removing copper from the top of copper node will reveal dirt underneath, however there is much much more copper below the dirt (only a small amount of copper on top)

I mine copper a different (safer) way... I dig along the edge of the copper, then dig straight down as far as it lets me, then turn and dig right into the copper node at the bottom...

https://steamcommunity.com/sharedfiles/filedetails/?id=2919888706

Digging into the copper like this will give an underground "cave" inside it, and enemies can't / won't be able to reach you, as long as you keep the top of it (at ground level) intact.... This also removes any dirt (wherever you dig). inside the copper node.

Once you have carefully dug out the inside of the copper node, you can actually set up things you need like a workbench (for tool repair), portal, coal kiln, smelter, cooking fire, bed etc...

https://steamcommunity.com/sharedfiles/filedetails/?id=2908646625

https://steamcommunity.com/sharedfiles/filedetails/?id=2858961419

This gives you a safe, easy place to process your copper ore, without having to transport it all back to some distant base, and once you process some of the copper you can craft a forge and actually make bronze and various tools/weapons right at the mining site.

Even if you don't want to make an outpost under the copper, It is still safer to mine it this way (from under it) because the enemies can't get you unless you open up large holes in the top, also this removes all the dirt so you can mine ALL the copper.