Aminex, an exploration company focused on East Africa, fell on Tuesday after the firm said its Chief Executive was to leave immediately.The firm said Stuard Detmer was also stepping down as a director of the company "to pursue other business interests" with immediate effect.Chairman Brian Hall will assume the role of Executive Chairman assuming all related duties, the company said."Stuard Detmer initiated the important strategic process of divesting non-core assets in order that the company could focus on its core African activities, a process in which we have made significant progress and which the company expects to continue," Detmer said."We wish him every success in his future endeavours," he added.Aminex shares were down 6.2% at 08:30 following the announcement.MM