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Abandoned mine site characterization using digital field mapping, UV-VIS-NIR spectroscopy, and water sampling: an integrated method

Abstracts

Design and implementation of a non-invasive water sampling program to characterize thetemporal variation of stream and river water quality effects of three abandoned Cu-Znmines in the Sierra Nevada Foothills, California: combining GIS, digital field data, and

time-series chemical data (oral presentation)

Takagi, Tina K. and Brimhall, George H, Dept. of Earth & Planet. Sci., University of Californiaat Berkeley, Berkeley, CA 94720-4767

The state of California alone has tens of thousands of abandoned mines. The mines rangefrom those that are environmentally problem-free to those that clearly produce damaging acidmine drainage and require cleanup, and there is a necessity to screen and classify all of thesemines in a timely manner. We have developed a method for rapid and non-invasive mine sitecharacterization with a digital mapping system and periodic water sampling. Access to themyriad of abandoned mine sites is a serious impediment to site characterization. Our approach,which includes helicopter-based GPS and laser digital mapping and spectroscopy, providescritical environmental data and is particularly useful since many current owners are reluctant toallow access to their properties for research. This method is being utilized to characterizehistorically mined volcanogenic massive sulfide deposits in the Sierra Nevada Foothills due totheir unique potential for acid generation. The mappable soluble salts that precipitate on thesurface of mine waste dumps are washed down to the streams and rivers that drain these minesites in the wet season, contributing to increased metal loading. Monthly and bimonthly watersampling and analysis by atomic absorption spectroscopy characterizes this temporal variation inwater chemistry and its link to the changing surface mineralogy of these abandoned mine dumps.Design of the sampling program began with the compilation of watershed and monitoring stationmaps, property boundary maps, and street maps. Those data were used in combination withgeologic and topographic maps to determine appropriate sampling locations. In the field, watersampling sites were located to sub-meter accuracy using a differential GPS and were mapped ona pen computer using U.C. Berkeley’s GeoMapper software. Features not shown on publishedmaps, such as intermittent or small stream drainages, old mine structures, access roads, gates andfences were also located and mapped. The water chemistry data and field measurements, alongwith the published and digitally-produced field maps, provide powerful tools for determining theeffect of acid mine drainage on water quality.

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An integrated approach to screening of abandoned mines for remediation: digital fieldmapping, IR spectrometry and time-series water chemistry (poster presentation)

Takagi, Tina K., Montero S., Irene C. and Brimhall, George H, Dept. of Earth & Planet. Sci.,University of California at Berkeley, Berkeley, CA 94720-4767

Remediation of abandoned mines is a critical environmental issue worldwide. In theU.S.A. alone, the hundreds of thousands of abandoned mines that dot the landscape have thepotential to contribute to serious acidification and heavy metal loading of rivers. In order toinventory abandoned mine sites and classify the extent to which they negatively impact theenvironment, a new method for rapid and accurate screening of mine sites is necessary ifavailable funding is to effectively resolve this important environmental issue. Making use ofcurrently existing technology and methods, only the most serious cases stand to benefit fromremediation efforts, while the sheer volume of abandoned sites have not been fully characterized.The Earth Resources Center of the University of California, Berkeley has developed a methodthat integrates new digital technology for screening abandoned mine sites. For their role as primegenerators of acid mine drainage, we focus on volcanogenic massive sulfide deposits and use anintegrated field method, combining digital sub-meter accuracy GPS and laser-based mappingwith infrared and visible reflectance spectroscopy, supported by periodic water sampling andAAS geochemistry. At these sites, pyrite oxidation in combination with surface runoff,evaporation and capillary rise creates soluble secondary minerals that release contaminants intoadjacent watersheds and groundwater aquifers upon dissolution. Using this integrated mappingsystem, the mine sites are surveyed and their surface mineralogy mapped in a minimal amount oftime. This method is particularly useful for difficult-to-access areas, whether due to distance,time, or property access permissions, because survey parameters such as grid size and samplingdensity can be adapted according to the initial results obtained and viewed in the field in realtime. In addition, site-specific or temporally varying features can be mapped using GeoMappersoftware in detail: zonation of secondary minerals, country rock geology and its potential foracid neutralization, intermittent and small stream drainages, old mine structures, rock/soil andwater sampling sites, boundaries of disturbed vs. undisturbed waste rock, types of mineralprocessing waste. Our environmental mapping, in combination with periodic water sampling andanalysis, provides a powerful tool for relating the mineralogical dynamics of mine dumps to riverchemistry. By identifying and mapping products of sulfide oxidation that are indicative ofacidification (such as copiapite and jarosite) via ground and helicopter surveys, it becomespossible to screen the most problematic sites for further characterization and selectiveremediation.

