Mineral Potential of Australia: Background and Methodologies

• Assessments
• Assessments at 1:250 000 scale
• Assessments at 1:1 million scale
• Geoprovince-scale assessments
• Table 1: An example of the assessment matrix used for the porphyry style copper-molybdenum-gold deposit style
• Resources and advice decision support system
• References
• Related links

Introduction

The Mineral Potential project and its predecessors have conducted assessments of the potential for undiscovered mineral resources for more than 10 years. These assessments have been made in response to requests from Australian Government agencies for input on land use issues. There has been increasing emphasis on enhancing the understanding of Australia's mineral potential outside the known mineralised areas and highlighting opportunities for mineral exploration. Areas of assessment have varied from a few square kilometres to regions in excess of 100,000 square kilometres. Three broad scales of assessments used are:

• Detailed assessments of specific regions at a scale of 1:250 000;
• regional geoprovince scale of around 1:1 million; and
• national scale geoprovince scale assessments at 1:2.5 million.

Detailed prospectivity analyses of specific areas using weights of evidence, fuzzy logic and neural network techniques are planned for the future.

[back to top]

Assessments

Assessments at 1:250 000 scale

Most mineral potential assessments in the past have been conducted using qualitative methods of mineral potential assessment, but recent major project undertaken jointly with State geological surveys involved a GIS based qualitative assessment. Carried out at a scale of 1:250 000, the assessment involved a total of 12 areas in five States as part of the Regional Forest Agreement (RFA) process. The GIS based qualitative assessment method which was developed combines:

• Elements of a qualitative method used by the United States Geological Survey;
• mineral deposit models compiled by Cox and Singer (1986); and
• numerical ranking of levels of mineral potential and the weighting of different types of mineral deposits to facilitate computer processing and visualisation of assessment results.

Regional scale criteria for specific types of mineral deposits was used to delineate mineral potential tracts for each deposit style and assign levels of mineral potential as High, Moderate to High, Moderate, Low to Moderate, Low and Unknown. Levels of certainty for each tract also were assigned according to the amount of information available for each tract.

Assessments for individual deposit styles in the same area were then combined to produce 'composite' and 'cumulative' mineral potential maps for the region. Individual deposit styles also were weighted against each other in terms of economic significance and weighted tracts were combined to produce 'weighted composite' and 'weighted cumulative' mineral potential maps.

The assessment methodology used for the RFA regions is fully described in the reports on mineral resource assessments for Southwest Western Australia RFA and for the Upper North East RFA region in New South Wales.

[back to top]

Assessments at 1:1 million scale

Mineral potential assessments at 1:1 million scale are being introduced for the assessment of mineral potential of some geological regions being studied by Geoscience Australia and the State and Territory geological surveys under the National Geoscience Agreement such as the North Australia Project. Assessments at this scale will be gradually introduced in the more advanced stages of these projects, as new information and data become available.

[back to top]

Geoprovince-scale assessments

The current emphasis for the project is the preliminary national geoprovince 1:2 500 000 scale assessment of selected significant mineral deposit styles for gold, base metals and uranium. The boundaries of these geoprovinces are largely defined on Geoscience Australia's 1995 1:2.5 million scale geotectonic province map based on WD Palfreyman's Bureau of Mineral Resources Bulletin 181 and on the map of major structural elements (GW D'Addario, WD Palfreyman & JM Bultitude, 1979). Boundaries of subdomains of these geoprovinces are derived from more recent datasets defined by past and current Geoscience Australia regional projects.

Initially, preliminary assessments for selected types of mineral deposits in specific geoprovinces are being prepared by Geoscience Australia to trial the methodology being used. The follow-up stage of the assessments will involve consultation with the State and Northern Territory Geological Surveys to advance the preliminary assessments, incorporate data from the geological surveys and integrate results of assessments of mineral potential by the States and the Northern Territory.

The methodology used is a modified version of the GIS-based qualitative assessment applied by Geoscience Australia for the assessment of Regional Forest Agreement areas. The stages of assessment include:

• Compilation of the latest geology mineral occurrences/deposits for the geoprovince being assessed;
• determination of styles of mineral deposits likely to be present in the area including:
• types of mineral deposits known to exist in the geoprovince; and
• those not known to be present but for which assessment criteria indicate that a favourable environment exists in the geoprovince;
• compilation and updating of time-event plots for the geoprovince;
• preparation of descriptive mineral deposit models incorporating minerals systems criteria for source of elements/fluid pathways/traps; and
• definition of geoprovince scale assessment criteria for deposit styles.

Geoprovince scale assessment criteria are compiled in a matrix format which are used for the assessment of mineral potential for that particular style of deposit. An example of assessment matrix for porphyry style copper-molybdenum-gold deposit as shown below.

Table 1: An example of the assessment matrix used for the porphyry style copper-molybdenum-gold deposit style

Province:
Potential:
Certainty:
Index (out of 10):

The level of mineral potential for each style of mineral deposit is assessed using the criteria outlined in the matrix, such as in the above case for porphyry copper-molybdenum-gold deposits. The level mineral potential is scored on a scale of zero to five with the highest level of potential being represented by five and zero representing no score for 'unknown'. For instance, Lachlan Fold Belt will return a mineral potential level of five for porphyry style copper-molybdenum-gold deposits while the New England Fold Belt and the Yilgarn Craton may return scores of four and two respectively for the same style of deposit.

The level of certainty is scored on a scale of zero to five also and is based on the amount of evidence available for mineralisation process having taken place.

Individual mineral deposit styles also can be indexed according to levels of economic significance. As for the Regional Forest Agreement areas, geoprovince scale mineral potential tracts for individual deposit styles can be combined to produce 'composite' and 'cumulative' mineral potential maps as well as 'weighted composite' and 'weighted cumulative' mineral potential maps.

The mineral potential maps/GIS layer would show levels of mineral potential and certainty for specific types of mineral deposits for a given geoprovince and the layer can be linked to:

• Time-event plots of geoprovinces;
• mineral systems based deposit models;
• names and locations of major deposits;
• world-wide or local grade and tonnage data for deposit styles; and to
• more detailed assessments of mineral potential if available.

[back to top]

Resources and advice decision support system

The GIS-based method of producing simple and weighted composite and cumulative mineral potential maps for the Regional Forest Agreement process was combined with ASSESS, which is a GIS developed by the Bureau of Resource Sciences, the predessor of the Bureau of Rural Sciences for the resources and advice decision support system (RADSS). The RADSS can be loaded as an ESRI Arcview 3.2 extension and requires Arcview Spatial Analyst.

[back to top]

References

• GW D'Addario, WD Palfreyman, & JM Bultitude, 1979. Major Crustal Elements. In: BMR Earth Science Atlas of Australia. Bureau of Mineral Resources, Australia, Earth Science Atlas Series.
• DP Cox & DA Singer, 1986. Mineral deposit models. U.S. Geological Survey Bulletin 1693.
• WD Palfreyman, 1984. Guide to the geology of Australia. Bureau of Mineral Resources Bulletin 181.

[back to top]

Related links

• Mineral Potential of Australia
• Mineral Potential of Australia: Historic Products