AIM-listed Zanaga Iron Ore is considering developing a project in the Republic of Congo on a phased basis, leading to a fall in its shares.A feasibility study had confirmed the "attractive economics" of its Zanaga iron ore project, but on the basis of a staged development, the group said.Stage one would consist of a 12 million tonnes per annum (mtpa) operation, with Stage Two expanding the operation by a further 18 mtpa to produce 30 mtpa of ore over a 30-year mine life.Zanaga said the phased approach was cheaper than earlier proposals and the stage one operation could self-finance stage two through project cash flows, limiting any need for extra equity.The group said it had applied for a mining licence, was working on the project's tax regime and would shortly take on engineering contractors.But investors were unimpressed, sending the shares down 2.5p or 10.4% to 21.5p by 12:06 in London. PW