M.public of SOU," Africa l\4Ipubliek van Suid-Afrika

DEPARTMENT OF MINES DEPARTEMENT VAN MYNWESE

Annals of the Geologi~al SUI·vey Annale van die Geologiese OpnaDIe

Vohllue .'uargallg 4~ 1965

Copyright reserved Kopiereg voorbehou

Prllltad by and obtainable from the Government Printer, Bosman Street, Pretoria. O.druk dour on verkrygbaar van die Staatsdrukker, Bosmanstraat, Pretoria.

CONTENTS-INHOUD

Part I-DeeI I PAGE

BLADSY

I. INTRODUCTION........................................................... 1

2. ONDERSOEKE IN VERB AND MET SINKGATVORMING EN INSAKKINGS IN DOLOMITlESE GEBlEDE.............. .......................... ........ 4

J. GENERAL GEOLOGy......... ............... .............................. 5

4. NIE-ORGANIESE DELFSTOWWE.. . . . . . . . . . . . . . . . . .. . . . . . . . .. .. .. . . .. . . .. . . 12

5. KERNKRAGSTOWWE ...................................... :............... 16

6. FUELS..................................................................... 17

7. ONDERGRONDSE WATER................................................. 19

8. GEOPHySICS.............................................................. 22

9. ENGINEERING GEOLOGy...... ............................. .. .... .. .... .. 23

10. PALEONTOLOGI:?......................................................... 32

II. GEOLOGIESE NAVORSING IN ANTARKTIKA.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

12. LABORATORy............................................................. 35

13. WERKWINKEL............................................................ 36

14. MUSEUM.................................................................. 37

15. TEKENKANTOOR......................................................... 38

16. INFORMATION AND PUBLICATIONS...................................... 40

17. LIBRARy.................................................................. 42

Part 2-D eel 2

.. Gletservloer in die Pakhuisberge, Distrik Clanwilliam ", by J. N. J. Visser. . . . . . . . . . . . 43

.. Thicknesses of the Cape and Karroo . ystems in the Eastern Cape ", by J. A. H. Marais and M. R. Johnson..... ....... . .... .. ..... . . . .................................. 49

.. Strllctllra I Aspects of the Flagstone Deposits in the Vici,lity of Lekkersing, Namaqualand District ", by E. J. H. F. Rouffaer.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 59

.. The Geology of the Dwars River Fragment, Lydenburg District, Transvaal ", by W. C. J. Vln Rensbllrg... . . . . . . . . . . .. . .. . . . . . . .. . .. .. . . . . . . .. .. .. .. . . .. . . .. . . .. . .. .. . . . . 69

" Intrusions of Alkali e Rocks Along the SteeJpoort River, Eastern Bushveld Complex, Transvaal ", by E. C. 1. Hammerbec (,. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

.. Radiomctric Dating of Certain Pegmatite, in the Kenhardt and Gordonia Districts, Cape Province ", by A. J. Burger, P. J. Hugo and F. W. E. Strelow.. . . . .. . . . . . . . . . . . . . . . . . 87 .

.. Dellteric Alteration in the Charnockitic Adamellite-porphyry of the Northwest Cape Province "', by J. W. von Backstrom.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

.. Magn'ctic Chromitite of the BU'hveld Complex," by W.c.J; van Rensburg... . ........ IG9

.. The Mineralogy of the Titaniferous Magnetite and Associated Sulphides on Kennedy's Vale 361 KT, Lydenburg District, Transvaal", by W. C. J. van Rensburg.............. 113

.. Determination of the Optical Properties of Orthorhombic Opaque Minerals ", by W. C. J. van Rcnsbllrg... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 129

.. The Chromilite Deposits at Nietverdiend, Marico District, Transvaal ", by H. Kruparz and W.c.J. van Rensburg............... .... .. . .... ....... ...................... 137

.. Ground-water Prospecting Methods Used in the Republic of South Africa", by L. E. Kt'nt and J. F. Enslin.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 151

.. New and Little Known Zululand and Pondoland Ammonites ", by E. C. N. van Hoepen 157

.. New Ammonites from Zllllliand ", by E. C. N. van Hoepen ........................ '.' 183

INDEX......................................................................... 193

111

Ground-water Prospecting Methods Used Republic. of South· Africa *

by

L. E. Kent, M. Sc., PH. D., and J. F. Enslin, D. Sc.

ABSTRACT

• tn the

The successful development of supplies of ground-water is a prerequisite for the utilisa­tion of the arid and semi-arid 65 per cent of the country.

