The Welgevonden Fault Aquifer of the Central Transvaal and its

REPUBLIC OF SOUTH AFRICA
REPUBLlEK VAN $UID_AFRIKA
DEPARTEMENT VAN MYNWESE
DEPARTMENT OF MINES
GEOLOGICAL SURVEY
GEOLOGIESE OPNAME
The
Welgevonden Fault Aquifer of the
Transvaal and its Thermal Water
Central
GROUNDWATER SERIES 2
GRONDWATERREEKS 2
by
B. N. TEMPERLEY, Ph.D.
Met 'n opsomming in Afrikaans deur P.
J.
Smit, B.Sc.
Copyright reservedjKopiereg voorbehou
1975
Printed by and obtainable from The Government Printer, Bosman
Street, Private Bag X85, Pretoria, 0001
Gedruk deur en verkrygbaar van Die Staatsdrukker, Bosmanstraat,
Privaatsak X85, Pretoria, 000 I
CONTENTS
Page
1
1
1
1
2
Abstract
I.
11.
Ill.
IV.
V.
VI.
VII.
VIII.
IX.
X.
In troduction
Previous Work
..... .
............
. ......... .
Geology
. ... . .. . . .. .
Recharge of the Fault Aquifer ..
. .................... .
.. .. ... .
. ......... .
Water Movement in the Fault Aquifer
........
. .. , . , . . . . . . .
Discharge of the Fault Aquifer . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Behaviour of the Groundwatcr Level and the Potentiality of the Supply ..
Quality of the Water
. . . . . . ..
Conclusions ., . . . . . . . . . . . . . .
Acknowledgements . . . . , ... , ..
References . . . . . . . . . . . . . . . .
Opsomming in Afrikaans . . . . . . .
. ...................... .
7
7
13
17
20
21
21
21
ILLUSTRATIONS
Page
Figure
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Central Transvaal fault system and the more important thermal springs associated with it .
Geological map of the area cut by the eastern part of the Welgevonden fault . . . . . . . . .
Topographic contours on the catchment areas of the Welgevonden fault system . . . . . . .
Longi tudinal profile along the Welgevonden fault system . . . . . . . . . . . . . . . . .
Annual rainfall as a curve of cumulative departure from the mean . . . . . . . . . .
Pumpage from Union Tin Mine, original spring flow and estimated total spa abstraction
Plan of boreholes at Libertas spa . . . . . . . . . . . , .. , . , . , . . . . . . . . " .... " ..
Plan and section of boreholes at Lekkcrrus spa " . , ... ,." .. ,'"
Plan of. boreholes in the neighbourhood of Rondalia spa _ " " " " "
Schematic illustration of deduced ground water conditions at Libertas spa
Water-level hydrograph analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
4
between
4 and 5
5
6
8
between
8 and 9
10
12
14
between
14 and 15
THE WELGEVONDEN FAULT AQUIFER OF THE CENTRAL TRANSVAAL AND ITS
THERMAL WATER
Abstract
343 KR, while the large Lekkerrus resort, also on the
latter farm, is based on thermal groundwater found in
boreholes sited by a diviner where no spring existed
before. As all these boreholes are close to a major
fault known as the Welgevonden fault, whose presence
is clearly responsible for the strength of the boreholes
and the warmth of the water, it is desirable that an
account of the geohydrology of this important thermal
aquifer should be made available.
Thermal water pumped from the Welgcvonden fault composite aquifer, with a maximum temperature of 47°C, is used for
bathing at the four popular holiday resorts of Rondalia,
Rhemardo, Libertas and Lekkerrus. Chemically the water belongs to Bond's (1946) 'alkali soda carbonate' class but the
mineralization is so weak that the water is almost tasteless.
It contains, however, many times the fluoride content recommended for drinking water.
This bulletin is based on field work done at intervals
between August 1965 and August 1966, on the results
of the chemical analys~s of water samples collected
during that period, and on an interpretation of the
hydrographs recorded up to the end of February 1974
by automatic water~level recorders erected at the end
of the field period on three disused boreholes, one at or
near each of the thermal water localities.
The geology of the Welgevonden fault is briefly described,
and its geohydrology in as much detail as is possible with the
limited amount of infonnation available, It is deduced that
recharge of the fault is mainly from local shallow groundwater
and that the water gains its heat by convectIve circulation in
the plane of the fault. The diabase that crops OUt at the spa
localities is a sill and the thermal water is not pumped directly
from the fault fissures, but from the weathered zone of the
n. PREVIOUS WORK
diabase, where it is mixed with local cold shallow groundwater.
The water in the diabase is locally semi-confined, as may also be
that in the fault, but there is no reason to assume that either
aquifer is, as a \\fhole, fully confined.
Kynaston, Melior and Hall (1911) were the first to
map the area traversed by the Welgevonden fault and
they stated that both of the thermal springs occur on the
course of the fault and are undoubtedly closely connected with it. Von Backstrom (1938) gauged the springs and
thought that, as the fault dips northwards under the
Waterberg plateau, that plateau must be the recharge
area and that the groundwater moves southwards through
the impermeable felsite into the Welgevonden fault by
way of other faults.
The groundwater levels in the diabase far from tlle producing
thermal boreholes, fluctuate
with the rainfall when this is
expressed by a monthly curve of cumulative departure from the
mean, in the manner characteristic of shallow weathered-zone
aquifers in South Africa. Near the thermal boreholes, this
natural fluctuation is masked by other water-level depth variations due to unrecorded short-period changes in the rate of
abstraction.
The area along the fault was remapped by Van
Rooyen (Kent, 1949), who considered that the southward-moving groundwater is arrested by a diabase
dyke in the plane of the fault and that the water rises
in the fault beside the dyke. Kent quote~ analyses, among
others, of two water samples from the springs. He repeats the views of Von Backstrom and Van Rooyen and
adds his own and Russell's (1948 and 1949) on the
Loubad and Buffelshoek springs, and illustrates the
last by diagrammatic sections that portray the movement
of groundwater towards the fault as resembling that in
an artesian basin.
After the water-level had declined considerably during the
period of thermal water development from 1955 to 1966 the
mean depth, about which the water-levels fluctuate seasonally
or otherwise, stabilized and has remained stable in spite of
various changes that have occurred in the rates of abstraction.
Thus, under the present rainfall and abstraction regimes, there
is no overdraught. Data provided by the observation borchole
hydrographs from Lckkerrus and Rondalia spas indicate that
the rate of abstraction at these two localities could probably
safely be increased if necessary.
I. INTRODUCTION
Wilke (1963) remappcd the area with the help of air
photographs and his map was used as the basis of the
present investigation.
During the last twenty years the popular holiday
resorts of Rondalia and Rhemardo have developed
around strong thermal water boreholes that have replaced
the former warm spring, Die Dog, on the farm Rietfontein 345 KR, Potgietersrus District, Transvaal. The resort
Libertas has grown up around similar boreholes that
have replaced a warm spring on the farm Welgevonden
Ill. GEOLOGY
Figure 1 shows that the Welgevonden fault passes
within about 14 km of Naboomspruit. It is a member
1
of a system of faults that extends for 270 km from
Thabazimbi to Zebediela, The system roughly follows
the crest of a complex anticline that lies between the
Waterberg and Transvaal structural basins, Most members
of the system are reverse faults, overthrusts or tear
faults, the overriding movement having generally been
from the north,
fault, the felsite is covered unconformably by the still
more steeply dipping basal conglomerate of the Waterberg System. Interbedded with the felsite are tuffs,
agglomerates, shales and quartzites but these formations
do not seem to have any special hydrological significance.
Intruded with a complicated cross~cutting relationship, there is a thick diabase sill that plays an essential
part in determining the pattern of groundwater movement. Owing to the topographical relief and the throw
of the fault, this diabase sill has several separate outcrops and abuts against the fault breccia, here on one
side and there on the other: All three thermal spa
localities are situated where diabase lies against the fault
breccia in the zone of weathering,
The Buffelshoek thermal spring is associated with
the western part of the system, while the Loubad
spring occurs in a wide gap in the middle. The Wc1gevonden fault constitutes the western part of the eastern
half of the system. This eastern half carries no thermal
springs other than those described here but a branch
loop south of the main line of the system provides the
thermal water of the Warm Baths, Visgat and Driefontein
springs.
The displacement of the basal Waterberg conglomerate
at two places indicates that west of Libertas the downthrow side of the fault is the southern, and northeast
of Rondalia it is thc southeastern. The relative altitudes
of the diabase outcrops on either side of the fault west
of Rondalia confirm the fact that at the spas the downthrow is to the south,
The main elements of the geology of the country
traversed by the eastern parr of the Welgevonden fault
are shown in figure 2. Except in the Libertas-Rondalia
reach, the course of the fault and of its two western
branches can be exactly located because the fracture
zone has been so strongly silicified that, at the outcrop,
ithas the form of a white quartz vein that varies in width
from about 5 to 20 m and is excellently exposed. Its
outcrop forms a low ridge in most places which shows
up well, both on the ground and on the aerial photographs.
Throughout the greater part of its length the fault
dips to the north at angles that vary from place to place
between 45° and 90° (i.e. much more steeply than 30°,
the angle stated by Von Backstrom) so that it is a reverse
fault and not an overthrust. West of longitude 28°30 'the
fault bifurcates and both branches extend for an extra
11 km. The country rock that crops out at this en d of
the fault is exclusively felsite (fig. 3).
Between Libertas and Rondalia spas no fault breccia
has been found, so evidently the fracture zone here has
not been silicified. Although this reach is low-lying, there
are no springs or seepages along it, so presumably the
fault fissures are here closed in the zone of weathering.
An electromagnetic survey along this reach failed to
indicate the fault, The disposition of country rock,
float and ferricrete here suggests that the course of the
fault lies a little farther to the south than the inferred
line on Wilke's map,
IV. RECHARGE OF THE FAULT AQUIFER
Along the greater part of its course the fault zone
crops out as a massive quartz vein. Although it is here
referred to as a breccia, the brecciated structure is
uncommon and very rarely can open spaces be found
between component blocks and fragments, At a few
localities only, there are open fissures up to about one
centimetre in width between drusy linings, but they are
short and do not appear to form a connected system of
openings. It is evident that the fault breccia and the
whole fault zone have been almost completely silicified
and the original fault fissures scaled with quartz. The
permeability of this structure must therefore be attributed to fractures, caused by post-silicification rejuvenation of the fault, that are not exposed at the
outcrop. Mr. R, Urcn, Manager of the Union Tin Mine,
has kindly provided the information that in the old
workings, which include the fault, there is a shear on the
footwall side: of the silicificd breccia, The writer
observed slickensidcs on both walls where the quartz
vein had been removed at the mouth of an adit in the
old worki'ngs, On the footwall they pitch at 68° to the
cast and on the hangingwall at 26° to the east. Clearly
the fault has thrown more than once, one movement
having had a large vertical component and the other a
In the first few kilometres cast of Rondalia no typical
silicified breccia was found but a fault that runs up the
escarpment north of Rondalia (referred to as the Rheeder
dip fault) displays a very well-exposed silicified breccia
with open drusy fissures in it at one point. The writer
therefore regards the Welgevonden fault as turning
northwards at Rondalia into the plateau and as being
unconnected with the far eastern or Zebediela member
of the system as far as its function as an aquifer is concerned,
The fault cuts mainly fclsite at the outcrop but must
pass down through porphyry into Bushvcld granite,
which is presumably underlain by noritc and the noritc
in turn by the basal part of the Transvaal System. Near
the course of the fault the felsite dips northwards at a
low angle but farther to the north the dip steepens and
Just below the crest of the escarpment that overlooks the
2
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SECTION A-B DIAGRAMMATIC
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Topografiese kontoerfJ van die opltOnggebiede van die
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LEGEND - LEGENDE
Points where Sterk River headwafers cross faults
Punte woor bolope van Sterkrivier oor verskuiwings ,000
590/361
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11,
,
--'l~O!l~':.~s~_,~
\.
