Derek,
Hard to tell with that amount of the bow remaining. Maybe someone will have a better idea based on an exact parallel.
Silver
fibulae with decorated bows are common in the Balkans where they date from 6th c BC to 2nd c AD. They are usually variations of more common Greek,
Celtic or
Roman fibulae styles with extra decorations on the bows.
It is hard to tell from what is remaining what yours was.
If you look at this wiki image
http://en.wikipedia.org/wiki/File:Fibulae02.JPG (which is actually of
fibulae from my
collection - I wrote the original wiki entry on
fibulae) you can see a Greek
bow fibulae on the far right. It has an extremely simple "wire" kind of bow. If you imagine this, in silver, with a fatter and decorated bow, and perhaps a large square catch plate instead of the triangular one on this example, you have one possibility for yours. It would be a Balkan (perhaps Thracian copy of a Greek
fibulae and date to 6th to 4th c BC.
On the other hand if you look at this image from the wiki page
http://en.wikipedia.org/wiki/File:Dacian_fibulae_Cluj_Musem_1st_century_BC.jpg (not my
fibulae) you get an idea of how your bow fragment could actually have been
part of a much later
type based on a
Celtic design of the 2nd c BC.
There are other options too. Copy of Pannonian
kraftig profilierte type of 1st - 2nd c AD. Copy of "Phrygian"
type of 7th - 5th c BC.
I am sorry to say that without the two ends of the
fibula I can't tell what it was, but perhaps someone who knows of a closer parallel to your example can
help.
Shawn