Originally posted by Pat Fenis:

Expose the whole thing removing dirt and undermine it to collapse.

Yeah, this statement is demonstrably false.

That doesn't work with copper deposits... or at least, the 4 times I did it expecting it to collapse like a house with no support didn't act like that. To add insult to injury, having to build scaffolding to be able to reach the floating voxels, then falling as soon as I break through was an exercise in frustration.

I don't know if there's a collision glitch, or something, but if my character can pass through the smallest gap between the copper and the surrounding dirt, it should absolutely collapse... but it doesn't.