Salt mines are a new building I'm adding to Ascendant Dawn. Salt was historically a very important commodity used to preserve food. The two main methods used to obtain salt were salt pools by the ocean that would evaporate sea water and leave behind salt and salt mines. 

Because Ascendant Dawn doesn't see far have a good way of checking for sea so far(technically I could do it but I haven't yet) salt mines are the only method I could easily implement. Salt mines aren't like other types of mines but rather buildings that can be built and upgraded everywhere. 

Salt is consumed by all population types and is a mid value trade resource.