remote sensing and gis for mineral exploration

8/8/2019 Remote Sensing and GIS for Mineral Exploration

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

Series ARC-SDSU-002

Integrated Use of Remote

Sensing 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.


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Affiliated Research Center

Final Report

Integrated Use of Remote Sensing and

GIS for Mineral Exploration:

A Project of the NASA Affiliated Research Center at


Project conducted by:La Cuesta International, Inc.

1805 Wedgemere Road

El 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 Universityand

Mr. John V. Kaiser

Department of Geography, San Diego State University

Report prepared for:

Dr. Douglas A. Stow, Principal Investigator


Department of Geography

San Diego, California 92182-4493

andCommercial Remote Sensing Program Office

National Aeronautics and Space Administration

John C. Stennis Space Center, Mississippi 39529

January 20, 1998


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EXPORT ADMINISTRATION

REGULATIONS 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 foreign

nationals in the U.S. or abroad without specific approval of a

knowledgeable NASA export control official, and/or unless

an export license/license exception is obtained/available from

the Bureau of Export Administration (BXA), United States

Department of Commerce. Violations of these regulations arepunishable by fine, imprisonment, or both.


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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 and

adjacent region...........................................................................................................................9

Figure 3. Diagrammatic representation of opposite polarity tilt patterns in extensional

terranes 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 River

extensional terrane, as based on CALCRUST and reprocessed industry seismic lines...........12

Figure 6. Diagrammatic model of crustal extension showing truncation of upper-plate normal

faults at depth into a gently inclined detachment fault. ...........................................................13

Figure 7. A SPOT-Landsat TM ratio threshold merge of the area around the southern

Chocolate Mountains illustrating extensional antiforms and areas of potential hydrothermal

alteration 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 a

newly interpreted accommodation zone...................................................................................16


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Figure 10. Landsat TM 741 color composite image of the southern Colorado River

illustrating extensional faults and the newly interpreted accommodation zone. .....................17

Figure 11. A SIR-C radar color composite with interpreted Tertiary upper-plate transport

directions and accommodation zone structure illustrated........................................................18

Figure 12. A Landsat TM ratio color composite of the area around the Mesquite mine. .......19Figure A-1. Diagrammatic representation of opposite polarity tilt patterns in extensional

terranes as separated by a strike-slip or transfer fault (A) or an accommodation zone (B). ....23


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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 the

program was to develop the procedures and demonstrate the feasibility of using broad-band

and 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 of

mineralization with unique extensional structures called accommodation zones. These zones

show little obvious deformation, yet focus fluid migration and mineralization into predictable

regions 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 an

unrecognized accommodation zone. Landsat Thematic Mapper (TM), Satellite Pour

l'Observation de la Terre (SPOT), and radar data were observed both separately and in a

merged format to extract spectral and spatial information using ER Mapper software. A

variety of images were produced to highlight important structural features along with areas of

hydrothermal alteration. Images produced include Landsat TM and Shuttle Imaging Radar-C(SIR-C) radar color composites, color ratio composites, principal components, thresholds and

Landsat TM-SPOT and Landsat TM-SIR-C radar merges. Hyperspectral data (Advanced

Visible/Infrared Imaging Spectrometer (AVIRIS) and Airborne Terrestrial Applications

Sensor (ATLAS)) where obtained though not processed, because the data did not cover the

study area.

The ARC project proved to be extremely beneficial in training LCI with remote sensing

procedures 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 anomalies

were related to hydrothermal alteration. Using the ARC template greater than 50% of

the 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.


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1.0Introduction

Recognition of major gold deposits formed in association with Tertiary crustal extensions in

the western U.S. has been established and similar occurrences are now being recognized

globally. In most cases, current mineral exploration concepts have failed to recognize the

association of mineralization with unique extensional structures called accommodationzones. These zones, described below, show little obvious deformation, yet focus fluid

migration and mineralization into predictable regions of the crust. Integrating remotely

sensed data with existing geologic data provides a unique opportunity to identify the location

of these previously unrecognized zones. Guided by an understanding of accommodation

zones, Landsat TM, SPOT, and radar data were utilized to locate an unrecognized

accommodation zone in which the Mesquite gold mine is located. Further remote sensing

efforts made possible by insights developed through this ARC effort support the association

between accommodation zones and precious/base metal deposition.

