The Geological Survey of NSW is developing a new approach to regional mapping that incorporates traditional field mapping, geophysical data interpretations and historical data into an interactive 3D environment. It is built throughout the mapping process which allows changes to be made progressively. The final product will be a traditional geological map with validated cross-sections and a 3D geological model. It will be viewed in a 3D framework and be available in a user friendly format that will enable the viewer to assess and query.

Project areas 3D key.

Koonenberry Belt 3D mapping project.

The increasing ability of geological software packages to integrate and visualise diverse data sets in a 3D framework allows for a more critical evaluation and convergence of interpretations. All available data sets (SEG Y, LAS, drill strings and surveys, cross-sections, magnetic and gravity data, as well as traditional surface mapping) can now be visually interrogated. This allows for a holistic approach to developing a better understanding and interpretation of both the exposed and covered geology.

The following project areas are currently being developed in a 3D framework:

• Koonenberry Belt
• Thomson Orogen
• Braidwood

Braidwood 3D mapping project.

Thomson Orogen 3D mapping project.

3D modelling

The progressive development of a 3D modelling project is as follows:

• Apply multiscale edge detection analysis to high resolution gravity and aeromagnetic data to produce ‘worms’.
• Points are created at the maxima of the horizontal gradient of gravity and magnetic data. They define edges of bodies at different upward continuation levels and link together to form ‘worms’.
• The ‘worms’ are then imported into Paradigm™ GOCAD® SKUA® to create an inferred 3D structural surface with X, Y and Z components.
• The ‘worm’ surfaces represent planes that separate geological bodies and/or structures at depth with different petrophysical properties, specific density for gravity data and magnetic susceptibility for magnetic data.
• Simple unconstrained geophysical models are then produced along proposed cross-section lines using Pitney Bowes ModelVision software.
• Geologists and geophysicists work together to construct a number of serial cross-sections (up to 9 sections per
  1:100 000, sheet) that are then geophysically modelled to check and, if necessary, be modified for admissibility.
• Higher degrees of complexity are introduced into the ModelVison-derived geophysical bodies based on the constraints imposed by the geological structures detailed in the cross-sections.
• Geological cross-sections (constructed in Geo-Logic, Systems LithoTect™), mapped geology and geophysical bodies are imported into a 3D framework in GOCAD® SKUA®, where inconsistencies can be observed and, if required, reinterpretations done.
• Complex solid geology constructed in GOCAD® SKUA® using geophysical/geological constrained bodies are built between cross-sections and tested against mapped geology and geophysical properties.
• Multifaceted GOCAD® SKUA® produced bodies are then validated in ModelVision, which requires that the bodies be completely sealed and that boundaries between bodies be flawless.
• The geophysical interrogation of complex geological bodies that span more then one section line allows the solid geology of the entire map sheet area to be forward-modelled.
• Subsequent inversions run in ModelVision, while considering all geological geometries in a spatial sense, generate a 2¾d geophysical model that will validate, or invalidate, the 3D geological model over the whole area and locate areas requiring further input.
• Validation of the 3D model is achieved in ModelVison by constrained inversion along lines in a range of orientations.

For further information please contact the Geological Mapping Team.

(Last updated on 18/08/2011)