Dragon Flight

Free Routes:

Draconium Ore - The Azure Span
Draconium Ore - Ohn'ahran Plains
Draconium Ore - The Waking Shore

Shadowlands

Free Routes:

PhaedrumOre - Ardenweald
SoleniumOre - Bastion
OxxeinOre - Maldraxxus
SinvyrOre - Revendreth

Battle For Azeroth

Free Routes:

Osmenite Ore - Nazjatar
All BFA Ores - Tiraguard Sound

Legion

Free Routes:

Empyrium Ore - Krokuun
Felslate - Suramar

Warlords of Draenor

Free Routes:

Blackrock Ore / True Iron Ore

Mists of Pandaria

Free Routes:

Ghost Iron Ore - Valley of the Four Winds

Cataclysm

Free Routes:

Obsidium Ore - Abyssal Depths
Pyrite Ore - Uldum

Wrath of the Lich King

Free Guides:

Cobalt Ore - Borean Tundra
Saronite Ore - Wintergrasp

The Burning Crusade

Free Routes:

Fel Iron Ore - Terokkar Forest

Vanilla

Free Routes:

Tin Ore - Ashenvale
Copper Ore - Durotar
Thorium Ore - Silithus
Iron Ore - Western Plaguelands