Unknown Omega Tank - Very excited - Maybe it's gold coated silver?

I bought this Omega Tank blindly, unsure whether it even works, but it just mesmerized me and really piqued my curiosity, there aren't many Omega tank variations apart from the common 19mm lugged case

This one appears to be a 20mm lug width case from my approximations, and (to be google'd in the future) it says "ARGENT PLAQUE OR G20" on the back, there are some Cartier tanks that both say this, and have 925 etched, so my hope is that thing near the crown could indeed be a hallmark and it could be silver

I really hope it works, if the internals are clean want to try making it a daily driver - but to be honest the gold color will probably not grow on me, my dream non-C-Case fantasy watch is a handwind white gold Omega Tank, it could exist but for some reason they didn't make many Tanks for Men, for example I've never seen a JFK Omega in the wild

I think you are right..it's silver and gold plated. The problem is that i search on google for silver hallmarks and i did not see that small key as a hallmark. I remember that i seen that key with other occasion but i do not remember where..I am sure that other member from here with more experience know about that symbol.

Stamp looks like a Portuguese import stamp

Watch arrived and it's in pretty awesome condition, it's from 1977



The battery that was left inside luckily didn't leak and with a new battery it works perfectly! Started wearing it

For future reference it's a 1351 cal. and the inner inscriptions are: 925 1439 1110

Googling 1439 1110 only brings up another example from Germany / eBay

Would’ve been pretty awesome if it was bare silver with a silver coloured dial