Affiliated Research CenterF I N A L R E P O R T

Series ARC-SDSU-002-97

Integrated Use of RemoteSensing and GIS for Mineral

Exploration

La Cuesta International, Inc.

San Diego State University

Commercial Remote Sensing Program,National Aeronautics and Space Administration

La CuestaInternational, Inc.

Affiliated Research CenterFinal Report

Integrated Use of Remote Sensing andGIS for Mineral Exploration:

A Project of the NASA Affiliated Research Center atSan Diego State University

Project conducted by:La Cuesta International, Inc.

1805 Wedgemere RoadEl Cajon, California 92020

Report prepared by:Mr. W. Perry Durning

La Cuesta International, Inc.and

Mr. Stephen R. Polis and Dr. Eric G. Frost,Department of Geologic Sciences, San Diego State University

andMr. John V. Kaiser

Department of Geography, San Diego State University

Report prepared for:Dr. Douglas A. Stow, Principal Investigator

San Diego State UniversityDepartment of Geography

San Diego, California 92182-4493and

Commercial Remote Sensing Program OfficeNational Aeronautics and Space Administration

John C. Stennis Space Center, Mississippi 39529

January 20, 1998

iii

EXPORT ADMINISTRATIONREGULATIONS NOTICE

This document contains information within the purview of theExport Administration Regulations (EAR), 15 CFR 730-744,and is export controlled. It may not be transferred to foreignnationals in the U.S. or abroad without specific approval of aknowledgeable NASA export control official, and/or unlessan export license/license exception is obtained/available fromthe Bureau of Export Administration (BXA), United StatesDepartment of Commerce. Violations of these regulations arepunishable by fine, imprisonment, or both.

iv

Table of Contents

EXPORT ADMINISTRATION REGULATIONS NOTICE .................................................. iii

Executive Summary ................................................................................................................. vi

1.0 Introduction..........................................................................................................................1

2.0 Structural Mapping ..............................................................................................................2

3.0 Alteration Mapping..............................................................................................................3

4.0 Radar ....................................................................................................................................5

5.0 Results and Conclusions ......................................................................................................5

6.0 References............................................................................................................................6

Appendix A. Technical Proposal .............................................................................................20

Appendix B. Commercial Proposal .........................................................................................24

Appendix C. Schedule .............................................................................................................25

Figures

Figure 1. Tertiary dip domain map of the southern Basin and Range Province. ......................8

Figure 2. Generalized geologic map of the northern part of the Colorado River Trough andadjacent region. ..........................................................................................................................9

Figure 3. Diagrammatic representation of opposite polarity tilt patterns in extensionalterranes as separated by a strike-slip or transfer fault (A) or an accommodation zone (B). ....10

Figure 4. Geometric and kinematic characteristics of Neogene extensional deformation,Colorado River extensional corridor, NV, AZ, and CA. (Frost and Heidrick, 1996)..............11

Figure 5. Detachment fault-fold geometry and deep-crustal structure, Colorado Riverextensional terrane, as based on CALCRUST and reprocessed industry seismic lines. ..........12

Figure 6. Diagrammatic model of crustal extension showing truncation of upper-plate normalfaults at depth into a gently inclined detachment fault. ...........................................................13

Figure 7. A SPOT-Landsat TM ratio threshold merge of the area around the southernChocolate Mountains illustrating extensional antiforms and areas of potential hydrothermalalteration highlighted in yellow. ..............................................................................................14

Figure 8. A SIR-C radar Landsat TM threshold merge of the area around the Mesquite mine.15

Figure 9. An over-simplified structural model depicting the Mesquite mine located within anewly interpreted accommodation zone...................................................................................16

v

Figure 10. Landsat TM 741 color composite image of the southern Colorado Riverillustrating extensional faults and the newly interpreted accommodation zone. .....................17

Figure 11. A SIR-C radar color composite with interpreted Tertiary upper-plate transportdirections and accommodation zone structure illustrated. .......................................................18

Figure 12. A Landsat TM ratio color composite of the area around the Mesquite mine. .......19

