The Lupon magnesitc deposits are concentrated at the extremities of seaward-jutting spurs of an elliptical mass of peridotite. Peripheral remnants of layered gabbro suggests an original domal structure for the ultramafic complex, later messed up during 2 separate periods of deformation, namely: (1) an early period of thrusting movements, and (2) a later period of strike-slip movements. The complex is cut by late gabbro and anorthosite dikes which apparently came up during a quiet interval between the 2 periods of major deformation.