Z-W2tJO? J/~~ l 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 explana­ tion 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 0 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. 3 2 PREVIOUS GEOLOGICAL WORK PREVIOUS GEOLOGICAL WORK

The area, which is the northern continuation of King's (1951, 1952) The basaltic lavas, which covered most of the area, extended east­ Transvaal Lowveld, is a flat one sloping southwards to the Limpopo wards from Botswana past Fort Tuli to the Bubye River. Sedimentary River with a few hills and east-trending ridges. The highest point is rocks outcropped only in the coalfield area near the Umzingwane River Gongwe Hill at 2 450 feet (747 m) elevation in the north-east, and the where they lay unconformably on the metamorphic rocks. All these lowest point is on the Limpopo River in the south at 1 650 feet (493 m). rocks were intruded and metamorphosed by dykes. The coalfield The area is crossed by four major rivers which meander through covered an area of several square miles and contained a 3!-foot seam alluvium-bordered valleys to join the Limpopo. The Shashi, Tuli and of semi-bituminous coal. The only fossil found in the whole area Umzingwane flow S.S.E. and the Bubye E.S.E. Their tributaries flow (Molyneux, 1901) came from the coal seams near Morgan's Hill, and east or west, and a few of the larger ones southwards. Two probable was described by E. A. Arber (Molyneux, 1903, p. 689) as a pith cast examples of river piracy were seen, the Mutshilashokwe from the of a calamite resembling Calamites approximaJa, Brongiart. Umzingwane and the stream 4,5 km S.S.E. of the Shashi Dam. MelIor (1905) wrote that although glacial beds of the Dwyka Series The interfluves between the Shashi and Umzingwane rivers and had been found in the northern Transvaal, none had been found in between the Umzingwane and Mtetengwe rivers slope at about 18 feet Rhodesia. However, Mennell (1905) identified them among specimens per mile (3,5 m per km), and the interfluve between the Mtetengwe and collected by Molyneux. Later (1906, 1907, 1908 and 1910) he wrote Bubye rivers at about 9,6 feet per mile (2,9 m per km) southwards, that the Tuli Coalfield, though not connected with the Karoo rocks showing the flatness of the mapped area. north-west of Bulawayo, resembled them. The coalfield contained basal Dwyka conglomerates, shales and sandstones, a coal-bearing series, PREVIOUS GEOLOGICAL WORK basalt lavas. and later intrusions which were often glomeroporphyritic, A three-foot seam of coal was discovered outcropping in the east never ophitic. and sometimes contained olivine. bank of the Umzingwane River near Morgan's Hill in about 1895 by Zealley (1910) reported that there was a 3!-foot seam of semi­ De Gruyter, and the area became known as the Tuli Coalfield. De bituminous coal, and Molyneux (1909 and 1911) included the coalfield Gruyter's and other coal claims were acquired by Consolidated Gold strata in a correlation of the Karoo rocks of Rhodesia, South Africa Fields of South Africa Ltd. in 1896 and transferred in 1897 to a and Gondwanaland. Maufe. in generalized accounts (1913, 1919. 1924 Bulawayo company, Tuli Consolidated Coal Fields Ltd. (Mehliss, 1951). and 1929), stated that little fieldwork had been done in the Tuli Coal­ The exploratory work was reported upon by F. M. Watson in 1896, field since 1903, but it had been found that discontinuous outcrops of R. Sneddon (1896), by W. H. Chandler in 1897 and R. T. Southwood Karoo rocks extended as far east from it as the Sabi River. Dwyka (1898). The company's holdings were visited in April, 1899, by A. J. C. beds appeared to be limited to the Tuli Coalfield (1919). He gave Molyneux who reported that the coal occurred in three separate, dis­ (1913) the following sequence of strata in the Tuli Coalfield. which was connected basins (a) the Western or Umsingwane basin, (b) the Central estimated to have reserves of about 45 million tons of coal: or Mungesi basin and (c) the Eastern or Letitengwe basin (Mehliss, 1951). By 1903 several boreholes and shafts had been sunk, but as the Tuli Basalts Samkoto Beds=Forest Sandstone railway had by then reached Wankie Colliery interest in the Tuli Coal­ Coal Series field waned. Basal Beds A. J. C. Molyneux (1903) gave the following succession in ascending Anonymous writers (1920 and 1921) gave accounts of the Coalfield order for the strata in the coalfield: and its resources. Renewed interest in the potential of the coalfield Tuli Lavas resulted in Mehliss (1951) examining and reporting to the Gold Fields Umsingwani coal-bearing beds of South Africa Ltd. on their Special Grant No. 15 area, and the Unconformity Samkoto veined sands tones company exploring the coalfield under Exclusive Prospecting Order Uncontormity No. 19 (PelIetier. 1955, and Morrison. 1974). Their work and that of Metamorphic rocks Messina (Rhodesia) Development Co. Ltd. on E.P.O. No. 393 (Johnson, Gneiss and granite KAROO SYSTEM s 4 PRECAMBRIAN ROCKS

1973) provided a great deal of new information on the geology and the Jopempi and Dijana Hills. In the latter. about 7 km south of Tongwe coal resources of the area. Swift (1961) had stated that there were two Dam, there are occurrences of asbestos and magnesite. workable seams in the coalfield with extractable coal reserves of about Quartzite forms a ridge in the Precambrian rocks on River Ranch 40 million tons. and that the coalfield resembled the Malilongwe and and Benfer Estate near the Umzingwane River on the south side of the Sabi coalfields (Swift et al .• 1953) to the east. Karoo rocks. and calc-silicate granulites form hills about 1 km to the east. Garnets are abundant in the sandy shallow watercourses in this The geology of the area is referred to in papers on Karoo stratigraphy area and also about 2 km to the west of Gwawe Dam. by Tyndale-Biscoe (1949) and Bond (1952. 1955 and 1967) and on The Precambrian rocks around the Towla and Jopempi hills to the palaeontology by Lacey (1961) and Bond (1973). The Karoo igneous north of the area of the Mazunga map have been described by Robertson rocks of what is known as the Nuanetsi Igneous Province (mainly adjacent to the mapped area) have been described and discussed by (1973). Tyndale-Biscoe (1949). Worst (1962). Cox et al. (1965). Cox et al. (1967). Jamieson (1966) and Macdonald (1967). KAROO SYSTEM Robertson (1967). with a party of schoolboys. conducted a very INTRODUCTION successful study of the Karoo rocks along the north bank of the The rocks of the Karoo System are widely distributed in southern Limpopo River and the south-west corner of Sentinel Ranch where Africa but in Rhodesia are confined to down-faulted blocks in the they discovered and excavated reptilian fossil remains. Limpopo and Zambezi valleys. From the Zambezi valley Karoo rocks Macgregor (1939) reported upon an abortive search for an alleged extend in tongues across the Rhodesian Craton to near Bulawayo. gold occurrence in the Karoo lavas and dykes that form the ridge at Gwelo and Felixburg. Gokwe and Que Que, and the Charter District Gong's (Gongwe) Poort. 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 PRECAMBRIAN ROCKS from this part of the Craton. Only those outcrops in the Limpopo The mapped area lies in a portion of the North Marginal Zone of Mobile Belt remain. the Precambrian Limpopo Mobile Belt which consists of intensely In the drainage area of the Zambezi River where they have been deformed rocks. mainly gneisses that have been raised to the upper extensively studied. the stratigraphy and palaeontology of the Karoo amphibolite and granulite facies of regional metamorphism (Robertson. System are quite well known. and the beds have been correlated with 1973). The Mesozoic Karoo rocks have been deposited on them with the standard succession of the Karoo System in South Africa (Bond. a major unconformity and subsequently down-faulted in most places. 1952. 1955. 1967 and 1973; Lightfoot. 1929; Maufe. 1913. 1919. 1924. against the Precambrian rocks. As this reconnaissance survey was only 1929; Mennell. 1910; Molyneux. 1901. 1903. 1909. 1911; Swift, 1961; concerned with the Karoo strata. little attention was paid to the Pre­ Worst. 1962). The Karoo System in the Limpopo valley is less well cambrian rocks which are not differentiated on the three geological maps. known and. in the Muzunga area. only in connexion with the search for coal (Johnson. 1973; Maufe. 1924. 1929; Mehliss. 1951; MenneII. The Precambrian rocks surrounding the Karoo outcrop are pre­ 1905; Molyneux. 1903. 1909; Pelletier. 1955; Robertson. 1967; Zealley. dominantly quartzo-feldspathic gneisses. Epidote-rich gneisses abound 1910). In this account the stratigraphic nomenclature used is largely that in the northern part of the Tuli map area. particularly a few kilometres of Mehliss (1951). During the last quarter of a century more work has south of Hwali Store. Unakite. a colourful pink and green variety used been done to the east between the main road from Beitbridge to Fort as a gemstone, has been produced from the Bertie Claims. Banded iron­ Victoria and the Sabi River (Cox et al. 1965; Cox et al. 1967; Morrison. stones form the cores of ridges such as Gwawe. Chamalaya and the 1974; Swift et al. 1953; Tyndale-Biscoe. 1949). However. the strati- northern extension of Nyongwe. and bodies of serpentinite outcrop in 6 KAROO SYSTEM INTRODUCl'ION 7

graphy and palaeontology are not sufficiently well known to correlate form large, intermittent and generally fault-bounded outcrops around the the strata with the Karoo rocks of the Zambezi basin and South Africa. margins of the Karoo rocks of the Mazunga area. They probably cover The pre-Karoo landscape over much of Rhodesia appears to have an area of about 160 km long and 40 to 50 km wide. They are essen­ been an extremely flat plain from which isolated hills and ridges, mainly tially an argillaceous series of grey, brown and black carbonaceous Precambrian banded ironstones, quartzites and serpentinites, rose shales and mud stones which tend to become slightly more arenaceous abruptly. and reddish or purplish in colour in the upper part. The few sandstones and rare pebble beds present are discontinuous. The coal horizons The Karoo basin of the Limpopo Valley was probably bounded on suggest cyclic sedimentation with a cold to temperate climate in a its northern side by a watershed . that extended from south of the shallow-water to swampy basin that was subsiding rhythmically. The Matopos Hills, through Bala Bala, south of Selukwe, east of Felixburg source of the sediments was the Precambrian rocks and probably Dwyka to near Rusape, then eastwards to south of Inyanga and southwards deposits. Fossil plant remains have been identified as Glossopteris, through the Melsetter and Chipinga Districts to the southern end of Phyllotheca, and Calamites which suggest an Ecca or Permain age for the Umkondo Group. The floor of the basin was metamorphosed these beds. Precambrian rocks belonging to the Basement Schists, cratonic granites and gneisses, the highly deformed granulite facies gneisses of the The Escarpment Grit appears to be present throughout the Mazunga Limpopo Mobile Belt, and a small part of the Great Dyke. Between area and to lie conformably between the Fulton's Drift Mudstones and the Precambrian rocks and the Karoo rocks there is a major uncon­ the Red Beds. It consists of 1 to 15 m of coarse-grained sandstone formity. The Karoo rocks found in the Mazunga area, which extend in with scattered pebbles up to 30 mm long. and occasionally pebble time from the glacial deposits of the Permian or Carboniferous through layers or beds. Generally the sandstone is white to pale grey in colour, a temperate climate to an arid sand desert climate with volcanic activity but may be pink or greenish and contain clayey bands. Often it becomes in the early Jurassic period, have been subdivided as follows: finer grained upwards. The sand grains and pebbles in it all appear to have originated from the Precambrian rocks. No fossil remains have Doleritic dykes and siUs Intrusive contact been found. Basalt lavas with intercalated Mbaka Beds Minor unconformity The Escarpment Grit of the Zambezi basin marks the end of a period "Forest Sandstone" of extensive and widespread erosion of the Lower Karoo rocks, but Red Beds "Escarpment Grit" the Escarpment Grit of the Limpopo basin appears to mark only changes Fulton's Drift Mudstones in sedimentation accompanied by uplift of the source area, more rapid Minor unconformity sinking of the basin floor and, as is shown by the introduction of red Basal Beds Major unconformity colouration, the beginning of a change of climate. The Basal Beds lie on the deeply eroded Precambrian granulite facies The Red Beds outcrop in fault-bounded areas around the margins gneisses and other metamorphic rocks of the Limpopo Mobile Belt. As of the Karoo rocks throughout the area and consist of brightly coloured they very rarely outcrop little is known about them or their relationship red, purple. green and white siltstones that contain calcareous nodules to the mudstones and shales which everywhere overlie them. They appear along with some beds of fine-grained sands tones containing scattered to be discontinuous erosional relics of various types of glacial deposits, small pebbles, and a very few lenses of siliceous limestone. Cross-bedding generally ill-sorted conglomerates and sandstones, up to about 25 m and scour-and-fill structures are common though some beds are structure­ thick, of the Dwyka Series which had covered the whole of Rhodesia, less. In places there are fragments of desiccated and sun-cracked mud­ and served as a source of material for the later sedimentary rocks. stone. Only some of the larger sand grains are spherical and often there is an abundance of minute sharp and extremely angular, grains and The Fulton's Drift Mudstones are 50 to over 120 m thick and lie splinters of quartz. These and the clay minerals may have come from unconformably on either the Basal Beds or the Precambrian rocks. They Dwyka rocks; the rest came from Precambrian rocks. By this time the BASAL BEDS 9 8 KAROO SYSTEM

BASAL BEDS lake must have expanded northwards considerably and either had joined. or was about to join. that of the Zambezi basin. The Basal Beds of the Karoo System are poorly exposed and were only seen in a few scattered and isolated localities. These outcrops are In these typical semi-arid red beds the remains of the large reptilies too small to be shown on the geological maps. The beds. which all appear Massospondylus carina/us and Gryponyx africanus have been found. to be of glacial origin. lie with marked unconformity on the Precambrian They are characteristic fossils of the Upper Forest Sandstone of the gneisses. and are probably unconformably overlain or pass into the beds Zambezi basin and the Triassic Red Beds of South Africa (Bond. 1973. of the Fulton's Drift Mudstones. Outcrops of tiIlite of the Dwyka Series page 73). seem to be absent in the area. The Forest Sandstone lies conformably on the Red Beds and probably Mehliss (1951) found three poor exposures of the Basal Beds near the covers much the same area. It consists of about 80 to 100 m of fine- to Umzingwane River in the vicinity of Morgan's Hill and Fulton's Drift. medium-grained sandstone that is pinkish-white when fresh but develops Here. a coarse conglomerate. about 1.2 m thick. consisted of sub-angular a surficial. brownish-red skin. The lower. more calcareous portion. was fragments of Precambrian gneisses. banded ironstone and quartz, probably deposited under water but the upper part shows dune bedding randomly scattered without any traces of sorting or bedding. in a pale and was probably formed as large dunes in an arid, hot. sand desert. No shaly matrix. It lay unconformably on the Precambrian gneisses. but fossils have been found. upwards passed without a break into a dark gritty shale and then the coaly shales of the Fulton's Drift Mudstones. The Karoo Basalts lie unconformably on the dune-covered surface of the Forest Sandstone. They are the most widely exposed Karoo rocks in Poor exposures of a congIomeratic bed occur on the road 2 km the Mazunga area. but their thickness is not known. They were probably S.S.W. of Lutope Dip on Jopempi Block (Gongwe map) and in places erupted from fissures. though one possible crater. 600 m in diameter. it has been indurated by dolerite dykes. The drab-brown coloured rock occurs in the Machuchuta T.T.L. Provisionally they have been subdivided shows light grey spotting on fresh surfaces and. though poorly sorted. upwards into (a) olivine-bearing rocks (b) aphanitic basalts (c) a crude bedding structure. It is composed of a heterogeneous mixture of porphyritic basalts containing large feldspars. (d) vesicular basalts and angular fragments of Precambrian gneisses and quartz in a fine-grained (e) the more normal basalts. Petrologically they belong to the Nuanetsi matrix. the larger fragments. which are under 20 mm long. being sub- Igneous Province and are different from the more uniform basalts of the rounded. Zambezi basin. Similar rocks. also metamorphosed in places by dykes. outcrop in the The Mbaka Beds are scattered. comparatively narrow and discon­ watercourses 1.5 km S.S.E. of Gwawe Hill on Jopempi Block (Gongwe tinuous beds of fine-grained to very fine-grained sandstones that vary in map) and the following section was measured there: colour from drab or reddish-brown to light red. Occasionally they are Thickness finely bedded or cross-bedded. in metres A period of dilation followed the extrusion of the basalts. and it was Thinly bedded sandstones with 150 mm clay pellet layer at base...... 1.0 marked by the last igneous event in the area. the intrusion of numerous. Conglomerate of pebbles less than 60 mm across in easterly. sub-ophitic dolerite dykes and fewer sills. coarse-grained sandy matrix of gneiss. quartz and feldspar . . . . . 0.15 Drab-coloured coarse gritty sandstone 2.0 Subsequently there was uplift and extensive erosion along the Limpopo Coarse pebbly conglomerate 1.0 Mobile Belt before the subsidence which permitted Cretaceous and Base not seen possibly Tertiary marine invasions into the Limpopo valIey. Uplift. Several of the boreholes drilled for coal on Nottingham Ranch. erosion and climatic changes followed. resulting in the current landforms River Ranch and in the Mtetengwe Tribal Trust Land passed through and superficial deposits. 2 10 KAROO SYSTEM FULTON'S DRIFT MUDSTONES 11 l

what are probably Basal Beds lying below the Fulton's Drift Mud­ Precambrian quartz containing a few minute inclusions and bubbles; stones and on the gneisses. The approximate positions of these bore­ the rest are a few clouded grains of sericitized feldspar. Some clasts have holes are given on the southern part of the Mazunga map and their a rim, about 0,02 mm thick, where matrix minerals have penetrated logs, which are not always very clear, are given in Table ill. into them. The microcrystalline, brownish matrix is a felt of micaceous In borehole MRDI Basal Beds 24 m thick are recorded (Johnson, minerals, a small amount of angular quartz grains, and a few porphyro­ 1973) between 432 and 456 m depth. They are a structureless, dirty blastic tufts of mica up to 0,Dl mm long. Prof. G. Bond (personal greenish-grey sandstone that is poorly sorted and contains scattered communication). was of the opinion that the rock was probably a patches of grit, angular pebbles of green to khaki-coloured shale, and glacial outwash gravel deposited in a high-energy environment as the occasionally of quartz. Downwards, the sandstone passes gradationally ratio of clasts to matrix was too high for a tillite. The rock had been into greenish-brown gneiss. A specimen taken at 432,4 m is described slightly metamorphosed, and there had been some reaction between· the as a structureless, blotchy, light grey rock with 45 to 50 per cent. of clasts and the matrix. The feldspar grains must have been fresh when quartz grains, 0,05 to 5,0 mm across, which decreased in size down­ they were deposited, otherwise they would have been comminuted. wards, 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 FULTON'S DRIFr MUOSTONES minerals. Calcite, which formed about 5 to 10 per cent. of the rock, The Fulton's Drift Mudstones are a typical Karoo coal measures replaces the clay in areas up to 10 mm diameter. sequence of grey to black argillaceous rocks, coal-bearing horizons and a few discontinuous lenticular sandstone beds. They outcrop sporadically In borehole TI, 9,4 m of unbedded brownish-white mudstone was around the periphery of the main Karoo area and have been named found on top of the gneisses. It became coarser grained downwards and after their most important outcrop which is around Fulton's Drift across contained much visible chiastolite. In borehole T3 a bed of very fine­ the lower Umzingwane River on River Ranch. The beds have a total grained whitish mud stone with a taIcy feel contained boulders of thickness of about 50 to over 120 m and rest unconformably on either gneiss and schists. It is 9,4 m thick, lies on the gneisses, and is covered the Precambrian gneisses or the Basal Beds of glacial origin. They are by a medium- to coarse-grained sandstone. A bed 9,3 m thick in bore­ covered by a widespread arenaceous horizon, named the Escarpment hole T4, lying on top of the gneisses, was logged as tillite. It consisted Grit, with a variable degree of unconformity. In them Robertson (1967) of sub-angular to rounded boulders in a mixed matrix of sand and clay_ found plant impressions identified as Glossopteris and Phyllotheca and In borehole T6 the gneisses were covered by 2 m of very dark grey­ Mehliss (1951) found Thinnfeldia (Dicroidium) in the upper part only. green, spotted and sheared mud stones, and on it was 1,4 m of con­ glomerate composed of shale fragments up to 6 mm long. A bed of The coal horizons are dealt with more fully in the section on medium-grained grey feldspathic sandstone with marly shale in its Economic Geology. upper part, lay on the gneisses in borehole T8. It was 13,7 m thick and lithology may belong to the Basal Beds, but has been included in the Fulton's Argillaceous rocks, which have been named mudstones and shales by Drift Mudstones. different geologists (probably subjectively) in the borehole logs, are the predominant rocks. Most are light to dark grey or brownish in Petrography colour, but towards the Escarpment Grit at the top of the sequence Slides 21354* and 21355 of the conglomeratic rock from 2 km S.S.W. they frequently develop a red or purple tint. In places the shales are of Lutope Dip on Jopempi Block consist mainly of angUlar, often black and carbonaceous, and are distinctly fissile, whereas the mudstones ragged edged, clasts measuring from less than 0,05 mm in length tend to break into rectangular blocks. Laterally the shales, may become scattered through a very fine-grained matrix. Only rarely are the clasts more sandy and pass into grey to brown siltstones. Thin beds of white in contact with each other. The majority are strained grains of to light grey sandstones occur sporadically through the sequence, and often are either shaly or somewhat pebbly. Conglomerate beds com­ -Numbers refer to slides in the Geological Survey slide collection, Salisbury. posed of white quartz pebbles are thin and rare. 12 KAROO SYS1EM FULTON'S DRIFT MUDSTONES 13