Figure A-1. Diagrammatic representation of opposite polarity tilt patterns in extensionalterranes as separated by a strike-slip or transfer fault (A) or an accommodation zone (B). ....23

vi

Executive Summary

The Affiliated Research Center (ARC) program was conducted with La Cuesta International,Inc. (LCI) and supported by San Diego State University (SDSU). The purpose of theprogram was to develop the procedures and demonstrate the feasibility of using broad-bandand hyperspectral, remotely sensed data to identify extensional geologic structures(accommodation zones) associated with precious/base metal deposition. In most cases,current mineral exploration concepts have failed to recognize the association ofmineralization with unique extensional structures called accommodation zones. These zonesshow little obvious deformation, yet focus fluid migration and mineralization into predictableregions of the crust. The Mesquite gold mine, located in southeastern California,approximately 60 km east of the Salton Sea, was studied to determine if it resides within anunrecognized accommodation zone. Landsat Thematic Mapper (TM), Satellite Pourl'Observation de la Terre (SPOT), and radar data were observed both separately and in amerged format to extract spectral and spatial information using ER Mapper software. Avariety of images were produced to highlight important structural features along with areas ofhydrothermal alteration. Images produced include Landsat TM and Shuttle Imaging Radar-C(SIR-C) radar color composites, color ratio composites, principal components, thresholds andLandsat TM-SPOT and Landsat TM-SIR-C radar merges. Hyperspectral data (AdvancedVisible/Infrared Imaging Spectrometer (AVIRIS) and Airborne Terrestrial ApplicationsSensor (ATLAS)) where obtained though not processed, because the data did not cover thestudy area.

The ARC project proved to be extremely beneficial in training LCI with remote sensingprocedures that resulted in the following:

• The recognition of an accommodation zone within which the Mesquite gold mineresides.

• The establishment of a template to identify hydrothermally altered areas from LandsatTM data. Prior studies in a non-ARC area showed less than 10% of TM anomalieswere related to hydrothermal alteration. Using the ARC template greater than 50% ofthe TM anomalies checked in the field showed hydrothermal alteration.

• The discovery of two virgin mineral systems in another non-ARC exploration area asa direct result of Landsat TM data interpretations using the template described above.

Thus, this study has provided an immediate positive impact for LCI by providing a templateto process TM imagery to successfully evaluate large areas of interest for mineral potential,focus field evaluations, and ultimately provide a higher probability for exploration success.

1

1.0 Introduction

Recognition of major gold deposits formed in association with Tertiary crustal extensions inthe western U.S. has been established and similar occurrences are now being recognizedglobally. In most cases, current mineral exploration concepts have failed to recognize theassociation of mineralization with unique extensional structures called accommodationzones. These zones, described below, show little obvious deformation, yet focus fluidmigration and mineralization into predictable regions of the crust. Integrating remotelysensed data with existing geologic data provides a unique opportunity to identify the locationof these previously unrecognized zones. Guided by an understanding of accommodationzones, Landsat TM, SPOT, and radar data were utilized to locate an unrecognizedaccommodation zone in which the Mesquite gold mine is located. Further remote sensingefforts made possible by insights developed through this ARC effort support the associationbetween accommodation zones and precious/base metal deposition.

Accommodation Zones

In areas of crustal extension, the crust breaks along a multitude of normal faults, commonlytermed an "array," with different segments having different transport directions as shown inFigures 1, 2, and 3. These segmented sections occur at a scale of 50 - 500 km along strike.Within these extensional terranes, transport of major regions is in one uniform direction(Bosworth et al., 1986; Lister et al., 1986). However, zones with opposite transport generallyexist in adjacent domains. Between these zones of opposite transport, a zone of deformationmust exist to allow opposite motion to occur during the same deformational phase. Thesezones have been called "accommodation zones," and have only recently been recognizedwithin extensional systems on a worldwide basis. Accommodation zones link the normalfault arrays of opposing transport directions. These regions are often zones of little obviousdeformation, appearing not as strike-slip faults, but brecciated “null” zones because the entirevolume of rock has been affected (Anderson, 1971; Bosworth et al., 1986).

Because accommodation zones represent areas of vergence reversal within extensionalterranes at the up-dip tips of the regional faults (Figures 3 and 4), they focus fluid migrationand mineralization into predictable regions of the crust. The Nelson District in southernNevada is an excellent example where alteration and mineralization occur within anaccommodation zone (Faulds et al., 1987; Frost and Heidrick, 1996). This zone is betweentwo opposite facing regions of extensional transport that can be discerned on the regionaltectonic maps and appears to point directly to the major gold mineralization.

The three-dimensionality of extended crust has been well documented by researchers in thepetroleum industries through high-quality, three-dimensional seismic investigations. Theseseismic studies have demonstrated the presence of accommodation structures in nearly all theextensional terranes in the world. Within these zones, fluids flow toward and saturateportions of the accommodation zones. Knowledge of how accommodation-zone tectonicslocalize fluid flow allows researchers to target discrete areas for detailed exploration withinthe much larger extensional terrane.

