Thomson Orogen Project
The Thomson Orogen, which underlies sedimentary rocks of the Great Australian Basin in northwest NSW, is one of the state's major greenfields regions. The orogen has potential for orogenic, magmatic arc and oceanic crust -related gold and base metal deposits. Variable cover over the region has previously restricted exploration. However, the New Frontiers initiative will significantly reduce exploration risk by acquiring and interpreting seismic, magnetic and radioelement data, gravity, regolith mapping, regional geochemistry, drilling, depth-to-basement maps and 3D modelling of mineral systems.
Depth of Basement Map of the Thomson Orogen
Thomson-Lachlan Seismic Project
The Lachlan and Thomson orogens form part of the Tasmanides of eastern Australia, which is part of the interaction between the growing Australian craton (part of Gondwana) and the proto-Pacific plate from the Neoproterozoic through to the Mesozoic. The boundary between the orogens lies in the far northwest of NSW and its curved east-west trend is highly unusual in terms of Tasmanide tectonics.
reflection project showing the basic interpretation
The Thomson-Lachlan seismic reflection project was designed to test the scientific and metallogenic nature of the boundary, and, in particular, the reason for the prominent gravity anomaly that lies parallel to, and just north of, the boundary. Results to date indicate that the boundary is a major north-dipping thrust fault that offsets the Moho. Latest movement on the fault was in the Carboniferous (Figure 1). The seismic data also indicate the possibility of Mississippi Valley-type mineral systems along the margins of the Mt Jack High that marks the thrusted southern edge of the Nelyambo Trough.
Thomson Orogen regional geochemistry
baseline geochemical survey of the Thomson Orogen
The surface geochemistry of the NSW Thomson Orogen is now better constrained due to results of the combined work of NSW DPI, (former) CRC LEME, Geoscience Australia, University of Adelaide, Australian National University and MMI Technologies. A low density baseline geochemical survey was conducted across the Thomson Orogen (Figure 2). The technique involved collecting 700 samples from 99 sites in catchment areas, using a variety of mediums, including overbank soil, vegetation, lag and NITON (portable XRF) soil sampling. The results of the baseline survey showed that there was a negative correlation of metal content with depth to (base of Cretaceous) basement. The survey also indicated elevated base metal values in areas of base metal mineralisation in the Bourke area. Other techniques such as lag and vegetation were shown to have good vectoring capability in gold and copper rich areas in the Tibooburra-Milparinka area in the western area of the Thomson Orogen.
The baseline geochemical report can be downloaded from the CRC LEME website.
Thomson Orogen regolith mapping
Regolith mapping and associated studies in the NSW Thomson Orogen by NSW DPI, (former) CRCLEME and University of Adelaide, has helped to elucidate its landscape history since the Cretaceous.
A number of maps at various scales are available for free download from the CRC LEME website.
Thomson Orogen products
New Frontiers work-in-progress products are now compiled on a single DVD available through geoscience.products@industry.nsw.gov.au.
The updated DVD (Version 2) includes a revised interpretation, new age dating, improved depth-to-bedrock 3d model, and upgraded geophysical imagery.
The compilation includes:
- a preliminary 3d depth-to-basement data set presented as an interactive 3d Adobe PDF (viewer included), and text files of the drill hole database. Version 2 includes gridded and point geophysical data for the basement surface.
Contact: Stephen Dick 02 4931 6721 - a 1:250 000 interpretative regolith map generated from supervised classification of spectral response in satellite and radioelement data.
Contact: Marta Vega Faundez 02 4931 6677 - a preliminary geophysical/geological interpretation map of the Thomson Orogen based on regional geophysical datasets (particularly aeromagnetics), and integrating available geological information.
Contact: Rosemary Hegarty 02 4931 6597 - The CRC LEME Explorers' Guide
Thomson Orogen Explorers Guide
A significant piece of work to come out of the Thomson Orogen Project is the 'Guide for mineral exploration through and within the regolith in the southwestern Thomson Orogen, NSW', by Steve Hill (University of Adelaide), John Greenfield, Phil Gilmore and Bill Reid (NSW DPI). It represents a concise summary of the results of over ten years of research in northwestern NSW.
The Thomson Region Explorers' Guide can be downloaded free from the CRC LEME website.
Geophysical-geological interpretation maps
The geophysical-geological interpretations are based on enhanced images of ground-based and airborne geophysical data and satellite data, controlled by outcrop geology and drillhole information. The final products are 1:250 000 scale interpretation maps showing likely basement lithologies and structural elements.
Completed interpretations include the Milparinka, Cobham Lake and Bourke sheets and those in process are Louth, White Cliffs, Urisino, Yantabulla and Enngonia sheets. The provisional maps are available by emailing geophysics.products@industry.nsw.gov.au
Zircon dating used for a stratigraphic template
Probability plots and data were collated and the preliminary results were presented in DIGS report GS2010/0379. The significance of detrital zircon provenance results and granite crystallisation ages are discussed as a first attempt to build a stratigraphic template for the region and help understand its tectonic history. The context for each age date is discussed in relation to unit distributions and structural elements which are indicated on the geophysical-geological basement interpretation map.
Age dating of rock samples from the Thomson Orogen was undertaken with Macquarie University (GEMOC) and Geoscience Australia.
Thomson Orogen 3d mapping
The geology of the Thomson Orogen is being developed in a 3d framework. The basement surface now includes an increased number of basement picks from drill hole data (1081 water bores and petroleum /mineral drillholes); increased usage of seismic reflector control using 700 km of sections; 14 000 km2 of interpretation maps and ground truthing of the model by core tailing NSW Office of Water drilling projects (DIGS report GS2010/0173).
The depth to basement surface for the Thomson Orogen is available as gridded and point data in the Version 2 DVD of the Thomson compilation. The data package includes the surface as .dat, .tif and .jpeg format; the .dat files of data points for water bores, petroleum and mineral holes; and seismic control points.
Thomson Orogen 3D mapping.
For further information please contact the Geological Mapping Team.
(Last updated on 18/08/2011)