I'm sorry, but are minefields meant to be invisible through the fog of war? I always thought they were represented by a black 'x', like everything else.
Yes, minefields are meant to be represented by a black X if they're unknown. They're not totally invisible.

War Phase - Turn 1 // Gen. Marshall
Highlights:
Gen. Marshall's elite armor crushes Canadian_95_RTS' garrison at 11.01, taking 5 damage in the process.
It's still Gen. Marshall's turn.