I broke Gold Mining!?

I love this game!

I was mining 2k gold per harvest. I added some additional gold mines (3 or 4) and resourced them with workers. I expected to receive more gold per harvest. But now I’m getting less (1.5k).

Similar layout just extended upwards. Same starting shot. What have I messed up? I’m thinking it’s something to do with workers allocated but I can’t figure out how that would be impactful.

Purely for mining gold not other resources. please help?!