From what I have gathered from discussion is that by having multiple mines developed, it gives the flexibility to move your crews around to keep productivity at a maximum. There is a lot of work planning and then developing the stopes before the ore faces are ready to mine. If you have a glitch in one mine or face, the crews can be moved to work another vein. Proper exploration and planning can be done on each vein or lense as to minimize dilution and maximize productivity. Another example would be a breakdown of the A shaft hoist. Workers could be diverted to any one of the ramp accessed surface mines. If the company is paying these hard rock miners productivity bonuses, you better have a face for them to work or they are not going to be very happy.(neither are we)