IntroductionThe California Department of Conservation estimates that there are approximately 39,000

historic and inactive mines in California (OMR AMLU, 2000). It is estimated that over 4,000 ofthose mines present some sort of environmental hazard, whether it is in the form of acid rockdrainage, heavy metals, residue from processing chemicals, or sedimentation. Each of thesecontaminants negatively affects water quality and can be transported for long distances instreams and rivers. Fig. 1 is a map of the known copper mines in California, which dot nearly theentire state.

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100 0 100 200 Kilometers

Clearly, the need to inventory and characterize these mines is both overwhelming andpressing. The Earth Resources Center has developed an integrated method for accuratecharacterization of mine sites and is using this method at three locations in the Sierra NevadaFoothills Cu-Zn belt. The integrated method involves periodic water sampling, Ultraviolet-Visible-Near Infrared (UV-VIS-NIR) spectroscopy, and a digital mapping system. Periodic watersampling and laboratory analysis allow the investigator to assess a mine site’s impact on waterquality through time. UV-VIS-NIR spectroscopy provides a rapid method for identifying thevarious oxide, sulfate, hydroxide, and oxyhydroxide minerals that precipitate on mine dumpsurfaces, allowing the worker to interpret what their presence means chemically. The digitalmapping system consists of a set of tools that facilitate data collection and storage in a uniform

Figure 1. Abandoned copper minesin California counties. From the GISdatabase of Ferderer, 1996. The minesof the Sierra Nevada Foothills Cu-Znbelt are flanked by the red arrows.

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format such that any number of workers can understand and use it with minimal training. Thatdata is then displayed as a map that allows the user to make important decisions regarding thepresent state of the mine and the effect it has on its surroundings.

The Copper-Zinc Belt of the Sierra Nevada Foothills provides a unique chance to testmethods of abandoned mine site characterization due to the high pyrite content of itsvolcanogenic massive sulfide deposits and to the climate in the Foothills: arid, with long dryperiods throughout most of the year, and a short but heavy rainy season in winter. Pyrite in themining waste rock of the old mine dumps oxidizes, releasing metals and acid into solution. Thissolution is brought to the mine dump surface via capillary rise or seepage, and subsequentevaporation causes the formation of soluble salt minerals.

Those soluble salts that have formed and accumulated on mine dump surfaces throughoutthe preceding dry months, storing metals and acid in their structures, are dissolved by the firstmajor storms and carried by runoff into nearby streams to be transported along the waterway. Itis important to examine the extent to which the effects of this are measurable downstream, andwhat those effects are. In some locations, fish kills have been attributed to this salt dissolutionduring the first rain (Dagenhart, 1970).

Thus the frequency and timing of water sampling are important factors. Sampling wateraround mines only once in the dry season will not give an accurate picture of the dynamic natureof the water chemistry. Because the duration of the winter storm events that dissolve the solublesalts and their resulting effect on the stream are only on the scale of hours to days it is necessaryto sample throughout the year, taking care in the winter to anticipate major storms and schedulesampling runs accordingly.

Likewise, mine dump surface mineralogy and mineral distribution varies with seasonand/or with any sort of physical disturbance. The mapper must be conscious that the mineralogyobserved on the surface during field work that day is only a snapshot of a dynamic surfaceenvironment.

This extended abstract describes our integrated method, which aims to provide accuratecharacterization of abandoned mine sites for decision-making, while taking into account thedynamic nature of both the water chemistry and the surface environment associated with thoseabandoned mine sites. The initial stages of abandoned mine site characterization using thismethod are discussed: how water sampling and abandoned mine project sites were chosen, howground surveys are conducted, and how abundant data is stored and displayed in a useful format.

Water Sampling ProgramAny environmental characterization of an abandoned mine site is incomplete without

some knowledge of its effect on watershed chemistry. For the three abandoned mine project siteschosen in the Sierra Nevada Foothills Cu-Zn belt: Spenceville Mine, Newton Mine, andCopperopolis, there are a total of 27 water sampling sites at present, being sampled on anapproximate monthly basis. A summary map of their locations relative to the mines is shown inFig. 2. Water sampling sites were chosen to characterize the water chemistry immediately in thevicinity of the mine sites, as well as to determine the measurable extent of downstream effect themine runoff has on river chemistry throughout the year.

