A number of base metal finds have recently focussed attention on the North Western Cape Province of South Africa as an area of great potential mineral wealth. From the point of view of competitive mineral exploration it was essential that an insight into the regional geological controls of the base metal mineralization of the area be obtained as rapidly as possible. Conventional methods of producing a suitable regional geological map were considered to be too time-consuming and ERTS-1 imagery was consequently examined. This imagery has made a significant contribution in the compilation of a suitable map on which to base further mineral exploration programmes. The time involved in the compilation of maps of this nature was found to be only a fraction of the time necessary for the production of similar maps using other methods. ERTS imagery is therefore considered to be valuable in producing accurate regional maps in areas where little or no geological data are available, or in areas of poor access. Furthermore, these images have great potential for rapidly defining the regional extent of metallogenic provinces

Viljoen, R. P.

English

NASA Technical Reports Server

Paper G 15 
'ERTS-1 IMAGERY' AS AN AID TO THE UNDERSTANDING OF THE REGIONAL 
SETTING OF BASE METAL DEPOSITS IN THE NORTH WEST CAPE PROVINCE, 
SOUTH AFRICA 
Dr. Richard P. Viljoen, Geological Research Department, P.O. Box 2, Randfontein. Rep. of South Africa 
ABSTRACT 
A number of base metal f i n d s  have recent ly  focussed a t t e n t i o n  on the 
North Western Cape Province of South Africa as an area of great poten t ia l  
mineral wealth. Extensive exploration programmes were i n i t i a t e d  by many 
organizations but these programmes were hampered by the fact that the  area 
is geologically unsurveyed. Available geological maps cover only a s t r i p  
of country along the south bank of the Orange r i v e r ,  and areas t o  the west 
and south of the Springbok - O'Kiep copper mining region. 
From the point of view of competitive mineral exploration it  was e s s e n t i a l  
that  an ins ight  i n t o  the regional geological controls  of the base metal 
mineralization of the area be obtained as rapidly as possible. Conventional 
methods of producing a s u i t a b l e  regional geological map were considered t o  be 
too time-consuming and ERTS-1 imagery was consequently examined. 
This imagery has made a s i g n i f i c a n t  contr ibut ion i n  the  compilation of 
a s u i t a b l e  map on which t o  base f u r t h e r  mineral exploration programmes. 
Major s t r u c t u r a l  features ,  including fo lds ,  f a u l t s  and lineaments, as 
w e l l  as the lateral  extent  of various important s t r a t i g r a p h i c  uni t s ,  
are c l e a r l y  discernable on the ava i lab le  images. Important new da ta  
have come t o  l i g h t  even i n  areas where published maps are available.  
I n  some instances,  older  s t r a t i g r a p h i c  trends can be deciphered through 
t h i n  f la t  lying younger cover sequences. 
Reconnaissance f i e l d  work aimed a t  the i d e n t i f i c a t i o n  of major rock 
units and other  conspicuous fea tures  seen on the images was found 
t o  be important p r i o r  t o  in te rpre ta t ion .  
map was produced by ident i fying less obvious features on the  images from 
a l i g h t  aircraft f l y i n g  at an a l t i t u d e  of approximately 2 000 m above 
ground level.  
The time involved i n  the compilation of maps of t h i s  nature was found 
t o  be only a f r a c t i o n  of the time necessary f o r  the  production of 
similar maps using other  methods. ERTS imagery is therefore considered 
t o  be valuable i n  producing accurate regional maps i n  areas where l i t t l e  
o r  no geological da ta  are avai lable ,  o r  i n  areas of  poor access. 
Furthermore, these images have great poten t ia l  f o r  rapidly defining the 
regional extent  of metallogenie provinces 
I n  addi t ion a more de ta i led  
63 
797 
https://ntrs.nasa.gov/search.jsp?R=19740022647 2020-03-17T15:06:12+00:00Z
INTRODUCTION 
The region discussed i n  t h i s  paper comprises a port ion of the north western Cape 
Province of t h e  Republic of South Africa and l ies  mainly t o  t h e  south of the 
Orange river. 
on the northern a ide  of the  river and is bounded by l a t i t u d e s  28 S . 31 s and 
longitudes 16'E - 24 E. 
