This is an absolute punt on my part, but given the fact that...

This is an absolute punt on my part, but given the fact that there is vms-type mineralisation at the surface of AC 109, and maybe ACs 111 and 112 as well, and descending as per the detail, could this be the remains of a gossan? - one that has eroded over hundreds of millions of years so as to be not an outcrop anymore?

A few years ago I researched some Horseshoe Lights history. It was found in 1946 by prospectors looking for gold. They located a gossan and dug. Gossans were, i believe, the outcroppings that prospectors and exploreers looked for. They found the gold, also some copper which was cast aside it seems. To cut a long story short below was a cu/au vms deposit, the first one found in the Bryah Basin.

DeGrussa might have had a badly eroded gossan. Red Bore, another vms deposit and just to the east of Degrussa, was evidenced i believe by a gossan.

Anyway here is an oldish research paper on gossans if interested.

http://crcleme.org.au/RegExpOre/5-samplemedia.pdf