Paleoproterozoic stratigraphy and gold mineralisation in the Granites-Tanami Orogen, North Australian Craton

Abstract

The Granites-Tanami Orogen (GTO) is a significant auriferous province located in the poorly exposed southwestern part of the North Australian Craton. The stratigraphic succession of the Paleoproterozoic Tanami Group in the orogen is hard to define conclusively, owing to the general lack of outcrop, and is best understood by studying orientated diamond drill holes, such as those at the Dead Bullock Soak and Tanami goldfields, and the Groundrush and Coyote gold deposits. The group is broadly a succession of turbiditic sedimentary rocks included in the Killi Killi Formation conformably overlying shale, mafic volcanic units associated with abundant dolerite and diorite sills, and chert nodules and bands in the Stubbins and Dead Bullock formations. The Mount Charles Formation, previously inferred to be younger than the Killi Killi Formation, is lithologically similar to the Stubbins Formation and also overlain by the Killi Killi Formation. Based on whole-rock and trace-element geochemistry, geochronology, lithostratigraphy and the principles of superposition, the ca 1864 Ma Stubbins, Dead Bullock and Mount Charles formations are here correlated and assigned to the Dead Bullock Formation of the Tanami Group. The deposition of the now extended Dead Bullock Formation was in a back-arc basin setting to the east of the Halls Creek Orogen. Deposition in the basin changed with the introduction of sand-dominated turbiditic successions forming the Killi Killi Formation before ca 1850 Ma when collisional tectonics between the GTO and Halls Creek Orogen resulted in the development of northerly trending isoclinal (FGTO1) folds and associated layer-parallel faults. A second (DGTO2) major collisional event followed at ca 1795 Ma, which is associated with orogenic lode-gold deposits at Callie, Groundrush, Old Pirate and Coyote, and the intrusion-hosted Buccaneer gold deposit in the GTO. This was a period in the history of the GTO when granitic rocks were emplaced shortly before or synchronously with gold mineralisation at ca 1795 Ma.