This document discusses alluvial diamond deposits in Africa. It begins by explaining the primary and secondary sources of diamonds, with primary sources being kimberlites and secondary sources being various types of placer deposits. It then provides a diagram labeling the principal types of placer deposits in Africa, including retained placers on the craton, transient placers on the craton and coastal plain, and terminal placers in oceans or seas. The rest of the document discusses specific examples of terminal placer deposits in southern Africa and factors contributing to the development of large, high-quality mega-placer deposits.

1. MARINE ALLUVIAL DIAMOND DEPOSITS:
THE AFRICAN PERSPECTIVE CONTINUED…..
John Ward
October 2012
Diamonds and their Primary and Secondary Sources
University of Pretoria
In collaboration with Brian Bluck, Jurgen Jacob, Spaggs Spaggiari and the Namdeb (& former CDM) geologists

2. CRATON = SOURCE
OCEAN / SEA = SINK
AFRICAN CRATON (SUBDUED RELIEF)
PRIMARY SOURCES = KIMBERLITES (1)
SECONDARY SOURCES = RETAINED & TRANSIENT PLACERS (2, 3, 4, 5, 6)
CARTOON OF THE PRINCIPAL TYPES OF ALLUVIAL DIAMOND PLACERS DEVELOPED IN AFRICA
COASTAL PLAIN
LITTORAL
OCEAN / SEA
SECONDARY SOURCE = TERMINAL PLACERS (8)
1
1
2
3
5
4
6
7
8
7
MARGIN
SECONDARY SOURCES =
TRANSIENT PLACERS (7)
MOUNTAINS
& HILLS
Adapted from: Bluck et al., 2005
RIVER
TERMINAL PLACERS = OCEAN OR SEA:
8: LITTORAL, PREDOMINANTLY MARINE WITH SUBORDINATE AEOLIAN
(BOTH SUB-AERIAL & SUB-MARINE SETTINGS BECAUSE OF SEA LEVEL FLUCTUATIONS)
LITTORAL, PREDOMINANTLY MARINE WITH SUBORDINATE AEOLIAN

3. FLUVIAL CONDUIT
SINK
DELTA
TERMINAL PLACERS: ENDPOINTS OF TRANSIENT SYSTEMS

4. TERMINAL PLACERS: FLUVIALLY DOMINATED DELTAS - INEFFECTIVE

5. TRANSIENT PLACER – COASTAL PLAIN – TERMINAL PLACER INTERFACE
ORANGE RIVER MOUTH: WAVE-DOMINATED DELTA

6. TERMINAL MEGA-PLACER: SPERRGEBIET COAST & OFFSHORE , NAMIBIA
Image: D. Apter, 2004
ORANGE
ORANGE
VAAL
LIMPOPO
ZAMBEZI
KUNENE
TUGELA
OLIFANTS
ATLANTIC OCEAN
NAMIBIAN MEGA-PLACER
>100 Million Carats
95% Gem Quality

7. SOURCES: WILLIAMS, 1932;
VARIOUS FIELD GUIDES,
INCLUDING DE BEERS.
FERTILE KAAPVAAL CRATON THROUGH GEOLOGICAL TIME
(ca. 80Ma through to ca. 1600Ma)

8. Oranjemund
Total drainage area 891,780 km2
36%Drainage on craton
Total area of craton 585 000 km2
Orange river drainage basin
Cape Town
Orange River
All drainage in this area > 1km elevation
B
0 km 500
HIGH PERCENTAGE OF DRAINAGE DERIVED FROM CRATON

9. ±
0 250 500 750125
Kilometers
UPINGTON
DURBAN
ORANJEMUND
CAPE TOWN
SOURCE
KIMBERLEY
SINK
LOWER % GEM QUALITY
ORANGE
2
3
1
1 Fluvial Conveyor
2 Marine Conveyor
3 Desert Conveyor
VAAL
95% GEM QUALITY
UPGRADING THE QUALITY OF DIAMONDS
PRINCIPAL SEDIMENTARY CONVEYORS: SOURCE TO SINK

10. ORANGE RIVER FLOOD 1988
LINEAR BEACH PLACERS
BARRIER BEACH PLACERS
ORANJEMUND
HIGH ENERGY
COASTLINE
SUBMARINE BEACH
PLACERS
FLUVIAL / MARINE CONVEYOR INTERFACE: PROXIMAL TERMINAL PLACER
• ORANGE RIVER MOUTH = A WAVE-DOMINATED DELTA
• EXTENSIVE BEACH PLACER DEVELOPMENT ONSHORE & OFFSHORE WITH COARSE TO MEDIUM SIZED DIAMONDS
POCKET BEACH PLACERS
ORANGE RIVER