Near the dolerite dykes the argillaceous rocks have been indurated On Nottingham Ranch, near the confluence of the Gushu and and metamorphosed, occasionally to hard, chert-like, lydianite. Limpopo rivers, the following sequence of upper mudstones was ., measured below the Escarpment Grit. Distribution and Field Relations Thicknell in The Fulton's Drift Mudstones form flat, low-lying country with very melre~ few exposures and are best known from the coal exploration and bore­ Khaki or buff-coloUIed mudstone 8,55 Grey mudstone...... 0,92 holes in the outcrop area around the drift and the nearby Morgan's Red siltstone blotched grey. Iron-rich and sandy in Hill. Their soil-covered surfaces are frequently littered with quartz 0,05 places . . . 0,20 pebbles from the Escarpment Grit, and fragments of ferricrete, hard Light grey flint clay . Dark grey mudstone ...... 12,40 brown ferruginous sandstone, or metamorphosed shale near dolerite Black, red blotched, iron-stained carbonaceous shale 0,92 dykes. Dark purple to red, ferruginized siltstone 1,53 Grey mudstone . The Mudstones occur in fault-bounded, isolated outcrops, generally Base not seen of small extent, all around the margins of the Karoo rocks. In the Around Fulton's Drift, on River Ranch and in the Mtetengwe T.T.L.. area of the Mazunga map they outcrop along the southern margin at excavations were made to expose the coal seams, and, later. mapping (a) on the east side of the Mpandi River where, on Nottingham Ranch, and diamond drilling were done '(Mehliss, 1951; Pelletier, 1955 and they lie unconformably on the Precambrian gneisses and in a strip Johnson, 1973). The approximate positions of the boreholes are shown extending for 6,5 km northwards from the Limpopo River, dipping on the southern part of the Mazunga map and the generalized logs flatly westwards under the Escarpment Grit, (b) on both sides of the are given in Table Ill. Umzingwane River in an area about 6 km long and 1,5 km wide on In 1895 F. M. Wilson recorded the following section in the almost River Ranch and the Mtetengwe T.T.L. where they have been prospected horizontal lower shales on the west side of Morgan's Hill (Mehliss, for coal, and (c) small, fault-bounded areas in the Mtetengwe T.T.L. 1951). Above it was over 21 m of sandstone which was pinkish and on both sides of the Mtetengwe River near its confluence with the pebbly at the base, white and gritty in the IDiddle and reddish at the Mazunga River. top. Thickness In the area covered by the Gongwe map the Fulton's Drift Mudstones in outcrop on both the north and east margins of the Karoo rocks. They metres outcrop for 16 km west and 9 km east of where the Bubye River bends Soft shale 9,14 Ironstone. 0,15 from south to east. Their outcrop, which is about 1 km wide, is much Shale . 0,61 disturbed by faults trending between E.S.E. and north-east. Along much Ironstone. 0,15 1,52 of its length the beds lie on Precambrian gneisses and dip flatly south­ Black shale Ironstone. 0,30 wards under the Escarpment Grit. Farther east there is a narrow out­ Shale . . 3,66 Coal and shale 1,35 crop, 2 km long, to the north-east of Chimonya Dip (Gongwe map) 0,91 and a larger fault-bounded outcrop on Nuanetsi Ranch east of the Slate Bubye River. Near ,the main road from Beitbridge to Fort Victoria, In 1896 R. Seddon measured a section at the coal outcrop near the and extending from Swanscoe Ranch in the north to the Mtetengwe Umzingwane River and gave the following results: T.T.L. in the south, are several outcrops bounded by east-trending Thicknes$ faults. Because of the lack of exposures little is known about these in mm Black laminated shale . outcrops. The only area on which there is much information is the Coal of very good quality 280 coalfield extending east and west of the Umzingwane River near Fulton's Shale . . . . 125 Drift. Coal of very good quality 230 Water level 14 KAROO SYSTEM FULTON'S DRIFT MUDSTONES 15

In a shaft, 11 m deep, sunk about 1,6 km east of this cutting. R.T. Southwood recorded the following section in 1898: 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 ThicknU8 directly on the gneisses. in metres The second cycle is largely dark grey to black mud stone with thin DIad: shale 11,60 Coal 0,05 sandstones under the coal horizon in the west (T3 and T4) and near Shale 0,10 the base in the east (TO). The coal horizon is thin in the west, but Coal 0,18 around 6 m thick in the east. Shale 0,15 Coal 0,30 The third cycle consists of dark carbonaceous shales in the west and Shale 0,30 Coal 0,46 grey shales in the east. The coal horizon is missing in boreholes MRDl Shale 0,92 Coal and T7 where there are thick beds of sandstone, and in borehole T6 0,38 where there is a great thickness of grey shale. In boreholes TI and T4 Grit . . . 0,92 Precambrian gneisses the thick coal horizon contains much shale. In TO and T8 the horizon is Excavations made by the McDonald brothers in 1971 near the road thin, around two metres thick. crossing the low ground north·east of Morgan's Hill exposed 4,6 m of The third cycle marks the beginning of a change in sedimentation. The Jight to dark grey mudstones. A generalized section down the slopes of 1,9 m of medium- to coarse-grained sandstone in borehole MRDl has Morgan's Hill is as follows: bedding planes marked by thin black layers (Johnson, 1973). Towards the Escarpment Grit Yellowish·buff or khaki-coloured mudstone Red or maroon mudstone TABLE I White shale GENERALIZED STRATA IN FULTON'S DRIFT MUDSTONES Red or dark brown mudstone Grey flint clay Dark grey carbonaceous mudstone Thickness Base not seen in m Strata

A total of seven boreholes, MRDl, T7, TI, T4, T6, T8 and TO, have ESCARPMENT GRIT been sunk through the FuIton's Drift Mudstones along a strike of 15-31 Grey and brown shales becoming red near top. In borehole T8, 4,9 m roughly 21 km from Nottingham Ranch in the west to the Mtetengwe of coal and shale on 3,4 m grey shale. 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 0-7,3 Coal and shale horizon. 2,7-7,3 Light to dark grey or black shales. Absent in boreholes MRDl and T7 in the boreholes was affected by faulting is not known, but boreholes where 6,4 to 9,2 m of sandstone with thin conglomerate and in T6 T5, n, Tl and TlO-redrilled were stopped in doleritic rocks, and TlO where 4,6 m of sandy mudstone. passed through several bodies of dolerite which may have marked 1,2-5,8 Coal and shale horizon. fault planes. 4,6-10,7 Grey and black shales. A thin sandstone underlies the coal horizon in boreholes T3 and T4 and sandy beds occur in T8 and TO. The strata recorded in the boreholes suggests cyclic sedimentation in at least four cycles which are summarized in Table 1. The base of 1,8-6,4 Coal and shale horizon. 3,5-18,3 Grey, brown, white and black shales with thin conglomerate under coal the first cycle is the Basal Beds or the Precambrian gneisses (TO and T8). horizon in borehole T7. Grit, sandstone and conglomerate beds occur and the earliest sediments are light to dark grey mudstones with thin near the base in boreholes T3, T6 and T8 with a coal horizon 2,1 m beds of gritty sandstones (MRDI, T3 and T8) and conglomerate (T6 thick in bore hole TO. and T8). Upwards these pass through grey to black carbonaceous Unconformity mud stones into the coal seams with partings of carbonaceous shales. BASAL BEDS or PRECAMBRIAN G NEISSES ESCARPMENT GRIT 17 16 KAROO SYSTEM base, the sandstone becomes gritty and contains rounded granules and the overlying Red Beds, was named the Escarpment Grit by Mehliss pebbles of quartz up to 40 mm in diameter. Under it is 0,5 m of well­ (1951) and this name has been retained in this account. Mehliss. largely packed conglomerate composed of sub-rounded to rounded pebbles of on lithological grounds, suggested the correlation with the Escarpment white and grey quartz, and whjte or pink to pale purple quartzite. These Grit of the Zambezi Karoo basin, but this correlation cannot be have a dirty yellow sandstone matrix. Towards the base of the conglo­ established with any degree of certainty. The Zambezi Escarpment Grit merate some of the c1asts are flat and at the base, lying on blue-grey consists of beds of white pebbly grits and sandstones which lie with a shaly marl, is a 0,15 m layer of pyrite and pebbles. In borehole T6, which markedly transgressive unconformity on the Madumabisa Mudstones and is about 2 km S.S.E., there is a bed of white sandstone 7,7 m thick with older rocks, which it separates from the overlying Ripplemarked Flags a gritty layer at its base. and other arenaceous sediments of the Stormberg Series. The Escarpment Grit bed being described here lies with little or no unconformity on the A possible fourth cycle occurs only in borehole T8 where grey shale Fulton's Drift Mudstones and is overlain, probably conformably, by the passes upwards into a poorly developed coal horizon 5,8 m thick. In the Red Beds. Robertson (1967) found that in the southern part of Notting­ other boreholes a thick sequence of grey shales, that are almost devoid ham Ranch, west of the Gushu River, the Escarpment Grit bed lay of carbonaceous shales, extends upwards to the Escarpment Grit. In the conformably on the Fulton's Drift Mudstones and that both dipped very west their upper part is red and purple mudstones, and in the centre gently westwards. It would seem that the Escarpment Grit marks an and east there are sandstone horizons. In borehole T2 there is 5,3 m arenaceous interlude in an essentially continuous sedimentation, which of white sandstone and in TI 8,2 m of white sandstone with shale layers. separates the generally grey and often carbonaceous argillaceous beds In TlO there is 10 m of pebbly sandstone and 10 m of pink mudstone of the Fulton's Drift Mudstones from the calcareous red or purple underlying the Escarpment Grit. marls and siItstones of the Red Bed sequence. The top and bottom Fossils of the Escarpment Grit must also mark gradational tectonic and climatic changes in the area. 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. Lithology Plant impressions were also found by Robertson (1967) in the upper The Escarpment Grit is a hard sandstone about I to 15 m thick which part of the sequence at two localities on Nottingham Ranch, one 0,6 km forms small hillocks, ridges and scarps that rise above the flat country W.N.W. and the other 3,9 km N.N.W. from the confluence of the Gushu of the FuIton's Drift Mudstones. It is easily distinguished from the and Limpopo rivers. They occurred in red-brown, ferruginous mud stone, sandstones of the Mudstones by its distinctly coarser grain-size and and there were fragmentary remains in the carbonaceous shales and coal pebble content. It is usually white or pale grey in colour, but locally layers. The better preserved fossils were identified as Glossopteris may be tinted red, green or orange-yellow. Generally it is a coarse­ indica, G. browniana and possibly Phyllotheca sp. They are figured in grained sandstone containing angular fragments of quartz up to 5 mm his Plate 5. Remains of Equisitites sp. are recorded (Bond, 1973, page across, though it can pass into fine-grained and sometimes argillaceous 71) as coming from the Urnzingwane River, Tuli Coalfield (probably from sandstone. Often layers or sheets of small pebbles give a vague bedding around Morgan's Hill), and E. A. Arber (Molyneux, 1903, page 689) to the otherwise structureless sandstone. These pebbles and the larger identified a pith cast from the coal seams near Morgan's Hills as grains stand out on the weathered surfaces and the rock tends to split resembling Calamites approximata. These fossils suggest an Ecca age along the pebble beds. often producing quite extensive. rough, cobbled for at least part of the FuIton's Drift Mudstones. 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. EsCARPMENf GRIT 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 The extensive bed of sandstone, which separates the grey to red Precarnbrian rocks. Intercalated with the sandstone are a few thin beds mudstones forming the upper part of the Fulton's Drift Mudstones from 3 18 KAROO SYSTEM RED BEDS 19

of conglomerate and sometimes beds of greenish-grey shale or mudstone At the west end, in borehole MRDI on Nottingham Ranch, the bed containing, in places, feldspars (Mehliss, 1951). is only 0,6 m thick and consists of 0,2 m of conglomeratic sandstone Distribution and Field Relations 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 The Escarpment Grit has a comparatively small outcrop area. Along green shaly marl and below it 0,2 m of current-bedded mar! which the northern margin of the main Karoo area it is either faulted against shows slump structures in its upper part. Under this mar! is a well­ the Precambrian gneisses or lies on the FuIton's Drift Mudstones, packed conglomerate bed which is 0,2 m thick and consists of pebbles dipping southwards under the Red Beds. In the area of the Gongwe map of fine-grained, yellowish·green sandstone up to 20 mm long in a matrix it outcrops as a strip extending from 4,5 km west of Gwawe Hill to the of fine-grained sandstone. Between it and the underlying deep purple main road from Beitbridge to Fort Victoria. Here, it is broken into mud stone, which contains clay pellets, there is no visible unconformity. blocks by faults. On the eastern end of the Karoo area it outcrops as In borehole T3 there is over 7,6 m of fine- to coarse-grained white long east-striking strips, bounded by faults, close to the main road on Safari and Lesanth ranches. 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 On the southern margin of the Karoo outcrop the flat, westerly in borehole T5 consists of 6,3 m of well-jointed, fine-grained sandstone dipping Escarpment Grit forms a strip 2 to 4 km wide which extends on lying between beds of red or purple mar!. It.s colour changes downwards Nottingham Ranch for 5 km north of the Limpopo River to a major from purple to greenish and finally cream. E.N.E. fault (Robertson, 1967). It lies between the Fulton's Drift The Escarpment Grit in borehole T2 is broken up into 1,5 m of Mudstones and the Red Beds and is traversed by several large east­ fine-grained grit that passes gradationally downwards into O,B m of grey trending doleritic dykes. Farther east it outcrops and dips northwards mud stone underlain by 7,B m of greenish grit containing scattered on the Fulton's Drift Mudstones from 2 km east of the Umzingwane pebbles up to 2 cm long. In borehole Tl there is I,B m of coarse­ River to near the Mtetengwe River where it is down-faulted against the grained grit composed of sub-angular to sub-rounded quartz grains in Precambrian gneisses by a major east-north-easterly fault. Here, it is a matrix of green mar!' Above, the grit is white and below, grey overlain by Red Beds and is intruded by dykes. To the north, there is mud stone. Borehole TB contains lO,6 m of fine-grained white sandstone a small area of Escarpment Grit near the confluence of the Mtetengwe which becomes coarser grained downwards. In it are thin bands of and Tongwe rivers. mud stone. In borehole TlO the total thickness of 1l,9 m is split into In the Nottingham Ranch area the Escarpment Grit forms a small an upper 6,4 m of light green to red pebbly sandstone separated by scarp rising above, the flat mudstone country (Robertson, 1967). It is a 3,4 m of green mudstone from a lower 2,1 m of sandstone. In the coarse-grained, buff-coloured sandstone with interbedded layers of redrilled TlO 4,6 m of metamorphosed sandstones with pebbly layers pebbles up to 30 cm thick. The rounded pebbles are 0,5 to lO mm long lies above doleritic rock. and are mainly of Precambrian vein quartz and quartzites. A few of the quartzite pebbles contain green fuchsite and hair-like needles of RED BEDS sillimanite. In the sandy matrix there are occasional layers that are The Red Beds are a widespread sequence, probably about 300 m rich in detrital magnetite, sphene and epidote. The sandstone consists thick, of fine-grained sandstones, marls and mud stones which are usually of sub-rounded grains of quartz and, more rarely, of chert about 0,5 mm red or purple in colour but may be brown, greenish or white. Frequently across. They are closely packed in a matrix of fine-grained quartz and they contain small scattered pebbles and calcareous nodules and some­ clay minerals. tinles they are cross-bedded or contain scour-and-fill structures. Their contact with the underlying Escarpment Grit is rarely exposed, but is In the boreholes drilled for coal in the southern part of the Mazunga thought to be more or less conformable, and they seem to be con­ map area the bed identified as the Escarpment Grit is of quite variable formably overlain by the Forest Sandstone. The few reptilian fossils composition and its thickness ranges from 0,6 to 17,4 m (Table Ill). found in them are Massospondylus carinatus and Gryponyx africanus. 21 20 KAROO SYSTEM RED BEDS

They suggest a correlation with the Forest Sandstone beds of the . south side. The beds are displaced by major east-north-east trending Zambezi Karoo basin. faults and are cut by easterly dykes. In the southern part of Nottingham Ranch between the Tomani and lithology Mpandi rivers are outcrops of very fine-grained sandstones cut by The Red Beds contain a variety of rocks ranging from mud stones to calcareous veinlets. and in them are thin lenticular beds. up to 1.2 m fine-grained sandstones with occasional pebbly grits and partly silicified thick. of grey siltstone (Robertson. 1967). Near ,the homestead of limestones. The sandstones are very fine-grained to fine-grained red, Sentinel Ranch the banks of the Limpopo and Ipayi rivers are very purple. green. white or cream-coloured rocks which are massive and fine-grained pink siltstones composed of sub-rounded grains of quartz. rarely show bedding in their outcrops. The silts tones, marls and mud­ a small amount of feldspar and a siliceous cement. Among the siltstones stones are similarly coloured rocks. which often have small pebbles of are beds of pink sandstone with mudstone layers abom 10 cm thick. very fine-grained red sandstone scattered through them. and they are The sandstone consists of sub-angular grains of quartz, a small amount characterized by sparse to abundant calcareous nodules. The rare lenses of feldspar. accessory amounts of iron ores and muscovite and a cal­ of light grey limestones are massive. aphanitic rocks and have siliceous careous cement. The mud stone layers are frequently a mass of cracked nodules and veinlets protruding on their weathered surfaces. and unorientated fragments.

