REPUBLIC OF SOUTH AFRICA

RfPUBLIEK VAN SUID-AFRIKf,

DEPARTMENT OF MINES DEPARTEMENT VAN MYNWESE GEOLOGICAL SURVEY GEOLOGIESE OPNAME

< ITHE GEOLOGY OF THE COUNTRY AROUND STANDERTON

AN EXPLANATION OF SHEET 2628D (BALFOUR) AND 2629C (STANDERTON)

by

H. JANSEN, D.Se., K. E. SCHALK, Dr. Rer. Nat.,

A. LEUBE, Dr. Rer. Nat., A. A. SNYMAN, M.Se., A. P. A. STEYN, B.Se., F. S. J. de JAGER, D.Se. and H. M. BEeR, Dr. Phil.

With a contribution on

THE EV ANDER GOLDFIELD

by

The Mines Geological Department, Evander (Union Corporation Ltd)

Mel In opsomming in Afrikaans onder die opskrif: DIE GEOLOGIE VAN DIE GEBIED RONDOM STANDERTON COPYRIGHT RESERVED!KOPIEREG VOORBEHOU 1972

PRINTED BY AND OBTAINABLE FROM THf GEDRUK DEUR EN VERKRYGBAAR VAN GOVERNMENT PRINTER, BOSMAN STRUT, DIE STAATSDRUKKER, BOSMANSTRAAT, PRIVATE BAG X85, PRETORIA PRIVAATSAK X85, PRETORIA

GEOLOG'ICAl MAP IN COlOUR ON A GmLOGlfS~ KAART IN KLWR OP 'N SCALE OF 1:125 000 OBTAINABLE SKAAL VAN 1:125 000 APART VER­ SEPARATELY AT 60e, OVERSEAS 75c KRYGBAAR TEEN 60c, OORSEE 75c CONTENTS

Page ABSTRACT-Part I and Part II .. (v)

Part I.-THE GEOLOGY OF THE COUNTRY AROUND STANDERTON I. INTRODUCTION. A. LOCATION AND EXTENT OF AREA .. B. COMMUNICATIONS...... C. PREVIOUS WORK ..... D. PRESENT INVESTIGATIONS .. 1. Distribution of Work . . 2. Base-Maps ..... 3, Acknowledgements.

n. PHYSIOGRAPHY .. A. RELIEF ... B. CLIMATE AND DRAINAGE .... 2

III. GEOLOGICAL FORMATIONS .. 2

IV. ARCHAEAN COMPLEX .. 2 A. SWAZILAND SYSTEM .. 3 1. Onverwacht Series .. 3 2. Fig Tree Series, .. 3 B. MOODIE SYSTEM ... 3 C. JAMESTOWN IGNEOUS COMPLEX .. 3 D. GRANITE AND GNEISS .... 3

V. WITWATERSRAND SYSTEM. 3 A. HOSPITAL HILL SERIES .. 4 B. GOVERNMENT REEF SERIES ...... 5 C. JEPPESTOWN SERIES ... . 5 D. MAIN-BIRD SERIES .. . 6 E. KIMBERLEY-ELSBURG SERIES ...... 6 F. WITWATERSRAND SYSTEM IN THE NORTHERN AREA .. 7

VI. VENTERSDORP SySTEM .... 8

VII. TRANSVAAL SYSTEM .... 9 A. BLACK REEF SERIES .. 9 B. DOLOMITE SERIES ... 9

VIII. KAROO SySTEM .... 9 A. DWYKA SERIES .. 9 B. ECCA SERIES ... . 9 1. Lower Stage .. . 10 2. Middle Stage . . 10 3, Upper Stage .. 10

IX. RECENT DEPOSITS ... 10 A. GRAVEL ...... 10 B. SAND ...... 10 C. ALLUVIUM ...... 10 D. LATERITE AND FERRICRETE. I1 E. SCREE 11

