As far as I know, there is no mine. I believe the way you get ores is by smashing rocks you can find in the rivers and such. In winter, you can smash through the ice in one place and I think there are rare ores/jewels there.... I think.
There are no rare ore/gems if you smash through ice. All of the gems and ores can be bought at Lloyd's bazaar shop, the ore rocks during winter, or Diego's bazaar shop.