Accommodation Zones

In areas of crustal extension, the crust breaks along a multitude of normal faults, commonly

termed an "array," with different segments having different transport directions as shown in

Figures 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 generally

exist in adjacent domains. Between these zones of opposite transport, a zone of deformation

must exist to allow opposite motion to occur during the same deformational phase. These

zones have been called "accommodation zones," and have only recently been recognized

within extensional systems on a worldwide basis. Accommodation zones link the normal

fault arrays of opposing transport directions. These regions are often zones of little obvious

deformation, appearing not as strike-slip faults, but brecciated null zones because the entire

volume of rock has been affected (Anderson, 1971; Bosworth et al., 1986).

Because accommodation zones represent areas of vergence reversal within extensional

terranes at the up-dip tips of the regional faults (Figures 3 and 4), they focus fluid migration

and mineralization into predictable regions of the crust. The Nelson District in southern

Nevada is an excellent example where alteration and mineralization occur within an

accommodation zone (Faulds et al., 1987; Frost and Heidrick, 1996). This zone is between

two opposite facing regions of extensional transport that can be discerned on the regional

tectonic maps and appears to point directly to the major gold mineralization.

The three-dimensionality of extended crust has been well documented by researchers in the

petroleum industries through high-quality, three-dimensional seismic investigations. These

seismic studies have demonstrated the presence of accommodation structures in nearly all the

extensional terranes in the world. Within these zones, fluids flow toward and saturate

portions of the accommodation zones. Knowledge of how accommodation-zone tectonics

localize fluid flow allows researchers to target discrete areas for detailed exploration within

the much larger extensional terrane.


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The association of accommodation zones with mineralization is due to three main factors:

1.Accommodation zones are deep-crustal breaks that often become syntectonic volcaniccenters because they localize the magmatic material, thus becoming an elongated volcanic

and plutonic center that intrudes existing fault zones and provides the thermodynamic

energy to drive mineralized fluids.2.There is an increase in brecciation and the number of faults with a net decrease in the

average fault slip within the accommodation zone, making the faulting more subtle but

opening much larger volumes of extended rock. This provides excellent long-term

permeability 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 from

multiple normal faults toward the accommodation zones where mineralization can occur

repeatedly 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 are

so large, interpreting field data and large scale maps easily misses the location of

accommodation zones. Since the recognition of opposite dip domains has not been part of

field investigation methodologies before, many of the geologic maps and their synthesis are

simply inadequate to discern accommodation zone structures. Optical and radar data show

geologic structure and enable the geologist to synthesize the tectonics and also discern the

potential locations of hydrothermal alteration. This image analysis, coupled with an

understanding of the tectonic processes and significance of the localized alteration, provides a

powerful tool for exploration.

2.0Structural Mapping

The antiformal-synformal character of the detachment fault system is one of the best ways of

finding unrecognized large-scale normal faults and determining where accommodation zones

might be found. Because of the regional perspective provided by the images and the display

of spectral and topographic data with optical and radar images, the antiformal-synformal

character of ranges can be readily discerned. In most areas, the long axis of the antiforms is

parallel to the upper plate transport direction, much like megamullion structures elongated in

the transport direction (Figures 5 and 6). These mullion structures appear to have a fairly

consistent 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 that

the 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 and

radar imaging provides feature recognition for these targets, and enables potential

hydrothermally saturated antiforms to be highlighted. Figure 7 is a SPOT- Landsat TM ratio


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threshold merge of the area around the southern Chocolate Mountains. The image illustrates

the ability to map and target extensional antiforms and areas of potential hydrothermal

alteration highlighted in yellow. The strongest alteration signature in the image is along the

detachment fault antiform located closest to the Mesquite mine and the Mount Barrow pluton

responsible for the Mesquite gold mineralization (Frost, 1990). By changing the SPOT

backdrop 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 and

fracture patterns.