X. INTRUSIVE ROCKS. 11 A. IGNEOUS ROCKS OF PRE-KAROO AGE ... I1 B. IGNEOUS ROCKS OF POST-KAROO AGE .. 11

Xl. STRUCTURAL GEOLOGY ... 11

(iii) y" Part 1-The Geology of the Country around Standerton

1. INTRODUCTION 2. Base Maps A. Location and Extent ot Area Base maps 011 the scale 1: 50 000 were used. These The area is situated in the South-eastern Transvaal. are the I: 50 000 topographical sheets of the Republic In the southern part a very small portion falls in of South Africa and also 1: 50 000 cadastral sheets the Orange Free State. It is bounded by latitudes obtained from the Surveyor General, Pretoria, for the areas of which topographical maps were not yet 26° 30· and 27° south and longitudes 28° 30' and 29° 30' east and is approximately 5400 km' in extent. available during the time of compilation. It includes portions of the Heidelberg, Nigel, Beth«l, 3. Acknowledgements Standerton and Frankfort Districts and is well popu­ lated. Standerton is the principal town and is a The Geological Survey is greatly indebted to the farming centre. In the western portion arc the towns management of Union Corporation and to their staff of Balfour and Greylingstad and in the north-eastern of the Mines Geological Department at Evander for portion the village of Charl Cilliers. the contribution on the Evander Gold Field which is incorporated in the explanation of the sheet. This B. Communications contribution deals mainly with the geology of the The area is well served by roads and railways. The Evander Gold Field and summarises data which have national road and the main railway line between accumulated during years of mining operations. Johannesburg and Durban pass through Balfour, Grey­ These data have also facilitated correlations between lingstad and Standerton. Railwav lines branch off from the subdivisions of the Witwatersrand System of the Balfour to Villiers and from Grootvlei to Vereeniging. Evander basin and the main Witwatersrand basin, the The towns are linked by a network of provincial and eastern and south-eastern rims of which are present district roads. in the area. C. Previous Work AenowJcdgement is also made to the authors of that contribution for the northern portion of section The investigations of A. W. Rogers (1922) on the A-B accompanying the map. country around Heidelberg partly covered the north­ western portion of the area and dealt mainly with The Geological Survey is also greatly indebted to the Witwatersrand System. L. T. Nel surveyed the area the Anglo American Corporation Ltd and General around Balfour, Greylingstad and to the south ot Mining and Finance Corporation Ltd for information them during 1921 and 1922. His results have not been furnished and to the management of the Springfield published but served as a basis for later investigations, (Grootvlei) Collieries for information furnished and in particular on the correlation of the subdivisions facilities afforded for the investigation of the colliery. of the Witwatersrand System in this area. The South -Rand Gold Field which occurs partly in II. PHYSIOGRAPHY the far western part of the area was investigated by D. A. Pretorius of the Economic Rescarch Unit, A. Relief University of the Witwatersrand in 1964 mainly in The area is part of the Highveld and lies between conncction with the potential economic value of the I 480 and 1 800 m above sea-level. The gently goldfield. The approach to the problem of the gold lindulating plain of the eastern part has an average mineralisation is based mainly on new data on the altitude between 1 560 and 1 620 m. structural and the sedimentary geology of the area and the entire ¥litwatersrand basin. The topography of the country underlain by pre­ The economic potcntial of the Standerton Coal Karoo formations in the west is partly the effect of pre-Karoo denudation and partly the result of erosion Field was investigated by K. H. L. Sehlke in 1959. after removal of the Karoo beds. The pre-Karoo D. Present Investigations surface is in general undulating but locally it displays 1. Distribution of Work