Overall, looking at the piece again, I tend to agree with you.

But, it should be noted that gummite can occur in sandstone  in U ore pods (for example at the Pick’s Delta mine  the San Rafael Swell, UT).

I think the key on gummite vs ‘carnotite group’ is  whether  the environment is oxidizing or not. If it is oxidizing, then I agree ‘carnotite group ?’ is appropriate. 

I am also having a hard time discerning the matrix for this piece, which seems to imply the yellow material is  encapsulating the sandstone(?) grains which would be more in line with ’carnotite group’.  I also don’t see any uraninite (anther vote for ‘carnotite group’).

It will be interesting to see the results once this piece gets analyzed. Either way, it is definitely an interesting piece.