A U.S. shipping firm is suing Alcoa for $300 million saying it suffered losses after the aluminium maker breached a contract with the Guinean government concerning bauxite shipments from the world's top exporter, court documents showed. Nanko Shipping and its president Mori Diane filed a civil complaint in the U.S. district court of the District of Columbia last week saying it had been harmed by Alcoa's refusal to honor the terms of the 1963 joint-venture mining deal with the Guinean government. That agreement established the Compagnie des Bauxites de Guinee (CBG), the largest bauxite mine in the West African country, and gave the government the right to choose a company to ship half of its production, according to a copy seen by Reuters.