Please Google it don't take my word for it but the vets I work for get many cases over the winter from pets ingesting road salt.
Its common knowledge, ice-melting chemicals commonly contain sodium chloride, heavy metals, calcium chloride, potassium chloride, magnesium chloride, and urea, also known as carbonyl diamide, sheep and deer may lick it and move on as it is unpalatable, dogs walking on roads and getting irritated paws and cleaning their feet have needed vet care due to the chemical compositions ingested, its quite common.
Lick blocks on the other hand are a natural source of essential nutrients to supplement the regular diet. This pure form of salt contains up to 90 trace minerals that provide nutrition to animals. Furthermore, salt licks are perfectly safe and you don't have to worry about over-consumption.