Colleges, Departments, and Organizations: Recent submissions
Now showing items 21-40 of 16814
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Geophysical Surveys in the Harshaw Creek Area, Patagonia Mountains, ArizonaOver 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.
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Geophysical Surveys in the Blue Nose Mine Area, Patagonia Mountains, ArizonaThe 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.
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Geophysical Surveys in the Lead Queen Mine Area, Patagonia Mountains, ArizonaIn late 2015, after abnormally heavy monsoon rains in the Coronado National Forest south of Patagonia Arizona, an orange discharge was observed in the creek bed below the entrance to the abandoned Lead Queen Mine. This caused the U.S. Forest Service and United States Geological Survey (USGS) to mobilize to determine the cause and investigate actions to prevent future occurrences. Our studies included Transient Electromagnetics (NanoTEM), DC resistivity, EM-31 and Ground Penetrating Radar (GPR) surveys around the Lead Queen Mine for the United States Geological Survey. Data collected around Lead Queen Mine show a large highly conductive layer within the immediate area of the mine. Data from the NanoTEM and DC resistivity surveys show an anomaly with resistivities less than 6 ohm-m at depths varying from 20 to 60 meters. This anomaly is present in all TEM transects and the DC resistivity line. The DC resistivity line also shows a high-resistivity area near where the adit has been predicted to be. Further west, near another adit, a low-resistivity layer does not appear until beyond 60 meters depth. Data collected using the EM-31 shows no change in resistivity or conductivity along the stream-bed near Lead Queen Mine. GPR data did not effectively show a response to the adit, even with extensive manipulation using the RADAN software.
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Near-Surface Geophysics Surveys at Empire Gulch in the Las Cienegas Conservation Area, SE ArizonaElectrical resistivity and induced polarization surveys were conducted in the Las Cienegas National Conservation Area for the Nature Conservancy and in accordance with the Bureau of Land Management. Data collected around Empire Ranch HQ shows a thin, high resistivity layer at the surface underlain by a lower resistivity layer, indicative of typical regional alluvium. H0 and H1 show resistivity of approximately 80 Ω-m down to 5 and 10 meters, underlain by 25 Ω-m and 20 Ω-m respectively. H2 and H3 shows resistivity of 60 Ω-m down to 5 and 15 meters, respectively, underlain by 20 Ω-m resistivity. Moving east, the data displays a distinct change. A thin, high-resistivity surface layer is underlain by an extremely low resistivity layer, typical of clays. H5, Z2 and H6 display surface resistivity between 20 Ω-m and 15 Ω-m, typical alluvium values. The massive underlying layer displays resistivity values of approximately 5 Ω-m. Continuing east, H7 shows a thick layer of high (80 Ω-m) resistivity surface material down to 25 meters, underlain again by a massive, low resistivity layer with a typical clay value of 5 Ω-m. H8 and Z3, collected in the Cieneguita cienegas complex, both display a 5 Ω-m surface layer down to 5 meters, indicative of clays. The surface layer is underlain by a 15 Ω-m, low-porosity layer, essentially devoid of clays, interpreted as Late Tertiary and Quaternary basin fill.
