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1

Geophysical Surveys in the Blue Nose Mine Area,

Patagonia Mountains, Arizona

Geophysics Field

Camp 2019

Laboratory for Advanced Subsurface Imaging

LASI-19-1

May 12, 2019

Osvaldo S. P. Bambi, Ryan K. Brock, Elsa D. Domingos,

Figueiredo C. K.

Evaristo, Kenneth C. Gourley, Michael T.

Hanna-Wilson, Miguel Alberto Kilezi, Tyler S. Kuehn, Echo Li, Ivo Lima, Richard Marcelain, Rui T. Mariamba, Jonas Joaquim Mulato, Charles K. Nault, Lucas M. Pedro, Venancio Fernando J. Pedrosa, Sean P. M. Purdy, Farid Najmi Rosli, Brianna

Rupkalvis, Nicholas R. Shea, Ben K. Sternberg

2

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. 3

Table of Contents

1. Introduction..............................................................................5

2. Location Maps and Elevation Profiles...............................................17

3. Transient Electromagnetic (TEM) Survey..........................................31

4. DC Resistivity Survey..................................................................56

5. Electromagnetic Induction (EM-31 and EM-38) Survey..........................64

6. Ground Magnetic Survey..............................................................82

7. Petrophysical Laboratory Analysis..................................................106

8. Combined Analysis....................................................................120

4

Acknowledgements

The University of Arizona Field Geophysics class (GEN/GEOS 416/516), would like to thank the United States Geological Survey (USGS) for providing funding and support for this project. Jamie Macy has played a vital role in our Geophysics Field classes for many years, providing the required equipment, teaching us how to operate the equipment, and processing the data. We would like to thank Floyd Gray from the USGS for giving us a detailed introduction to the area and the project before our first weekend in the field. Without the assistance of the USGS this project would not have been possible. Finally, we would like to thank Zonge International for their 33 years of support of this class as well as providing relevant information for the report and presentation. 5

1. Introduction

1.1 History

The Blue Nose Mine resides within the Bisbee Formation and was a former underground and small surface mine located on the west side of Harshaw Creek, about 10 km south of Patagonia, AZ and 25 km northeast of Nogales, AZ. The mine had four previous owners and was operated on-and-off from 1884 to 1956. The mineralization in the area is primarily composed of pockets of argentiferous galena and other sulfides. These are located in a northwest-trending fault zone in Jurassic-Triassic volcanic rocks interbedded with limy, siliceous sediments (Mindat, 2015). The limestone contains intrusive lenses of rhyolite, which has small crystals of pyrite and chalcopyrite with white, talc-like ore pockets. The vein dips 40° to the northwest and was mined to a depth of about 60 m with tunnel operations totaling 440 m in length (Schrader and Hill,

1915).

1.2 Project Background

The U.S. Geological Survey, in cooperation with the U.S. Forest Service, is undertaking a study on the environmental effects of historical mining on the current water and sediment properties. This study is focused on the Harshaw Creek watershed, upstream of Patagonia, AZ, which is in the vicinity of Blue Nose Mine. The removal of the tailings piles from Blue Nose Mine is also of concern. This study was set in motion because of the observation of bright orange sludge discharge from mines within the area after strong , monsoon-related precipitation in September of

2014 (Figure 1.1).

The University of Arizona, in conjunction with the USGS, conducted a field study during the days of February 9, 10, 16, and 17 of 2019. Data were collected 300 m from the main entrance of

Blue Nose Mine to the

southwest and approximately 270 m from a creek adjacent to the tailings plies. During these days, subsurface measurements were performed using the TEM (transient electromagnetic), DC (direct current) resistivity, ground conductivity (EM-31/38), and total field magnetic methods. The primary objective of this report is to compile geophysical data on the 6 area for the identification of fracture networks. These networks may transport water into the Harshaw Creek watershed from naturally occurring deposits and the tailings piles, because they lead directly to Harshaw Creek. The results from this study will give a better understanding of the subsurface properties of the mine, allowing for a more informed response in reducing possible discharge recurrence.

1.3 Geologic Background

A geologic map of the Patagonia Mountains (Figure

1.2 ) is reproduced from Vikre et al. (2014). Blue Nose Mine is located within the Cretaceous Bisbee Formation which overlies Jurassic - Triassic volcanic and sedimentary rocks. In addition, we saw lenses of rhyolite dikes flare out at the surface at points that could correlate to the Laramide batholith that more noticeably exists in other portions of the Patagonia mountains. The mine also exists with in the intersection of the Harshaw Creek and Blue Nose faults to the East and West, respectively. This faulting and fracturing allowed hydrothermal water to travel through the subsurface and mineralize sulfide deposits, as the mine exists within the intersection of pyrite and shear zones.

