Well what we used to do was take a few of the brown mineral blocks and an ax/maul, and chop them up into chunks. Than we took the chunks and used them to rebuild a section of old stonewall. The section we rebuilt just happened to be at the opening through the hedge row, which was across from my stand. This was done during summer, and the chunks would break down over time from the rain, the area under the wall is quite rich in salt and mineral, which has leached into the ground, and than the deer tear it all up. By hunting season there is nothing left of the chunks of blocks.
I have never actulay seen any deer useing the mineral, but I know that they are.