Building on Chasly's answer.  IF a device was able to do this.

Essentially, it would be an "ultra-htper-amazing *mining* device".

So, it would have the (astonishing) ability to mine (completely underground) for likely *100s or even 1000s of miles in all directions* ...

(perhaps sending out small mole-probe things {which would need an unbelievable amount of self-contained power} or alternately drilling/sealing/etc incredibly long shafts in all 3D directions...}

... so as to gather the various raw materials it would need.

Even if you do hand-waving about energy (so, far beyond mere anti-matter batteries, it uses some sort of astounding Inertial-frame-Mach®™ extraction of energy with physics unimaginable to us, so that it just has an insane amount of power at all times), 

the whole thing would have to be an unprecedented "secret mining system" which gets the stuff it needs on a *continental-scale*, with a massive web of underground tunnels/whatever 100s to 1000s of miles long. (While maintaining secrecy, etc.)

Cool!