Figure 1.1. Pictures of orange precipitate discharge from tailing piles around the Patagonia Mountains,

AZ in September of 2014 after a monsoon. Photos courtesy of Glen E. Goodwin. 7

1.4 Hydrology and Heavy Metal Concentrations

Inactive and abandoned mines, once rich in mineral and ore deposits, now have emerging safety, health, and environmental risks. These include heavy metal contamination of groundwater, surface water, and soils. This geophysical investigation focused heavily on mineralogical, geologic, and hydrologic effects caused by mining. Emerging hydrologic questions in clude (1) whether or not contaminants are leaching into the groundwater; (2) whether or not they are contaminating the groundwater source; and (3) whether or not contaminants are being transported in surface runoff. By examining the groundwater and surface water conditions, the impacts from thi s abandoned mine can be examined and possibly remediated in the future.

Mountain terrain

s occupy 20% of the Earth"s land surface, and their hydrologic characteristics are defined by fractures and faults. Surface water elevation in these regions are dependent on lower hydraulic conductivity, nested flow systems, and ephemeral streams with abundant losing reaches. With limited access to the subsurface, certain geologic structures limit groundwater flow between aquifers, increase seepage, and produce higher streamflow (Garfias, 2009; Ball et al.,

2014). Any regional increase in precipitation can lead to drastic runoff and stream discharge in

Harshaw Creek, especially with rising water heights within the Patagonia Mountains. In 1915, the Blue Nose Mine had an estimated 60 m depth to groundwater (Schrader and Hill

1915). Over the

next 100 years, the groundwater elevation changed due to well installation, pumping, climate, and changing surface conditions.

Water levels, based on the Arizona

Department of Water Resources (ADWR) Wells 55 Registry, were interpolated using kriging (Figure 1.3) and inverse distance weighted spatial analysis. Based on these analyses, the current level at the Blue Nose Mine Site is approximately 25 m below the surface (Figure 1.4). Floyd

Gray at the USGS approximated

the water level at an abandoned shaft to be 22 m below the surface. The ADWR also provides Groundwater Site Inventory (GWSI), which uses water levels from the Hydrology Division"s Basic Data Section, the USGS, and other agencies. A GWSI livestock well, located approximately 5 m from the northeast extent of the field survey, observed

7 m depth to water on December 10, 1987 (Figure 1.5). Another GWSI well, located in the

8 central Cienega Creek Groundwater Basin, had a 5% difference between modeled and observed water levels in 2016 (Figure

1.6). Continuous distributions of water between measured points are

assumed for the calculated model. A spatial correlation matrix was used to analyze the interpolated water levels and the 5 m digital elevation model (DEM) raster from the USGS (Figure 1.7). The matrix gave a correlation of -0.53, implying that elevation and water levels have a moderately negative relationship in the Cienega Creek Basin. The interpolation does not account for the complex geology at this site. Thus, the geophysical survey will improve on the simple geometric shape assumption of the aquifer. The Blue Nose Mine lies within the Santa Cruz watershed in southeastern Arizona (Figure 2.3). Harshaw Creek, one of the primary tributaries of the Santa Cruz River, is the nearest alluvial system to the mine. The study site has a long history of mining activity which has produced moderate concentrations of heavy metals including antimony, cadmium, cobalt, chromium, copper, iron, lead, manganese, molybdenum, and zinc (Eddleman, 2012). Included in this report are modern concentration samples of aluminum (Figure 1.8) and cadmium (Figure 1.9). At 20°C, aluminum has a resistivity of 2.82x10 -8 ohm-m and a conductivity of 3.5x10 7

S/m. At 20°C,

cadmium has a resistivity of 6.84x10 -8 ohm-m and a conductivity of 1.46x10 7

S/m. An

understanding of the hydrological and geochemical processes that resulted in the mineralization, transport, and infiltration of these heavy metals into the soil, as well as their effect on the subsurface conductivity, will lead to a better understanding of geophysical data retrieved at the study site. 9 Figure 1.2. Geologic map of the northern Patagonia Mountains. Inset square shows location of study area . Modified from Vik re et al., (2014). 10

Figure 1.3.