Gravel and sand aquifers are scarce and of very limited extent and the rocks, for the most part, have no inherent permeability. Most of the 500,000 bore-holes drilled for water are in bed-rock and only half gave initial yields exceeding 100 g.p.h. Only 2 per cent yielded over 5,000 g.p.h.

Most of the aquifers are secondary in origin and have formed thr.ough fracturing and weathering. They are often narrow zones which are difficult to locate. Scientific methods of ground-water prospecting have resulted in savings up to 50 per cent on the costs of developing usable supplies in these secondary aquifers.

In selecting drilling sites, logs of existing bore-holes, chemical analyses of their water and indications given by vegetation are taken into account. Geological reconnaissance using aerial photographs is useful for tracing dykes, zones of fracturing and other favourable structures. Geophysical surveys, sometimes using more than one method, often have to be resorted to­they are essential when the potential aquifers are hidden by soil or alluvium.

Magnetometers are employed for locating the margins of dykes and sills that have intruded sedimentary rocks- the contact-zones are often good aquifers. The electrical resistivity method is used mainly for locating basins of weathering in the igneous rocks that cover about a third of the country. In such basins, the main supplies are found in the partially weathered and broken contact-zone between fresh and weathered rock. An electromagnetic method is used for locating water-bearing fissure-zones in rocks where weathering is too shaUow. Examples are given illustrating the application of these methods.

When bore-holes are drilled, electrical logging is often employed to eliminate unnecessary deep drilling.

INTRODUCTION

The utilisation of the semi-arid and arid 65 per cent of the Republic of South Africa depends very largely on development of underground water and, even in the relatively well-watered parts, supplementary underground supplies are usually essential for efficient farming.

Thick deposits of sand and gravel, and permeable sandstone, the principal aquifers in countries such as the U.S.A., are scarce in South Africa and most of the c. 500,000 bore-holes are in bed-rock. With the exception of some sandstone, the rocks have virtually no inherent permeability; the aquifers are secondary in origin and have formed by fracturing, weathering and solution. They are often narrow zones which are difficult to locate under soil cover. The percentage of weak and dry bore-holes is thus very high.

• This paper was presented at the United Nations Conference on the Application of Science and Technology for the Benefit of the less Developed Areas held in Geneva in 1962. As the papers were issued only in ron eo form and are not being published, the permission of the Secretariat was obtained for it to be included in the" Annals of the Geological Survey".

10680-5

152

Percentage of Bore-holes Initial Yield Exceeded

2 ................................... .

11 ................. : ................. .

21 ................................... .

31 ................................... .

42 .................. '" .............. .

50 .......................... , ........ .

5000 g.p.h.

2000 g.p.h.

1000 g.p.h.

500 g.p.h.

200 g.p.h.

100 g.p.h.

As the vast majority of the holes are drilled for stock watering and for domestic purposes on farms, a successful bore-hole is generally taken as one with a yield exceeding 100 g.p.h.

Water-divining has been, and still is to some extent, used for locating drilling sites-usually with very disappointing results. Scientific methods developed by the Geological Survey for South African conditions have proved valuable in con· siderably reducing the number of failures and the costs of developing usable supplies. Savings of up to 50 per cent have been effected (De Villiers, 1961; Enslin, 1961; Vegter and Ellis, 1961; Van Wyk, 1961).

PRELIMINARY STUDIES OF GEOHYDROLOGICAL DATA

Logs of the c. 85,000 bore-holes drilled by government drills and files of water analyses provided useful indications as to the nature of the aquifers, depth to water, and quantity and quality to be expected (Frommurze, 1953).

INDICATIONS FROM VEGETATION

Dykes, which are often flanked by water-bearing zones, are generally marked by lines of trees and more luxuriant bushes, so also are some crush-zones and major joints.

On the Transvaal Highveld a grass, Fingerhuthia sesleriae-formis, seems to flourish only where the underlying rocks are permeable and the water-table is very near the surface. Using it is an indicator, successful bore-holes have been drilled in sedimentary rocks within short distances of failures. It is believed that the very shallow water-table required by this grass is maintained by ground-water flow from the higher lying areas.