'.
'~
\~
~
w
Fault bifurcation
N-S Rood /Pod
m
1600
Stark River
Verskuiwingsvurk
I
FOUl!
E-W Rood
O-W Pod
~
---------
1500
~
j
~
Union Tin Mine
m
Main shaft collar __
HoofskOQkroag
E S
~
RondoJia Spa
'/0
Liebenberg's bore holes
\\
Gl'OcJiii?;j _
Spa
__ _
&<:l
f,2~
o
'<.<>
""-
20
15
!
10
,
1400
waterdraer(?)
q,~
W.V.
5
FIG.4.-Longitudinal profile along the Welgevonden fault system
Lengteprofiellangs die Welgevondenverskuiwingsisteem
WL
0
..
0
~
x
----------'
Welgevonden Fault closed(?)
. . We/gevondenverskuiwing Sluit dig{?)
!
%
~
0
0
!-.t<J
.~'lJ l'fb
<p~~0
W.L.
9th level fissure __
Spleef op 9de vlok
25
,·.\ed?)
"0::\'1)\ ~e{$kuiwinQ
,r::.';:' q,\\\{\Q,'&
~~
km
:::
Breksie baie sterk
Rhemardo
Liebenberg se bOOrQate
.......
X
1300
1500
.~
/'
Volley bottom
lem f 2 o ;--'Volle!beddinQ
Gro(j'- _
1400
N
Breccia very strong
Lekkerus Spa
~
0
'" "."'
r
Sterk River tributary
Sytok van Sterkrivier
5
!
1300
Spring flow ceo!BO
Fontein hou op met vloei
Woter-Ieve! obs.ervotion period
Woterv!okwaornemingsperiode
+
l
} !OOmm
111!
0
0
Ol
••
•~
w
l~
f
~:~rddeld 615 mm
I
,
, ,
,
I
I
. 1910
I
•
,
I
,
1920
,
I!
1930
1940
\950
1960
FIG.5.'- Annual rainfall as a curve of cumulative departure from the mean. Based on overage
of three stations,Boekenhout 632/297, Noboomspruit Police 590/361 and Vostrop
633/463
Jaarlikse reenva/ os n kurwe van kumu[atiewe afwyking van die gemiddelde. Gebaseer
op die gemiddelde van drie stasies I Boekenhout 632/297, Naboomspruit-Polisie
590/361 en Vastrap 633/463
1970
considerable horizontal one.
unconfined and only semi-confined1j where the fissures
happen to be closed at the depth at which the waterlevel would otherwise have stood.
The fault breccia is inclined so steeply that it must
lie at a very great depth below the Waterberg Plateau,
which is si tuated 10 km north of the course of the
fault; the kind of groundwater circulation contemplated
by Von Backstrom seems therefore impossible. The map
and longitudinal profile (figs. 3 and 4) show that recharge
of the fault is more likely to take place mainly in the
relatively high country south of the Swaershoekberg,
which is traversed by the western branches of the
fault, and in the small area of high ground northeast
of Rondalia spa. Shallow ground water in the weathered
zone of the felsites and Waterberg sandstones to the
north of and higher than these extremities of the
fault, must percolate southwards towards them.
There was no spring at Lekkerrus but as this spa
is also situated at a low point along the course of the
fault, there was probably sub-surface overflow seepage
before the water-level was lowered by abstraction.
Regarding the heat of the water (max. temp.47°C),
there is no evidence of any other source than the
normal thermal gradient.
In view of the probability that the water pumped is a
mixture of hot water from the fault aquifer and cold
water from the shallow weathered zone of the country
rock, it is most unlikely that the temperature of the water
abstracted is closely related to the depth to which the
water in the fault circulates. The result of the calculation of any such depth would be invalid.
The perennial headwaters of the Sterk River cross the
western branches of the fault at the five points marked
A to E in figure 3. Whether conditions at these points are
influent or effluent with regard to the shallow weatheredzone aquifer in the felsite, groundwater is being constandy drawn off into and along the fault, thus providing storage space for both local shallow groundwater
and for surface water that may be infiltrating from the
perennial streams. North of the Paardeplaats fault, the
southern branch of the Welgevonden fault, there is a
surface water catchment area of about 80 km 2 , most of
which stands at an altitude of between 1 460 and 1 710 m
above sea-level, where it enjoys.a mean annual rainfall of
over 600 mm.
There is no need to assume that the water requires a
long passage at depth from the recharge to the discharge
areas in order to gain its heat, as portrayed by Kent
(1949). All that is required is a connected series of
openings in the plane of the fault that extends to the
necessary depth, and that the openings are sufficiendy
wide and suitably distributed to allow the development
of a convection celL Wherc such openings exist, the
water heated at depth must rise to be replaced by cooler
water. This vertical circulation may be totally independent of any lateral movement in the aquifer. How many
convection cells there are and where they are situated,
are not known.
The mode of recharge of the eastern or Rheeder dip
fault part of the aquifer is not so clear. The surface
water catchment here is only about 2,6 km 2 and no
perennial stream crosses the fault, but the fault does
intersect another one on the plateau. It is assumed that
recharge of this eastern part of the fault takes place·
either from a system of undetected interconnected
faults on the high ground to the north of it or by the
eastward movement of water in depth between Libertas
and Rondalia spas.
VI. DISCHARGE OF THE FAULT AQUIFER
Die Oog (now Rondalia spa) and the Welgevonden
spring (now Libertas spa) were replaced by bore holes
in 1954 and 1955 respectively because they had ceased
to flow, so that pumping from boreholes was the
necessary consequence, not the cause, of their failure.
V. WATER MOVEMENT IN THE FAULT AQUIFER
As there is no rainfall station nearer than NabooInspruit, distant 16 km, the rainfall for each year or
month, as the case may be, at the spas is assumed to be
the average for the corresponding period at the three
nearest rainfall stations, whose positions and reference
numbers arc shown on the inset map of figure 3. The
rainfall regime is expressed by curves of cumulative
departure from the mean because groundwater level
fluctuation in South Africa normally corresponds more
closely with such curves than with any other kind of
graphical representation.
The longitudinal profile (fig. 4) shows that the western
reaches of the fault and its branches could carry a
water-table with an overall gradient of a little over 1
per cent, so that water finding its way into the fault
must flow eastwards towards the spas. The Rheeder dip
fault could carry a water-table with a much steeper
gradient declining southwards towards Rondalia and
Rhemardo spas. All the spas are in fact situated
exactly where overflow from the fault should be expected. Although one of the boreholes at Rondalia that
replaced the spring, Die Gog. flowed before the waterlevel was lowered by pumping, it is unnecessary to
assume that the water in the fault is or ever was, as a
whole, confined. More probably it is in general free or
The annual cumulative departure curve for the whole
of the rainfall record (fig. 5) shows that the springs failed
near the middle and end of a four-year-Iong phase
(1953-56 inclusive), during which the mean annual
7
10000
5700
5000
r.tv.
rfY
("v.
SPAS
'0/,7;
m'ld
e- 1000
1000
r-
."•• ."••
~
~
e
2e
.E
;;
e
•e
U
0
•>
~
~
"'..
e
."
.E
"-
u
:f1"
!<
Ze .E~
"-
"
:8
500
~
e
~
rSPAS
I-
u
~
500
e
.~
.~
"'e
"'.5 u•e
.
e
.E
,-;
'"
,
,...
~
r-
SprinQ$ flow 1939
Vloei van fonteine 1938
o
,-r-I--
0
>
•
1955
.-
rI-
I-
1965
1960
1970
o
FIG.S.- Pumpage from Union Tin Mine ,original spring flow and estimated total spa abstraction
Onttrekking uit Union Tin-myn,oorspronklike vloei van fontein en berekende totale
spa-onttrokking
8
I //
i,
\
\\
\,
tf
\
x
\
I
~J(
,:
Lb02
\
\
J(
1
!
::
DIABASE
x
IX
IX
0
'
\
1
\
,
Lb22:
X
I
ROII~rvoir
t
x
:
,j
x
I
--t---
:
'
_~!:'-;<.--
"
VERS/(~r~G
,/
I
!(
° 28
I
I
.
'
FElSIET
-
HUlshoodellke voorrood
0
lb8
4,5m~/h
._._._._._._.
°
'\:'
----
~
Lbl
f
0
°6'i::bl
lb3
"COld/
..
\:,{Olld
P'rQdOCifIQ 'ho,,,,,,1 00,.1>010
014,9-9,lm¥h 43°_34°C '\
Tg,mi."g PtodUk.iOOOOrQOI;lS
14,9-9,lm~/h 43°-34°C
;\$
~K~~~._. _ _ _. _ . _ . _ . _ _
196Cold
j
1
<0
'--1.--.:to~
° :;;'0<;
"o,..'\:-.1bo
"'o~
50
~,
.'f...-'f.
FIG.7.-Plofl of boreholes 01 LiberlQs Spo os in April 1974
Plan van boorgate by Libertas-Spa soos in April 1974
0
50
I
;
O'\~i
FElSITE
~
~.
~,~
"
~lbl6
~.
.--'~
'"
Koud/Coid
'"4 0
?b
l~1229 50C
lb7 ~
°
\\ "tb'5
0
Balh.
~,
"'" ",_,
'" Hol/
Sad<fcno
2SOC
Hot"'cold
x
'f...-'f.