It a l s o  includes a small port ion of southern SouJh WestoAfrica 
0 (Figure 1). 
The region is one of very low r a i n f a l l ,  so t h a t  i n  most places vegetation 
cover is sparse o r  non-existent. Erosion caused by the Orange r i v e r  has 
resu l ted  i n  the development of a broad s t r i p  of excel lent  rock exposures 
along both f lanks of the r iver .  
outcrops become progressively poorer and eventually the o lder  geological 
formations of the r i v e r  val ley are covered by f la t  ly ing  younger strata at  
an elevat ion of some 500 meters above the  r i v e r  bed. 
To the  north and south of t h i s  zone, 
Despite the fact t h a t  copper deposits associated with small plugs of basic 
igneous rock have 
(Springbok - O'Kiep area) f o r  many years , the rest of the area was never con- 
s idered t o  be p a r t i c u l a r l y  i n t e r e s t i n g  as far as base metal mineralization 
was concerned. 
eastern p a r t  o f  t h e  region (Prieska area) several  years  ago, followed by 
o ther  s ign i f icant  base metal f i n d s  between t h i s  occurrence and the Spring- 
bok - O'Kiep copper occurrences, i t  became apparent t h a t  the e n t i r e  region 
might represent a metallogenic province of considerablg economic importance. 
been known and mined i n  the  western portion of the t e r r a i n  
With the discovery of a major Cu - Zn deposit  i n  the 
Numerous organisations commenced exploration i n  the area and from a com- 
p e t i t i v e  point  of view 
t h e  various d e p o s i h  arid the regional geology of the area be establ ished as 
rapidly as possible.  
i t  was imperative t h a t  the re la t ionship  between 
Previous geological work i n  the region included good mapping along the 
Orange r i v e r  by the  South African Geological Survey, as w e l l  as mapping 
i,n areas t o  the west and south of t h e  Springbok - O'Kiep copper mi-ing 
d i s t r ic t  where most of t h e  work has been car r ied  out by Dr .  Joubert of 
the  Precambrian Research Unit of the University of Cape Town. (See fig. 
Nevertheless, large areas and p a r t i c u l a r l y  those where the  new base m e t a l  
f i n d s  were made, remained .unmapped and the  regional s t r u c t u r e  of the  
t e r r a i n  w a s  not understood. 
regional geological maps were considered t o  be too time consuming and 
ERTS-1 imagery was consequently examined. 
Conventional methods of producing sui table .  
METHODS OF STUDY 
Eight ERTS-1 colour composite images enlarged t o  a scale of 1:500 000 were 
used f o r  the compilation of a regional geological map of the  area. e 
A mosaic constructed from the images used i n  t h i s  compilation has been 
reduced i n  fig. 2 t o  a scale of approximately 
A generalized map i l l u s t r a t i n g  the i n t e r p r e t a t i o n ' i s ~ h o m i n  fig. 3. 
A number of d e t a i l s  have been omitted from this in te rpre ta t ion  because 
of the  competitive nature of mineral exploration i n  t h e  area at the 
present time. 
1:2 000 000 
798 
nz N 
Before any interpretat ion w a s  carried out, a detailed st 
available published maps was made i n  order t o  co 
of various formations with features seen on the 
Reconnaissance road traverses were undertaken i n  both the mapped areas 
and unmapped areas t o  establish ground truth. 
w a s  carried out after a cer ta in  amount of mapping had been clone d i rec t ly  
on the images correlat ing geological features from a light aircraft f ly ing  
at an a l t i tude  of about 3 000 meters above ground level.  
then plotted onto 1:500 000 topographic sheets, somewhat s impl i f i  
finally reduced to  a scale of approximately 1:2 000 000 
te  
images. 
Final interpretat ion 
These 
(fig. 31. 
