Create vector (Line or area) along "join" of two intersecting surfaces?

CarrickCon

Does anyone know how to create a vector e.g. line or area along the "join" when you combine two intersecting surfaces?
For example when I combine a mine pit shell surface with natural topography surface (using Analysis/Combine/Minimum Elevation) I need to be able to extract the line where the pit crest intersects or "daylights" with the topography. Another example is when I combine a Waste Rock Dump surface with natural topography surface ((using Analysis/Combine/Maximum Elevation) and I need the toe line where the two surfaces intersect. 
My current workaround is to contour the combined surface at a tight interval and then manually digitise the "break" between the proposed landform and the natural topography.  However this is tedious for complex shapes... :-(
Any and all help much appreciated!
Cheers,
/al

sphillips

A couple of ideas here - my method at the bottom works fine: https://www.globalmapperforum.com/discussion/10474/intersection-of-two-elevation-grids

CarrickCon

Buddy you are a star! I know there would be a work around in GM (I love this software) I just couldn't figure out what it would be. That Combine/Compare surfaces is so powerful!
Cheers,
/al