This pic shows the SE leading spur off the top of Mt McArthur that leads down to Lower Olderog biv.

You sidle on the right hand side of the ridge below the higher bumps then cut left through either of the two lower saddles to access easy going on the other side. From there you don't take a bee line for the biv but head east sticking to the more open going until on top of the ultramafic band above the biv. (there are two areas of sparse scrub with rough tracks thru them to cross on this section) From the top of the ultramafic band you can see the biv on a clear day. Head south to the biv. The TL side of the gut running up from the biv is easiest going.