USING INFRARED SPECTROMETRY TO DEDUCE FLUID HISTORY FROM A
GEOTHERMAL ENERGY EXPLORATION CORE AT EMIGRANT PEAK
GEOTHERMAL PROSPECT, NORTHERN FISH LAKE VALLEY,
NEVADA, U.S.A.
by
Chinomso N. Madubuike
APPROVED BY SUPERVISORY COMMITTEE:
______Dr. Thomas Brikowski, Chair
______Dr. John Oldow
______Dr. William Manton
Copyright 2016
Chinomso N. Madubuike
All Rights Reserved
To God Almighty for His kindness towards me. I cannot thank Him enough.
USING INFRARED SPECTROMETRY TO DEDUCE FLUID HISTORY FROM A
GEOTHERMAL ENERGY EXPLORATION CORE AT EMIGRANT PEAK
GEOTHERMAL PROSPECT, NORTHERN FISH LAKE VALLEY,
NEVADA, U.S.A.
by
CHINOMSO N. MADUBUIKE, B. TECH
THESIS
Presented to the Faculty of
The University of Texas at Dallas
in Partial Fulfillment
of the Requirements
for the Degree of
MASTER OF SCIENCE IN
GEOSCIENCES
THE UNIVERSITY OF TEXAS AT DALLAS
December 2016
ACKNOWLEDGMENTS
I would like to thank my supervisor, Dr. Tom Brikowski, for making out time to carefully review my work and offer insightful input to this project, from start to finish. I appreciate his patience, kindness, and superb teaching skills. Thanks to Dr. John Oldow, one of my committee members for helping to simplify the complex structural geology of my study area.
He was a valuable resource. To my other committee member - Dr. William Manton, thanks for your support and for showing interest in my project. I am also grateful to Ellison Miles
Foundation and Pioneer Natural Resources for their financial support. I appreciate John
Deymonaz and Linda Williams for their generous in-kind support provided to me during my stay in Dyer for fieldwork. Thanks to all the Geoscience department staff and faculty, especially Kyong Edwards, Gloria Eby, Dr. Carlos Aiken, Dr. Robert Stern and Dr. John
Ferguson for their assistance and guidance. I appreciate my colleagues at the University of
Texas at Dallas, particularly Nick Mueller, Ann Moulding, Kelly Ables (helpful during data acquisition in Dyer), Jackie Horn, Michael Anekwe and Hesham Buhedma who helped in various magnitudes leading to a successful project. Thanks to all my family and friends, especially Toochukwu Onwuliri, my best friend for his constant support and companionship all through the duration of my program. I also appreciate my loving brother Tochi Madubuike for his encouragement and moral support. To my awesome parents, Mr. and Mrs. Emeka
Madubuike, thank you for all your prayers and financial support. Finally, I am most grateful to God for granting me good health, favor, provision and protection through the years. Thank you all!
November 2016
v
USING INFRARED SPECTROMETRY TO DEDUCE FLUID HISTORY FROM A
GEOTHERMAL ENERGY EXPLORATION CORE AT EMIGRANT PEAK
GEOTHERMAL PROSPECT, NORTHERN FISH LAKE VALLEY,
NEVADA, U.S.A.
Publication No. ______
Chinomso N. Madubuike, MS The University of Texas at Dallas, 2016
ABSTRACT
Supervising Professor: Dr. Thomas Brikowski
The purpose of this study was to test the possibility of using infrared (IR) spectrometry in mineral identification from a core (EM 17-31), from the Emigrant Peak geothermal prospect in northern Fish Lake Valley, Nevada. The use of IR spectrometry in the identification of minerals has led to notable progress in quantifying rock alteration in magma-hydrothermal systems. Similar progress may be possible for the amagmatic geothermal systems common in western U.S., despite their much weaker rock alteration. The stratigraphic sequence includes shallow Tertiary intermediate and silicic volcanic rocks, Paleozoic greenschist-facies metamorphosed sheared carbonates and pelites, infrequent lithons of Mesozoic granodiorite, all in detachment fault contact with Precambrian gneissic metamorphic tectonites. IR-detected minerals exhibited a steady downhole progression from smectite to illite to muscovite (total depth of 2900 ft.), reflecting shallow diagenetic alteration merging smoothly into much older regional metamorphic assemblages. IR scalars, based on ratios of reflectance at diagnostic wavelengths, indicate a steadily increasing alkali phyllosilicate maturity with depth (Illite
vi
Spectral Maturity or ISM), largely independent of lithology. At 2400 ft. depth, this trend reverses with decreasing maturity in silicified Paleozoic metasiltstones overlying the Silver
Peak-Lone Mountain Detachment Fault at 2733 ft. A distinct change to ISM values consistent with the shallow diagenetic zone occurs at and below the detachment. Chlorite Spectral
Maturity (CSM) scalar exhibits similar trends. This suggests a relatively cool hydrothermal event, with fluid temperatures in the range of those observed in nearby amagmatic geothermal systems, primarily restricted to the detachment fault and below. The reappearance of smectites and iron oxides in this depth range also indicates relatively epithermal conditions. At an even finer scale, minimum maturity ISM values are spatially correlated with smectite mineral occurrences near and below the detachment, suggesting the movement of relatively cool fluids younger than 5 Ma indicating pathways for recent amagmatic geothermal circulation.
vii
TABLE OF CONTENTS
ACKNOWLEDGMENTS ...... v
ABSTRACT ...... vi
LIST OF FIGURES ...... x
LIST OF TABLES ...... xii
CHAPTER 1 INTRODUCTION ...... 1
1.1 GENERAL OVERVIEW ...... 1
1.2 LOCATION AND GEOLOGY OF STUDY AREA ...... 3
1.2.1 REGIONAL GEOLOGIC FRAMEWORK ...... 3
1.2.2 GEOLOGY OF STUDY AREA ...... 6
1.2.3 AN AMAGMATIC GEOTHERMAL SYSTEM ...... 9
1.2.4 SUBSURFACE GEOLOGY OF THE EM 17-31 CORE ...... 10
1.3 RESEARCH FOCUS ...... 12
1.4 AIMS AND OBJECTIVES ...... 13
1.4.1 AIMS...... 13
1.4.2 OBJECTIVES ...... 13
CHAPTER 2 METHOD ...... 14
2.1 INFRARED (IR) SPECTROSCOPY ...... 14
2.2 DATA ACQUISITION WITH INFRARED SPECTROMETER ...... 15
2.3 PETROGRAPHIC THIN SECTION ANALYSIS ...... 17
2.4 GEOGRAPHIC INFORMATION SYSTEM INCORPORATION ...... 17
CHAPTER 3 RESULTS AND DISCUSSION ...... 20
3.1 INFRARED SPECTROMETER MINERAL RESULTS FOR EM 17-31 ...... 20
viii
3.1.1 DISTRIBUTION OF HYDROTHERMAL ALTERATION MINERALS ...... 22
3.2 HYDROTHERMAL ALTERATION MINERAL ZONATION ...... 25
3.2.1 DOWNHOLE SMECTITE-ILLITE-MUSCOVITE PROGRESSION ...... 26
3.2.2 DOWNHOLE PROGRESSION OF APPARENT METAMORPHIC ZONES 27
3.3 INFRARED SCALARS ...... 28
3.4 POTENTIAL RECENT ALTERATION ZONES ...... 31
CHAPTER 4 CONCLUSIONS AND RECOMMENDATION ...... 33
4.1 CONCLUSIONS ...... 33
4.2 RECOMMENDATION ...... 35
APPENDIX A PHYLLOSILICATE MINERALS ...... 36
APPENDIX B THIN SECTION ANALYSIS ...... 42
APPENDIX C EM17-31 MINERAL DISTRIBUTION ...... 47
REFERENCES ...... 83
VITA
ix
LIST OF FIGURES
Figure 1.1. Map of southwestern United States with the study area outlined in red...... 3
Figure 1.2. Location map of the EM 17-31 geothermal exploration well relative to major structural features of west-central Nevada...... 5
Figure 1.3. Satellite image of northern Fish Lake Valley of Nevada showing locations of some wells ...... 8
Figure 1.4. Stratigraphic column representation ...... 12
Figure 2.1. (a) First author at the Emigrant Peak Geothermal Prospect – EM 17-31 drill site with a portable VNIR-SWIR spectrometer and (b) first and third authors scanning core ...... 16
Figure 3.1. EM 17-31 borehole temperature graph...... 21
Figure 3.2. Some important minerals distinguishable with infrared spectrometer along the EM 17-31 core...... 24
Figure 3.3. Distinguishable mineral zonation along the EM 17-31 core ...... 26
Figure 3.4. General geology (left), IR-identified mineral assemblages indicating metamorphic facies (center) and IR scalar "Illite Spectral Maturity" vs. depth at EM 13-71 .... 28
Figure 3.5. IR-based scalars Illite (ISM) and Chlorite (CSM) spectral maturity vs. depth, EM 13-71 ...... 30
Figure 3.6. Detailed protolith and alteration mineralogy, 2680-2700' depth, EM 13-71 ...... 32
Figure A.1. Phyllosilicate sheet structure ...... 36
Figure A.2. Phyllosilicate mineral bearing a centered hydroxyl ion (OH-)...... 37
Figure A.3. The two groups of phyllosilicate minerals ...... 37
Figure B.1. MR006 in plane polarized light ...... 42
Figure B.2. MR006 in cross polarized light ...... 43
Figure B.3. MR008 in plane polarized light ...... 43
Figure B.4. MR008 in cross polarized light ...... 44
Figure B.5. MR009 in plane polarized light ...... 44
x
Figure B.6. MR009 in cross polarized light ...... 45