2

The association of accommodation zones with mineralization is due to three main factors:1. Accommodation zones are deep-crustal breaks that often become syntectonic volcanic

centers because they localize the magmatic material, thus becoming an elongated volcanicand plutonic center that intrudes existing fault zones and provides the thermodynamicenergy to drive mineralized fluids.

2. There is an increase in brecciation and the number of faults with a net decrease in theaverage fault slip within the accommodation zone, making the faulting more subtle butopening much larger volumes of extended rock. This provides excellent long-termpermeability for multigenerational fluid flow and subsequent mineralization.

3. The geometry is such that a localized compressional stress regime forms anticlinalculminations located structurally up-dip from the normal faults it separates or"accommodates" on either side. This extensional geometry provides a flowpath frommultiple normal faults toward the accommodation zones where mineralization can occurrepeatedly as the faults continue to break through time.

Combining optical and radar remote sensing and image processing provides a powerfulapproach to search for accommodation zones. Because the areas of opposite dip domains areso large, interpreting field data and large scale maps easily misses the location ofaccommodation zones. Since the recognition of opposite dip domains has not been part offield investigation methodologies before, many of the geologic maps and their synthesis aresimply inadequate to discern accommodation zone structures. Optical and radar data showgeologic structure and enable the geologist to synthesize the tectonics and also discern thepotential locations of hydrothermal alteration. This image analysis, coupled with anunderstanding of the tectonic processes and significance of the localized alteration, provides apowerful tool for exploration.

2.0 Structural Mapping

The antiformal-synformal character of the detachment fault system is one of the best ways offinding unrecognized large-scale normal faults and determining where accommodation zonesmight be found. Because of the regional perspective provided by the images and the displayof spectral and topographic data with optical and radar images, the antiformal-synformalcharacter of ranges can be readily discerned. In most areas, the long axis of the antiforms isparallel to the upper plate transport direction, much like megamullion structures elongated inthe transport direction (Figures 5 and 6). These mullion structures appear to have a fairlyconsistent orientation on a regional scale and appear to be more pronounced as more relativemotion has taken place on the fault structures. An obvious cause of this relationship is thatthe once moderate angle faults with their fluted fault patterns have tilted over more and more,making the mullions into whale-like, antiformal highs and trough-like synformal lows.

Due to the regional nature of these distinctive antiformal-synformal features, optical andradar imaging provides feature recognition for these targets, and enables potentialhydrothermally saturated antiforms to be highlighted. Figure 7 is a SPOT- Landsat TM ratio

3

threshold merge of the area around the southern Chocolate Mountains. The image illustratesthe ability to map and target extensional antiforms and areas of potential hydrothermalalteration highlighted in yellow. The strongest alteration signature in the image is along thedetachment fault antiform located closest to the Mesquite mine and the Mount Barrow plutonresponsible for the Mesquite gold mineralization (Frost, 1990). By changing the SPOTbackdrop to radar (Figure 8) and keeping the Landsat TM alteration data, the topography isreadily observed as it highlights antiformal-synformal geometry, as well as dipslopes andfracture patterns.

By mapping a larger area, the Mesquite mine was discovered to be located within anaccommodation zone (Figure 9). The southern Chocolate Mountains dip to the southwest,and are interpreted to have had a Tertiary northeast upper-plate transport direction, while theTrigo Mountains, located to the northeast across the Colorado river in Arizona, have had anopposite or southwest Tertiary upper-plate transport direction. The Mesquite mine ispositioned at the southwest termination of the accommodation zone between these two dipdomains, which is characterized by a northeasterly striking topographic low. Thisaccommodation zone was first observed through a Landsat TM Bands 7-4-1 color compositeimage where volcanic dipslopes, extensional faults and dikes, and the general geometry of theranges were mapped (Figure 10). Radar data used to image the structure highlighted thelinear topographic low of this accommodation zone that trends through the Mesquite mineand continues northeasterly for more than 60 km (Figure 11).

3.0 Alteration Mapping

The goals for producing alteration images for the ARC were to optimally depict all spectralproperties that may be related to alteration and then prioritize all targets for field evaluation.There are generally two common types of images used to map hydrothermal alteration: ratiosand select principal components analysis (Loughlin, 1991). In this study, ratio images werecombined with SPOT or radar data to enhance the structural geology that ultimately controlsthe areas of mineralization.

