New Tech: Archaeology

Archaeology
Requires Nationalism
Effect: Any wonder that will obsolete will stay for 32 more turns (4 golden age period in normal speed) after a certain technology is discovered.
Option Tech, but also leads to Scientific Method

Maybe. Not bad. How about cost? How about 2100?

Make it really expensive, make it after Scientific Method, lose Nationalism requirement, and get +1 gold from all mined hills per turn, and I think it's a good idea.