Figure B.7. MR013 in cross polarized light, location with almost no identifiable sheet silicate…………………………………………………………………………46
Figure B.8. MR013 in cross polarized light, location with abundant apparent sericite in a single grain ...... 46
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LIST OF TABLES
Table 2.1 Field sample locations with minerals and ISM values detected by the infrared spectrometer ...... 19
Table 3.1 Main formations and alteration minerals encountered along EM 17-31 core...... 21
Table C.1 Mineral distribution (490–498.5 ft)………………………………………………46
Table C.2 Mineral distribution (498.67-845.5 ft)……………………………………………47
Table C.3 Mineral distribution (846.17-1042.6 ft)…………………………………………..48
Table C.4 Mineral distribution (1042.6-1139 ft)…………………………………………….49
Table C.5 Mineral distribution (1139.5-1392.4 ft)……………………………………...…...50
Table C.6 Mineral distribution (1392.8-1486.1 ft)………………………………………...... 51
Table C.7 Mineral distribution (1486.5-1528.5 ft)…………………………………………..52
Table C.8 Mineral distribution (1528.6-1566 ft)…………………………………………….53
Table C.9 Mineral distribution (1566.5-1748.5 ft)…………………………………………..54
Table C.10 Mineral distribution (1749-2018 ft)……………………………………………..55
Table C.11 Mineral distribution (2018.5-2287.3 ft)…………………………………………56
Table C.12 Mineral distribution (2287.7-2551.1 ft)…………………………………………57
Table C.13 Mineral distribution (2551.7-2615 ft)…………………………………………...58
Table C.14 Mineral distribution (2615.8-2642.9 ft)…………………………………………59
Table C.15 Mineral distribution (2643.3-2660 ft)…………………………………………...60
Table C.16 Mineral distribution (2660.2-2670.8 ft)…………………………………………61
Table C.17 Mineral distribution (2671-2681.5 ft)…………………………………………...62
Table C.18 Mineral distribution (2681.7-2692.3 ft)…………………………………………63
Table C.19 Mineral distribution (2692.5-2703.1 ft)…………………………………………64
Table C.20 Mineral distribution (2703.3-2712 ft)…………………………………………...65
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Table C.21 Mineral distribution (2712.2-2719.7 ft)…………………………………………66
Table C.22 Mineral distribution (2719.8-2727.4 ft)…………………………………………67
Table C.23 Mineral distribution (2727.6-2737.3 ft)…………………………………………68
Table C.24 Mineral distribution (2737.4-2748.4 ft)…………………………………………69
Table C.25 Mineral distribution (2748.8-2763.8 ft)…………………………………………70
Table C.26 Mineral distribution (2764.2-2779.8 ft)…………………………………………71
Table C.27 Mineral distribution (2780-2796 ft)……………………………………………..72
Table C.28 Mineral distribution (2796.2-2812.2 ft)…………………………………………73
Table C.29 Mineral distribution (2812.5-2826.5 ft)………………………………………….74
Table C.30 Mineral distribution (2826.8-2842.4 ft)…………………………………………75
Table C.31 Mineral distribution (2842.6-2857.3 ft)…………………………………………76
Table C.32 Mineral distribution (2857.5-2872 ft)…………………………………………...77
Table C.33 Mineral distribution (2872.1-2880.3 ft)…………………………………………78
Table C.34 Mineral distribution (2880.5-2887.7 ft)…………………………………………79
Table C.35 Mineral distribution (2887.9-2896.8 ft)…………………………………………80
Table C.36 Mineral distribution (2896.9-2907 ft)…………………………………………...81
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CHAPTER 1
INTRODUCTION
This thesis is an expansion of the text and content of an already published and peer-reviewed paper titled, “Using Infrared Spectrometry to Deduce Fluid History from an Exploration Core,
Emigrant Peak Geothermal Prospect, Northern Fish Lake Valley, Nevada, U.S.A.”
(Madubuike et al., 2016). However, to get a concise version of the research project, refer to the actual paper in the 2016 Transactions published by the Geothermal Resources Council
(GRC). The project supervisor – Dr. Thomas Brikowski, and a Ph.D. student – Ann Moulding coauthored the paper.
1.1 GENERAL OVERVIEW
There is strong evidence that gases emitted from the burning of fossil fuels are perturbing climate and ecosystems through the emission of carbon dioxide (CO2), and for these reasons, policies have been put in place to rapidly develop cleaner energy alternatives. Geothermal energy is one of the cleaner energy alternatives being developed. Scientists have been carrying out extensive research to understand how heat from reservoirs in the earth’s subsurface can be easily located and harnessed, in a bid to contribute to cleaner energy production and reduce
CO2 emissions. Burning of coal, oil or natural gas is not required in the generation of geothermal energy; there is no emission of CO2. This makes geothermal energy a cleaner form of energy.
Unfortunately, a major struggle with geothermal energy is that most of the resources not associated with magma are discovered “blind”- with no major surface expressions like
1
fumaroles or hot springs, to give any indication of massive steam or hot water reservoirs beneath the earth’s surface. Therefore, continuous research is required for improved understanding of the geology that supports the localization of geothermal reservoirs, and how these reservoirs can be harnessed effectively to produce energy.
Infrared (IR) spectrometry and identification of minerals have led to notable progress in quantifying rock alteration in magma-hydrothermal systems. Similar progress may be possible for the amagmatic geothermal systems common in the western U.S., despite their much weaker rock alteration. Application of the visible, near-infrared through short-wave-infrared (VNIR-
SWIR) reflection spectroscopy to assess alteration in magmatically-driven systems is well- established, however, has not been explored in detail in the more subtle amagmatic systems typical of the Basin and Range Province of the United States of America (USA). This project makes an initial assessment of the utilization of VNIR-SWIR spectroscopy in detecting potential roots of modern geothermal circulation in a hot but dry well near the California-
Nevada border (Figure 1.1). Finding evidence of recent amagmatic geothermal circulation at this site could bolster the potential of this promising but unproven prospect.
This study will contribute to existing knowledge that will be utilized to understand geothermal energy play localization, especially in Nevada which hosts over 20 geothermal energy production plants and produces over 500 megawatts of electricity (Matek, 2016). Nevada’s geothermal energy production makes up about 15% of total production in the United States, making it the second largest geothermal energy producer after California.
This study includes a summary of previous work done on the tectonics, structural history, and geothermal exploration carried out in the Fish Lake Valley basin. The results of this project can be integrated into existing and future work to come up with geomodels for this prospect
2
area. The models will guide future exploration and development plans for this site, in addition to other amagmatic geothermal energy prospects, especially in Nevada.
Figure 1.1. Map of southwestern United States with the study area outlined in red. The study area is located in the northern portion of Fish Lake Valley, Nevada (Modified from ESRI, 2016).
1.2 LOCATION AND GEOLOGY OF STUDY AREA
1.2.1 REGIONAL GEOLOGIC FRAMEWORK
The subject of the study is the Emigrant Peak Geothermal Prospect (EPGP; Hulen et al., 2005b) which is located in northern Fish Lake Valley, Nevada east of the California border. The White
Mountains and the Silver Peak Range border the Fish Lake Valley to the west and east
3
respectively (Figure 1.2). The area is located in a broad transtensional zone where large magnitude strike-slip displacement along the Death Valley-Fish Lake Valley Fault steps to the east to merge with the faults of the Central Walker Lane – one of the most seismically active parts of the western Great Basin (Rogers et al., 1991; Faulds et al., 2005; Oldow et al., 2008).
Here, dextral fault movement started in the late Cenozoic period, between about 15 and 6 Ma
(Stewart, 1980; Dilles and Gans, 1995; Reheis and Sawyer, 1997; Stockli et al., 2003; Surpless et al., 2002; Faulds et al., 2005; Mueller et al., 2014) due to the relative motion between the
Pacific and North American plates. This system of dextral faults accommodates 20 to 25 percent of the plate motion between the Pacific and North American plates; the other 75 percent is being taken up by the San Andreas Fault system to the west (Dokka and Travis, 1990; Oldow,
1992; Faulds and Henry, 2008).
