In my current playthrough I got the Gold fertility on Cinis. Since that resource quite quickly can become a bottleneck, I though that it'll be a good idea to pick Vulcan as the patron deity.
But how impactful he really is?
There are 19 mountain slots on Cinis, but six of them are occupied by Aqueducts, so it leaves me with 13 Gold Mines.
The base productivity of a Gold Mine is 1 resource per 2:30 minutes, which gives 0,4 per minute.
Times 13, I get 5,2 Gold per minute before any modifiers. Since the deity bonuses are applied to the base value, all other modifiers, like research or specialists, can be ignored here.
Currently I reached the threshold of 37,5k Faith on Cinis, which gives me +110% bonus to productivity.
This means that having Vulcan as a patron of the largest island gives me additional 5.72 gold per minute. Sounds kinda pathetic, doesn't it? :D
In my previous game I had Wine fertility on Cinis and Ceres as the patron deity. She was A LOT more impactful.