The document discusses ore deposits related to clastic sedimentation, specifically focusing on placer deposits in the Witwatersrand gold and uranium deposits in South Africa. It describes how weathering processes contributed to mineral resources through various means. It defines different types of placer deposits that form in various environments, such as alluvial, beach, glacial, and fossil placers. It then provides details on the stratigraphy, tectonic setting, sedimentation processes, and gold and uranium occurrences within the Witwatersrand deposits, which are fossil placers formed in an ancient freshwater lake. Mining in the region has been ongoing since the late 1800s.

1. Seminar on ore deposit
related to clastic
sedimentation

2. INTRODUCTION
• Weathering: In general weathering processes
acting upon rocks contributes to the overall
mineral resource may gives in five ways:
– Produce new minerals in site.
– Cause the redistribution of valuable elements.
– Released fine debris and chemical complexes.
– Released hard rocks into softer or useable rocks.
– Released of resistant minerals like gold.

3. PLACER DEPOSITS
• Hails in 1976 he defined placers as the surficial
mineral deposits formed by mechanical
concentration, commonly by allurial but also
by marine, aeoline, etc.of heavy minerals
particles such as gold from weathered debris.

4. TYPES OF PLACER DEPOSITS
• Eluvial - Formal site of destruction
• Deluvial - Formal down hill
• Proluvial - Accumulation formal foot
of a slope
• Alluvial - Placer carried out by rivers
of streams
• Laterial of beach - Formed along the shores
of lakes seas, etc.
• Aeolian - By action of wind
• Glacial - By activities of glacier
• Fossils placer/paleo placer - Those placer deposits
buried under younger rocks.

5. WITWATERSTRAND GOLD AND U
DEPOSITS IN REPLUBLIC SOUTH OF
AFRICA
• District lies in South Africa between
Johannesburg and Welkom shown in fig.
1

6. • “The Rand” is well known because of gold
deposits.
• Yield 35 millions Kg of gold value at nearly $60
billion
• It is a fossils placer types of deposits.
• Most of the debris were transported from North,
North West and South-West.
• Viljoen Saagar in 1970 showed that types of
sedimentations.
• Later Kappel and Saager in 1974 studies of
Isotypes
• Presence of isotopes contribute debris to the
witwatersrand basins.

7. STATIGRAPHY:
• The basemsent is Archean precambrian rocks
• The basement was unwrapped to steeply
diapiric domes represented by B in Fig 2

8. • It is made up of granite, granitic gneiss and greenstone Terrances.
• The domain group lie next to the basement.
• Made up of district of quartz carbonate gold veins and younger potassic
granite bodies with accessories minerals, uraninite.
• Witwatersrand super group overlie unconformably to basement and
domain group
• Made up of sequence of thin conglomerate and thick lava flows
• It’s divided into two – lower and upper unit or west rand group and
central rand group.
• Lower west rand group of witwatersrand consist of shales, quarzites, grits
and conglomerate.
• Upper younger central rand group is 90% of quarizite grits and rare shales.
• More gold bearing conglomerate.
• Tilting and erosion of Witwatersrand supergroung and followed by
igneous activity formed ventersdrop supergroup.
• Erosion and subsidence ventersdrop formed Transvaals supergroup.
• It is made up of thick sequence of clastic and dolomite limestones.
• Bushveld age of igneous activities marked the end of transvaal
supergroup.
• Lastly, Karroo Supergroup was formed.

10. TECTONIC SETTING
• Large synclinorium of 400 km long and 150 km wide
elongated north Easternly direction.
• Frame of synclinorium was formed as a part of complex
fabric of regional and distinct scale interference folding.
• Folding produce domes.
• Coincide of of anticlinal axes and intersected with synclinal
axes.
• Broad witwatersrand synclinal basin filled by shallow broad
intracratonic freshwater lake.
• Bottom accept the witwatersrand sediments.
• Synchlinorium is complicated.
• Several mine areas has abandoned.

12. SEDIMENTATION
• Goldfield constitute only a small fraction of Witwatersrand
sedimentations.
• Goldfield develop on Rand.
• The Rand fan shaped auriferous conglomerate systems
interleaved into the arenite thickness of the supergroup.
• These are six major goldfield mining areas in the district.
• Each presenting a wedge of sediment entry into the basin.
• Central Rand group consist series of sedimentation cycles
that range in thickness from 30 to 600 meters averaging 250
meters.
• Defined by basal unconformities mark by lag gravels
• It composed of major sand, minor conglomerate and
include siltstones, sandstones, etc.

13. • In Witwatersrand gold and Uranium placers
are not extracted occurs in at least four
geologic sites in the goldfields as given below
along with figure 5.

14. • 1. In the fan head – In the sandy near the base of fluvial
pebbles supported conglomerates was filled by sand
sized heavy minerals grains from the sediments flux.
• 2. In mid-fan – In pyrite trough cross bedded sands in
erosiion deposition with Golds, Uraninite or foresets, in
bottom set spoons and sours.
• 3. In upper-fan base – in sheets of cross bedded sands
by winowing of quartz grains, leaving thin layers of
heavy minerals as lag deposits.
• 4. In the fan base – In carbonaceous layers on
unconformeties in scour pools and in algal mats which
acted both as mechanical riffle trops and as chemical
trops.

15. • The ore bearing conglomerate strata in the Witwatersrand
area are know as reefs or bankets.
• The strata are not contineous as in a layer cake, but fans are
qualitatively similar
• The origin of the Witwatersrand conglomrate and quartzite
was based on gold origin.
• During depositions several environments have been
included, marines, shorelines, large ddeltas enclosed basins,
etc.
• The Witwatersrand rocks have been mildly metamorphosed
to greenschist faciest.
• Except presence of quartz pebbles dynamics sedimentations.
• Stretched during metamorphism.
• Sphericity and roundnes has been retained
• Space between pebbles are occupied by locally abundant
pyrite, zircon, rutile, etc.

16. CONCLUSION
• Another aspect of gold and uranium occurrence in Rand sediment
concerns local post depositional re-distribution of those elements
especially Uranium. Near the end of World War second, when interest in
fissionable materials was gaining momentum, it was discovered that the
frequently mentioned ‘Carbon’ of the Rand ores was actually a Uraninite –
Carbon agregate earlier, but improperly called Thucholite (Davidson and
Bowie 1951). Mineraloid whose very name describe its Thorium, Uranium,
Carbon, Hydrogen and Oxygen composition.
• Serious mining in the Witwatersrand district began in 1886 when the
‘Gold Rush’ started this activity. Since that time, many mines have been
developed along the 400kms of strike of the Witwatersrand
conglomerate, Beds on the northernly and southwesternly sites of the
Witwatersrand basin. Several mines are operating at depts of more than
300kms. The east Rand property mine operates at the dept of about
3.5kms. The western deeps mine near Carletonville, the deepest in the
world, has reached nearly 4Kms. Even deeper mines are planned to reach
further down along ore bearing strata, descent now locally more than
30Kms downdip.

17. THANK YOU