Billiton, the UK-listed South African mining group, is planning to target US investors with its $750m (€836m) secondary offering of shares, which it announced this week, because more than 40% of its shareholder base will be excluded from the sale.

One source close to the deal said that regulatory restrictions on capital movement excluded South African shareholders from the sale, who represent 42% of its investor base. Billiton has maintained a large number of South African shareholders since it moved its primary listing to London in 1997.