UNION OF SOUTH AfRICA UNlf VAN SUIO·AFRIKA DEPARTMENT OF MINES DEPARTEMENT MYNWESE GEOLOGICAL SURVEY GEOLOGIESE OPNAME THE GEOLOGY OF THE COUNTRY AROUND VEREENIGING AN EXPLANA nON OF SHEET 62 (VEREENIGING) by L. T. Nel, D.Se., and H. Jansen, D.Se. (A'dam.) With a contribution on coal by J. F. Cillie, B.A., B.Sc., and one on refractory materials by D. J. L. Visser, D.Sc., F.G.S .. of the University of Pretoria Met In opsomming in Afrikaans onder die opskrif: DIE GEOLOGIE VAN DIE GEBIED RONDOM VEREENIGING COPYRIGHT/KQPIEREG YOORBEHOU 1957 Ptintud by and obtainablo from Godruk deur on vorklygbaM Vlln tho Govornrnonl Printer, BOlman dio St~~t~dIUkkol, So$lnllosirllat, Stroot, Pretoria P,"toria GoolOSlical map in colour> on " Goologle.o k..... t ;n klou" op 'n .,1110 of 1,125,000, obtainable Jka~1 vlln 1:125,000, apart vo.· $oparololy at tho prico of 6s. krygballltoen dio prys 61. THE GOVERNMENT PRINTER/DIE STAAT$DRUKKER PRETORIA, 1957 G.P.-S.l024342-1957-S-2,OOO. 78 prnclicaUy of quartz grains only, with very little felspar, magnetite, and olher Illllleral grams. The grains are from rounded to angular, and arc covered with a film of iron oxides, XTII.-THE UNDERGROUND WATER-RESOURCES In an' industrially expanding area which is at the same time an important farming district, the underground water-resources are of the ~reatest i~portance, The following account is the result of a preliminary IIlvestlgatlOn based on mformatlOn about wells and bore-holes, The infor­ mation was either obtained from farmers or compiled from existing bore~ hole records, , A SUPPLIES IN THE ARCHAEAN GRANITE The Archaean Granite in the southwestern part of the area occupies fiat ground in the core of the Vredefort "Dome ", Supplies from springs and seepages are small and inconsistent; most springs are depression­ springs in the valleys, The supplies from wells and bore-holes a[0 weak, as borne out by the averages of 30 successful bore-holes, Average total depth in feet", ,,, ,,, ", ,,, ,,, ,,, ,,, ", 79 Average depth at which water was struck ,,, ." ,,, ,,, 52 Average depth to which water rose,,, ,,, ." ,,, ,,. ,,. ,,, 36 Average tested yield in gallons per hour ." ,,, ,,. 392 Total percentage of failures,,. ,,. ,,. '" ,., ,., ,., ,,. ,., 39 B, SUPPLIES IN THE WlTWATERSRAND SYSTEM L THE SOUTHWESTERN OCCURRENCE The whole of the Witwatersrand System, including intrusive sheets of basic rocks, is exposed in the southwestern part of the area, The main tributary of the Vaal River there is the Kromellenbogen Spruit which roughly flows parallel to and on the softer beds at the top of the Lower Witwatersrand Division, A smaller longitudinal stream on Witkop 51 (A I, B, I)-on the opposite side of the Vaal River­ follows a similar course, The course of tributaries across the Witwaters­ rand beds in some localities were determined by transverse faults, Fa vourable conditions for springs and seepages are confined to some valleys in hilly country where there is faulting, The yields from fracture- and contact-springs in these valleys may be considerable. On Doornput 94 (8, I) about 15 springs with a maximum daily yield of 14,000-20,000 gallons are located within a small valley, On Wit­ fontein 398 (R I) the output of two springs is approximately 50,000 gallons per day, On Bloemfontein 11 (B, I) springs are located in the valley along the Parys-Lindequesdrit road and along the contact of Hospital Hill quartzite and Government Reef slate, Apart from the instances mentioned above, the conditions for supplies from springs are not very favourable, as for instance in the Kimberley-Elsburg Series where the relief is less pronounced, . The Witwatersrand beds in this part of the country are a rather poor and erratic water-bearer, Most boreholes are located on shale with a low permeability underlying the valleys between quartzite ridges, 79 The averages of 46 successful boreholes sunk in the different Witwatersrand bods, are as follows:- Average total depth in feet .... , .. ,. '" 74 Average depth at which water was struck 52 Average depth to which water rose ..... 33 A verage tested yield in gallons per hour 513 Total percentage of failures ... .,. .,. .. 18 The averages for each of the subdivisions of the Witwatersrand System are listed in the following table:- - KimberJey- EIsburg Jeppestown ! Government Hospital and Series Reef Hill Main-Bird Series Series Series Number of bore·llOles.,: ... .. 11 10 20 5 Average total depth in feet .. 96 76 62 65 Average depth at which water was struck ... , ........ , ... 56 53 45 56 Average depth to which water rose., .......... , ........ 38 40 27 25 Average tested yield in gallons per hour ..... , ......... , .. 