"My question is what do you use as inputs? Assay results or in field spectrometer readings?"

I'm not sure I understand, they should be one-in-the-same. I believe that spectrometer readings, obviously, come easily and quickly, they just don't carry any official weight - can't be shared with the public. Again, this may be an outmoded rule, but we have to live with it for now.

Look at what happened at Big Chunk regarding the deal with Northern Dynasty for an example.