'''""',
lb 17
Domestic sllPply-""o 3,2m3/h
-'-"
~
E 'x
.--'
FElSITE
I
0
1. GO!o/Hok
c,
DDfaOg
0
Bolh hO""O
x
~,~
'
,I
o
lbl036m3/h
0 C
X
,,,t,,::::::.·:~~:~S;';'~;""-:~---·--2='i"-'_, __--.-.-.-.-.-.---.-.-.-.-.~9~·-·-·_~T·---·
,,,
Lbl5
(
"
Dry"
Lb9 1,8m37h
-------1,4 m¥h 290C
Water-level recorder 1966-1974
Walervlakregis1reerder 1966-1974
~!,.<:-:;----
\,
'0
'""
affiCa~"MOQr
~
lbl3
DIABAAS
I
'-
Lb 14
IN """""" "'"
X
lb 18
0
"cP~------:::::::::;:::::---------':-:::::::":'A---::'---':---=C;::':::'-:"~~=~9:.:::..__:..________
'O~"';-:;:---u\-i,<.";.":./
r/
\
23°-29°C
__________
FE LS J ET
I
x
\
Lg 19
-------------
X
\
3
Cold 18,2 m /h
Domesfic supply
HuishOlldelike V()orroad
I
,
\
0
---_
/
x
I
Ix
',
FELSIET BO-OP DIABAAS
----- __ _
28°C
DIABASE
1ORO'ONOi,
'
\\
0
X
'
I
,
I
x
/
,:
:
'\
I
,
OVER D1ABASE
\
°1
r
FELSITE
\
~
Lbll
-f'
//// 1
//
'/
100
I~O
m
.
~
"
,;<
rainfall was 110 mm (18 per cent) above the long~term
mean of 615 III III , 'I'll<: monthly cumulative departure
curve from January 1953 to December 1955 (not here
IHeS{:lllcd) shows that the distribution of rain during
each of these three years which preceded or included the
years of spring failure, differed little from the average
distrihution. There was therefore no rainfall deficiency
or non-llverage distribution of rain within the year such
!lS would reduce the rate of recharge and so lower the
ground water rest-level.
At the time of completion the tested yield of the
producing borehole Lb 4 was 14,1 m 3 /h, but when
retested later at an unrecorded date the yield had
declined to 9,1 m 3 /h. The temperature of the water in
this hole changed while drilling was in progress. When
the depth of the hole w.as only 12 m the water temperature was 35°C, but when it was 24 m the temperature
was 43°C. After completion to 33,S m the water
remained at the latter temperature for two months
(presumably while abstraction was in progress) and then
declined to 34°C, which has been maintained subsequently.
The only place in the neighbourhood where any
considerable abstraction of groundwater was taking
place when the springs failed was the Union Tin Mine.
The rate of pumping (fig. 6) was at that rime only
about 100 m' /day, about half of the flow of the two
springs together when measured in 1938, The main
shaft is situated 0,6 km north of the Welgevonden fault
and 6,5 km west of Libertas spa, where the nearest
former spring occurred. Although some of the old
shallow workings were on the fault itself, no deep
workings at that time came near to the fault, and
diamond drill holes, sunk subsequently, that penetrated the fault at a depth of 120 m, were dry. It is
therefore very improbable that pumping from the
mine caused the springs to faiL The cause remains
unknown.
The temperature of the water in borehole Lb 8
(not in table) also changed during drilling, for it was
hot when the borehole reached a depth of 30 m and
cooled considerably by the time it had reached 50 m.
When borehole Lb 17 was drilled the temperarure of
the water was 28°C, which was high enough for the
water to be used in the baths, but it subsequently
cooled so much that by 1966 it was being used only
for domestic purposes.
In the case of Lb 19 (not in table) the temperature
of the water after drilling was completed was 29°C at
the bottom of the hole and only 23°C at the water-level.
The yields and water temperatures of nine boreholes
when drilled were compared with their distance from the
fault breccia but, as no systematic relationships were
found, it is concluded that the thermal water moves
rapidly away from the fault in some places, presumably
along branching fissures, and much more slowly in
others.
The distributions of the known boreholes at the
spas are shown in figures 7,8 and 9 and the yield, water
temperature and other drilling data of the principal
boreholes, as provided verbally by the spa managers
mainly from memory, are given in table 1.
At Libertas spa (fig. 7) all but one of the numerous
boreholes were drilled either on the quartz-breccia
outcrop or on the northern side of it, which is both the
topographically higher side and the side on which the
diabase occurs, one being situated as much as 230 m
from the fault. Those on the north side of the quartz
vein or breccia either penetrate diabase only or go
through felsite before reaching diabase. The breecia
dips to the north, so that those boreholes that were
sited on its outcrop pass out of it into felsite before
reaching water. There is no exposure of the breecia
near the producing borehole Lb 4 beside the Sterk River
but the course of the fault probably passes close to it.
This borehole is reporred to have penetrated quartzite
and decomposed felsite over diabasc, Water was struck
about 12 m below the level of the river bed when this
hole was drilled in 1965, and the water~levcl remained at
that depth.
Borehole Lb 6 in the fdsite on the southern side of
the fault yielded 1,14 m 3 /h of cold water,
At Lekkerrus spa (fig. 8) all the boreholes are on
the southern side of the fault, which is here the downslope and the diabase side. The three producing holes
are situated about 30 m from the fault and the silicified
breccia dips to the north away from them. They vary
in depth from SO to 60 m and water was struck near the
bottom of each, They are reported to have penetrated
decomposed diabase over felsite but there are insufficient
details to enable a proper geological section to be
compiled. It seems probable that the water was struck
in the feslitc at the lower contact of the diabase sill.
The water rose to levels that varied from depths of 1,5
to 2,7 m in different holes; it is therefore locally confined or semi-confined, presumably under the~diabase
whieh must be so highly decomposed as to be virtually impermeable.
From the Sterk River the ground surface slopes up"
wards to the west along the course of the fault so that
the depths of the boreholcs and water-levels increase in
that direction and the diabase, which is hcre on the
north side of the fault, is covered by felsitc.
When tested after drilling, the producing boreholes
yielded between 20 and 30 m 3 /h and the temperature
of the water was between 42° and 47°C. In July 1973
9
,1/
·i/A
...."'/
",Q<:-I/
.~y;
.,""
~
IV
~
~
~
~'I/
PLAN
/j
/i
I!
I!
,
~
~~
~:::::-...
"'~
-.. . ;:
~
'"
~
-. . : : : ~ ~
OffIce
:::===::::::::-:~1,i:::::::.c-~~~~-~~~:~~~:---::::::::::::::::::.:.:-_-_-_-_~~-~-s~-;;;~~~~~ ~~v9rskui".in(jsbra:~~eno
Do~esl'c
HUlshoudelik
Lk4
A
Lk 50
Disu!Wd
,:,~
In onbruik
~ 8/
/./
~
-f'
,
~
fOwl,sWlrl
~::::::::.
W L recorder 1966-74
SectIon l,ne
W V reOlslraerdor 1966-74
Lk2
t:://;
~
~
~ Lk6
Lkl
==~
boo<'gole
_'_'-P;;t·\~·-·-·Kr~\~n
'7
50
!
B
f:::)
_.-.-.-.-
~,(7
0,
Lk7
t. Produ_cino
thermal, bore holes
Term'Erse produks,e8aths/Saddens
'7
10
,
Lk 8/9 130 m -+'
lOOm
,
SECTION A- B
PROFIEL A-B
o
D<:lmestic
Recorder
Stood-by
fiuist\oudelik
Re-o i 51reeroer
Reserwe
W
Lk4
,
Lk3
r--.
ProduCing thermal boteholes _ ,_ __
Lkl
Lk2
l
I
L\J
Termiese produksieboorQ<lle
L\7
:
m
360
_
I_f?-L..
350
R.Ii.
,whe/)
__drilled
•
-...... ___
09geb"O;,;:-:__
lS
_----,.
-...__ _ _ _ _ -
w.s
oo'C
300
_ Diobos8
.,-
f
l__--c=~c=~~~~==::==~=i':;~;=~~::r
_ ___ - - , , ; ; , ; ; - ; ; - - '
350
/',
f9s$
___
I&,,~::::
&/ ........
*1,&11..... -
~:;7
'"
I/
R.L
~
R.H
O;oboos
Oiabose
/'fl.
340
;t\\\e
------------ :>._------
= Rushoogte
---I.
TY~~;9m%
Re$I_level
W.S
~
W.R
= Waler rookyeboor
= Tested yield
I+- Pump/Pomp
320
Felsile
WS.l
TY49,7m3/h
Co!d/Koud
W.R
330
Fels;el
Fels;et
Woter struck
T. V
G.L.= Geloetste le ... ering
m
360
-'-Rusho~e l(le
Felsile
330
"0
_-R.L lIuctual!cm range by
n!corder 1966 -1970
Geregislreerdt skommel;ng
in R.H 1966-1970
340
320
11
-. Ii';;,_
----...,.
E(O
i
3
G.L.29,5m /h
42°C
FIG.8.- Plan and section of boreholes ot Lekkerrus Spa as in April 1974
Plan en profiel van boor90te by lekkerrus-Spa soos m April 1974
ws
~
,
TV 20,5mjlh
3>0
42°-47°C
TY 20,5
m~h
40°-44 SOC
J;ws
300
TABLE 1.-
Name of
spa and
no. of
borehole
Rhemardo Rd 1
DRILLING AND TESTING DATA OF THE MORE IMPORTANT BOREHOLES, AS PROVIDED BY THE SPA MANAGERS. COLLAR ALTITUDES
ARE RELATED TO THAT OF RHEMARDO RD 1, TAKEN AS DATUM 304,8 M
Date
drilled
*Collar
altitude
m
Depth in metres of
Borehole
Water
struck
Rest-level
when
drilled
pump
Tested yield
when drilled
m'th
Test
Temperature of
water when borehole was drilled
°c
1966 (? )
304,8
54,9
30,5
10,7
42,7
24,6
37°
1955
1958
298,8
297,4
22,9
42,7
1,5 - 1,8
5,8 - 4,6
flowing
21,6
39,6
Tested together
38° - 39,5°C
38° - 39,5°C
1963
1965
1966
1966
1957
1969
308,3
308,3
39,7
65,5
47,2
64,0
44,5
61,0
21,3
30,5
19,8
22,0
19,8
31,4
12,2
17,1
19,2
18,3
19,5
26,0
26,2
36,6
18,2
33,5
48,8
91,4
107,9
90,8
86,6
33,5
12,2
12,2
30,4
45,7
24,4
57,9
36,6
25,6
30,4
24,4
48,8
24,4
49,7
39,6
48,8
61,0
27,4
30,5
45,7
24,4
45,7
36,6
48,8
61,0
24,4
24,4
Geological
formations
penetrated
diabase
Rondalia
Rn 1
Rn2
90,0
diabase over felsite
diabase over felsite
Liebenberg
Lg 1
Lg2
Lg 3
Lg4
Lg7
Lg 12
28°
33°
cold
cold
hot
25,5° (cold)
felsite over diabase
felsite over diabase
14,1
2,6
0,8
2,1
3,2
1,8
18,2
43°
cold
29°C
28°C
28°C
cold
cold
27°C
felsite over diabase
fe1site
felsite over diabase
diabase
felsite
felsite
diabase
felsite
1,8
12,5
1,8
29,6
15,9
42°C
diabase over felsite
diabase over fe1site
felsite
2,4
2,4
24,4
24,4
20,5
20,5
0,9
7,3
51,8
18,2
3,2 - 4,5
2,3
9,1
felsite
felsite
felsite
felsite
over diabase
over diabase
over diabase
and breccia
~
~
Libertas
Lb 4
Lb 8
Lb 9
Lb 10
Lb 17
Lb 20
Lb 22
Lb 23
1965
1963
1963
1965
1957
1966
1965
1966
30,4
Lekkerrus
Lk 1
Lk 2
Lk 3
Lk4
Lk 6
Lk 7
Lk 8
Lk 9
1959
1959
1959
1959
1959
1959
1959
1959
354,6
351,4
355,4
361,5
362,9
·Of principal boreholes open to water-level measurement at the date of the survey_
?
cold
40°C
42 - 47°C
40 - 44,5°C
27°C
?
fe1site
diabase over felsite
diabase over fe1site
boulders
fault breccia over fe1site
/
DIABASE
W.J. RHEEDER
L04
OCold/Koud
_Liber!OS
_ _ _ :::::
==:=::=:. -
-
-
:::= :=: ::=;:::::
RHEMAR DO SPA
/
x==.==
\
W~ Hot'~
0""
_'-'-'-._
~i
>18,2m 3/h 28-33 0 C LQ2.