high relief (see also Chapter VIII). The entire area has been mapped and partly revised Along the north-western boundary there are several on aerial photographs (scale approximately 1: 18 000) parallel ridges of Hospital Hill quartzite. They reach by several members of the Geological Survey and the . I 800 m on Groenfontein 395 IR and gradually work was distributed as follows: the area around decrease in .height towards the south. Balfour by A. A. Snyman, the country between In the country around Balfour and Greylingstad the Grootvlei and Villiers by K. E. Schalk, the area between Ventersdorp lavas form prominent hills which rise to Grcylingstad mtd the Vaal River by A. Leube, the a height of 210 111 above the surrounding area. Several area north-east of Greylingstad by B. F. Liebenberg hills reach altitudes of between 1 830 and I 842 m and the area around Grcylingstad by A. P. A. Steyn, and their summits most probably represent an old who also revised portions of the other areas. The area land surface. In the lava hills west of Heidelberg there around Standerton was surveyed by K. H. L. Sehlke is more evidence of the cxistenee of an old pene­ (1957-1958). plane at approximately 1 800 III (Nel and Jansen, The investigation by Sehlke is partly incorporatcd 1957, p. 4, 5). With the exception of the ridges of in Bulletin No. 30 (1959). Finally, portions of the Hospital Hill quartzite mentioned a.bove, the ridges map were revised by B. Sckirsky (1965) and H. Jansen formed by Witwatersrand quartzites are in general (1966). lower than those formed by Ventersdorp lavas. The section on coal was written by F'. S. J. de In thc large area covered by Karoo beds low flat­ .I ager and that on gas by H. M. Beer. topped hills are formed by dolerite sheets, B. Clilnate and Drainage the courses of streams have been influenced by valleys The area has warm summers and cold winters. of pre-Karoo age, which are partly determined by The mean daily temperature is 16° C with a range faults and covered by Karoo Beds. of 5,9° C to 25, 1°C between the coldest and Pans arc a C0111lDon feature, in particular on Karao warmest periods of the year. The annual rainfall sediments, and a few are situated on Karoo dolerite. varies between 625 and 780 mm. Only two pans, namely those on Groenfontein 395 JR (AI) and Leeuwkraal 517 IR (A2) arc at present The entire area is drained by the Vaal River and drainage centres. Thc Groenfontein pan, according to its tributaries of which the most important are the Rogers (1922, p. J2), is a shallow rock basin of Suikerbosrand, Kalkspruit, Silverbank and Waterval pre-Karoo age from which the overlying Karoo beds Rivers. The drainage pattern of some of the rivers, have been partly rcmoved, probably during a more in particular the Suikerbosrand River is superimposed. arid period. The group of pans on Modderbult 511 The Suikerbosrand River follows a course indepen­ lR (AI) and Rielfontein 508 IR (AI) occurs on a dent of the structural and lithological make-up of the local topographical high. area. In its upper course it flows through a broad alluvial valley but downstream it cuts through ridges IV. ARCHAEAN COMPLEX of Witwatersrand quartzites, which form local base­ The rocks of the Archaean Complex form scattered levels of erosion, as for instance on Kuilfontein 502 outcrops in the western portion of the map area. IR (AI). West of the western boundary of the map it However, borehole data show that these rocks are has incised a steep-sided valley in the lava hills (Nel and widely distributed under the Karoo rocks in the central, Jansen, 1957, p. 7). A tributary of the Suikerbosrand southern and eastern portions. They also extend under River, however, flows through a poort on Rietbult the Karoo cover from south of Villiers into the area Estates 505 IR (AI) which is situated along a fault. around Grootvlei. More cases of superimposed drainage are represented Metamorphic, sedimentary and igneous rocks of the by tributaries of the Kalkspruit River, which locally Archaean crop alit north of Fortuna and north of

