I can tell you it's old. One, look at the dates of items found under the street there, then look at the level of wear on this pendent. Somebody wore that for a long time before losing it. It's so worn, that I can't make out the wording, but hopefully someone else here can. It looks to use a number of single letters in the place for words, and I haven't seen that on modern religious medals. If you aren't familiar with what I'm referring to, it used to be a common occurrence to use "OPN" in the place of "ora pro nobis" which is latin for "pray for us".
Lastly, is this silver? I know it looked bad when you dug it, but I thought it had that silver look, and now that it's mostly cleaned, it looks a LOT like silver. Just curious if you have tested it.