The sinuk iron deposits are outcrops and residual concentrations of botryoidal and loosely cellular limonite and goethite about 25 miles northwest of Nome on the Seward Peninsula, Alaska. The iron minerals occur in a belt of metalimestones south of the Stewart River and are most abundant in the area between the headwaters of Cripple River and the hills on the west side of the Sinuk River. The surface concentrations have been estimated to include in excess of 600,000 tons of rock containing 10 to 45 percent iron and about 0.005 percent managanese dioxide in a limestone gangue. The botryoidal and mammillary limonite of the sinuk deposits resembles material found on known sulfide outcroppings in the Seward Peninsula area. The Sinuk and similar iron deposits of the Seward Peninsula differ from the usual gossans; boxwork structure is absent or very rare and typical oxides derived from sulfide deposits are scarce.