If you use the granulated trace mineral salt mixed with di-calcium phosphate, it is the calcium and phosphate that is most beneficial to lactating does.
Di-Cal is non palatable unless mixed with trace mineral salt or any salt.

We dug a 3' x 3' hole in the ground about 10–12 inches deep. And just turned up all of the clay (didn't remove any clay). Then we do about a half a 50 pound bag of trace minerals from TSC. And then add 5 gallons of water (no water on our property unfortunately). And then we mix up all of the mud and minerals together. And it just creates a sloppy wallow sort of thing. The deer flock to the minerals and the water. The clay holds the water for quite some time even in the SC summer. But every time we go out we will add more water and stir up everything again. And then we add the remaining 25 pounds of trace minerals later in the year. I guess it works for us because we have clay, if you had loose beach sand it probably wouldn't work because it wouldn't hold the water. But just thought I would chime in as we have truly seen a difference on our property of them hitting minerals in the spring and summer. Not only do the deer use it, but the raccoons and the possums and the birds all frequent it as well.

Just to add on, we never had any luck at all with salt blocks or mineral blocks of any sort. Don't know why! We must have some picky deer.

As Squash mentioned. Does benefit much more in the spring from mineral supplements than bucks.

Against the law to put out salt in mi. even for cattle However our main roads have divots down the centerline to keep you awake while driving these fill with salt so Here salt is unhealthy for deer and porky's

we use water softener salt the deer and moose pick up the little tablets all year long have some monster holes from deer pawing the ground the bags of salt are cheap and easy to find

Thanks for all the tips and suggestions everyone. I’ve just been winging it with experiments over cameras. I don’t deer hunt but I do enjoy watching them and have been trying to figure this all out.
Thanks again everyone.
Jim