The Karroo amygdaloidal basalt in the Central Transvaal tends to weather to only shallow depths. Locally it is cut by vertical fissure-zones that are generally hidden by soil. During the dry winter months the soil dries out, and before the first rains very little water is available to the indigenous plants, saVe deep-rooted ones situated over fissure-zones that form aquifers. In early spring, lines of green trees demarcate these aquifers and very successful boring sites have been selected.

153

GEOLOGICAL SURVEYS

Geological reconnaissance, using aerial photographs which cover almost the entire country, is useful for tracing dykes, zones of fracturing and other favourable structures. In the fields, the topography is noted in relation to the disposition of the rocks and their dips, if layered, to obtain an idea whether recharge of aquifers is likely under the local conditions of climate, soil and vegetation. In some cases it is possible to deduce the hydrological properties of some rocks at depth and select sites (Frommurze, 1953). Examples folIow:

In parts of Zululand, the Karroo basalt is cut by dykes of volcanic breccia that form conspicuous bushy ridges. About 60 per cent of the bore-holes drilled in or next to these dykes proved successful as compared with 28 per cent success on non-geological/geophysical sites (Van Wyk, 1961).

If the contacts of Karroo dolerite dykes cutting sedimentary rocks are weIl exposed, drilling sites may be selected so as to penetrate the contact-zones below the water-table. Some of the narrow dykes are themselves extensively fractured and very successful bore-holes have been drilled in them (Vegter and Ellis, 1961).

Fault-zones have been found in cliffs and cuttings and projected to soil-covered areas where sites were required, Some have yielded fairly large supplies.

The geohydrological section, folder 1. was prepared by geological mapping and plotting the logs of a row of experimental bore-holes. Five aquifers, representative of some of the more important types in the country, were delineated. Nos. 1 and 4 are formed by weathered diabase and are relatively shaIlow; Nos. 2 and 3 are shales that have acquired fairly high permeabiIities through jointing and cleavage :and extend much deeper. No. 5 is the fracture-zone of a vertical fault; it is recharged by rain falling on the bate quartzite face of the ridge immediately to the south and also by influent seepage from a river further east. The underground water overflows from No.5 into No.4 and from there into the one with the largest storage, No.3, which has been fully developed for spray irrigation. No. 2 is recharged by seepage from the adjoining aquicludes at about 2,000 g.p.h. Such experimental drilling facilitates the selection of successful boring sites.

GEOPHYSICAL SURVEYS

Geophysical surveys, using sometimes more than one method, often have to be employed to supplement geological ones and are essential when the potential aquifers are hidden by soil or aIluvium.

Surveys of the Vertical Magnetic Field.-These have proved valuable for tracing dykes and the margins of intrusive sheets.

The generally almost flat-lying sandstone, mudstone and shale of the Karroo System (Carboniferous to Triassic), which covers nearly half the country, usually have very low permeabilities and specific yields. On some farms over a hundred bore-holes have been drilled in them without striking more than a few gallons per hour. It was found that narrow, indurated zones of intense jointing along the margins of many of the numerous dolerite intrusions form aquifers that are recharged by percolation from adjacent aquicludes.

The dolerite dykes are generally 15 to 30 feet wide and the indurated contact­zones seldom exceed 1·5 feet. Bore-holes must thus be sited with great precision

154

to strike such narrow aquifers at optimum depths. Fortunately most of the dykes are magnetic and a technique of interpretation of their magnetic anomalies has been developed to locate their margins accurately even under deep soil cover (Enslin, 1950). Folder 2 is a typical example. Eighteen bore-holes had been drilled near the homestead on this farm, but all were failures. A long magnetometric traverse revealed the presence of a dyke which was traced by a series of short traverses. Both 'positive and negative peaks occur, which mark the contacts of the hidden dyke. Under deep soil a dyke generally gives rise to only a single, rather wide anomaly due to superposition of anomalies from individual poles; however, if sufficient traverses are made, some will show anomalies with two or more peaks (Enslin, 1955a). The two parallel lines joining the outer peaks approximate within 3 feet to the contacts of the dyke. On the farm in question the indurated zone was first just missed; the machine was moved 3 feet nearer the contact and a supply of 1,800 g.p.h. was then obtained.

