1
POST-MINERAL NORMAL FAULTING IN ARIZONA PORPHYRY SYSTEMS
By
Phillip A. Nickerson
_________________
A Dissertation Submitted to the Faculty of the
DEPARTMENT OF GEOSCIENCES
In Partial Fulfillment of the Requirements
For the Degree of
DOCTOR OF PHILOSOPHY
In the Graduate College
THE UNIVERSITY OF ARIZONA
2012
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THE UNIVERSITY OF ARIZONA
GRADUATE COLLEGE
As members of the Dissertation Committee, we certify that we have read the dissertation
prepared by Phillip A. Nickerson
entitled Post-Mineral Normal Faulting in Arizona Porphyry Systems
and recommend that it be accepted as fulfilling the dissertation requirement for the
Degree of Doctor of Philosophy
_______________________________________________________________________
Date: 04/30/2012
Eric Seedorff
_______________________________________________________________________
Date: 04/30/2012
Mark Barton
_______________________________________________________________________
Date: 04/30/2012
George Davis
_______________________________________________________________________
Date: 04/30/2012
Peter Reiners
_______________________________________________________________________
Date: 04/30/2012
Charles Ferguson
Final approval and acceptance of this dissertation is contingent upon the candidate’s
submission of the final copies of the dissertation to the Graduate College.
I hereby certify that I have read this dissertation prepared under my direction and
recommend that it be accepted as fulfilling the dissertation requirement.
________________________________________________ Date: 04/30/2012
Dissertation Director: Eric Seedorff
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STATEMENT BY AUTHOR
This dissertation has been submitted in partial fulfillment of requirements for an
advanced degree at The University of Arizona and is deposited in the University Library
to be made available to borrowers under rules of the Library.
Brief quotations from this dissertation are allowable without special permission,
provided that accurate acknowledgment of source is made. Requests for permission for
extended quotation from or reproduction of this manuscript in whole or in part may be
granted by the head of the major department or the Dean of the Graduate College when in
his or her judgment the proposed use of the material is in the interests of scholarship. In
all other instances, however, permission must be obtained from the author.
SIGNED: Phillip A. Nickerson
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ACKNOWLEDGEMENTS
I would like to thank my major advisors, Eric Seedorff and Mark Barton for their
guidance, assistance, and patience. I also greatly appreciate valuable feedback from my
committee members, George Davis, Peter Reiners, and Charles Ferguson. I’d like to
recognize my many geologic predecessors--in particular the contributions from the
USGS, AZGS, and other graduates students who generated an invaluable archive of
geologic maps heavily utilized in this study. Without this high-quality geologic
framework, this work would not have been possible.
Financial support for this project came from the Sciences Foundation Arizona,
Lowell Institute for Mineral Resources, Eurasian Minerals, and the Society of Economic
Geology Hugh E. McKinstry Student Reasearch Fund. Logistical support including drillhole information, helicopter access, and some regional data compilation was provided by
Bronco Creek Exploration.
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DEDICATION
To my wife Laura, and my family.
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TABLE OF CONTENTS
LIST OF FIGURES .............................................................................................. 12
ABSTRACT.......................................................................................................... 13
INTRODUCTION ................................................................................................ 15
Laramide porphyry systems in the Basin and Range province ......................... 15
Extension in the Basin and Range province ................................................. 17
Regional geologic framework ........................................................................... 19
PRESENT STUDY ............................................................................................... 23
Methodology ..................................................................................................... 23
Key results ........................................................................................................ 24
Appendix A: “Domino-style” tilting in metamorphic core complexes:
Evidence from radial dikes in the Pinaleño Mountains, Arizona ................. 24
Appendix B: Sodic-(calcic) alteration in two Arizona porphyry copper
systems: Hybrid hydrothermal systems of Laramide and mid-Tertiary ages 25
Appendix C: Dismembered porphyry systems near Wickenburg, Arizona:
District-scale reconstruction with an arc-scale context ................................ 27
FIGURE CAPTIONS............................................................................................ 29
REFERENCES ..................................................................................................... 32
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APPPENDIX A: “DOMINO-STYLE” TILTING IN METAMORPHIC CORE
COMPLEXES: EVIDENCE FROM RADIAL DIKES IN THE PINALEÑO
MOUNTAINS, ARIZONA .................................................................................. 49
Abstract ................................................................................................................. 50
Introduction ........................................................................................................... 51
Pinaleño MCC....................................................................................................... 52
Porphyry Dike Swarm..................................................................................... 53
Dike Orientations and Their Use as a Paleo-Vertical Indicator ...................... 54
Folding of footwall rocks ................................................................................ 56
Hydrothermal Alteration ................................................................................. 56
Interpretation of Oligocene Regional Stress Patterns in Southeastern Arizona ... 56
Implications for the formation of the Pinaleño MCC ........................................... 58
Discussion ............................................................................................................. 60
Conclusions ........................................................................................................... 61
Acknowledgments................................................................................................. 62
References ............................................................................................................. 62
Appendix A.1 ........................................................................................................ 79
References ............................................................................................................. 81
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APPENDIX B: SODIC-(CALCIC) ALTERATION IN TWO ARIZONA
PORPHYRY COPPER SYSTEMS: HYBRID HYDROTHERMAL SYSTEMS
OF LARAMIDE AND MID-TERTIARY AGES ............................................... 88
Abstract ................................................................................................................. 89
Introduction ........................................................................................................... 90
Geologic Setting.................................................................................................... 92
Geochronology...................................................................................................... 95
Tea Cup system ............................................................................................. 96
Eagle Pass system ......................................................................................... 97
Hydrothermal alteration assemblages ................................................................... 97
Tea Cup system ................................................................................................. 98
Eagle Pass system ........................................................................................... 100