The dextral strike-slip faults of the Eastern California Shear Zone (OV-WMFZ and FLVFZ) step to the east at a regional releasing bend known as the Mina Deflection (MD) (Ryall and
Priestly, 1975), forming the Northern Fish Lake Valley pull-apart basin and hosting the
Emigrant Peak Geothermal Prospect (EPGP) in the northeastern part of Fish Lake Valley
(Figure 1.2). The Mina Deflection links faults of the central Walker Lane with those of the
Eastern California Shear Zone (Ryall and Priestly, 1975; Oldow, 1992, 2003). The faults step over at a complex deformation of ancient crust south of the Mina deflection, which is exposed in the Silver Peak-Lone Mountain Metamorphic Core (extensional) Complex (Figure 1.2), as west-northwest-trending turtleback structures (Oldow et al., 1994, 2008, 2009; Kirsch, 1971).
4
Figure 1.2 Location map of the EM 17-31 geothermal exploration well relative to major structural features of west-central Nevada (Oldow, 2008). High-angle fault zones are shown in black lines and the low-angle faults are shown in red lines. Abbreviations are NV-Nevada; CA-California; SPLM-Silver Peak-Lone Mountain, SPR-Silver Peak Range; FLVFZ-Fish Lake Valley Fault Zone; WM-White Mountains; FCFZ-Furnace Creek Fault Zone; OVF- Owen’s Valley fault. Blue arrow shows the average NW extension direction, causing the formation of a pull-apart basin.
5
The exposed turtleback structures are a major fault structure in this extensional complex named the Silver Peak-Lone Mountain detachment fault (SPLMDF) and locally known as the Mineral
Ridge (MR) detachment. For purposes of this document, this fault system will be referred to by its local name - Mineral Ridge detachment fault. The MR detachment fault is often described as a doubly-plunging shallowly northwest dipping detachment fault system which was initiated at 12 to 8 Ma and continued activity into the early Pliocene (Oldow, 2008).
Eventually, this detachment system became folded and inactive about 5 Ma due to progressive deformation which locked the fault and terminated its motion (Petronis et al., 2002; Oldow,
2008; Katopody, 2015). The MR detachment fault system’s northwest extension juxtaposed an upper-plate assemblage of upper Miocene volcanic and volcaniclastic rocks and moderately metamorphosed lower Paleozoic rocks onto a lower plate composed of amphibolite facies metatectonites and intrusive granites (Kirsch, 1971; Oldow, 2008). It is important to note that the EM 17-31 well was drilled about 12 km northwest from the exposed detachment fault system and the well penetrated the MR detachment fault at 2735 feet (Hulen, 2006a).
1.2.2 GEOLOGY OF STUDY AREA
The EM 17-31 well is a geothermal exploration well in the Emigrant Peak Geothermal Energy
Prospect (EPGP). It was drilled in 2006 to support the on-going Department of Energy’s
Geothermal Resource Exploration and Development (GRED) III project called the Emigrant
Slimhole Drilling Project. The goal was to determine the commercial viability of the northern portion of the Fish Lake Valley.
The exploration well site is surrounded by fascinating geologic structures in a seismically active zone. The geology of the area has been extensively studied and documented by
6
numerous geoscientists (e.g. Turner, 1902; Robinson et al., 1968; Albers and Stewart, 1972;
Oldow et al., 1994; Reheis and Dixon, 1996; Reheis and Sawyer, 1997; Stockli et al., 2003;
Faulds and Henry, 2008). The Emigrant Peak, the Silver Peak Range, the White Mountains and the Volcanic Hills, which host similar geothermal wells (Figure 1.3), surround the EM 17-
31 well.
Emigrant Peak to the north of the well site is composed of Paleozoic rocks from the Cambrian
(Mule Spring Limestone and Emigrant Formation) and Ordovician (Ordovician Palmetto
Formation) periods (Albers and Stewart, 1972). Tertiary volcanic welded and nonwelded tuffs are also predominant in the Emigrant Peak. All are usually in complex faulted contact.
Southeast of the EM 17-31 well lies the Silver Peak Range where the low-angled MR detachment fault is exposed. This range is made up the Precambrian Wyman Formation,
Paleozoic rocks (like Campito Formation, Poleta Formation, Harkless Formation, Mule Spring
Limestone, Emigrant Formation and Ordovician Palmetto Formation), and Mesozoic granitic intrusions (quartz monzonite plutons) (Albers and Stewart, 1972). Many of these units were encountered in the EM 17-31 borehole.
The White Mountains to the southwest of the well location are made up of Precambrian Wyman
Formation exposures intruded by coarse-grained Jurassic to Tertiary granitic rocks and superimposed partially by Tertiary basalts and ash flow tuffs (Albers and Stewart, 1972). Large fault scarps are common on the eastern edge of the mountain, showing that faulting in this area is very active. Quaternary faults can be seen cutting into recent alluvium.
The Volcanic Hills to the west of the EM 17-31 well hosts geothermal production wells and a hot spring (Figure 1.3). This area is made up of predominantly Tertiary volcanic ash flow tuffs and tuffaceous sedimentary rocks. Evidence from some drilled wells shows that the MR
7
detachment fault lies underneath the geothermal production wells in Volcanic Hills and there is speculation that the detachment fault might play a role in the localization and permeability of geothermal prospects within the northern portion of the Fish Lake Valley, Nevada. The EM
17-31 well penetrated the low-angle MR detachment fault; the role played by the fault in influencing fluid migration will also be explored.
Figure 1.3. Satellite image of northern Fish Lake Valley of Nevada showing locations of some geothermal production wells (in red) and the hot spring (in yellow). The EM 17-31 geothermal exploration well (in blue), is located to the east of the Volcanic Hills.
8
1.2.3 AN AMAGMATIC GEOTHERMAL SYSTEM
Despite the anomalously high heat flow of geothermal prospects in the Fish Lake Valley basin, there have been no links to a magmatic heat source. These geothermal prospects are considered to be tectonically driven. Therefore, they are classified as extensional amagmatic geothermal systems. The EM 17-31 core was drilled in a dextral fault right step-over zone; a type of complex structural setting proposed as most favorable for hosting geothermal systems in the western Great Basin (Faulds et al., 2004, 2013; Siler et al., 2015). This kind of complex setting leads to high fracture density, which often enhances fracture permeability, hence providing conduits for fluid flow (Barton et al., 1995; Caine et al., 1996; Sibson, 1996; Wisian et al.,
1999). On-going extensive faulting and fracturing in the area provide conduits for meteoric water to infiltrate great depths and get heated; it also serves as a means for hot fluids to migrate up towards the surface.
The metamorphic history of this region is crucial to this research. Pre-Tertiary rocks in the
Silver Peak-Lone Mountain extensional complex have been metamorphosed to various grades; from low-grade facies in the Paleozoic rocks of the MR detachment fault’s upper plate to amphibolite-facies in the Proterozoic metamorphic tectonites of the lower plate (Oldow et al.,
2008). Metamorphism in this region occurred in the Cretaceous (100Ma), before the Miocene fault extension (Stewart and Diamond, 1990) which exposed lower-plate rocks to mid-crustal levels and to temperatures less than 350°C (Kohler et al., 1993). It is interesting to note that prior to metamorphism, there was shuffling of the Cambrian-Ordovician sequence during a fault thrusting event in the Devonian (Figure 1.4) and a regional metamorphism signal overprinted this (Figure 3.4). This research seeks to identify a likely subtle lower temperature overprint on the higher temperature metamorphic protolith in the EM 17-31 core. Any low-
9
temperature alteration signatures identified, especially in the metamorphic protolith zones, might indicate locations of relatively recent geothermal fluid circulation along the core.
Strongly developed hydrothermal mineral zonation typical of magmatic systems (e.g.
Kavalieris and Bat-Erdene, 2011) is unlikely here, although assemblages typical of the argillic zone of magmatic systems (<200°C) should be expected within the core.
1.2.4 SUBSURFACE GEOLOGY OF THE EM 17-31 CORE
An earlier extraordinarily detailed visual examination and interpretation of the EM 17-31 core addressing the mineralogy, alteration and structures penetrated by the core hole has been done
(Hulen, J.B., 2006a; Hulen, J.B., 2006b). A limited number of X-ray diffraction (XRF) and fluid-inclusion microthermometry (FIM) data were also obtained at selected points in the core
(Deymonaz et al., 2008).
According to Hulen in Deymonaz et al. (2008), the Paleozoic section below the Tertiary and above the lower plate of the MR detachment fault, exhibited low permeability despite the zones extensive fracturing, shearing and brecciation. Prior to drilling, it was expected that these units would be the geothermal reservoir rock (Hulen, 2005). According to Craig et al. (2003) and
Oldow et al. (2003), the permeability is low because of mineral alteration, high clay content and secondary mineralization above the MR detachment zone. Hulen (2008) believes that together with the impermeable Tertiary volcaniclastic sequence, the Paleozoic section above the detachment fault forms a thick cap rock over the underlying potential geothermal reservoir.