By mapping a larger area, the Mesquite mine was discovered to be located within an

accommodation 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 the

Trigo Mountains, located to the northeast across the Colorado river in Arizona, have had an

opposite or southwest Tertiary upper-plate transport direction. The Mesquite mine is

positioned at the southwest termination of the accommodation zone between these two dip

domains, which is characterized by a northeasterly striking topographic low. This

accommodation 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 the

ranges were mapped (Figure 10). Radar data used to image the structure highlighted the

linear topographic low of this accommodation zone that trends through the Mesquite mine

and continues northeasterly for more than 60 km (Figure 11).

3.0Alteration Mapping

The goals for producing alteration images for the ARC were to optimally depict all spectral

properties 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: ratios

and select principal components analysis (Loughlin, 1991). In this study, ratio images were

combined with SPOT or radar data to enhance the structural geology that ultimately controls

the areas of mineralization.

Landsat TM Ratios

Band ratioing is a technique that has been used for many years in remote sensing to

effectively display spectral variations (e.g., Goetz et al., 1975). Properly computed band ratio

images display little topographic or geomorphic information because the ratio of reflectivity

of 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 are

many types of band ratio images, though a threshold-modified four-component technique

(Crippen, 1989) provided the best results of any ratio combination used for alteration

mapping in the arid to semi-arid terranes of this study (Figure 7). Crippens four-component

technique 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 then

reintroduces the spatial detail using an achromatic SPOT image or TM band 4 that contains


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spatial detail. Thus, in the final image, colors display spectral information while intensity

primarily displays topographic and geomorphic information.

The three ratios, 3/1, 5/7, and 5/4 of the four-component technique are selected for their

sensitivity to lithologic variables, as previously described, and for their lack of statistical

redundancy (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), ferrous

iron (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 ratio

images, 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 in

red, (3/1) and blue (5/4), and variations in hydroxyl-bearing minerals (and/or carbonates) as

variations 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, and

hydrothermally altered areas are yellow. Many other rocks are depicted in blue, green,

magenta, or white (Figure 12). Although this image contains both lithologic and alteration

information that is extremely useful in geological reconnaissance, it is not the best image for

either independent alteration or lithologic mapping. We have found that a threshold

modified, four-component image (Figure 7) provides the best ratio alteration images, while a

7-4-1 color composite (Figure 10) is the best for general lithologic mapping.

Assigning the highest digital numbers to three separate images performs the threshold

modification, while pixels with intermediate to low values are nullified. A 5/7, 3/1, and a

5/7+3/1 combination was used, and was intended to highlight areas of hydroxyl-bearingminerals, iron-oxides and anomalous concentrations of both hydroxyls and iron-oxides

respectively. 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). The

specific areas of hydrothermal alteration are easily observed in the threshold images due to

the sharp boundaries generated in Figures 7 and 8, as compared with Figure 12. Yellow

pixels 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 argillic

alteration. The yellow signature circled in red in Figures 7 and 8 is a hydrothermally-altered

gold bearing breccia.


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4.0Radar

Synthetic Aperture Radar (SAR) differs from optical sensors in that optical systems, such as

Landsat TM, are passive and rely on the electromagnetic energy generated from the sun to

image the earths surface. Since optical data are collected at frequencies similar to what the

human 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 allow

for atmospheric penetration and, under certain conditions, the penetration of very dry sand or

soil, ice, and vegetation canopies, allowing for exploration not otherwise attainable. This

ability to penetrate clouds and vegetation canopies has established radar as a viable

exploration tool around the mid-latitudes where near constant cloud cover exists and outcrops

are few due to jungle cover. However, this study shows that radar can be very beneficial in

arid to semiarid terranes due to its ability to highlight subtle structures unobservable by

optical data.

Figure 11 is a color composite SIR-C image of the southeastern California, southwestern

Arizona area. It was produced by assigning red, green, and blue to C band (6-cmwavelength) horizontally transmitted and horizontally received, C band horizontally

transmitted and vertically received, and L band (24 cm wavelength) horizontally transmitted

and horizontally received, respectively. The look angle is to the northeast with an incidence

angle of 44 degrees. This highlights topographic and roughness features that are northwest

striking, and inclined toward southeast or the look angle. The color differences are a

consequence of topographic changes, moisture content, and surface roughness. The most

important feature in this image is the northeast-trending topographic low between the red

arrows. This feature is interpreted to be a transfer fault related to the late stage development

of an accommodation zone structure that trends for approximately 60 km and cuts between

the two major orebodies that comprise of the Mesquite mine. Figure 8 is an L band

horizontally transmitted and horizontally received SIR-C gray scale image with a Landsat

alteration drape. The radar-alteration merge provides an effective way to locate structurally

controlled hydrothermal fluids associated with mineralization.

