Sedimentary geochemistry, geochronology and sequence stratigraphy as tools to typecast stratigraphic units and constrain basin evolution in the gold mineralised Palaeoproterozoic Tanami Region, Northern Australia

Rare earth elements (REEs), high-field strength elements and detrital zircon populations typecast and establish the provenance of siliciclastic sedimentary rocks of the Palaeoproterozoic Tanami Group. This group is the main host of gold in the Tanami Region, an important Proterozoic gold province in Northern Australia. These data also define chronostratigraphic surfaces which provide a framework for constructing sequence-stratigraphic models for the Tanami Basin. This basin model provides insight into the likely spatial distribution of deep-water facies, which are the best trap rocks for epigenetic gold deposition. The largest gold deposits are hosted in the well-bedded carbonaceous siltstone of the Dead Bullock Formation, which is the basal unit of the Tanami Group. At the Callie deposit, which is the largest deposit in the region, the host Dead Bullock Formation is characterised by: (1) enrichments of MgO, TiO2, Cr, Sc; (2) light REE depletion (relative to PAAS): (3) a dominant population of detrital zircons with an age of similar to 2500 Ma. In contrast, turbidites of the overlying Killi Killi Formation, which is less strongly mineralised, are characterised by: (1) enrichments in Zr, La/Sc, La/Sm, (2) relatively flat REE pattern, and (3) the presence of a major population of detrital zircons with ages of 1880-1840 Ma. These characteristics are independent of grain size and are interpreted to indicate that the Dead Bullock Formation was derived from a provenance dominated by Archean malic and felsic rocks, whereas the Killi Killi Formation was derived from a provenance dominated by felsic rocks of Palaeoproterozoic age. These characteristics, which are best shown using Zr/Sc versus Th/Sc diagrams, can be used as an exploration tool to differentiate the more favourable Dead Bullock Formation from the less prospective Killi Killi Formation. These data combined with regional geologic data provide a first order understanding of the make-up of the Tanami Basin fill, with implications for the distribution of siltstone-dominated facies that are the best host rocks for gold. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.