idelfreebird opened a text book!   Random excerpt from mining 101 textbook. 
Well done sir!

If you only spent this time articulating how these deposits are economically feasible while not knowing how effective the technology they are using is.

idlefreebird wrote: Underground operations

Ramp decline to destination

 drilling round, loading round with explosives ,blasting ,mucking and ground support all the way down to ore body , ground support is 8-10 ft rebar , 4/8 meshed screen ,split sets ,amex powder and  resin for all rebar..also sumps need to be developed to accumulate water from levels

Water and Air lines ,electrical,communication lines plus ventilation need to follow this ramp and to all headings

Supply of water ,compressed air ,electricity and ventilation air all set up from surface wich require large compressors and pumps, sub stations and large fans for ventilation....high electrical cost..
safety bays and refuge stations set up on levels approx. every 100 meter decline..refuge stations supplied with water and compresd air in case of fire to pressurize room..

time factor is long 1 round per 10 hr shift

Ore body at 700 meters now requires a shaft, rail crew ,skips,hoist operators and much trucking waste and ore at those levels aren't economical..

machinery required but also in the open pit

Open PIT 

drill,blast,load and haul...