RE:Perkoa Life-of-MineGalv,
caveat - I have not done any significant research into Perkoa mine plans
Reserves are based on a specific cut off grade (tied to the value of the commodity), in Perkoa's case in 2018 it was $1.20 / lb. As a general rule of thumb, when prices are significanty above the forecast price, mines have the flexibilty of going after lower grade ore because it is now profitable to do so.
Sometimes when you see decreasing head grades, decreasing production and increasing costs ==> it's simply ineptness but sometimes it's a short -term change in mine plans developing these slightly lower grade ores (that are now profitable) and leaving the high grade ores for later extraction. this extends the mine life without for further exploration
Rockaur