 Solutions travelling downward from the leached zone react with other primary minerals in the oxidised zone to form secondary minerals such as sulfates and carbonates, and limonite, which is a characteristic product in all oxidised zones.In the formation of secondary carbonates, primary sulfide minerals generally are first converted to sulfates, which in turn react with primary carbonates such as calcite CaCO3, dolomite CaMg(CO3)2 or aragonite (also CaCO3, polymorphic with calcite) to produce secondary carbonates.Soluble salts continue on down, but insoluble salts are left behind in the oxidised zone where they form.