1. 7th National Opal Symposium
“Unlocking Australia’s Opal Wealth”
OPAL DOMES
7th National Opal Symposium
Lightning Ridge
25-27 July 2011
David Horton

2. AUSTRALIAN OPAL MINING CENTRES

3. east
Early
west
Late 80 90
110
120
130
CRETACEOUS
100
Kumbarilla Beds
Bungil Formation
Griman Ck Formation **
Surat Siltstone
Doncaster Member **
Coreena Member
Mackunda Formation
** These units host precious opal
Cadna-Owie Formation
Winton Formation **
Allaru Mudstone
Toolebuc Formation
Bulldog Shale **
Wallumbilla Formation
Schematic cross-section showing opal-bearing geological units

4. 24 Ma 60 Ma fresh host rocks silcrete chemically weathered host rocks
20 km
Stage 2: Arid sub-tropical climate; lowering of alkaline water table
during warping; remobilisation of silcrete; opalisation
Stage 1: Wet temperate to sub-tropical climate; high acidic water table;
chemical weathering of sediments; pedogenic silcrete
60 Ma
24 Ma
later sediments
opalisation

5. 10 Ma - present Opal horizon Stage 3: Scarping
20 km
Note: Vertical scale is highly exaggerated

6. AUSTRALIAN SEDIMENTARY OPAL – WHY IS AUSTRALIA UNIQUE?
Australian Gemmologist, 21,
Published December 2002

7. Shuttle Radar Topography Mission
Specially modified radar system that flew onboard the Space Shuttle Endeavour during an 11-day mission in February 2000

8. WINTON DOME
Length: 90 km
Width: 40 km

9. JUNDAH DOME
Length: 145 km
Width: 70 km

10. EROMANGA DOME
Length: 145 km
Width: 45 km

11. GRAWIN - GLENGARRY DOME
LIGHTNING RIDGE DOME
Length: 30 km Width: 30 km
Length: 45 km Width: 45 km

12. ANDAMOOKA ?DOME
Length: ?? km
Width: 20 km

13. COOBER PEDY ?DOME
Length: 100 km
Width: +40km