\
_'_'-'-'
" - . _ /"
L - 2_~l91 WotervlokreQistreerder
/-91
Jul. 1966-0as1967
•
-----~
Lgl4
o
o
To/No Lg 10
_40m
Lg 8
-""OCOld/Koud
Lgl5
o
I
Residence
0/
Water level recorder
Waning'
July 1966-Dec.1967
/ FELSITE OVER DJABASE
Water level r e c o r d e r ; '
Watervlokregistreerder
JoI'I.l968-Apr.1974
Butchery
Slogtary
\
'S){
~s
.~\«
'v'
-Jet";;
LEGENDE
/'
,.
rn
1>,\ 'O,,~...
-:&
".c-.... ,.
~
:..- ...
LEGEND
•
o
Other boreh(tles
Ander boorgate
~I
,.
9
LgS
~e o
e¥"";;
/
e~
~~
~
-
-~
~
J,.------
R:::2
-------
------
DIABASE OVER FELSITE
DIABAAS BO-OP FELSI£T
•
0.,.,
./
Cold \
Koud
,
/
./.
L 6
/
'J.
RONDALlA SPA
/'
\,
(~'--,
'---~~/:m
"".
\
Thermal boreholes
Termiese boorgate
j.
./38 -39,SoC l •
\
0
c\o
~ev"
S.W.UEBENBERG
:3
90~ 'h <
/
OLg7 Hot/Worm-'-'_'--.l
[Z]
/
•
FELSIET BO-OP D I A B A A S .
Jan.1968-Apr.1974
N
;i :2.~~ '5 'T:::/,~.(?) 3c'-CC
/
POd:=:
Lgll Koud
Lgl3
DI4Stdl.S
x-="x_x
== == ==
== ~ == - _ _ _
~~~-~",~
- - --'--'--'--,--x~x-- "~-....:::::.~ =:;:~==::::::::::: ==--
Lg3 RO:d
Cold 0
/
/
\
\
50
---.--.---
'--'--'--
0
\,
\
FIG.9.-Plan of boreholes in, the neighbourhood of Rondolia Spa os in April 1974
Plan van boorgate in die omgewing van Rondolia-Spa soos in April 1974
50
100
150
~
(c). Although no direct relationship is evident,
the temperature of the water is higher near the outcrop
of the fault breccia,
the water temperatures were reported to vary between
39° and 46°C. Information kindly provided by tbe
manager is shown in the section but the 1966 water~level
in borehole Lk 2 has been added, as also has the recorded
range in water~levcl fluctuation in Lk 3 during the
period 1966~70. Why the water-level was so much
deeper in borehole Lk 3 than in the other holes,
although they were all drilled at about the same time,
is not understood.
(d) In the case of at least 2 boreholes the tem~
perature of the water decreased after pumping had been
in progress for sometime.
The following conclusions drawn from these obser~
vations are illustrated diagrammatically in figure 10.
At Rondalia and Rhemardo spas (fig. 9) there are
18 boreholes distributed near the junction of three
properties, viz. Rondalia spa where two boreholes
replaced the spring Die Oog, Rhemardo Spa with
originally one borehole, and Mr. Uebenberg's farm
with 15 boreholes but no spa development,
Observation (a) shows that the basal part of the
zone of weathering of the diabase is the only formation
permeable enough to yield water to a borehole at a
practicable rate.
Observations (b) and (c) show that, at some places
at least, the temperature of the water varies both
with its depth in the weathered~zone aquifer. and from
place to place in the aquifer. Both are consistent with
the view that the water pumped is a mixture of hot
water from the fault and ordinary cold shallow ground~
water.
In 1973 borehole Lg 4, originally Liebenberg's, was
supplying cold water to Rhemardo spa for domestic
purposes.
There is only one exposure of quartz breccia in the
vicinity of the boreholes and it is uncertain whether it
is t'n situ or not. The course of the fault probably runs
northeastwards from this exposure, passing between the
Rondalia and Rhemardo boteholes to the point where
it is again exposed a few hundred metres farther in that
direction, All the holes penetrate diabase but at some
of them the diabase is covered by an outwash fan of
felsite rubble, The reported logs of formations penetrated are very contradictory and, if correct, the
diabase in some places may occur as two sheets with
felsite between,
Observation (d) is also consistent with this view, for
it is probable that the faU in water temperature during
abstraction is due to the lowering of the water~table
or pressure surface in the diabase aquifer. The rate of
supply of hot water from the fault to the diabase
aquifer is probably almost constant because it must be
regulated by the width and number of interconnected
fissures in the fault breccia, and the long time that
must be taken by most of the water in moving in the
plane of the fault from the recharge to the discharge
areas, a period during which the amplitude of the
seasonally fluctuating rate of recharge is considerably
reduced. The rate of supply of cold shallow local ground~
water will, however, vary with the local gradient of the
water~table or pressure surface towards the boreholes,
Under such circumstances of dual supply, as the rest~
level is lowered by abstraction so the rate will increase
at which the local groundwater in the zone of weathe~
ring moves towards the boreholes, and the increasing
proportion of cold water will lower the temperature
of the mixture pumped.
The tested yields of the 6 thermal boreholes varied
from 2,3 to 45 m'/h, the higher figure being half tbe
total yield of the two Rondalia boreholes pumped
simultaneously. The depth at which water was struck
varied from 1,5 to 30 m, The water generally rose to a
level higher than the depth at which it was struck and
it originally flowed from one of the Rondalia boreholes
without being pumped.
The temperature of the water in the Rondalia holes
when tested was 39°C. At the Liebenberg holes Lg 1 and
2 it was 28° and 33°C respectively, while at Lg 5 it was
38°C when the hole was completed, but ran cold later.
Should this conclusion be correct, there must be a
slight seasonal fluctuation in both the maximum yield
of the boreholcs and the temperature of the water
pumped. No such variations have been reported but this
is probably because the producing boreholes have not
been retested, nor have temperatures been measured
often enough.
The following conditions, evident mainly at Libertas
spa, are believed to be significant regarding the under~
standing of the geohydrology of this thermal water
supply.
(a) The thermal water is pumped from the diabase,
not the fault breccia.
VII. BEHAVIOUR OF THE GROUNDWATER LEVEL
AND THE POTENTIALITY OF THE SUPPLY
(b) The temperature of the water struck in some
of the boreholes changed during the dritling,
Since the failure of the springs, which must have
been due to a decline of the ground water level, no
13
Silicified breccia cl Welgevonden fault
s
N
Verkieselde breksie van die WelQevondenverskuiwing
Thermal borehole
1
~~"""")))')))).,.,.,,-;
Termiese boorQot
o
. 0
Diobase,decomposed, impermeahle
Diobaos, verweer, ondeudolend
?
o
o
•
Cold water-level
Kouwatervlok
Thermal
water-Ieve!
Fractured, permeable
Gebreek, deurlotend
...
Felsite
(Impermeable)
+
+
Felsiet (Ondeurlotend)
+
+
+
+
Hot,rninerolized \ \
+
+
+
+
Diabase
Oiabase, fresh, impermeable
Dioboas, vars,ondeurlalend
Dioboos
COld,fresh
Warm ,geminerallseerd \ \Koud,vors
Convection/ Konveksie
LEGEND
~
Hot water in fault
~ Warm water in verskuiwing
[SJ
LEGENDE
Warm mixed. water pumped
Warm gemengde water wet
gepomp word
COld water in weathered zone
Koue water in verweerde sone
FIG {O.-Schematic illustration of deduced ground water conditions at Libertas Spa
Skematiese iIIustrasie van afgefeide grondwatertoestande by Ubertas- Spa
;--:,: -~:.::::}::::::\)
!:\
/\,~/.
\~ .~:)">/
:~:~v{,~,,<
:~-~::''I<,:--:~::,
\/
~
...
~--
\~~:~:>'
.,'
,,~,'
20
;;;
'
//
0
E
0
Q
2
c
.0
3
~
4
5
~
4
C
m
10
L
J
15
~
~
9
~
~
:~
1
Rest-level when drilled ( 1965)
8 Woter struck 21 m
Roshoogte toe geboor is( (965)
Waler gekry OJ) 21 m
FLUCTUATION OF WATER-LEVEL IN BOREHQl£S Lg8 AND Lg! AT RONDALtA IN RELATION TO ABSTRACTION
VERHOUDING TUSSEN SKOMMELlNG VAN WATERVLAK EN QNTTREKK!NG VAN aCORGATE Lg8 EN Lgl OP RONDALlA
Rest·lavel when drilled (1963)
- L I Waterstruck 17-45m
9 Rushaogle loo geboor is( 1963)
Water gokry op 17-45 m
RW1
l;;;------·.----- ///.----."---.---.-~
20
e
lE
Im1i;1J
Imi~
.L~
,400'
-
IdO'},
l;-;-\>~"~;-~--\_.'
--<::,::,_,
i'i',
" '_0'/" "
f;:::r:.~~,
~
_-,-' -(,,;'::/.;::t'\:::";,"''''"f_\',:~l--:'r:.-;>':q:-''',\/p'oo~--'O'
, '
25
J
V
'
"
.....
