Yilgarn craton ~ 3.7 B years old

Oldest and most stable rocks on earth

Granite bed ~ 15 km thick

Feldspar in thick granite bed chemically weathered to form primary kaolin clay bed

Kaolin clay bed ~260-70M years old

Sandy Ridge is in the Big Bell suite -thick, flat, stable, dry clay bed ~150 km long, ~20 km wide and in places ~ 40 m thick. ~15 to 2.6 Mya mostly an impermeable layer of silcrete and laterite formed on top of the kaolinized clay adding another natural barrier or cap

Sandy Ridge - geology & site

Man made and natural permanently isolate wa biosphere, plus the site (semi-arid area), high e the site is dry (no aquif practice site selection c surface geological repo