After drilling, the metamorphic tectonite rock below the detachment was classified as an excellent reservoir rock because it is silicified, brittle, highly fractured with maintained opened
10
holes (Deymonaz et al., 2008). Recall, however, that EM 13-71 encountered no fluid entries despite reaching economic temperatures for geothermal production.
Correlation with surficial geologic formations by Hulen (2006a) indicates the following units penetrated by the core. From top to bottom, the geologic units encountered are (Figure 1.4):
1. Tflvf: Mio-Pliocene Fish Lake Valley assemblage of tuffaceous sedimentary rocks (426
ft. thick),
2. Tic: Miocene Icehouse Canyon assemblage of weakly welded rhyolite ignimbrite (202
ft. thick),
3. Єem: Cambrian Emigrant Formation limestone and siltstone member (121 ft. thick),
4. Op: Ordovician Palmetto Formation carbonaceous shaly siltstone and limestone (468
ft. thick),
5. Єhu: Cambrian Harkless Formation upper unit (73 ft. thick),
6. Єhs: Cambrian Harkless Formation siltstone member (618 ft. thick),
7. Єhqs: Cambrian Harkless Formation quarzitic siltstone member (289 ft. thick),
8. Pz: Unidentified Paleozoic Formation(s) (119 ft. thick) and
9. pЄw: Proterozoic Wyman Formation (186.4 ft. thick).
The folded and fractured Cambrian Emigrant Formation (Єem) limestone and siltstone member lie in thrust contact with the Ordovician Palmetto Formation (Op) in the prospect area (Hulen et al., 2005a).
11
Figure 1.4. Stratigraphic column representation adapted from Hulen (2006a) (depth, not to scale).
1.3 RESEARCH FOCUS
This research focuses on using infrared spectrometry to understand the alteration mineralogy along a drill core (EM 17-31) from an amagmatic geothermal energy prospect at the northern portion of the Fish Lake Valley. More attention is paid to likely “recent” geothermal fluid flow along the MR detachment fault, which the core passed through. The role the low-angled detachment plays is also investigated.
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1.4 AIMS AND OBJECTIVES
1.4.1 AIMS
The aims of this project are:
1. To test the ability of infrared spectrometry to quantify rock alteration (likely subtle) in
amagmatic geothermal systems.
2. To extend existing knowledge on the localization of geothermal energy prospects in
northern Fish Lake Valley, Nevada.
1.4.2 OBJECTIVES
The objectives of this project are:
1. To use the portable TerraSpec Halo infrared spectrometer, a mineral identifier to scan
core (EM 17-31) from the Emigrant Peak Geothermal Prospect and determine if it is a
suitable geothermal energy prospecting tool.
2. To analyze spectral data from the infrared spectrometer.
3. To study the alteration mineralogy of the EM 17-31 drill core rocks.
4. To investigate evidence for recent tracks of geothermal fluid circulation.
5. To produce logs showing results of data variation with depth.
6. To identify the exact role of the MR detachment fault in the localization of the
geothermal prospect.
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CHAPTER 2
METHOD
Chapter 2 presents the methods used for the project. The chapter discusses the data acquisition with infrared spectrometry - a technique that can be used to study hydrothermal alteration minerals in rocks.
2.1 INFRARED (IR) SPECTROSCOPY
Infrared spectroscopy is the study of how infrared radiation, which has a longer wavelength and lower frequency than visible light, interacts with materials. The portable infrared instrument used to scan the EM 17-31 core combines the visible to near-infrared (VNIR) and short-wave infrared (SWIR) of the electromagnetic spectrum (i.e. 350 to 2500 nm). When combined, the VNIR-SWIR of the electromagnetic spectrum is a powerful technique, which has been used effectively to distinguish rocks and minerals based on unique spectral signatures materials produce when light is absorbed (Adams, 1975; Hunt, 1977; Salisbury, 1993; Clark,
1999). Materials absorb and reflect radiation at specific wavelengths due to electronic and vibrational processes: the technique works by detecting vibrations in the carbonate and hydroxyl (OH) bonds, giving it the ability to identify minerals (Farmer, 1974; Hunt, 1977).
Visually obscure changes in sheet silicates (phyllosilicates) like micas, chlorites, and clay minerals are readily identifiable using this powerful technique.
Infrared spectrometry has become a typical mineral exploration method (Yang et al., 1999;
Ross et al., 2013). Many studies have made use of this technique to examine alteration mineralogy in epithermal (Carrillo-Rosa et al., 2009), geothermal (Yang et al., 2001; Martinez-
14
Serrano, 2002; Mas et al., 2006, 2003; Calvin and Solum, 2005; Mielke et al., 2015; Guisseau et al., 2007; Calvin, 2016) and deeper hydrothermal systems (Ducart et al., 2006; Harraden et al., 2013). However, this thesis will focus on comparing infrared results gotten from magma- driven hydrothermal systems with amagmatic geothermal systems, which is the kind of system specific to the study area.
Hydrothermal alteration is the change a rock undergoes when hot fluid passes through it.
Numerous scientists using infrared spectrometry or other methods (e.g. Browne, 1970; Yang et al., 2000; Yang et al., 2001; van Ruitenbeek et al., 2005; Kristmannsdóttir, 1975), have effectively characterized hydrothermal alteration minerals in geothermal systems. Shallow formations (< 230°C) affected by argillic alteration are usually zoned into smectite, smectite- illite mixed-layer clays and illite (Mielke et al., 2015); our prospect should mimic this trend downhole.
2.2 DATA ACQUISITION WITH INFRARED SPECTROMETER
The EM 17-31 core was scanned at variable intervals (down to cm spacing within a core box,
Figure 2.1b) using the ASD (PANalytical) TerraSpec Halo mineral identifier. The mineral identifier is a portable infrared spectrometer that measures only spectra between the VNIR-
SWIR ranges of 350 to 2500 nm in the material of interest and immediately matches the recovered spectrum to the internal instrument mineral library. The portable device allows for easier and faster logging along the drill core. This method proved to be less tedious and time- consuming than X-ray powder diffraction (XRD) analysis, which requires exhaustive sample preparation. However, minerals in the feldspar, silica, chloride, spinel and sulphide groups cannot be identified using the VNIR-SWIR spectrometry.
15
Selected parts of the core were scanned at a core shed in Dyer, Nevada owned by Esmeralda
Energy Company (Figure 2.1b); this was done during a period of about 6 days during the summer of 2015. The core depth spanned the depth interval of 490 to 2907 feet (149 to 886 meters). The portable spectrometer acts entirely as a contact investigator sampling an area with a diameter of 0.4 inches (1 cm) (Figure 2.1b).
Figure 2.1. (a) First author at the Emigrant Peak Geothermal Prospect – EM 17-31 drill site with a portable VNIR-SWIR spectrometer and (b) first and third authors scanning core.
Mineral spectra were collected from 1920 points along the core, at 2 to 6 inch (5 to 15 centimeter) intervals with more concentration at crucial zones like the detachment fault zone and possible zones of hydrothermal alteration. The data acquired consists of up to seven identified minerals at each scanned point (and a qualitative measure of identification confidence), as well as scalar values like illite spectral maturity (ISM) and chlorite spectral maturity (CSM) computed from spectrum features generally correlatable with subtle changes in geochemistry. Illite, chlorite, muscovite, phengite, montmorillonite, stilpnomelane and calcite were the most frequent minerals identified. Calibration of the instrument via an external
16
Spectralon® target was made each time the instrument was turned on. The TerraSpec Halo also contained an internal white reference that calibrated occasionally; about 15 minutes throughout the day to ensure measured reflectance spectra remained accurate. Pictures of scanned core boxes were also taken.
2.3 PETROGRAPHIC THIN SECTION ANALYSIS
Limited thin-section analysis was performed in order to identify petrographic features of the core that might correlate with IR scan features and identified minerals. Petrographic thin sections from outcrop samples (Table 2.1) were prepared by a commercial laboratory. These slabs of thin section were studied and imaged using a petrographic microscope, to determine the lithology, mineralogy and possible alteration of the stratigraphic units at the MR detachment fault zone exposed at the surface, on the Silver Peak Range (Figure 1.2). This study allowed for a direct comparison between the mineral results from the scanned outcrop at the MR detachment fault (exposed on the Silver Peak-Lone Mountain extensional complex), and the petrography of the thin sections from the outcrop. Appendix B contains pictures and brief descriptions of some samples as identified under the petrographic microscope by Dr.
Brikowski.