Interpolated depth to groundwater levels (ft) using kriging. Water level data was obtained from the ADWR Wells 55 Registry. 11 Figure 1.4. Same as Figure 1.3, but zoomed into the study area. 12 Figure 1.5. Hydrograph for GWSI well 637238, which is one of the closest wells to the field site. Figure 1.6. Hydrograph for GWSI well 604551, which is one of the closest wells to the field site. 13

Figure 1.7. Statistical analysis of the interpolated water levels from ADWR (layer 1) and 5 m DEM from

the USGS (layer 2). The correlation matrix between the two raster layers indicates a moderately negative relationship between water level and elevation. 14 Figure 1.8. Map of Harshaw Watershed samples tested for aluminum concentration. Blue Nose mine is located at the bottom left of the figure. Courtesy of Floyd Gray (USGS). 15 Figure 1.9. Map of Harshaw Watershed samples tested for cadmium concentration. Blue Nose mine is located at the bottom left of the figure. Courtesy of Floyd Gray (USGS). 16

1.5 References

Ball, L.B., Caine, J.S.,

and S. Ge, 2014, Controls on groundwater flow in a semiarid folded and faulted intermountain basin, Water Resources, 50, 6788-6809.

Eddleman, K., 2012,

Bioaccumulation of heavy metals from soils to plants in watersheds contaminated by acid mine drainage in SE Arizona, Unpublished Master"s Thesis, The

University of Arizona, Tucson, Arizona.

Garfias, J., 2009, Groundwater in mountain regions, In Groundwater: Vol. I, EOLSS Publishers,

Oxford, UK.

Mindat, 2015,

Blue Nose Mine (Abe Lincoln Mine; War Horse Mine; Big Chief Mine; Big Jim Mine; Blue Nose Extension Mine; Home Again Virginia Hay claims), Harshaw, Harshaw District, Patagonia Mts, Santa Cruz Co., Arizona, USA, https://www.mindat.org/loc-

33875.html, accessed April 15, 2019.

Schrader, F.C. and J.M. Hill, 1915, Mineral deposits of the Santa Rita and Patagonia Mountains,

Arizona, USGS Bulletin 582, 278-279 & 373.

Vikre, P.G., Graybeal, F.T., Fleck, R.J., Barton, M.D., and E. Seedorff, 2014, Succession of Laramide magmatic and magmatic-hydrothermal events in the Patagonia Mountains, Santa Cruz County, Arizona, Economic Geology, 109, no. 6, 1667-1704. 17

2. Location Maps

and Elevation Profiles

2.1 Geographic Location Information

The overall location of the study area is shown in Figure 2.1. Location data for each geophysical method station was collected using Garmin 64st GPS units. Proper headings for each line survey were maintained using each GPS unit"s internal compass. The recorded coordinates were imported into ArcMap and Google Earth Pro in order to facilitate georeferencing. The UTM coordinates fall within zone 12R with the range of eastings 0525350 to 0525750 and northings

3479250 to 3479500.

2.2 Elevation Data

The elevation of the field site and surrounding area is seen in Figure 2.2. Elevation data came from four different sources: multiple Garmin 64st GPS units, a Nikon Forestry Pro laser rangefinder, Google Earth Pro, and the Shuttle Radar Topography Mission (SRTM). While the Garmin GPS tended to be largely unreliable for accurate elevations, Google Earth Pro , the

SRTM data

and the laser rangefinder proved more dependable. Elevation profiles from all four sources are provided.

2.3 Geophysical Survey Locations

Thirteen TEM loops, 20m on each side, were laid roughly East to West with a 235º/55º trending azimuth for Line 1 (Figure 2.4). Five TEM loops, 10m on each side, were laid over the tailings piles, roughly East to West for Line 2 (Figure 2.5). This adds up to around 5200m 2 of study area for Line 1, and 500m 2 of study area for Line 2. In order to avoid excessively steep terrain and minimize the disruption of ground vegetation, some of the loops were shifted off the center axis of each line 18 There were two DC Resistivity lines, Line 1 and 2, that were parallel to each other and 280m in length (Figure 2.6). Each line consists of 28 electrodes, each spaced 10m apart, the true locations of which are plotted as red dots in Figure 2.6. EM-31 and EM-38 surveys consisted of two lines above the tailings piles, one (Line 1) running roughly East to West, the other (Line 2) running roughly North to South (Figure 2.7). The total field magnetic survey consisted of ten East to West lines of measurements, each line consisting of twenty -two stations, making for 220 data points (Figure 2.8). Almost every data point is evenly spaced 15m apart, except where rough terrain required a station to be shifted.

This survey covers over 3150m

2 , which is most of the field area.

