Lol, do a little Google search for something called a potash tailing pile. Gigatons of free salt, usually a little contamination of potassium, clay, various carnalites, and sometimes some chemicals from the milling process, but still about 98% salt.

The problem is that salt is so INCREDIBLY cheap, it's not worth refining to get that 2% contamination out. It's usually cheaper to mine it in a more pure form, and then ship it a thousand kilometers to where it needs to be sold.