THE GEOLOGY OF THE AREA AROUND LlCHTENBURG

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1 THE GEOLOGY OF THE AREA AROUND LlCHTENBURG EXPLANATION OF SHEET 54 (LiCHTENBURG) by J. W. von Backstrom, B.Sc., F. W. Schumann, B.Sc., H. D. Ie Roex, M.Sc., L. E. Kent, M.Sc., Ph.D., F.G.S.,.\<:'~~\.~:':"::':~" and A. L du T oit, D.Sc., F.R.S., F.G.S. ",,,,,, :i GEOLOGICAL SURVEY (Translated by the Translation Bureau from the original Afrikaans) Published by Authority of the Honourable the Minister of Mines 1953 UNION OF SOUTH AFRICA DEPARTMENT OF MINES (Copyright) G.P.-S

2 47 7. UNDERGROUND WATER' Surface water is scarce throughout the area, not one of the rivers, creeks, or pans having perennial water. Farmers are largely dependent on underground water, and the future growth and progress of the area are closely bound up with the extent to which new sources can be developed. At present water is drawn from springs, wells, bore-holes, and storage-dams on the surface. The depth, quality and amount in each case are dependent on the particular formation from which the water is derived. The Archaean granite is mostly covered by a porous layer of sand and drift of varying thickness. The amount of the yield is directly related to the porosity of the covering, the extent of weathering of the granite, and the rainfall-all of which are favourable, so that the formation has become known as a good aquifer. Column I of the accompanying table has been compiled from data collected by Frommurze(") and shows the resnlts obtained from bore-holes in the Archaean granite. Seepage from thc porous covering has been observed along riverbanks on Varkfontein 69 (B. 4), Rietvly 299 (B. 4), and Kaalkraal 106 (S.4). Contact-springs have been formed where the Archaean granite is overlain by Ventersdorp sediments on Gruisfontein 114 (A.4) and Kaalkraal 106 (B. 4). The yield of water obtained from the Vemersdorv System and its mode of occurrence dcpend 01) the lithological composition of the rocks of which the system is constituted. As appears from column 2 of the table, a satisfactory yield may be obtained from the lava, depending on whether some or all of the following factors are prcsent:-- (i) an adequate depth of weathering of the lava; (ii) fissures, cracks, fault-planes, and breccia-zones; (iii) a sufficient number of blow-holes, steam-holes, and other openings and cavities resulting from the earlier viscosity and flow-movements of the lava, to allow of water collecting along horizontal planes; (iv) impermeable dykes, sills or chertified layers which may serve as barriers; (v) the lava not being of a fresh, unweathered and fine-grained, compact type that has not been disturbed. It is difficult to strike water in strongly chertified tuf!, but considerable quantities are to be found in the laminated, softer types. The sandy sediments of the Ventersdorp System hold fairly considerable quantities of water. On Doornhoek 39 (A. 4) and Kaalfontein 6 (A. 4) water is found locally under artesian conditions, due to small folds which appear, in the main, as domes with accompanying small basins. The occurrence of springs in the lava along Putte-se-loop on Putfontein 70 (A. 4) and along the Taaibosch Spruit on Klipfontein 120 (B. 4) must be ascribed to the nature of the topography. No formation in this area is more varied and uncertain as regards the quantitie..(;j of water it yields than the Dolomite Series. The number of unsuccessful bore-holes drilled in it has been high. The hydrological properties of this series are reflected in the results shown in column 3 of the table. *By J, W. VOn Backstrom.

DATA RELATING TO BORE-HOLES IN THE VARIOUS FORMATIONS 1 2 3 4 5 Formation.... '.

3 DATA RELATING TO BORE-HOLES IN THE VARIOUS FORMATIONS Formation.... '... '.. '.. '..., Archaean Ventersdorp Dolomite Dwyka Recent granite System Series Series deposits Total number of bore-holes [rom which data were obtained Average total depth of bore-holes ft. 98 ft. I 104 ft. 144 ft. 140 ft. Average depth at which water was struck ft. 70 ft. 70 ft. 87 ft. 7l ft. Average level to which water rises (rest-level) ft. 37 ft. 40 ft. 31 ft. 28 ft. Average daily yield ,,240 gai1. 21,500 gall. 33,100 gall. 15, 000 gall. 22,100 gall. Failures... ".".".".'.. '.. '... "."." per cent. 17 per cent. 30' 5 per cent. Nil 11 per cent. Bore-holes over 300 feet Nil O' 1 per cent. 3' 7 per cent. 5 8 per cent. 7' 3 per cent. Flowing bore-holes...,... Nil 0,5 per cent. 0'9 per cent. Nil Nil Bore-holes with exceptional yields (over 100,000 gall. of water daily)... '...,. Nil Nil 3' 7 per cent. Nil Nil I.. _-

49 The absence of surface-water over such an extensive area of the gravel-covered Dolomite Series must be ascribed to the joints which occur within it.

