Looks like a blacktail. Probably shot along time ago. It was a big thing in the old days (pre-1970's) to lacquer your horns with varnish to make them shine like that. Also most people hung their horns outside or in a barn and it would preserve them. Just my two cents. If it is a muley, its a real nice buck. If its a blacktail, its a monster trophy! My guess is that it is a blacktail but I'm not sure.