Distribution and Field Relations 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 sand­ The Red Beds outcrop discontinuously almost everywhere around stone; in other places it is white sandstone. A fine-grained green sand­ the margins of the Karoo outcrop. They form low. flat-topped hills. or stone is exposed in a cutting on the main road from Beitbridge to country devoid of marked features. They are covered by fine. sandy. Bulawayo at 5 km north of Mtetengwe School, and a coarser-grained maroon-coloured soil that is fertile and extensively cultivated. Near the sandstone 3 km south-west of Gwawe Hill on Jopempi Block (Gongwe Escarpment Grit outcrops the soil is coarser and stony with numerous fragments and pebbles from the Grit. map). About 4.5 km E.N.E. of the airstrip at the Tuli Irrigation Scheme Along the northern margin. in the area of the Tuli map. there are are outcrops of light grey to pinkish-buff. rudaceous rocks which have narrow faulted strips of Red Beds between the basalts and the Pre­ a vague bedding. Here. a gritty rock with numerous grains of angular cambrian gneisses. They extend eastwards across the Dibilishaba and to sub-angular quartz. 4 to 5 mm long. set in a clayey matrix. contains Dendele Tribal Trust Lands as far as the Umzingwane River in the area fragments of mudstone and Precambrian gneisses up to 30 mm long of the Mazunga map. Farther eastwards they outcrop near the and 10 mm wide. as well as large blocks of mudstone up to 3 m long Umtshabezi River and the main road from Beitbridge to Fort Victoria. and 0.6 m thick. 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 At the base of the Forest Sandstone which forms the Chamtoko dipping flatly southwards under ,the Forest Sandstone. Along the east Hills on River Ranch about 3.5 km west of Fulton's Drift. is an margin of the Karoo outcrop long. east-north-east. fault-bounded strips irregular bed of grey siliceous limestone that is 1.5 to 3.0 m thick. In outcrop from Swanscoe Farm in the north to Safari Ranch in the south places it is highly siliceous. Beds of siliceous limestone also outcrop with a small area on Lesanth Ranch. about 4 km south-west of the homestead on Sentinel Ranch and 1 km north-west of the Shambekazana reservoir on Jopempi Block (Mazunga Along the southern margin of the Karoo rocks there are extensive map). areas of Red Beds. lying on the Escarpment Grit and passing under the Forest Sandstone. from the confluence of the Shashi and Limpopo The borehole MRDl on Nottingham Ranch penetrated a total thick­ rivers eastwards across the Umzingwane River to just beyond the ness of 289,4 m of Red Beds which. downwards. consisted of 164.2 m Tongwe River. where they are faulted against the gneisses on their of red sandstone. 12.3 m of red marl. 3.9 m of white sandstone and 9.0 m RED BEDS 23 22 KAROO SYSTEM

of Special Grant No. 15. This beacon is on the east bank of the of green marl lying on Escarpment Grit (Johnson. 1973). The upper Umzingwane River and the locality is about 2 km north of Fulton's red sandstone contained green to white beds and irregular green patches. False bedding and scour-and-fill structures were common. and occasion­ Drift. ally burrows 3 to 4 cm long were found. The rocks were generally During the course of the survey bone fragments were found in thin uniformly fine-grained. but contained scattered pebbles of very fine­ beds of nodular, fine-grained sandstone lying on pink sandstone and grained sandstone up to 4 mm long and. occasionally. carbonate veinlets. overlain by grey sandstone at the base of a rock pillar 7 km south­ There were also thin beds of open-packed pebbles. west of the homestead on Sentinel Ranch. The pure white. fine- and even-grained sandstone had narrow false Robertson (1967) found some rather poorly preserved and distorted bedding. scour-and-fill structures. and a greenish-tinted upper surface bones in the north bank of the Limpopo River east of the Ipayi con­ that had been eroded. The generally massive and structureless red marl fluence and 90 m west of the Sentinel Ranch homestead. The bones was sometimes clayey. showed cross-bedding and scour-and-fill structures. were excavated from a friable pink siltstone cut by calcareous veins, and occasionally contained a few angular pebbles of fine-grained red which outcropped for 140 m along the bank at up to 3 m above river sandstone. The basal green mar! was similar. but in it were disturbed level. The bones, which were partly silicified and had a silt filling in their areas of slabs. 1 to 3 cm thick. probably the result of sun cracking. interstices, were first photographed in situ (Robertson, 1967, Plates 1 to In borehole T6 the upper 33 m was a fine-grained sandstone which 4). and later were tentatively identified as Massospondylus carinatus. was mainly red. pink or purple in colour. but had white layers (Mehliss. They consisted (a) an almost complete post-dorsal vetebra. (b) left 1951 and Pelletier. 1955). In it were a few layers of cracked mudstone femur articular end including trochanter minor, and an almost complete or of pebbles up to 20 mm long. The lower 42 m were red or purple right femur from separate individuals. (c) two separate ischia. (d) mud stones with occasional grey patches and sandy layers. Calcareous fragments of the head of a tibia and (e) various rib and other fragments. nodules up to 40 mm long were common. A digit and claw. probably of Gryponyx africanus. are said (Bond. The Red Beds were represented in borehole T5 by 2 m of greenish 1973. pages 88-89) to have been found in the same area. These two sandstone lying on 49.8 m of purple and red mads with greenish and reptiles are characteristic fossils of the Forest Sandstone Formation of white bands and. in places. scattered pebbles. Interbedded with them the Zambezi Karoo basin. and have not yet been found in the underlying were thin sandy layers and beds of pebbly sandstone. Borehole T2 red beds of the Molteno Stage and Pebbly Arkose Formation. passed through over 134 m of red or purple mar! containing irregular calcareous nodules. interbedded layers of greenish. white or cream­ Petrography aoloured marls. a few thin beds of red or white sandstone. and some Specimens of fine-grained sandstones were collected at 2 km S.S.E. of pebble layers. Mangombe Hill on Nottingham Ranch (slide 21356). 2,5 km north-east In borehole TIO the Red Beds were over 186 m thick. The upper of the homestead on Sentinel Ranch (slide 21357). 5 km north of part consisted of alternating beds of fine-grained sandstones. which Mtetengwe School in the Mtetengwe T.T.L. (slide 21358). and 1,5 km were red. white. or more rarely green in colour. and red mar! containing north-west of the airstrip at the Kongoni Irrigation Scheme in the calcareous and sandy nodules. Some of the sandstones were structure­ Shashi T.T.L. (slide 21359). less and others cross-bedded. In the lower third of the borehole the In slide 21356 a few 0.5 to 1.0 mm sub-angular to rounded grains of rocks were red. purple. or grey mudstones containing calcareous and quartz and microline are scattered in a matrix of 0.05 to 0.15 mm sandy nodules. and scattered pebbles up to 50 mm long. angular to sub-angular. grains of quartz and a very small amount of feldspar with much red-brown clayey cement. Fossils Slides 21357 and 21358 are well-sorted sandstones composed of 0.1 Mehliss (1951) records finding reptilian bones. which he did not to 0.3 mm grains with a few as large as 0.3 mm across. They are remove. in a bed of red mar! about 1.2 km north-east of the BB beacon 24 KAROO SYSTEM FOREST SANDSTONE 25

angular grains of quartz with very thin rims of secondary growth. and clay minerals. A similar rock (slide 21364) was collected in the Dendele rare grains of fresh microline. In slide 21357 the grains are closely T.T.L. at 4,5 km west of the Machuchuta road gate in the north fence packed with a small amount of siliceous cement containing red and of Shobi Block. and another nodular rock (slide 21365) was collected black ferruginous dust. but in slide 21358 the grains rarely touch and from 3 km N.N.W. of Mtetengwe Store in the Mtetengwe T.TL. The there is about 30 per cent. of brown siliceous cement containing some latter is an aphanitic. light grey. massive rock containing abundant. magnetite dust. Slide 21359 has a few scattered 0.5 to 1,0 mm. sub­ rounded to elongated. dark grey nodules about 5 to 15 mm long. They angular to rounded grains of quartz and microcline in a matrix of very are composed of dirty carbonate crystals measuring om to 0.05 mm angular. almost splintery. to sub-angular grains of quartz, a very little across. A few. very irregular, 0.5 to 1.0 mm calcite crystals are replacing feldspar, and a fairly large amount of brown. clayey cement. Slide 21359 the very fine-grained crystals. Between the nodules and separating them. is less well sorted and has a disrupted structure with a large amount of is a small amount of intergrown carbonate and clay minerals less than brownish siliceous cement containing a little opaque dust. This sand­ 0.01 mm across. stone 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 An impure limestone (slide 21366) from the hill 1 km north-west stained plagioclase and clear microcline. of Shabekazana borehole on 10pempi Block is a light grey, aphanitic rock which contains small cherty veinlets and nodules that stand out on A brownish-grey siltstone (slide 21360) was collected from 4.5 km weathered surfaces. It consists of 0.005 to 0.010 mm, intergrown crystals south-east of Mangombe Hill on Nottingham Ranch. Less than half the of carbonate and a small amount of clay minerals. There are some rock consists of angular to sub-angular grains of quartz and a few of minute. incipient porphyroblasts. red-stained plagioclase. the balance being an isotropic clayey matrix full of black and brown iron ore dust. The sand grains in these Red Bed rocks are formed of quartz. clear microcline. stained plagioclase, and very fine-grained quartzites. all of A light grey rock with 2 to 5 mm dark grey. angular fragments in which have been derived from the Precambrian basement. Most contain an aphanitic groundmass outcrops 4.5 km E.N.E. of the Kongoni Irriga­ inclusions (sometimes minute needles of sillimanite). which suggest that tion Scheme airstrip (slide 21361). About one-third of the rock is they have been subjected to upper amphibolite and possibly granulite angular. and often irregularly shaped fragments of very fine-grained facies regional metamorphism; the quartz is always strained. Accessory Precambrian quartzite and vein quartz. the balance being clayey heavy minerals are very scarce and micas appear to be absent. The material containing a few silt-sized grains of quartz and opaque iron carbonate, which has undergone some redistribution, appears to be of ores. inorganic, concretionary origin. The majority of the sand grains are sub-angular; very few are well-rounded and possibly of aeolian origin. Many of the Red Bed rocks contain calcareous nodules. A carbonate­ Minute sharp-edged chips and splinters of quartz are abundant in rich. fine-grained arkose (slide 21362-3) from the track 6 km south-west slides 21358 and 213560, numerous in slides 21364 and 21365, and 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 scarce in slides 21357, 21359 and 21362. Their size. less than 0.1 mm shape. Some have larger marginal crystals of carbonate which have long, and appearance suggests that they may have come from the finely partly replaced the adjacent rock. The poorly sorted rock is composed ground rock flour of Dwyka-age glacial deposits. mainly of quartz. much microcline. a little brown-stained plagioclase. and a few rounded grains of mud stone and very fine-grained Pre­ FOREST SANDSTONE cambrian quartzite. The grains. which vary from angular to well-rounded. The name Forest Sandstone was given by Mehliss (1951) to the and from low to high sphericity. have a disrupted framework. the sandstone lying between the Red Beds and the basalt lavas, and is grains seldom touching each other. The few larger 0.5 to 1.0 mm. retained here without implying any correlation between it and the Forest grains are in a matrix of very angular. 0.05 to 0,20 mm. grains of the Sandstone of the Zambezi Karoo basin. lohnson (1973) called it the same minerals and a dirty brownish-coloured cement of carbonate and Cave Sandstone. 4 26 KAROO SYSTEM FOREST SANDSTONE 27

The Forest Sandstone is a pale-coloured, fine-grained rock, which is which were once occupied by Stone Age people, in the cliffs of the probably around 80 to 100 m thick and lies conformably on the Red rugged Chamtoko Hills (Robertson, 1967). 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 Alongside the doleritic dykes the Forest Sandstone has been meta­ are variable. The greater part of the sandstone seems to be sub-aerial and morphosed and indurated, often to a quartzite, and on weathering forms only the lower part sub-aqueous. So far no fossils have been found in it a double line of low ridges with the weathered dyke rock in the trough making correlation with other areas impossible. between them (Robertson, 1967). In places the metamorphosed sand­ stone contains hard concretions that stand out like warts on the weathered Lithology surfaces. The larger ones, up to 6 cm diameter, are roughly spherical The Forest Sandstone is white to pale pinkish-white when fresh and some, lying on the surface about 4,5 km S.S.W. of Rangamano (Johnson, 1973), but when it weathers it develops an outer layer, 1 to Hill on Nottingham Ranch, look like cannon balls. 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 Distribution and Field Relations breaks down to a red-brown sand. The fresh rock is even-grained and Along the northern margin of the Karoo outcrop thin slivers of massive with a grain-size ranging from fine to medium. Frequently it Forest Sandstone occur on the north side of the basalt lavas in the shows dune bedding and is generally well-jointed, the joint planes Dibilishaba and Dendele T.T.L. (Tuli map) and near the Umzingwane sometimes being silicified. and Umtshabezi rivers (Mazunga map). Farther east a wide strip of The lower part of the Forest Sandstone is more calcareous than the Forest Sandstone, lying on the Red Beds and dipping flatly southwards upper part and contains a few irregular grey nodules of carbonate under the basalts, extends eastwards from 3 km south of Gwawe Hill to (Johnson, 1973). In it Mehliss (1951) found rare beds of limestone the road from Beitbridge to Fort Victoria (Gongwe map). around one metre thick. At 1 to 2 m below the base of the basaIts Along the southern margin of the Karoo rocks, the Forest Sandstone Robertson (1967) records the occurrence of irregular to spherical cal­ lies conformably on the Red Beds and is covered with a more or less careous nodules up to 20 cm long and a boxwork of silica veinlets. slight unconformity by the basalts. It dips flatly in a northerly direction. Coarse-grained, gritty sandstone beds outcrop in the Siyoka T.T.L. Its frequently faulted outcrops extend along the north side of the at 4,7 km N.N.E. of Mabafu Store and 7 km north-east of Baemura Limpopo River eastwards from the Shashi confluence to the Makawa School, and in the Dibilishaba T.TL at 1,9 km E.S.E. of the Bertie Hills. Farther east the sandstone forms Zwibwale Hill, and eastwards, Claims. from Penemene School to the main road from Beitbridge to Fort Victoria, the sandstone dips gently northwards under the basalts and Over much of the area the Forest Sandstone forms low hills which is down-faulted against the Precambrian gneisses in the south. 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 On Sentinel and Nottingham ranches the lower part of the Forest the bridge across the Bubye River, it forms several isolated hills rising Sandstone is well exposed in cliffs and rock pillars. It is faintly bedded above flat country. North-eastwards from the bridge the Forest Sand­ and contains occasional calcareous nodules and rare, thin beds of stone consists of broken slabs standing on end. They are due to impure limestone. Here, the sandstone appears to have been deposited faulting. under water. It grades imperceptibly upwards into a slightly coarser grained and redder, dune-bedded sandstone of aeolian origin. Its upper In the south, the Forest Sandstone forms the impressive hills and surface in contact with the overlying basalt lavas is a distinctly irregular cliffs of the Homba Hills on Sentinel and Nottingham ranches, and one which shows deflation. The first lavas appear to have flowed along numerous rock pillars such as the one about 2,5 km north-east of the the troughs lying between large sand dunes and to have affected the Sentinel Ranch homestead. There are numerous caves and shelters, sandstone down to a depth of 1 to 2 m. 28 KAROO SYSTEM FOREST SANDSTONE 29

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 30 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 0 and 1800 with a maximum 20 0 0 of 31 readings between 090 and 120 • 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 10 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 ~ 1WAW~AW"Az//MlM1 ' , P7Z7lJJ homestead on Cawood's Mazunga Ranch, numerous pipe-like structures o 030 060 090 120 150 180 210 240 270 300 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 Bearing in degrees are circular in cross-section and have an external diameter of about FIG. I. Directions of dune bedding in the Forest Sandstone. 40 to 50 cm and an internal diameter of 3 to 20 cm. Their walls consiSt of about 25 mm of hard silicified sandstone. Petrography The fine-grained sandstone (slide 21367), which outcrops 3 km north­ TABLE n west of ChandabaIini in the Siyoka T.T.L., is a pale brownish-pink rock DffiEcrroNS OF DUNE BEDDING IN FOREST SANDSTONE 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 well­ Grid Bear- Grid Bear- Grid Bear- reference No. ing reference No. ing reference No. ing rounded. 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 72045910 I 185 76635507 6 128 79705705 9 140 73865962 I 176 76645519 4 088 79765710 3 073 growth surrounds the grains and they are separated by a layer, under 79126108 I 178 77055576 5 066 80535650 3 100 0,01 mm wide, of reddish-brown cement. The cement is probably a 19886096 4 142 77345559 6 116 80685712 3 094 21626078 1 039 77355590 4 180 19755724 3 000 mixture of clay, silica and the red-brown iron ores which colour the 74485446 5 154 78475598 1 090 21005718 1 091 rock. Similar fine-grained sandstones were collected from a low rise 75045478 8 098 78845630 2 071 21765734 I 041 2,5 km W.N.W. of Gwawe Hill (Gongwe map) (slide 21368) and from 76235509 I 345 78905625 I 211 21945817 5 106 76355492 4 125 78775664 6 092 22545826 I 180 0,5 km east of the north-west corner of Shobi Block (slide 21369). The 76405518 10 065 79055669 2 034 - -- -- fine-grained, well-sorted sandstone (slide 21370) from River Ranch. 31 30 KAROO SYS1EM FOREST SANDSTONE

1,5 km north-west of the Chamtoko Hills is composed of angular to being clayey cement rich in brown iron ore dust. The grains average sub-rounded grains of quartz along with very few grains of feldspar, about 0,2 mm across but range from 0,1 mm to a few 4,5 mm pebbles. quartzite and metasiltstone of medium sphericity. They vary in size from The larger sand grains are quartz with some brown-stained plagioclase 0,1 to 0,5 mm and average about 0,2 mm. They are very well packed, and metasiltstone. The smaller grains are quartz and a few of fine­ and are separated by a thin film of siliceous cement coloured by iron grained quartzite and stained plagioclase. ore dust. The rock is a pale pinkish-brown colour and weathers through The bulk of the sand grains in these sandstones has been derived a zone 30 mm thick from reddish-brown to a brown surface coated with from the Precambrian rocks with comparatively little wear, most being black. angular to sub-angular. Rounded grains are comparatively scarce and The fairly well sorted, fine-grained sandstone (slide 21371) from a are usually the larger grains. Micas are absent, heavy minerals rare, and low rise 4,7 km N.N.E. of Mabafu Store in the Siyoka T.T.L. has a fairly the small quartz chips and splinters seen in the Red Beds are scarce. open framework and an average grain-size of about 0,15 mm. The The calcareous nodules, abundant in the Red Beds, are also very scarce, grains are angular to sub-angular, and only a few of the larger grains and there seems to be less red-brown dust in the cement of the paler are welI-rounded. Their sphericity varies from Iow to high. Most are coloured Forest Sandstone. 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 TABLE III of brownish specks of iron ores. BOREHOLES ON E.P.O. No. 19 AND 393 A welI-sorted, fine-grained sandstone with a slightly more open Extracted from final reports. Positions are approximate and collar elevation~ unknown. framework (slide 21372) was collected in the Dendele T.T.L. about two To To kilometres east-north-east of the gate on the Machuchuta road in the metre. Strata metres Strata north fence of Shobi Block. The grains, which are angular and of low BOREHOLE No. TO. 1,5 km 277° from 36,32 Dark sandy shale sphericity, are mainly quartz with a small amount of fresh microcline Fulton's Drift on the Umzingwane 36,88 Black shale 41,45 No core and plagioclase, and rare grains of stained plagioclase. They range in River, on Lot I, River Ranch. Oct., 1953. 41,66 Black and grey shale size from 0,05 to 0,30 mm and average about 0,1 mm. The siliceous 3,66 Soil 41,71 Carbonaceous shale cement, which forms about 20 per cent. of the rock, contains some 14,33 Grey and yellow shale 41,76 Coal 15,90 Shaly coal with pyrite 41,78 Grey shale clay and iron ore dust. 16,59 Grey shale 41,89 Grey sandstone 16,66 Coal and shale BOREHOLE No. TO. Redrilled 17,4 m ''L- A finely bedded sandstone (slide 21373) with alternate medium- and 17,37 Grey shale