5.0Results and Conclusions

The use of digitally enhanced optical and radar data has proven to provide profound

exploration insights when interactively used by the field geologist. This integration of

interactively used imagery data with a regional understanding of extensional terranes and ore

genesis 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 new

method for LCI to efficiently inspect large areas of interest for mineral potential by using a

straightforward yet sophisticated procedure developed by the highly knowledgeable members

involved from the SDSU Geology and Geography Departments.

The computer and remote sensing training provided by SDSU and NASA were recognized to

be extremely beneficial to LCI whereby they were immediately adopted and integrated into


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ongoing exploration programs conducted concurrently with the ARC program. This proved

to 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 than

10% 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 TM

scenes.

These successes have furthered an established relationship between LCI and SDSU, andmany students have expressed an enthusiastic interest in working with remotely sensed

data in an exploration mode. Besides Steve Polis, who represented LCI in this study and

completed his thesis on the same topic ultimately leading to a related career, other SDSU

graduate students are now working with LCI with similar aspirations. One of these

students has already demonstrated the utility of multispectral thermal infrared imageryfrom the NASA Stennis ATLAS system in discriminating mineral alteration. This is

viewed as a positive relationship whereby LCI can benefit from ongoing related academic

research, while SDSU students and faculty can stay abreast with industry needs to provide

future geoscientists to find the much needed natural resources that the world demands.

6.0References

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 Gregorys rift: The

structural 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 of

neotectonic 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 retention

of 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-ratio

selection to maximize spectral information in color composite displays, in preparation for

submission to International Journal of Remote Sensing.


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Faulds, J. E., Mawar, C. K., and Gaisaman, J. W., 1987, Possible modes of deformation

along "accommodation zones" in rifted continental crust: Geological Society of America

Abstracts with Programs, v.19, p.659-660.

Frost, D.M., 1990, Gold ore has distinctive lead isotopic "fingerprint": Geological Society of

America Abstracts with Programs, v.22, no.3, p.24.

Frost and Heidrick, 1996, Tertiary extension and mineral deposits, Southwestern United

States: 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 image

processing to regional problems and geological mapping in northern Arizona, JPL Technical

Report 32-1S97.

Lister, G. S., Etheridge, N. A., and Symonds, P. A., 1986, Detachment faulting and the

evolution of passive continental margins: Geology, v. 14, p. 246-250.

Loughtin, W. P., 1990. Geological exploration in the western United States by use of airborne

scanner imagery. ERIM Conference: Remote Sensing, an Operational Technology for the

Mining and Petroleum Industries. London, 29-31 Oct., pp. 22~241.


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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 and

volcanic 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). The

Province is divided somewhat proportionally into three mega-domains including the Lake

Mead, Whipple, and San Pedro. Each of these domains can be traced along strike for 250-300

kilometers and covers between 30,000 and 35,000 square kilometers. These domains are

separated along complex lateral transfer and accommodation zones. (Frost and Heidrick,

1996)


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

and adjacent region.

The area of the Colorado River trough is surrounded to the west, north, and east by large

zones showing only minor amounts of extension at exposed crustal levels. Within the

Colorado River extensional corridor, however, stretching factors (B) vary between 1.5 and

2.5. The boundary separating the WSW-tilted Whipple domain from the ENE-tilted Lake

Mead domain is referred to as the Whipple-Lake Mead Accommodation Zone. Data

modified after Faulds et al. (1988). (Frost and Heidrick, 1996)


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Figure 3. Diagrammatic representation of opposite polarity tilt patterns in extensional

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 faulting.