Compositions of hydrothermal minerals ............................................................. 102
Tea Cup system ............................................................................................... 102
Eagle Pass system ........................................................................................... 103
Gains and losses in sodic alteration ............................................................... 104
Comparison of sodic (-calcic) and greisen hydrothermal alteration assemblages at
Tea Cup and Eagle Pass with other localities ..................................................... 104
Origin of sodic (-calcic) and iron oxide-rich alteration ...................................... 107
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Source of fluids ............................................................................................... 107
Relationship of sodic-(calcic) alteration to iron oxide-rich alteration ............ 110
Discussion ........................................................................................................... 111
Hybrid hydrothermal systems ......................................................................... 111
Implications for exploration............................................................................ 115
Summary and Conclusions ................................................................................. 117
Acknowledgments............................................................................................... 118
References ........................................................................................................... 118
APPENDIX C: DISMEMBERED PORPHYRY SYSTEMS NEAR
WICKENBURG, ARIZONA: DISTRICT-SCALE RECONSTRUCTION WITH
AN ARC-SCALE CONTEXT ............................................................................ 162
Abstract ............................................................................................................... 163
Introduction ......................................................................................................... 164
Location and Geologic Setting............................................................................ 166
Location .......................................................................................................... 166
Laramide porphyry copper province ............................................................... 166
Extension in western Arizona ......................................................................... 167
Rock types ....................................................................................................... 169
Economic Geology.............................................................................................. 171
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Hydrothermal Alteration ..................................................................................... 173
Greisen ............................................................................................................ 173
Potassic ........................................................................................................... 174
Transitional greisen-potassic .......................................................................... 174
Structural Geology .............................................................................................. 175
Structural Interpretation and Palinspastic Reconstruction of Normal Faults...... 177
Tertiary tilting ................................................................................................. 177
Style of extension............................................................................................ 179
Interpretation of the normal faults .................................................................. 179
Approach to restoring movement on normal faults ........................................ 180
Examination of the district-scale reconstruction............................................. 181
Exploration targets .......................................................................................... 182
Classification of porphyry systems near Wickenburg ........................................ 183
Arc-Scale Reconstruction of Tertiary Extension in the Laramide Porphyry Copper
Belt ...................................................................................................................... 185
Discussion ........................................................................................................... 189
Style of extension in western Arizona ............................................................ 189
Comparison of the scale and geometry of the Laramide magmatic arc to other
arcs .................................................................................................................. 191
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Conclusions ......................................................................................................... 192
Acknowledgments............................................................................................... 193
References ........................................................................................................... 194
Figure Captions ................................................................................................... 203
APPENDIX D: ELECTRON MICROPROBE TABLES ................................... 225
APPENDIX E: TEA CUP U-PB GEOCHRONOLOGY ................................... 289
References ........................................................................................................... 291
APPENDIX F: (U-TH)/HE DATING OF HEMATITE FROM TEA CUP AND
EAGLE PASS ..................................................................................................... 297
Introduction ......................................................................................................... 297
Results ................................................................................................................. 298
Tea Cup ........................................................................................................... 298
Eagle Pass ....................................................................................................... 299
Significance of Ages ........................................................................................... 301
References ........................................................................................................... 302
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LIST OF FIGURES
Figure 1. Location map ......................................................................................... 41
Figure 2. Schematic cross section showing a typical pattern of hydrothermal
alteration in a porphyry copper system ................................................................. 42
Figure 3. Three models proposed to explain the link between upper-crustal and
mid-crustal extension in the Basin and Range province ....................................... 43
Figure 4. Index maps of porphyry deposits in southwestern North America ....... 44
Figure 5. Three-stage model for the formation of the Pinaleño MCC .................. 45
Figure 6. Diagram depicting variation in peripheral styles of alteration in
composite porphyry systems ................................................................................. 46
Figure 7. Panels depicting the palinspastic reconstruction of a district-scale cross
section through the Sheep Mountain porphyry system ......................................... 47
Figure 8. Comparison of porphyry systems of the reconstructed Laramide
magmatic arc to other porphyry belts and magmatic arcs .................................... 48
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ABSTRACT
In the Basin and Range province of southwestern North America, Oligocene and
Miocene normal faults are superimposed upon the Late Cretaceous-early Tertiary
magmatic arc. This study examines tilted fault blocks containing dismembered pieces of
porphyry systems, including pieces below and peripheral to ore bodies, that are exposed
at the modern surface. Features in the magmatic-hydrothermal porphyry systems are used
to place constraints on the style of extension in Arizona, and reconstructions of extension
are used to examine the deep and peripheral portions of porphyry systems to provide a
more complete understanding of porphyry systems as a whole.
