W geologii zasoby bilansowe = recoverable resources. Przyjmuję, że chodzi o górnictwo węglowe, stąd "coal" w odpowiedzi.

recoverable reserves - portion of known demonstrated reserves that actually can be extracted from the earth and delivered to market with today's mining techniques
http://www.ket.org/Trips/Coal/glossary.html

seam--A bed of coal lying between a roof and floor. Equivalent term to bed, commonly used by industry
http://www.eia.doe.gov/cneaf/coal/reserves/glossary.html