there's a mexican miner called Primero (candian listed) with one...

there's a mexican miner called Primero (candian listed) with one narrow vein mine in i think its Sonoma state that has been running with less than 2 years mine life for the past 4 years at least, that's been operating for 100+ years

its common to not have much reserve i older narrow vein.

starting without a resource though is a lot less usual. but the reason behind both is the same - unless you happen to drill along seam of the vein you will psend a lot of money drilling but get not much idea about the amount of gold contained (unless the veins are very uniform)