It just isn't that simple...I wish it were.
If you are feeding mineral that contains salt and you have alkiali spots in your pasture, your cattle probably need a mineral with less salt. (Cows won't overeat salt unless they are forced to; and they won't overeat phosphorus. Both are limiters.)
Cattle can also build a tolerance to salt if fed too much. That is why we don't want anyone mixing the salt with the mineral. If you want to feed extra salt, put it beside the mineral, not mixed in. The salt requirement for cattle isn't very high and is mostly important during hot weather. What benefit do we get from over feeding salt? I can't think of any. Ranchers use it to cut down on mineral costs, but the mineral can't do its job as well when it is diluted with salt. I explain it this way: "You wouldn't give your cow a 1/2 dose of vaccine, would you?" Same thing applies to adding salt to mineral.
Cattle on gumbo won't eat much mineral. You have to feed a special kind in that situation; one with lower phos and no salt.
In our area, which is a big area, most of the cattle eat the same mineral based on grass samples. There really isn't a wide variation. Once in a great while, we will find a tie-up or something odd, but we only have one ranch in a huge area that has to feed a different blend. Our customers basically use one of three blends and everyone is very satisfied.
Interesting that Simmental and Charolais cattle have higher mineral requirements than other cattle. This information has been documented in many studies. It has something to do with their metabolism being slower.
Hope this helps, and I didn't confuse you. I got a little off-track there.