Reduced is the opposite of oxidised - it is water low in oxygen (chemists would say low oxygen fugacity, but don't worry about names). With certain types of gold deposit, the ore fluids are hot and reduced and neither acid or alkaline (intermediate pH - but don't worry re names)- in water of this probable metamorphic origin that rises from many km depth, significant hydrogen sulphide can be present. Hydrogen sulphide bonds with gold as gold bisulphide complex and in this way the water can carry a lot of dissolved gold (ordinary fresh water would not dissolve gold). This water rises to shallow depth where it hits ironstone or carbon and the gold bisulphide ion reacts with either of these to deposit metallic gold (e.g. if it reacts with iron the sulphur will form pyrite - iron sulphide - from the sulphur in solution as the gold drops out, so you will see pyrite and gold together with ironstone and carbon-rich slate). This ironstone is commonly magnetite because the iron minerals hematite and limonite do not cause the same effective reaction. So there is a good chemical reason why gold occurs associated with ironstone (eg Hill 50 at Mt Magnet) or carbon-rich slate (eg Bendigo).
This is not the only way that gold moves around. In the low-temperature zone of weathering close to surface, the pyrite in an already-formed gold ore body will oxidise (in contact with oxygen-rich rainwater) to form acid (low pH) water and if the water is very saline like in the outback, the gold will dissolve as a gold chloride complex (ie salty water contains sodium chloride, common salt). Ordinary dilute (non-acid, non-alkaline but neutral pH) rain water will not dissolve gold but highly saline and acid groundwater formed from rain and salt and oxidising pyrite will). This will trickle to greater depth with its contained gold (only tens of metres as a rule) and react with ironstone to deposit gold again. This is where you commonly see coarse gold associated with weathering ironstone (ferricrete), often in rock that is altered to white kaolin clay. A lot of the ironstone will be hematite and limonite in this case. Sometimes bauxite is also present (an extreme aluminium-rich product of weathering formed when even the silica gets dissolved out of clay to form aluminium minerals such as gibbsite and diaspore without silica). The upper levels of Boddington were of this type, and bauxite (aluminium ore) was produced as a by-product, but nowadays they mine the original primary ore at greater depth below the bauxite, clay and ironstone (ie in deeper in fresh rock).
I can understand how these two different processes can become confused in people's minds when they read different accounts, one discussing how the original high temperature gold deposit forms, the other discussing how the ore deposit is subsequently modified by weathering near surface. I hope I have made it clearer.
Of course some gold deposits can form by other means, but are less common (eg if you heat rock salt deposits buried in rocks at depth and dissolve them, gold can travel to shallow depths in these hot fluids, also as gold chloride complexes, and be reduced and deposit gold when they hit ironstone at shallower depth (eg gold around Cloncurry such as Ernest Henry, or perhaps Olympic Dam and Tennant Creek ore bodies).
Another method is in very hot chloride and hydrogen sulphide-rich fluids that are emitted from molten igneous intrusive bodies (eg Cadia).
And once any of these high temperature gold deposits form, they can also be later modified in the weathering zone as described above....
This is why gold is not simply "where you find it" - it forms in specific places following well-understood chemical processes. So a bit of knowledge increases your odds of success....