Dreamwalking
Peter
It looks to me to be most likely a banded fine-grained pyrite in shale and very likely formed in Precambrian times. Pyrite is common in many hydrothermal veins, shales, coals, various metamorphic rocks, and massive sulfide deposits. These sulphides originated as mentioned by Stalker whilst Australia was 80% submersed beneath the ocean, eventually in the drying stages the sulfate source becomes evaporitic gypsum which when subjected to metamorphism ( compression and heat ) created the pyrite crystals. The coloured bands are more so due sedimentary deposits of different particles sizes deposited during erosion ... same as when you are panning off ... the amount of force (water flow) determines the size and weight of your residue.