Preproduction is the mining ore that results from building the infrastructure of the mine. Our mine is considered to be in production this Dec. While the build the ramps and sills, they can mine from the upper sill, at the same time as the remove the rock to build the ramps to the lower levels where there will be an additional sill and midway (approx ) where there will be another one. So ideally when they finish the midway sill, they can mine the upper sill and middle sill and continue building the ramp to the lower level. The sill is like a hallway and we will create "rooms" where they will lay charges, blast and then take the rock "ore" away. Sometimes this is done over two days. Then the process is repeated all over again until they have finished the area. Anyway, that was how it was explained to me.