(B) shows how opposite polarity tilt domains can be produced using opposite-tilted

detachment faults separated by an accommodation zone, which is a model suggested for

African rifts by Bosworth (1985). Domains in this model are linked by the accommodation

zone, which is almost a null zone of apparent surface deformation rather than a strike-slip

fault. (Frost and Heidrick, 1996)


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Figure 4. Geometric and kinematic characteristics of Neogene extensional deformation,

Colorado River extensional corridor, NV, AZ, and CA. ( rost and Heidrick, 1996)


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Figure 5. Detachment fault-fold geometry and deep-crustal structure, Colorado River

extensional 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). As

normal faults offset ductile fabric, exhumation of once middle-crustal rock is a product of the

offset on the normal faults and tilting over of the bounding normal faults. Extensional fabric

traced westward from the Whipple terrane extends, perhaps somewhat discontinuously, to the

Central Mojave detachment terrane mapped by workers such as Roy Dokka and Allen

Glazner. (Frost and Heidrick, 1996)


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Figure 6. Diagrammatic model of crustal extension showing truncation of upper-plate

normal 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, or

fluted detachment surface. Such truncation of the upper-plate fault panels is readily visible on

TM and radar images and can identify the presence and geometry of the major detachmentfaults. (Frost and Heidrick, 1996)


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Figure 7. A SPOT-Landsat TM ratio threshold merge of the area around the southern

Chocolate Mountains illustrating extensional antiforms and areas of potential

hydrothermal alteration highlighted in yellow.


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

mine.

This image highlights the hydrothermal alteration from the TM data, as well as the

antiformal-synformal geometry, dipslopes, and fracture patterns from the radar.


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Figure 10. Landsat TM 741 color composite image of the southern Colorado River

illustrating extensional faults and the newly interpreted accommodation zone.


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Figure 11. A SIR-C radar color composite with interpreted Tertiary upper-plate

transport 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 and

vertically received, and L band (24-cm wavelength) horizontally transmitted and horizontally

received, respectively. The look angle is to the northeast with an incidence angle of 44

degrees.


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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), and

variations in hydroxyl-bearing minerals (and/or carbonates) as variations in green, (5/7).


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Appendix A. Technical Proposal


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 firm

specializing in precious metal ore deposit exploration in the United States, Mexico, and Latin

America.

The proposed project is to develop the procedures and demonstrate the feasibility of usingbroad-band and hyperspectral remotely sensed data to identify extensional geologic structures

associated with precious metal deposition. The resulting procedure will provide the basis for

making available a new exploration service for the mining industry.

Recognition of major gold deposits formed in association with Tertiary crustal extension in

the western U.S. has been established and similar occurrences are now being recognized

globally. Current mineral exploration concepts have failed to recognize the association of

mineralization with unique extensional structures called accommodation zones. These zones,

described below, show little obvious deformation, yet focus fluid migration and

mineralization into predictable regions of the crust. Integrating remotely sensed data with

existing geologic data provides a unique opportunity to identify the location of these

previously unrecognized zones. Guided by an understanding of accommodation zones,

remotely sensed data would be utilized to locate appropriate structural targets, which would

then be inspected with hyperspectral data and ground verification, to establish the viability of

the target area. This procedure is not a simple cookbook process for companies like La

Cuesta who are familiar with the geology, but unfamiliar with remote sensing and spatial

information technologies. La Cuesta is highly motivated to work with remote sensing and

recognizes 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 Figure

A-1. These segmented sections are at a scale of ~50 to 300 km. Within these extensional

terranes, transport of major regions is in one uniform direction. However, zones with

opposite transport generally exist in adjacent domains. Between these zones of opposite

transport, some zone of deformation must exist to allow opposite motion to occur during the

same deformation phase. These zones have been called accommodation zones, and have

only recently been recognized within extensional systems on a worldwide basis.


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Accommodation zones link the normal fault arrays of opposing transport directions. These

regions are actually zones of little obvious deformation, appearing not as strike-slip faults but

brecciated zones because the entire volume of rock has been affected.

Because accommodation zones represent areas of vergence reversal within extensional

terranes 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 Nevada

is an excellent example where alteration and mineralization occur within an accommodation

zone. The zone is between two opposite facing regions of extensional transport which can be

discerned on the regional tectonic maps and point directly to major gold mineralization.

