Why doesn't "Izumo" province produce gold?

[Trin Tragula]

Actually, Gold seems to be any extremely valuable mineral. The gold mine in La Mancha is actually a mercury mine iirc.

It's used for gold, silver, mercury (we could hardly avoid covering the source of the wealth of Europes most powerful banking family) and diamonds (Golconda). In Burma there's also a gold province due to high general concentration of rubies and other gemstones iirc.
It's reserved for extremely valuable commodities though.

The reason there's only one gold mine in Japan is indeed balance. The decision dates back to version 1.0 though and balance has changed a lot since then. It's something that we might reconsider in the future.

 

[Trin Tragula]

Not to mention Konigsberg which is just a massive amber deposit.

You're probably thinking of a mod

 

[Trin Tragula]

Why not add silver? Silver was important to the Spanish (Potosi mines in Bolivia). The economy tab could say Precious Metals instead of gold and when you put your cursor over it, it can specify how much income from gold and silver separately.

What would functionally be the difference?

 

[Trin Tragula]

It still wouldn't really catch everything it's used for though. We have the same situation with some other trade goods (spices include opium and dates for instance).