TABLE ill (continued) TABLE ill (continued) To To To To metre. Strata metres Strata metres Strata metres Strata 41,15 Grit with 15 mm pehbles of 106,68 Dark grey, purplish marl 20,12 Carbonaceous shale, coal streaks BOREHOLE No. T4. 19,6 km 243 0 from quartz and ironstone 109,93 Grey marl 20,73 Black shale Fulton's Drift. On Nottingham Ranch. 41,68 Sandstone 112,24 White mudstone, cross-bedded 21,03 Coal Nov., 1953. 44,33 Dark grey shale 114,07 Greenish grit 21,34 Carbonaceous shale 2,44 Soil 44,81 Carbonaceous shale, some coal 135,48 Dark grey marl, red nodules 21,85 Coal 7,01 White sandstone and pyrite 137,16 White quartzite 22,86 Black shale 22,19 Grey shale 45,21 Grey shale 137,46 Dark grey shale 22,99 Coal 22,26 Coal 45,42 Coal 137,57 Sandstone 23,67 Black shale 23,87 Black shale 45,57 Carbonaceous shale and coal 137,79 Dark grey shale 23,80 Coal 23,95 Coal 46,08 Coal 139,60 White sandstone and shale bands 25,91 Black shale 24,25 Shale 46,25 Carbonaceous shale and coal 140,38 Sandstone 26,24 Coal 24,59 Coal 46,43 Coal 143,71 Pebbly sandstone 27,74 Black shale 24,80 Dark shale 46,58 Carbonaceous shale and coal 177,39 Dolerite 27,83 Coal 24,95 Coal 48,16 Dark grey shale 28,02 Black shale 25,21 Black shale 48,36 Coal BOREHOLE No. n. 4,2 km 248 0 from 28,52 Coal 25,66 Coal 48,44 Carbonaceous shale Fulton's Drift. On River Ranch. Sept., 28,80 Carbonaceous shale 32,51 Dark shale 48,82 Dull coal 1953. 29,01 Coal 32,84 Coal 49,00 Carbonaceous shale and coal 25,91 Red marl, calcareous nodules 29,34 Carbonaceous shale 33,05 Carbonaceous shale 49,24 Carbonaceous shale 26,06 Sandy red mar! 29,69 Coal 33,28 Coal 49,40 Carbonaceous shale and coal 39,32 Red-purple marl, calcareous 36,02 Black shale 33,50 Shale 55,78 Fractured dark grey shale nodules 36,58 Coal 33,62 Coal 56,18 Carbonaceous shale and coal 46,33 Cream bedded mar! 36,70 Black shale 33,67 Shale 58,52 Fractured dark grey shale 68,88 Purple mar!, calcareous nodules 37,34 Coal 33,82 Sandstone 58,53 Coal 69,04 Dolerite 37,74 Grey sandstone, cross-bedded 33,97 Shaly sandstone 58,83 Fractured dark grey shale 76,10 Purple-red marl, calcareous 42,11 Black shale 34,38 Grey shale 60,86 Pulverized coal nodules 42,13 Grit 34,43 Sandstone 61,06 Dark grey shale 76,76 Porphyritic dolerite 42,25 Coal 38,79 Dark shale 62,64 Gneiss 88,70 Purple-red marl 43,59 Black shale 38,93 Coal 101,80 Greenish-white mudstones, 43,64 Coal 39,19 Shale, coal streaks BOREHOLE No. Tt. 1,4 km 2760 from cross-bedded 44,63 Carbonaceous shale 40,26 Coal Fulton's Drift. On Lot I , River Ranch. 44,65 Carbonaceous shale 106,68 Purple mar!, calcareous nodules 44,73 Coal Sept., 1953. 107,52 No core 44,93 Dull coal 8,53 Red marl 117,68 Purple marl 45,11 Carbonaceous shale 45,09 Carbonaceous shale 11,28 Sand 117,98 Pale green mar! 45,58 Coal 45,21 Coal, shaly 28,65 Red marl, calcareous nodules 118,16 Dolerite 46,25 Carbonaceous shale 45,42 Carbonaceous shale 29,79 Sandy red mar! 118,36 Pale green marl 45,67 Dull coal 31,09 Red marl, calcareous nodules 128,27 Purple marl 46,42 Coal 46,18 Dark shale 31,24 Pebble band 128,63 Pebble band 46,48 Carbonaceous shale 46,29 Shaly coal 32,61 Red mar!, calcareous nodules 134,44 Grey sandy marl 47,17 Coal 60,33 Black shale Quartz porpbyry 32,69 Pebble band 135,94 Sandstone 47,26 Black sbale 60,86 40,54 Red marl 136,19 Grey mudstone 61,37 Boulder bed 48,77 Red to purple mar! 143,97 Pebbly grit, pyrite 47,54 Coal 70,71 Gneiss 55,78 Purple marl 60,20 Black shale 149,91 Red-grey mudstone 0 64,01 Red and purple mar! 151,41 Pebbly grit 61,26 Grey-brown mudstone BOREHOLE No. T5. 10,4 km 242 from Fulton's Drift. On Nottingham Ranch. 68,28 Purple mar!, calcareous nodules 155,30 Sandstone 61,47 Quartz porphyry 70,41 White sandy mar!, wavy cross- 172,01 Dolerite Feb., 1954. bedding 61,55 Carbonaceous shale 15,24 No core 75,90 Purple and white mar!, cross. BOREHOLE No. T3. 22,3 km 248 0 Ifrom 61,87 Burnt coal 16,61 Pale green sandstone bedding Fulton's Drift. On Nottingham Ranch. 61,95 Black shale 17,02 Pebbly grit 20,02 Red-purple marl 95,71 Dark grey to purple mar!, Nov., 1953. 62,96 Sandstone greenish near base. Gritty 4,88 Soil 26,99 Red marl, sandstone bands nodules 7,62 Pebbly sandstone 65,00 Boulder bed 27,58 Dolerite 103,02 Dark purple mar! 19,81 Shale 74,68 Gncis, 31,75 Red mar! 5 34 KAROO SYSTEM BOREHOLES 35

TABLE ill (continued) TABLE ill (continued) To To metres To To Strata metres Strata metres Strata metres Strata 31,80 Sandstone 52,60 Dark mudstone 164,74 34,04 Red mar1 Grey shale 195,89 Shale 53,36 Coal 164,97 Coaly shale 196,60 Coal 34,14 Pebbly grit 53,75 Grey mudstone 165,00 37,09 Red mar! Coal 196,65 Shale 54,12 Coal 166,45 Grey shale 196,75 Coal 37,29 Pebbly grit 60,22 Dark mudstone 46,94 166,75 Dull coal 196,85 Shale Red mar!, pebble bands 60,66 Coal 167,05 Grey shale 197,61 Coal 47,55 Dolerite 60,76 Shale 55,47 167,31 Carbonaceous shale 197,89 Shale Red marl, pebble bands 61,99 Coal 167,56 Coal 198,12 Shaly coal 58,83 Red mar! 62,03 Grey mudstone 58,90 167,97 Carbonaceous shale 211,78 Dark shale Pebbly grit 62,05 Coal 168,40 Coal 213,21 Shaly conglomerate 65,99 Red-purple marl, sandy bands 62,20 Carbonaceous shale 77,27 168,86 Carbonaceous shale 215,24 Grey shale Purple-crearn sandstone 62,56 Conglomerate 169,16 Coal 228,90 Sandstone, feldspathic 77,42 Pebbly shale 64,16 Grey mudstone 83,82 169,94 Grey shale 266,09 Gneiss Grey shale 64,34 Coal 170,18 Coal 85,65 Purple mudstone 65,78 Dark mudstone 0 114,91 173,56 Grey shale BOREHOLE No. T9. 2,5 km 352 from Dolerite 75,23 Brown-white mudstone 173,91 Coal Fulton's Drift. In Mtetengwe T.T.L. 119,79 Gneiss 0 175,21 Grey shale May, 1954. BOREHOLE No. T6. 16,9 km 247 from 175,49 Coal 12,50 No core Fulton's Drift. On Nottingham Ranch. BOREHOLE No. T8. 4,7 km 2980 from April, 1954. 175,69 Carbonaceous shale 36,58 Dolerite Fulton's Drift. In Mtetengwe T.T.L. 176,17 Coal 4,88 No core May, 1954. 0 37,19 176,33 Carbonaceous shale BOREHOLE No. TlO. 2,6 km 42 from Pink sandstone 7,01 No core 176,61 Coal Fulton's Drift. In Mtetengwe T.T.L. 79,25 Red marl, calcareous nodules 7,32 White sandstone July, 1954. 83,21 176,84 Carbonaceous shale Pebbly red sandstone 7,87 Red mudstone 177,49 Coal 9,75 No core 84,12 Cavity 9,85 White sandstone 96,62 179,83 Grey shale 19,79 Red mudstone Pebbly red sandstone 10,06 Red mudstone 180,24 Coal 21,11 Sandstone 119,18 Sandy purple mudstone 15,95 Red sandstone, cross-bedded 34,85 Red mudstone 128,93 Purple 180,39 Grey shale mudstone, calcareous 18,36 Sandy red mudstone 180,47 Coal 35,61 White sandstone, unbedded nodules 18,44 Basalt 183,79 Grey shale 51,21 Red sandstone, cross-bedded 154,84 Grey mudstone 19,58 Sandstone, cross-bedded 57,07 Red mudstone, calcareous na- 159,26 184,07 Coal Sandy grey mudstone 19,86 Red mudstone 184,25 Grey shale dules 160,32 Grey mudstone 20,02 Basalt 58,62 167,49 184,35 Coal Sandstone Grey fireclay, coal streaks 26,49 Red mudstone, calcareous no- 184,46 Grey shale 59,72 Red mudstone 172,06 Grey mud stone dules 176,02 185,01 Coal 60,02 Red-white sandstone Dark shale and burnt coal 27,66 Sandstone 185,09 Grey shale 63,45 Red mudstone, nodules 179,22 Dark shale 53,95 Red mudstone, calcareous na- White sandstone 189,05 185,37 Coal 65,40 Dolerite dules, grit bands 188,57 Black shale 65,99 Red mudstone 189,74 Black mudstone 54,96 Basalt 66,29 White sandstone 192,96 192,00 Sandy shale Green-grey mudstone 70,10 Red mudstone 193,23 Coal 73,91 Red mudstone 193,40 Conglomerate 73,46 White sandy mudstone 75,44 White sandstone, cross-bedded 195,38 192,30 Shale Green-grey mudstone 75,90 Red mudstone • 192,48 Coal 76,15 Red mudstone, nodules 198,73 Gneiss 83,82 White sandy mudstone 193,11 Grey shale 76,45 Purple sandstone 84,73 Red mudstone 0 193,30 Coal 77,67 Red mudstone BOREHOLE No. T7. 26,3 km 244 from 90,50 White sandy mudstone, bedded 194,18 Grey shale 78,33 Purple sandstone Fulton's Drift. On Nottingham Ranch. 91,82 Purple-grey mudstone 194,33 Coal 79,71 Red mudstone June, 1954. 107,59 Grey-purple mudstone, cal- 194,46 Grey shale 87,78 Purple sandstone 12,19 No core careous nodules 194,54 Coal 98,98 Red mudstone 37,80 Grey and purple mudstone, 107,90 Grey sandy mudstone 194,61 Shale 99,84 Purple-white sandstone weathered 108,81 Purple mudstone 194,74 Coal 100,07 Red mudstone 44,35 White sandstone 136,70 Grey mudstone 194,83 Shale 103,94 Purple sandstone, cross-bedded 46,99 Grey mudstone with coal 147,29 White sandstone 195,35 Coal 112,42 Red mudstone, nodules 50,12 Dark mudstone 147,98 Grey shale 195,66 Shale 115,52 Purple sandstone, cross-bedded 50,50 Coal 148,29 Dull coal 195,78 Coal 135,86 Red mudstone, nodules 36 KAROO SYSTEM BASALTS 37

TABLE ill (continued) BASALTS To To metres Strata metres Strata The Basalts, which are the uppermost member of the Karoo strati­ 139,35 Green-red sandstone 202,69 White siltstone graphic sequence, occupy the greatest part of the mapped area. They 139,67 Red mudstone 217,93 Dolerite enter it from Botswana at the Shashi River and continue eastwards to 139,83 Green sandstone 162,76 Red-grey mudstone BOREHOLE MRDl. 26,8 km 250 0 from near the main road from Beitbridge to Fort Victoria, a distance of about 174,96 Grey mudstone Fulton's Drift. On Nottingham Ranch. 160 km. Their width from north to south is around 40 to 45 km, but 176,78 Pebbly mudstone 1971. 186,54 Purple mudstone 78,00 Amygdaloidal basalt their thickness, which must be large, is not known. They lie with 192,94 Pebbly sandstone 79,3 Sandstone dyke in lava varying degrees of unconformity on the Forest Sandstone and are 196,29 Grey mudstone 79,7 Sandstone traversed by many large faults trending east-north-east to north, and 198,42 Sandstone 92,3 Lava flows 208,48 Pink mudstone 171,4 White sandstone by easterly dykes which were the last phase of the Karoo igneous 218,39 Grey pebbly sandstone 195,0 Red and green sandstones activity. 219,00 Grey shale 200,0 Red pebbly sandstone 222,20 Black shale, coal bands 202,5 White sandstone Formerly the basaIts extended far to the north-west and south-east 226,62 Grey shale 242,0 Red sandstone 228,00 Dolerite 264,0 White sandstone of the Limpopo River, but have long since been removed by erosion. 230,20 Grey mudstone 267,0 Red sandstone Their former presence is indicated by amygdaloidal agates in the super­ 231,65 Grey argiIJite 270,0 White sandstone 234,19 Dolerite 296,6 Pebbly red sandstone ficial deposits and by the olivine-bearing lavas around Featherstone in the 240,13 Black shale 306,0 Green sandstone Charter District (Worst, 1962). In the mapped area they have been 247,70 Grey shale 335.6 Pebbly red to green sandstone preserved by extensive down-faulting in the Limpopo Mobile Belt. 263,55 Grey-cream argillite 336,6 Red mar! 263,98 Dolerite 347,9 Red mudstone Similar basalt lavas occur to the east of the main road to Fort Victoria 268,83 Cream argillite 351,8 White sandstone and continue eastwards into Moc;:ambique. They have been described 275,39 Cream clay rock 360,8 Green mudstone 361,0 Pebbly grit by Tyndale-Biscoe (1949), Swift et al. (1953), Cox et al. (1965, 1967), 361,2 Shaly marl Jamieson (1966) and Macdonald (1967). BOREHOLE No. no. Redrilled 91,5 m 361,4 Conglomerate SSW. 372,0 Purple mudstone Because of the large-scale faulting and discontinuous exposure, it 78,03 Red sandstone, pebble bands 392,9 Brown mudstone 106,38 Red mudstone, pebble bands 3948 White sandstone was not possible during this reconnaissance survey to map the basalts 106,53 Dyke 395,3 Conglomerate in detail or with a high degree of accuracy. However, a provisional 132,59 Purple muddy sandstone 410,7 Black shaly mudstone subdivision of the basalts has been made, and from the base upwards 133,35 Quartzite 415,0 Shale and coal 133.81 Dolerite 420,4 Black shaly mudstone it is (a) the olivine-bearing Mabuli basalts, (b) the hypocrystalline, 137,16 Purple muddy sandstone 422,1 Coal aphanitic Marawanerit basalts, (c) the porphyritic Chandabalini basaIts 138,68 Grey mudstone, calcareous no- 432,0 dules Black and brown mudstone with their large tabular feldspars, (d) the vesicular basalts and volcano­ 140,21 456,0 Basal grits Dyke 465,8 Gneiss 140,67 Sandstone clastic rocks, and (e) the Tuli basalts which form the top of the Karoo 160,32 Grey mudstone BOREHOLE MRD2. About 2,8 km west succession. 164,90 Sandstone, pebbly of road to Machuchuta and NE. of dam 176,78 Dolerite on upper Shobi River near south 179,22 Carbonaceous shale boundary of Dendele T.T.L. (not shown lithology 179,83 Grey shale on Tuli map). The basalts are hard, well-jointed rocks which vary in colour from 179,91 Coal 75,9 Buff to grey sandstone 180,75 Grey shale 109,73 Dolerite 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 39 38 KAROO SYSTEM BASALTS traversing them are filled with green celadonite. and white. grey or Specimens of olivine basalt were collected from 400 m along the cream-coloured agate. quartz. zeolites and calcite. 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 Distribution and Field Relations hypocrystalline with panidiomorphic textures. Slightly ragged calcic The more massive basalts form flat-topped hills, terraces and cliffs, plagioclase laths, 0,2 to 0,8 mm long and 0,05 to 0,15 mm wide, form and in the southern part of the area they frequently form a capping most of the rocks. In slide 21376 the laths are slightly altered and have on the hills and ridges of the Forest Sandstone. The vesicular lavas a dirty appearance. Down their centres are thin zones of inclusions. form gentler slopes and the olivine basalts tend to weather more rapidly Augite occurs as equant, intergranular crystals 0,05 to 0,20 mm across. and form flat country. Exposures are generally good, especially in the It is very slightly chloritized in slide 21377 and forms rare micropheno­ streams and rivers, but there are large areas of basalt covered by black crysts in slide 21376. In all three slides a few idiomorphic to hypidio­ or grey, clayey soils. In these soils calcrete is common to abundant. In morphic olivine crystals, 0,1 to 0,5 mm long, are outlined with iron some places, noticeably the Tuli National Area, the soil is stony, either ore dust. The majority are altered to barely pleochroic iddingsite which with rounded to spheroidal boulders of basalt, or with rough, angular ranges in colour from deep brown to a bright orange-red. Dark brown fragments of the almost indestructible agate. 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 The basal lavas appear to have flowed across a dune-covered surface microcrystalline matrix. One of the oHvine basalts (slide 21376) is of Forest Sandstone (Robertson, 1967) and produced a more or less vesicular and contains widely scattered amygdales up to 5 mm long unconformable surface. In the Homba Hills the basalt cappings on the that are completely filled with marginal agate and celadonite, and sandstone hills are several metres higher than the basalt in the flat coarsely crystalline carbonate cores. 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 A limburgitic basalt (slide 21378) from 2 km south-east of Lutope inwards into a hoIlow in the top of the Forest Sandstone. Similar Hill on Jopempi Block contains idiomorphic to hypidiomorphic pheno­ unconformable relationships can be seen in many places along the crysts of oHvine 0,5 to 2,0 mm long. They contain much brownish south margin of the Karoo rocks from the Shashi River eastwards to glass-like dust and narrow cracks filled with iron ore needles and dust. the Mtetengwe River. Around them a pale orange-brown reaction rim appears to be a mixture of pyroxene and antigorite. There are also a few allotriomorphic pheno­ The Mabuli Olivine and Limburgitic Basalts crysts, 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 The Mabuli basalts, which are thought to be the earliest lavas erupted, phenocrysts which they sometimes penetrate. Rather less than half the are named after the MabuIi borehole on Jopempi Block in the north­ rock is pale brownish glass that is full of microlites and globules. An west corner of the Gongwe map area (grid reference 19266071). analysis, Lab. No. 73/17, is given in Table N. 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 Another limburgitic basalt (slide 21379) from 3 km west of Panini in outcrop on the south side of the Bubye River. Near Chandabalini an the Mtetengwe T.T.L. has many allotriomorphic to idiomorphic olivine olivine basalt overIies a red vesicular basalt, and near Mabuli horehole phenocrysts, which are 0,2 to 2,0 mm long and average 0,5 to 1,0 mm, a limburgitic basalt is exposed about 30 m above the Marawanerit in groups and scattered grains. They have many dusty inclusions and basalts. are cut by numerous narrow cracks filled with chrysotile and antigorite crystals that have grown perpendicular to their walls. There are a few The olivine basalts are massive, dark olive-grey, aphanitic rocks. and pyroxene phenocrysts about 0,5 mm long and abundant long rods and the limburgitic basalts are heavy, dark greenish-grey rocks in which skeletal crystals of i1menite. Nearly half the rock is a sepia brown glass. minute black specks of olivine can be seen. 40 KAROO SYSTEM BASALTS 41

