Am I wrong to think of metal deposits as just "rust mixed with rock"? It doesn't seem like the rock part (i.e. the details of what it is mixed with) should be critical for the extraction process?
> Am I wrong to think of metal deposits as just "rust mixed with rock"?
They're concentrated rust mixed with rocks, otherwise it's not economically viable to extract.
Like, iron is ridiculously common, relatively speaking: on earth as a whole it's more common than oxygen, for the crust it ranks 4th at 5% by mass, meaning if you went at it randomly you'd need to sift through 20kg of materials to get 1kg of iron.
Currently, we exploit formations as low as 15% iron (banded iron formations / taconite), that's the lower limit of the economically feasible, and those results in absolutely enormous amounts of tailings (waste materials).
Pre-industrialisation, unless you had no other choice (e.g. only had ironsands to work with) you really wanted to exploit natural (or "direct-shipping") ores, in the 60~70% range, the extraction is way too much work otherwise.
