Interesting question, I've also wondered how they would mine something like Humaspunco. I'd imagine that simply mining the veins and mantos would soon leave the hill unstable - also probably not easy where the mantos are flat or shallow-dipping. Certainly a fair bit of infilling and stabilisation works would be required.
On the other hand, removing the whole hill and effectively building it up again slightly smaller not far away would leave you handling a lot of waste and cost a lot of money... unless the Peruvian government wants to build a highway nearby, then you could crush up the waste and sell it as road base or fill material.
I suppose the material will require drill & blast unless it's rippable - I think the host rock is a limestone, but that can mean a lot of things in terms of rock strength - here in VIC we've got some limestones that are very hard and some that barely deserve the name "rock" and can be dug up with an excavator or a dozer. Some of the rock faces in the photos from Humapunco look like fairly competent rock to me, though.
By the way, a friend of mine who is an actual geotechnical engineer (unlike me, I just fell into a bucket of alphabet soup when I was three years old) tells me that it's not necessarily the strength of a rock that determines whether it's rippable - it's the defect spacing. Suck on that!
So, perhaps they could strip off the southern slope of the hill a few metres down to get most of the mantos, and then selectively mine the veins?
So now I've talked a lot, but I still don't have the answer.
Better go, looks like someone has FINALLY made me a father's day breakfast.
