Ann: PRE-FEASIBILITY STUDY AND UPDATED ORE RESERVE FOR CGP, page-58

someone else should check what they have used to get such a different IRR from original values.
My back of envelope calculation:
As an example just by changing the time period the first value below is 17% and the second is 37%
using IRR equals FV/PV All to power of reciprocal of time period and minus 1 from this result.
Thus
at 8 years using say FV of 3000 and PV of 850 gives 17% for IRR
BUT
same calculation and changing time period to 4 years gives 37% for IRR
DYOR