Collada export to ARKit

I’m trying to export a model using the Collada format for use with Apple’s ARkit. I have a simple test scene - a cube using a principled shader with colour, metallic, normal and roughness maps applied. I’ve selected the ‘Copy’ option in the texture export settings but only the colour map gets exported.

I’ve also tried with 2.79 and 2.8 and get the same results.

Are there any steps I’m missing? Am I asking too much of the Collada exporter?
Thanks in advance.