mine, mineral, ore
礦 centers on raw mineral resources extracted from the earth: a mine, ore, or mineral substance.
礦 combines 石 (stone) with 廣, which likely contributes the sound and the idea of broadness, suggesting a broad stony place where minerals are found.
The left side 石 means stone, and the right side 廣 suggests something broad. Picture a broad rocky area where miners dig for ore.
For コウ, imagine a miner shouting 'Coal!' when finding ore: coal -> コウ, and the mine yields mineral riches.