Question

Hi,
I am trying to apply real option valuation to a non listed company. It’s a brine mining company. Now I wonder how to go about finding a relevant standard deviation. In case of a stock it is doable. But in this case I have only estimated future cash flows and need to come up with an idea about the volatility. I was thinking to make use of certain indexes for instance a Brine index, if it exists, as a proxy.
Thoughts on how to go about it are welcome!
Cheers, Sander