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Figure 2. Simplified map of water sampling sites and the path of downstream drainage (in green) into majorCalifornia rivers, relative to mine project sites. Spenceville Mine waters drain into Little Dry Creek and DryCreek, which eventually merges with the Bear, Feather, and Sacramento Rivers, in order. The Newton Mine isdrained by Copper Creek, which merges with Dry Creek and then the Mokelumne River. The mines ofCopperopolis eventually drain to Black Creek and the Stanislaus River. To avoid crowding, not all of the 27 sites areindividually labeled; for example, sample C3 actually consists of samples C3a, C3b, and C3c.

For each mine site, the nearest stream affected by the mine dumps was identified. Onewater sampling site was always chosen upstream from the point at which that stream wouldbegin receiving runoff from the mine dumps. Another site was chosen about the middle stretch ofthe mine dumps along the stream. A third site was chosen downstream at the point where thestream would no longer be receiving mine dump effluent. Subsequent downstream sites aimed tosample around confluences; one site would sample the ‘polluted’ water coming from the mine,another would sample the ‘clean’ water coming from the adjoining river, and yet another site waslocated after the two rivers had merged. This is best shown by sample sites N4, N5, and N6 in

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Fig. 2: the creek that runs along the Newton Mine merges with the creek along which site N4 islocated. Sample site N5 is located on the Mokelumne R., before the creek joins it. Site N6 islocated immediately after the creek empties into the Mokelumne River.

In order to choose water sampling sites, the drainage network of waters potentiallyaffected by the mines had to be identified. NHDView (USGS, 1999) was useful for tracingdownstream drainages from the abandoned mine sites. The watersheds corresponding to theareas of study were identified, and their data was downloaded from the web. In NHDView, theuser can pick hydrologic features of interest, retrieve their associated information from the GISdatabase, and then follow their progression downstream. For this project, we picked the nearbystreams that receive runoff from the abandoned mine dumps and followed the network of largerstreams and rivers downstream. Figure 3 is the path of the water from Little Dry Creek, whichreceives runoff from the Spenceville Mine, out to the Bear and Feather Rivers, and eventuallythe Sacramento River.

After the drainage network was determined, locations of potential water sampling siteswere chosen from an assemblage of maps: topographic maps of various scales, county assessor’smaps, road maps. Criteria for each site depended on the following:

1. Location downstream from the mine2. Accessiblility from public roads3. Location on passable property, either public or as allowed by owner4. Distance from parking area5. Physical and personal safety factors

Once potential sites were identified, their feasibility as actual sampling sites wasconfirmed by a visit. If the site met the criteria above, its location and given site name wererecorded in UTM coordinates using a GPS.

The water sampling sites were plotted in Geomapper (Brimhall and Vanegas, 2000)software based on their UTM coordinates. In order to put these water sampling sites in a contextthat was easy to understand, it was necessary to make a map that displayed the water samplingsites relative to other geographic features. Fig. 4 is a screen capture of a Geomapper display,showing several water sampling site locations relative to a georeferenced topographic map. Thisis also a useful tool for navigation, as the driving route can be mapped and plotted.

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Figure 4. Water sampling sites (red symbols) and partial driving route (blue line), with a georeferencedUSGS 1:500,000 topo map used as a backmap. Screen capture of GeoMapper display. The displayed backmapfacilitates navigation, and allows for fast geographic recognition of location. By leaving the GPS unit on, thesamplers can watch the route being mapped on the screen while driving; they can also map and enter into thedatabase any roads or other geographic features which may not exist on this backmap. Area in green rectangle isenlarged in Fig. 5.

Fig. 5 is an enlargement of the southeast corner of Fig. 4. The backmap was carefullygeoreferenced, so that even at such an enlarged scale, the driving route as mapped with a GPS(shown in blue) generally overlies the roads shown in the backmap. Roads that are not shown onthe 1:500,000 scale backmap were also mapped and are also visible here.

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Figure 5. Water sampling sites around Copperopolis and Tulloch Reservoir. Enlargement of SE area in Fig. 4.For ease of viewing, the color backmap has been switched to grayscale; this is an option in the software. Watersampling sites are shown in red; roads (blue) have been mapped in with a GPS. The area denoted by the green arrowis further enlarged in Fig. 6.

