USE OF AIRBORNE GEOPHYSICS, REMOTE SENSING AND GEOLOGICAL MODELLING TO ASSIST AND UPGRADE 1:100,000 SCALE GEOLOGICAL MAPPING

Geological maps are a 2D geological image on an undulating terrain slice through a 3D geological model. Systematic national geological mapping by Federal and State geological surveys at progressively finer scales (1:250,000 to 1:100,000 to 1:25,000 etc.), most of it carried out with traditional methods (air photo interpretation, ground mapping etc.), underpins earth resource exploration, exploitation and management. In Australia total 1:250,000 and partial 1:100,000 scale coverage as well as selected mineral province geological mapping at finer scales, has been achieved.

Australia now has the benefit of nation-wide detailed to semi-detailed coverage with airborne geophysics (magnetics, radiometrics, airborne EM), gravity, magneto-tellurics, reconnaissance crustal seismic, SAR DTM, Landsat, ASTER and other remote sensing data. Most existing mapping: -

• was derived prior to the acquisition of, or without analysis / interpretation of, this geophysical and remote sensed information with the range of modern geophysical analysis and geological modelling software to value add the geophysical information for input to the geological mapping process; and
• precedes the recent rapid evolution of understanding of geological processes and capacity for 3D geological mapping.

Results from a desk-top case study in semi-arid terrain from Western Australia, show the benefits and workflow, of analysis of available geophysical and remote sensed data for expanding / improving 1:100,000 scale geological mapping, using existing 1:250,000 and neighboring 1:100,000 mapping and explanatory notes as preliminary ground truth, to guide on-ground 1:100,000 mapping and provide a resource mapping perspective. The workflow, utilising Intrepid, (ERDAS Imagine, ER Mapper, ArcGIS) or QGIS and GeoModeller software includes: -

• SAR DTM, radiometrics, Landsat and ASTER classification of terrain – pseudo-geomorphology, preliminary outcrop lithology identification and inference of micro-seismicity and recent fault reactivation (lineament analysis);
• Magnetic depth estimates and “worm” analysis for structural analysis and 3D modelling as well as definining pre-Cainozoic. "under-cover" basement fabric;
• Where gravity coverage justifies it, gravity modelling over selected areas;
• Airborne EM regional reconnaissance lines 1D or 2.5D inversion and if available assessment of available magneto-telluric data and crustal seismic reflection data; and
• As justified, 3D geological modelling to construct or improve selected key geological sections.