[TFT] So what the hell does "Mine 20 gold in one stage" mean?

Seriously, Riots TFT mission descriptions are atrocious; inconsistent and oblique. First we had the Carousel debacle (even ignoring the bug, the round number _didn't_ match up with the round given (2nd Carousel)...), now we have "Mine 20 gold in one stage". What exactly does 'mine' mean here? - Spend 20 gold in one stage (probably not but you never know with Riot...) - Reroll 20 gold in one stage? - Have 20 gold saved? I just don't know. The terminology 'mine' has not been used thus far, so why throw it in a mission now?!
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