Build a portal back to your main base before you start mining. You can drop off the stone and repair your pick. I built a huge (50 meter x 50 meter) base with an earthen berm and dry moat in the meadows and a 25 meter x 25 meter base with earthen berm in the plains just with stones that I gathered while mining and from killing graydwarves.

I still have 3 carts full of stone and a black metal chest full of stone that I haven't used yet.