I.OCAI.ITY MAP Of: T I E  NORTH WEST CAPE AND 
SOUTIJEKN SWA SI $OWING AREA 1NVES'l'lGA'TE.U 
--SCALE - 
PUBLlSHEO MAPS AVAILABLE 
NO PUBLISHED MAPS AWLABLE 
FIG. 1 
%OU)GICA& IN!FERPRETBTIOl 
ntroduction 
le-area under consideration is divis ible  in to  four main geological en t i t i e s ,  
le most important of which is an extensive 1 0 0 0  million years old, metaplorphic 
eiss te r ra in ,  the Bushmanland Metamorphic Complex, which is w e l l  exposed i n  
e valley of the Orange river.  This metamorphic te r ra in  is terminated to  
? east of Upington by a major Nmw' - SSE trending qone of dislocation ( the 
kbos f a u l t  zone). 
h older granite-greenstone te r ra in  lying t o  the east and known as the 
T h i s  f a u l t  zone separates the Metamorphites from a very 
799 
Kaapvaal craton. 
for the most par t  largely covered by re la t ive ly  unmetamorphosed, predominantlx: 
sedimentary rocks belonging to  a se r i e s  of extensive ancient 
Geochronological studies indicate that most of the basement 
Kaapvaal craton have ages i n  excess of 2.5 b i l l i o n  years. 
I n  the western portion of the area, i n  a region known as the Richtersveld 
(f ig .  3), the s t ruc tura l  s ty l e  and the grade of  metamorphism changes and a 
series of vulcano-sedimentary formations s t r i k i  roughly no 
associated with granite (the Vioolsdsift granite 7 which has 
1 8 0 0  million years. In  the north and south central portiona of the area 
the Bushmanland metamorphites are overlain by much younger flat-lying 
sedimentary formations belonging t o  the Nama and Karroo systems. Each of 
these major geological e n t i t i e s  w i l l  be described i n  turn. 
In  the area under consideration the Kaapvaal craton is 
800 
801 
Sedimentary formations of the Kaapvaal craton 
One of the most s t r ik ing  features seen on the ERTS 
discontinuity (the Brakbos f a u l t  zone) that  separa 
the eas t  from the Bushmanland metamorphic complex i n  the west. Although this 
zone has been described br ie f ly  by a number of authors and detailed mapping 
aimed a t  establishing geological relationships is a t  present being undertaken, 
no def ini t ive resu l t s  have as yet  been published. 
of features observed on ERTS imagery might well prove to  be invaluable i n  
the f i n a l  Bssessement of the problem. 
a. 
ages is the spectacular 
the Kaapvaal craton i n  
I n  t h i s  respect a number 
These are:- 
The existence of a number of major f a u l t s  para l le l  t o  and lying east of 
the Brakbos f a u l t  zone, c lear ly  discernible i n  the country immediately 
west of the town of Prieska. 
b. Intense deformation mainly i n  the form of folding of the north-south 
s t r ik ing  sedimentary formations as they approach the Brakbos f a u l t  
zone from the north east .  
e. All the sedimentary formations appear t o  have been abruptly truncated by 
the Brakbos f a u l t  zone and there is no evidence of them straddling this 
discontinuity +d thus being represented within the Bushmanland 
metamorphic complex as has been suggested. 
Flat-l.vinP Sedimentary cover rocks 
The imagery clear ly  reveals the dis t r ibut ion pattern of f la t  lying sedimentary 
beds belonging to  the Karroo and Nama systems which formerly covered most of  
the Bushmanland metamorphic complex. This pattern indicates both the erosive 
action of the Orange r ive r  and its t r ibu tar ies  and yield3information regarding 
the underlying basement s t ructure  (see later). 
The Karroo sediments are c lear ly  recognisable by t h e i r  grey or dark grey colours 
whereas the Nama strata are  characterized by brownish hues. 
and thin Karroo cover are also apparent, especially i n  the region t o  the south 
of Pofadder. 
be mapped i n  great  de t a i l  from the images and i n  many instances 
Areas of thick 
In addition doler i te  dykes and sills within t h i s  formation can 
appear: to  be 
l i nea r  features  as i n  the area t o  the south west of 
Numerous salt pans especially i n  the area t o  the south of 
on the map) a re  even more strongly controlled by these 
l i nea r  features. 