Landsat TM Ratios

Band ratioing is a technique that has been used for many years in remote sensing toeffectively display spectral variations (e.g., Goetz et al., 1975). Properly computed band ratioimages display little topographic or geomorphic information because the ratio of reflectivityof any two bands for a given material is not a function of illumination. Thus, the distinctionbetween foreslopes and backslopes is lost, while spectral contrasts are enhanced. There aremany types of band ratio images, though a “threshold-modified” four-component technique(Crippen, 1989) provided the best results of any ratio combination used for alterationmapping in the arid to semi-arid terranes of this study (Figure 7). Crippen’s four-componenttechnique uses three band-ratio images (one each for the red, green, and blue output channels)for the chromatic components of the image (Crippen et al., 1990). The technique thenreintroduces the spatial detail using an achromatic SPOT image or TM band 4 that contains

4

spatial detail. Thus, in the final image, colors display spectral information while intensityprimarily displays topographic and geomorphic information.

The three ratios, 3/1, 5/7, and 5/4 of the four-component technique are selected for theirsensitivity to lithologic variables, as previously described, and for their lack of statisticalredundancy (Crippen, 1989, Crippen et al., 1988). In the arid to semi-arid regions in whichwe studied (Mojave desert of California and Arizona, NE Baja California, and Durango,Mexico), these ratios generally are directly related to the presence of ferric iron (3/1), ferrousiron (5/4) and clays, carbonates and hydroxyl-bearing minerals, and vegetation (5/7).Adjustment of the data for atmospheric factors is suggested prior to calculation of the ratioimages, otherwise significant distortions of the data, many of which are difficult to detect,may result (Crippen, 1989). Application of noise-removal routines, such as destriping(Crippen, 1989), is also beneficially applied to ratio images.

The result of this processing is an image that depicts variations in iron content as variations inred, (3/1) and blue (5/4), and variations in hydroxyl-bearing minerals (and/or carbonates) asvariations in green, (5/7). Typically, water is black, vegetation is green, desert varnish is blue,cinder cones are magenta, playa deposits are green if clay rich or red if silty, andhydrothermally altered areas are yellow. Many other rocks are depicted in blue, green,magenta, or white (Figure 12). Although this image contains both lithologic and alterationinformation that is extremely useful in geological reconnaissance, it is not the best image foreither independent alteration or lithologic mapping. We have found that a thresholdmodified, four-component image (Figure 7) provides the best ratio alteration images, while a7-4-1 color composite (Figure 10) is the best for general lithologic mapping.

Assigning the highest digital numbers to three separate images performs the thresholdmodification, while pixels with intermediate to low values are nullified. A 5/7, 3/1, and a5/7+3/1 combination was used, and was intended to highlight areas of hydroxyl-bearingminerals, iron-oxides and anomalous concentrations of both hydroxyls and iron-oxidesrespectively. These three images, 5/7, 3/1, and a 5/7+3/1 were then classified into green, red,and yellow opaque colors and draped over a SPOT or radar image (Figures 7 and 8). Thespecific areas of hydrothermal alteration are easily observed in the threshold images due tothe sharp boundaries generated in Figures 7 and 8, as compared with Figure 12. Yellowpixels in Figures 7, 8, and 12 are anomalous concentrations of both hydroxyls and iron-oxides that may be indicative of limonite, and/or pyritized sericite and/or pyritized argillicalteration. The yellow signature circled in red in Figures 7 and 8 is a hydrothermally-alteredgold bearing breccia.

5

4.0 Radar

Synthetic Aperture Radar (SAR) differs from optical sensors in that optical systems, such asLandsat TM, are passive and rely on the electromagnetic energy generated from the sun toimage the earth’s surface. Since optical data are collected at frequencies similar to what thehuman eye perceives, they are unable to “see” in darkness or cloud cover. SAR alternativelyis an active system that sends its own microwave energy down to earth. Microwaves allowfor atmospheric penetration and, under certain conditions, the penetration of very dry sand orsoil, ice, and vegetation canopies, allowing for exploration not otherwise attainable. Thisability to penetrate clouds and vegetation canopies has established radar as a viableexploration tool around the mid-latitudes where near constant cloud cover exists and outcropsare few due to jungle cover. However, this study shows that radar can be very beneficial inarid to semiarid terranes due to its ability to highlight subtle structures unobservable byoptical data.