"i; \}:\;.:-:--~-:::<:::d
,'f"
~
-~
"
\/'
,c:
'0
i
E
o
b)/7/))/) / ) / / / / ) / / / ) / ;t; / /);)/7 /7 ///7))77) /) /
0
Q
c
.0
~
Jl4
2
3
200
Original spring discharge 1938
OOrspronldike vlaei van fontein 1938
VERHQUDING TU$SEN SKOMMEUNG VAN WATERVLAK EN ONTTREKKING VAN BOORGAT Lb 9 QP UBERTAS
lb 9 Rest-level when drilled (1963)
Water struck 45,7m
Rushoogle too geboar )s(1963)
Water gekry ap 45,7m
30
';fr-.---.-.-.~'-...--..'-._ ~-. . . . . . ~I'm
f"···
~
u
- - 5 days-
..... _ ...................... , •••••••••••>....... •?-.....................
35
"
Nearby borehDle tested
~
•
.............--......
Nabygelee boor-gat getaets
Nearby borehole tasted
Nabygalee boorgot gatoets
j
M·- /-"
-~ /
-"'-'1'
~------~._.~. . r~,·-._____._____ jV
Original spring discharge 1938
Oorspranklike vlaei van fontein 1938
40
o
F M
1966
A M J J A SON
0
8c
1967
1968
1969
1970
1971
64
64
64
16
16
.2
~
3
V/////////////////////J
4~
11
4
200
FLUCTUATION OF WATER-LEVEL IN BORE HOLE Lb9 AT UBERTAS IN RELATION TO ABSTRACTION
o
~
~
~
200
fl'U/J//ijP///PU/P
4
m
~,
:1;) / >/; /'//;) /)7)// /;7'7 A/ )//////)/)7//»)/////;V ) ///)))7// ) / '/)))) ) ;/ ) ) 1;////)))/; // // hh) /) /j/, // /
314
FIG.!I.-Water-!evel hydrograph analysis
Watervlakhidrogroafanalise
.~~
~-"L :L L L'l/'
"---'"',,::~f::::;::::<:
"
,Wu:,u:="
:
\\
~~'
:'~'U:"~F:
\/
,.,
__
.::~/:~~:::: ·_-:\V;;'-""'- /-,
"ff~/.7/_7_ffmff/.7>~
~>
,.
"
.
//
i/
.<;:?:
-
'''',:~,.
,7hU"",'dM,'" ,,,",
V"
""'f
nw,=="70/7=-»: V
'q
rJT/.7M7H
20
,>, ;I /1
\C. , I ''
---, ',-</
0
g
I
i
2
Q
3
.~
4
5
0
~
0
FLUCTUATION OF WATER-LEVEL IN BOREHOLES Lg8 AND Lgl AT RONDAUA IN RELATION TO ABSTRACTION
VERHOUD!NG TUSSEN SKOMMEUNG VAN WATERVLAK EN ONTTREKKING VAN BOORGATE Lg8 EN Lgl OP RONDALlA
m
10~
m
10
Rest·lovel when drilled (1963)
- L ! Woterstruck 17-45~
g Rughooglo loo geboor ts( 1963)
Woler Qokry op 17-45 m
15
--------
~
o
NW1
L~
'_:~
.~:,.
/
L:;'\/"':---:::::~::,-:::::;/:}~,;:::/.~\::::»,:j";:":'
j/pq,~~"
\jP'"
.
--~
4 doe
"i
Imlty
Iml'~
,
20
IdaY
'~
"
.,
J;;"'t~:':>:~:--:~:::1';i C:C::~l!
.
§'
c
~
~
. .r,.\
~~\
-t\
"'.'"
25
.,
~
200
/,
200
200
200
;;-
I
0
2
rehole tested
. - . -...... .
~l'm
............... --......
oorgot getoets
1968
1969
64
64
......
Neorby borehOle tested
Nobygelee boorgot getoets
j
t
'-.-
/--'-...·-..........~~.-.....~.,.
~
S
§
4
~0
m
VERHOUDING TUSSEN SKOMMElING VAN WATERVLAK EN QNTTREKKING VAN BOORGAT Lb 9 OP LlBERTAS
+--5 doys-
E
Q
3
FLUCTUATION OF WATER -LEVEL IN BORE HOLE Lb9 .&T LlBERTAS IN RELATION TO ABSTRACTION
fy.-~.-.-.-'-....-.
-,
1
1l
0
v ' .... ....r-....
.---------.....--. ~
'
..
'-.------./
30
~
0
"~
•
0
c
35
~
li0
0
I
1970
1971
1972
16
16
16
1973
r~O t1l
I
~
0
2
3
4
FIG.! 1.- Water-level hydrogroph analysis
Woterv/akhidrogroafano/ise
Q
:?
:B
~
"
0
MONTHLY RAINFALL AS A CURVE OF CUMULATlVE DEPARTURE FROM THE MEAN. BASED ON THE AVERAGE OF THE THREE STATIONS OF FIG
MAANDEUKSE REENVAL AS'N KURWE VAN KUMULATJEWE AFWYKING VAN DIE GEMIDDELDE. GEBASEER OP DIE GEMIDDELDE VAN DIE DRIE STASIES
I
11
A
•. /
....
···••. ,~o-roin slope
...••.....
Hailing vir geen reenvol
.4...-Moon
•
Gamiddalde
if
-- ______ =~O_m~_______ ~
~1111}loomm
~'S53'~------
._--
..
7"-'~-- ____ :l.?.!ll_m___ _
------:.!.~-n:..n:.. ____ _
____t~~~~---------·
---:-
Monthly meon 51, 2mm
Moondellkse gemiddelde 51,2 mm
JFMAMJJASOND
1967
1966
o
m
1968
1969
1971
1970
B
Rest·level when drilled (1950)
WaterstrUCk 0145, 7m
-RuShoogta toa geboor is( 1950)
Water gekry op 45,7 m
FLUCTUATION OF WATER-LEVEL IN BORE HOLE Lk3 AT LEKKERRUS IN RELATION TO ABSTRACTION
VERHOUDING TUSSEN SKOMMELlNG VAN WATERVLAK EN ONTTREKKING VAN BOORGAT Lk 3 OP LEKKERRUS
5
,-'"
~
v
~
"
//
I<f-/
10
---.\
--+-\
.. __ 1.
",
/1/
-',
..
,""m'"t~
Manuol maa
hand
Meting per
--~-,:\
\
o___ ~__ "
<0
. -:--,/
15
Im!V
ImlV\
----~"
-,--«,~(/ ImlVtv
!"do;
o
~
-~-
idaY
~
'~":.,:--:::~::::::::,:::>
~::~:i,;::c:>:,;.(.:)'
,,',.
I dog
;-',
.',
"
,'.
//;'\
" .:~:/ ,~~',> --'\'~;:;/-'<
::-~::'\'::::---~~-"
"
~~'
/1/
'--'
.,'
'.,,'
20
~
0
;;
0
E
I
0
Q
2
3
c
i
~
~
363
363
363
546
545
546
4
5
~
m
1C
10
L
J
\i
15
~
1i
{l
I
"
II
20
ResHavel when drilled( 1965)
8 Woterslruck 21 m
Rushoogle toe geboor is( 1965)
Wotergekry op 21 m
:1
l;8'-·---'.----/,//.. ----·----'·'-.. '~
FLUCTUATION OF WATER-LEVEL IN BOREHOLES Lg8 AND LgI AT RONDALlA IN RELATION TO ABSTRACTION
VERHOUDING TUSSEN SKOMMELlNG VAN WATERVLAK EN ONTTREKKING VAN BOORGATE Lg8 EN Lgl OP RONDALlA
Rest,level when drilled (1963)
_ _ L ! Water struck 17 -45 m
9 Rushoogte too geboor is( 1963)
Water \iekry op 17-45 m
mlW
[f%l
,V<.:'dO;
L:;-\-;~':~;:---··'\::'\'
~
Iml~
o1/!o:IA
.:'.
'j
.-,-.... -,
.;., .<~,
/(
'J
~
MONTHLY RAINFALL AS A CURVE OF CUMULATIVE DEPARTURE FROM THE MEAN. BASED ON THE AVERAGE OFTHE THREE STATiONS OF FIG. 5
AANDELlKSE REENVAL AS 'N KURWE VAN KUMULATIEWE AFWYKING VAN DIE GEMIDDELDE. GEBASEER OP DIE GEMIDDELDE VAN DIE DRIE STASIES VAN FIG.5
+
... ~ "" ~o- roil'! slope
~elling vir geen reenvol
.....,
--______
______ _
:~o_~
.::-.:::"_______:.!§!'"'_m____
------.::-!..~.!l?.m..~_
t\IOm rfl
---->
1969
1968
!llf
_ ____+]9. ~~ -- --- - -",--
.~
--------------
t~9.~~_
1970
1971
1972
o
100 mm {
-----
-
J973
m
o
FLUCTUATION OF WATER-LEVEL IN BOREHDLE Lk3 AT LEKKERRUS IN RELATION TO ABSTRACTION
VERHOUDlNG TUSSEN SKOMMELlNG VAN WATERVLAK EN ONTTREKKING VAN BDORGAT Lk 3 OP LEKKERRUS
5
... ..
~" """m"t~
,,~
~
..
Iml\J\
-----~,
------,
~---!.--:\
'\ .---~--,:;--
---
.
ida;
"\" ?;J.
'-'-.-,---,
0,_/ ___._- "
_. ___•__ ,
",/----<:'<:
\/
36,
;:\
\~
/\,/0
.:::::' '-~/
Iml1l
.--'\~;;/--'~' ::-~::'v:::-~~~
10
/f"
I,'
./
363
.
g
g
/"
o
15
I
l?
/,~
'___'_: '_ J/l
'..,/
"~
o
~~l,,~~lr"\"'"',,"","=~:"'
,(,.
,,.-.',
"o
l'
20
0
g
I
~
2
Q
3
4
5
0
g
:<
~
C
0
10
~
m
FLUCTUATION OF WATER-LEVEL IN BQREHOLES Lg8 AND Lg I AT RONDAUA IN RELATION TO ABSTRACTION
VERHOUD1NG TUSSEN SKOMMEUNG VAN WATERVLAK EN ONTTREKK1NG VAN BOORGATE Lg8 EN Lgl OP RONDALlA
m
10
Rest-level when dnlled (1963)
- - L I Wolerslruck 17-45m
9 Rushoogte toogeboorls(1963)
Water gekry op 17-45 m
15
~l;D!\
.
~--- ...
',-,.
,
-~-. ~-.
