There are ridiculous gobs of minerals everywhere, it will literally not be possible to exhaust them all, though finding good sites to mine can be difficult. In one game I have 62 ships in the 10k to 20k range parked over my capitol sucking down a lot of resources(12k of all types per year), but there are 4 thousand mines spread out over 5-6 mining colonies producing minerals for my capitol so despite having 3 full taskforces, I have quite the reserve of minerals and the ability to crank out ships should it become necessary. The mineral I have the least of is neutronium, at 128k in the stockpile, and the mineral I have the most of is Duranium with 1.693M.
What I lack at this level is cash, quite simply because I have enough resources to build way too much with 3000 construction factories, 400 labs, and 13 shipyards with 42 slipways between them.