Another very exciting possibity that I haven't previously given...

Another very exciting possibity that I haven't previously given much thought to; is the potential to mine Weolyu, Kochang and other hilly sites by Adit or Drift mining.
The picture of the sub horizontal drilling with the Weolyu Hole 3 implies to me that horizontal shafts could be a very efficient way to mine these areas. Perhaps this is another huge reduction in the cost of mining. It could also speed up the process of extracting the first ore, far more than other types of UG mining.

https://en.m.wikipedia.org/wiki/Adit