Unlocking Australias Opal Wealth OPAL DOMES David Horton

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

AUSTRALIAN OPAL MINING CENTRES

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

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

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

AUSTRALIAN SEDIMENTARY OPAL – WHY IS AUSTRALIA UNIQUE? Australian Gemmologist, 21, 287 -294 Published December 2002

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

WINTON DOME Length: 90 km Width: 40 km

JUNDAH DOME Length: 145 km Width: 70 km

EROMANGA DOME Length: 145 km Width: 45 km

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

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

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