International Geologiical Congress - Oslo 2008

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OCE-01 Oceania and the 34th IGC in Brisbane

 

Major mineral systems of Australia

 

Richard Blewett, Geoscience Australia (Australia)
David Huston, Geoscience Australia (Australia)
skirrow roger, Geoscience Australia (Australia)
 

 

Australia is colloquially described as "The Lucky Country", and in terms of mineral endowment it certainly is. Australia hosts some of the world's great mineral deposits, including Olympic Dam (Cu-U-Au), Mt Isa & Broken Hill (Zn, Pb, Cu, Ag), Kalgoorlie (Au), Pilbara (Fe), Sydney-Bowen (coal), Argyle (diamonds), Wodgina (Ta), and Weipa (Al) to name a few.

A mineral system can be analysed holistically and with a process understanding by 'asking' five questions that characterise the ore-forming system, viz: what are the 1) geodynamic evolution; 2) architecture; 3) sources and reservoirs of fluids and metals; 4) fluid pathways and drivers; and 5) transport and metal depositional processes. We will address the question as to why Australia is so well endowed, by considering three world class mineral systems (Kalgoorlie, Mt Isa and Olympic Dam). This style of analysis not only aids improved understanding of 'why a deposit is there', but more importantly provides a basis for predicting the locations of undiscovered deposits.
The Archaean Kalgoorlie gold system (∼2500 tonnes Au) developed with the following characteristics: 1) rapid crustal growth in an extensional back-arc setting with high heat flow and mantle input; 2) mantle connectivity through deep faults linked to upper crustal granite-cored domes; 3) multiple fluid sources (including mantle) of contrasting chemistry; 4) reactivation (inversion) of a complex extensional architecture; and 5) strong physico-chemical gradients permitting fluid mixing.
The Proterozoic Mt Isa-Hilton-George Fisher base metal system (∼35 Mt Zn; 21 Mt Pb; 45 kt Ag) developed with the following characteristics: 1) back-arc extension leading to rift then sag basins (including mafic rocks); 2) ancient suture and diverse crustal blocks; 3) basinal brines and metals sourced from mafic rocks; 4) inversion of rift-related structures; and 5) oxidised fluids reacting with reductants.
The early Mesoproterozoic Olympic Dam Cu-U-Au system (∼7.7 Bt Cu; U; Au) developed with the following characteristics: 1) possible far-field back-arc setting with high heat flow, A-type magmatism and mantle input; 2) contractional then extensional reactivation of Palaeoproterozoic structures at the margin of an Archaean craton; 3) deep- and surface-sourced fluids of contrasting chemistry and contribution of metals from mantle-derived sources; 4), regional-scale Fe-oxide-K-silicate and Na-Ca alteration; and 5) epizonal to sub-volcanic settings permitting fluid mixing and reaction of oxidised fluids with reductants.
This talk will illustrate the power of integrating geological and geophysical data/information to better understand the processes of forming giant mineral systems. Advanced 3D maps (models) provide the necessary tools for integrating these multiple datasets in a common space, and examples from Kalgoorlie, Mount Isa and Olympic Dam will be illustrated.

 

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