The Australian Mineral Systems project aims to improve the level of knowledge about the regional and district scale controls on Australian ore deposits as well as their distribution in space and time. It seeks to develop quantitative models which enable geoscientific information to be linked to exploration strategies and methodologies.
To develop realistic models that are relevant for the exploration industry, the essential ingredients which constitute the mineral system on a district to regional scale need to be identified. Realistic mineral system process models are multifaceted and usually involve several physical and chemical processes with complex interdependencies (Etheridge and Henley, 2003). Once developed, thermodynamic modelling will be used to simulate and test the validity of the mineral system models.
In part, work on this project contributes to the Predictive Mineral Discovery Cooperative Research Centre (pmd*CRC) Program 4 - Fluids and Program 5 - Modelling. The project also is closely related to the Geoscience Australia Felsic and Intermediate Igneous Rocks project.
Figure 1: Changes in the dominance of ore deposit types through time adapted from Hutchison (1981). Select for larger version of image [23KB]
Mineral systems can be defined as all geological factors which control the generation and preservation of mineral deposits and stress the processes that mobilise ore components from a source, transport and accumulate them in a more concentrated form and then preserve them throughout the subsequent geological history (Wyborn et al., 1994).
Investigations into the time control of deposit types (Figure 1) are based on the known fact that the dominance of certain ore deposits change with time (e.g., Hutchison, 1981). For example, iron (Fe) hosted copper (Cu) and gold (Au), or iron oxide-copper-gold, occurs only in two restricted time intervals. Banded iron formations are most prominent in the late Archaean - Palaeoproterozoic. There also appears to be an evolution of Cu, zinc (Zn) and lead (Pb) deposits from volcanogenic hosted deposits in the Archaean through shale hosted in the Proterozoic to a more diverse series of deposit types in the Phanerozoic. Porphyry and epithermal deposits dominate in the Phanerozoic.
The reasons for this variation in deposit types with time are not well understood. Some researchers believe that the dominance of porphyry and epithermal deposits in the younger terrains is a function of preservation. This project argues that the time dependence of ore deposit types is related to changing physical and chemical conditions through time as the earth evolved (mantle cooling, evolution of the oxygenated atmosphere, etc).
As an example of the work in time controls on deposit types, the project is investigating the importance of geothermal gradients to igneous and metallogenic events as well as their importance to a study of the high geothermal gradients in the Proterozoic terranes of Australia (Figure 2). Data from these terranes indicates that heat production rates were 25-30% greater in the Proterozoic than in the present day (McLaren et al., 2003), which will significantly affect their metallogenic potential.
Currently, most of the work on the spatial control of ore deposit types is being undertaken in the Felsic and Intermediate Igneous Rocks Project. This project is undertaking a comprehensive data collation and synthesis program on intermediate to felsic intrusive rocks and their associated host rocks. Staff from the Australian Minerals Systems project will work closely with colleagues from the Felsic and Intermediate Igneous Rocks Project to develop mineral systems process models for intrusion related deposits.
All ideas developed in this project will be tested by quantitative geochemical modelling. This modelling will be used to develop and generate new process models critical to the modelling of mineralising systems, with a particular emphasis on the processes of fluid flow, fluid mixing and fluid/rock reactions which may occur during transport from the source to the trap site. These models will be refined and constrained by the available geological data from the provinces of interest. Work on this aspect is closely integrated with the pmd*CRC.
Figure 2: A map of Australia showing the region of high heat flow in the Proterozoic (shaded in red) and some of Australia's major Proterozoic mineral deposits. Select for larger version of image [34KB]
An enhanced understanding of the 3-D and 4-D processes which control the distribution of Australian mineral systems in space and time. This involves the development of exploration models which are complemented and tested by high quality geochemical modelling of mineral systems processes. The geochemical modelling will be constrained by mineralogical data where it is available, or where it can be derived from hyperspectral datasets.