%
%
3
%
4
%
5
%
SiO,
AI,O, .
Fe,O, .
TiO, .
Cao .
MgO .
Na,O.
K,O . . . .
Ign. loss at 640° C
8,70
72,40
0,50
1,60
1,60
0,01
0,08
0,13
14,60
2,54
80,02
0,02
1,00
1,00
0,17
0,Q7
0,06
14,50
1,26
80,22
1,20
1,40
0,85
0,84
0,06
0,06
14,70
4,60
77,20
0,40
1,60
1,47
1,00
0,07
0,09
14,10
1,72
77,90
1,10
1,20
4,00
0,77
0,05
0,07
13,60
TOTALS
99,62
99,38
100,59
100,53
100,41
Calcined
material
%
3,0
90,0
1,4
1,9
Information regarding the gravel deposits was brought to the attention
of Vereeniging Refractories Limited in South Africa, and the nodules
were determined by X-ray fluorescence to be composed essentially of
diaspore. In 1970 two Exclusive Prospecting Orders were granted to a
subsidiary of this company who examined the area and concluded that
diaspore constituted 2 per cent. by weight of the gravels on average. The
company pegged two blocks of claims covering the better sections before
revocation of the orders in 1971. The results of analyses done in the
laboratories at Vereeniging are given in Table IX.
GOLD
In the north-eastern part of Jopempi Block there is a high, easttrending ridge of Karoo basalts and dykes and, where the Tongwe
River cuts through it, is Gong's Poort (now Gongwe Poort) which was
once the site of a police camp on a very old road from Fort Tuli to
Fort Victoria. A rumour arose that the reddish-coloured basalts contained gold and in 1912 R. M. Nairn of Bulawayo sent Llewellyn Davis
and a party to sample the then deserted area. They collected about
200 samples of "the most likely rock" and these were assayed. It is
said that one contained 103 g/t gold (60 dwt. per ton), about 12 carried
more than 8,6 g/t (5 dwt. per ton), and the majority no gold at all.
Probably around 1923, the Gold Fields Rhod. Dev. Co. Ltd. sampled
the ridge and found no gold in the samples panned. Seven samples
were assayed and contained a trace or no gold.
74
ECONOMIC GEOLOGY
A Major Miller raised the issue once more in 1939, and a party of
three Government Mining Engineers, Messrs. F. Elliott, E. A. Richardson and Bennett, thoroughly examined the area. They collected 163
samples which were assayed. One contained 0,3 g/t gold, two contained
0,2 g/t gold, 14 contained 0,09 g/t gold and 146 a trace or no gold.
A. M. Macgregor (1939) visited them in August, 1939, and reported
that the ridge consisted of successive flows of basalts with amygdaloidal
layers at the top and bottom of each flow. The lavas were cut by dolerite
dykes, some of which contained interstitial quartz, and the poort was
due to a cross-fault.
MAGNESITE
On top of a small rise about four kilometres north of the confluence
of the Shashi and Limpopo rivers lumps of white and pale grey
magnesite are strewn over an area measuring approximately 1000 by.
200 m ·and underlain by Mabuli limburgitic basalt. The lumps often
have a rough mammillary form. Some are very pure white in colour
and resemble a tightly packed cauliflower stripped of its leaves. They
vary considerably in size, the larger ones measuring about 30 cm in
diameter and weighing about 5 kg.
Similar occurrences, usually containing smaller lumps and granules
of magnesite up to 5 cm in diameter, were noted at several other
localities on the basalts. On the slopes down to the Bubye River, in the
vicinity of Lupako Dip, magnesite admixed with calcrete is thought
to have been derived from the nearby limburgite.
The genesis of this magnesite is not clearly understood although it
is almost certainly directly associated with ultramafic Karoo lava flows
or penecontemporaneous ultramafic differentiates in sill-like intrusions
into them. It probably occurs primarily as a network of ramifying
veinlets in the lavas or sills. In the Karoo basalt areas magnesite
nodules can usually be distinguished from surface calcrete by virtue
of their being much whiter, harder, heavier and more compact.
WATER
In a hot, arid area such as the Beitbridge District the presence of
underground water supplies is of great importance. The average annual
rainfall is only 380 mm and for nine months of the year the average
daily maximum temperature exceeds 30°C. In consequence the
evaporation rate is very high and successful storage of run-off water
WATER
75
presents a major problem, particularly in the basalt terrain which
occupies the greater part of the mapped area. For one reason or another
a large number of both earth-fill gravity dams and concrete structures
built on basalt have failed or have been breached during floods. Those
that have not, hold water only for a month or two after the cessation
of the rains. Dams founded on the Karoo sediments are more successful,
but sites are limited. The Gwawe and Tongwe dams are two examples
which retained water supplies, even after the 1971-72 droughts.
Boreholes in the basalts have not provided good supplies of water.
Thirty-two such holes drilled in the Tribal Trust Lands to depths
varying between 30 m and 70 m, but mainly of the order of 60 m, have
yields of between 0,08 and 2,53 litres per second (60 and 2000 g.p.h.).
They average about 0,67 litres per second (550 g.p.h.) and are adequate
for domestic purposes and the watering of a small number of stock, but
for no other uses. It is probable that at greater depths in the basalt,
especially at the contact between basalt and underlying sediments, there
may be very large artesian aquifers. Their location and exploitation,
however, will have to await a detailed geophysical investigation of the
structural pattern of the Karoo-rock basin.
At present the only supplies adequate for crop irrigation are those that
have been obtained by drilling to bedrock through the sands and gravels
in the alluvial flats along the major rivers. A programme instituted early
TABLE X
WATER BOREHOLES IN ALLUVIUM
Locality
River
Property
Shashi .
Maramani T.T.L.
Limpopo
Sentinel Ranch
Umzingwane .
Nottingham Ranch
Bishopstone
.
Gem Ranch. .
Mazunga Ranch .
Grid re!
Depth
metres
Yield
litres per sec.
390515
396500
580466
635849
580466
717507
840725
840725
837725
877673
881686
880672
865690
28,5
27,8
25,0
20,5
23,0
20,0
26,0
24,4
25,5
21,5
21,0
23,0
22,5
117,0
114,0
36,0
114,0
48,9
42,6
114,0
85,2
114,0
114,0
39,8
92,3
142,0
ECONOMIC GEOLOGY
REFERENCES
in 1973 by the Provincial Water Engineer, Matabeleland, gave the
satisfactory results detailed in Table X.
REFERENCES
76
Six irrigation schemes in the area, three along the Shashi River, two
along the Tuli River, and one on the banks of the Umzingwane River
are based on this type of water supply and have an annual aggregate
consumption of 6,6 million cubic metres.
77
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78
79