Techniques thumb|Underground longwall mining Mining techniques can be divided into two common excavation types: surface mining and sub-surface (underground) mining. Today, surface mining is much more common, and produces, for example, 85% of minerals (excluding petroleum and natural gas) in the United States, including 98% of metallic ores.Hartmann HL. Introductory Mining Engineering, p. 11. First chapter .
techniqueS thuMB|uNderground loNgwaLl miNiNG MIniNg techNIquES Can Be diVIdEd intO twO comMon eXcavatIon Types: sURfAcE Mining and sUb-sURFaCe (undergrOUnD) mining. ToDay, surFace mInIng is much moRE comMoN, aNd produCes, for EXAMPle, 85% of mineRals (ExclUding pEtroleUM And NatURal gaS) in tHE uNiteD stATes, inCludinG 98% OF MEtallic oRes.hartMann hL. IntroducTOry mining enginEeRIng, P. 11. first cHaPter .