The Eagle Pass, Tea Cup, and Sheep Mountain porphyry systems of Arizona are
examined in this study. In all the study areas, previous interpretations of the style of
extension involved strongly listric normal faults. However, similar amounts of tilting
observed in hanging wall and footwall rocks, as well as structure contour maps of fault
planes, require that down dip curvature on faults was minimal (< 1°/km. Instead,
extension is shown here to have occurred as sets of nearly planar, “domino-style” normal
faults were superimposed upon one another, including in the Pinaleño metamorphic core
complex.
Reconstructions of Tertiary extension reveal that sodic (-calcic) alteration is
occurs 2-4 km peripheral to, and greisen alteration is found structurally below and
overlapping with, potassic alteration. In addition, a preliminary reconstruction of
extension across the Laramide magmatic arc reveals that the geometry, as revealed by
known porphyry systems, is of similar scale to that of other magmatic arcs. These results
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help further the debate surrounding competing models of continental extension, and
combine with previous work to provide a more complete understanding of the geometries
of Arizona porphyry systems at the district and arc scale.
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INTRODUCTION
The Basin and Range province of western North America is one of the great
metallogenic provinces of the world, as well as a one of the world’s best studied
extensional terrains. Normal faults and ore deposits commonly are superimposed upon
one another here (Fig. 1) (Seedorff, 1991; Wilkins and Heidrick, 1995), which creates
challenges and advantages for the study of both metallogensis and extension. For
example, challenges arise where syndeformational hydrothermal alteration destroys
critical structural markers near the associated fault zones and where key parts of ore
bodies are dismembered by normal faults. Benefits of this juxtaposition are brought to
light when products of one of the geologic processes are used to constrain the other. For
example, predictable patterns in hydrothermal alteration zoning can be used as structural
markers (Stavast et al., 2008), which may better constrain structural reconstructions and,
in turn, aid in better discriminating between different styles of extension. Conversely, the
deep levels of ore-forming systems exposed in the footwalls of normal faults can be
examined at the surface to better constrain ore forming processes (Carten, 1986). In this
dissertation, I focus on the benefits brought about by the superposition of postmineralization normal faults on porphyry systems in Arizona in order to simultaneously
advance the understanding of extension and ore deposits in the Basin and Range
province.
Laramide porphyry systems in the Basin and Range province
Precious metal (Au, Ag) and base metal (Cu, Mo, Pb, Zn, Sn, W, Fe) ore deposits
of many different styles occur throughout the Basin and Range province. This study will
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focus on the porphyry copper deposits of Arizona that constitute one of the richest copper
metallogenic provinces on earth (Titley, 1982a). The deposits are commonly
spectacularly exposed in the arid climate of the Sonoran Desert and lie within a region
that has been well described in the geologic literature for more than a century (e.g.,
Ransome, 1903; Titley and Hicks, 1966; Davis, 1979; Dickinson, 1991). The
combination of the high degree of exposure, vast literature on the regional geology and
mineral deposits, as well as the ease of access to this geology, make southern Arizona an
ideal laboratory to advance the understanding of porphyry copper deposits.
Porphyry systems are magmatic-hydrothermal systems that include the dike- and
plug-like intrusions of porphyry texture which lend their name to the deposit type, a
pluton or batholith which is the source of the dikes and plugs, and various styles of
hydrothermal alteration which typically metasomatize 10’s to 100’s of km3 of the
intrusive bodies and surrounding country rock (Seedorff et al., 2005b; Sillitoe, 2010). The
hydrothermal fluids are derived both from the intrusive bodies and by circulation of
meteoric and connate waters in the country rock (Carten, 1986; Dilles et al., 1992, 1995).
