Not really comparable. These guys have gotten as far as a preliminary feasibility study, proving the economics of the deposit and moving ounces into P&P. GNH's ounces are really still just inferred, so they get valued lower. Also, Vista has existing utility infrastructure (gas & hydro).
On the other hand, of course, Vista's grades are pretty darn uninspiring, and their after-tax IRR (the only IRR worth looking at) is frankly terrible - especially since they're only using a 5% discount factor (naughty naughty). The capex is way high too, so that should weigh down on their price. Such a deposit should be hard to sell - this release reads like the company knows it.
I'm no expert at this so the above may be wrong - I'm just going by what I've been learning by reading valuation newsletters.