From my experience PFS studies generally work on a pretty broad...

From my experience PFS studies generally work on a pretty broad costing base, in the order of +/-20%. Basically it gives the company an early indication of if the project is looking like being feasible. Obviously Bawdwin will be economically feasible, this study will just outline indicative costs and the sort of margins that could be expected.
Once they clear this hurdle the BFS or DFS will tighten up the costs and margins, and streamline the processing route etc.
Cheers
MTC