Older volcano-sedimentam formations of the west coast 
A number of generally north-south trending vulcano-sedimentary formations have 
been mapped i n  the Richtersveld area adjacent t o  the w e s t  coast ( f ig .  3). 
These rocks have not been involved with the 1000 million years old metamorphic 
overprinting which has affected the rocks of the Bushmanland sequence. They 
have been intruded by grani tes  which have radiometric ages of approximately 
1800 million years and thus form part  of a zope tha t  is probably marginal to  
the Bushmanland Metamorphic Complex. 
which comprises one of the most important components of the volcano sedimentary 
formation under consideration,is c lear ly  discernible on the ERTS imagery (fig. 3). 
The extent of the Stinkfontein formation, 
802 
The Reoloav and s t ructure  of the Bushmanland Metamorphic Complex 
The Bushmanland Metamorphic Complex forms par t  of a more extensive be l t  of 1000 
million years old metamorphic rocks which e x t e d a c r o s s  the southern portion of 
South Africa snd includes both basement and S u p r a c w t a l  sequences. Rock types 
encountered i n  the l a t t e r  group are of considerable importance from an 
economic point of view and comprises a large variety of quartw-felspathic 
gneisses with variable amounts of b io t i t e  and muscovite, banded amphibolitic 
and calc si l icate assemblages and a variety of quar tz i t ic  rocks. The base- 
ment upon which they r e s t  is ill defined but is probably represented by 
porphyroblastic augen gneisses. 
The en t i re  assemblage has undergone intense deformation and several  periods of 
folding have been described by Joubert from the area t o  the west and south of 
the Springbok - O'Kiep mining d i s t r i c t .  Numerous f a u l t  zones and lineaments 
also feature prominently and have played an important par t  in the overall  
tectonic framework of the region. 
The supracrustal sequence has been recognised from a point some 30 kilometers 
from the west coast s t r ik ing  i n  an easter ly  direction towards a major zone of 
dislocation (the Tantal i te  valley f a u l t  zone) s i tuated a short  distance t o  the 
north eas t  of the town of Pofadder and trending NW - SE (f ig .  3) .  
As each major sequence of east-west s t r ik ing  rocks crosses this zone of dis- 
location 
north dastern side. 
but are  themselves deformed by younger folds  with axes trending pa ra l l e l  t o  
the Tantal i te  vaEley f au l t  zone. 
area immediately north o f  the Orange r ive r  by the sequence of rocks which 
commences i n  the Goodhouse area. 
by the black ornament which commences i n  the region t o  the north west of the 
Springbok - O'Kiep mining d i s t r i c t  and s t r ikes  i n  an overall  east east  
direction towards'the town of Pofadder. 
assemblage s w i n g s  sharply northwards and thfnnorth west culminating i n  a 
position t o  the west of Kakamas on&e Orange r iver  (fig.  3). 
The s t ra t igraphic  sequence lying t o  the south of the Springbok - O'Kiep 
mining d i s t r i c t  a lso s t r ikes  east - west but is covered as one proceeds 
east ,  f i r s t l y  by sand and then by younger f la t  lying sediments of the Karroo 
system. When these rocks again make t h e i r  appearance from under the Karroo 
cover i n  the v ic in i ty  of Kenhardt, they s t r ike  i n  a generally north west 
direction from t h i s  town to  Kakamas on the Orange r ive r  ( f ig .  3). 
relationship between mineral deposits and various s t ra t igraphic  components of 
the sequences described above is naturally of great importance and i n  t h i s  
respect 
a most important and inveluable guide t o  the longer tern planning of mineral 
exploration programmes. The r e su l t s  of the exploration carried out t o  date 
are  encouraging and fur ther  work is continuing. 
i t  i s  deflected t o  form large refolded lobate s t ructures  on the 
The l a t t e r  s t ructures  have a general north-south s t r ike  
This phenomenonis well i l l u s t r a t ed  i n  the 
It is a lso  shown by the sequence portrayed 
Immediately east of the town the 
The 
the regional geological map presented i n  t h i s  paper has acte? as 
Faults and l inear  features 
Numerous well defined l inear  features,some of them undoubtedly representing 
faults and i n  most cases not mapped previously, const i tute  conspicuous features 
803 
804 
on the imagery. 
t o  a large extent. 