lII. GEOLOGICAL FORMATIONS The following geological formations are represented in the area: Recent Deposits. Alluvium, scree, sand, riverMterrace gravel, ferri­ erete-. rUpper Stage ...... Shale. rEcca Series ...... i Middle Stage ... . Shale, sandstone, arkose, conglomerate, marl, Karoo System. .. .. -< sandy limestone, coal seams. LLower Stage .. . Shale, sandy shale (only in boreholes). I Dwyka Series ... Tillite, shale, sandstone, siltstone (only in boreM l holes) Transvaal System. .... f Dolomite Series ...... Dolomite, chert. 'l Black Reef Series .. . Quartzite, grit, conglomerate, shale. Upper Group. Shale, sandy shale, argillaceous sandstone, con­ Ventersdorp System. ... f glomerate, tuff. j Lower Group. Andesitic to dacitic lava, amygdaloidal and non­ l amygdaloidal and porphyritic lava, tuff. rKiJl1berleY~EISbtlrg Series. Passage beds: shale, tuff, lava, quartzite, grit, conglomerate. Quartzite, grit, conglomerate, shale. Main-Bird Series .... Quartzite, grit, conglomerate, amygdaloidal lava, shale. Witwatersrand System ...... J Jcppcstowll System. Shale, quartzite, amygdaloidal and non-amygM , daloida! lava. I Government Reef Series .. . Slate, ferruginous or magnetic in part; quartzite grit, graywacke, conglomerate, tillite. I Hospital Hill Series ...... Slate, ferruginous, magnetic and contorted in part; quartzite, grit. Quartzite (Orange Grove), COUM l glomerate, slate. Moodie System* .. Quartzite, grit, arkose, conglomerate, phylWe, qllartz~sericite schist, ta1cose rocks(?). rFig Tree Series( q) .. ... Slate, schist, quartzite, graywacke, magnetic Swaziland System. quartzite. .i Onverwacht Serics( ?) .. Metamorphosed amygdaloidallava (chlorHe-talc l schist). Intrusive Rocks Post-Karoo ...... Dolerite, coarse grained and porphyritic. Post-Ventersdorp to Post-Transvaal. Quartz dolerite, diabase, norite, gabbro, pyfOxe~ nite. Archaean .. Jamestown Igneous Complex. rGranite, gneiss. . .. \Serpentinite, amphibolite, talc sehist(?). cut across quartzite ridges on Daspoort 564 IR (AI) Grootvlei. Mutual relationships between the different and Panfontein 452 IR (AI). types and also between the Archaean granite and younger formations are as a rule obscured. The for­ The courses of streams on the Karoo rocks in mations represented are correlated with the Swaziland general do not seem to be greatly influenced by and Moodie Systems, and the subdivisions of the differences in hardness between sedimentarv rocks and dolerite. According to Pretorius (I964, p. 267) the drainage pattern and linear features on aerial photo­ '" The Geological Survey, in compliance with the recommen­ dations of the Place Name Committee, has recently adopted graphs in the Karoo-covered Grootv!ei area reflect the name Moodie, the name being derived from a Mr Moodie the continuations of faults established to the west and who owned a concession in the Barberton Mountain Land. east in older formations. In the Greylingstad area Moodies is however still used on the map.

