hmm.. well if you look at the Lydia drill holes that @Uttsy has...

hmm.. well if you look at the Lydia drill holes that @Uttsy has started putting in, in particular, and then also look at an existing mine structure in a similar geological area (eg Doray's Andy Well just as a generalised example right).. you can really visualise what THX are technically looking for. Let me demonstrate what i mean by a few screen grabs:

to get an idea of what a real mine looks like.
(http://mapability.com.au/interactive/clients/drm/andywell/)

to get an idea of what THX are doing at Lydia.. looking for similar structures.
(https://corebox.net/properties/thundelarra-garden-gully/lydia)

I'm not a geologist. I just feel that looking at these 3D visualisation helps me imagine what they're trying to find and how they go about doing it. It would be good to have a proper experienced opinion on the matter though