mining methods

• Surface mining:

  • Soil and rock overlying the mineral deposit is removed and then the mineral is removed 
• Underground mining:

  • Overlying rock is left in place, and the mineral is removed through shafts and tunnels 
• Surface mining:

  • Open pit mining 
  • most minerals extracted this way 
  • Near the surface 
• Open pit:

  • Stability of slopes 
  • Horizontal benches are cut 
  • Rock bolts 
  • Prevents landslides 
• Open pit:

  • Pit is filled in after extraction 
  • Reluctant to fill mines due to future exploitation chances 
• Surface mining:

  • Strip mining 
  • Shallow, horizontal deposits 
  • Remove one layer at a time 
• Surface mining:

  • Visual - reduce overburden and make baffle mounds 
  • Noise - restrict times of blasting 
  • Dust - spray roads with water during dry weather 
  • Water - settling ponds to collect dust contaminated water 
• Underground mining:

  • Used when deposits are deep below the surface 
  • Vertical shaft or inclined passageways 
  • Drifts and crosscuts made to expose faces 
  • Broken rock hauled from face up to surface 
• Drift mines;

  • Horizontally into side of a hill 
• Underground:

  • Shafts drilled at a slope angle - slope mine 
• Shaft:

  • Vertically drilled shafts 
• Slope mining:

  • Pillar and stall 
  • Pillars support roof 
  • Extract In a grid around pillars 
  • Pillars are wasted 
• Pillar and stall:

  • If pillars fail then surface subsidence occur 

   
• Longwall mining:

  • Two parallel tunnels with a working coal face at 90 degrees 
  • Coal cutting machine cuts coal by passing along the working face and moving into new areas of coal 
  • Coal is removed by conveyor 
  • Hydraulic roof supports are removed to control subsidence 
• Deep coal mining hazards:

  • Coalification releases methane 
  • A spark and presence of oxygen creates explosions 
  • Coal dust burns easily, making the explosion more dangerous 
  • Oxygen is used and carbon monoxide is made 
• Coal explosion preventions:

  • Good ventilation to prevent build up of gas 
  • Monitoring gas levels
  • Enclosing electrical parts of machinery 
• Flooding:

  • Working takes place below the water table 
  • Water is pumped out as it infiltrates 
  • No breakage of water filled voids 
• Flood prevention:

  • Breathing apparatus if flooding occurs
  • Research mine for rock types and previous flooding 
• Groundwater pollution:

  • Dust from drilling 
  • Release of toxic heavy metals from ores 
  • Hydrocarbons from fuel 
• Roof collapse:

  • Weight of overlying rock causes collapse
  • Roof supported by steel bands or shotcrete - tunnels 
  • Seams - pillar and stall and longwall 
• Roof collapse:

  • Shallow mines are found in more weathered rock and are less stable 
  • Need extra support 
• Deep mining hazards:

  • Opening shafts releases pressure, may result in cracking or jointing 
  • Rock bolts used to limit impact 

   
• Deep mining hazards:

  • Heat 
  • Temperature increases with depth 
  • Air conditioning mines to ventilate