Lg I
'/
'-----~~-."
q~
Iml tJr
fifty
/1''':,\
\
~l
TABU!. 2,'0-
ANNUAL ABSTRACTION AT THE WELGEVONDEN THERMAL SPAS AND AT THE UNION TIN
MINE FOR THE YEAR 1938, AND FROM 1966 TO 1972 INCLUSIVE, IN M' /DAY
1938
Lekkerrus
Libertas
Liebenberg
Rondalia
Rhemardo
59,1 *
145,5*
1966
1967
1968
1969
1970
1971
1972
546
15,5
13
136
53
546
15,5
13
136
47
363,7
63,7
363,7
63,7
363,7
63,7
100
100
100
100
100
100
546
15,5
13
136
53
1241,1
627,4
627,4
627,4
763
763
757
381,9
691,0
586,4
986,3
5000
5700
10 000
5 763
6463
10757
545,5
381,9
113,7
100
100
•
Spa total
204,6*
Union Tin Mine
Spas plus mine
205
1623
1 318
1214
1 596
*Spring flow.
precise information regarding the behaviour of the
groundwater level was available until July 1966, when
three automatic water-level recorders were set up on
unused boreholes, one at each spa area.
Unfortunately these were unattended from November 1966 to March
1967 and did not register correctly during this period.
After that the instruments were checked monthly by
manual depth measurements but as they often failed
to work properly between visits, their records are considerably interrupted. At Rondalia the recorder had to
be moved from one boreholc to another in February
1968 because the first caved in to a depth above the
water-level.
The situation of each observation borehole is shown
on the spa locality plans (figs. 7, 8 and 9). The recorders
indicate the depth of the water-level in the country rock
or diabase near the fault, not in the fault aquifer
itself. Because the observation holes are too distant from
most of the producing holes and the pumps are never
rested long enough to let the pumping levels become
rest-levels, the hydrographs fail to register the most
critical factor of all, the changes of available drawdown
at dle abstraction bore holes. These boreholes have no
openings for such measurements.
The thermal water abstraction data available are
unfortunately very unreliable because no written records are kept by the spa managers. The figures provided, which were calculated from either badl volumes
and remembered frequencies of bath fillings or from
pump yields and remembered pumping hours, are set
out in table 2.
In figure 6 the total annual abstractions at all four
spas together are superimposed on the histogram of
pumpage from the Union Tin Mine since this started
in 1953, and the annual abstraction of each spa locality is expressed as a histogram below its relevan t hydrograph in figure 11, an inverted histogram because the
greater the abstraction rate the lower the mean water-
level stands.
The first borehole for thermal water was drilled at
Rondalia in 1955, and in 1959 the total abstraction
from all three spas together, 205 m 3 /day, exceeded for
the first time the combined rate of the two springs when
they were gauged in 1938. Abstraction must have risen
during the period of active drilling up to 1966, when the
total spa abstraction was 1 240 m 3 /day. The sudden
fall in the spa abstraction rate between 1966 and 1967
was due to the installation of recycling and reheating
plants at Rondalia and Libertas. Why the abstraction
rate at Lekkerrus also declined at the same time although
no such plant was erected, is not understood. Since this
decrease the total spa abstraction rate has stabilized at
about 700 m 3 /day, which is about three-and-a-half times
the flow of the springs in 1938.
Pumpage at the Union Tin Mine had reached 700
m 3 /day by 1967, since when it has rapidly increased and
was 10000 rn' /day in 1972.
The three hydrographs on figure 11 show that,
during the period of active drilling and increasing
abstraction (1955 -66), the water-Ievel'at the observation
borehole at each of the three spas declined considerably
from its original rest-level to the pumping level registered in it in 1966. At Libertas this decline was 5,5
m in three years, at Rondalia (observation borehok
Lg 1) 7 m in three years, and at Lekkerrus 14 m in
seven years.
The corresponding declines in the producing hoks
are not known. Since 1966, when development cca~cd,
there has been no overall decline in the pumping
level at any of the observation boreho1cs.
If the depth at which water was stl'uci( In the ob"
servation boreholes is regarded as the d,!pth of tlw
aquifer and this is considered ns the limit of ~ufc dI'llW'"
15
down in those boreholcs, and if the pumping levels jn the
observation boreholcs arc assulTled to be rest-levels, then
if the observation boreholes were to be used for production, the available drawdowns in them at the
present time would be as follows:
Depth of
Spa
Libertas
water
struck
inm
46
Mean
depth of
pumpmg
level
inm
Mean
available
drawdown
inm
35
46
17
Rondalia
21
25
The most important conclusions that can be drawn
from the three hydrographs arc as follows:
11
...-...
Lekkerrus
The producing bordlOks Ht) I nnd Hn 2 at the site
of the forlllCf spring, Dit: OO!{, sland III a slightly lower
level than the observation hon'hok nnd about 180 m
from it. As these were the first holes \0 be drilled, it is to
be expected that dedillc of 1lH' rcsl-Ievd will have been
greatest there. I !owevcr, there i... 110 evidence to indi~
cate what the depth of rhe n:s\,·kvd is at" present, nor is
the depth of the base of the aquif(:r known, so that the
present available draw down (:annot I)(! deduced.
--.-~-
1. Under the present abstraction regime no further
depletion is taking place .
29
._----_.
mi nus 4
2. Regarding the present available drawdown in the
producing boreholes, the following deductions have
been made.
(Lg 1)
The negative value at observation borcho!e Lg 1 at
Rondalia means that this boreholc could not be used for
production simultaneously with the others.
(a)
What is really required is some idea of the availahk
drawdown in the producing boreholes.
(b)
At Lekkcrrus the available drawdown is probably at least 25 m.
At RonJalia, in production borehole Lg 1 there
is probably at least 6 m of available drawdown
and in bor-ehole Rd 1 there probably remains
an available drawdown of about 19 m. At boreholes Rn 1 and Rn 2 the present available
drawdown cannot be estimated.
At Libertas the observation borehole is situated so
far from the producing hole and stands at so much
greater an altitude, that the available drawdown in
it gives no indication of that in the producing hole.
(c)
At Libcrt"as
IlO (~Sl"illlllt"e
can be made,
At Lekkerrus the observation borehole is close to the
producing holes and at only a slightly lower level (fig. 8).
It would thus be possible, if necessary, to increase
abstraction with safety at Ltl<kcrrus and Hondalia but
whether this can be done at Libertas remains unknown.
As the mean rest-levels in the producing holes cannot be
lower than the mean pumping level in the observation
borehole, there must remain at least 25 m of available
drawdown in the producing holes.
Further analysis of the water-level hydrographs regarding the reaction of the groundwatcr level to rainfall
and abstraction variation is interesting, though of
academic rather than practical value.
At Rondalia the second observation borehole Lg 1
is situated only about 10 m from onc of the producing
holes, Lg 12, and has about the same collar altitude;
yet surprisingly the recorded depths at which water was
struck differ by about 10 m, being 21 m in the observation hole and 31 m in the producing hole. The present
mean depth of the pumping level in the observation hole
is 25 m which, although deeper than the top of the aquifer in that hole, is 6 m shallower than the top of the
aquifer in the producing hole. In the producing hole
there must therefore be an available draw down of at
least 6 m.
At Libertas, where the observation borehole is
situated farthest from the producing holes, the amplitude
of the water-level fluctuation due to tht twice-daily
starting and stopping of the pumps is lcast, and the
seasonal fluctuation of the water-level due to rainfall
variation is least disturbed by unrecorded shorter period
abstraction variation, It will be noted that during the
rainfall years of 1967-68 and 1972--73 there was no
rise of the water-level during the wet season. Each of
these two rainfall years followed years of exceptionally
great wet-season accumulations of excess monthly rain~
fall departure from the mean, Under these circumstances
shallow aquifers are commonly overcharged, and it is
a normal consequence that during the following year,
while the excess watcr is still draining out of the
aquifer, the groundwatcr level does not rise as a result
of the recharge of the wet season. This characteristic
The producing borehole Rd 1, which has about the
same collar altitude as the observation borehole and is
about 250 m away from it, was drilled in about 1966 at
the end of the development period, so its recorded
rest-level at a depth of 11 m has probably changed little
since then. Water was struck at 30 m so there probably
remains an available drawdown of about 19 m.
16
can be observed also in the Lekkerrus hydrograph.
comparison in columns 8, 9 and 10 of the same table.
At Lekkerrus, where the observation borehole IS
nearest to the producing holes, seasonal fluctuations of
the waterMlcvel dominate the hydrograph during those
rainfall years in which the wet season involved the
greatest accumulations of excess monthly rainfall deparM
ture from the mean, while in other years the hydrograph
is dominated by water· level fluctuations due to unrecorded abstraction variations.
According to Kent's (1949) classification by tempera
ture, the Welgevonden Spa waters are 'hot or hypoM
o
thermal' (37°'50 C). According to Bond's (1946) classi,
fication by chemical composition the Lekkerrus water,
with a total solids content of only 119 ppm, falls within
the 'pure water' class (up to 150 ppm), while the other
waters with total solids of 311 ppm at Libertas, 200 ppm
at Liebenberg's borehole and 257 ppm at Die Oog, fall
in onc of the mineralized classes. There is, however,
so little dissolved material in these waters that it is
hardly perceptible to the taste. The relatively high
bicarbonate content and the low sulphate and chloride
place these waters in Bond's 'alkaline soda carbonate'
class. According to the Piper classification, all these
waters fall in the 'fresh water' class (total solids
0-1 000 ppm).
A
At Rondalia, where the observation borehole is near
the producing boreholes of two spas, the water-level
reacted clearly to the seasonal rainfall variation of the
year 1966-67 only, the year of the wettest rainy season
of the observation period. During the rest of this
period water-level fluctua,tions due to rainfall variation
were almost completely masked by those due to ab M
straction variation.
A feature of all three hydrographs that is not understood is that, while the water-levels at Lekkerrus and
Rondalia reacted strongly to unrecorded abstraction
variations with periods of two months or less, not one of
the three hydrographs shows that any waterMlevel reaction resulted from the very considerable recorded
changes in the annual abstraction rates that occurred
between 1966 and 1967 at all three areas, and between
1969 and 1970 at two of them. The rises in the
water-levels during the 1966-67 wet season can be fully
accounted for by the exceptional wetness of that
season.
The Welgevondcn spa waters, together with the local
surface water and groundwaters, and the Loubad water,
form a fairly compact group from which the Buffelshoek
and Warmbaths water differ by their much greater
proportion of sodium chloride. As far as the anions are
concerned, the Wc1gevonden waters are all of bicarbonate
type (HCO, ) 60 per cent). The relative proportions of
the different cations are much more variable. The mine
fissures water is calcium-ion rich (Ca) 60 per cent).
The shallow groundwater, the Lekkerrus, the Liebenberg
and the Loubad waters contain calcium, magnesium and
sodium ions in fairly equal proportions, while the
Sterk River and Libertas waters contain very much morc
calcium and sodium ions than magnesium, with the
first two in fairly equal amounts. Although Die Oog
spring site is very close to the Liebenberg borehole, the
ion content of its water is surprisingly different with a
much higher proportion of sodium ions and a slightly.
higher proportion of chloride ions.
