Ah, I see, the penny's dropped - you've used EXT's costs and...

Ah, I see, the penny's dropped - you've used EXT's costs and discounted them by 20% and 30% etc. So total operation cost = e25 = $c25 * e23

This isn't really a valid way of determining costs. We're dealing with two issues here - processing the amount of rock dug up from the ground, and processing the uranium from the ore.

The first step - processing the rock dug up - will require much the same costs EXT & BMN as they dig up the same amount each, but it is reasonably cheap. The second step - getting the U out - uses expensive acid leaching etc, that is based upon cost per lb of U, not per lb of the raw rock dug up.

So, in this case, EXT and BMN both dig up 15 Mt of ore each year, but at different grades. So I would expect that the capex would be similar - the price of the digging rigs, the trucks to transport it, and the rolling/crushing mills. But the price to extract the U would be closer than in your spreadsheet.

Let's take EXT as an example - $23.60 per lb U. Let's assume that, say, one-third of this is due to digging up all the dirt and rock in the first place (dependant on per tonne of ore), and the remaining two-thirds is extracting it (dependent upon the U ppm).

(rounding) we get $8 per lb of U to dig up, and $16/lb of U to extract

Now, 1 tonne of rock = 1.074 lb of U at 487 ppm (EXT). We said it was about $8 per lb to dig up, so about $8.59 per tonne of ore. That will be the same for BMN, because it doesn't matter what the ppm is, this is the cost to get that much tonnage of rock out of the ground in the first place, and to grade and crush it for processing.

So, both BMN and EXT dig up 15 Mt or ore each year, at a cost of $8.60 per tonne (rounded) = $129m

In addition, they each extract the U at a cost of $16 per lb of U. EXT has 16.1 Mlb of U, so EXT costs are $258m. BMN has 6.7 Mlb of U, so BMN costs are $107m. Add them up:

EXT: $387m for 16.1 Mlb = $24.04 /lb <- a good check of our sums
BMN: $236m for 6.7 Mlb = $35.22 / lb <- a more reasonable outcome

I hope this is clear, it's difficult to explain. I'd like to know what the split is between costs per tonne or ore, and costs per lb of U (I assumed a 1:2 split). It would be easy to work out a generalised average from other operators' using their cost data.