Isn't the idea here to gasify the rock by essentially microwaving it? With ultrasound, wouldn't you still need to remove the leftover rocks?

[Thermal fracturing or spallation, meant to displace or weaken the material for excavation] does gasify some of the water and minerals, but excavation is still necessary.

I started designing a combined unit for this (mmwave + ultrasound) with TLA+ and Rust, but don't have any use for drilling and tunneling myself.

I got into this because a bronze scepter of certain dimensions might carry a 28 khz resonance for ~30s, which - with nanodiamond drilling sand from e.g. pyrolyzed ash and sand - could explain the observed ancient copper core drilling speeds.