Nickel silver based and in a very good, slightly worn condition with a typical patina. 
Not marked but a known variation that has been attributed to the company of C.E. Juncker, Berlin. See Philippe de Bock, The German Panzer Assault Badge, p.41–45.
Probably the most desirable and mother of all Panzer Assault Badges.

C.E. Juncker NS PAB in silver (Porsche Type)