Figure 11 is a color composite SIR-C image of the southeastern California, southwesternArizona area. It was produced by assigning red, green, and blue to C band (6-cmwavelength) horizontally transmitted and horizontally received, C band horizontallytransmitted and vertically received, and L band (24 cm wavelength) horizontally transmittedand horizontally received, respectively. The look angle is to the northeast with an incidenceangle of 44 degrees. This highlights topographic and roughness features that are northweststriking, and inclined toward southeast or the look angle. The color differences are aconsequence of topographic changes, moisture content, and surface roughness. The mostimportant feature in this image is the northeast-trending topographic low between the redarrows. This feature is interpreted to be a transfer fault related to the late stage developmentof an accommodation zone structure that trends for approximately 60 km and cuts betweenthe two major orebodies that comprise of the Mesquite mine. Figure 8 is an L bandhorizontally transmitted and horizontally received SIR-C gray scale image with a Landsatalteration drape. The radar-alteration merge provides an effective way to locate structurallycontrolled hydrothermal fluids associated with mineralization.

5.0 Results and Conclusions

The use of digitally enhanced optical and radar data has proven to provide profoundexploration insights when interactively used by the field geologist. This integration ofinteractively used imagery data with a regional understanding of extensional terranes and oregenesis has already provided new opportunities for LCI, and, potentially in time, the entiremining industry as a result of this much valued ARC study. This study has provided a newmethod for LCI to efficiently inspect large areas of interest for mineral potential by using astraightforward yet sophisticated procedure developed by the highly knowledgeable membersinvolved from the SDSU Geology and Geography Departments.

The computer and remote sensing training provided by SDSU and NASA were recognized tobe extremely beneficial to LCI whereby they were immediately adopted and integrated into

6

ongoing exploration programs conducted concurrently with the ARC program. This provedto be extremely advantageous and resulted in multiple business accomplishments:

• A greater than 50% success rate in the recognition of hydrothermal systems throughLandsat TM alteration mapping was accomplished as compared to a previous less than10% success rate from prior “hard copy interpretations” of the same general area.

• In a separate area of interest, Landsat TM interpretations resulted in the discovery of twovirgin mineral systems that where targeted from the mapping of five full Landsat TMscenes.

• These successes have furthered an established relationship between LCI and SDSU, andmany students have expressed an enthusiastic interest in working with remotely senseddata in an exploration mode. Besides Steve Polis, who represented LCI in this study andcompleted his thesis on the same topic ultimately leading to a related career, other SDSUgraduate students are now working with LCI with similar aspirations. One of thesestudents has already demonstrated the utility of multispectral thermal infrared imageryfrom the NASA Stennis ATLAS system in discriminating mineral alteration. This isviewed as a positive relationship whereby LCI can benefit from ongoing related academicresearch, while SDSU students and faculty can stay abreast with industry needs to providefuture geoscientists to find the much needed natural resources that the world demands.

6.0 References

Anderson, R. E., 1971, Thin skin distension in Tertiary rocks of southeastern Nevada:Geological Society of America Bulletin, v. 82, p 43-58.

Bosworth, W., Lambiase, J., and Keislar, R., 1986, A new look at Gregory’s rift: Thestructural Style of continental rifting: EOS (American Geophysical Union Transactions), v.67, p. 577- 583.

Crippen, R. E., 1989, Development of remote sensing techniques for the investigation ofneotectonic activity, eastern Transverse Ranges and vicinity, southern California, Ph.D.thesis, Univ. of Calif., Santa Barbara, 304p., 1989b.

Crippen, R. E., R. G. Blom, and J. R. Heyada,1988, Directed band ratioing for the retentionof perceptually-independent topographic expression in chromaticity-enhanced imagery,International Journal of Remote Sensing, 9, 749-765.

Crippen, R. E., E. J. Hajic, J. E. Estes, and R. G. Blom,1990, Statistical band and band-ratioselection to maximize spectral information in color composite displays, in preparation forsubmission to International Journal of Remote Sensing.

7

Faulds, J. E., Mawar, C. K., and Gaisaman, J. W., 1987, Possible modes of deformationalong "accommodation zones" in rifted continental crust: Geological Society of AmericaAbstracts with Programs, v.19, p.659-660.

Frost, D.M., 1990, Gold ore has distinctive lead isotopic "fingerprint": Geological Society ofAmerica Abstracts with Programs, v.22, no.3, p.24.

Frost and Heidrick, 1996, Tertiary extension and mineral deposits, Southwestern UnitedStates: Society of Economic Geologists, v. 25, p. 26-37.

Goetz, F. H., F. C. Billingsley, A. R. Gillespie, M. J. Abrams, R. L. Squires, E. M.Shoemaker, I. Lucchitta, and D. P. Elston,1975, Application of ERTS images and imageprocessing to regional problems and geological mapping in northern Arizona, JPL TechnicalReport 32-1S97.

Lister, G. S., Etheridge, N. A., and Symonds, P. A., 1986, Detachment faulting and theevolution of passive continental margins: Geology, v. 14, p. 246-250.

