Help with Russian / Cyrillic - niello locket

It's a Russian-style niello locket and sure looks Russian. I need to get the marks under a loupe to be sure. It has a word written across the back and I can about read place names (sometimes) but that's as far as I get. Caucasus? I did some digging and I think that's what it says?

 

Yes, it's Caucasus written with the letter Ъ in the end which is not used in modern spelling. It means it was made before 1917 (or it's a modern remake of an old piece, sometimes this letter is used to make a piece looks old)

 

There's a photograph inside that's distinctly older than dirt; I'll have to get a loupe on the marks but it feels old.