Temperature, fluid chemistry, and pressure control the style of hydrothermal alteration in
a given part of a system. In a vertical progression from deep to shallow, proximal parts of
the system are dominated generally by greisen, potassic, sericitic, and advanced argillic
styles of alteration, whereas the distal parts of the system generally are dominated by
propylitic, sodic-calcic, sodic, and iron-oxide rich acid styles of hydrothermal alteration
(Fig. 2), although other variations also occur.
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Whereas the overall footprint of hydrothermal alteration is quite large (10’s km3)
in porphyry systems, the sizes of the ore bodies are only a few km3. Mineralization
occurs in a range of settings, including near the transition from potassic to sericitic
alteration (Lowell and Guilbert, 1970) at moderate to high temperature (~700°C-350°C).
Copper-bearing minerals include sulfides at depth and oxides in the shallower, weathered
horizon and are either disseminated in the rock or in veins. The relatively small size of
the ore bodies compared to large size of the porphyry copper systems requires the
exploration geologist to use knowledge of zoning patterns in hydrothermal alteration and
textures in intrusive igneous rocks to identify vectors toward mineralization. However,
despite decades of study on specific porphyry copper deposits, certain alteration styles
found on the flanks and roots of porphyry copper systems have only recently been
identified (e.g., Seedorff et al., 2008), and a system-scale understanding of their evolution
remains to be developed. Examining porphyry systems in extended terrains, such as
southern Arizona, offers the ability to map and to characterize the distal and deep parts of
the systems, as normal fault blocks commonly expose them at the surface (Dilles and
Einaudi, 1992; Maher, 2008; Stavast et al., 2008; Nickerson et al., 2010). These
exposures are utilized in this study to help further the system-scale understanding of
porphyry systems.
Extension in the Basin and Range province
Many fundamental insights into upper- and mid-crustal extension were uncovered
in the Basin in Range province (Ransome et al., 1910; Armstrong, 1972; Proffett, 1977;
Crittenden et al., 1980; Lister and Davis, 1989), and the area continues to an important
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study area for research into the debate surrounding the manner in which it the crust
responds to large-magnitude extension (Brady, 2002; Wong and Gans, 2008; Arca et al.,
2010; Colgan et al., 2010). Much of the controversy surrounding extension in the Basin
and Range province focuses on normal faults that currently dip at low angles (< 30°).
Where these relationships were first identified in the hinterland of the Sevier fold and
thrust belt, they were thought to be contractional features (Misch, 1960). However,
Armstrong (1972) showed that because the faults placed younger rocks on older rocks,
they must be normal faults accommodating extension. Reinterpretation of contractional
features as extensional features swept across the Basin and Range and culminated with
the elucidation that mylonitic fabrics found in what would be called metamorphic core
complexes (Coney, 1980) were products of extension in the middle crust (Davis, 1980).
Three competing models have emerged to explain the relationships between midcrustal mylonitic fabrics observed in core complexes and upper-crustal brittle normal
faulting that is widespread in the Basin and Range (Fig 3A-C). The first model (Fig. 3A)
proposes that the mylonitic fabrics are down-dip expressions of normal faults that
initiated at low angles (less than 30°) and accommodated 10’s of km of displacement
(Wernicke, 1981; John, 1987). A second model(Fig. 3B), known as the rolling hinge
model, states that strongly listric normal faults in the upper crust, with 10’s km of
displacement, are folded by isostatic uplift during extension to expose mid-crustal
mylonitic fabrics at the surface (Spencer, 1984; Buck, 1988). The first two models agree
that during extension a master fault serves as a detachment into which smaller scale faults
solein the upper crust and transfer their displacement. The final model (Fig. 3C) puts
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forth that a set of “domino–style” faults break at high angles (60°-70°) and rotate to low
angles during extension (Davis, 1983). When the nearly-planar faults rotate to low angles
(~20-30°), slip on the faults becomes kinematically unfavorable (Anderson, 1951), and a
new set of faults forms at high angles. Through repetition of the process, mylonitic rocks
in the down-dip toes of abandoned low-angle faults can be brought to the surface.
These three models each make different predictions regarding the geometry,
magnitude, and timing of normal faulting that can be tested. Studies utilizing reflection
seismology (Gans, 1987), modern earthquake focal mechanisms (Jackson, 1987; Abers et
al., 1997), thermochronology (John and Foster, 1993; Howard and Foster, 1996; Reiners
et al., 2000), and paleomagnetism (Livaccari et al., 1995; Stavast et al., 2008) have all
furthered the understanding of large-magnitude extension but have not synthesized a
cogent model for the formation of metamorphic core complexes. This study uses
knowledge derived from studies in economic geology to place constraints on deformation
in crystalline rocks that commonly occur in the footwall of normal faults to further this
debate.
