An orogenic cycle typically follows a sequence of events or stages. These are basin formation and magmatism during extension, inversion and crustal thickening during contractional orogenesis, and finally extensional collapse of the orogen. The Archaean granite-greenstone terranes of the Eastern Yilgarn Craton (EYC) record a major deviation in this sequence of events. Within the overall contractional stage, the EYC underwent a lithospheric-scale extensional event between 2665 Ma and 2655 Ma, resulting in changes to the entire orogenic system. These changes associated with regional extension include: the crustal architecture; greenstone stratigraphy; granite magmatism; thermo-barometry (PTt paths); and structure. Synchronous with these changes was the deposition of the first significant gold, and it is likely that the intra-orogenic extensional event was one of the critical factors in the region's world-class gold endowment.

Predictive mineral discovery is concerned with the application of a whole of system process understanding to mineral exploration as opposed to an empirical deposit type approach. A mineral system process understanding can be derived from a consideration of five key questions, namely what is/are the: 1) geodynamic setting; 2) architecture; 3) sources and reservoirs; 4) drivers and pathways, and; 5) depositional mechanisms. The answers to these questions result in the identification of critical processes necessary for the function of a mineral system within a particular terrane, and permit the development of a targeting model. In this contribution we identify district scale critical orogenic gold mineral system processes for the late Archaean eastern Yilgarn Craton of Western Australia. During the geodynamic history of a terrane the critical processes which result in mineralisation change with time resulting in variations in mineralisation style. Proxies for critical processes have been mapped in an integrated GIS and are termed mappable mineral system process proxies (or MMSPP). In recognition of this, three separate time slices and a geochemical theme were analysed. Each MMSPP is given a weighting factor (WF) which reflects the spatial accuracy/coverage of the data and process criticality. For each theme/time-slice, a separate prospectivity map was created by summing the overlay or union of the spatial extent of each MMSPP, and adding the WF. A final target or prospectivity map was generated by a union of the four theme/time-slice prospectivity maps, and is tested against the known major deposits. The map 'discovered' the main gold camps and accounts for over 75% of the known gold in 5% of the area. This test verifies the process-based understanding and the appropriate mapping of the critical proxies. A further outcome from the map was the identification of a number of new target areas not known for significant gold mineralisation in what otherwise is thought to represent a mature terrane for gold exploration. The approach taken here has been to consider the Late Archaean gold deposits as a holistic system. Despite the recurring areas of uncertainty, this systems view has resulted in new findings that have generic applications to other mineral systems.

F2 presentation

Fluids overview presentation

Cleverley J.S & Oliver N.H.S, 2004. Geochemical models (and preliminary geophysical correlations) pertinent to magmatic contriubtions to ore system hydrology at Wallaby & elsewhere in the Yilgarn

Cleverley J.S. & Olver N.H.S., 2005. JCU/EGRU/CRC Masters Program at JCU. Geochemical Modelling

Fisher, L., 2005. Fluid inclusion compositions and conditions at Osborne; preliminary results.

Mustard, R., Mark, G., Ulrich, T., Foster, D., and Gillen, D., 2005. Geochemsitry of magmatic fluids from intrusions in the Williams-Naraku batholith, Cloncurry district, NW Queensland: preliminary results from laser ablation ICPMS analysis.

Annual Review Nov 2003

Annual Review Dec 2002