Again, not a geologist (or glaciologist), but glaciations happen frequently, in geological terms - every 40k? years or so. And, they don't dig very deep. Mines

Again, not a geologist (or glaciologist), but glaciations happen frequently, in geological terms - every 40k? years or so. And, they don't dig very deep. Mines go >1km deep, so are below what I think any glaciation would have an effect on.