11. FLUTING ON BEDROCK BY SAND LADEN WINDS
MARINE AND DESERT CONVEYOR DRIVING FORCE IN TERMINAL PLACER ZONE
• AGGRESSIVE, LONG-LIVED SOUTHERLY WIND REGIME DRIVES UNI-DIRECTIONAL SAND DISPERSAL AWAY FROM
PROXIMAL & MID TERMINAL PLACER ZONES
• ARIDITY ENABLES SAND TO BE READILY TRANSPORTED IN SUB-AERIAL ENVIRONMENT

12. ENERGETIC WAVE REGIME AND COASTAL EROSION
SOUTHERLY WINDS DRIVE LONGSHORE DRIFT
NORTHWARD ACCRETING SAND SPIT
MARINE CONVEYOR: REMOVAL OF SAND FROM TERMINAL PLACER ZONE
• VIGOROUS & PERSISTENT NORTHWARD-BOUND LONGSHORE DRIFT UNDER SOUTHERLY WINDS
PELICAN POINT
LIGHTHOUSE

13. POCKET BEACH PALAEO-MARINE DEPOSITS
HEADLAND
POCKET BEACH EMBAYMENT
HEADLAND

14. BEDROCK - FLOORED
DEFLATION BASIN
DEFLATION PLACERS
BARCHAN TRAIN
PROXIMAL DESERT CONVEYOR
• SAND THROUGH-PUT FROM COAST TO MAIN NAMIB SAND SEA VIA DEFLATION BASINS
• EXTENSIVE WINNOWING & UPGRADING OF LOCALISED DEFLATION PLACERS WITH MEDIUM TO FINE SIZED
DIAMONDS

15. LOG SPIRAL BAY
AEOLIAN TRANSPORT CORRIDOR
SAND DRIVEN ONSHORE FROM LOG SPIRAL BAYS
POCKET BEACH
PLACERS
MARINE / DESERT CONVEYOR INTERFACE
• RETURNING SAND ONSHORE IN DISTAL TERMINAL PLACER ZONE
• LIMITED MARINE (POCKET BEACH) PLACERS WITH MEDIUM TO FINE SIZED DIAMONDS

16. AEOLIAN PLACERS
DESERT DUNE CONVEYOR
• AEOLIAN DUNE AND SAND SUPPLY TO MAIN NAMIB SAND SEA
• THIN BUT LATERALLY PERSISTENT AEOLIAN PLACERS WITH FINE DIAMONDS

17. DESERT CONVEYOR MOVING SAND ONSHORE

18. WALVIS BAY
LÜDERITZ
CRESCENTIC DUNES
BARCHAN DUNESTAR DUNE
LINEAR DUNE
ORANGE RIVER
KUISEB RIVER
MAIN NAMIB SAND SEA
DISTAL DESERT CONVEYOR: DISTAL TERMINAL PLACER & BEYOND
• MAIN NAMIB SAND SEA = PRINCIPAL REPOSITORY OF ORANGE RIVER DELTA SEDIMENTS

19. COARSE GRIT TO SMALL PEBBLES
TERMINAL PLACERS: DESERT DEFLATION AND AEOLIAN TYPES
• CONCENTRATION OF FINE DIAMONDS IN HYDRAULICALLY EQUIVALENT AEOLIAN DEPOSITS

20. Diamond picking in Namibia (1908-10). Original discovery by Zacharias Lewala, in 1908, he
recognised diamonds whilst clearing a railway line at Kolmanskop and August Stauch took
the matter further, opening up what has turned into one of the world’s mega-placers....

22. Photo: Jacob, 2004

23. ORANGE RIVER FLOOD 1988
LINEAR BEACH PLACERS
BARRIER BEACH PLACERS
ORANJEMUND
HIGH ENERGY
COASTLINE
SUBMARINE BEACH
PLACERS
FLUVIAL / MARINE CONVEYOR INTERFACE: PROXIMAL TERMINAL PLACER
• ORANGE RIVER MOUTH = A WAVE-DOMINATED DELTA
• EXTENSIVE BEACH PLACER DEVELOPMENT ONSHORE & OFFSHORE WITH COARSE TO MEDIUM SIZED DIAMONDS
POCKET BEACH PLACERS
ORANGE RIVER

24. TERMINAL PLACERS: ENERGETIC COASTLINES

25. MODERN (SKELETON COAST) & ANCIENT (SPERRGEBIET) EXAMPLES OF BEACH (INTERTIDAL) PLACERS
TERMINAL PLACERS: ENERGETIC COASTLINES
INTERTIDAL INTERTIDAL
INTERTIDAL INTERTIDAL

