The oxidized lead deposits are hosted in a silicified, dolomitic, collapsed breccia with cerrussite (lead carbonate) being the predominant mineral. The mineralization is unusual in that there are no sulphides present. The deposits are thought to represent the residue from ancient sediment-hosted base metal mineralization that underwent prolonged weathering, which led to dissolution, volume reduction and oxidation of the lead mineralization. Other metals were dissolved and fortuitously the climate changed to an arid environment before the heavier lead minerals were also washed away.