English: Part of the Transvaal Supergroup, viz. the upper formations
of the Chuniespoort Group and the Pretoria Group between
Zeerust and the border with Botswana, was mapped. The metamorphic
aureole of the Bushveld Complex as developed in the
Transvaal Supergroup in this area decreases in metamorphic
grade both along and across the strike as a result of an
apparent reduction in the thickness of the mafic rocks towards
the west. The presence of the metamorphic index
minerals tremolite, anthophyllite, cummingtonite, cordierite
and almandine indicates rocks of the hornblende-hornfels
facies in the east. West of long. 25°53'E (which transverses
the strata), the metamorphic assemblages are typical of the
albite-epidote-hornfels facies and contain minerals such as
talc and epidote. Total fluid pressure in the mapped area
is unlikely to have exceeded 4 kb. Temperatures are estimated
to have been between 300 and soo 0 c for the albiteepidote-
hornfels facies and between 500
hornblende-hornfels facies.
0 and 600 C for the
Few of the complex structures present in adjoining Botswana
enter South Africa. A low-angle strike fault zone is an
exception, however, and enters South Africa near Skilpadhek
to cut out a large part of the Malmani Subgroup. The postBushveld
linear structures, which are predominant in most of
the mapped area as well as in a large part of the Kaapvaal
province, viz. the NNW faults and the ENE photo-lineations,
were formed under tensional conditions. En echelon NNW faults
appear to be a result of crustal adjustments in response to an isostatic rise of the underlying Gaberone basement granite
dome, which is part of the Vryburg arch. ENE and EW photolineations
appear to be the surface manifestations of diabase
dyke systems. EW faults are rare.
Several lateral lithofacies changes in the sedimentary layers
of the area indicate a higher energy environment in the west.
This, together with an increase in the amount and size of
detrital chert near Botswana, suggests a nearby original
margin of the Transvaal basin in Botswana.
Uplift and erosion of the Chuniespoort Group after its deposition
did not remove the Penge Formation, with the result
that the basal layer of the Pretoria Group is a chert conglomerate
and not a residual chert breccia as elsewhere in the
Transvaal basin. The sequence of the Rooihoogte Formation
at Skilpadhek,as indicated by the cores of four boreholes,
represents a delta partly destroyed by strong currents and
superseded by linear elastic shore deposits. Lava of the
Hekpoort Andesite Formation was extruded subaerially and has
an upper, metamorphosed, residual paleosoil cover.
Nsutite, a battery-active manganese dioxide, is mined between
Skilpadhek and Livingstone's Poort. The ore body originated
by replacement of a layer of stromatolitic,dolomitic limestone
in the Polo Ground Member of the Rooihoogte Formation and
has a dip of 15° to the north or northeast, a strike length
of 10 km and a thickness of between O and 7 m. Ore formation
could still be in progress in the oxygen-rich zone of the
ground water, which would curtail the extent of the ore to between 30 and 40 m below ground level.
Lenses of magnetite occur in a thick noritic sill above the
Daspoort Quartzite Formation. Many small iron ore bodies
exist in the Transvaal Supergroup. Carbonaceous slates are
usually rich in sulphides, especially pyrite.
Afrikaans: 'n Gedeelte van die Transvaalsupergroep nl. the boonste
forrnasies van die Chuniespoortgroep en die Pretoriagroep
tussen Zeerust en die Botswanagrens, is gekarteer. Die
rnetarnorfe oureool van die Bosveldkompleks wat ontwikkel is
in die Transvaalsupergroep, verrninder in rnetarnorfe graad
langs sowel as dwarsoor die strekking weens 'n blykbare
afnarne in die dikte van die rnafiese gesteentes na die weste.
Die teenwoordigheid van die rnetarnorfe indeksrninerale trernoliet,
antofilliet, curnrningtoniet, cordieriet en alrnandien in
rnineraalassosiasies dui op gesteentes van die horingblendehoringfelsfasies
in die ooste. Wes van die lengtegraad
25°53'0 wat dwarsoor die gelaagdheid sny, is rnetarnorfe assosiasies
wat tipies is van die albiet-epidoot-horingfelsfasies
en rninerale soos talk en epidoot bevat. Dit is onwaarskynlik
dat die totale vloeistofdruk ooit 4 kb oorskry het. Die ternperatuur
het blykbaar gewissel tussen 300 en 50o0cvir die
albiet-epidoot-horingfelsfasies en tussen 500
vir die horingblende-horingfelsfasies.
0 en 600 C
Min van die ingewikkelde strukture in die aangrensende gebied
in Botswana dring Suid-Afrika baie ver binne, behalwe vir 'n
sone van vlakhoekige strekkingsverskuiwings wat 'n groot
gedeelte van die Malrnanisubgroep afsny in die Skilpadhekorngewing.
Na-Bosveldse lineere strukture is dominant in
die grootste gedeelte van die gebied asook in 'n groot gedeelte
van die Kaapvaalprovinsie. Die linearnente bestaan uit NNW-verskuiwings
en ONO-fotolineasies, wat beide onder tensie toestande ontstaan het. Die en echelon, NNW-verskuiwings
is skynbaar te wyte aan aanpassings van die aardkors wat
genoodsaak is deur 'n isostatiese styging van die onderliggende
Gaberone-koepel van Argeiese graniet, wat deel
uitmaak van die Vryburgboog. Die ONO-en OW-fotolineasies
is waarskynlik oppervlakverskynsels van diabaasgangsisteme.
Daar is min OW-verskuiwings.
Etlike laterale litofasiesveranderinge in die sedimentere
lae van die gebied dui op 'n hoer energie omgewing in die
weste as in die ooste. Daar is ook 'n styging in die hoeveelheid
en grootte van detritale chert naby Botswana.
Hierdie verskynsels dui op 'n nabygelee oorspronklike grens
van die Transvaalkom in Botswana.
Opheffing en erosie van die Chuniespoortgroep na afsetting
het nie die verwydering van die Pengeformasie tot gevolg
gehad nie, met die gevolg dat die basale laag van die Pretoriagroep
'n chertkonglomeraat is en nie 'n residuele chertbreksie
nie soos elders voorkom in die Transvaalkom. Die
opeenvolging van die Rooihoogteformasie in die Skilpadhekomgewing
soos aangedui deur die kerne van vier boorgate, stel
'n delta-afsetting voor wat gedeeltelik vernietig is deur
sterk seestrome. Lineere klastiese kusafsettings volg bo-op
die oorblyfsels van die delta. Lava van die Hekpoort Andesiet
Formasie het op land uitgevloei. Die boonste laag lava is verander
na 'n gemetamorfoseerde residuele paleogrond.
Nsutiet, 'n battery-aktiewe mangaandioksied word in die Skilpadhek-
Livingstone's Poortgebied ontgin. Die ertsliggaam is 'n vervanging van 'n laag strornatolietiese dolornitiese
kalksteen wat voorkorn in die Polo Groundlid van die Rooihoogteforrnasie
en het 'n helling van 15 o noord of noordoos,
'n strekkingslengte van 10 km en 'n dikte van tussen Oen
7 rn. Vorrning van die erts kan rniskien nog aan die gang
wees in die suurstofryke sone van die grondwater, wat die
diepte van die erts sou beperk tot tussen 30 en 40 rn onder
die grondoppervlak.
Magnetietlense korn voor in 'n dik noritiese plaat bokant
die Daspoortkwartsietforrnasie. Baie ander klein ysterertsafsettings
is in die studiegebied opgernerk. Koolstofryke
skalie bevat gewoonlik heelwat sulfiede,veral piriet.
