A network of magnetite veins occurs in a Triassic diabase pluton at Laurel Hill, near Jersey City, New Jersey. The veins are typically less than three cm thick and occupy a steeply dipping planar joint system. The diabase adjacent to the veins has been altered and leached of most of the iron that was originally present in the ilmeno-magnetite and pyroxene of the rock. The magnetite veins provide field evidence supporting the hypothesis that iron-bearing deuteric fluids existed in the Triassic diabase. It is proposed that the deuteric fluids transferred iron from the wall rock to the joints at Laurel Hill and may also have formed the Cornwall-type magnetite deposits.