 High wall mining can produce thousands of tons of coal in contour-strip operations with narrow benches, previously mined areas, trench mine applications and steep-dip seams with controlled water-inflow pump system and/or a gas (inert) venting system.Sub-surface mining consists of digging tunnels or shafts into the earth to reach buried ore deposits.Ore, for processing, and waste rock, for disposal, are brought to the surface through the tunnels and shafts.