2.4 GEOGRAPHIC INFORMATION SYSTEM INCORPORATION
Google Earth and ArcGIS were used to make location maps in Chapter 1. Dr. Oldow and his students provided shape files for fault interpretations within the Fish Lake Valley basin. Ann
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Moulding downloaded the well locations from the Nevada Bureau of Mines and Geology website (http://www.nbmg.unr.edu/Geothermal/WellInfo.html).
18
sure
instrument has of the mineral being present in the rock; with 3 being the highest confidence rating. in being highest confidence the the rock; with 3 being instrument present mineral of the has
Table 2.1. Field sample locations with minerals and ISM values detected by the infrared spectrometer. Rating represents mea represents Rating spectrometer. infrared the by detected values ISM and minerals with locations sample Field 2.1. Table the of confidence
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CHAPTER 3
RESULTS AND DISCUSSION
Chapter 3 discusses the mineral and spectral scalar results identified by the portable infrared spectrometer, as reported in the published Geothermal Resources Council paper (Madubuike et al., 2016). Dr. Thomas Brikowski produced most of the figures in this chapter.
3.1 INFRARED SPECTROMETER MINERAL RESULTS FOR EM 17-31
EM 17-31 well reached economic temperatures of 322°F or 161°C (Figure 3.1). Unfortunately, no fluid entries were encountered; however, spectral results have shown evidence of relatively recent fluid migration, which left rocks altered. The well penetrated the MR detachment fault at about 2735 feet (Hulen, 2006a) and spectral data collected shows lower temperature alteration overprint on higher temperature protolith at the fault region. The detachment fault region could have been either an upflow zone for hot fluids or a conduit zone for cooler fluids, which is now locally inactive.
Some of the minerals identified in the core using an infrared spectrometer are montmorillonite, beidellite, stilpnomelane, illite, kaolinite, halloysite, dickite, chlorite, chamosite, muscovite, phengite, hematite, goethite, jarosite, epidote, clinozoisite, biotite, calcite, ankerite and lepidolite. Reported in Appendix C is an excel spreadsheet table of these identified minerals at each scanned depth (in feet) along the core. The confidence scale was also noted with three being the highest scale of confidence. Table 3.1 below shows the formations encountered along the core and their most common mineral alteration products.
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Temperature (°F) 0 100 200 300 400 0
500
1000
1500
2000 Depth (ft)Depth
2500
3000
3500
Figure 3.1. EM 17-31 borehole temperature graph. The well reached economic temperatures of 322°F or 161°C (reference for plot data).
Table 3.1. Main formations and minerals encountered along EM 17-31 core.
Main formations Common alteration minerals Tertiary volcanic tuffaceous sedimentary Montmorillonite, stilpnomelane, rocks Tertiary volcanic rhyolite ignimbrites Montmorillonite, stilpnomelane, kaolinite Cambrian Emigrant Formation Calcite, muscovite, hematite Ordovician Palmetto Formation Montmorillonite, stilpnomelane, illite, chlorite, chamosite, muscovite Cambrian Harkless Formation Illite, kaolinite, chlorite, chamosite, muscovite Unidentified Paleozoic Formations Montmorillonite, stilpnomelane, beidellite, illite, kaolinite, chlorite, chamosite, muscovite, phengite, epidote Proterozoic Wymann Formation Montmorillonite, stilpnomelane, beidellite, illite, kaolinite, chlorite, chamosite, muscovite, phengite, jarosite, epidote, biotite
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3.1.1 DISTRIBUTION OF HYDROTHERMAL ALTERATION MINERALS
The distribution of some identified minerals in EM 17-31 well is shown in Figure 3.2.
Appendix C gives more detail of minerals at each scanned point; no depth scale correction was done on that table.
Smectite is a hydrated expanding clay mineral present in some quantities in the near-surface portion of EM 17-31 core and at the MR detachment fault zone. Figure 3.2 shows zones where smectites (montmorillonite or beidellite minerals in our case) with high confidence ratings were identified. Smectite consistently occurred near the surface, at the low-temperature zone of the core in the Tertiary volcanic rocks that were sampled. It is interesting to note that while progressing downwards, smectite becomes scarce but reappears at about 2600 feet, as it approaches the detachment fault zone (2735 feet) which has a metamorphic protolith.
The presence of abundant chlorite, epidote, muscovite and biotite (Figure 3.2) in the pre-
Tertiary rocks of the core shows evidence of metamorphic rocks in the greenschist-facies and amphibolite-facies. There is a gradual increase in mineral crystallinity, thermal maturity, dehydration and metamorphism with depth. Biotite related to protolith occurs abundantly at higher temperature towards the end of the core from 2750 feet in the unidentified brecciated
Paleozoic Formations and the metamorphic tectonites. Biotite is usually used as an indicator of high temperatures more than 280°C (Bird et al., 1984; Reyes, 1990). According to Lagat et al. (2004), authigenic biotite is sometimes present in several geothermal systems like Salton
Sea, Cerro Prieto, Philippines, and Ngawha.
The infrared spectrometer also detected iron oxides like hematite, jarosite, and goethite along
EM 17-31 core, especially along the fault zone. Iron oxides are also a type of low-temperature mineral alteration like smectites, characteristic features of extensional detachment fault zones
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(Spencer and Welty, 1986; Long, 1992). These oxides have been tied to fluid flow concentrated along detachment faults (Seidel et al., 2005). There is also a link between iron oxides and recharge zones of geothermal systems (Reyes, 1990). This overprint of extensive low- temperature alteration like iron oxides and smectites on metamorphic protolith
(metasedimentary rocks and metamorphic tectonites) along the MR detachment fault zone suggests relatively recent fluid movement along this fault. The low-temperature overprint is also evident from the illite spectral maturity (ISM) and chlorite spectral maturity (CSM) charts which are discussed in subsequent sections (Figure 3.5).
Illite is a non-expanding clay mineral detected in significant quantities in most portions of the core. Overall, K-rich illite was the most common illite mineral identified in EM 17-31 core, the others were Mg-rich (Al-OH peak at 2196 to 2208 nm) illite and Na-rich (<2194 nm) illite.
In a geothermal field study by Yang et al. (2001), illite with longer Al-OH wavelengths represented permeable intervals and active fluid flow zones (higher temperature) in particular.
The location of the Al-OH peak generally tracked with Halo-ISM (i.e. smaller wavelength correlates with smaller Halo-reported ISM) and was not separately analyzed in this study.
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Figure 3.2. Some important minerals distinguishable with infrared spectrometer along the EM 17-31 core. Geologic Formations shown on the left, refer to Section 3.1 for detailed descriptions. Narrow hot pink bands indicate thicker occurrences of tectonized Mesozoic granitic intrusives. Zones of continuously abundant minerals indicated by solid symbols. “MR detach” is the Mineral Ridge detachment fault. “LCZ” is a lost circulation zone.
Some unusual minerals were identified by the IR spectrometer. Lepidolite is a phyllosilicate mineral and a secondary source of lithium. The instrument identified this mineral in primarily nondescript metasiltstone cataclasites in the depth range of 2600 to 2800 feet. What role does
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this play in characterizing the geothermal play? From Deymonaz, J.E.’s personal communication with Dixie Hambrick of U.S. Borax in 1984, the company - U.S. Borax drilled one of their largest lithium deposits in the area (Deymonaz et al., 2008). The deposit was said to have contained elevated levels of lithium and strontium, which is believed to be associated with both modern and fossil geothermal systems. Lepidolite and strontianite were paired in some IR results in cuttings obtained from a nearby Fish Lake Valley geothermal well during this study. Increasing Li has been found to indicate cooling fluid conditions in Li-Na-Mg geothermometers (Fouillac and Michard, 1981).
Temperature, permeability, the detachment fault and lithology (especially in the case of carbonates) seem to be the major control on the distribution of IR-detectable minerals.
3.2 HYDROTHERMAL ALTERATION MINERAL ZONATION
Hydrothermal phyllosilicate zonation in the EM 17-31 amagmatic geothermal well exists and was quite distinguishable. An upper smectite zone, a middle illite zone, and a lower illite- chlorite zone were defined in the core (Figure 3.3) despite the geothermal system’s more subtle alteration, compared to magmatic hydrothermal systems that show a similar trend (e.g. New
Zealand: Yang et al., 2000, 2001; Guadeloupe: Mas et al., 2006).
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Figure 3.3. Distinguishable mineral zonation along the EM 17-31 core superimposed on Figure 3.2; similar to trends seen in magmatic hydrothermal/geothermal systems.
3.2.1 DOWNHOLE SMECTITE-ILLITE-MUSCOVITE PROGRESSION
A steady downhole progression is obvious, with strongly hydrated and poorly crystalline alkali phyllosilicates near the surface grading into more dehydrated and crystalline forms at depth.
