I have no idea about that case. No Omega triangle and no marks that I'm familiar with.
Thanks speedb and JimInOz (and all who've contributed).
So if I was to summarise from the thread:
It's an Omega Geneve
Comprising an 18k solid gold case made in Barcelona for (or later used for) an Omega movement 562 dated to 1961. It's had a replacement crown at some point and likely a repainted dial (probably during servicing).
Sound about right?
Thanks all again for your time and knowledge