RE: Salt blocks and mineral blocks?
I've had mineral licks out for 3 years now and they definetly get used from late march through late august. Before that and after that they will get visited but not as often. Personally digging and spreading granular mineral (3' to 4') is the best (you can put a block there to if you want) Granular mineral they actually eat the ground, not lick. If you want them to consume the mineral for rack growth granular mineral is the way to go. Salt is a good attractant, but isn't going to help out in the rack department. When ever I starta new mineral lick I'll put some corn on it and mix it in every couple days for a couple weeks so they find it and get a taste of the mineral site.
Good Luck!