Electrical Prospecting Methods Applied to Shallow-Water Mineral Exploration

The applicability of two electrical prospecting methods-controlled-source audiomagnetotellurics (AMT) and resistivity profiling with surface- and bottom-towed arrays-to underwater mineral exploration was tested in shallow waters along the north shore of Keweenaw Peninsula in Lake Superior. These methods were first used in Copper Harbor, where there are known underwater copper veins, and later applied in Great Sand Bay to determine whether offshore extensions of onshore copper veins exist. They proved successful in detecting conductivity anomalies associated with known underwater veins, lithologic boundaries, and sands with a high heavy-mineral content. Probable copper veins located along underwater projections of onshore veins were discovered in both areas. These methods hold promise in exploration for placer and vein deposits in the shallow marine environment.