Eisenberg massive brooch

I was lucky to find this gorgeous piece of Eisenberg jewelry last weekend. I have researched the mark and identified that it is from the 40s.

I don't see many images on line for this type of brooch, nor the size.

I am curious as to whether there is anyone that can tell me whether the piece is gold vermeil over sterling, sterling or the metal content.

The piece is very intricate on the back and with the naked eye I can't see any other marks besides the script E.

All comments and information posted will be truly appreciated.

From a vintage jewelry lover, Delia.