Loughtin, W. P., 1990. Geological exploration in the western United States by use of airbornescanner imagery. ERIM Conference: Remote Sensing, an Operational Technology for theMining and Petroleum Industries. London, 29-31 Oct., pp. 22~241.

8

Figure 1. Tertiary dip domain map of the southern Basin and Range Province.This map shows the strike and dip of tilted mid-Tertiary (35-15 Ma) sedimentary andvolcanic rocks as summarized by Rebrig and Heidrick (1976, Fig. 4). Superimposed on thedata is the tilt-block domain terminology proposed by Spencer and Reynolds (1989). TheProvince is divided somewhat proportionally into three mega-domains including the LakeMead, Whipple, and San Pedro. Each of these domains can be traced along strike for 250-300kilometers and covers between 30,000 and 35,000 square kilometers. These domains areseparated along complex lateral transfer and accommodation zones. (Frost and Heidrick,1996)

9

Figure 2. Generalized geologic map of the northern part of the Colorado River Troughand adjacent region.

The area of the Colorado River trough is surrounded to the west, north, and east by largezones showing only minor amounts of extension at exposed crustal levels. Within theColorado River extensional corridor, however, stretching factors (B) vary between 1.5 and2.5. The boundary separating the WSW-tilted Whipple domain from the ENE-tilted LakeMead domain is referred to as the Whipple-Lake Mead “Accommodation Zone.” Datamodified after Faulds et al. (1988). (Frost and Heidrick, 1996)

10

Figure 3. Diagrammatic representation of opposite polarity tilt patterns in extensionalterranes as separated by a strike-slip or transfer fault (A) or an accommodation zone

(B).(A) is a drawing of the model of Liggett and Ehrenspeck (1973), which was developed forthis region to explain the interrelationship between extension, tilts, and strike-slip faulting.(B) shows how opposite polarity tilt domains can be produced using opposite-tilteddetachment faults separated by an accommodation zone, which is a model suggested forAfrican rifts by Bosworth (1985). Domains in this model are linked by the accommodationzone, which is almost a null zone of apparent surface deformation rather than a strike-slipfault. (Frost and Heidrick, 1996)

11

Figure 4. Geometric and kinematic characteristics of Neogene extensional deformation,Colorado River extensional corridor, NV, AZ, and CA. (Frost and Heidrick, 1996)

12

Figure 5. Detachment fault-fold geometry and deep-crustal structure, Colorado Riverextensional terrane, as based on CALCRUST and reprocessed industry seismic lines.

Multiple normal faults descend into middle-crustal ductile zone and offset early-formedmylonitic zone. Active mylonitic zone remains sub-horizontal (parallel to earth's surface). Asnormal faults offset ductile fabric, exhumation of once middle-crustal rock is a product of theoffset on the normal faults and tilting over of the bounding normal faults. Extensional fabrictraced westward from the Whipple terrane extends, perhaps somewhat discontinuously, to theCentral Mojave detachment terrane mapped by workers such as Roy Dokka and AllenGlazner. (Frost and Heidrick, 1996)

13

Figure 6. Diagrammatic model of crustal extension showing truncation of upper-platenormal faults at depth into a gently inclined detachment fault.

Just as the faults are truncated at depth, they are truncated along strike by the wave-like, orfluted detachment surface. Such truncation of the upper-plate fault panels is readily visible onTM and radar images and can identify the presence and geometry of the major detachmentfaults. (Frost and Heidrick, 1996)

14

Figure 7. A SPOT-Landsat TM ratio threshold merge of the area around the southernChocolate Mountains illustrating extensional antiforms and areas of potential

hydrothermal alteration highlighted in yellow.

15

Figure 8. A SIR-C radar Landsat TM threshold merge of the area around the Mesquitemine.

This image highlights the hydrothermal alteration from the TM data, as well as theantiformal-synformal geometry, dipslopes, and fracture patterns from the radar.

16

Figure 9. An over-simplified structural model depicting the Mesquite mine locatedwithin a newly interpreted accommodation zone.

17

Figure 10. Landsat TM 741 color composite image of the southern Colorado Riverillustrating extensional faults and the newly interpreted accommodation zone.

18

Figure 11. A SIR-C radar color composite with interpreted Tertiary upper-platetransport directions and accommodation zone structure illustrated.

The composite is produced by assigning red, green, and blue to C band (6-cm wavelength)horizontally transmitted and horizontally received, C band horizontally transmitted andvertically received, and L band (24-cm wavelength) horizontally transmitted and horizontallyreceived, respectively. The look angle is to the northeast with an incidence angle of 44degrees.