For navigational purposes, a georeferenced large-scale map is effective. However, after acertain point a more accurate, smaller-scale backmap is desirable as a user begins to do moredetailed mapping or needs more information. Fig. 6 is an enlarged area of Fig. 5, but at this scalethe 1:500,000 topo map is no longer useful and has been substituted with a georeferencedassessor’s map at an original scale of 1”=200’. For our project, in which issues of access toproperty and permission are highly important, this is an effective use of digital mapping.

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Figure 6. Water sampling site C2 (red symbol), driving route (double blue lines) and labeled georeferencingpoints. This is a further enlargement of the area denoted by the green arrow in Fig. 5. The backmap has beenchanged from the 1:500,000 USGS topo map to a georeferenced assessor’s map showing lots and propertyboundaries. The roads on the backmap deviate slightly from the actual geometry of the road in places, as is clearlyshown on the bottom lefthand side. With this backmap, it is easy to see on which property you are currently located,when you cross property boundaries, and to avoid properties for which permission to access has not been obtained.

Mine site characterizationSite selection. The three abandoned mine sites—Spenceville, Newton and

Copperopolis— were identified as desirable locations in which to test the application of ourintegrated approach for abandoned mine site characterization. The method for choosing thesesites was similar to the approach described above for water sampling locations. Once thepotential sites were identified, their feasibility as project sites was confirmed by a visit. In thecase of the abandoned mines, the following criteria were examined:

1. Good exposure of mine dump surfaces (i.e., little or no vegetation, minor disturbanceof the dumps, few structures over the dumps)

2. Accessibility from existing roads3. Location on passable property, either public or as allowed by owner4. Physical and personal safety factors

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After the visit, maps and literature were amassed for each of the mine sites. A trip wasalso made to the assessor's office of each county in which the mines were located. Propertyowners were contacted for permission to access the land, and based on their responses, the scopeof the study was modified for each mine site.

Spenceville Mine. Located on Department of Fish and Game land, Spenceville Mine wasthe site to which full access was granted for this research. A ground survey was completed first,and a helicopter-based survey was performed in May 2001. Another ground survey andhelicopter survey are both planned for Fall 2001. Water sampling is ongoing at 6 sites within thearea shown in Fig. 7. The site is currently undergoing remediation, and so an additional factor ofinterest in this research will be to track the effect of remediation efforts and dump materialtransport on watershed chemistry.

Figure 7. Aerial view from the southeast of Spenceville Mine and ongoing remediation.. Grey-coloredrectangular shape in the center is a liner inside a pit, into which part of the waste rock will be moved. The pit lake isthe dark-colored area to the right of the blue trailer. Much of the seepage and runoff drains into the pit lake, butduring the rainy season runoff also enters Little Dry Creek, which runs along the east side of the mine, and into DryCreek, which is obscured by trees and runs parallel to the dirt road extending right to left in the foreground.

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Ground survey. Fig. 8 is a cartoon of the ground-based survey method. This can beadapted for a low-altitude airborne (helicopter) platform as well.

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Figure 8. Diagram of ground-based survey. Operator 1 walks a grid (dashed black line) over the site of interestwith a portable UV/VIS/NIR spectrometer, taking spectra of the ground surface at each point (green dots). Thesespectra are recorded as automatically numbered individual files in the subnotebook computer that runs thespectrometer. Operator 2 has used the GPS unit to fix the position on which the laser tripod stands, and then fires thelaser at Operator 1 to obtain the coordinates of each point at which spectra are taken. These coordinates are thenrecorded and mapped by GeoMapper software in the pen computer and displayed on the screen. By this method bothoperators can concentrate on obtaining useful data as displayed on their respective computer screens: Operator 1concentrates on collecting noise-free spectra, and Operator 2 concentrates on obtaining accurate location points.

The map from the ground survey at Spenceville Mine is shown in Fig. 9, and is explainedin greater detail in Figs. 10 and 11. A large variety and amount of information can be stored inthe file generated during the ground survey by digital mapping. The uniformity of the databasesand the mapping legends minimizes confusion amongst various users. This data, in conjunctionwith the water sampling data, allows managers to make informed decisions regarding the futureof the mine site.

Operator 1

Operator 2

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Figure 9. Screen capture of ground survey at Spenceville Mine. The backmap shows topography, vegetation, themine pit lake, Little Dry Creek, and wells. The brown line is the extent of mine waste as mapped by walking theperimeter with a GPS unit. Dirt roads through the mine site were also walked with a GPS unit and are shown in blue.The red eye-shaped symbols are points at which UV-VIS-NIR spectra were acquired with a portable spectrometerfor surface mineral characterization. Points at which rock samples were taken are denoted by the green hammersymbols.

