Copper nodes can run pretty deep and pretty wide. What you see on the surface is nothing compared to what else is hidden. I usually get between 100 and 120 copper per copper vein.

I usually start mining by going around the surface of the copper node that I see and mining as far down as the game lets me. Then I mine underneath in a big circle and finally, come on top and mine that.

It helps me to build a workbench and campfire underneath in the pit that I'm working on so that I can repair my pick and get my rested buff.