19

Figure 12. A Landsat TM ratio color composite of the area around the Mesquite mine.The image depicts variations in iron content as variations in red, (3/1) and blue (5/4), andvariations in hydroxyl-bearing minerals (and/or carbonates) as variations in green, (5/7).

20

Appendix A. Technical Proposal

National Aeronautics and Space Administration

ARC PROJECT SUMMARY

Project Title: Integrated Use of Remote Sensing and GIS for Mineral Exploration.

Technical Abstract

La Cuesta International is a San Diego, California-based mineral exploration firmspecializing in precious metal ore deposit exploration in the United States, Mexico, and LatinAmerica.

The proposed project is to develop the procedures and demonstrate the feasibility of usingbroad-band and hyperspectral remotely sensed data to identify extensional geologic structuresassociated with precious metal deposition. The resulting procedure will provide the basis formaking available a new exploration service for the mining industry.

Recognition of major gold deposits formed in association with Tertiary crustal extension inthe western U.S. has been established and similar occurrences are now being recognizedglobally. Current mineral exploration concepts have failed to recognize the association ofmineralization with unique extensional structures called accommodation zones. These zones,described below, show little obvious deformation, yet focus fluid migration andmineralization into predictable regions of the crust. Integrating remotely sensed data withexisting geologic data provides a unique opportunity to identify the location of thesepreviously unrecognized zones. Guided by an understanding of accommodation zones,remotely sensed data would be utilized to locate appropriate structural targets, which wouldthen be inspected with hyperspectral data and ground verification, to establish the viability ofthe target area. This procedure is not a simple cookbook process for companies like LaCuesta who are familiar with the geology, but unfamiliar with remote sensing and spatialinformation technologies. La Cuesta is highly motivated to work with remote sensing andrecognizes the vast potential it offers to the mineral exploration profession.

Accommodation Zones:In areas of crustal extension, the crust breaks along a multitude of normal faults, commonlytermed an “array,” with different segments having different transport directions as in FigureA-1. These segmented sections are at a scale of ~50 to 300 km. Within these extensionalterranes, transport of major regions is in one uniform direction. However, zones withopposite transport generally exist in adjacent domains. Between these zones of oppositetransport, some zone of deformation must exist to allow opposite motion to occur during thesame deformation phase. These zones have been called “accommodation zones,” and haveonly recently been recognized within extensional systems on a worldwide basis.

21

Accommodation zones link the normal fault arrays of opposing transport directions. Theseregions are actually zones of little obvious deformation, appearing not as strike-slip faults butbrecciated zones because the entire volume of rock has been affected.

Because accommodation zones represent areas of vergence reversal within extensionalterranes at the up-dip tips of the regional faults (Figure 1), they focus fluid migration andmineralization into predictable regions of the crust. The Nelson District in southern Nevadais an excellent example where alteration and mineralization occur within an accommodationzone. The zone is between two opposite facing regions of extensional transport which can bediscerned on the regional tectonic maps and point directly to major gold mineralization.

The three dimensionality of extended crust has been well documented by petroleumindustries through high-quality, three-dimensional seismic investigations. These seismicstudies have demonstrated the presence of accommodation structures in nearly all theextensional terranes in the world. Within these zones, mineralized fluids flow toward andsaturate portions of the accommodation zones. Knowledge of how accommodation zonetectonics localizes fluid flow processes allows researchers to target discrete areas for detailedexploration within the much larger extensional terrane.

The association of accommodation zones with mineralization is due to three main factors;1. Accommodation zones are deep-crustal breaks that often become syntectonic volcanic

centers because they localize the magmatic material, thus becoming an elongate volcanicand plutonic center that intrudes out from existing fault zones and provides the thermaldynamic energy to drive mineralized fluids.

2. There is an increase in brecciation and the number of faults with a net decrease in theaverage fault slip within the accommodation zone, making the faulting more subtle butopening much larger volumes of extended rock. This provides excellent long-termpermeability for multi-generational fluid flow and subsequent mineralization.

3. The geometry is such that a localized compressional stress regime forms anticlinalculminations located structurally up-dip from the normal faults it separates or“accommodates” on either side. This extensional geometry provides a flow-path frommultiple normal faults toward the accommodation zones where mineralization can occurrepeatedly as the faults continue to break through time.