The borehole MRDl on Nottingham Ranch started in olivine basalt 0,6 mm across. Patches of very dark brown interstitial glass with almost and continued in it to a depth of 78 m (Johnson, 1973). It is described black cores and a few microlites, form less than 25 per cent. of the as a dark grey to black amygdaloidal rock containing small phenocrysts rock. Iron ores are comparatively scarce and occur as very thin rods, of augite and altered olivine in a fine-grained matrix. The white and needles and skeletal growths up to 0,2 mm long. There are also a few green amygdales, which were about 10 mm long, were filled with chal­ 0,02 to 0,03 mm octahedra of magnetite and a very small amount of cedony, quartz, calcite and chlorite. A specimen taken at 33 m depth orange-red iddingsite or chlorophaeite around or in cracks in the contained about 25 per cent. olivine phenocrysts, 0,5 to 1,5 mm long, pyrpxene crystals. that were partly or completely altered to serpentine, 20 per cent. of randomly distributed and very slightly chloritized, 0,05 to 0,4 mm The ChandabaIini Basalts 4 grains of augite, and 15 per cent. of acicular iron ores up to 1 mm long. The Chandabalini basaIts are aphanitic, reddish-grey, brownish-grey, These crystals were enclosed in a semi-vitreous matrix of light grey to or almost black rocks which occasionally contain small amygdales. They colourless grains less than 0,001 mm across. X-ray studies indicated the are characterized by large greenish-white feldspar phenocrysts, which presence of nepheline and oligoclase. have a roughly sub-parallel flow structure. They measure about 20 to This upper lava was separated from a lower lava at between 78 m and 30 mm by 10 to 15 mm and are 0,5 to 2 mm thick. Viewed one way 79,7 m depth by a bed of fine-grained, white sandstone which extended they form lustrous patches, and viewed the other way long thin rect­ upwards for 0,4 m into the lava as a baked, dyke-like body. The upper angles. They form about 10 to 25 per cent. of the rock. contact of the sandstone was scoured, grooved and pitted, and the bulk These basalts are best developed in the north-central portion of the of it was cross-bedded. The lower half of the bed was greenish and area of the Mazunga map around Chandabalini borehole (Grid reference tuffaceous. From 79,7 m to 80 m depth there was glassy lava and from 77936042), along the north boundary of Jopempi Block, and in the 80 to 91 m a coarsely amygdaloidal, fine-grained basalt which between adjacent Siyoka Tribal Trust Land. Similar porphyritic basalts outcrop 87 and 89 m was veined with white material. Downwards from 91 m 7( in the Umzingwane River 2 km south-east of Baemura School, in the there was basalt riddled with small, calcite-filled amygdales to the chilled Hwali River in the Dibilishaba T.T.L., and near the road to Tuli in base at 92,3 m which was lying on top of dark coloured, tuffaceous, the north-central part of the Tuli map area. Like the Marawanerit very fine-grained Forest Sandstone. basalts, they lie on olivine and Iimburgitic basalts and are covered by red to purple vesicular basalts. The Marawanerit Basalts A specimen with abundant feldspar phenocrysts (slide 21381) was The Marawanerit basaIts, which are named after the Marawanerit collected from the Umzingwane River in the Siyoka T.T.L. 1,5 km borehole on Jopempi Block in the north-west corner of the Gongwe ..j( south-east of Baemura School, and one with slightly fewer phenocrysts map area (Grid reference 20286076), are massive, black, aphanitic rocks (slide 21382) from 1,5 km south-west of the airstrip at the Kongoni which sometimes contain microphenocrysts of augite. They form a flat Irrigation Scheme in the Shashi T.T.L. In slide 21381 the clear, twinned plain around the borehole where they overlie the Mabuli basalts and phenocrysts are slightly cracked and their ends fractured. They are set are covered, mainly to the west, and south-west, by red to purple, in a matrix of twinned, and sometimes zoned, laths of hypidiomorphic vesicular lavas. Elsewhere they outcrop in small areas. 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. A specimen (slide 21380) collected from an aphanitic black basalt In the matrix are numerous irregular patches, 0,2 to 1,5 mm long, of flow about 1,5 km E.N.E. of Lupako Hill on Jopempi Block, is a brownish to opaque and skeletal iron ores. hypocrystalline rock with very few microphenocrysts, 0,5 to 1,2 mm long, of augite. It has an intergranular to interstitial, somewhat tholeiitic In slide 21382 there are fewer phenocrysts with a poorly developed texture, and is composed of fresh idiomorphic laths of calcic plagioclase, parallelism. They are well-twinned, cracked and slightly fractured, and 0,1 to 0,4 mm long, and hypidiomorphic to granular pyroxenes, 0,2 to are in a matrix of plagioclase laths, 0,05 to 0,20 mm long, and inter- 42 KAROO SYSTEM BASALTS 43 stitial allotriomorphic augite grains, 0,03 to 0,10 mm across. The Among the basalts in the Machuchuta T.T.L. at about 4 km north­ comparatively abundant iron ores are either thin rods and skeletal west of Maramani village is a ring of hills about 15 m high and 600 m crystals 0,1 to 0,2 mm long, or 0,01 to 0,03 mm granules. There is a in diameter. The central flat floor is drained by two watercourses very small amount of brownish glass, and a few widely scattered running east and west through gaps in the hills. It is thought tbat the amygdales up to 1,5 mm long that are completely filled with green structure is the remains of a small central volcano (McCall, 1967, page celadonite and sometimes some chalcedony or quartz. 51). A specimen (slide 21386) from the crater rim is a pale purplish and white spotted ignimbrite or agglutinate in which heterogeneous The Vesicular Basalts fragments of gneiss up to 15 mm long, and of vesicular basalt up to The vesicular basalts generally lie on top of all the basalt lavas 40 mm long conform to a faint laminar flow structure. The slide is except the Tuli basalts, which are younger. They are widely distributed largely a dark brown, almost opaque, matrix containing scattered feld­ from one end of the mapped area to the other, but their thickness is spar crystals, minute grains of iron ores and pinpoint-sized vesicles. The not known. The majority are on the margins or edges of lava flows, smaller feldspars, about 0,1 mm long, are fairly fresh but the larger where they were formed by escaping gas. The changes in their appear­ feldspars, up to 2,5 mm long, are irregular and partly resorbed crystals ance and colour from massive to vesicular lava are both distinctive and of much altered and partially uralitized oligoclase. In slide 21387 from abrupt as is shown by specimens from 1 km north-east of Ngulumbi the same locality the laminar texture is not so clear. The groundmass is Hill (slide 21383) and 5 km south-east of Chamagundawa borehole opaque and the slightly altered feldspars, which occur singly or in (slide 21384) on Jopempi Block (Mazunga map). The former is an clusters, are more shattered. aphanitic, red, jasper-like rock in which oxidized and opaque volcanic glass is traversed by irregular white veinlets up to 1 mm wide. These The Tuli Basalts 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. The light grey, brownish-grey to black Tuli basalts are aphanitic to very fine-grained rocks which occasionally contain individual or clusters Slide 21384 is from a deep reddish-brown rock containing patches of of feldspar phenocrysts up to 20 mm long. They are characterized by minute vesicles. In it abundant angular fragments of clear feldspar, numerous vesicles, 0,5 to 80 mm long, though most are under 10 mm 0,05 to 0,20 mm across, are scattered along with 0,02 to 0,06 mm grains in length. These vesicles are partly or completely filled with celadonite, and dust of iron ores in a clear isotropic groundmass. Veinlets of black agate, quartz, zeolites or, more rarely, amethyst, calcite and gypsum. basaltic glass containing a few laths of feldspar cut across the rock. They form warty or knotty protruberances on the weathered surfaces, An aphanitic, black and highly vesicular or scoriaceous lava (slide which have a dark brown to black skin up to 10 mm thick. Frequently 21385) from a hill west of the airstrip on Jopempi Block, 8,5 km south the stony ground is littered with agate fragments. of Mazunga, has been fractured and penetrated by an irregular network of veinlets, up to 5 mm wide, that are filled with microcrystalline agate. The Tuli basalts, which are the youngest of the Karoo Iavas, are very quartz and zeolites. widely distributed on top of the horizons of vesicular lavas and agglo­ merates. They form most of the south-western part of the Tuli map area, Many of the lava flows contain, along with airborne volcanic bombs including the Tuli National Area, and the tops of all the high hills from and lava fragments, large pieces of highly vesicular or pumiceous lava, Gongwe westwards to Gongwe Poort, around Ngulumbi Hill and in the and reworked blocks of solidified basalt that were picked up and south-west corner of Lot 5 of River Ranch. 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 A specimen (slide 21388) from Jopempi Block 9 km S.S.W. of of lava fragments up to 45 mm long set in a mixture of fragments under Mazunga has about 25 per cent. of randomly arranged, tabular pheno­ 10 mm long cemented with a pink zeolite. Among the vesicular lavas crysts of plagioclase, that are 5 to 10 mm across and 1 to 2 mm thick, in a number of places are boulders and lenses of massive lava which set in an aphanitic, yellowish-brown matrix. Amygdales, 0,5 to 2 mm may represent examples of liquid immiscibility (McCall, 1967, p. 51). long with a few as large as 12 mm, are abundant. They are completely \ 44 KAROO SYSTEM MBAKA BEDS 45 filled with dark green celadonite, though a few have a thin rim of agate TABLE IV or cores of calcite. The well-twinned and sometimes zoned feldspar ANALYSES OF KAROO BASALTS phenocrysts are slightly fractured and, unlike the clear phenocrysts of the Chandabalini basalts, they contain small patches clouded with Lab. No.. 73/17 73/18 73/15 73/16 zoisite, epidote and more sodic plagioclase. The ground mass is chiefly Slide No .. 21378 21390 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 SiO, 46,62 47,74 47,86 48,29 0,10 mm across. Minute grains, 0,03 to 0,10 mm across, of allotrio­ AI,O, . 7,30 14,23 12,56 18,87 Fe,O, . 4,07 2,54 4,27 2,69 morphic iron ores are abundant, and there are a few small interstitial FeO 6,70 7,04 6,85 5,21 patches of brown glass. MgO. 20,25 8,03 11,30 2,89 CaO 5,35 10,70 9,25 7,28 A brownish-grey, amygdaloidal basalt (slide 21389) from near the Na,O. 0,93 3,27 1,90 4,09 K.O 1,92 1,23 0,85 3,91 pumps at the Shashi Irrigation Scheme in the Maramani T.T.L., con­ H,O+ 2,77 2,14 1,38 4,27 tains very few twinned feldspar phenocrysts under 5 mm across that are H,O- 0,74 0,36 0,61 0,38 CO, 0,10 0,07 0,07 0,05 now brownish and clouded. The small irregular shaped amygdales are TiO, . 2,46 1,72 2,62 1,21 mainly 2 to 5 mm long, and are completely filled inside a thin layer P,O, . 0,42 0,45 0,32 0,57 of brownish chalcedony by coarsely crystalline zeolites. The ground mass MnO. 0,14 0,16 0,15 0,15 consists of randomly scattered, 0,05 to 0,10 mm feldspar laths enclosed TOTALS 99,77 99,68 99,99 99,86 in mottled brown to black glass. S.G. 3,06 2,98 3,04 2,70 A microporphyritic amygdaloidal basalt (slide 21390) from a hill on Jopempi Block, 3,5 km north of Mabina Dip, contains a few hypidio­ Analyst: B. J. Radclyffe. morphic phenocrysts of augite and plagioclase, about 0,5 mm long, and NIGGLI MOLECULAR NORMS a very few, widely scattered and zeolite-filled amygdales up to 2 mm Q 0,16 across in an aphanitic groundmass. Feldspar laths, 0,05 to 0,10 mm 11,55 7,40 5,10 24,05 F {orAb 8,45 24,95 17,30 22,45 long, with rare needles up to 0,5 mm, a few 0,05 to 0,10 mm grains of An 10,10 21,00 23,73 22,48 pyroxene, and a little pale coloured glass form the groundmass. Ne . 2,94 9,51 5,40 11,94 8,08 4,42 Scattered through it are minute grains of iron ore. An analysis, Lab. No. Di En . 5,02 9,12 32,14 2,80 75/15, is given in Table IV. Fs . 0,38 2,82 4,24 1,62 H Eo. 30,86 y Fs . 2,34 Mbaka Beds 01 Fo . 15,78 10,29 4,17 Fa . 1,20 3,17 2,45 The Mbaka Beds, which are named from the Mbaka Dip on the east rMt 4,31 2,73 4,52 2,96 Ilm 3,48 2,50 3,74 1,74 bank of the Mtetengwe River on Jopempi Block, about 11,5 km south­ Ap 0,91 0,91 0,75 1,23 east of Mazunga, are sandstones interbedded at various horizons in the Cc 0,22 0,22 0,22 0,12 Karoo basalts of the area. They occur as small, isolated outcrops Localities: scattered throughout the basalt area and one main outcrop, which is 73/17 Limburgitic basalt. About 2 km soutb-east of Lutope Hill, Jopempi Block, over 27,5 km long and around 200 m wide. It extends from 3,5 km Beitbridge District (Gongwe map). 73/18 Basalt. About 3 km north-west of Lamulas homestead, Jopempi Block, west of the Mazunga River eastwards past Mbaka Dip, Machokovere Beitbridge District (Gongwe map). Hill and the Tongwe River to the Pofu borehole on Jopempi Block near 73/15 Basalt. Hill 31- km north of Mabina dip, Jopempi Block, Beitbridge District (Mazunga map). Kuruwalemba Hill. It may continue farther east-north-eastwards under 73/16 Basalt. About 5 km north-west of Gongwe Poort, Jopempi Block, Beitbridge the alluvium of a small valley. District (Gongwe map). 46 KAROO SYSTEM DOLERITIC INTRUSIVE ROCKS 47

At Pofu borehole and Machokovere Hill a bed of drab-coloured iron ores covers all the grains and gives the rocks their body colour. sandstone lies on a thinly bedded, light red-coloured sandstone, and at The grains are generally angular to sub-angular. Only in slide 21392 Pofu the following incomplete stratigraphic section was measured. 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 Thickness in very angular and in slides 21396, 21399 and 21400 there are small metres splinters of quartz. Sphericity is Iow to medium except in slide 21397 Reddish-purple, compact, cross-bedded sandy siltstone 1S,2 where it is high, and the packing and sorting varies from poor in slides Drab, shaly sandstone ...... 12,2 Red, compact, thinly cross-bedded, fine-grained sandstone 4,0 21396, 21398 and 21400 to good in slides 21394 and 21397 (both Soft, poorly exposed greyish-drab, siltstone 9,2 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 In the area of the Tuli map a small outcrop of fine-grained reddish­ densely stained to almost opaque with iron ore minerals, varies quite brown sandstone occurs in the south-west of the Maramani T.T.L. at widely in amount from rock to rock. In slides 21398 and 21399 it is 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 siliceous. 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 DOLERITIC INTRUSIVE ROCKS west of the homestead on Cawood's Mazunga Ranch, (d) on the fence A large number of dykes, which generally trend between E.S.E. and 3 km W.N.W. of Chamunyu tank, and (e) on a hill 1,3 km west of the E.N.E. and dip at high angles, along with a few sheets and sills, intrude confluence of the Mazunga and Manange rivers. all the rocks in the mapped area from the oldest Precambrian gneisses The Mbaka Beds are fine- to very fine-grained sandstones that range to the youngest Karoo lavas. They mark the last phase of Karoo igneous in colour from red-brown or drab to mouse-grey. Sometimes they have activity in the area, and where probably intruded along existing fault surface calcareous encrustations. Generally they are hard, massive and planes during a period of N.N.W. to E.S.E. regional dilation soon after structureless rocks which break with a conchoidal fracture, but in the the extrusion of the lavas to which they bear a close resemblance, main outcrop around Pofu and Machokovere Hill, some are very finely especially the olivine-bearing and feldspar phenocryst types. Virtually bedded or cross-bedded. They appear to be mainly sedimentary rocks, all contain some basaltic glass but few are holocrystaIline, ophitic and only the rocks near Pofu and north of Limpopo Store are probably dolerites; most of the coarse-grained rocks are sub-ophitic. The holo­ of aeolian origin. hyaline types consist of glass containing microlites and all appear to have been intruded at a comparatively shallow depth into cool wall­ Petrography rocks. A number of specimens were collected for detailed study from near The majority of these intrusive rocks are dykes. Sills and sheets are Pofu borehole (slides 21393-4), Machokovere Hill (slide 21395) and remarkably rare and probably most of the sills recorded in the bore­ Mbaka Dip (slide 21396) on J opempi Block. Other specimens were holes are steeply dipping dykes. Only one sill-like body, 1,5 km north­ collected from 1 km north of Limpopo Store in the Maramani T.T.L. west of Mtetengwe Store, was seen during the mapping of the area. (slide 21397), on Gem Ranch at 3,5 W.S.W. of the homestead on and MehIiss (1951) records only three sills of olivine dolerite, which Cawood's Mazunga Ranch (slide 21398), 4 km south-west of Zebra were less than 430 m long. in Special Grant No. 15. 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 Doleritic dykes are widely distributed throughout the whole of the them is strained quartz with many minute inclusions, that came from Limpopo Valley (Tyndale-Biscoe. 1949; Cox et al. 1967; Robertson. the Precambrian rocks. With it are rare grains of twinned plagioclase, 1967. 1973) and the mapped area. where they appear to be more muscovite, augite, basaltic lavas, and partly devitrified volcanic glass. abundant in the south than in the north. but this may be due to thicker A thin pellicle of densely coloured, red-brown or occasionally black, covers of soil and vegetation in the north. Some of the dykes have 48 KAROO SYSTEM DOLERITIC INTRUSIVE ROCKS 49 weathered into low walls and others into soil-filled troughs which run Two specimens of fractured dolerites were collected from 0,5 km straight for considerable distances across country. Those dykes with south of Shashi Store (slide 21403) and from 8,5 km north-west of the chilled, fine-grained or glassy margins, or with walls or hard meta­ homestead on Sentinel Ranch (slide 21404). Both are medium-grained morphosed or silicified rocks weather into V-shaped structures with low rocks composed of 1 to 3 mm crystals of plagioclase and augite which side walls and a central depression. The dykes with large feldspar have been cracked, disrupted and slightly corroded by the intrusion of phenocrysts are always deeply weathered, and many of the east-trending a small amount of very dark brown basaltic glass. Most of the larger lineaments seen on the air photographs probably mark dykes with a crystals are idiomorphic, 1,5 to 2,0 mm crystals of greenish augite that good cover of soil and denser vegetation. have been locally cracked internally and are surrounded by thin reaction Generally the dykes are composed of dark coloured rocks. Only the rim. The 1 to 3 mm, hypidiomorphic and interstitial feldspar laths are porphyritic dykes are light to dark grey, and the contaminated dykes twinned and poorly zoned. They have been cracked and marginally are spotted a pale greenish-grey. Those dykes that are less than one corroded. Isolated fragments in the glass have been reduced to a vermi­ metre wide, and the margins of some of the wider dykes, consist of form mass that in places is stained greenish. black glassy rocks which are brittle and break with a conchoidal Specimens of fine-grained, sub-ophitic dolerite came from 7,5 km fracture. One dyke, on the road 1 km south of the Bill Irrigation E.S.E. (slide 21405) and 9 km south-west (slide 21406) of Tshibilingwe Scheme, has a 60 m-wide core of fine-grained porphyritic basalt and Hill on Sentinel Ranch. In them a few feldspar crystals up to 3,5 mm chilled margins about 9 m thick on both sides. long and very few, 0,1 to 1,5 mm, crystals of purplish augite occur in The somewhat variable soils formed from the dykes are generally a holocrystalline ground mass of 0,5 to 1,0 mm laths of plagioclase and stony and are full of fragments 50 to 100 mm long. Spheroidal weather­ granular augite. ing and large boulders are rare. Skeletal crystals of iron ores in slide 21405 and tabular crystals Petrography 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 A holocrystalline olivine basalt (slide 21401) was collected from a chlorophaeite, in slide 21406. dyke at the airstrip 7 km south-west of Tshibilengwe Hill on Sentinel Ranch. It is a fine-grained rock composed essentially of hypidiomorphic * ' Samples of the feldspar porphyry type were collected on Cawood's to idiomorphic laths of plagioc1ase feldspar, 0,2 to 0,4 mm long with Mazunga Ranch about 3 km north of Giraffe Dam in the Mtetengwe a few up to 1,5 mm long, and two varieties of augite, one in purplish, T.T.L. (slide 21407), 7 km south-east of Limpopo Store (slide 21408) in very weakly pleochroic, hypidiomorphic crystals 0,4 to 0,6 mm long, the Maramani T.T.L., and from 300 m east of Fly Dam (slide 21409) and the other a pale greenish augite in 0,2 to 0,7 mm interstitial grains on Jopempi Block (Mazunga map). All contain tabular plagioc1ase which produce a sub-ophitic texture. A small amount of fresh olivine phenocrysts, 3 to 10 mm wide and 1 to 2 mm thick, set in a groundmass in idiomorphic crystals 0,1 to 0,2 mm long is scattered through the rock of feldspar laths 0,1 to 1,0 mm long and smaller interstitial grains of and the accessory minerals are iron ores, frequently in 0,1 to 0,2 mm augite, and, in slide 21407 and 21408, less than 20 per cent. of brown octahedra, and rare brownish-red biotite. glass containing microlites and orange-brown patches resembling chloro­ phaeite. Grains, needles and skeletal crystals are accessory in all. An altered olivine basalt (slide 21402) from 8,5 km south-east of Marimani School in the Marimani T.T.L. contains olivine phenocrysts, Similar, but altered rocks, were found at 2,5 km N.N.W. of Gwawe 0,5 to 1,0 mm long, that are now almost completely altered to serpentine Hill on Jopempi Block (slide 21410) and 1 km north-east of Mangombe minerals and are outlined by a rim of iron ores. The groundmass is 0,2 on Nottingham Ranch (slide 21411). In them the large tabular feldspars, to 0,8 mm long feldspar laths which show flow structure, a little inter-. and the few augite phenocrysts in slide 21410, are corroded, cracked stitial augite, some light coloured glass and accessory iron ores that and clouded with alteration products. Their groundmass consists of are 0,2 to 0,3 mm long and only 0,01 to 0,03 mm wide. 0,5 to 1,0 mm crystals of plagioclase and augite, skeletal iron ores up so KAROO SYSTEM STRUCI'UIm SI to 0,5 mm long, and small patches of brown glass. In slide 21411 the one to possibly three kilometres of Karoo and younger deposits have groundmass feldspars are clouded and the augite cracked. been removed.