2 Within the Standerton sheet area natural: gas has The most important factors controlling the distribu­ been reported from the farms Clare 228 IS, Dde­ tion of gas in the area seem to be thc lateral discon­ fontein 137 IS, Goedehoop 290 IS, Grootvlei 293 IS, tinuity of porosity in the sandstones and the cover Kafferskraal 289 IS, Kromdraai 128 IS, Lecuwspruit provided by surface dolerite shects and shale layers in 134 IS, Trichardtsfontein 140 IS, Vlakspruit 308 IS the upper part of the Middle Ecca sequence (H. M. and Winkelhaak 135 IS (A4), in the Bethal area. Beer, 1970). No gas occurrences are reported from In the Balfour area, natural gas has been reported pJaces outside the area with effective dolerite and shale from Brakspruit 359 IR and Wildebeestspruit 356 cover-rock. I R (A2), and in the Standerton area from the farms There seems to be a reasonable amount of gas in the Grootpan 592 IR, Langverwacht 282 IS, Middelbult area. This may be of the order of millions of cubic 284 IS, Rietkuil 513 IR, Salpeterkrantz 351 IR, meters. Determination of gas reserves is, however, im­ Springbokdraai 277 IS, Twistdraai 285 IS, Witkl"i­ possible. fontein 131 IS and Zandfontein 130 IS. Two hypotheses regarding the origin of the Evandcr The gas flows from Middle Ecea rocks. i.e. sand­ gas have been formulated, distillation of Ecca coal and stone, shale and coal-seams, which are underlain by carbonaceous shale by dolerite intrusions, or formation Dwyka sediments and pre-Karoo rocks. The Middle of gas in the Middle Ecca shale during normal diage­ Ecca Stage sediments were deposited on an almost nesis. The results of the reinvestigation of the Evander stable shelf in a fluviatile-deltaic environment. Glau­ gasfield (H. M. Beer, 1970) favour the first hypothesis. conite-bearing layers at the beginning of the fluviatile cycles mark short marine incursions (H. M. Beer, 1970). Sediment/dolerite and volatile/fixed carbon ratio Facies maps of the Middle Ecea suggest meandering values (Cv /Ct values), the latter showinr, the loss of deposition channels, which run in a north-south direc­ coal volatiles, demonstrate the genetical relationship tion (H. M. Beer, 1970). between dolerite intrusions and gas occurrences (H. M. Beer, 1970). According to Snyman (1963) the distillation The Karoo rocks arc intruded by dolerite. There of a small proportion of the total coal reserves of arc up to three thick dolerite sheets and a number about 5500 million metric tons in the I::vander area of thinner dykes in the area. would account for the Evander gas. Structures within the Karoo rocks arc of the com­ The partly deltaic-paludal environments of the paction type, due to irregularities in the pre-Karoo Middle Ecca sediments are not unfavourable for the topography and to a minor extent to dolerite intrusions. preservation of organic matter. Some Middle Ecca No folding took place in the Evander area and minor shales have also been classified as gas source rocks. faults are dolerite induced. It is, however, doubtful whether enough shale of the The average composition of the Evander gas is 96 right quality was present to .account for more than a per cent mcthane, 2,90 per cent nitrogen and 0,61 small proportion of the gas m the area. That the gas per cent helium (P. J. Hugo, 1964). It is dry and con­ originated in pre-Karoo rocks seems to be even 1110re tains virtually no higher hydrocarbons. improbable. The flow rates and the gas pressurs of the gas­ D. Building Stones and Road Materia! emitting boreholes were measured by the Standard Vacuum Oil Company of S.A. in 1961 and by the Ecca sandstone is used locally as a building stone. Geological Survey during the years 1964 to 1969. The Weathered lava and dolerite are quarried for road­ bcst gas producer in the Evander area, which in the building purposes at several localities but fresh lava 1950's delivcred gas at a flow rate of about 40 cubic was used in constructing the national road to Durban. mctres pcr minute lics, howevcr, outside the sheet on thc farm Watervalshock 350 IR in thc Balfour area. XIII. UNDERGROUND WATER RESOURCES Within the sheet area borehole U.c. 346, Kafferskraal Save for a strip along the western margin, the Sheet 289 IS (A.3), emitted gas in 1961 at a flow rate of 3 falls within the area dealt with in Geological Survey 0,88 m /m; Uc. 138 in 1961 measured 1,73 m'/m Bulletin 50: "Boorplekaanwysing vir water op die and U.C. 77 measured in the same year 0,70 m'/m; Serie Ecca en meegaande doleriet van Suidoos-Trans­ these three boreholes are in the Bethal District. A few vaal" (with a summary in English) by J. R. Vegter other boreholes emittcd natural gas at flow rates of and G. J. Ellis (1968). These rocks cover by rar the 0,3 to 0,6 m'/m and most of the boreholes gave less greater part of the Sheet and the reader is referred than 0,2 m'/m. to this publication for detailed information on the Shut-in prcssure measurcments indicate mostly low­ mode of occurrence of underground water in them, pressure conditions in the reservoirs. A pressure of including springs, techniques that have been developed 0,245 bar was measured from 1967 to 1968 in Uc. for selecting drilling sites, and chemical analyses of 415 on Driefontein 137 IS (A.3), Bethal, 0,186 bar was water. mcasured from 1967 to 1968 in Uc. 77 on Winkel­ haak 135 IS (A.3), Bethal and a relatively high pres­ Data on the underground water in the mines of the sure of 3,31 bar was measured during 1969 in U.c. Evander Goldfield are given in the accompanying con­ 207, Langverwacht 282 IS (A.3), Standcrton. tribution by the Mines Geological Department, Evander. The gas measurements suggest that there is no con­ Up-to-date information on the occurrence of under­ tinuous gas reservoir. The gas appears to be flowing ground water in the rocks of the Archaean Complex from different sandstone reservoirs or fracture systems. and the Witwatersrand and Ventersdorp Systems is Porosities of the Middle Ecca sandstones vary from unfortunately not available. Some moderately strong poor to fair and permeabilities from poor to good. springs occur in the Witwatersrand rocks. One on Riet­ It is difficult to locate the reservoirs as the depths of hult Estates 505 IR is located on the Sugarbush Fault the gas occurrences in the boreholes have been record­ in the poort near the boundary with Rietfontein 504 ed in only a few cases. There is no water head in the IR (A.l). area and there is also no correlation between gas Artesian water was struck in a deep prospecting occurrences and compaction structures induced by the borehole on Rietbult Estates 505 JR, and a borehole pre-Karoo topography. on Springfontcin 549 IR also flow<.