If you look at the major" underground " production companies they never show their entire hand. They only keep 1-2 million oz's ahead of production dependant on how much they produce. For San 1 million ozs is basically ten years mine life at 100k ozs per year. As production increases they will build reserves to keep it in the 10 year mine life category. Different with low grade high volume producers such as Redback and Osisko, where they have to prove up the entire property to see if it will be econonmic. Requires massive amount of drilling before a pre-feasibility study is done and they pretty well know entire reserves available before they mine the first ore. Requires huge tonnage to be profitable and major expenditure. Osisko ordered mills and trucks 3- 4 years ago and moved an entire town. Production is just going to start.

Hardrock shrink stope narrow vein mining is the most difficult type of mining there is, but it also usually returns the highest grades per ton and if grade is high enough sustainable because of low cost.