Contaminated basalt specimens were collected from dykes 1,5 km FAULTS S.S.E. of Gawe Hill (slides 21412-3) on Jopempi Block, 2,5 km north­ The Karoo rocks have been affected by a system of large faults which west of the homestead on Safari Ranch (slide 21414), and 3,5 km east of trend in a general east-north-easterly direction and dip at over 50 Penemene Store in the Mtetengwe T.T.L. (slide 21415). All consist of degrees except in the east where, in places, dips as flat as 20 degrees dirty brownish plagioclase laths enclosed in brownish glass containing were observed. Their displacement of the Karoo rocks is very variable microlites. In the glass are a few scattered fragments, about 0,5 to 3,0 and, in some, may be of the order of hundred and perhaps thousands of mm across, of strained quartz and also in slide 21414 rare fragments metres. The fewer northerly striking faults have much shorter strike­ of dirty brown feldspar from the Precambrian rocks. These fragments lengths and smaller displacements. have been much corroded and have smooth, rounded outlines. These major faults post-date the youngest basalts and generally Fresh basalt specimens were collected from dykes at 9 km south-east bound the Karroo outcrop with down-throws inwards towards the of Limpopo Store in the Maramani T.T.L. (slide 21416) and 2,5 km centre. They and the doleritic dykes were probably formed during a south-west of Penemene Store in the Mtetengwe T.T.L. (slide 21417). period of regional N.N.W. and E.S.E. dilation with a vertical maximum In them small allotriomorphic laths of plagioc1ase and some greenish pressure. This dilation may have been due to a readjustment of the augite grains, less than 0,05 mm across, occur in a small amount of a crust under a load of about one kilometre of sedimentary rocks and at pale glass in slide 21417 and much black glass in slide 21416. Altered least 1,5 km of basalt lavas, and the emptying of the deep-seated magma basalt containing clouded and partly altered feldspars and augite in chambers which supplied the extrusive and intrusive igneous rocks. 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 In the area covered by the Tuli and Mazunga maps the Karoo Mazunga map (slide 21419) and 2 km north of Lupako Hill on Jopempi boundary faults bring the basalts into contact with the gneiss along much Block in the area of the Gongwe map (slide 21418). 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 STRUCTURE the boundary fault 1,5 km south on the east side, and for a short distance In the mapped area the highly complex structures in the Precambrian there are outcrops of up to 3 km of sedimentary rocks on the south rocks have not been studied, only those of the flat-dipping Karoo rocks. side. In the area of the Gongwe map the fault forming the north The Karoo rocks of the Limpopo basin once covered a very large area boundary of the Karoo rocks passes into the gneisses W.N.W. of Gwawe but the present outcrops are comparatively small erosional relics that Hill and Karoo sediments either lie unconformably on the gneisses or are have been preserved by the trough faulting that followed the outpouring displaced in a complex manner by easterly or northerly faults. Among of the Basalts. the Karoo rocks there are small outcrops of gneisses in an area of poor exposure. The Karoo sedimentary rocks were deposited in a flat shallow basin with a floor of gneisses and metamorphic rocks of the Limpopo Mobile The southern boundary of the Karoo rocks enters the area of the Belt. From Dwyka (Permian) to Stormberg (early Jurassic) times the Mazunga map near the confluence of the Gushu and Limpopo rivers. floor subsided gently under a growing cover of sedimentary and, at Here sedimentary rocks rest on the gneiss for about 7 km north of the the end, volcanic rocks. Then regional dilation produced fissures occu­ confluence to where they are faulted against the gneisses as far as the pied by dykes and major normal faults. Subsequent vertical movements Umzingwane River. Another fault to the south of it starts east of the have resulted in one and perhaps two marine invasions, but mainly Umzingwane and becomes the boundary fault. Its displacement increases uplift and very extensive erosion in the mapped area. Over much of it eastwards until the basalts are in contact with the gneisses, and then STRUCfURE 53 52 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 Micro-shears are abundant in some of the Karoo sedimentary rocks (Fig. 2), particularly the Forest Sandstone, and often secondary silicifi­ main road, several large easterly faults and smaller northerly faults cation has produced veinlets in them so that on some weathered out­ produce a ragged termination to the Karoo rocks. crops they form prominences over 300 mm high though most are only While it is easy to recognize the large easterly faults along the margins a few millimetres high. The micro-shears are usually 2 to 5 mm wide of the Karoo outcrop they could not be detected, although probably with some over 100 mm across. Their slickensided surfaces show both present, in the extensive central outcrop of basalts. 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 DYKES and lineaments, though some have a northerly strike. Where displace­ The whole area is traversed by dykes of doleritic rocks and remarkably ments occur the offsets are mainly in an easterly direction. few sills which intrude all the Karoo rocks and adjacent gneisses. Their In an exposure of the Forest Sandstone 4,5 km south of the homestead composition and textures show that they are related to the basalts (some \ on Joco Ranch (Gongwe map) a micro-shear cuts nodules which are possibly having been feeders to fissure eruptions) and were intruded considered to have been formed during the eruption of the basalt lavas. into cool or cold wall-rocks at no great depth. That they came from The micro-shears therefore appear to have been formed after the a deep magma chamber is shown by the largely digested inclusions extrusion of the basalts. 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 o 50 mm (approx.) 20 km long, extends north-eastwards from the south-west corner of I Sentinel Ranch to just south of Gawana Dam (Mazunga map).

FIG. 2. Micra-tau Its in silty sandstone trom the Forest Sandstone 2 km north­ LINEAMENTS east ot Lupako Hill, Jopempi Block. Beitbridge District. A remarkable number of lineaments that are visible on the air photo­ graphs could not be identified on the ground. Like the dolerite dykes JOINTS and the faults, the majority trend nearly eastwards and only a few in directions between north-east and north-west. They probably represent The frequency of occurrence of joints in the mapped area is shown faults, dykes and, particularly in the Tuli National Area joints which on figure 3 with those in the Karoo sedimentary rocks nearest the are not exposed but are marked by a change in soil or vegetation. The centre and those in the basalts on the outside. By far the majority of breccia on the hillock 4,5 km north-east of Massabie's Drift may be a joints strike between 000° and 030· and fewest between 330° and diatreme on a lineament which extends north-westwards from the 000°. However, in the sedimentary rocks the joints show a maximum Limpopo River. between 300° and 330· and minimum between 330° and 000· and in 54 SUPERFICIAL DEPOSITS SUPERFICIAL DEPOSITS 55 the basaltic rocks a maximum between 000· and 030 0 with none between and Bubye rivers. Only a narrow strip of alluvium extends along the 0 330· and 000 • Because only a small number of readings were taken north bank of the Shashi River until below the Tuli confiuence. Here over a very large area it is unsafe to draw conclusions from these there are the Bili, Jalunganga and Shashi Irrigation Schemes extending figures. up the valleys of minor tributaries. Only narrow discontinuous strips N. 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 con­ fluence with the Umzingwane, and around basalt islands in the 1--. 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. W.' I 1· ···· ······· ·······...... -· ··;···-·:· , ..... '...... __ .1 E. I Earth movements, some of them comparatively recent, are thought to be partly responsible for the formation of alluvium, as for example FIG. 3. Joint directions in the Karoo rocks of the Mozunga area. 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. SUPERFICIAL DEPOSITS Alongside the major rivers the alluvium is composed of gravel and An extension of the banded ironstone rubble, described by Robertson sands, but along the smaller rivers it is finer grained sand which is (1973, p. 152) as littering the slopes of Mount Towla, .the Jopempi ridge better sorted and darker in colour. Sometimes the alluvium is dirty white and the surrounding country to the north of the Mazunga map area, and calcareous, as for example that north of Gongwe Poort which is continues southwards as far as Mazunga and the access road to light grey and very dusty when dry. 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 Bishop­ Calcrete is widely distributed throughout the mapped area and is stone Estates, some 40 km south of its nearest possible source. usually less than one or two metres thick. It occurs as light grey, rounded concretions that are best developed in the black clayey soil The unconsolidated rubble bed, which is under one metre thick. is overlying some basalts, particularly the more mafic varieties such as composed of rounded fragments of banded ironstone and much vein the Mabuli limburgitic basalts. Along the watercourses in these areas it quartz partly cemented with carbonate. Most fragments are 100 to 150 is often seen to contain fragments of basalt and ferricrete. A large mm long and the largest 250 mm long. The deposit on the access road patch of calcrete occurs 3 km W.S.W. of the Lamulas homestead on is about 220 feet (67 m) and that on the hillock 100 feet (30 m) above Jopempi Block (Gongwe map). the level of the Umzingwane River. Alluvium occurs along the banks of all the main rivers and their Ferricrete grains up to 10 mm across occur mainly in the sandy soils. larger tributaries, and is best developed in the valleys of the Umzingwane They are quite widely distributed, but never form large deposits. 56 ECONOMIC GEOLOGY COAL 57

ECONOMIC GEOLOGY CoAL CLAYS Probably the only outcrop of coal in the mapped area was discovered Hill Although poorly exposed the Fulton's Drift Mudstones have a large in the east bank of the Umzingwane River near Morgan's in about outcrop area and could contain clays of value to the refractory and 1895 by De Gruyter. His and other interests in the area were acquired ceramic industries. Four samples were collected and the partial analyses in 1896 by Consolidated Gold Fields of South Africa Ltd. and trans­ ferred to a subsidiary Bulawayo company, Tuli Consolidated Coal 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 Fields Ltd., the following year. F. M. Watson had visited the Umzing­ wane area in 1895 and near Morgan's Hill measured the section already firing tests have been done on them. given under the Fulton's Drift Mudstones. In mid-1896 R. Sneddon In 1970 samples of a pale grey clay from the Mtetengwe T.T.L. (1896) collected a sample of coal (Table VI) which had a S.G. of 1,36. about 1 km south-east of Fulton's Drift were analysed for Mr. W. A. He records that about 1,6 km east of the outcrop in the river, a shaft Ferguson of Benfer Estate, and the Mac Nic Syndicate was formed to had been sunk to 11 m in what became known as the Umzingwane produce flint clay for refractory bricks. However, title to the deposit Coalfield (Fig. 4). could not be obtained. The railway line from Cape Town reached Bulawayo in 1897 and it Five samples from excavations in an area 1,5 km east of Mtetengwe was proposed to extend it northwards to Salisbury with a line going Store, near the bridge over the Mtetengwe River on the Bulawayo from near Gwelo down the Sanyati valley and across the Zambezi River road, had alumina contents of 26,9 to 37,2 per cent. and silica contents near Kariba to the Congo. Another line from Bulawayo was to serve of between 49,0 and 59,5 per cent. 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 TABLE V in the northern Transvaal. This line would cross the Umzingwane Coal­ PARTIAL ANALYSES OF FULTON'S DRIFT MUDSTONES field which could not only supply the locomotives but also the Gwanda mines and Matabeleland. Lab. No, . 73 /11 73 /12 73 /13 73 /14 The Tuli Consolidated Coal Fields Ltd. had a capital of £15 000 and % % % % Ign. loss 14,6 18,4 10,3 12,3 held the rights to 24697 ha (55 630 acres) in the Umzingwane and SiO, 48,0 46,8 53,8 53,8 Singwesi coalfields (RS.A. Co. 1900, p. 364 and 1902, pp. 413-4). The 32,0 AI,O, . 33,8 32,0 32,8 principal shareholders included the Matabeleland Gold Reefs and Fe,O" 1,3 1,1 0,8 0,8 MgO . 0,3 0,2 0,3 0,2 Estates Co. Ltd. (RSA Co. 1899, pp. 81-9; 1900, pp. 218-9 and 1902. Cao 0,5 0,3 0,5 0,3 pp. 231-9), Rhodesia Ltd. (RSA Co. 1899, pp. 133-6. and 1902, p. 331) Na,O. 0,2 0,1 0,3 0,1 K,O 0,7 0,5 0,7 0,7 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 TOTALS 99,4 99,4 99,5 100,2 Gwanda Railway Syndicate and several other coal exploration com­ Analyst: B. J. Radc1yffe. panies was A. I. C. Molyneux. Localities: 73/11 About 2 km south-east of Gwawe Dam, Jopempi Block, Beitbridge District Work began in 1896, and by 1897 the outcrop in the Umzingwane (Gongwe map). 73/12 Old shaft, 4 km north of the confluence of the Gushu and Limpopo rivers, River had been trenched and No. 1 shaft sunk 1,6 km east of it. During Nottingham Ranch, Beitbridge District (Mazunga map). 1898 five shafts measuring 4 feet by 6 feet had been sunk, and, on 73 / 13 Pit, 1 km north of Lupako Dip on track to the Bubye River, Jopempi Block. account of water problems, hand drilling was started in April, 1899. Beitbridge District (Gongwe map). 73/14 Northern slope of hill, 300 m west of Lupako Dip, Jopempi Block, Beitbridge No. 1 hole had just been completed when, because of the outbreak of District (Gongwe map). war in South Africa, the company had to withdraw from the area and 58 ECONOMIC GEOLOGY COAL 59 its wagons, animals, etc., were requisitioned by the Imperial Forces at Borehole 1, 2 and 3 were on the west side of the Urnzingwane River Fort Tull. Work was not resumed until April, 1901. Three holes were and borehole 4 on the east side (Fig. 4). Borehole 1 is said to have drilled and by the end of the year it was stated that a 96,5 cm seam of found 107 cm coal at 12,2 m and 12 cm coal at 22,9 m, and borehole good bituminous coal extending over 450 ha (1 000 acres) of the 2 found 122 cm coal at 17,1 m and 122 cm coal at 22 m (D in Urnzingwane Coalfield would yield 9241 tonnes per hectare (3800 tons Table VI). Borehole 3 passed through 91 cm coal at 16,8 m (E in per acre). 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. 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'. ~ ~)jc"t. C 6ord'lOI, .... E. Five shafts and three boreholes were completed on the Singwesi Coal­ ~L .,-.. field. 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 FIG. 4. Sketch map of the Umzingwane, Singwesi and Letengwe Coalfields (1904). 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 considerable amount of work was done on the Umzingwane Coal­ a borehole. field between 1896 and 1904 (Fig. 4). The outcrop in the east bank of The Massabi Coalfield on Nottingham Ranch lies to the north of the the Umzingwane River was exposed in a trench 6,1 m long, 1,2 m wide Limpopo River and to the west of the Gushu River (Fig. 5). An area and 0,6 m deep and was sampled (Table VI). To the east of it five shafts of 405 ha (1 000 acres), Special Grant No. 23, was acquired by the were sunk. No. 1 shaft was sunk to 22,1 m depth without encountering Gwanda Railway Syndicate in which the Matabeleland Gold Reefs and much water. It passed through 13,5 m of dark shale, 46 cm coal, 46 cm Estates Co. Ltd. was a large shareholder (B.S.A. Co. 1899, pages shale, 91 cm good bituminous coal and 150 cm shale and sandstone to 81-89; 1900, pages 218-219; 1902, pages 231-239 and 311-321). Shaft the top of the gneisses. Drives were made in the coal for 30,5 north-east, sinking began in 1899 but, because of the South African war, all work 30,5 m east and 4,6 m south-west of the shaft. No. 2 shaft was sunk to ceased between November, 1899, and April, 1901. Five shafts were sunk the north-east and after going through 16,3 m of brown shale was .and in No. 2 shaft four seams, 51, 132, 38 and 122 cm thick were stopped in hard sandstone at 19,5 m depth. No. 3 shaft also went to found. The coal (I in Table VI) was said to be a good quality bituminous 32 m depth without finding coal. No. 4 shaft reached a depth of 21,3 m coal which caked well and formed an ash which did not clinker. in the gneisses. It passed through 16,7 m of dark shale, 46 cm coal, Molyneux (1903) estimated that two seams of good coal, 120 and 180 56 cm shale and 112 cm coal (sample F in Table VI) which was driven cm thick, had been proved over an area of 40 km' . 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 Little is known about the Letengwe or Mashanga Coalfield around the clay, 2,1 m sandstone, 0,3 m shale, a 2,7 m sheet of dolerite and 15,4 m confluence of the Mtetengwe and Tongwe rivers, which earlier were of drab shale. It is said that a borehole found a 107 cm coal seam at called the Letetengwe and Letombwe rivers (Fig. 4). This area of 40 ha 34,4 m below the floor of No. 5 shaft. (100 acres) to the east of the Singwesi Coalfield was acquired in 1900 60 ECONOMIC GEOLOGY COAL 61

TABLE VI PROXIMATE ANALYSES OF COALS, 1896-1902 A

M V.M. F.C. Ash C.V. Sample % % % % MJlkg

A 2,32 38,36 54,06 15,26 ~ eI No.3 .­,.. B 2,07 23,27 57,95 16,71 27,68 ...", C 1,77 21,31 61,86 15,06 29,54 ~No.5 ...... D 0,68 19,98 53,48 25,86 24,42 ~ E 1,49 23,38 56,57 18,56 28,14 }- F 1,02 22,55 52,37 24,01 23,49 ..t' G 0,96 9,33 70,56 19,15 23,96 ...... H 0,96 9,33 70,56 19,15 23,96 0;..- I 1,17 35,58 54,54 8,71 31,40 ...... A ,~,.,.,,~ Analyst: Samples B-1, G. A. Pingstone, Bulawayo. ~ ..~~~NO.2 ' ~ C Localities: ~~, ~ ",." . ~o.1 ~No.4 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. o 1 MILE H Singwesi Coalfield, 107 cm (42 inches) seam at 24,4 m in Borehole No. 3, January I I 1902. I Massabi Coalfield, two 122 cm (48 inches) seams, November, 1901.