Broad-band remotely sensed image processing provides a powerful method to search foraccommodation zones. Because the aerial extent of opposite dip domains is so large, thelocation of accommodation zones is easily missed by traditional methods of looking only atthe field data and large-scale maps. Because recognition of opposite dip domains has notbeen part of traditional field investigation methods, many of the geologic maps and theirsyntheses are simply inadequate to discern accommodation zone structures.

Remote sensing literature documents the capability of broad-band airborne and satelliteimagery to detect geologic structure and in some instances, hydrothermally altered areas.Broad-band imagery shows geologic structure and enables the geologist to synthesize thetectonics and also discern the locations of hydrothermal alteration. By studying the linkage

22

between alteration and accommodation zones, exploration targets for analysis can beidentified. Unfortunately, broad-band data cannot distinguish individual “indicator” mineralsrequired to further evaluate target areas. Hyperspectral sensor resolution allows theidentification of many indicator minerals based upon their characteristic narrow absorptionbands. However, by combining broad-band and hyperspectral data into an integratedcollection and analysis method, broad-band data can be used to identify structural featureswhich in combination with traditional geologic data can indicate the presence ofaccommodation zones, while hyperspectral data can provide the ability to detecthydrothermal alteration and indicator minerals. Image analysis coupled with an understandingof the tectonic processes and significance of the localized alteration provides a powerful toolfor exploration.

The suggested program would involve several stages. First, existing geologic andgeochemical data would be assembled and entered into a geographic information system(GIS) as required. Broad-band remotely sensed imagery would be acquired and inconjunction with GIS-processed geologic data be analyzed to define regional areas likely tocontain accommodation zones. Hyperspectral data would be acquired for accommodationzone target areas and analyzed to determine the presence of hydrothermal alteration and ore-body indicator minerals. Field surveys may be required to refine remote sensingdiscrimination signatures to improve detection and refine spatial distribution.

Geologic, geochemical, fault, gravity and stream-sediment maps will be obtained from stateand Federal sources by La Cuesta. Broad band imagery will be acquired from SDSU archivalsources. Selected hyperspectral data from existing NASA (JPL) archives will be requestedfrom NASA ARC. GIS and remote sensing software and computing support will be providedby SDSU. Technical guidance and assistance in developing the data integration and analysisprocedures will be provided by SDSU with occasional consultations with NASA remotesensing specialists. La Cuesta will commit a full-time geologist to work with SDSU. LaCuesta principals and technical specialists will be available to participate with SDSU staff asappropriate.

23

Figure A-1. Diagrammatic representation of opposite polarity tilt patterns inextensional terranes as separated by a strike-slip or transfer fault (A) or an

accommodation zone (B).(A) is a drawing of the model of Liggett and Ehrenspeck (1973), which was developed forthis region to explain the interrelationship between extension, tilts and strike-slip faults. (B)shows how opposite polarity tilts domains can be produced using opposite-tilted detachmentfaults separated by an accommodation zone, which is a model suggested for African rifts byBosworth (1985). Domains in this model are linked by the accommodation zone, which isalmost a null zone of apparent surface deformation rather than a strike-slip fault.

24

Appendix B. Commercial Proposal

National Aeronautics and Space Administration

ARC PROJECT SUMMARY

Project Title: Integrated Use of Remote Sensing and GIS for Mineral Exploration

Commercial Applications

Remotely-sensed imagery is a powerful tool for mineral exploration when properly utilized.Unfortunately, many geologists are skeptical of the use of remote sensing products because ofprevious false “positive” indicators which resulted in “chasing” spectral anomalies. This islargely due to the gap in information integration between geologists and the remote sensingcommunity. The need for understanding regional geology and structure is critical for remotesensing to be a fully effective exploration tool. La Cuesta feels that the existing resistance tousing remote sensing products by geologists provides an excellent business opportunity tosynthesize geologic understanding with image-processing and provide an improved andvaluable exploration service for mining companies.

Today’s computer technology has provided a method by which geologists can use remotesensing and GIS software to integrate field knowledge, structural geology, and remote sensedimagery. NASA’s Affiliated Research Center (ARC) program provides an excellentopportunity for La Cuesta to demonstrate the practical application of the approach as animproved method of mineral exploration and a basis for developing future explorationcontracts with the mining industry worldwide.

25

Appendix C. Schedule

1997

Jun Jul Aug Sep Oct Nov Dec

Integrated Remote Sensing and GIS VIP Project Schedule

Project Tasks

Prepare MOA

Data Collection

Software Training

Broad Band Analysis

Progress Assessment

Hyperspectral Training

Data Integration & Analysis

Final Report Preparation

Project Evaluation

2 12

8 17

8 19

30 31

6

23 30

20 31

25 22

4