585 600 I 422 575 2. THE NORTHEASTERN OCCURRENCE The beds of the Witwatersrand System south of Heidelberg dip at a relatively low angle in contrast with those around the Vredefort "Dome". All the subdivisions are represented. In consequence of the low to moderate dips the gradients and differences in elevation are never very much pronounced and the run-off is comparatively small. The small run-off, and fractures in the quartzite beds are favourable factors in promoting replenishment of underground water. The formation is a good and fairly eonsistant aquifer. There are not many springs on the Witwatersrand beds due mainly to the absence of artesian conditions and to the flatness of the country. In places there are fracture-springs, as for instance on Rietfontein 178 (B. 3, B. 4) and Stryfontein 100 (B. 3), where the Kimberley-Elsburg quartzite and the Ventersdorp lava are cut by faults. Supplies from bore-holes are generally satisfactory and exceptionally high yields arc sometimes. obtained, as for instance in the Main-Bird quartzite on Platkoppie 63 CA. 3, A. 4) and Nooitgedacht 261 (A. 4), and also in the Kimberley-Elsburg quartzite at several localities. These rocks are good aquifers by virtue of the faults and fractures in them. The averages of 52 successful bore-holes are as follows:- A verage total depth in feet ... ... ... ... ... 100 Average depth at which water was struck 74 Average depth to which water rose ..... , 33 Average tested yield in gallons per hour 1.305 80 . In the following table the figures for the subdivisions are listed:- Kimberlcy- Main-Bird r Jeppestown 1 Government EIsburg s' Reef Series Series I , enes I Series -_ .. _-- Number of bore~holcs ....... 26 16 7 3 Average total depth in feet. 102 94 94 130 Average depth at which water'I' was struck .............. ,. 69 75 67 115 A~~:e~~ .d.e.p.t~. ~~. ~~i~~. ~~t~~ I 33 29 24 63 ~~e:l~g~o~e:.t~. ::~l~.:~ .~~l~~~~ }~~ __ ..J!.~O~_._~~~~ __ ._1,180 ___ _ C. SUPPLIES IN THE VENTERSDORP SYSTEM Like those of the Witwatcrsrand System rocks of the Ventersdorp System occupy large parts in the southwestern and northeastern parts of the area. In the southwestern pan of the area the curved belt of lava and tuff is largely covered by .Karroo beds and they are only exposed in small isolated outcrops on the high ground to the northeast of the Kromellcnbogell Spruit. Only in the hills near the Vaal River the lava outcrops more continuously. Data on bore-hole supplies are scanty. Nearly all available informa­ tion concerns bore-holes on Weilbach US (B. I), Berlin 394 (B. 1) and Vlakfontein 161 (B. I) where the lava is covered by a thin layer of Ecca beds-about 50 feet in thickness on Weilbach and about 20 feet on Berlin. The averages of 10 successful bore-holes are as follows:- Average total depth in feet ... ... ... ... ... 69 Average depth at which water was struck 45 Average depth to which water rose ... 29 Average tcsted yicld in gallons per hour 800 Total percentage of failures ... ... ... ... 56 On Witkop 51 (A. I) and Oorbictjesfontein 20 (A. 1, B. 1) a few bore-holes sunk in lava give exceptionally high yields. Between Heidelberg and Vaa!dam in the northeastern part of the area the Vcntersdorp System is well exposed and is essentially composed of lava with some tuff. The average dip of the lava is about 100 to 150. The lava forms either a moderately undulating country, as for instance nea'r the Klip River, or prominent hills west and southwest of Heidelberg. In the gen\ly undulating areas large tracls of lava, mainly along depressions and valleys, are covered by a layer of decomposition products which is usually thin but attains a considerable thickness in the low-lying areas .. This layer facilitates the infiltration of water and retains a fair amount of the precipitation. Several intermittent streams, as for instancc on Boschkop 72 (A. 3) and De Hoek 68 (A. 4), derive most of their water from this source. On the other hand, most of the precipitation in the hilly country is carried away by small streams. 81 The bulk of the underground water in the lavas occurs in areas where the rocks are weatbered deep enough. It is impossible to locate suuh areas with any degree of accuracy from surface indications. hence tk high percentage of dry bore-holes and the many bore-holes with " low yield. There are. however. a few bore-holes with strong supplies. as for instance on Schoongezicht 64 (A. 3). These strong supplies may be partly due to the fact that the bore-holes are located at the foot of hWs which are built of lava flows favourable for water 'percolation. and partly also to the Platkoppie dyke which acts as a barrier. Around Riversdale the average yield of bore-holes is very low and the same applies to the dolomite in the vicinity. The averages of 86 successful bore-holes in lavas and tuffs are as follows:- Average total depth in feet ..