Discovery of Martin Frobisher's Baffin Island "ore" in Ireland

Abstract

Five cobbles of metamorphosed ultramafic rock from the shores of southern Ireland are believed to have been derived from the ship Emanuel of Bridgwater in 1578. The Emanuel, one of Martin Frobisher's fleet, had loaded what was thought to be gold ore from three localities in southeast Baffin Island and, on the return journey, was wrecked and then beached on the western side of Smerwick Harbour, close to where the cobbles were found. One type of cobble, with brown hornblende, forsterite, and ilmenite, is similar to rock collected from Countess of Sussex mine, Baffin Island, which accounted for 25% of the Emanuel's lading and 30% of the ore mined by Frobisher in 1577 and 1578. It was Frobisher's largest mine, and the rock resembled ore stored by Frobisher in Dartford, England. The other type of cobble, composed of green hornblende, diopside, and ilmenite, could not be matched with Baffin Island or Dartford rock. K–Ar ages of the two rock types were 1810 Ma (hornblende + diopside) and 1881 Ma (hornblende + forsterite), consistent with a Hudsonian overprint on southeast Baffin Island. Hornblende-rich "ore" from Frobisher's first mine (not loaded on the Emanuel) gave a K–Ar age of 1722 Ma. The K–Ar ages and ultramafic rocks are unlike any known in Ireland.