2:2:1 ratio of white stock salt to brown trace mineral salt to dicalcium phosphate. The first two you can get at about any farm store. The dical can be harder to find, but usually grain elevators have it. In big cattle country its easier to find, as it is used as a cattle supplement. Avoid any mineral mixture that contains grain byproduct, distillers grain bypro, or wheat middlings.... it gets rotten fast when dumped and I've never known deer to use it.
The dical is a better mineral for them, but the taste of the salt keeps them using it.
R