Victorian Banded Onyx Brooch With Fly On Top

Quite what the hidden meaning is of a fly on top of a banded sardonyx is beyond me!   The mount is pinchbeckAn early 18th century alloy of copper and zinc (9 parts zinc and 48 parts copper) invented by Christopher Pinchbeck. Another formula consisted of 83 parts copper and 17 parts zinc. It looks like gold, wears well and maintains its colour. with a rope border. and there is a glazed locket section to the reverse.  Either way it is an unusual brooch to wear and would be sure to attract comment.  It was made circa 1860-1880.