The three dimensionality of extended crust has been well documented by petroleum

industries through high-quality, three-dimensional seismic investigations. These seismic

studies have demonstrated the presence of accommodation structures in nearly all the

extensional terranes in the world. Within these zones, mineralized fluids flow toward and

saturate portions of the accommodation zones. Knowledge of how accommodation zone

tectonics 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 volcaniccenters because they localize the magmatic material, thus becoming an elongate volcanic

and plutonic center that intrudes out from existing fault zones and provides the thermal

dynamic 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 but

opening much larger volumes of extended rock. This provides excellent long-term

permeability for multi-generational fluid flow and subsequent mineralization.3.The geometry is such that a localized compressional stress regime forms anticlinal

culminations located structurally up-dip from the normal faults it separates or

accommodates on either side. This extensional geometry provides a flow-path from

multiple normal faults toward the accommodation zones where mineralization can occur

repeatedly as the faults continue to break through time.

Broad-band remotely sensed image processing provides a powerful method to search for

accommodation zones. Because the aerial extent of opposite dip domains is so large, the

location of accommodation zones is easily missed by traditional methods of looking only at

the field data and large-scale maps. Because recognition of opposite dip domains has not

been part of traditional field investigation methods, many of the geologic maps and their

syntheses are simply inadequate to discern accommodation zone structures.

Remote sensing literature documents the capability of broad-band airborne and satellite

imagery to detect geologic structure and in some instances, hydrothermally altered areas.

Broad-band imagery shows geologic structure and enables the geologist to synthesize the

tectonics and also discern the locations of hydrothermal alteration. By studying the linkage


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between alteration and accommodation zones, exploration targets for analysis can be

identified. Unfortunately, broad-band data cannot distinguish individual indicator minerals

required to further evaluate target areas. Hyperspectral sensor resolution allows the

identification of many indicator minerals based upon their characteristic narrow absorption

bands. However, by combining broad-band and hyperspectral data into an integrated

collection and analysis method, broad-band data can be used to identify structural featureswhich in combination with traditional geologic data can indicate the presence of

accommodation zones, while hyperspectral data can provide the ability to detect

hydrothermal alteration and indicator minerals. Image analysis coupled with an understanding

of the tectonic processes and significance of the localized alteration provides a powerful tool

for exploration.

The suggested program would involve several stages. First, existing geologic and

geochemical data would be assembled and entered into a geographic information system

(GIS) as required. Broad-band remotely sensed imagery would be acquired and in

conjunction with GIS-processed geologic data be analyzed to define regional areas likely to

contain 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 sensing

discrimination signatures to improve detection and refine spatial distribution.

Geologic, geochemical, fault, gravity and stream-sediment maps will be obtained from state

and Federal sources by La Cuesta. Broad band imagery will be acquired from SDSU archival

sources. Selected hyperspectral data from existing NASA (JPL) archives will be requested

from NASA ARC. GIS and remote sensing software and computing support will be provided

by SDSU. Technical guidance and assistance in developing the data integration and analysis

procedures will be provided by SDSU with occasional consultations with NASA remote

sensing 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 as

appropriate.


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Figure A-1. Diagrammatic representation of opposite polarity tilt patterns in

extensional 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 for

this 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 detachment

faults separated by an accommodation zone, which is a model suggested for African rifts by

Bosworth (1985). Domains in this model are linked by the accommodation zone, which is

almost a null zone of apparent surface deformation rather than a strike-slip fault.


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Appendix B. Commercial Proposal


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 of

previous false positive indicators which resulted in chasing spectral anomalies. This is

largely due to the gap in information integration between geologists and the remote sensing

community. 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 to

using remote sensing products by geologists provides an excellent business opportunity to

synthesize geologic understanding with image-processing and provide an improved and

valuable exploration service for mining companies.

Todays computer technology has provided a method by which geologists can use remote

sensing and GIS software to integrate field knowledge, structural geology, and remote sensed

imagery. NASAs Affiliated Research Center (ARC) program provides an excellent

opportunity for La Cuesta to demonstrate the practical application of the approach as an

improved method of mineral exploration and a basis for developing future exploration

contracts with the mining industry worldwide.


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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

remote sensing and gis for mineral exploration

Documents