Unfortunately it has not proved possible to determine the dips of the dykes from their magnetic anomalies, which are almost entirely due to remanent magneti­sation (Enslin, 1950). Dip indications may be obtained from their traces if they cross valleys, and from logs of existing bore-holes. Usually it is necessary to drill trial holes to establish the attitudes of a dyke so that bore-holes may be sited to strike one or other of the contact-zones below the water-table. Near-surface tilting of some dykes has caused difficulties (Enslin, 1950).

In areas underlain by dolerite sheets, the water is generally found in the upper and (or) lower contact-zones, if not too deeply buried. The lower is usually the better aquifer, especially fairly near the denuded edges of the intrusions (Vegter and Ellis, 1961). In general, conditions are favourable where the contact-zones dip and are unfavourable where they are horizontal.

Electrical Resistivity Surveys.-These are mainly used for locating basins and closed troughs of weathering in igneous rocks which cover almost a third of the country (Enslin, 1955a).

It has been found that it is much faster to use an alternating current or reversed direct current, with steel electrodes, than direct current with non-polarising electrodes. The Wenner configuration (four electrodes equally spaced in a straight line) is usually used, with a 5-man crew. Due to the difficulty of getting current into dry ground, it is often necessary to drive the electrodes to depths of 3 feet or more. Their extraction is often difficult and time-wasting. A combined electrode and hammer was thus recently developed. It consists of a steel electrode 4' 5 feet long with a collar at its upper end. A tubular hammer is fitted and a sleeve welded on to the inside of its lower end to prevent the electrode falling out. It is easily driven by downward strokes of the hammer and is readily extracted by a few upward jars.

Depth-probe traverses are generally resorted to. To avoid excessive lateral effects, the electrode spreads are orientated, if possible, parallel to the strike of layered rocks and dykes. The depths to the contact between weathered and solid rock are empirically determined in the field from apparent resistivity/electrode separation curves (Enslin, 1948 and 1955a). When deep weathering is found, the traverse is expanded into a grid. Resistivity sections are drawn through the depth­probe centres and lateral effects eliminated (Enslin" 1948). A geohydrological interpretation is then made.

Folder 3 shows part of a farm on Bushveld granite where a basin of weathering, with a maximum depth of 115 feet was found. Note that the subcontours of the basin are not related to the surface contours. This is nearly always the case; in some granitic areas the deepest weathering is on broad ridges between watercourses, and boring sites are much more successful there than in the valleys.

155

In basins and troughs of weathering, the main supplies of water are generally struck in the irregular, partially weathered and broken zone just below the weathered rock. For this reaSDn drilling should continue to a depth of as much as 50 feet below the depth of weathering deduced from depth-probes (De Villiers, 1961), A" broken" zone is essential for successful bore-holes in basic igneous rocks which weather to clayey materials with very low permeabilities. Unfortunately its presence cannJt be established by electrical resistivity surveys and failures have been proved, by electric logging, to be due to its absence in basins or sections of basins. The yicld of a bore-hole is affected by the slope of the floor of the basin, as steeper pressure gradients can develop under pumping in thin, dipping aquifers than in hJrizontal ones (Enslin, 1948 and 1955a).

The electrical resistivity method is also used to determine the thickness of sedimentary rocks overlying dolerite sheets and to trace old river channels filled with water-bearing sands and gravels. Resistivity logging is extensively used to determine the actual depths, thicknesses and resistivities of aquifers and, for bore­holes in progress, tJ indicate whether deepening is justified. Such logging eliminates much fruitless drilling.

The Electromagnetic Method.-This method is used for locating fissures under soil cover in rocks that are not weathered sufficiently deeply to form basins, and in which fractures are not associated with magnetic dykes and also do nJt show on aerial photographs. The method fails, however, if the conductivity of the fissured zone is the same as the country-rock.

An alternating current of audio-frequency is introduced conductively into the ground (Bellairs, 1955). Measurements of the tangential component of the hori­zontal electromagnetic field are taken on concentric circles around the current ~ource. Peaks indicate current concentrations due tJ narrow conducting zones which are generally water-filled. If such peaks are obtained on the circles, they are further traced by measurements on short arcs (Enslin, 1955). In open country 20 morgen can be covered per day by a 6-man crew. Supplies of up to 10,000 g.p.h. have been obtained.