This is best illustrated by the transition from prevalent smectite (primarily montmorillonite) to illite then to phengite/muscovite at depth (Figure 3.2). Similar smectite-illite transitions are typical of geothermal systems (e.g. Yang, et al., 2000, 2001; Mas et al., 2006) and can extend to muscovite in hotter hydrothermal systems (e.g. Tillick et al., 2001). While at least the
26
smectite-illite progression is consistent with present-day temperatures, the entire progression is better defined by consideration of metamorphic facies. Note that near and below the detachment fault, the low-temperature minerals (including smectite and iron oxide) return.
This feature was not revealed by previous visual and limited XRD studies of the core. The relatively smooth reversal of this trend suggests upward propagation of the altering fluids from the vicinity of the detachment.
3.2.2 DOWNHOLE PROGRESSION OF APPARENT METAMORPHIC ZONES
The IR-identified minerals can be combined into approximate metamorphic facies assemblages
(Figure 3.4). Here the downhole progression to higher temperature alteration/metamorphism is slightly clearer, as is the sharp return to lower-temperature assemblages near the detachment fault. Remarkable is the occurrence of biotite and muscovite above the detachment, suggesting that orogenic regional metamorphism did extend to greenschist and amphibolite facies. Below the detachment, the rocks are noticeably older, and the amphibolite facies has no direct relationship to metamorphism observed in the upper plate. Also not considered here are the effects of protolith, where the predominance of carbonates in the Ordovician Palmetto (Op) and siltstone in the Cambrian Harkless (Єh) significantly influence the occurrence of chlorite
(Figure 3.2 & Figure 3.4). The mineral occurrences and other temperature indicators affected by Cretaceous regional metamorphism provide the backdrop upon which any signal from later geothermal/hydrothermal alteration are superimposed.
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Figure 3.4. General geology (left), IR-identified mineral assemblages indicating metamorphic facies (center) and IR scalar "Illite Spectral Maturity" (ISM, decreases with increasing maturity) vs. depth at EM 13-71. Green symbols are different assemblages consistent with greenschist facies
3.3 INFRARED SCALARS
Recent infrared spectrometers can internally calculate and report scalar values as the spectra are measured. The scalar values represent ratios of reflectance peaks and subtle changes in geochemistry influence these peak ratios. The reported scalars are relatively independent of specific mineralogy, and those intended to indicate relative ratios of mineral crystallinity to hydration (i.e. “spectral maturity”) appear to be the most useful. For the illite series, this is the
ISM (illite spectral maturity), a function of normalized absorption at the Al-OH peak (varies with the degree of crystallinity) vs H2O (varies with the degree of mineral dewatering). ISM is generally defined so that increasing values represent increasing maturity (absorption-based,
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Doublier et al., 2010); ISM reported by the spectrometer in this study decreases with maturity
(reflectance-based; ASD Corporation, 2013) with increasing values. Reflectance-based ISM values greater than 1 are regarded as relatively immature; for example, typical in the Late
Cenozoic/Tertiary volcanic sequence in the upper portion of the core (Figure 3.5). Note that
ISM is not determined in strictly carbonate sequences high in organic carbon (dark), e.g. the
Ordovician Palmetto (Op, Figure 3.5). Absorption ISM is generally similar to XRD- determined crystallinity measures (e.g. Illite Crystallinity or IC, Verdel, et al. 2012).
The ISM trend with depth in EM 13-71 indicates steadily increasing maturity until around 2400 ft. depth, then apparently decreasing maturity in the heavily silicified Cambrian Harkless siltstone (Figure 3.5). At the detachment fault and below, a number of narrow depth zones are present that exhibit ISM values more typical of the mildly altered (lower diagenetic zone) volcanic rocks. This suggests one or two episodes of overprinting of upper greenschist/amphibolite facies assemblages by cooler fluids. The change in ISM trend to reduced maturity suggests somewhat cooler (anchizone) fluids, possibly associated with migration along the detachment, developed the silicification of the Harkless. The highly silicified and altered formation might have been a geothermal reservoir at one point in time when the MR detachment fault was still active about 5 Ma. The significantly less mature zones at and below the detachment fault are more consistent with lower diagenetic zone conditions and may represent a younger, even cooler hydrothermal event also influenced by the MR detachment.
Field scanning of the metatectonites indicates more soluble lithologies (i.e. carbonate) exhibit much less mature ISM, while more resistant lithologies (quartz mylonite) appear to preserve high maturities consistent with their metamorphic grade. Similar highly mature ISM values
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appear at the margins of Mesozoic granodiorite lenses found above the detachment, suggesting a concentration of high-temperature alteration at those margins. The smooth progression of increasing maturity across a structural age reversal (thrusting of Cambrian Emigrant Formation over Ordovician Palmetto Formation) indicates the formation of the ISM trend comes after the structural shuffling of the Paleozoic units.
Figure 3.5. IR-based scalars Illite (ISM) and Chlorite (CSM) spectral maturity vs. depth, EM 13-71. Black squares show intervals that were IR scanned. Fit curves obtained using LOESS (local polynomial regression) in the R statistics software (Core Team, 2016).
Chlorite Spectral Maturity (CSM) is similar in functionality to the illite-based ISM series
(Doublier, et al., 2012). For the chlorite series, the CSM is defined as a function of the weighted sum of normalized absorption at the Mg-OH and Fe-OH peaks (varies with the degree of crystallinity) vs H2O (varies with the degree of mineral dewatering). Although less continuous,
30
CSM shows the same trend of increasing dewatering, thermal maturity and crystallinity with depth. There is a reversal of that trend several hundred feet above the detachment, and notably immature values in zones below the detachment (Figure 3.5). Insufficient chlorite was present above 1350 ft. depth to allow determination of CSM in the topmost part of the core.
3.4 POTENTIAL RECENT ALTERATION ZONES
A major goal of this study was to identify potential zones of recent fluid flow to understand the nature of the convective circulation that must be causing high subsurface temperatures in this prospect area. The limited zones of marked low-maturity ISM and CSM values near and below the detachment are likely candidates for such “tracks” of lower temperature, presumably amagmatic geothermal circulation.
An example 75 to 100 feet above the detachment indicates these immature ISM zones are associated with low-temperature mineral assemblages (smectite/montmorillonite and iron oxides). Somewhat distinctive occurrences of beidellite (an expansive smectite) are within a few feet of several of these low-maturity spikes, but in general, the spikes are not equivalent to unique occurrences of low-temperature mineral assemblages. Furthermore, these apparent zones of enhanced low-temperature alteration do not occur in visually remarkable portions of the core (e.g. left side, Figure 3.6).
The infrared scalars appear to be the most precise indication of the relative temperature of alteration and trends, while mineral assemblages give a much more muddled indication in this core.
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Figure 3.6. Detailed protolith and alteration mineralogy, 2680-2700' depth, EM 13-71. Left: Detailed lithology log from Hulen (2006), center: occurrence of low-temperature alteration minerals, right: ISM log.
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CHAPTER 4
CONCLUSIONS AND RECOMMENDATION
4.1 CONCLUSIONS
The Emigrant Peak Geothermal Prospect exhibits many promising features, including a broad area of elevated surface heat flow, location in a transtensional stress regime, strong evidence of active faulting and structurally localized areas of surficial mineralization. However, it lacks surficial thermal waters and direct observation of subsurface thermal fluids, even after drilling of several shallow wells and one deep exploration well that reached commercial temperatures of 322°F (161°C). Active convective heat transport must be going on somewhere in this prospect, and the focus of this study was to identify any remnant “tracks” of geothermal fluids via potentially subtle changes in alteration mineralogy in the exploration core. Infrared scanning of cores and outcrop has been highly successful in characterizing such changes in epithermal metal deposits and magmatic geothermal systems. The amagmatic geothermal systems typical of the U.S. Basin and Range Province are likely to exhibit more subtle or restricted alteration, making this a potentially challenging goal. Working with a very well visually characterized core, we were able to reach the following conclusions based on detailed
IR scanning:
1. An initial fluid “event” yielding a downward increase in illite-chlorite maturity pattern
(increasing crystallinity, thermal maturity, and dehydration) most consistent with burial
metamorphism. This pattern is continuous across structural shuffling of the Paleozoic
units and Mesozoic granodiorite intrusive dikes in the upper plate of the metamorphic
tectonites at the Mineral Ridge detachment fault. The most mature ISM values are
consistent with anchizone-epizone conditions.
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2. This initial trend of downward increase in maturity is overprinted by cooler alteration,
concentrated within 500 ft. of the detachment in the lower plate. If the less mature ISM
near the detachment in the upper plate is related to spatially equivalent silicification of
metasiltstone units of the Cambrian Harkless, it could represent a second fluid event
similar to mid-Cenozoic detachment-related silicification in northern Nevada (e.g.
Cline, et al., 2005). Alternatively, this trend may be the upward diffusive extension of
the following fluid event.
