This Iron Ore farming guide will show you the routes that I use for farming Iron Ore in Classic WoW. Some of the areas changed in Burning Crusade Classic because some mobs became non-elites, but the farming routes are still the same for both Classic Era and TBC Classic.
If you want to farm different ores, please see my other guides:
Copper Ore Tin Ore Mithril Ore Thorium Ore
Arathi Highlands is one of the best places to farm Iron Ore. There are 4 caves marked with red circles on the map, make sure to go all the way to the end of each cave because you won't see all the mining veins from the entrance.
Low level players should skip all 4 caves, and low level Alliance players should take a detour and go south of Hammerfall!
Desolace is also a very good place to farm Iron Ore. This route is easy to follow and you don't have to go inside any caves.
You will get fewer Iron Ore than in the previous two zones because there are also a lot of Tin and some Copper, but still a decent place to farm.