VIII. QUALITY OF THE WATER
Data derived from the chemical analysis of thermal
water samples taken from Lekkerrus and Libertas
(borehole Lb 4) Spas and' from Liebenberg (borehole
Lg 2) during the present investigation are presented in
columns 4, 5 and 6 respectively of table 3. Corresponding data of water samples from the former spring,
Die Oog (now Rondalia), quoted by Kent (1949), are
repeated in column 7.
The general resemblance of the analyses of all the
Wclgevonden water samples is consistent with the view
that they arc all rainwater that acquired a content of
dissolved salts by contact with the local soil or rock at
the surface or underground. The increase in the content
of total solids from ~he surface water, through shallow
to deep groundwater to the thermal spa waters, presumably indicates that the quantity of material dissolved
increases with underground residence time or rock
temperature or both.
For comparison with these, data for Sterk River
water, shallow groundwater from a borchole in the
Kloof near the Union Tin Mine, and deep groundwater
from the fissure on the ninth level of this mine, are
provided in columns 1, 2 and 3.
Columns 1, 2, 3 and ,4 are arranged to represent an
increasing depth of the water source, while columns 1,
2 and 3 (together), 4,5,6 and 7 represent a change from
west to cast in the sample localities.
But the differences in detail from one ground water
sample to another, even when the sampling points are
close together, suggest that at cach locality the water
comes into contact with various kinds of rock assembled'
in a different relative proportion. This is likely to be so
if the water at each locality has a different underground
route or a different path of convective circulation.
Chemical data, quoted from Kent (1949), from analyses of waWr from Loubad, Buffelshoek and Warmbaths springs, which arc situated on or associated with
othcr mcmbers of this fault system, are also provided for
17
(
ThBLE 3.-
CHEMICAL ANALYSES OF THE WELGEVONDEN SPA WATERS, OTHER LOCAL WATERS AND THE WATERS OF LOUBAD, BUFFELSHOEK AND
WARM BATHS
2
1
3
Union Tin Mine.
Shallow
Sterk River.
Ions
Surface
groundwater
"Kloof"
water
borehole
mg/l Nll000 mgll
NH4
Mine.
9th level
groundwater
Lekkerrus Spa. Libertas Spa.
Thermal
groundwater
groundwater
Borehole
Borehole
No.?
No. Lb 4
Nil000 mg/l
Nll000 mg/l Nll000
n.d, n.d.
n.d. -
Thermal
mgll NIlOOO
n.d. -
7
8
9
Loubad*
Buffelshoek'"
10
S.W. Lieben·
berg.
Thermal
groundwater
Borehole
Rondalia Spa.
Thermal
Warm Baths·
Ions
groundwater
No. Lg2
mgll Nll000
n.d.
mgll
NIIOOO
mgll
0,006
nil
2,02
8,2
0,36
0,1
N/l000 mg/l N/l000 mgll
NIlOOO
n.d.
NH4
2
0,087
3
0,130
5
0,217
18
0,783
21
0,913
18
0,783
K'
8 0,205
6
0,153
10
0,256
6
0,153
2
0,051
2
0,051
0,38
0,010
2,8
0,07
5,7
0,15
2,9
0,07
K
Mg"
1 0,082
4
0,329
5
0,411
15
1,234
0,082
15
1,234
0,84 0,070
5,6
0,46
4.7
0,39
1,8
0,15
Mg"
Ca '"
5
0,546
36
1,796
21
1,048
1,297
36
1,796
26,4
1,32
27,1
1,35
13.0
0,65
Ca"
Sum of cations
~
-
Union Tin
6
Na'
Al ... and Fe"
00
n.d.
5
4
0,252
n.d.
11
-
n.d. -
16 0,626
24
1,158
F'
nil
0,8
Cl'
3 0,084
4
NO,
nil
HC0 3 '
C03
31
0,508
56
26
n.d.
n.d. -
60
3,218
0,042
0,8 0,042
6
0,316
3,5
0,184
5,0 0,263
0,113
7
7
0,197
7
0,197
4
-
0,197
nil
50
2,343
nil
nil
-
2
0,042
21
0,437
5
0,104
12
0,250
64
1,049
122
1,999
107
1,754
110
1,803
nil
nil
-
Sum of anions
34 0,592
70,8
1,246
Si0 2 (with
N!l000 as
25 0,832
10
0,333
nil
nil
150,8 2,675
nil
-
71
3,864
0,113
nil
0,93
66,22 3,036
6,59
2,21
189,1
132,5
5,76
n.d. -
nil
tr
43,0
151,6
8,58
150,2
F'
0,30
0,49
0,03
6,6
0,35
11,0
0,58
0,70
3,6
0,10
138,5
3.91
85,2
2,40
8,2
0,17
3,704 109,8
1.80
nil
tr
122,0
2.00
35.1
2135
12,1
0.25
102,0
3,40
nil
Total sum of
items
125
2,371
132,5 2,434
235
4-.080
6
0,200
128
158
5,261
14851 2.910
126,09
2,13
18,9
0,63
393.7
8,-1-9
210,3
6,63
48,2
1,61
12
0,400
4,2.62
42,0
1,40
44,8 14,9
n.d.
75
NaHC03
17
found
N!1000 as
Si03")
32
Sought but not
Sum of anions
SiO z (with
Total dissolved
solids" ..
NaZC03
50 4 "
HCO,
C0:3'
Si0 3 " )
Dissolved H2 S
Cl'
N0 3 '
nil
0,73
3,50
Al'" and Fe"
Sum of cations
5,7
nil
Na'
6,63
24,8
0,01 0,0002
nil
226
18,6
n.d. -
n.d.
2,680
nil
nil
S04
n.d. -
46,4
2,050
n-<i.
104,8 2,737
218,8 5,755
191
155
129
65
0,202
,,-d.
n.d.
17
5,789
129
200
nil
nil
nil
nil
NO'Z
NO'Z
NO'Z
NO'2
NO'Z
0,655
464 13,205
-
nil
n.d.
310,5 9,039
0,202
nil
55
n.d. -
34
0,405
-
59
n.d. 256,73 7,405
nil
nil
187,99
4,97
627,6 18,56
408,7
0,702
14,87
Total sum of iterns
Total dissolved
solids u
n.d.
n.d.-
nil
Dissolved Hz S
nil
NaHC03
- 93,3
137,8
Na2C03
Sought but not
,
NO'Z
NO'Z
found
T."",LE
3.- (roo.mued)
Uoion Tin Mine.
Sterk River.
Ions
Surface
water
Shallow
groundwater
"Kloof"
borehole
mgl! N/looO mgfl
7,2
pH
Dianic conductivity at 20°C
Date and
50
1966 J. Dry
3
2
1
Union Tin
Mine.
9th level
ground water
4
Lekkerrus Spa. Libertas Spa.
ThennaI
groundwater
100
1966 J. Dry
analyst
7,6
Borehole
No. ?
No. Lb 4
1966
7,6
200
240
J. Dry
Thermal
groundwater
Borehole
N11000 mgl! N/1000 mgl! Nil000
7,4
1965
7,5
1965
J. Blig-
naut and
J. Dry
*
~
'"
From Kent, 1949.
** Calculated from dianic conductivity.
S.W.
8
7
9
10
Lieben~
berg
Thermal
groundwater
Borehole
Roodalia Spa.
Thenn:a.l
Loobad"
Buffelshoek*
loos
Wann Baths"*
grOUDd-ft"'2.~r
No. Lg 2
mgfl N/l000 mg/l NIlOOO
200
J. Dry
6
5
i.6
mg/l
NflOOO
n:i!:g/l
Nil 000
at
1965 J. Blig- 1939 CF.].•'";lD
J. Dry
NJlooo !in:gfi SllOOO
D10nic COOdUcrl..ity
310
nautand
~
pH
n.d.
derWalt
20°C
1941 CF.J.;;m 194+ W.Sunkej 1940 W. Sun..1cel Date and
der Wait
a.."la.1-""St
5.
The fault is probably recharged mainly by
shallow groundwatcr moving downslope in the weathered
zone of the fclsite country rock towards the fault on the
Swacrshockberg plateau, which is traversed by the
western branches of the fault, and perhaps also in part
directly by strcum water from some of the headwaters
of the Sterk River! which flow over the fault branches
at several points, Some recharge may also occur on the
plateau north of Rondalia where the eastern end of the
fault turns northwards and intersects another fault.
From the health point of view the only substance
present in the spa waters in significant quantities is the
fluoride ion. The fluoride contents are 6,0 mg/l at
Lekkerrus, 3,5 mg!1 at Libertas, 5,0 mg!1 at the Licbenberg boreholc and 5,7 mg!1 at the former Die Oog spring
(Rondalia). The highest of these is seven times. the
recommended optimum concentration for drinking water
(0,8 mg/l) and six times the recommended upper limit.
In 1966, when this investigation was made, the
water used for domestic purposes, including drinking, at
Libertas and Lekkerrus was the thermal water but at the
former spa it was from borehole Lt 17, where the
water had cooled so much that it was no longer hot
enough to be used in the baths. No analysis of this
particular water is available, At Rondalia spa the
domestic supply comes from the Naboomspruit muni~
cipal reservoir on the Sterk River and at Rhemardo spa
domestic water, of which no analysis is available, is
taken from the cold water borehole Lg 4.
6.
Water in the greater part of the fault moves from
west to east with the overall gradient of the topographi~
cal profile along its course, but east of Rondalia the
water probably moves from northeast to southwest.
The fault aquifer is locally semiMcunfined but there is no
need to assume that it is! as II whole, confined, The
groundwater movement in no way resembles that in
an artesian basin. There may be several cells of convec M
tive circulation and they may be quite independent of
the lateral movement of the water.
Very small quantity of gas is emitted by the spa
water, Kent (1949) records an analysis of gas collected
by Von Backstrom at Die Gog (Rietfontein spring) in
1938. As in similar waters from the same and related
formations, this gas consists mainly of nitrogen and the
inert gases.
7,
The thermal water has been found only where
portions of a diabase sill that arC disphIC{~d by the fault
abut against it and arc deeply weathered, These localities are at the same time the three lowest points along
the course of the fault, at twO of which spring overflow
from it occurred, As all such localities arc already sites
of thermal spas, further discoveries of hot or warm water
are improbable,
IX. CONCLUSIONS
1.
The thermal groundwater at the holiday resorts
of Lekkerrus, Libertas, Rhemardo and Rondalia is of
meteoric origin; it owes its heat (up to 47°C) to deep
convective circulation in the plane of the Welgevonden
fault and its content of dissolved solids to long contact
with the rocks traversed by the fault,
8.
The thermal water pumped is a mixture of hot
water from the fault aquifer and cold water from the
weathered zone of the diabase and country rock,
mainly on the topographically higher side of the course
of the fault at the spas, It is pumped from the
weathered zone of the diabase and, if the water-level
should be lowered any further by an increase in the
rate of pumping, the temperature of the water will
probably fall owing to a larger proportion of cold water
being drawn into the boreholes. As re*circulation and
rc-heating plants have been installed at two of the spas
and this can be done at the others, the abstraction rate
need not be increased but if it were, a consequent fall
in temperature would not matter seriously.
