Is there a "rule-of thumb" going rate for a Coal...

Is there a "rule-of thumb" going rate for a Coal resource.
Compared with peers, what's a tonne of coal in the ground mormally worth.
And what's 30 Billion tonnes worth?....(presuming SPX has that much).....Just trying to get a handle on a possible future valuation.

If we had 30 Bill tonnes it appears that the market would currently be valuing each tonne at a tenth of 1c!

If we have 3 Bill (which looks like it will be easily proved) we are valued at 1c per tonne.

Is $1 a tonne normal?....50c?