Antique C closure brooch

I found this interesting brooch at a thrift store in Vero Beach, FL. I was drawn to it first because of the C clasp, so I assumed its at least 80 maybe 100 years old? I also love that the leaves have the most detailed veins of the front and the back.
My questions if anyone might know: is this brass, bronze, copper? It looks like it could have a slight silver or metal sheen on some leaves. Is this art deco, art Nuevo, neither? Would love to find out more about this neat brooch. Thanks!