26. TERMINAL PLACERS - MINING OF PALAEO-STRANDLINE DEPOSITS ONSHORE
SPERRGEBIET COAST, NAMIBIA

33. TERMINAL PLACERS - MINING OF PALAEO-STRANDLINE DEPOSITS ONSHORE
SPERRGEBIET COAST, NAMIBIA

35. 25m
N
TERMINAL PLACERS: SUBMERGED PALAEO-BEACH DEPOSITS

36. TERMINAL PLACERS - MINING OF SUBMERGED MARINE PALAEO-PLACERS

37. TERMINAL MEGA-PLACER: SPERRGEBIET COAST & OFFSHORE , NAMIBIA
Image: D. Apter, 2004
ORANGE
ORANGE
VAAL
LIMPOPO
ZAMBEZI
KUNENE
TUGELA
OLIFANTS
ATLANTIC OCEAN
NAMIBIAN MEGA-PLACER
>100 Million Carats
95% Gem Quality

38. Shelf by-pass in area of end-Cretaceous
inversion
CAPE TOWN
Wedge of mainly fine Tertiary
sediment with clinoforms
Wedge of mainly fine Tertiary
sediment with clinoforms but no
significant unconformaties
Shelf by-pass-part of area of end-
Cretaceous inversion
Namib sand sea: latest of sand seas
beginning in Eocene ?
Cape Fria
Toscanini
Cape Cross
Henties Bay
ATLANTIC
LÜDERITZ
CARTOON OF THE ORANGE RIVER DELTA DISPERSAL SYSTEM IN THE CAINOZOIC
• INFLUENCE ON TERMINAL PLACER DEVELOPMENT & DIAMOND SIZE DISTRIBUTION
SOURCE: Bluck , 2000

39. LUDERITZ
ORANJEMUND
HOTTENTOTS BAY
Elizabeth Bay
Chameis
1.0
0.8
0.6
0.5
0.4
0.4
0.4
0.3
0.2
0.1
0.25
0.15
0.25
..
1.0 - 2.0
AVERAGE STONE SIZE DECREASES NORTHWARDS FROM ORANGE RIVER MOUTH
NAMIBIAN MEGA-PLACER
YIELDED >100 MILLION CARATS
AT >95% GEM QUALITY

40. DRAINAGE BASIN:
1.On high % of fertile craton and peripheral traps
2. Uplift, incision, steeping river profiles and increase in drainage
density
3. Repeated, plateau-type uplift with low sediment yields and extensive
terrace development yielding transient placers
CRATON:
1.Fertile
2.Long history of kimberlite
intrusions
3.Minimum loss
4.Repeated reworking
Steep incision tract, upgrading diamond
population and supplying coarse resistant
sediment to form traps in this tract and at
the terminal placer
TERMINAL PLACER:
1. High energy to fractionate sediment
2.Drift system to transport sediment fractions to
separate regions
3 Energy sufficient to transport gravel and generate
trapping sediment regimes
4. Sea-level changes on shallow shelf to spread the
placer
Wave orthogonals
Width of
sea-level
change
SALIENT POINTS FOR THE DEVELOPMENT OF A DIAMOND MEGA-PLACER

41. AFRICAN ALLUVIALS – A CHALLENGE? - YOU BET!;

42. CRATON = SOURCE
OCEAN / SEA = SINK
AFRICAN CRATON (SUBDUED RELIEF)
PRIMARY SOURCES = KIMBERLITES (1)
SECONDARY SOURCES = RETAINED & TRANSIENT PLACERS (2, 3, 4, 5, 6)
CARTOON OF THE PRINCIPAL TYPES OF ALLUVIAL DIAMOND PLACERS DEVELOPED IN AFRICA
COASTAL PLAIN
LITTORAL
OCEAN / SEA
SECONDARY SOURCE = TERMINAL PLACERS (8)
1
1
2
3
5
4
6
7
8
7
PLACER TYPES LEGEND
RETAINED PLACERS (ON CRATON):
2. EPICLASTIC CRATER FACIES WITHIN KIMBERLITE PIPE (PRESERVATION FACTOR)
3. OLDER INTRA-CRATONIC BASIN
4. KARST
5. INTERNAL DRAINAGE
TRANSIENT PLACERS (CRATON & MARGIN):
6. RIVER TERRACE ON CRATON
7. RIVER TERRACE THROUGH CRATON MARGIN & ON TO COASTAL PLAIN
TERMINAL PLACERS (OCEAN OR SEA):
8: LITTORAL, PREDOMINANTLY MARINE WITH SUBORDINATE AEOLIAN
(BOTH SUB-AERIAL & SUB-MARINE SETTINGS BECAUSE OF SEA LEVEL FLUCTUATIONS)
MARGIN
SECONDARY SOURCES =
TRANSIENT PLACERS (7)
MOUNTAINS
& HILLS
Adapted from: Bluck et al., 2005
RIVER