![yilgan](https://tellusholdings.com/wp-content/uploads/2019/12/yilgan.jpg)
Yilgarn craton ~ 3.7 B years old
Oldest and most stable rocks on earth
![granite](https://tellusholdings.com/wp-content/uploads/2019/12/granite.jpg)
Granite bed ~ 15 km thick
Feldspar in thick granite bed chemically weathered to form primary kaolin clay bed
![kaolin-clay](https://tellusholdings.com/wp-content/uploads/2019/12/kaolin-clay.jpg)
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](https://tellusholdings.com/wp-content/uploads/2019/12/sandy-ridge.jpg)
Sandy Ridge - geology & site
Man made and natural barriers permanently isolate waste from the biosphere, plus the site has low rainfall (semi-arid area), high evaporation rates, the site is dry (no aquifer) and meets best practice site selection criteria for near surface geological repository