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Captains Flat-Michelago Geological Mapping Project

Project Aims

The aim of the project is to complete 2nd edition mapping of the mineralised middle Silurian to Early Devonian rift basins of the southeastern Lachlan Orogen. This mapping follows directly on from recently completed regional mapping of the Braidwood 1:100 000 and Goulburn 1:250 000 map sheet areas and follows the acquisition of detailed airborne geophysics over the southeastern part of NSW.

Mapping of the remaining Siluro-Devonian basin sequences will provide a new understanding of regional volcanosedimentary stratigraphy and relationships gleaned from the Goulburn and Braidwood mapping projects. The mapping will provide a better understanding of the timing of VHMS and replacement style base metal (±gold) mineralisation and could lead to improved exploration targeting of specific stratigraphic units for these mineralisation types. Other potential mineralisation types within and on the flanks of the Silurian basins include sediment-hosted disseminated gold deposits in the shale and limestone-bearing sequences common at the base of the rift basin sequence, and replacement-type base-metal mineralisation in limestone-rich shelf sequences on the flanks of the rift basins. In particular, the mapping should better constrain the structural architecture and history, and identify potential fluid pathways including basin growth faults.

Project Status

The project runs from February 2011 to July 2013. At February 2012, the project had seen the completion of:

• pre-fieldwork research and compilation of existing maps and reports
• 10 weeks fieldwork in five trips, completing field work in the Captains Flat Belt
• collection and analysis of six felsic igneous samples for zircon-dating on the SHRIMP II machine at Geoscience Australia
• identification of Late Ordovician graptolites in rocks previously mapped as Silurian
• contact with relevant mineral explorers and landowners

A project update with more detail on work to date and some preliminary findings was released in December 2011.

Future Work

Future work in the project will broadly consist of:

• 3D airphoto interpretation
• 2 weeks fieldwork in 2012
• geochemistry, petrology, palaeontology and geochronology services as required
• map compilation
• explanatory notes compilation
• provisional product release in 2013

Products

• 2nd edition geological mapping of Siluro-Devonian basin sequences uploaded into the statewide geodatabase
• 1:100 000 or 1:50 000 thematic 'special' map product of the project area
• explanatory notes including unit descriptions and geological synthesis
• GIS data package that includes field observations, palaeontology, geochemistry and petrology
• palaeontological and petrographic GS reports
• updated mineral occurrence database
• new exploration models for VHMS and replacement style base metal (±gold) mineralisation

(Last updated on 18/04/2012)