Several radioactive hornfels and granite boulders have been found scattered through the Hawks Crag Breccia in the Big River and Lower Buller Gorge areas., Uraninite has been identified in the radioactive biotite hornfels from the Lower Buller Gorge. An unidentified, iron-rich, uranium-bearing mineral occurs in the radioactive biotite hornfels from the Big River area. The radioactivity in the biotite granite from the Big River area is concentrated in the zircon and apatite inclusions and to a lesser extent in the biotite.