SPONTANEOUS POLARIZATION POTENTIALS AND CLAY AND LIMONITE DEPOSITS IN THE GATESBURG FORMATION OF CENTRAL PENNSYLVANIA •

Geophysical investigation of clay and limonite deposits related to the lower Paleozoic of Central Pennsylvania shows the existence of broad belts of self-potential minima above the outcrops of the Cambrian Gatesburg formation. These S.P. minima are related to the peculiar sandy residual soil covering the Gatesburg. A working hypothesis in terms of shale and liquid junction potentials is advanced to account for the phenomena. This appears to be confirmed by the "mirror image " relationship of S.P. profiles with resistivity profiles. The method may be useful in prospecting for clay deposits and in locating certain geological boundaries. PURPOSE OF THE INVESTIGATION THe. limonite deposits under consideration were worked for their iron content by open pit operations during the early days of the American iron and steel industry. Renewed attempts at exploitation were undertaken as late as 1942 or 1943 at Scotia when the increasing war-time demand made marginal de-posits attractive. The operations proved unsuccessful. Associated white kaolinitic clays, however, are still being worked in a few cases (e.g., th