I don't see much risk in any pegmatites being too deep to...

I don't see much risk in any pegmatites being too deep to commercially mine particularly as there is exposure at surface. Have a look at Liontown where the lithium pegmatites are so deep they are developing an underground mine. The first hard rock underground lithium mine globally. I know LTR has one of the biggest lithium resources on the planet and a market cap of over $6 billion but it does show that deep deposits (>60m) can be exploited even in very remote areas with zero infrastructure, which is what LTR has. By comparison, SBR is infrastructure rich and likely very shallow cover over any pegmatites. IMHO.