What is the world generator mod used in the Tekkit big dig pack?

Solution 1:

This used to be the Metallurgy mod-pack originally (so may be of use to you if you are wanting to use it separately for this purpose)

Taken from the big dig changelogs for v 1.3.2

Removed Metallurgy (taken over by CoFH Core)

It was taken out and replaced instead by CoFH Core (part of Thermal Expansion), the makers of which can be found on this thread.

As a side note, big dig and the current version of tekkit use very different mods, i can't guarantee that you can just copy a map across without causing issues. Though i will test this when i get home and update this post accordingly