A number of prominent directions have influenced the geology 
a. 
b e  
C. 
NNW - SSE Direction 
A very strong set of fractures conforming to thie direction, which 
para l le l s  the west coast, occurs i n  a s t r i p  of country occupying the 
coastal  region f o r  a.distance of some 120 kilometers inland. Features 
such as the termination of younger cover sequences at this point, the 
preservation of cover sequences i n  a NNW - SSE trenMng be l t  between 
the eastern Richtersveld and the Springbok - O'Kiep mining area, the 
north south trending zones of older vulcano-sedimentary rocks i n  the 
Richtersveld and the general attenuation of the Bushmanland supracrustal 
rocks i n  t h i s  area, suggest tha t  the en t i re  coastal  s t r i p  has been an area 
of act ive u p l i f t  wi th  attendant faul t ing which has preserved both younger 
and older sedimentary sequences i n  the area. 
0 
This  direction of fracturing becomes l e s s  intenseve fur ther  east  but is again 
manifested by the large f au l t  zone t o  the east of Goodhouse which clear ly  
controls the dis t r ibut ion pattern o f  the younger f lat  lying cover sequences. 
Features with the same direct ion are also clear ly  to  be seen i n  the area to  
the north east  of Pofadder and to the south west and north west of Kenhardt, 
and the Brakbos f au l t  zone i t s e l f ,  fur ther  east ,  const i tutes  a spectacular 
expression of t h i s  direction. 
The l a t t e r  zone with its associated para l le l  f au l t s  also represents a zone 
of re la t ive  u p l i f t  as is manifested by the southward s w i n g  of the outcrop 
pattern of younger cover rocks between Kenhardt and Prieska and the north- 
ward swing of similar rocks t o  the north of Upington. 
NW - SE Direction 
The Tantali te Valley f a u l t  zone is the most important l inear  feature  conforming 
to  th i s  direction and can clear ly  be traced through Karroo cover i n  the area 
to  the south east  of Kenhardt. This fault zone has acted as the basis f o r  
the intrusion of gabbro plugs i n  the area t o  the north west of Pofadder. (fig. 3 ) .  
Paral le l  l inear  features are t o  be seen to  the north and south west of 
Pofadder and i n  the area surrounding the Springbok - O'Iliep copper mining 
district  . 
NE - SW Direclion 
Linear features conforming t o  this direction a re  well developed along the 
west coast zone par t icular ly  between the Richtersveld and the Springbok - 
O'Kiep area. The intersect ion of these with the other f racture  directions 
described probably acts as the locus f o r  the emplacement of younger igneous 
rocks including the Post Karroo a l k a l i  intrusives  of the Iiichtersveld. (fig.  3). 
805 
CONCLUSIONS 
ERTS imagery has proved t o  be invaluable i n  compiling a regional geological map of the 
N.W. Cape Province of South Africa. The area represents one i n  which few Published 
logical  maps ex is t  but i n  whiph important base metal deposits have been located. 
Interprgtation of the imagery w$s carried out with a limited amount of ground truth. 
Mapping d i rec t ly  onto the images from a l igh t  aircraft has c lear ly  defined the l a t e r a l  
extent of potential  zones of mineralization and is considered to  be an important 
technique. This has acted as the main basis f o r  the implementation of regional 
mineral exploration progr-es i n  the area. 
has been w e l l  established and s ignif icant  geological features have been recorded 
even i n  areas where published maps exis t .  
before are clear ly  seen on the imagery and have played a large part  i n  contributing 
to  the overall  geological pattern. 
the extent of metallogenic provinces i n  a re la t ive ly  short  period of time, 
especially i n  unmapped o r  poorly mapped areas, i s  unrivalled. 
during this study could act as the framework for similar investigations i n  other 
regions. 
The s t ruc tura l  framework of the area 
Major l inear  features not appreciated 
The use of ERTS images i n  defining accurately 
Techniques developed 
80 6 


ERTS-1 imagery as an aid to the understanding of the regional setting of base metal deposits in the North West Cape Province, South Africa

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