This is in the sense of oxidation state (ie; Redox). The copper is coming in an oxidised state (say, copper chloride ions) given off by, and I'm just pulling this out my butt because there's no clear mechanism to form Thaduna at 1575 Ma (no deformation, no magmatism, nada), some lower crust event. So the copper is oxidised and comes into contact with reduced rocks or minerals, and the chloride ions exchange with the sulfide ions, and this drops the copper out of solution. It forms minerals.
The minerals are formed by replacement of pyrite. This occurs commonly in fault-associated epigenetic deposits like Walford Creek (seriously check out AML's results) where copper-bearing fluids come into contact with sulfidic shales of a pre-existing SEDEX deposit. The copper displaces iron and converts pyrite to chalcopyrite.
Because there's a fixed amount of sulfur in the system, as more copper is added the tenor of the sulfides increases. This can be seen by looking through Ventnor Resources announcements, where they report chalcopyrite-pyrite-bornite in the top of Thaduna, then chalcopyrite-bornite, bornite, bornite-chacocite as depth increases. This goes from 25% Cu in sulphide to 80% copper in sulfide; so you make the copper deposit richer with depth.
The same *may* occur here. It's based on the report of faulting, vein arrays, etc. The difference is Thaduna is in greywacke made up of partly mafic derived sediment, with bitumen (the alleged graphite alteration). Graphite is reduced (all carbon is reduced), so it is the reductive trap. Look at Ventnor's photos of their "black shale" breccia; it's bitumen. it's a fault, filled with oil prior to the copper coming into it.
At Forrest, Wodger, etc, the reductive lithology is probably the basalt, maybe the magnetite bearing turbidites.
It will be interesting to see how SFR goes targeting similar structures in the Bryah. The prime places to look will be the Johnson Cairn Shale, and the shaley parts of the Karalundi Formation, and even the Killara-Maralouu in the eastern Yerrida. GTE, KZR, and yes even Riva have plenty of fault zones on the Thaduna trend. And SFR has just picked up a massive JV with GTE. Difficult place to explore, but it could be hiding wads of this stuff that won't show up readily on heli-TEM.
