Ann: 2021 BFS Confirms Citronen as World Class Zinc Project, page-20

The main reasons give in the release are more conservative assumptions being used around:
- NPV discount rate of 8% used rather that 5%
- CAP costs increased due to inflation / change in mine plan.
- Less bullish zinc price forecast.
- Tax being accounted for more conservatively.

In other words, a level of realism with built in contingency that a banker prefers to see, almost a worst case as it were, rather than what you think is actually likely to happen.

My reading is that there is lots of contingency built into the numbers so more likely to actually be achieved and exceeded than the previous BFS that was more likely to not be met (some overly optimistic assumptions). It is a good testiment to management credibility that they have adopted this approach.

If you put up a BFS with some assumptions that aren't realistic and without some contingency built in bankers tend to be less comfortable - so I personally think it is a good result overall and reflective of an appropriate management approach.

If you used the same IRR, tax approach and Zinc price it would have actually improved according to the announcement.

Just my opinion DYOR.