The content of dissolved solids is so small that
2,
these substances are hardly perceptible to the taste but
the water contains a much higher proportion of fluoride
than is recommended for drinking, Chemically the water
belongs to Bond's 'alkali soda carbonate' class, which is
characteristic of the- older igneous and sedimentary
rocks.
3,
The Welgevonden fault is a member of a system
that crosses the Transvaal from west to east, and is
characterised by reverse faults, tear faults, and over~
thrusts with overriding from the north. Some of the
faults carry thermal or mineralized springs. Springs on
other members of the fault system are those of Buffels~
hoek, Loubad, Warm baths, Visgat and Driefontein.
9.
The reason for the decline in the groundwater
level that caused the failure of the springs at Libertas
and Rondaliain 1954 and 1955 has not been ascertained.
Hydrographs from three automatic water~level recorders
which have been in operation since July 1966 show
that the water-levels in the observation boreholes drilled in
the diabase or coun try rock near the faul t declined 5,5 m,
7 m and 14 m at the different areas during the development period 1955 to 1966. Since 1966, water-levels have
fluctuated about a stable mean, either seasonally under
the influence of fluctuating recharge from rainfall or in
shorter periods due to fluctuations in the rate of abstrac~
The Welgevonden fault is a heavily silicified
4.
fault zone that crops out as a quartz vein, Its permeabi~
lity is probably due to a connected system of fault
fissures within or alongside the quartz vein, caused by
post~silicification rejuvenation.
20
tion, or else in response to both these factors.
WILKE, D.P., 1963. Gcology of the southwestern portion of
Area 2428 B; Map and Expl. sht. 2428 B, Geo!. Surv. S,
10. While the available drawdown that remains Il1
the production boreholes cannot be measured directly,
the behaviour of the water-levels in the observation
boreholes suggests that the rate of abstraction could if
necessary be safely raised at Lekkerrus and Rondalia,
though to what limit cannot be estimated. No dcduc~
cion on this matter can be made for Libertas.
•
x.
Afr. (Unpuhl.).
OPSOMMING IN AFRIKAANS
deur
P.]. Smit
[nleiding
ACKNOWLEDGEMENTS
The author is indebted to the spa managers for
nearly all the information presented regarding the
tested yields, water temperatures and other drilling
details of the numerous boreholes and for the water
consumption estimates that thcy provided; and to
Messrs. R. Uren and R.H. Rastall, respectively Manager
and Geologist at the Union Tin Mine, for supplying
pumpage and drilling data, geological sections (not
included in this report) and other relevant information,
Die gewilde vakansieoorde Rondalia, Rhemardo,
Libertas cn Lekkerrus is warmwaterbronne wat in die
afgclopc 20 jaar ontwikkel het by bestaande warmwaterfonteine en ~boorgate. Almal is gelee langs die sogenaam~
de Wclgevondenverskuiwing wat die sterkte sowe1 as
temperatuur van die water van die boorgate wat gebruik
word, bcpaal.
Vorige Werk
Kynaston, Miller en Hall (1911) het oorspronklik die
gebied geoJogies ondersoek en het destyds reeds opgemerk dat wannwatcrfonteine geassosicer is met die
verskuiwing. Von Backstrom (1938) het later die sterkre van die fonteine gcmcct en aangevoer dat die water
afkomstig is vanaf die plato ten noorde van die
verskuiwing, langs ander verskuiwings. Van Rooyen
(Kent, 1949) het later die gebied weer ondersoek en het
gereken dat die diabaasgang in die verskuiwing die
suidwaartse bcweging van die grondwater swit en vanaf
REFERENCES
BOND, G.W., 1946. A geochemical survey of the underground
water supplies of the Union of South Africa: Mem. gco!.
Surv. S. Afr., 41, p. 208, Govt. Printcr, Pretoria.
'n diepte laat opstyg tot aan die oppcrvlakte,
DEPARTMENT OF TRANSPORT, WEATHER BUREAU, 1954.
Climate of South Africa: Part 1, Climate statistics: WB 19,
Geologie
Govt. Printer, Pretoria.
Die verskuiwing is deel van 'n vcrskuiwingsone wat
vanaf Thabazimbi tot by Zebediela strek (fig. 1), 'n
afstand van 270 km. Die meeste van die verskuiwings
langs die sone is opskuiwings, oorskuiwings en dwarsverskuiwings, met beweging vanaf die noorde.
REPUBLIC OF SOUTH AFRICA, 1967. Rep. Commission of
inquiry into fluoridation: Govt. Prin ter, RP 17/1967, Pretoria.
KENT, L.E., 1948, The warm springs at Loubad, near NyJstroom, Transvaal: Trans. roy. Soc. S. Afr., 31, p. 151-168.
Die dagsoom van die verskuiwing is gewoonlik 'n
lac rug gevorm deur die verkieselde brcksiesone, wat
die voorkoms van 'n kwartsaar het, ongeveer 5 tot
20 m wyd. In die omgewing van Libertas en Rondalia is
die breksiesone nie sigbaar nie, moontlik omdat dit
dall< nie verkiesel is nie. Net oos van Rondalia swaai die
Wdgevondenverskuiwing volgens die mening van die
skrywcr noordwaarts in die rigting van die plato (fig. 2).
Die verskuiwingsvlak hel noordwaarts met die 'valkant aan
die suide en sny deur felsiet wat porfiere, Bosveldgra!lict en noriet oorie. Die basale konglomeraat van die
Sistcem Waterberg wat diskordant op fclsict \C, is ook
vcrskuif in die omgewing van Lekkcrrus en ROlldalia.
In die gebied tussen Lekkerrus en I{ondalia korn 'n dik
rransgrcssiewc diabaasplaat in of langs die verskuiwing-
1949. The thermal waters of the Union of South
Africa and South Wt'st Africa: Trans. gcol. Soc. S. Afr., 52,
p.231-·2()'L
KENT, L.E. und HUSSELI., 1I.D., 1949. The warm spring on
Buffclsboek, JH:nr TllHi>wl.imJ>i, Transvaal: TrailS. roy. Soc.
•
S. Afr., 32, (2), p. !(i!
KYNASTON,
1'15<
11., MELLOI{,
E.'I". alld
IIALL,
A.L., 191!.
The geology of the eOllJltry round i'otgi('j('rsrllS(: Expl. sill.
7, Geol. Surv. S. Afr., Cov!. PriJlI('I", I'r('toria.
VON
BACKSTHi)M,
J.w., J93H. An illv(:stigat!oll of lhe
thermal sprinbrs in thc i'olgielt'rsrusl l)istrict:
g.q). gcol.
Surv. S. Afr., (Unpubl.).
21
konveksieselle in sekere dele van die vcrskuiwingswaterdraer waar verhitte water vanuit diepte opstyg om
verplaas te word deur die kouer vlakker water. Die
temperatuur van die water wat uitgepomp word is
egter nie 'n ware indikasie van die diepte van die
konveksiestrome nie ifillgesien daar vermenging met
die koue vlak water van die verweringsone plaasvind
(fig. 10).
None VQOr.
Daar bestaan geologiese bewyse wat daarop dui dat
bewcging langs die verskuiwing tydens meer as een
tydperk plaasgevind het.
Aanvulling;'l verskuiwingswaterdraer
Aangesien die verskuiwingsvlak teen 'n hoe hock
noordwaarts hell moet dit noodwendig op 'n baie groot
diepte onder die plato aanwesig wees en die water in die
verskuiwing kan dus nie van daar gevoed word n}e.
Die grondwater in die verskuiwing is eerder afkomstig
vanaf die hoogliggende gebied suid van die Swaershoekberge en noord van Rondalia(fig. 3 and 4). Die standhoudende stroom van die Sterkrivier kruis die westelike
vedenging van die verskuiwing in etlike plekke (gemerk
A tot E in fig. 3) vanwaar die verskuiwingswaterdraer
aangevul kan word.
Lewering van verskuiwil1gswaterdraer
Die twee bronne Rondalia en Libertas het in 1938
saam 200 m 3 /dag gelewer. In 1954 hetdiefonteine om
'n onverklaarbare rede ophou vIaei en moes boorgate
geboor word om in die behoeftes van die oorde te
voorsien. Die opdroging toon geen vcrband met die
jaarlikse reenval geplot as 'n akkumuIatiewe afwyking
van die gemiddeld nie (fig. 5). Die totale verbruikhet
sedert 1970 konstant gebly op 750 m'/dag.
Gedrag van grondwatervlak
Beweging van grondwater in
verskuiwingswaterdraer
Die grondwater in die waterdraer vorm 'n oop watervlak wat ooswaarts vanaf die Swaershoek- en Paardeplaatsverskuiwing daal teen 'n gradient van omtrent
1,2 persent (fig. 4). Die grondwatervlak in die Rheeder
se heIlingsverskuiwing daal suidwaarts in die rigting van
Rondalia teen selfs 'n steiler gradient. Die oorspronklikc
warmwaterfonteine vanaf Lekkerrus tot by Rondalia
kan dus deur die grondwatergradiente en topografie verklaar word.
Die grondwatervlak is scdert 1966 waargeneem in
3 boorgate wat elk by of naby die produksiegate van
Rondalia, Lekkerrus en Libertas geld~ is. Volgens hierdie metings het die watervlak sedert 1966 op 'n sekere
diepte redelik konstant gebly, met waarneembare skommelinge wat 'n verband toon met die jaarlikse aanvulling
volgens die reenval en die direkte effek van onttrekking in gevalle waar die waarnerriingsgat baie na aan 'n
produksiegat gelee is. Die gedrag van die watetvlak dui
aan dat die onttrekking by Lekkerrus en Rondalia met
veiligheid verhoog kan word.
Die fonteine vloei nie meer nie aangesien langdurige
onttrekking uit boorgate in hulle onmiddellike omgewing die grondwatervlak op 'n lacr vIak hOll.
Kwaliteit van water
Volgens die klassifikasie van Bond (1946) behoort
die water chemics tot die alkaliese soda-karbonaat
klas. Die bikarbonaatkonsentrasie is relatief hoog en
die van sulfate en chloriede is laag (tabel 3). Die
totale opgcloste stowwe wissel tussen 110 en 257 mg/I.
Die fluoorkonsentrasie is tussen 3,5 en 6,0 rug/l wat
aansienlik hoer is as wat vir drink water aanbeveel word.
. Die water het 'n maksimum temperatuur van 47°C wat
te wyte is aan 'n norrnale terrniese gradient. Die temperatuur is nie noodwendig te wyte aan beweging van die
water oor lang afstande vanaf 'n groot diepte vanuit
'n aanvullingsgebied nie, soos voorgestel deur Von
Backstrom (1938), maar kan bloot gekoppel word met
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