Mine is used literally and figuratively to describe a place where previously untapped resources can or are being produced.
The literal meanings (1-3) and figurative meaning (4) are (from Dictionary.com)
- an excavation made in the earth for the purpose of extracting ores, coal, precious stones, etc.
- a place where such minerals may be obtained, either by excavation or by washing the soil.
- a natural deposit of such minerals.
- an abundant source; store: a mine of information.
The corresponding verb is used to show the figurative use in this article, Oregon Truffles, Mining Oregon's Culinary Gold This shows how natural resources don't have to be resources to be produced (extracted) from the ground. Also, the resource doesn't necessarily have to be minerals in nature.
An article like this one, Mining Minerals from Seawater illustrates the point that mining physical doesn't need to be limited to working in the ground.
Also, let's not overlook the fact that any producer that is very productive of it's resources is often called a gold mine regardless of what is being produced.