This Cobalt Ore farming guide will show you the routes that I use for farming Cobalt Ore in Wrath of the Lich King Classic.
Howling Fjord is the best place for mining Cobalt Ore in WotLK Classic. But this zone is usually heavily farmed on higher population realms, so you might want to try out the other alternatives below.
Borean Tundra is also an excellent place if you don't like Howling Fjord for some reason or if someone else is farming there.
Lower-level players might want to skip some of the caves in Borean Tundra (depending on your level and gear).
Great farming place if you have a lot of competition in Borean Tundra and Howling Fjord.
You will find a few Saronite Deposit in this zone but it's mostly just Cobalt Ore.