Rio Tinto, the mining group, has found itself pitched against a rival company owned by billionaire Israeli diamond trader Beny Steinmetz in a struggle for control of a large iron ore deposit in west Africa.

Rio Tinto has been looking for iron ore at Simandou in Guinea for more than a decade, and earlier this year was promoting its work there as one of its best growth prospects, a key part of its defence against a hostile bid from BHP Billiton.