The example, folder 4, is a site on Archaean granite. A prJminent quartz vein had been used for siting a bore-hole (No.1), but only a small supply was struck and the second bore-hole away from the vein was dry. An electromagnetic survey disclosed an inclined fracture-zone up to 200 feet from the quartz vein. Sites selected tJ strike it at optimum depths gave satisfactory yields, The fissure­zone apparently branches off from the quartz vein, which is for the most part impermeable. In the case of such inclined zones, the electromagnetic peaks are displaced from the suboutcrop in the direction of dip. In general the depth below a peak to the fissure is about twice the thickness af the overburden (Enslin, 1955).

Seismic and Gravity Surveys.-These have been used recently with success to determine the configuration of an artesian basin.

BIBLIOGRAPHY BELLAIRS, G,FF., 1955. Instrumentation for a new electromagnetic geophysical field technique

as applied in South Africa: Geophysics, 20 (1), p. 155-162.

DE VILLIERS, S. B., 1961. Boorplekaanwysing vir water in Suidwes-Transvaal: Bul!. geo!. Opn. S.Afr., 34.

ENSLIN, J. F., 1948. Lateral effects on electrical resistivity depth-probe curves: Trans. geo!. Soc. S.Afr., 51, p. 249-270.

1950. Geophysical methods of tracing and determining contacts of dolerite dykes in Karroo sediments in connection with the siting of boreholes for water: Trans. geo!. Soc. S.Afr., 53, p. 193-204.

156

ENSLIN, J. F., 1955. A new electromagnetic field technique: Geophysics, 20 (2), p. 318-334.

1955a. Some applications of geophysical prospecting in the Union of South Africa: Geophysics, 20 (4), p. 886-912.

1961. Secondary aquifers in South Africa and the scientific selection of boring sites in them: Inter-Afr. Coni. Hydro!., CCTA Pub!., 66, p. 379-396.

FROMMURZE, H. F., 1953. Hydrological research in arid and semi-arid areas in the Union of South Africa and Angola, in Reviews of research on arid zone hydrology: UNESCO. p. 58-77.

VAN EEDEN, O. R., 1961. Locating ground-water in the mudstone of the Stormberg Series, Northern Transvaal (Summ.): lnter-Afr. Conf. Hydro!., CCTA Pub!., 66, p. 398.

VAN WYK, W. L., 1961. The selection of boring sites for water by means of the electrical resistivity method on Stormberg lavas, Zululand; Natal: Inter-Afr. Conf. Hydro!., CCTA Pub!., 66, p. 399-404.

VEGlER, J. R. and ELLIS, G. J., 1961. The selection of borehole sites for water on Ecca Series intruded by dolerite on the Highveld of the South-eastern Transvaal (Summ.): Inter­Afr. Conf. Hydro!., CCTA Pub!., 66, p. 390.

4{)OO

3800

North Noord

Proefplaaskop

10+@1 10+01 ~

GEOHYDROLOGICAL SECTION THROUGH PART OF THE PRETORIA'SERIES SHOWING AQUIFERS

GEOHIDROLOGIESE PROFIEL DEUR GEDEEL TE VAN DIE SERlE PRETORIA OM WATERDRAERS TE TOON

~ ~ ;

1 , :: " .. " " 0 0

0 ~ 0 0 0 ~ ,! ~

0 0

"' ';;; ~ 0; 0; 0; 0;

Ground-water level Water pressure level W~lerdrublak

Horizontal scale = Vertical scale

Horisontale skaal = Vertikale skaal

o N

x >< x x

• l 0

0

~~ -" 00 00 0_

i;i-~ ~:g ~~

~ "i

i~i "'-0 1 0

0 .".....,."" !l !l 2~~~ «>=,=

1000 Fault forming aQuiduile at shallow depth .2000 Versl:uiwing wat w3terhouer- OP vlak diepte vorm

Conduit along fault Watergeleidenda sona langs yers~uiwing

Weathered diabase Verweerde diabaas

Permeable shale Dew latende skalie

Aquifer Waterdraer

Fractured quartzite in fault·zone Gebreekte kwartsiet in verskuiwingsone

8!489l3600g.p.h.) No. of bPr"eahole and yield in g.p.h. No. van ]boorgat en lewering in g.p.u.

