43 CFR 3594.1: Ultimate maximum recovery.

(a) Mining operations shall be conducted in a manner to yield the ultimate maximum recovery of the mineral deposits, consistent with the protection and use of other natural resources and the protection and preservation of the environment—land, water and air. All shafts, main exits and passageways, as well as overlying beds or mineral deposits that at a future date may be of economic importance, shall be protected by adequate pillars in the deposit being worked or by such other means as approved by the authorized officer.

(b) New geologic information obtained during mining regarding any mineral deposits on the lease shall be fully recorded and a copy of the record furnished to the authorized officer, if requested.