The Tabac Project is located within the Yerrida Basin (referred to previously as the Glengarry Sub-basin), which lies on the northern margin of the Archean Yilgarn Block, and forms part of the Capricorn Orogen. The Yerrida Basin represents an intracratonic sag basin containing siliciclastic rocks and evaporites of the Windplain Group overlain unconformably by siliciclastics and mafic extrusive and intrusive rocks of the Mooloogool Group. Within the Project area, outliers of the Yelma Formation of the Earaheedy Group unconformably overlie rocks of the Yerrida Basin.
The Windplain Group includes the Juderina Formation, which crops out in the southern third of the Project. The Juderina Formation comprises of siliciclastics (deposited as continental “red beds” or haematite-rich sandstones and siltstone), evaporates, argillites, and locally turbidites. It includes the chertified stromatolitic carbonate and evaporitic sedimentary units of the Bubble Well Member, which is the likely mineralised host at Tabac.
The depositional environment for the Windplain Group is thought to be a shallow epicontinental (or inland) sea, locally with sabkha (salt flat) environments.
Archean rocks of the adjacent Joyner’s Find Greenstone Belt formed a number of basement highs (or coastal headlands) during the shelf sedimentation phase. Sediments deposited west of the headlands predominantly comprise shales, whereas those deposited between or east of the headlands are mainly composed of carbonates.
Within the southern parts of the Yerrida Basin, sediments are commonly flat-lying. Any folding is very gentle, and where described comprises north-northwest and northeast open folds. The overlying Earaheedy Group sediments appear to have undergone relatively minor structural deformation.
The palaeoenvironment at Tabac, including the types of rocks deposited (evaporites and carbonates), their age (Proterozoic), site of deposition (platform sediments), and the broader geological context of a developing fold and thrust belt, is analogous to Zambian Copperbelt and/or Kuferschiefer-style mineralisation.