Depth at which water was ·struck Diepte ~aarop water getref i~

LEGEND LEGENDE

GrOUI')d-water barrier Grondwaterversperring

~ Mudstone and clay ~ Moddersteen en klei

~ Impervious shale and sandstone ~ Ondeurlatende skalie en sandsteen

~ Graphitic shale ~ Grafit_iese skalie

Aquiclude . Waterhouer

Solid diabase Sol iede diabaas

~,' ',. Solid lava ~ Soliede lawa

Solid quartzite Soliede kwartsiet

Direction of movement of underground water Rigting van beweging van ondergrondse water Fault Verskuiwing

~J

FOLDER 1 VDUBLAD

South Suid

Meintjeskop

Voet

)< 44011

Aquifuge Keerbank

4200

4000

o

PLAN AND SECTION SHOWING AQUIFERS COMPOSED OF THE VERY NARROW ZONES OF INDU~ATED SEDIMENTS ALONGSIDE A

DOLERITE DYKE LOCATED UNDER SOIL COVER BY THE MAGNETIC METHOD. GOOSENS 47, SENEKAL DISTRICT

FOLDER 2 VOUBLAD

PLAN EN PROFIEL WAT WATERDRAERS SAAMGESTEL UIT DIE BAlE SMAL SONES VAN VERHARDE SEDIMENTE LANGS 'N DOLERIETGANG

WAT ONDER 'N GRONDBEDEKKING DEUR DIE MAGNETIESE METODE OPGESPOOR IS, TOON. GOOSENS 47, DlSTRIKSENEKAL

II "II ~II ~II l;1i II

~ N

I

-----

\

\ \ \ \ \ \ \ \ \ \ \ \ \

o

\

---\ 0

\ \ \ ,~ o w •

50 I

Feel

o w •

o G.1997 A

o

50 I

100 I

LEGEND LEGENDE

Successful bore·hole Suksesvolle boorgat

Bore~hole with inadequate yield

150 I

---

Boorget met onvoldoende lewering

100 I

Voel

Magnetic traverse (vertical component) Mognetiese waornemingslyn (vertikale komponent)

50

>00

Magnetiese anomalie

Succession of

shale and

sandstone

(Karroo System)

. . . · . . , , , , , , '0 ' , 0' ,- , ~ ,

x :=.: )C .<'t> X , , , , , , , , , , , , , , , · , .

>c x ". , , , , , , , , , , , , , , , , , , , , , '0 ,

, 0, x rn x

xx:~:xx , , , . . . , , , , , , , , , , , , · , ,

Water, struck7"' (1640g.p.h.)

Indurated zone

Verharde sone

, , , , , , , , , X x. x · , , x .x x , " . , , , · , , , , , , ,

x x'x x x-x , , , , , ,

Bore-hole Boorgat

Bore-hole in ind'urated zone

Boorgat in verharde sone

Qpeenvolging van

skalie en

sandsteen

(Sisteem Karoo)

4- Water getref (lOg.p.u.)

Water struck (lOg.p.h.) Water getref OOg.p.u.)

~.~ "U1G; c·-a." "8. . " ..,. 0.., • 0 ~. u~

0"" -0 w-

W

\ Site Plan

liggingsplan o

0-8 ~ ___ ~0-30

o

0-7

FOLOER 3 VOUBLAO

BASIN OF WEATHERING IN BUSHVELD GRANITE LOCATED BY THE ELECTRICAL RESISTIVITY METHOD,

SYFERKUIL 208 JQ, BRITS DISTRICT

VERWERINGSKOM IN BGSVELDGRANIET ~VASGESTEL DEUR DIE ELEKTRIESE WEERSTANDSMETODE,

SYFERKUIL 208 JQ, DISTRIK BRITS ~\ -7 0-15 -33

•••••••••••••••••• "0 " •••••• ", ',·-25 ....

'" 0 0-41 • -/4 0-33 ,. • .- 0-42

-13 0 -3i

-200 '. '-25

0 0 0

0 ~ '" ~'

0

ill. ( lQ.Il 50ft

WOrt

150 It

Fw 200 200 400 600 800 1000 Voet L!~-L~~ ______ ~! ______ -L! ______ ~!~ ____ -L! ______ ~!