2.4 Location and Elevation Error

The Garmin 64st GPS unit has a positional accuracy of up to 3.09m over a 60s average (US

Forest Service, 2017),

but elevation readings can have much higher errors. Comparing the GPS unit data to that from Google Earth Pro, elevation at DC Resistivity Line 1 is consistently lower in measurements from Google Earth Pro (Figure 2.11). For DC Resistivity Line 2, the GPS units show consistently lower elevations (Figure 2.12). Elevations for the TEM Loops are similar for both the GPS units and Google Earth Pro. The maximum difference for the 20m TEM Loops is at 70m: Google Earth Pro shows an elevation about 10m higher than the GPS measurements (Figure 2.9). The elevation measured by the GPS units is very similar to that from Google Earth

Pro for

the 10m TEM loops (Figure 2.10). Elevations measured at both lines for EM-31/38 are very similar. On Line 2, elevation measurements from the two sources follow the same trend, but measurements from the GPS units are always about 5-10m lower than those from Google Earth Pro (Figure 2.14). It is important to note that on Line 1, GPS unit measurements fluctuate a lot, but they are close to the measurements from Google Earth Pro (Figure 2.13). 19

Figure 2.1. Overview map of the Blue Nose Mine site, located south of Patagonia, Arizona, as shown in

the red circle. Reproduced from Patagonia Alliance (2016). 20

Figure 2.2. Regional elevation map of the Patagonia Mountains. Field site is marked by black rectangle.

21

Figure 2.3. Map of southeastern Arizona watersheds. The study area lies within the Santa Cruz watershed

(bottom left corner), which consists of the San Rafael Basin, Santa Cruz River, and its tributaries. 22

Figure 2.4. Location map for the 20m TEM loops along Line 1. Note that Loop 15 was not used in the inversion modeling.

23

Figure 2.5. Location map for the 10m TEM loops along Line 2 on the surface of the tailings piles. Note that Loop 5 was not used in the inversion

modeling. 24

Figure 2.6. Location map showing the DC resistivity lines in blue. The red data points are GPS locations collected at each electrode.

25
Figure 2.7. Location map of the tailings area showing the EM-31 and EM-38 data collection points. 26
Figure 2.8. Location map with all magnetic field stations represented as red dots. 27
Figure 2.9. Elevation profiles of DC Resistivity Line 1 from East (left) to West (right). Figure 2.10. Elevation profiles of DC Resistivity Line 2 from East (left) to West (right). 28
Figure 2.11. Elevation profiles of 20m TEM loops from East (left) to West (right). Figure 2.12. Elevation profiles of 10m TEM loops from East (left) to West (right). 29
Figure 2.13. Elevation profiles of EM-31/38 Line 1 on tailings from East (left) to West (right). Figure 2.14. Elevation profiles of EM-31/38 Line 2 on tailings from South (left) to North (right). 30

2.6 References

Patagonia Alliance, 2016, Southern Arizona"s Mountain Empire: Sanctuary for Rare and

Unusual Species,

sanctuary-rare-unusual-species/, accessed April 15, 2019.

US Forest Service, 2017, Tested Accuracies,

https://www.fs.fed.us/database/gps/mtdcrept/accuracy/documents/accuracy.pdf, accessed

April 15, 2019.

31

3. Transient Electromagnetic (TEM) Survey

3.1 Introduction and Meth

ods The Transient Electromagnetic (TEM) method is a geophysical technique used to image subsurface resistivity or conductivity. It can be used for subsurface geophysical investigations on scales of meters to

kilometers in depth. The goals of the survey used for this location are to identify zones of high and low

resistivity and to provide information on the depth of the tailings piles.

Two ungrounded loops are positioned on the ground, and a time-varying current flowing through the outer

(transmitter) loop generates an electromagnetic wave that diffuses through the subsurface (Figure 3.1).

Induced eddy currents from subsurface conductive layers produce secondary EM fields, which are picked

up by th e inner (receiver) loop. These eddy currents decay rapidly after the current is shut off. Depending

on the conductivity of the material, the decay can be fast or slow, where conductive materials have slower

decay times. When the current is turned off, the instrument records the resulting decay curves using the rec eiver loop in 31 windows from approximately 1.5 µs to 3 ms after the current is turned off. The instrument begins recording 1.5 µs after the current is turned off, because there is still a small amount of current flowing in the transmitter loop (Zonge International, 2019). Figure 3.1. Representation of TEM arrangement and the signal response in time domain (BGR, 2019). 32

3.2 Instrumentation and Field Procedures

The data were collected on two consecutive weekends, February 9-10 and February 16-17 of 2019. The instrumentation included the Zonge International GDP-32 II, a multi-function receiver, along with the Zonge International NT-20 transmitter, referred to as a Zonge NanoTEM system. The receiver records

multiple transient surroundings per loop, and computer modeling translates the time to depth. The square

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