Allan Quatermain and the Lost City of Gold (1986)

After his brother Robeson disappears without a trace while exploring Africa in search of a legendary 'white tribe', Alan Quatermain decides to follow in his footsteps to learn what became of him. Soon after arriving, he discovers the los City of Gold, controlled by the evil lord Agon, and mined by his legions of white slaves. Is this where Robeson met his end?