Silcrete is a surface or near-surface deposit of soil,...

Silcrete is a surface or near-surface deposit of soil, saprolite, or sediment that has been cemented by secondary silica to form an indurated mass.

Wopfner (1978) reports quartz silcretes in kaolinized profiles formed in acid groundwater environments. James Marsh has said that the water on the Eyre Peninsular had a pH of <2 which is why the deposit at Great White is so pure. The acid leached out the iron, potassium, magnesium etc.

Yes, the silcrete contains halloysite. You may have heard James Marsh say ADN may need to use a small amount of explosives to "pop" the silcrete. Although he didn't explain why it was previously waste I think the fact that the sand/quartz & kaolin/halloysite has been cemented together means it cannot be separated easily.

In the concrete app this separation is not required. The silcrete just needs to be crushed and sieved apparently.

I guess we will get more details in due course.

I don't expect there to be a big domestic market for the concrete app and the price will be modest, not $2500-3000t although >$1000t is still very good! But it will enhance OPEX.

There's a bigger story at Dorsal Fin. Ultra high purity kaolin there. Perfect for HPA5N!