I have been playing in this world for a while now (I am using Technic Pack), and I have been mining and exploring dozens of times, and in all my days of journeying, I have not come across one single abandoned mine. When I made the world, I had the Generate Structures option selected and everything. I have found a stronghold and a couple villages (Normal Minecraft villages, not Millenaire ones). So that's not the problem.
Is there a problem with my world? Or did abandoned mines just become very rare in the past few updates and I just haven't found one yet?
I remember finding tons of them in almost every mining journey back in 1.8 while playing Vanilla.
