Ore respawn rate

So i need about 20 stacks of thorium i found a nice cave in Winterspring and it has 5 thorium veins (3 of them are rich),i mine them ofcourse and then i wait over 30 minutes for them to respawn.Btw 1 just respawned 5 minutes ago not all 5 of them so can anyone tell me the respawn rate or does my apperance influence on the ores ?

I believe herb/ore nodes respawn dynamically.

e.g. there are 100 possible ore nodes in a zone, but only 15 are spawned at any given point in time.
you pick 4 of them, so 4 will respawn shortly, across all 100 possible nodes