The magnetite-rich host rocks of Razorback and associated iron ore prospects of the Braemar Iron Formation are located within Neoproterozoic basal sediments of the Umberatana Group, within the Nackarra Arc Region of the Adelaide Geosyncline.
A major geological province of South Australia, the Adelaide Geosyncline represents a complex system of successive intracratonic rifting and subsequent basin formation, and extends from Kangaroo Island in the south, through to the northernmost extent of the Flinders Ranges. The sedimentation of the diamictite-dominant Umberatana Group coincides with Sturtian Glaciation (750 to 700 Ma).
The Braemar Iron Formation is at its thickest in the Baratta Trough, a fault bounded basin located in the Yunta-Olary region of South Australia. The formation consists of a series of alternating bedded tillitic and interbedded magnetite rocks that represent cycles of glacial advances and retreats. It is also evident in the Hawson’s Knob area, SW of Broken Hill, NSW and is stratigraphically equivalent to the Holowilena Ironstone of the Central Flinders Ranges, South Australia. The Braemar Iron Formation is believed to be from the result of chemical precipitation during interglacial / postglacial periods and formed in coastal fringes, where oxygenated terrestrial sedimentary influence was strong. The iron was believed to be sourced from fault controlled conduits related to rifting during the evolution of the Adelaide Geosyncline.
The Braemar Iron Formation mineralogy is unlike that of banded ironstones seen in the Pilbara and Mid West, Western Australia in that Braemar sedimentary rocks are not made up of fine grained chert, but rather magnetite-bearing siltstones. This has significant cost saving for Braemar in regards to having lower rock hardness and abrasion during beneficiation and mining.
Updated November 2013