Valuation for Estate Purposes - TX


Hi, I’ve just found this forum and it looks like a great resource. I’m hoping someone can help me with a few questions please.

My dad passed away, and I have inherited some mineral rights associated with land that his family had owned at one time. He had three mineral interests in Texas, and all three are currently leased to a lignite mining company. For estate purposes, I need to place a value on the leases, and also (I assume) on the mineral rights themselves. I have copies of the leases, so I know how much the annual payments are (and they are very small amounts). My understanding is that there is currently no active mining taking place.

So my questions are:

  1. How do I assign a value to the leases? The leases have been in effect since 1992, and they get renewed at the end of each lease period. Is there some “rule of thumb” type multiplier? Do I project the payments out for some number of years? Do I calculate a present value of the stream of assumed future payments? I know how to calculate present values, if that is the answer. Of course a present value calculation would necessarily involve some assumptions, so then another question would be what reasonable assumptions would be for this type of calculation.

  2. How do I determine the value of the mineral rights themselves? I’m really not sure where to begin on this one …

Any information or insights would be much appreciated!
Thanks in advance!

p.s. I see that there are some similar questions answered here, but they seem to deal with oil and gas leases. My question is specifically for lignite leases (don’t know if that is different). Thanks.