Our rules keep it Simple. Each Oil Field can have an Oil Derrick built on it increasing the value of said territory by 1 IPC. Can be destroyed by strategic bombers, reducing IPC value back to original value. Once a territory is taken by the enemy that has a Oil Field or Iron Ore deposit (which I’m making stickers for Iron Ore deposits also) the occupiers receive a 1D6 plunder roll. The IPC value is half, rounded up, and is given to at end of round. Once controlled for 1 round then the occupier can build an oil derrick. Only 1 derrick per territory.
So, in our game we spend alot of money on infrastructure. I’m thinking you can make my underground factories into Iron Ore Mines and do the same increasing of IPC value of territory once a mine is built.