Results from the Captains Flat and Braidwood mapping projects

Exploration Data WorkshopGeological Survey Technical Talks1st June 2016, Orange

Results from the Captains Flat and

Braidwood mapping projects


Where are we?


Captains Flat• Release due mid 2016

Braidwood• Release due late 2016


Goulburn Basin


Goulburn Basin• late Silurian sequences hosts VAMS

mineralisation (e.g. Woodlawn)

• Intrusion-related mineralisation in the Early Devonian Braidwood Granodiorite (e.g. Dargues Reef)

• Skarns in the late Silurian limestones resulting from the Early Devonian plutons (e.g. Mayfield)


Goulburn Basin• late Silurian sequences hosts VAMS

mineralisation (e.g. Woodlawn)

• Intrusion-related mineralisation in the Early Devonian Braidwood Granodiorite (e.g. Dargues Reef)

• Skarns in the late Silurian limestones resulting from the Early Devonian plutons (e.g. Mayfield)


Stratigraphic Correlations

• Historical correlations very simple

• Based on a ‘layer cake’ stratigraphy

Modified after Davis 1990








Why do only some centres appear to be mineralised?


Why do only some centres appear to be mineralised?

large volumes of subsurface gabbro

and granites?


Late Silurian Intrusions

• Evidence of mixing the gabbro and the granites

• Geochemically the gabbros match the erupted basalts

• Potential heat source for the VAMS mineralising systems?


Late Silurian Basin Architecture


Mapping Outcomes• Basin-wide events can be correlated across the basin,

despite complex lateral changes

• SHRIMP age dating • Confirms the Late Silurian age of the volcanics and

comagmatic igneous rocks at Woodlawn and Captains Flat, aiding the correlation of this volcanic events across the basin

• Shows that not all rhyolitic volcanics are Late Silurian

• A coincidence between mineralisation and high-level bimodal intrusive complexes


Outcomes for Exploration

• Refining prospective areas• Previously targeted areas include areas now

recognised as Ordovician sediments and as Early Devonian sub-aerial volcanics

• Understanding the stratigraphy allows the targeting of specific horizons

• Identifying possible heat sources to VAMS systems, may explain why not all volcanic centers are mineralised and refine targeting

• Coeval mafic rocks in the sequence may help find ‘hotter’ parts of the system


Thank You

Government & Nonprofit

Results from the Captains Flat and Braidwood mapping projects