Summary:
The Panton Intrusion is a layered mafic-ultramafic intrusion situated within the structurally complex Central Zone of the Halls Creek Orogen (“HCO”), in the Kimberley region of Western Australia. The HCO consists of three north-north-easterly trending, highly deformed, medium to high-grade metamorphic zones comprising sedimentary, volcanic and intrusive rock suites. The HCO separates the Paleoproterozoic Kimberley Basin to the northwest, and the late Archaean Granites-Tanami Region to the southeast.
In outcrop the Panton intrusion is a 12km long, 3km wide and 1.7km thick layered, differentiated ultramafic-mafic body.
The Panton intrusion comprises a basal ultramafic zone of chromite rich olivine cumulate rocks; dunites, peridotites and transitional rocks, with an overlying mafic zone of similar thickness made up of leucogabbro, gabbro, ferrogabbro, gabbronorites, norites, pyroxenites, and anorthosite units.
The Panton intrusion has undergone a number of structural deformation events. These various events have resulted in large scale folding, faulting and widespread shearing of the ultramafic/mafic sequence. The intrusion is asymmetrically folded into a tight syncline, which gently plunges to the southwest. The fold is closed at the north-eastern end and faulted off at the southwest end. Other dominant structural features include the numerous small scale and lesser large-scale faulting. The main orientation of faults strike north-south and nearly all have a sinistral movement sense; with displacements from cm scale to in the order of 1,000m for the large fault separating the C and D sub Blocks. Faulting orthogonal to this set is present but less pronounced.
The interpreted weathering profile for Panton is relatively simple, showing a resemblance to the topographic profile. There is a thin veneer of highly weathered material, consisting of predominantly red-brown soil, alluvium and colluvium that covers much of the project area. Its depth ranges from a few centimetres to up to 10m but is largely confined to less than 1m.
In all there are three mineralised horizons, the Upper group chromitites (situated within the upper gabbroic sequence), the Middle group chromitites (situated in the upper portion of the ultramafic cumulate sequence) and the Lower group chromitites (situated toward the base of the ultramafic cumulate sequence). The primary PGM resource is contained within the upper portion of the ultramafic sequence, which in turn has been divided into five zones:
1. Top Reef Mineralised Zone: a sheared chromitite/talc-carbonate-chromitite rock zone (average 1.5m true thickness);
2. Upper Dunite: comprising all rocks between the top and middle reef mineralised zones;
3. Middle Reef Mineralised Zone: a thin (average 0.5m true thickness) chromitite reef with an associated talc-carbonate alteration halo;
4. Lower Dunite: comprising all rocks between the middle and lower reef mineralised zones;
5. Lower reef Mineralised Zone.