That and similar approaches do have merit to other metals and even to some non-metal resources.
I use an estimate of what the economical value is in the ground and devalue according to the development state of the company.

Basicly devalued to a percentage of gross in-ground value:
Early exploration such as surface samples, trenching are below one percent ( highly speculative).
Early drill results 1 to 2 %.
Some stucture defined, 2 to 4 percent.
An NI 43-101, means 5%.
Feasability study completed with reasonable semblance of financing, 10%
Permits, financing and basic infrastructure present ( commencement of mine construction ), 20%.
Mine built and starting operations, 40%.
That devalued $ number I distribute over shares outstanding.

Very crude but sufficient for me. Ed G.