Geophysical Surveys in the Blue Nose Mine Area, Patagonia Mountains, Arizona

Abstract

The US Geological Survey and the US Forest Service requested an investigation of the sediment and groundwater properties of the Blue Nose Mine in the Patagonia Mountains of southern Arizona to help with future remediation efforts due to historical mining of the area. Information on the depth of the existing tailings piles was also requested to aid in determining the best removal strategy. The surveys carried out in this investigation include direct current (DC) resistivity, transient electromagnetics (TEM), EM-31 and EM-38, total-field magnetism, and petrophysical laboratory analysis. The 20m TEM loop and DC resistivity data revealed low-resistivity regions, less than 10 Ohm-m, surrounded by several-thousand Ohm-m resistive features, indicating a large conductive zone around the existing mine workings. The 10 m TEM loops, as well as the EM-31, and EM-38 data, collected on the tailings piles indicate a conductive layer reaching 8 m in depth from the surface. These help to delineate the conductive tailings material from the surrounding hillside. The total-field magnetic survey was useful in determining several linear features and magnetic trends, including the Harshaw Creek Fault on the eastern edge of the study site. The petrophysical analysis aimed to help refine subsurface interpretations, but due to the small sample size only provides a limited correlation to the DC resistivity and TEM data. Correlations between magnetic and resistive datasets reveal three zones with differing electromagnetic properties, one of which may correlate with the Blue Nose ore deposit.