So HIGH GRADE ore bodies en mass will be the most highly profitable to operate. 

Gold is in the same quandry, HIGH grades are dissapearing at rapid pace to offset consumption.   Although HIGH grades of GOLD are really high in certain few projects, the real Giants are the Biggest mining companies, those already with Gigantic massive tonnage at low grades.  Just let me say Fort Knox, BARRICK,GLENCORE,NEWCREST,NEWMONT are Banking big sums garned from the low grade bulk tonnage projects. 

(?)  they are very cost sentric and are Masters of budget control over their projects.