Your item appears to be a heavily concreted cast brass or copper Colonial leather decoration piece, with two bent over prongs on the backside for attachment. To be honest, I looked at this photo a dozen times or more, and only saw a nondescript blob at first. This last time though, I saw a familiar shape, and recall having dug similar items on very early Colonial period sites, dating to the 17th and 18th Centuries. I believe you have an item that dates very close to 1680 or within a few decades.
CC Hunter