3. A much lower temperature, and apparently still younger overprint of smectite and iron
oxide mineralization is present near and below the detachment. This alteration likely
represents the kind of geothermal circulation sought in the exploration studies, although
may be millions of years old. Fe-oxide alteration is usually present in geothermal
recharge zones and might be evidence of the MR detachment fault being a down-flow
recharge zone. This episode of alteration was not visually discernable in the core, nor
was its extent revealed by limited XRD and fluid-inclusion analysis of the core.
4. The close spatial relationship of these youngest alteration events to the detachment
confirm that it is the major conduit for the horizontal flow of fluids in this area, with
the upper plate serving as a relative aquitard or cap to any geothermal circulation.
In applying IR spectrometer analysis to amagmatic geothermal systems, it appears that scalar values (computed from various spectral features) over continuous intervals may provide the most useful information. At EM 17-31, protolith does not appear to be the strongest influence on IR scalar trends. However, variations in protolith are a major control on the distribution of alteration minerals in such systems, and at least at EM 17-31 variations in smectite and iron oxide minerals gave only broad indications of likely hydrothermal alteration. Trends in
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spectral maturity scalars (especially ISM and CSM) coupled with good understanding of local geologic history allowed the discrimination of multiple alteration events at this site, and the determination of their relative timing. It is the continuity and fine spatial resolution of the scalar profiles that makes them most useful. Very low-maturity spikes in these scalars are likely to indicate the most recent hydrothermal/geothermal alteration at this site and other amagmatic settings. Typically, such zones will not be directly recognized by visual examination of core and cuttings, nor by limited XRD and/or fluid inclusion analysis. Indeed, at EM 17-31 ISM spikes tended to occur in relatively obscure units unlikely to catch the eye of even the most careful geologist.
4.2 RECOMMENDATION
In the future, thin sections from the EM 17-31 core should be prepared and analyzed by another student. Thin section samples from the core of the MR detachment fault zone, will allow for a future correlation between spectral results from scanned points and petrographic analysis of minerals.
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APPENDIX A
PHYLLOSILICATE MINERALS
The infrared spectrometer used for this research identified mostly phyllosilicates like montmorillonite, illite, kaolinite, biotite, muscovite, chlorite, lepidolite etc.
A phyllosilicate or sheet silicate mineral is a chain silicate that forms when each of the silica tetrahedron (or silicon-oxygen tetrahedron) building blocks shares three out of four oxygen
-2 atoms to form a sheet, giving a basic structural unit of Si2O5 and ratio of Si : O = 2 : 5. Each sheet has a 6-fold symmetry if undistorted (Plummer et al., 2007).
Figure A.1. Phyllosilicate sheet structure. The sheets are made up of many individual silica tetrahedrons (Nelson, 2015).
Most phyllosilicates are hydroxyl ion (OH-) bearing, with the OH group centered at 6-fold rings
-3 +2 of tetrahedra becoming an Si2O5(OH) group (Figure A.2). Usually, external cations like Fe ,
+2 +3 Mg or Al are bound to the silica tetrahedra sheets (SiO4) and they occur in octahedral coordination with two O and one OH ion of the tetrahedral layer.
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Figure A.2. Phyllosilicate mineral bearing a centered hydroxyl ion (OH-) (Nelson, 2015).
The cations in the octahedral sheet could be divalent or trivalent; this brings about the two (2) groups of phyllosilicates:
1. Trioctahedral phyllosilicates: An octahedral sheet silicate where each O or OH ion is
+2 +2 surrounded by three divalent cations, usually Fe and Mg e.g. brucite Mg(OH)2.
2. Dioctahedral phyllosilicates: An octahedral sheet silicate where each O or OH ion is
surrounded by two trivalent cations, usually Al+3. When the cations are trivalent, charge
balance is maintained e.g. gibbsite Al(OH)3 and corundum Al2O3
Figure A.3. The two groups of phyllosilicate minerals (Nelson, 2015).
When one tetrahedral and one octahedral sheet bind together (“t-o”), a general geometry of
layered lizardite Mg3Si2O5(OH)4 or kaolinite Al2Si2O5(OH)4 is obtained (Klein et al., 1993).
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Additional phyllosilicate members can be derived by joining tetrahedral sheets on both sides of the “o” sheet. This leads to “t-o-t” type layers like talc and pyrophyllite, which are electrically neutral and form stable structural units bound by van der Waals bonds. Structures like these have excellent cleavage, easy gliding, and greasy feel because of their weak bond
(Moore and Reynolds, 1989; Klein et al., 1993).
Phyllosilicates are divided into four (4) main groups. They are:
1. Serpentine Group
2. Clay Mineral Group
3. Mica Group and
1. Serpentine Group: The infrared device identified no serpentine mineral. The serpentine
group are layer structures, phyllosilicates with the formula - Mg3Si2O5(OH)4. They are
usually of a larger particle size than clay minerals (Moore and Reynolds, 1989). They
occur in three common polymorphs: antigorite, lizardite, and chrysotile. Antigorite and
lizardite are usually platy, while chrysotile is fibrous. Serpentine is found as an alteration
product of magnesium silicates, like olivine, pyroxene, and amphibole due to
hydration/hydrolysis (reaction with water) (Klein et al., 1993). It is frequently associated
with magnesite, chromite, and magnetite.
2. Clay Mineral Group: The infrared device identified many clay minerals. Clay minerals
are very fine-grained phyllosilicates and are easily studied or identified using infrared
spectrometry. Clay minerals are hydrous aluminum layer silicate substituting Mg or Fe in
part for Al and alkalies or alkaline earth minerals. Clays are made of stacks of tetrahedral
sheets and octahedral sheets. A single clay mineral could make up clays or clays could
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occur mixed with other minerals like carbonates, feldspars, micas, and quartz. They can be classified as 1:1 or 2:1. A 1:1 clay consists of one tetrahedron sheet stacking on one octahedral sheet (t-o) e.g. kaolinite. A 2:1 clay consists of two tetrahedral sheets and one octahedral sheet stacked in various ways (t-o-t) e.g. talc and montmorillonite. Some of the clay minerals identified by the infrared spectrometry are: i. Kaolinite Al2Si2O5(OH)4: It is a 1:1 layer type dioctahedral phyllosilicate. Kaolinite is
made up of a Si2O5 sheet bonded to a gibbsite Al(OH)3 sheet. The apical oxygens in
the tetrahedral sheet replace two out of three of the hydroxyls in the octahedral sheet.
Unlike smectites, kaolinite is nonexpendable and without interlayer swelling on contact
with water. Dickite, nacrite, halloysite belong to the same species as kaolinite; they are
chemically similar but show different t-o stacking from kaolinite. Kaolinite is a
secondary mineral formed by weathering, diagenesis or hydrothermal alteration of
aluminum silicates, especially feldspar. ii. Smectite: It is an expansible 2:1 layer phyllosilicate. This group is composed of t-o-t
layers of both dioctahedral and trioctahedral type. They sheets are joined by weak van
der Waal’s bonds and are easily separated by water. Smectites have the capacity to
absorb water molecules between the sheets and expand its structure on contact with
water. The dioctahedral members are montmorillonite, beidellite, and nontronite; the
trioctahedral members are hectorite and saponite. iii. Illite: This is a common mineral in many shales. It is a 2:1 clay-sized alkali-deficient
phyllosilicate with a similar structure to muscovite (Nelson, 2014). In illites, the
interlayer space has collapsed so there is no space for interlayer hydrated cation
exchange (Klein et al., 1993) making illite a non-expandable clay on contact with
water.
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Talc [Mg3Si4O10(OH)2] and pyrophyllite [Al2Si4O10(OH)2] are other kinds of 2:1 layer
clay minerals, trioctahedral and dioctahedral types respectively; however, they were not
identified by the infrared device.
3. Mica Group: Micas are coarse-grained phyllosilicates with variable chemistry, structure,
and origin. They are composed of t-o-t layers with interlayer cations with little or no
exchangeable water (Klein et al., 1993). They have a perfect cleavage, which is its most
prominent characteristic. Structurally, micas can be either dioctahedral (muscovite,
paragonite, margarite) or trioctahedral (biotite, phlogopite, annite, vermiculite).
The infrared device identified muscovite, biotite, and lepidolite, which belong to the mica
group of the phyllosilicates.
i. Muscovite: It is a common rock-forming phyllosilicate mineral of aluminum and
potassium with a chemical formula of KAl2(AlSi3O10)(OH)2. Muscovite is a
dioctahedral mica. The perfect cleavage of the mineral allows it split into thin
sheets, which are often highly flexible and elastic. The muscovite structure consists
of t sheets [(Si, Al)2O5] linked to octahedral gibbsite-like sheets to form t-o-t layers.
These layers have a net negative charge balanced by K or Na ions between them.