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Figure 10. Enlarged area of Fig. 9, showing ground traverses made by spectrometer operator for mine sitecharacterization. As shown in Fig. 8, Operator 1 walks over the ground surface, acquiring spectra. Operator 2handles the laser rangefinder and monitors the progress of the mapping on the computer screen, as shown here. Eachpoint along the traverse has a GIS database record associated with it, in which the automatically numbered spectramatch with the file number of the corresponding spectra in the spectrometer to be matched up at a later time. A timestamp is also stored in the database which can also be matched to the corresponding time stamp on the spectral file.If necessary at a later time, anyone can refer back to the original file in order to look up the GIS record of aparticular graphic item. Here, the operator chooses the infrared symbol on the far right (highlighted in bold red), andthe software returns the corresponding GIS information: UTM coordinates, internal index numbers, the spectranumber, and the time stamp.

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Figure 11. GIS database record of highlighted (bold red) rock sample symbol, from field work file. Thesoftware retrieves the GIS record associated with the mapped symbol, displaying the UTM coordinates of thesample location, index numbers, the sample number assigned to the rock, and a brief reminder and description inputby the operator at the time of collection. The operator or another person can conveniently refer to the file at a laterdate to find out when, where and why a particular rock sample was collected.

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Figure 12. Portion of completed surface mineralogy map for Spenceville Mine. GIS databases have beenexported from Geomapper and are displayed here in ArcView software. Mineral identification of UV-VIS-NIRspectra collected from the ground survey was performed by the FstSpecID algorithm of Montero S. and Brimhall(2001).

Figure 13. Helicopter over Spenceville Mine dumps, May 2001.

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ConclusionThe water chemistry data and field measurements, along with the published and digitally-

produced field maps, provide powerful tools for determining the environmental effect of a minesite accurately. Using a digital mapping system, a mine site ground survey can be carried outquickly with a minimum number of workers, and the software ensures a common legend andwell-organized accessible database for all users, minimizing confusion and loss of information.

The advantages of the integrated method are efficiency and flexibility. Many of thesemines are located on private property, leaving it to the discretion of the owner to grant or denypermission to workers hoping to access the land. Some mine sites may be distant or difficult toaccess due to a remote location and a lack of existing roads. Time is also a factor, as well as theseason in which site characterization is done. The integrated approach described here can beadapted to nearly any situation. When full access is allowed, a complete ground survey ispossible. If no access is granted or if the site is difficult to access, the platform can be adapted fora low-altitude remote sensing survey from a helicopter. Water sampling is non-invasive and canbe put into place upstream and downstream of abandoned mine sites, outside the boundaries ofinaccessible properties. Depending on the time available for each mine site, one or more surveyscan be carried out during the course of a year to determine its necessity for remediation. Ongoingwater sampling supplements the mine site surveys, and its frequency and number of sites can beadjusted as needed throughout the duration of the sampling program.

ReferencesBrimhall, G. H and Vanegas, A., Digital mapping of geology and ore deposits with GeoMapper:

GSA Abstracts with Programs, v. 32, n. 7, p. A-514.Dagenhart, Thomas V., 1980, The acid mine drainage of Contrary Creek, Louisa County,

Virginia: factors causing variations in stream water chemistry: Unpublished MastersThesis, University of Virginia, 215p.

Ferderer, David A., 1996, National Overview of Abandoned Mine Land Sites Utilizing theMinerals Availability System (MAS) and Geographic Information System (GIS)Technology: U.S. Geological Survey Open-File Report 96-549.http://geology.cr.usgs.gov/pub/open-file-reports/ofr-96-0549/ofr-96-549.html

Montero S., Irene C. and Brimhall, George H, 2001, Semi-automated fast mineral identificationalgorithm for ultraviolet, visible and near infrared reflectance spectroscopy, AnnualConference of the International Association for Mathematical Geology, this volume.

Office of Mine Reclamation Abandoned Mine Lands Unit, 2000, California’s abandoned mines,a report on the magnitude and scope of the issue in the state: Department ofConservation, Sacramento, CA, 246p.http://www.consrv.ca.gov/omr/AMLU/amlurpt/index.htm

United States Geological Survey, 1999, National Hydrography Dataset, http://nhd.usgs.gov/

AcknowledgementsThis research is supported by a grant from NASA Regional Earth Science Application

Center.