I've used the 50#, brown livestock mineral blocks for about 20 years or so in the same location, usually one in early spring and one in early summer. I placed the first block, years ago, on the ground and now there is a 2' hole that the block goes in. When the block disappears the deer eat the mineral rich dirt.
Spring and early summer is when the salt/mineral blocks are hit the hardest around here. I was told that as new, lush growth comes out the deer eat it and the heavy moisture content they get from this new growth flushes out their minerals thus the heavy use of these salt/mineral blocks during this time. They hit the "salt lick" all year long and over the years this salt lick had produced a major travel route for deer and other wildlife. All animals crave salt and minerals.