FIG. 5. Sketch map of the Massabi Coalfield (1904) showing shafts. The rights of the Tuli Consolidated Coal Fields Ltd. to the two parts of Special Grant No. 15, the Umzingwane and Singwesi Coalfields, and by the Gwanda Railway Syndicate on the advice of A. J. C. Molyneux the Letengwe Coalfield were transferred on 16th April, 1924, to the Gold who said that it was on the line of the proposed Gwanda railway. At Fields Rhodesian Development Co. Ltd. and are still held. Special Grant least two shafts and two boreholes were sunk. Shaft No. 1 is said No. 23 over the Massabi Coalfield, held by the Gwanda Railway Syndi­ to have found 30 cm of shaly coal, probably at 7,2 m, and No. 2 cate since 1901, was changed to Special Grant No. 30 on 24th November, shaft which was over 9 m deep found no coal; nor did the two bore­ 1903. It was transferred to CopthaU's Stores Ltd. on 27th April, 1914, holes. Later the area was included in Special Grant No. 15. and was terminated on 31st December, 1972. The greater part of the Tuli Coalfield which consisted of the Massabi, Umzingwane, Singwesi By 1902 the colliery at Wankie was being rapidly developed and the and Letengwe coalfields, is now covered by reserved areas. line of the northern railway was changed from Gwelo to Kariba, to BuIawayo to Victoria Falls. When the railway reached Wankie in 1903 In 1950 consideration was being given to a possible future shortage the colliery was ready to produce. The Gwanda and West Nicholson of coal in Rhodesia and the extension of the railway line from West gold mines did not reach expectations and the railway line to them from Nicholson to Beitbridge, past Special Grant No. 15 in which Gold Bulawayo was not completed until 1905. It still has not been extended Fields Rhod. Dev. Co. Ltd. had a 33t per cent. interest, Charter Trust beyond West Nicholson. In this changed situation, interest in the Tuli and Agency Ltd. 31 per cent., Willoughbys Conso!. Co. Ltd. 25 per Coalfield died, and the holding companies were liquidated. cent. and the London and Rhodesian Mining and Land Co. Ltd. an 11 62 ECONOMIC GEOLOGY COAL 63

per cent. interest. In 1951 an area of 184 km 2 (71 square miles) of the Grit, around 100 m of Fulton's Drift Mudstones, with under 10 m of grant was mapped geologically, on a scale of 1 : 20000 (Mehliss, 1951) Basal Beds lying unconformably on gneisses. The total thickness of sedi­ and, as it was discovered that the potentially coal-bearing ground mentary rocks is of the order of 500 m, but the thickness of the basalts extended well to the west and that Molyneux's idea of localized coal is not known. basins possibly was wrong. Gold Fields Rhod. Dev. Co. Ltd. applied for and was granted Exclusive Prospecting Order No. 19 from May, Although the Fulton's Drift Mudstones probably occur throughout 1953 to December, 1961, over an area of 259 km2 (100 square miles) the area of Karoo rocks, the extent, number, quality and behaviour (Morrison, 1974). A total of $29 540 was spent on road making, mapping of their coal horizons are quite unknown. The coal horizons probably on a scale of 1 : 50000 and 1 800 m of diamond drilling in 11 boreholes lie at depths in excess of 500 m, and possibly even of 1 000 m, over (Pelletier, 1955). After the expiry of the order the company was allowed the greater part of the Karoo area so are beyond economic mining to retain rights over part of the coalfields area. depths. Mining in the shallower parts will be complicated by the comparatively intense faulting and the presence of very large dykes Messina (Rhodesia) Development Co. Ltd. was granted Exclusive and sheets of late-Karoo dolerites. The temperature gradient will Prospecting Order No. 393 from 24th January, 1971, to 11th January, 2 probably be high in the Karoo shales which have a thermal conductivity 1973, over 1 295 km (500 square miles) from near the Limpopo River of around 5,7 x 10.3 cal/cm/secrC (Mossop and Gafner, 1951). At on Sentinel Ranch N.N.W. to the Dendele T.T.L. During the period Messina, about 50 km S.E., the thermal gradient is fairly high at 0,269 x of tenure, the company spent $14558 and sank two boreholes, MRDl 1O-3 °C/cm in Precambrian gneissic rocks which have an average thermal and 2 (Johnson, 1973; Morrison, 1975). The information, particularly conductivity of 5,1 x 10-3 cal/cm/sec/oC (Diment and Weaver, 1964). the drilling logs and coal analyses, given in various reports supplied by The permanent water level appears to be at 9 to 18 m. The rocks of the two companies, has been extensively used in this Short Report. the Fulton's Drift Mudstones are almost entirely impervious shales The Karoo strata in the mapped area is a synclinal structure which with hardly any porous sandstones, so that large quantities of under­ dips inwards at less than 10 degrees and plunges very flatly west-south­ ground water are likely to be encountered only in the vicinity of faults westwards from east of the main road from Beitbridge to Fort Victoria and bodies of dolerite. Methane is probably present and, like the water, for 165 km to the Shashi River. It continues beyond into South Africa may be trapped in large volumes under pressure near the faults and and Botswana. It is 50 to 55 km wide northwards. The structure is dolerites. There is probably much burnt coal alongside the igneous dominated by numerous long east-north-easterly faults which rapidly intrusions, but there is no information on the quantities to be expected. displace the Karoo rocks downwards towards the centre as a trough-like The coal seams are probably weathered to a depth of 3 to 10 m and structure. As a result, the basalts outcrop over practically the whole of recognizable outcrops are extremely rare, even in the riverbeds. In the the mapped area and the sedimentary rocks lying under them form small Tuli Coalfield the roof and floor of the coal seams is almost invariably discontinuous outcrops, never more than 10 km wide, along the margins shale which, in the early tunnelling at a depth of about 12 m, seems of the Karoo outcrop, mainly near the eastern end where they outcrop to have stood well. 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 In the early exploration of the Umzingwane Coalfield (Fig. 4), a lower margins, the basalts or upper sediments are down-faulted against the 46 cm of coal not far above the gneisses, was found separated by Precambrian gneisses. The lower sediments, including the coal-bearing around 50 cm of shale from an upper 90 to 100 cm of coal. Analyses, Fulton's Drift Mudstones, are exposed in a strip on the southern margin probably of picked or cleaned samples, are given in Table VI. In the for about 30 km west and 15 km east of where the Umzingwane River adjacent Singwesi Coalfield (Fig. 4) coal thicknesses of 41 to 107 cm crosses it. This strip, the Tuli Coalfield, is the only portion of the mapped were recorded and in the Massabi Coalfield to the west (Fig. 5) four area that has been partly explored for coal. Here, the downward seams of 51, 132, 38 and 122 cm, again not far above the gneisses, were sequence of Karoo sedimentary rocks under the basalts appears to be 80 found in shafts. The compositions of two of the seams is given in to 100 m of Forest Sandstone, 300 m of Red Beds,S to 10 m Escarpment Table VI. 64 ECONOMIC GEOLOGY COAL 65

Twelve boreholes were sunk in the area of Exclusive Prospecting TABLE VII (continued) Order No. 19 and two in the area of E.P.O. No. 393, but five (T5, T2, BOREHOLE T3 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 From To Width M V.M. F.e. Ash S of these boreholes in the Tuli Coalfield are shown on the Mazunga metres metres mm % % % % % e.V. S.T. area map, their generalized logs are given in Table ITI, and analyses 28,04 28,29 253 1,98 28,54 35,94 33,54 1,06 21,9 1 of the coals in Tables VII and VIII. It should be noted that there are 28,45 28,70 254 2,11 30,04 40,95 26,90 0,84 24,2 It 28,93 29,16 229 1,65 31,04 41,97 25,34 7,02 25,1 2t minor differences in the depths given in Tables ITI and in Tables vn 29,54 29,95 407 1,99 29,86 39,95 28,20 1,37 23,9 1 and VIII for what are obviously the same occurences' 35,86 36,14 279 1,71 29,96 37,75 30,58 4,02 22,8 It 36,14 36,60 457 1,82 34,02 46,30 17,86 0,93 27,6 2t Five boreholes (from west to east MRDI. 1'7, TI, T4 and T6) were 36,73 37,01 280 1,87 34,34 47,09 16,70 2,87 28,0 3 37,01 37,34 330 1,81 27,93 37,84 32,42 2,85 22,3 It all drilled on Nottingham Ranch, the western section of Pelletier (1955). 45,11 45,47 356 1,34 30,69 28,91 39,06 1,24 18,2 Here the Fulton's Drift Mudstones of the Massabi Coalfield strike 45,47 45,59 127 1,36 33,64 35,90 29,10 2,69 22,0 2t northwards from the Limpopo River for 6 km to a large E.N.E. fault 46,28 46,43 152 1,64 33,84 48,02 16,50 2,57 28,0 3t 46,51 46,84 330 1,44 32,32 41,62 24,62 0,68 24,7 3 which downthrows to the north. Boreholes 1'7, TI and T4 started in 46,84 47,42 585 1,23 36,18 33,71 28,88 0,80 22,4 2 the Escarpment Grit on the south side of the fault. On the north side 47,52 47,80 280 1,07 28,02 24,63 46,28 2,63 15,1 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 BOREHOLE T4 Mudstones. From To Width M V.M. F.e. Ash S In borehole MRDl the base of the bottom coal is at 422,1 m about metres metres mm % % % % % C.V. S.T. 34 m above the gneisses. The sequence upwards is 170 cm coal 22,17 22,48 304 2,45 29,02 39,63 28,90 1,84 22,S I 24,26 24,61 350 2,25 26,06 39,33 32,36 1,95 21,4 24,84 25,30 457 1,76 24,52 38,19 35,53 7,76 21,0 25,73 25,88 152 2,09 21,85 32,30 43,76 5,82 17,7 TABLE VD 25,88 26,09 204 2,09 27,80 39,17 30,94 2,03 21,9 32,41 32,74 330 1,93 26,36 47,ll 24,60 1,68 24,9 PROXIMATE ANALYSES OF COALS FROM E.P.O. No. 19 AND 32,89 33,20 305 1,69 29,04 51,41 17,86 1,95 27,7 E.P.O. No. 393 33,40 33,53 127 1,92 25,20 43,88 29,00 1,61 23,2 BOREHOLE TO REDRILLED 38,61 38,91 305 1,27 25,43 51,22 22,08 1,70 26,1 39,24 39,47 229 1,29 20,14 42,22 36,35 0,67 20,7 From To Width M V.M. F.C. Ash S 39,47 39,83 355 1,30 23,93 51,79 22,98 0,77 25,2 metres metres mm C.V. S.T. 39,90 40,26 356 1,13 23,45 51,04 24,38 0,66 25,2 % % % % % 40,26 40,39 127 1,31 15,49 24,52 58,68 0,51 12,0 19,05 19,30 254 1,80 22,80 36,90 38,42 3,82 20,0 45,44 45,57 128 0,77 31,46 20,15 47,62 0,36 13,1 23,27 24,23 450 1,92 20,38 35,10 42,60 2,97 18,4 24,1 24,69 25,30 609 1,92 24,68 46,40 27,00 1,73 BOREHOLE T7 33,58 33,96 382 1,93 18,03 30,74 49,30 1,84 15,8 34,42 34,70 279 1,58 25,58 38,33 34,51 2,47 21,5 1 From To Width M V.M. F.e. Ash 30,62 45,70 2,90 16,9 S 44,45 44,88 432 1,37 22,31 metres metres mm e.V. S.T. 44,91 45,24 330 1,40 27,64 47,35 23,61 1,49 25,3 3t % % % % % 23,63 43,78 31,22 1,26 22,0 It 45,24 45,62 381 1,37 50,11 50,50 381 1,61 32,19 42,38 23,82 1,73 25,6 3 45,62 46,08 465 1,79 26,89 44,90 26,42 1,71 23,2 It 52,60 53,03 432 1,55 27,09 35,40 35,96 32,04 4,60 21,3 2 1,28 21,1 3 46,25 46,58 330 1,38 26,52 40,06 53,03 53,44 406 1,47 32,35 40,95 25,23 2,31 25,1 48,44 48,82 382 0,90 29,50 16,36 53,24 5,30 11,5 3 53,75 54,13 381 1,61 27,43 35,12 35,84 2,63 21,0 It 55,78 56,18 407 1,35 23,94 30,86 43,85 0,88 15,7 60,22 60,68 457 1,46 32,31 42,81 23,42 17,76 62,04 0,27 7,7 1,28 25,6 3t 58,52 58,95 431 1,63 18,57 60,78 61,19 407 1,45 31,69 44,31 22,55 1,66 25,8 58,95 59,63 680 1,91 16,19 29,77 52,13 0,29 12,8 4 61,19 61,49 304 1,43 34,70 46,54 17,33 1,26 27,9 3t 59,63 60,22 590 1,97 15,99 34,37 47,67 0,35 13,6 61,49 61,70 203 1,56 27,30 38,14 33,00 60,22 25,20 60,10 0,34 8,5 1,76 22,0 2t 60,86 635 1,68 13,02 62,03 62,20 177 1,04 26,86 32,90 39,20 8,04 19,7 3 66 ECONOMIC GEOLOGY COAL 67

TABLE VII (continued) U . ~ ;::.,...,..r!;I~~~'j; ...... o ~ BoREHOLE T8 v:r r---"'I.lJ'" r-:'\O'" "'" oo"~" a\ 0\"'0\000-,'" ~ 11 U NNNNNNNNN MNNM .- 00 ::l..l( 168,86 169,19 330 1,23 17,22 31,39 50,16 8,28 15,9 .. - 170,00 170,20 210 I,ll 20,75 37,50 40,64 2,27 20,0 _t"')_\O 00 .,.. _CCMOO :S~SE .~'" 173,21 173,91 700 0,84 22,17 38,39 38,60 9,95 20,5 r.nX I I I I I I I I I ...;0.. ..:0.. 175,21 175,44 229 1,23 19,03 35,24 44,50 3,72 18,3 "1- 't ..,~- to~ 175,69 176,17 480 1,33 19,98 33,23 45,46 2,02 17,9 - - 176,33 176,61 280 1,02 23,70 40,44 34,84 2,10 21,9 1 d d E " 192,00 192,48 483 0,69 21,79 43,28 34,24 1,42 22,5 2 U" 0 :l :l 194,18 194,31 127 0,65 23,57 50,34 25,44 1,28 25,8 4t '" oor---oo\.OvO\ ___ '" o~ g.; c C V'irt'lvN ","- 194,46 194,66 202 0,69 20,53 42,60 36,18 0,72 21,4 It o\v.. "CJr---.. V"I.. ..:v.. -.:if""--.. M..s~ ~ ~ ~~ '4Sr---"'oO\O" 194,89 195,35 457 0,64 25,00 52,66 21,70 4,60 17,1 5 > Mf'I"'IMMMt'f1MMN ~ MMNN 0-"_ 195,60 196,14 554 0,92 16,39 42,57 40,12 0,82 19,3 1 ::E ,<;U ~ 196,24 196,57 330 0,70 24,57 46,27 28,46 0,84 23,7 It 0 ~ 11 ::; ~ ___ N _____ 196,70 197,18 483 0,68 19,99 39,09 40,24 2,26 19,4 It ::E~ -.:t.. OC!.\O.. o .. r---... "t"1.0.. ~ ~t---... ~V'i.. ~> ~ 17,0 ~ ·5 U "l 197,41 198,12 7\0 0,63 19,77 35,26 44,34 2,89 ---- E 11 ~ '"..l i:- .... Analysts: Gold Fields Laboratory, Johannesburg. w « _V"I\OOOt--OO\oN_ _OOM\O ·5 ... ~ ..l 0 i5x" OO\O.. ..;M U V;"~~g$"~"~~~" V':IM\OV '"'-0:: = il -S,a.'"'''''' ~ ~ ~ ~ .. " 0 :l ~ tfJ ..ci .J:> _1'000 ::: 11:::. Z \00\0 "'f'-O\oooo ~ .. . 0 g~~ r.f r"I"'I"'..: 0 N" M'" _'" eOV')" "'...... :0.. c .... U" MNf'I"'INMMNMN NC""I("Hf"I C E "':e f-> .. ~ .c .", '"~ BoREHOLE MRDl «.... 0 ..s!...-. .. MM"'""=,, .... ,,~o U 0.-:::" e __ \00 .... t'-~~~:q:;;bM~~__ \OONM"'\O "It'''It'M''' From To Width M V.M. F.C. Ash S ~ 6:2 E -d ;:;:~II e.V. S.G. ILl ~~ ,::l 11+00 metres metres mm % % % % % Z ----- •• ..1( ILl .c .!.!.. :::t::E::: MM "It' 00 M "It' M t'-\O M""'OOM 405,1 406,1 1000 1,74 26,06 18,07 54,13 1,32 2,33 ;:iE Ml-MOOVNl-MOO f'MOOV ,J:: »~ = -V",t--_Y)VMN VV"It--_ 406,1 406,7 600 1,89 20,33 33,87 43,91 0,96 2,23 ~E ___ MM « +.>01 2,13 16,73 47,19 33,95 1,30 1,97 .c 407,7 408,1 400 N-- 0; ::E~ U~N 410,8 411,2 400 1,40 27,71 8,14 62,75 4,40 2,68 0 o I H 412,4 413,0 600 2,13 14,49 54,20 29,18 2,26 33,0 1,93 OO...,.OOO\MOlnOO "It'000\ o~ v\MOOMM_r---",_ MOOMM '" :38 . 413,0 413,9 900 1,86 20,13 30,42 47,59 4,94 2,23 ...0 foot; ~~~"~~":(~"~~ ~~~~.. -=..:9 414,2 414,7 500 2,04 15,32 52,53 30,11 0,72 27,0 1,96 E '" " . 420,4 422,1 1 700 1,60 23,48 13,98 60,94 3,74 2,58 -- -..".2~ - 424,6 425,5 900 1,23 20,57 17,71 60,49 0,54 2,55 E~ f'OO_"d" ~ ~~ ol:: ~~~~~~~N~ OOM"d"N ,,"..." Analysts: Research Centre, Messina (Transvaal) Development Co. Ltd., S. Africa. ... ",,\lSMO\" ~ ~E" t.,.;-o"'''''''g.,.;"M"d"MMVl !:::~ Mf->f->f-> :! = 239 k ca1/kg = 0,443 1b./lb. S.T. = Swelling test S.G. = Specific gravity -..: ~~ COAL 69 68 ECONOMIC GEOLOGY analysed. Starting at 176.02 m depth and 19.36 m above the gneisses. (49.9 per cent. ash). 540 cm black mudstone. 430 cm coal and shale. the upward sequence was 46 cm coal, 40 cm shale. 15 cm coal. 16 cm 250 cm black shale. and 620 cm coal and shale. the top being at 402.0 m shale. 35 cm coal. 122 cm shale. 15 cm coal. 77 cm shale. 30 cm coal. depth. The upper coal and shale horizons consist of thin seams and 475 cm shale (167,49 m depth). 10 cm coal. 66 cm fireclay. 8 cm coal. lenses of coal. cut by perpendicular needles of aragonite. in carbonaceous 102 cm fireclay. 38 cm coal. 10 cm fireclay. 79 cm coal. 38 cm fireclay. shales with blebs of pyrite. 30 cm coal, 23 cm fireclay. 8 cm coal. 63 cm fireclay. and 15 cm coal The base of the coal in borehole T7 is at 61.59 m. about 11.3 m with the top at 162.59 m depth. 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.). Borehole T8. which lies on the east bank of the Umzingwane River. 609 cm dark mudstone. 38 cm coal (ash 35.8 and 25.2 per cent.). 39 14t km E.N.E. of borehole T6 and north of the Umzingwane Coal­ cm mudstone. 76 cm coal (ash 36.0 per cent). 210 cm mudstone. and field workings. gives quite a different succession. The floor of the bottom 38 cm coal (ash 23.8 per cent.). the top being at 50.12 m depth. 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 In borehole T3 the bottom of the coal is at 47.83 m and 17.17 m sandstone. The sequence up from 198,12 m is 23 cm of dull shaly coal. above the gneiss. Upwards the sequence is 59 cm coal (46.3 per cent. 28 cm shale. 28 cm dull shaly coal. 48 cm bright coal. 10 cm shale. ash). 10 cm shale. 66 cm coal (ash 28.9 and 24.6 per cent.). 7 cm 10 cm coal. 18 cm shale. 28 cm coal (ash 22.8 per cent.). 332 cm shale, carbonaceous shale. 16 cm coal (ash 16.5 per cent). 68 cm carbonaceous 15 cm coal. 28 cm shale. 53 cm coal (ash 21.7 per cent.). 8 cm shale. shale. 46 cm coal (ash 29.1 and 39,1 per cent.). 38 cm black shale with 13 cm coal, 7 cm shale. 8 cm coal, 13 cm shale. 15 cm coal, 88 cm coal streaks. 10 cm coal. 99 cm carbonaceous shale. 5 cm coal. 135 cm shale. 18 cm coal. 64 cm shale. 18 cm coal (ash 34.2 per cent.). 7 cm black shale. 10 cm coal, 3 cm grit. 437 cm black shale. 40 cm sandstone. shale. 23 cm coal (ash 34.2 per cent.). 663 cm shale. 28 cm coal (ash 64 cm coal (ash 32,4 and 16.7 per cent.). 12 cm black shale. 46 cm coal 31.3 per cent.). 8 cm shale. 55 cm coal (ash 29.8 per cent.). 11 cm shale. (ash 17.9 and 30.6 per cent.). 633 cm black shale. 35 cm coal (ash 28.2 10 cm coal. 18 cm shale. 28 cm coal (ash 22.8 per cent.). 332 cm shale. per cent.). 33 cm shale. 21 cm coal (ash 25.3 per cent.). 28 cm shale. 8 cm coal (ash 33.7 per cent.). 15 cm shale. 41 cm coal (ash 31,2 per 50 cm coal (ash 27.0 and 33.5 per cent.). 21 cm shale. and 7 cm coal. cent.). 234 cm shale. 65 cm coal and calcite (ash 31,6 per cent.). 23 cm the top being at 27.74 m depth. carbonaceous shale, 28 cm coal and calcite (ash· 34.8 per cent.). 16 cm In borehole T4 the floor of the bottom coal is at 46.28 m and 15.09 carbonaceous shale. 48 cm coal and calcite (ash 45, 5 per cent.). 20 cm m above the gneisses. The sequence upwards is 10 cm coal. 51 cm carbonaceous shale. 29 cm coal and calcite (ash 35,2 and 38,4 per cent.). black shale. 25 cm coal (ash 47.6 per cent.). 21 cm carbonaceous shale. 129 cm shale. 35 cm coal and calcite. 338 cm fireclay. 15 cm coal (ash 12 cm coal. 16 cm carbonaceous shale. and 28 cm coal. All this coal 40,6 per cent.). 87 cm shale. 30 cm coal (ash 50.2 per cent.). 46 cm is dull and shaly. Above it is 439 cm shale. 107 cm coal (ash 24,4. 23.0 shale. 43 cm coal, 41 cm shale, 25 cm coal, 56 cm shale. 30 cm dull and 36,4 per cent.). 28 cm shale with coal. 10 cm coal (ash 22.1 per coal, 92 cm shale. 2 cm coal. 51 cm fireclay. and 3 cm coal at 165 m cent.). 521 cm shale and sandstone. 10 cm coal (ash 29 per cent.). 22 cm depth. shale. 23 cm coal (ash 17.9 per cent.). 21 cm carbonaceous shale. 33 After the deposition of some 15 to 30 m of shale on either the Basal cm coal (ash 24.6 per cent.). 685 cm shale. 29 cm coal (ash 30.9 per Beds or the gneisses. the first coal horizon was deposited in the Fulton's cent). 17 cm dull coal (ash 43.7 per cent.). 26 cm black shale. 17 cm Drift Mudstones and the succeeding 15 to 20 m of strata consists of coal (ash 35.5 per cent.). 18 cm shale. 33 cm bright and dull coal (ash grey to carbonaceous shales and mudstones containing two to four coal 32,4 per cent.). 31 cm shale. 8 cm coal. 144 cm shale. 16 cm coal (ash horizons and very localized sheets of sandstone. The coal layers vary 28.9 per cent). 2 cm carbonaceous shale. 8 cm coal (ash 28.9 per cent). from a few centimetres to around a metre in thickness. and are separated the top being at 22.17 m depth. 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 In borehole T6 the coal between 170.06 and 176.02 m is recorded as variable ash contents within the coal seams suggests that the coals were burnt coal and the coal above 167,49 m as shaly coal; none was 70 ECONOMIC GEOLOGY DIASPORE 71 formed from the debris of small plants mixed with contemporaneous failure if their properties are not taken into account in design life and detrital clay or silt. Argillaceous sedimentation appears to have been structure of tbe road. According to Weinnert (1963) rocks rich in continuous to form the shales and mud stones. With the addition of plagioc1ase and ferromagnesian minerals, if incipiently weathered, are organic debris the shales passed gradationally through black and suspect, particularly in areas of high rainfall. This is very much a carbonaceous shales to become coals when the amount of organic matter generalization because there is probably no better road or building was very large. This appears to have been caused by rhythmical subsi­ aggregate than a fine-grained dolerite from the point of view of strength, dence which controlled the position of the shoreline, the depth of the durability and resistance to weathering. This rock is composed entirely water, and the amount of organic matter added. Neither macroscopic of calcic plagioclase and pyroxene, but its texture is the controlling nor microscopic studies of the coals have been made. factor. However, in the area in question the Tuli basalts would probably be superior to the Mabuli limburgites and the Chandabalini porphyritic From the meagre amount of information available it would be rash at varieties. this stage to draw conclusions about the quality, quantity or potential of the coal in the area; much more information is needed. Building Stone. Supplies of stone for building purposes are not a matter of importance in an area of such low population density and develop­ CoNSTRUCfION MATERIALS ment potential. Practically any variety of rock of pleasing appearance, not excessively weathered, and more importantly with rectangular joint­ Sand. The channels of the larger rivers in Mazunga area have deep pockets of sand suitable for most building and construction purposes. ing structure for ease of quarrying, could be utilized. Quarries could be Generally the sands are quite coarse and contain very little mica or established at some of the outcrops of indurated and silicified Forest few basalt fragments. The sands are composed of quartz and lesser Sandstone and small blocks of fine-grained reddish sandstone could be won from the exposures of the Red Beds Formation on Nottingham amounts of feldspar. The degree of rounding varies considerably, but and Sentinel Ranches. the quartz sands are always more angular than the basalt-derived sands, despite shorter distance of transport of the latter. These contain DIASPORE weathered and rounded particles of basalt, often coated with a film of During construction of the new main road from Beitbridge to Fort clay which renders them quite unsuitable as building material. River­ Victoria, two most unusual occurrences of diaspore, predominantly in bank sands are much finer grained and contain more mica and organic the form of almost perfectly spherical nodules, were discovered on matter than the channel sands. surface and in gravel excavations at points approximately 20 and 30 Road Metal. The Karoo sedimentary rocks are too soft and friable to kilometres respectively south-west of the Bubye River bridge. The provide a source of road metal except where they have been thermally general profile revealed in the pits is a 45 cm cover of red-brown sandy indurated by overlying basalt flows and adjacent dolerite intrusions, or loam with quartz fragments and rare diaspore balls, followed by 30 cm where they have been subjected to silicification in fault and shear-zones. of diaspore-bearing gravel composed of sub-rounded fragments of A large quarry has been established in metamorphosed Forest Sand­ indurated Karoo fireclay together with dolerite, quartz and granitic stone, 3 km for the main road along the access road to J oco Ranch. gneiss and lumps of calcrete. Primitive artefacts also occur in this gravel This is one of the very few suitable localities in the area as outcrops bed suggesting a PIeistocene age for its deposition. Below this level the of silicified, so-called "quartzitic rock", are rare. In its normal state calcrete content increases rapidly to bedrock of decomposed dolerite, the Forest Sandstone is a very soft and friable rock with a low crushing granitic gneiss and amphibolite at a depth of 1,5 m. The diaspore content strength. of the gravel layer was visually estimated to vary between one and 10 per cent. (Morrison, 1970). Of the Karoo rocks, the basalts and dolerites afford the most suitable materials, and deposits are numerous and extensive. The vesicular The source, and mode of formation particularly, of the diaspore was basalts and those containing an appreciable quantity of olivine are less puzzling although it seemed reasonable to assume that the nodules were reliable than others and are more likely to result in base and sub-base in some way associated with the alumina-rich Karoo shales of the 72 ECONOMIC GEOLOGY GOLD 73 area and had either grown as concretions in these shales or were the TABLE IX result of some metamorphic effect on them. Confirmation of this view ANALYSES OF DIASPORE NODULES is provided by Morrison (1973) who was afforded the opportunity, at Messina Mine, of examining specimens of Karoo shale from eastern Calcined Botswana which contain casts and diaspore nodules paler in colour but Sample 2 3 4 5 material otherwise identical in all respects to those in the gravels near the Bubye River. During the course of the present survey it was further substan­ % % % % % % SiO, 8,70 2,54 1,26 4,60 1,72 3,0 tiated by the discovery of diaspore balls in situ in borrow pits along­ AI,O, . 72,40 80,02 80,22 77,20 77,90 90,0 side the old road some 5 km north of Bubye River bridge. Here there is Fe,O, . 0,50 0,02 1,20 0,40 1,10 1,4 TiO, . 1,60 1,00 1,40 1,60 1,20 1,9 a tendency to latitudinal parting in the balls which presumably Cao . 1,60 1,00 0,85 1,47 4,00 reflects original bedding in the Karoo-age, Fulton's Drift Mudstones, in MgO . 0,01 0,17 0,84 1,00 0,77 which they occur. At this locality there is a flat-dipping dolerite intrusion Na,O. 0,08 0,Q7 0,06 0,07 0,05 K,O .... 0,13 0,06 0,06 0,09 0,07 which has metamorphosed the mudstones and apparently by some Ign. loss at 640° C 14,60 14,50 14,70 14,10 13,60 obscure process, patchily raised the alumina content from some 40 per TOTALS 99,62 99,38 100,59 100,53 100,41 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 Information regarding the gravel deposits was brought to the attention shape and range from 1 to 5 cm in diameter. The irregular ones may be of Vereeniging Refractories Limited in South Africa, and the nodules grotesquely formed or have a muffin or sausage shape, and a type of were determined by X-ray fluorescence to be composed essentially of dumb-bell form with two spheroids joined by a bar of similar diameter diaspore. In 1970 two Exclusive Prospecting Orders were granted to a to the spheroids themselves has been noted. At the locality north of the subsidiary of this company who examined the area and concluded that river biscuit -like discs up to 7 cm in diameter are present. All are diaspore constituted 2 per cent. by weight of the gravels on average. The characteristically heavy (S.G. 3,11-3,26), very hard, tough, extremely fine­ company pegged two blocks of claims covering the better sections before grained and with a greasy lustre. They have a patina less than 1 mm revocation of the orders in 1971. The results of analyses done in the deep, in various shades of drab-brown and internally are somewhat laboratories at Vereeniging are given in Table IX. 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 GOLD encompassing mudstones. A cut surface sometimes exhibits faint irregular In the north-eastern part of Jopempi Block there is a high, east­ veining but no suggestion of radial or concentric texture is discernible. trending ridge of Karoo basalts and dykes and, where the Tongwe A microscope slide (slide 21420) is not very revealing. It consists River cuts through it, is Gong's Poort (now Gongwe Poort) which was essentially of slender diaspore prisms averaging 0,015 mm in length. once the site of a police camp on a very old road from Fort Tuli to These usually occur clustered and with a completely random orientation. Fort Victoria. A rumour arose that the reddish-coloured basalts con­ The matrix is too fine-grained for positive determination. It is sensibly tained gold and in 1912 R. M. Nairn of Bulawayo sent Llewellyn Davis isotropic and lowly refracting; in parts it resembles chalcedony but and a party to sample the then deserted area. They collected about usually merges imperceptibly into the several lenticular voids in the 200 samples of "the most likely rock" and these were assayed. It is slide and the mounting medium at the edges. Judging by chemical said that one contained 103 g/t gold (60 dwt. per ton), about 12 carried analyses that have been made, this matrix must consist of some other more than 8,6 g/t (5 dwt. per ton), and the majority no gold at all. form of hydrated aluminium oxide. In addition, a small amount of Probably around 1923, the Gold Fields Rhod. Dev. Co. Ltd. sampled opaque ore minerals is scattered throughout the slide and there are the ridge and found no gold in the samples panned. Seven samples patches in which calcite may be recognized. were assayed and contained a trace or no gold. 74 ECONOMIC GEOLOGY WATER 75

