This marble is mined by the dwarves of the area and shipped out as building stone. Parts of the city of Irongate are constructed of this high quality Iron Hills marble. Rumor has it that a few diamonds have been found in some streams deep within the Headlands. Stories abound about a lost diamond-bearing kimberlite deposit. Few believe it.
Some coal is imported, but most smelting is done with charcoal made from the local trees.
As a geologist in real-life, I'm compelled to point out a few things. Limestone gives a great landscape filled with caves, ripe for adventuring, but on its own contains little in the way of gems and native metals which, according to the WoGH Gazetteer, are supposed to be present. Therefore I've used the presence of scattered volcanic intrusions to supply the source material for these resources. While all of these minerals can be found in these general rock types, each depends on wildly different variations in the chemistry of the original source rocks. In other words, it would be impossible to find them all present in the same location.