Newbie confused about copper

We are new to sheep, and I am really confused about feeding sheep copper. I had read several places about copper toxicity in sheep, and that it should be kept out of sheep mineral licks. But now, in reading "Natural Sheep Care" by Pat Coleby, she mentions the importance of putting copper in a lick, and lists all of the benefits of making sure sheep are getting enough copper (resistance to worms, coccidia, etc.) Copper Sulphate is one of the four ingredients she gives in a lick recipe to be available to the sheep at all times. Can anyone enlighten me on this? We live in the Pacific NW, and maybe it is just something in my area?
Thanks!