Lunar Mining Strategies
                                                           by David Dietzler 2008

Three Strategies

!) Scavenging. This method involves  using wheeled robots to shovel up regolith over wide areas, process the valuable materials out of the regolith onboard, and dump the spent regolith.  This will be used to recover substances in regolith that exist in very low concentrations like volatiles (H2, H2O, CO, CO2, CH4, N2, He and Ar.  H,C and N are deposited in the regolith by the solar wind and react with oxygen and hydrogen during roasting to form various compounds), iron fines that contain 5% nickel and 0.2% cobalt and probably ice crystals mixed with regolith in permanently shadowed polar craters.

See: Wireless Spiral Volatile Mining
Above) An iron fines miner.  See: Blister Steel and   Blister Steel 2
2) Open Pit MIning. Drag lines and mining shovels will dig large open pits for materials that are more abundant in the regolith and don't require covering millions of square meters to obtain.  This will be done to get regolith for magma electrolysis furnaces and titanium production.  Huge machines will work in the maria and dig pits 33m by 33m by 10m deep to obtain about 10,000 cubic meters of regolith or about 20,000 tons of it.  This will be processed in electrostatic separators to extract ilmenite that will be processed to titanium, iron and oxygen.  See: Titanium Production
From 20,000 tons of regolith about 400 tons of titaniium can be produced at 100% recovery but in reality more like 50% recovery is likely, thus 200 tons of titanium can be produced from a pit like the one described above.

After ilmenite extraction the regolith would be fed to several  magma electrolysis furnaces to get oxygen and impurities of Na, K, P and S that will be filtered out in cooling traps and have value in themselves; ferrosilicon and ceramics that will be cast in "ice cube tray" molds with cooling.  See:  Molds and Mold Materials.  
A 70 tons magma electrolysis unit using 3 MWe could process 5000 tons of regolith per year and yield 1000 tons of oxygen and 4000 tons of FeSi and ceramic blocks (1).
See: Magma Process
ABOVE) A dragline.  These machines can dig massive pits.  We would have to upport the dragline in parts and assemble it on the Moon.  If we can produce enough steel by scavenging for iron fines and using the blister steel method we might be able to extrude the parts for the trusswork and weld it up on the Moon, so we'd need to upport an extruder first. We could make the steel cables also on the Moon.  Power will come from a cable connected to a solar power plant. The dragline digs deep but doesn't move far from the main base.  Other parts for the dragline might be made on the Moon by rolling steel into plates, casting steel, extruding frame parts, and making aluminum cable for electric motor coils.  By making part of the dagline on the Moon and upporting that which can't be made on the Moon upport mass and costs are reduced.
3) Tunneling. It might be possible to blast tunnels into rock and into central crater peaks that might contain unusual minerals upthrust from the lunar mantle.  Perhaps layers of chromite exist deep beneath the lava plains (maria) of the Moon and some of this chromite has been upthrust into central crater peaks.

See: A Lunar Explosive.
1) Development of the Moon.  Michael B. Duke et al.  section 4.3.5.1 pg. 40
http://www.lpi.usra.edu/lunar_resources/developmentofmoon.pdf
ABOVE)  Dragline can mine massive amount of regolith. Auger feeds regolith into solar furnace that boils off sodium, potassium, iron oxide, silicon dioxide and magnesium oxide leaving a CaO and Al2O3 enriched mixture that can be mixed with water, "sand" and gravel to make concrete for use in metallic and inflated  pressurized habitat modules and in lava tubes.  Another auger moves cement mix out of solar furnace after roasting is complete.  Welded iron plate condensor separates Na, K, FeO, SiO2 and MgO. Exact dimensions will require computational fluid dynamics analysis and hard experimental data gained at research bases on the Moon.  Sodium and potassium form a euctectic alloy for solar thermal systems and can be converted to chloride salts for thermal systems and used for agriculture, sodium silicate adhesive and sodium hydroxide and table salt for soap and glycerin making.  Also KOH as hydrogen oxygen fuel cell electrolyte.  FeO can be reduced to iron with carbon and solar heat or tossed in magma electrolysis furnaces to save carbon. SiO2 will make pure silica glass for solar furnace windows and fused silica could be used for furnace linings.  MgO can be reduced with FeSi from magma electrolysis in a flux of CaO or possibly CaAl2O4 in a solar furnace.  Magnesium evaporates from the furnace running at 1200-1500 C at low pressure obtained from free lunar vacuum and is condensed.  Magnesium reflects 74% of light falling on it and is only 64% as dense as aluminum so it will make better low mass reflectors/solar collectors.