...... -:05 ----15 o

o

0-83 " .

-450 ••••••••

" '. ...... " 0-36

,.:;",,,,+"". /",:$.+ ++ 1

,"'"'I-++++t/ !+ +++/'" '~-t...:t-..... ,..

....... .... _15

Depth-probe curves (Apparent resistivity in ohm .. cm) Dieptemetingkrommes (Skynbore resistiwiteit in ohm-cm)

0 0 0 0 0 0

'" '" g g

" " '" " '" g i'i

l!. l!! !l9.

\

r-108 I

Interpreted geological section Ge1nterpreteerde geologiese profiel

Bor!t-h<:>.te 96 B . j oO~9at

118 I

.Weathered granite 'lerweerde graniet

110 I

B !

146 ! I ! ,

'~ Stored ground-water +/> W t ~ Gestoorde Qrondwat";;; + + + .... e" Water-level a crv 0 _ -

++·!'1lf!lob --- r'--- $0(\8 +++++++++++ 1t++++·J",z latef\~ -++ + + Soliede graniet

50!

100

50_

1(10'01

Feet 0

g

"

++++ + +l'Of'l,f!++ + ++++++++++++ + .... 'Solid granite' .... +

++++ +++++

0

~

150

0118 -79

~ ........ + + +P..!Uj.)""+ + .... + .... + .... + + .................................... ~ WoJe.! struckr180d' h / .. + + .... + .... + ........

+ Water getref'1 .. _ ... _9,:J~:_._ ~_~p.~?~ ...... + ~ + .... + + + . ++++~+~++++++++++++++++++++

,"0 750 1(100 1250

LEGEND LEGENDE

·1;.1~trical depth-probe with number and elevati9.l.1 of base of weathered zone (feet) relative to datum-level

El~_ktriese diep~emeting '~t ~~_mer Em hoogte ~an basis van verweerde s~ne (voet) relatief tot ultgangshOogte

Position and number of depth-oprobe on section Posisie en nommer van dieptemeting op profiel

Surfa,ce contour (feet)

~\ @

Oppervlakkontoer (voet)

." Contour of basin floor (feet) Kontoer van komvloer (vaet)

Bore-hole site selected Boorplek aangewys

Granite outcrop Granietdagsoom

• • -" u • Cl

• ...

5

10

~5 u • Cl

WATER-BEARING FRACTURE-ZONE IN ARCHAEAN GRANITE LOCATED

BY AN ELECTROMAGNETIC METHOD. KELVIN TOWNSHIP

WATERDRAENDE BREUKSONE IN ARGE'iESE GRANIET OPGESPOOR

DEUR 'N ELEKTROMAGNETIESE METODE. KELVINDORPSGEBIED

Fee! 100 0 ," " I

100 200 ! !

300 400 Voet I I

I 10

, lOry) 1010091

L~_--U6 U~~~~~::=::::~\-~\~l~ir\e~th~IO:U9h electromagnetic peaks indicating posit~on of fracture-zone 1300 g.p.h.1

(Originally artesian) jOolsoronklik armies) f!?

~ {609·P·'·)

25

/ 20

Electromagnetic fields around observation circles and arcs of setup No.7 . Elektromagnetiese velde om waarnemingsirkels en ·boe van opstelling no. 7

50-yard-radius circle 20

Observation points

Sirkel met straol 80 tree 20

Waarne!'rlin9spunltt:e_~~~,y

Observet ion points

LEGEND LEGENDE

Bore-hole with number Boorgat met nommer

Quartz vein Kwartsaar

50

100

Feet Voet

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+

+

+

+

+

+

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t5

o

lyn deur elekuomagnetiese piake wat posisie van breuksone loon

Section with bore-holes projected Pratie1 met boor gate geprojekteer

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+ + + + + + + + + +

~ + + + <;: is + + +

+ + + + +

+ + + + + • Granite ~+

'''1: i§ Graniet

+ + + tr

+ + + + r$ +

+ + + + +

+ + + + +

+ + + + + + + + + 5~ Observation point ~ Waarnemingspunt

Electromagnetic peak Elektromagnetiese piek

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+ + +/1+ + Ho+rizontal :cale+ = ~p.rlj;:\1 R:':;:lp.