Muscovite is the most common mica found in igneous (granites, pegmatites) and
metamorphic (gneisses, schists) rocks. In some schistose rocks, muscovite occurs
as fibrous aggregates of small scales with a silky sheen called sericite; it is a
common alteration mineral of feldspar. White mica is another name for muscovite.
ii. Biotite: It is a common rock-forming phyllosilicate mineral with the chemical
formula - K(Mg,Fe)3AlSi3O10(OH)2. Biotite is a trioctahedral mica. The sheets are
weakly bound together by potassium ions. Black mica is another name for biotite.
40
The mineral is found in igneous (granite pegmatites, granites, diorites, gabbros,
peridotites) and metamorphic rocks.
iii. Lepidolite: It is a member of the mica group with formula K(Li,Al)2-
3(AlSi3O10)(O,OH,F)2 with coarse- to fine-grained scaly aggregates. It is a lithium-
bearing mineral often intergrown with muscovite.
Phlogopite [KMg3(AlSi3O10)(OH)2] and margarite [CaAl2(Al2Si2O10)(OH)2] are other
minerals in the mica group, however, they were not identified by the infrared device.
4. Chlorite Group: The infrared device identified some chlorite group minerals like chlorite
and chamosite. It has a chemical formula of (Mg,Fe)3(Si,Al)4O10(OH)2·(Mg,Fe)3(OH)6
and usually occurs as foliated massives or in fine scattered particles (Klein et al., 1993).
1- Chlorite’s composition is made up of t-o-t layers [Mg3(AlSi3O10)(OH)2] interleaved
brucite-like sheet with one out of the three Mg2+ ions substituting Al3+, resulting in a
1+ composition of [Mg2Al(OH)6] . After the composition of the t-o-t layer and the brucite-
like sheet are added, it results in a complex formula - (Mg,Al)6(Si,Al)4O10(OH)8. They
are also called 2:1:1 minerals.
Chamosite, clinochlore, pennantite and sudonite are examples of members of the chlorite
minerals. Chlorite has a characteristic green color and it is a common mineral in igneous
(as an alteration product of pyroxenes, amphiboles, biotite, and garnet) and metamorphic
rocks. Chlorite group minerals exist over a wide range of temperature and pressure
conditions making them abundant minerals within low and medium temperature
metamorphic rocks and some igneous rocks.
41
APPENDIX B
THIN SECTION ANALYSIS
Appendix B contains pictures and descriptions of some field sample thin sections viewed underneath a microscope; under plane polarized light (PPL) and cross-polarized light (XPL).
Refer to Table 2.1 for sample name, location, minerals identified and ISM value.
1. MR006: Green phyllite. ISM = 0.779; CSM = 2.597; chamosite and muscovite. 45%
rounded unstrained quartz; 30% greenish chlorite and 20% muscovite (higher order
birefringence than chlorite).
Figure B.1. MR006 in plane polarized light
42
Figure B.2. MR006 in cross polarized light
2. MR008: Iron altered fine metasiltstone. ISM = 1.003; CSM = N/A; Goethite and K-
illite. 25-30% sericite; 20% mildly strained 0.2mm quartz; 15% calcite veinlets; 10%
opaque dust (goethite or hematite).
Figure B.3. MR008 in plane polarized light
43
Figure B.4. MR008 in cross polarized light
3. MR009: Muscovite metasiltstone. ISM = 1.027; CSM = N/A; Gypsum and K-illite.
80% mildly strained 1mm quartz; 8% muscovite; 5% late veins (gypsum? muscovite?)
Figure B.5. MR009 in plane polarized light
44
Figure B.6. MR009 in cross polarized light
4. MR013: Phyllite, upper plate. ISM = N/A; CSM = N/A; Montmorillonite. 60%
strained 5mm quartz; 25% younger quartz-filled fractures, some calcite?; 5% sericitized
grains, 5% younger Fe-stained chlorite veins all cut by 0.1mm parallel fracture filled
with sericite.
45
Figure B.7. MR013 in cross-polarized light, location with almost no identifiable sheet silicates.
Figure B.8. MR013 in cross-polarized light, location with abundant apparent sericite in a single grain (lower part of slide, resembles strained quartz, but is K-feldspar?)
46
APPENDIX C
EM17-31 MINERAL DISTRIBUTION
Table C.1. Mineral distribution (490–498.5 ft)
47
Table C.2. Mineral distribution (498.67-845.5 ft)
48
Table C.3. Mineral distribution (846.17-1042.6 ft)
49
Table C.4. Mineral distribution (1042.6-1139 ft)
50
Table C.5. Mineral distribution (1139.5-1392.4 ft)
51
Table C.6. Mineral distribution (1392.8-1486.1 ft)
52
Table C.7. Mineral distribution (1486.5-1528.5 ft)
53
Table C.8. Mineral distribution (1528.6-1566 ft)
54
Table C.9. Mineral distribution (1566.5-1748.5 ft)
55
Table C.10. Mineral distribution (1749-2018 ft)
56
Table C.11. Mineral distribution (2018.5-2287.3 ft)
57
Table C.12. Mineral distribution (2287.7-2551.1 ft)
58
Table C.13. Mineral distribution (2551.7-2615 ft)
59
Table C.14. Mineral distribution (2615.8-2642.9 ft)
60
Table C.15. Mineral distribution (2643.3-2660 ft)
61
Table C.16. Mineral distribution (2660.2-2670.8 ft)
62
Table C.17. Mineral distribution (2671-2681.5 ft)
63
Table C.18. Mineral distribution (2681.7-2692.3 ft)
64
Table C.19. Mineral distribution (2692.5-2703.1 ft)
65
Table C.20. Mineral distribution (2703.3-2712 ft)
66
Table C.21. Mineral distribution (2712.2-2719.7 ft)
67
Table C.22. Mineral distribution (2719.8-2727.4 ft)
68
Table C.23. Mineral distribution (2727.6-2737.3 ft)
69
Table C.24. Mineral distribution (2737.4-2748.4 ft)
70
Table C.25. Mineral distribution (2748.8-2763.8 ft)
71
Table C.26. Mineral distribution (2764.2-2779.8 ft)
72
Table C.27. Mineral distribution (2780-2796 ft)
73
Table C.28. Mineral distribution (2796.2-2812.2 ft)
74
Table C.29 Mineral distribution (2812.5-2826.5 ft)
75
Table C.30. Mineral distribution (2826.8-2842.4 ft)
76
Table C.31. Mineral distribution (2842.6-2857.3 ft)
77
Table C.32. Mineral distribution (2857.5-2872 ft)
78
Table C.33. Mineral distribution (2872.1-2880.3 ft)
79
Table C.34. Mineral distribution (2880.5-2887.7 ft)
80
Table C.35. Mineral distribution (2887.9-2896.8 ft)
81
Table C.36. Mineral distribution (2896.9-2907 ft)
82
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VITA
Chinomso Madubuike, a.k.a. Nneoma was born in Detroit, Michigan, on March 12, 1991, to
Emeka and Imelda Madubuike. In 2012, she obtained a Bachelor’s degree in Geology (Honors) from the Federal University of Technology Owerri (FUTO), Nigeria. At FUTO, she completed a thesis research on groundwater accessibility using remote sensing technique. As an undergraduate, ExxonMobil offered her a five-month geology internship position where she worked on reservoir evaluation in a Niger Delta field. Prior to this, she gained fundamental knowledge of the seismic process while interning with CGG Veritas for a month.
Chinomso began studies in the Geosciences department at the University of Texas at Dallas
(UTD) in 2014. She is an active member of the American Association of Petroleum Geologists
(AAPG), and for a year, held the position of Vice-President for the organization’s student chapter at UTD. She also had the opportunity to represent the university at the AAPG Imperial
Barrel Award in 2015. In the summer of 2016, Chinomso took a break from her thesis project to intern with Chesapeake Energy in Oklahoma for three months. There she successfully completed a project on fracture analysis, correlation, and predictability in a carbonate reservoir.
From Chinomso’s thesis research, a paper titled “Using Infrared Spectrometry to Deduce Fluid
History from an Exploration Core, Emigrant Peak Geothermal Prospect, Northern Fish Lake
Valley, Nevada, U.S.A.” was produced. Geothermal Resources Council (GRC) in their 2016
Transactions published the paper. Her project supervisor – Dr. Thomas Brikowski and a Ph.D. student – Ann Moulding coauthored the paper. During the 2016 GRC Annual Meeting at
Sacramento, California, the paper featured in a poster session and an oral presentation.
Chinomso’s research poster was awarded Best Student Poster of the poster session at the GRC conference.
Chinomso in her spare time enjoys cooking, listening to music and spending quality time with family or friends. She serves in the children’s ministry and ushering ministry of Covenant
Church, McKinney.
Chinomso’s plan is to build a solid career in the energy industry and be a role model or mentor to the younger generation of geoscientists.