Seeking ID - Unknown fungus(?)

[Roots2Shoots]

Found this yellow-orange powdery film growing at the base of a large Quercus rubra approximately (130cm/51" dbh). There is extensive heartwood decay in the main stem of the tree and this film was noted in several locations around the base and on the lower 2 feet of the canopy where decay was present. My hunch is that this is some kind of root rot fungus, but I would like to be more sure. The client would like to preserve the tree and I believe this to be possible if the roots are sound, but I'll need to get to the bottom of this...

Looking for an ID or some leads to continue the search.

Taken in Hamilton Ontario