PGD General Discussion, page-6

There you go if you try hard enough all is not lost

CID Deposits with Surface‐Enriched Aluminium in Western AustraliaSeveral of the major Pilbara channel‐iron deposits show a clear upward increase in Al₂O₃ from the basal channel fill into the near‐surface pisolitic/duricrust zone:Robe palaeochannel (Robe Formation)Basal channel material: Al₂O₃ ~0.5–0.8%Near‐surface pisolite cortex: Al₂O₃ up to ~2.8%Marillana palaeochannel (Yandi deposits)Basal channel material: Al₂O₃ ~0.2–0.7%Near‐surface pisolite cortex: Al₂O₃ up to ~2.1%Smaller CID systems (e.g. Poondano) are reported to follow the same general pattern—lower Al₂O₃ at depth (<1%) grading upward to capping duricrust values approaching 2%–3%—though detailed assays are less widely published.