"I think the huge variation in estimations and biggest question mark we have is how much per pound is it going to cost to get the product out of the ground? That would be the deciding factor on how much I would want to pay."

There are different valuation approaches depending on the stage of the project.  There's a reason why you spend $80 Million to achieve a Bankable Feasibility Study.  It is so you don't have to use a severe disounting method like a "pennies per pound" approach.  On an early stage and poorly defined project a pennies for pounds valuation approach naturally gives the buyer a really big cushion or margin because of so many unknowns in terms of size, grade, recoveries, capex, opex etc etc etc.  Lots has to be spent to prove Feasibility/profitality and after all that it may not even be close to profitable so a seller can't ask for much.

However with a Bankable Feasibility Study there is so much more clarity and hence derisking done that you now naturally use a much more reliable and fair valuation method (NPV) that respects the derisking and feasibility proof at hand.   Only 1 in 10,000 deposits becomes a mine.  With a positive Bankable Feasibility Study your project is graduated to a completely different league.