TRANSIENT ELECTROMAGNETIC (TEM) INVESTIGATIONS INTHE UPPER SAN PEDRO RIVER BASIN, BENSON, ARIZONA

Abstract

Transient Electromagnetic (TEM) surveys were conducted in the San Pedro Valley starting approximately 1 mile northeast of Benson, Arizona, and extending about 2 miles farther northeast. The survey used loop sizes of 20x20, 100x100, and 200x200 meters with the objectives of determining the depth, thickness, and lateral extent of clay deposits, and comparing ground surveys with a previously acquired airborne TEM survey. The data were processed with Zonge Engineering smooth inversion software as well as Interpex TEMIX layered-earth inversion software. The interpreted depth to near-surface clay deposits was less than 5 m on the west end near the San Pedro River, and increased to about 15 m, 1.3 km to the east. Farther east, clay deposits were only detected at depths of 100 m or more. A possible bottom to the clay was detected near 100 m depth at selected stations in the western half of the survey, which would correlate with wells in the vicinity, but it was not laterally continuous. Surveys at the remainder of the stations did not detect a lower limit to the clay deposit. The results of the airborne survey versus the ground elevation surveys show similar resistivity values.