4 49 The absence of surface-water over such an extensive area of the gravel-covered Dolomite Series must be ascribed to the joints which occur within it. Where the formation is heavily jointed, considerable quantities of water _may be present, as appears from strong springs north of Lichtenburg. the more important of which are the Burgersdorp spring. a number of springs along the upper courses of the Harts River on Lichtenburg Townlands 313 (A. 3), two on Elandsfontein 35 (A. 3), and those along the upper reaches of the Harts River on Klipbankfontein (Manana) 82 (A. 3). The Burgersdorp spring no longer flows out at the surface. and water is pumped from an opening of some 75 feet by 45 feet (22'7 m. by 13' 7 m.). The spring (see fig. 4) yields over a million gallons (4,550,000 I.) of water per 24 hours, and this is used for local consumption. According to estimate between 500,000 and 750,000 gallons of water per 24 hours flow through the furrows past the upper end of the town at Doornfontein 79 (A. 3). If these furrows could be lined with cement and the springs properly cleaned, this quantity could probably be doubled. The situation of the springs on Lichtenburg Townlands 313 (A. 3) is shown in figure 4, and analyses of the water are given in the table below. Sample 1 Sample 2 ---c Mgm./litre! Njl,Q09 Mgm.{litre "Ni:O a 7"" --'} ' K' ~ Q... N 2 Saline ammonia......,,...,.... Albuminoid ammonia......,,.... Sum of cations.....,.... c.... F'... ".... S04" , HCO/.... NOg' , Sum of anions Sum of. ions Si0 2..., Total sum.,... " ' nil 217' Permanent hardness (as CaCl 2 ) nil 5 Temporary hardness (as COs)......,.., Total hardness...,..,...,.,.,..., 330 Na2COS...,..., nil Alkalinity (as CaCO,) Oxygen absorbed (4 hours at 27" C)... 1=~=~1====1=-'0'=."'4Q"=; Total solids...,....,,... '.... Specific resistance (60 0 F.)..., ph mgm./litre 355mgm., litre 2083 Sample 1.-Taken by L. E. Kent on 25th November, Analyst: W. Sunkel, Division of Chemical Services, Pretoria. Sample 2.-Taken by Town Engineer, Lichtenburg in March Analysis by Division of Chemical Services, Johannesburg.

5 50 The two springs on Elandsfontein 35 (A. 3) flow out strongly at the surface, particularly as the result of a bore hole drilled at the site of one of them. The situation of the springs along the Harts River on Klipbank fontein (Manana) 82 (A. 3) is shown in figure 5. The following explanation of the origin of the Burgersdorp spring and of those on Lichtenburg Townlands 313 (A. 3) is given by Enslin ("): -_. "By means of a magnetic survey the existence of a diabase sill with possibly a low dip to the north and a suboutcrop about 300 yards (274' 3 m.) south of the' eyes' was determined. The existence of this sill had not previously been suspected, as no outcrops are seen. The diabase sill, which forms a barrier to the large quantities of water that gravitate along the solution channels in the dolomite from the higher country to the north; forces the water to the surface and the 'eyes' are formed. All the fissures and solution channels immediately above and north of the sill are filled with water under pressure, and any bore hole cutting these underground water filled channels should yield a strong supply of water. In zones where the dolomite is solid bore holes may be drilled without striking any fissures, whereas in other zones, e.g. in the vicinity of the 'eyes' in the laagte, the dolomite is rather broken and the chances are excellent that one or more fissures will be struck if a bore hole is drilled to a depth of 100 feet to 150 feet (30'5 m. to 45'7 m.)." There is a strong probability that the springs on Elandsfontein 35 (A.3) and those on Klipbankfontein (Manana) 82 (A. 3) also owe their existence to the same sill, as they are situated in the direction of the ex tension of its strike towards the west and the east respectively. In the upper part of the Dwyka tillite, which is heavily weathered, sufficient water for domestic use is found in comparatively shallow wells. At greater depth the formation is compact, and contains a great deal of clay derived from the weathering of the Dwyka shales, so that if greater supplies of water are required, it is usually necessary to drill deeper so as to penetrate into underlying formations. The results obtained from a limited number of bore holes (see column 4, table of data regarding bore holes in the various formations), prove that a certain amount of water is always present in the weathered portions of the Dwyka Series. The water.supplies held in the surface limes(one vary according to the thickness and the porosity of the limestone and depends ou whether it is underlain by impermeable strata. The results obtained from bore-. holes in surface limestone are shown in column 5 of the table of data relating to bore holes in the various formations. In the viei limestone along the Harts River strong yields have been obtained at shallow depth; a well, sunk by the South African Railways, delivers 8,000 gallons (36,360 I.) of water per 24 hours. This water most probably arises from the underlying Dolomite Series. Strong supplies of water have been encountered in sink holes and fossil river runs in the dolomite, although, for the greater part of the gravel deposits, the depth is so slight that the description underground water supplies is hardly justified.

Soils, Hydrogeology, and Aquifer Properties. Philip B. Bedient 2006 Rice University

Soils, Hydrogeology, and Aquifer Properties Philip B. Bedient 2006 Rice University Charbeneau, 2000. Basin Hydrologic Cycle Global Water Supply Distribution 3% of earth s water is fresh - 97% oceans 1%