The Human race can harvest resources from any mine, same as the Orc race.
The Undead must harvest their resources from units of type "Haunted Gold Mine". The Night Elves must harvest their resources from a unit known as "Entangled Gold Mine".
Entangled Gold Mine seems to have quite a bit of background code that we cannot control. For one, the mine will only remain entangled while the Tree of Life that is associated with it remains alive and rooted. Also, some of the abilities on the "Entangled Gold Mine" unit seem to be very sensitive, in that if they are removed the game will crash when the ability is used.