AL, with 60 chickens, I'd be surprised if your left-overs would go very far.
This book
Mineral Tolerance of Domestic Animals, gives 2% dietary salt as the "maximum tolerable level" for chickens and turkeys. You should note that this is a lower level than for cows and sheep.
In
Nutrient Requirements of Poultry, none of their chick diets have as much as 1%.
With the adults eating say 110 grams of feed each day - 2 grams of salt would be only tolerable. Perhaps, 1/2 gram would be needed.
A teaspoon of salt is about 5 grams. It looks like that would be just about enuf to kill a hen. Maybe even a half of a teaspoon would be fatal.
On average, American adults are eating over 8 grams of salt a day but we are consuming that with about 2 pounds of food (still too much salt!). That's enuf food for 5 or 6 chickens. Two pounds of food is about 1,000 grams so our food is a little too salty for a chicken but IF WE'D JUST CUT DOWN on the salt - chicken and human should both be okay
.
Steve