Geophysical Surveys in the Harshaw Creek Area, Patagonia Mountains, Arizona

Abstract

Over the weekends of February 15-16 and 22-23, 2020 geophysical data were collected by students from the University of Arizona in cooperation with the US Geologic Survey. The survey was conducted in the Lower Harshaw Creek area of Patagonia, Arizona. The objective of this survey was to define features of the setting for surface water and groundwater across three ranch properties that had varying levels of potable water. Local mineralization in the area led to high concentrations of dissolved solids and low pH in certain wells. DC Resistivity and Transient Electromagnetic were the primary methods used in the survey, with the GEM-2 Frequency Domain Electromagnetic system used in a smaller portion of the survey. These methods allowed for subsurface mapping of the study area with respect to local resistivities. The results of these surveys determined that the likely cause of the varying potability was a shallow rock body containing a high percentage of sulfide minerals. The local geology and nearby area’s mineral occurrences suggest the observed anomalies can best be explained as a buried skarn or epithermal base metal vein-type mineralization. This deposit lies within a shear zone, which caused an uplift of the body under certain sections of the survey area. This zone with the sulfide rich body is the leading theory for the occurrence of non-potable groundwater in the survey area.