You absolutely do not want any zinc wheelweights in your melt. Any that have riveted on clips can be considered to be zinc. You can hold them in a vise and try to bend it by hitting with a hammer. Lead will bend some before breaking, zinc will snap in half without bending. When you melt wheelweights, bring the temprature up slowly to the slushy stage and the zinc ones will not be melted. They can be scooped out, do not allow them to melt or the whole batch will be ruined. Trying to cast lead with zinc contamination is a very frustrating process, sort of like trying to cast with melted bubble gum.