The Iron Bridge mineralisation lies within the Pincunah Member of the Soanesville Group, which is part of the Pilbara Super Group in the East Pilbara Terrane.
Regionally the rock sequence is dominated by mafic to andesitic volcanics and volcaniclastics, BIF’s and terrigenous clastic sequences intruded by Archaean granitoids. In the project area the rocks have been tightly folded, having a general strike of north-south with a steep sub-vertical dip.
The Pincunah Member forms an overturned north-south striking ridge through the North Star area of the deposit, dipping steeply to the west. Several vertical faults have been interpreted to rotate the Pincunah Member to north-west, parallel to the Mount Yule Granite complex in the north-west region of the project area.
Iron mineralisation at Iron Bridge occurs primarily within the Pincunah Member which outcrops across the entire project tenement. It is often masked by cemented caps of ferruginous weathered BIF, silcrete and detritus. A surficial weathered zone forms in upper (20–60 m) horizons dominated by maghemite and kenomagnetite, hematite and goethite after magnetite.
The hanging wall of the Pincunah Member is the Kangaroo Caves Formation and is composed of BIF bands interlayered with laminated, micro to mesobanded shales and chert. BIF units are up to 15 m in thickness and occur most commonly immediately adjacent to the Pincunah Member contact, while the remainder of the formation ........
