My horse ate copper is this dangerous?

ok well i have a 7 year old connemara gelding and i was out hacking with him yesterday, nt he way back he stated pulling me towards a gate then i realized why.... on the ground below the gate was a sheep salt lick (you know the ones that come in an Orange tub type thing) he went Straight for it licking biting and chewing chunks out of it i tried with all my might to stop him and eventually pulled him away however i believe it contained copper... will this harm him? will he become ill? at present he seems fine but im just not sure....