Some respawn nearly imideately Hickory Tree was back in about 15 minutes
Copper veins respawn overnight .. so several hours
Coal,Clay,Sand those once mined out are gone until server restart
Maybe check them and make them more useable? (Like coal is really rare at the monent as only 5 coal digs spawn per server restart netting around 5-8 coal lumps (depending on luck), and at best making bronze take minimal 3 + one lump for making molds for weapons at tinkers furnace .. )