The cost of constantly extending a decline tunnel that plays a part in the actual
extractive process is a revenue cost. The characteristics of such a decline tunnel are
that it is dug in a series of relatively small excavations. It follows the ore body and is
dug as close to the ore body as practicable. In addition, the decline allows for the
extraction of ore in the immediate vicinity, with the ore being extracted in a
relatively short period of time.