Hello, I have got a world which has been generated using mod Mineral Veins - http://forums.bukkit.org/threads/wgen-mineral-veins-1-4-1-ore-placement-overhaul-1-2-3-r01.35656/. How to make the plugin still work after I import the world?

This is not the correct place for this issue as it related to Multiverse-Core. You should probably follow the instructions in the wiki however: https://github.com/Multiverse/Multiverse-Core/wiki/Command-Reference#wiki-import