Hello Ian,
thank you for comment. There is of course the possibility that this is a composite piece but I have looked long to the ebay listing (
http://www.ebay.com/itm/251233220747...84.m1439.l2649) and the stating of the seller that the dagger could be 50-75 years old seems reasonable and believable when you look to the other offered items and descriptions. So I think/hope that the dagger is authentic.
I have found after some research this thread:
http://www.vikingsword.com/vb/showth...light=mandingo
So seems the use of brass blades not uncommon.
Regards,
Detlef