The field is formed on top of plutonic rocks, which were scoured by glaciation. At the south coast of Tierra del Fuego, volcanic activity provided the late Jurassic formation known as the Lemaire Formation. Later, during the Cretaceous, the Yaghan Formation consisting of marine sediments was deposed on top of the Lemaire Formation. The basement of Fueguino consists of an ophiolite of Late Jurassic to Early Cretaceous age. The ophiolitic sequence contains pyrrhotite, chalcopyrite, titanomagnetite, cubanite and pyrite.