The mines in Alterac Valley hold more than just minerals. Both the Frostwolf and Stormpike have cached excess supplies in the Irondeep and Coldtooth mines... that's not a bad idea, if we could only maintain control of them!
Capture a mine, then return to me. To capture a mine, enter one that we do not control and kill its leader. When you do that, the mine will be ours, and we'll send troops to protect it!
You did it! Well done, <name>!
When we control a mine and have troops stationed there, it's much easier to gather minerals and supplies from it.