1880 Melbourne International Exhibition Bronze/Lead Medal

I acquired an unusual medal as part of an estate. It is a medal from
the 1880 Melbourne International Exhibition. It appears to be in
bronze on one side with perhaps some silvering which may have for the
most part worn off, and the other side is lead or lead filled. I saw
one reference on Google where a similar piece went up for auction some
time ago, and I am contacting the auction house via email, but I also
wanted to see if anyone else had seen a similar item and whether they
knew anything about it, how to determine authenticity, etc.

Thanks for your help

Rick