A Major Miller raised the issue once more in 1939, and a party of presents a major problem, particularly in the basalt terrain which three Government Mining Engineers, Messrs. F. Elliott, E. A. Richard­ occupies the greater part of the mapped area. For one reason or another son and Bennett, thoroughly examined the area. They collected 163 a large number of both earth-fill gravity dams and concrete structures samples which were assayed. One contained 0,3 g/t gold, two contained built on basalt have failed or have been breached during floods. Those 0,2 g/t gold, 14 contained 0,09 g/t gold and 146 a trace or no gold. that have not, hold water only for a month or two after the cessation A. M. Macgregor (1939) visited them in August, 1939, and reported of the rains. Dams founded on the Karoo sediments are more successful, that the ridge consisted of successive flows of basalts with amygdaloidal but sites are limited. The Gwawe and Tongwe dams are two examples layers at the top and bottom of each flow. The lavas were cut by dolerite which retained water supplies, even after the 1971-72 droughts. dykes, some of which contained interstitial quartz, and the poort was Boreholes in the basalts have not provided good supplies of water. due to a cross-fault. Thirty-two such holes drilled in the Tribal Trust Lands to depths MAGNESITE 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.). On top of a small rise about four kilometres north of the confluence They average about 0,67 litres per second (550 g.p.h.) and are adequate of the Shashi and Limpopo rivers lumps of white and pale grey for domestic purposes and the watering of a small number of stock, but magnesite are strewn over an area measuring approximately 1000 by. for no other uses. It is probable that at greater depths in the basalt, 200 m ·and underlain by Mabuli limburgitic basalt. The lumps often especially at the contact between basalt and underlying sediments, there have a rough mammillary form. Some are very pure white in colour may be very large artesian aquifers. Their location and exploitation, and resemble a tightly packed cauliflower stripped of its leaves. They however, will have to await a detailed geophysical investigation of the vary considerably in size, the larger ones measuring about 30 cm in structural pattern of the Karoo-rock basin. diameter and weighing about 5 kg. At present the only supplies adequate for crop irrigation are those that Similar occurrences, usually containing smaller lumps and granules have been obtained by drilling to bedrock through the sands and gravels of magnesite up to 5 cm in diameter, were noted at several other in the alluvial flats along the major rivers. A programme instituted early localities on the basalts. On the slopes down to the Bubye River, in the vicinity of Lupako Dip, magnesite admixed with calcrete is thought TABLE X to have been derived from the nearby limburgite. WATER BOREHOLES IN ALLUVIUM The genesis of this magnesite is not clearly understood although it is almost certainly directly associated with ultramafic Karoo lava flows Locality Depth Yield or penecontemporaneous ultramafic differentiates in sill-like intrusions River Property Grid re! metres litres per sec. into them. It probably occurs primarily as a network of ramifying veinlets in the lavas or sills. In the Karoo basalt areas magnesite Shashi . Maramani T.T.L. 390515 28,5 117,0 nodules can usually be distinguished from surface calcrete by virtue 396500 27,8 114,0 Limpopo Sentinel Ranch . 580466 25,0 36,0 of their being much whiter, harder, heavier and more compact. 635849 20,5 114,0 580466 23,0 48,9 Nottingham Ranch 717507 20,0 42,6 WATER Umzingwane . Bishopstone 840725 26,0 114,0 840725 24,4 85,2 In a hot, arid area such as the Beitbridge District the presence of 837725 25,5 114,0 underground water supplies is of great importance. The average annual Gem Ranch. . 877673 21,5 114,0 Mazunga Ranch . 881686 21,0 39,8 rainfall is only 380 mm and for nine months of the year the average 880672 23,0 92,3 daily maximum temperature exceeds 30°C. In consequence the 865690 22,5 142,0 evaporation rate is very high and successful storage of run-off water 76 ECONOMIC GEOLOGY REFERENCES 77 in 1973 by the Provincial Water Engineer, Matabeleland, gave the REFERENCES satisfactory results detailed in Table X. ANON. 1920. Zambezi Coalfields. S. Afr. Min. and Engr. J. Mozambique and Six irrigation schemes in the area, three along the Shashi River, two Congo Spec. No. 1920, p. 63. ANON. 1921. Union and Rhodesia coal resources. S. Afr. Min. and Engr. 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Ser. A, Vol. 257, pp. 71-218. COX, K. G., MACDONALD, R. and HORNUNG, G. 1%7. Geochernical and petrographic provinces in the Karroo basalts of Southern Africa, Amer. Miner. Vol. 52, pp. 1451-74. DIMENT and WEAVER, 1964. NAS-NRC Pub. No. 1188, p. 75. JAMIESON, B. G. 1966. Evidence of the evolution of basaltic magma at elevated pressure. Nature, Vol. 212, pp. 243-6. JOHNSON, J. R. 1973. Final report on E.P.O. No, 393. Unpublished. Rhod. geol. Surv. Technical files. KING, L. C. 1951. South African scenery. 2nd Bd. Oliver and Boyd, Edinburgh. KING, L. C. 1952. The geomorphology of the eastern and southern districts of Southern Rhodesia. Trans. geol. Soc. S. Afr. Vol. 54, pp. 33-64. LACEY, W. S. 1%1. Studies in the Karroo floras of Rhodesian and Nyasaland­ Pt. 1. A geological account of the plant-bearing deposits. Proc. Trans. Rhod. scient. Ass. Vol. 49, Pt. I, pp. 26-53. LlGHTFOOT, B. 1929. The geology of the central part of the Wankie Coalfield. S. Rhod. geol. Surv. Bull. No. 15. MACDONALD, R. 1967. Geochernical and petrographic provinces of Karroo basalts. Proc. geol. Soc. London, No. 1637, pp. 44-6. MACGREGOR, A. M. 1939. Report on a visit to Gong's Poort, Mazunga, Gwanda District. Unpublished. Rhod. geo!. Surv. Technical files. MAUFE, H. B. 1913. The coal resources of Rhodesia in The coal resources of the World, pp. 393-6. Xlth In!. geol. Congr., Toronto, 1913. MAUFE, H. B. 1919. Recent advances in Rhodesian geology. Proc. geol. Soc. S. Afr. Vol. 22, pp. xxxi-xxxvii. MAUFE, H. B. 1924. An outline of the geology of Southern Rhodesia, S. Rhod. geol. Surv. Short Rep. No. 17. MAUFE, H. B. 1929. An outline of the geology of Southern Rhodesia. S. Rhod. geol. Surv. Short Rep. No. 24. McCALL, G. J. H. 1967. Geology of the Nakuru-Thomsons Fall&-Lake Hanning­ ton area. Geol. Surv., Kenya, Rep. No. 78. 78 REFERENCES REFERENCES 79

MEHLISS, A. T. M. 1951. Report on a general investigation of a portion of the TYNDALE-BISCOE, R. 1949. Notes on a geological reconnaissance of the Tuli Coal Grant (S.G. 15) and environs, Gwanda District. Unpublished. country east of Beit Bridge, Southern Rhodesia. Trans. geol. Soc. S. Atr. Rhod. goo!. Surv. Technical files. Vol. 52, pp. 403-11. MELLOR, E. T. 1905. A contribution to the study of the Glacial (Dwyka) WEINNERT, H. H. 1963. Test results on some Southern Rhodesian road founda­ Conglomerate in the Transvaal. Quart. I. geol. Soc., London. Vol. 61, tion materials in relation to climate. Proc. 3rd. Southern African reg. Con/. pp. 679--89. on Soil Mechanics and Foundation Engineering, Salisbury. pp. 135-8. MENNELL, F. P. 1905. Dwyka conglomerate. Proc. Rhod. scient. Ass. Vol. 5, WORST, B. G. 1962. The geology of the Mwanesi Range and the adjoining Pt. I, pp. lQ-11. Country. S. Rhod. geol. Surv. Bull. No. 54. MENNELL, F. P. 1906. The banket formations of Rhodesia. Trans. geol. Soc. S. ZEALLEY, A. E. V. 1910. The mineral resources of Rhodesia. Rep. natn. Mus. Afr. Vo!. 8, pp. 82-7. S. Rhod. No. 9, pp. 26-60. MENNELL, F. P. 1907. The mineral wealth of Rhodesia. 5th Ann. Rep. natn. Mus. S. Rhod. pp. 17-54. MENNELL, F. P. 1908. The Rhodesian miner's handbook. Rhod. Mus. Pub!. No. 4, Bulawayo. MENNELL, F. P. 1910. The geological structure of Southern Rhodesia. Quart. I. geol. Soc. Lond. Vo!. 66, pp. 353-75. MOLYNEUX, A. J. C. 1901. Notes on some fossils from the Sengwe Coalfields. Proc. Rhod. scient. Ass. Vo!. 2, pp. 88-93, 126-7. MOLYNEUX, A. J. C. 1903. The sedimentary deposits of Southern Rhodesia. Quart. I. geol. Soc. Lond. Vo!. 59, pp. 266-91. MOLYNEUX, A. J. C. 1909. On the correlation of the Karoo System in Rhodesia. Rep. S. Afr. Ass. Advance Sci. pp. 107-10. MOLYNEUX, A. J. C. 1911. Some problems presented by the Karoo System in Rhodesia. S. Afr. J. Sci. Vo!. 8, pp. 31-45. MORRISON, E. R. 1970. Notes on the occurrence of diaspore nodules, Bubye River, Bulawayo Mining District. Unpublished. Rhod. geo!. Surv. Technical files. MORRlSON, E. R. 1973. Diaspore. Unpublished. Rhod. geoL Surv. Technical files. MORRlSON, E. R. 1974. Exclusive Prospecting Orders No. 1-250. Rhod. geo'. Surv. Bull No. 72. MORRlSON, E. R. 1975. Exclusive Prospecting Orders No. 251-400. Rhod. geol. Surv. Bull. No. 74. MOSSOP AND GAFNER, 1951. I. Chem. Met. Min. Soc. S. Afr. Vo!. 52, p. 61. PELLETIER, R. A. 1955. Final report on E.P.O. No. 19 and Special Grant No. 15 with geological maps and borehole logs by A.T.M. Mehliss. Unpublished. Rhod. geol. Surv. Technical files. ROBERTSON, I. D. M. 1967. Geological report in 17th Expedition of the Rhodesian Schools Exploration Society - Maramani. pp. 34-8. ROBERTSON, I. D. M. 1973. The geology of the country around Mount Towla, Gwanda District Rhod. geol. Surv. Bull. No. 68. SNEDDON, R. 1896. Report on the Coal Measures recently discovered on the Bubye River, Mashonaland. Unpublished. Rhod. geol. Surv. Technical files. SOUTHWOOD, R. T. 1898. Report of the Tuli Consolidated Coalfields Co. Ltd. in British South Africa Co. Reports on the administration of Rhodesia. 1897-1898, pp. 199-200. SWIFT, W. H ., WHITE, W. C., WILES, J. W. and WORST, B. G. 1953. The geology of the Lower Sabi Coalfield. S. Rhod. geo/. Surv. Bull. No. 40. SWIFT, W. H. (Editor) 1961. An outline of the geology of Southern Rhodesia. S. Rhod. geol. Surv. Bull. No. 50.