You don't think you just dig a mine and the gold oozes out of the walls do you? They are "in production" it is as full as it can be and it doesn't matter how much ore you pull out if the yield is not enough to pay for it.
NBRI has yet to pull a sample of ANY kind that has enough gold to be feasible.
You can get whatever you consider "full" production and a .001 opt yield will shut you down.
Try mixing that DD with a cup of math and just a pinch of logic and you will understand the paradox of "full" production.