ore
鑛 centers on raw mineral material extracted from the earth: ore. It is the unrefined metal-bearing rock before smelting.
鑛 combines 金 (metal) with 廣, which likely contributes the sound コウ. The character originally referred to unrefined metal ore. 鑛 is the traditional form; the modern Japanese simplified form is 鉱.
The left side 金 (metal) sits beside the right side 廣, which looks like a wide cave or mine. Picture metal ore being dug out from a broad mine shaft.
For コウ, imagine a miner striking ore with a pickaxe and hearing a loud 'koh!' sound: koh -> コウ, the sound of metal ore being struck.