depends on how much you need to spend to retrieve the gold.
so old mate who trips over a 2 kg nugget reaches down and pockets 80 grand for the cost of his time and fuel.
you could have 10 Moz at such low grade and high cost of capital (not operating cost) which could sit there for 100 years and not be touched.
generally, for a small-mid size shallow open cut, from scratch (no infrastructure) you probably want 1Moz
at 1.5 grams/tonne to make a potential cash cow.
for narrow underground you probably want 3-5 grams/ tonne and 2 Moz plus.
for bulk UG you could probably go with 1-2 grams at 3-4 Moz plus.
really comes down to (metaphorically speaking) can you get it for a decent margin.
when starting from scratch you need to convince a whole bunch of money that it is worthwhile.
and you somewhat need to prove it.
If one were to find 1 Moz at 3 plus grams/tonne there should be a strong case most options considered.
but old mate with his lucky 2 kilo on surface might beat your return in all the interim uncertainty on all the factors that go into making a viable resource.
best rule of thumb is grade is king, secondly size, thirdly capital to activate.