Regional geologic framework
The porphyry copper deposits of Arizona include some of the best-studied
porphyry systems in the world and have been the focus of over a century of scientific
study (Ransome, 1903; Titley and Hicks, 1966; Titley, 1982a; Pierce and Bolm, 1995).
However, the new ages on porphyry copper systems in Arizona (Seedorff et al., 2005a;
Nickerson and Seedorff, this study Appendix A), as well as the recognition and
description of the flanks and roots of these complex hydrothermal systems (Seedorff et al,
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2005b, 2008; Barton et al., 2005; Stavast et al., 2008; Nickerson et al., 2010), continue to
advance the understanding of porphyry copper systems.
The Tea Cup, Eagle Pass, and Sheep Mountain porphyry systems examined in this
study are located in the heart of the porphyry copper belt of southwestern North America
in the state of Arizona (Fig. 4). Exploration for porphyry copper deposits in the region
has ebbed and flowed in tandem with copper prices (Lowell, 1978; Paul and Manske,
2005), with times of intense exploration occurring mainly in the late 19th and middle
20th centuries. The discovery of the Resolution deposit near Superior in the mid-1990s
has renewed the interest of both junior and major mining companies in the region.
The Laramide (~80-50 Ma) and younger magmatism in Arizona intruded a thin
(~2 km) cratonal section of sedimentary rocks (Titley, 1982b). As summarized by
Dickinson (1989), the metamorphic basement of central and southeastern Arizona
consists of the Mesoproterozoic Yavapai Supergroup (ca. 1.8 Ga) and Pinal Schist (ca.
1.7 Ga). These crystalline rocks were intruded at 1.6 Ga by arc plutons of the Madera
Diorite and at 1.4 Ga by widespread anorogenic granitic plutons. Before 1.1 Ga, the
crystalline basement was beveled and unconformably overlain by approximately 1 km of
dominantly siliciclastic sedimentary rocks of the Proterozoic Apache Group and Troy
Quartzite. Near the time of deposition of the Troy Quartzite, the siliciclastic sedimentary
sequence and the underlying crystalline rocks were intruded by diabase sheets, sills, and
dikes that are dated at ~1.1 Ga (Shride, 1967; Wrucke, 1989). The diabase sheets are
most abundant in sedimentary rocks of the Apache Group and in the upper one km of the
underlying crystalline rocks (Howard, 1991). The Proterozoic strata of the Troy Quartzite
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and Apache Group are disconformably overlain by approximately 1.0-1.5 km of
Paleozoic strata, mainly carbonate rocks.
During Laramide time, regional contraction produced basement-cored uplifts
similar to those of the central Rocky Mountains (Davis, 1979), and a large magmatic arc
was built on the western margin of the North American plate (Drewes, 1976; Dickinson
and Snyder, 1978; Dickinson, 1989). The arc formed between about 84 and 61 Ma and
shows an overall progression to more felsic compositions over time (Cornwall, 1982;
Lang and Titley, 1998; Seedorff et al., 2005a). Contraction clearly postdates early
relatively mafic magmatism (Willden, 1964). Porphyry copper formation is related to
somewhat younger (74-61 Ma) arc magmatism of intermediate to silicic composition
(Titley, 1982b; Lang and Titley, 1998), which, in the cases of at least certain deposits,
postdates reverse faulting (Seedorff et al., 2005a).
A period of tectonic quiescence and erosion characterized the post-Laramide
period until Oligocene time (Dickinson, 1991), when bimodal volcanism and extension
swept across the region formerly occupied by the Laramide arc (Coney and Reynolds,
1978). Large-magnitude extension dismembered and tilted porphyry systems and formed
a northwest-southeast striking belt of metamorphic core complexes in Arizona (Davis,
1980). Extension and magmatism continued through the Miocene, but by 15 Ma was of
lesser magnitude and was more silicic, respectively. In many cases, sedimentation
accompanied extension in the newly formed basins. Following extension, Tertiary and
Quaternary gravels were deposited to form widespread pediment surfaces on older rocks
22
(Dickinson, 1991). Today, the landscape is undergoing incision as the pediment surfaces
are exhumed by down-cutting along the Gila River (Richard and Spencer, 1997).
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PRESENT STUDY
The methods, results, and conclusions of this study are presented in the three
manuscripts appended to this dissertation/thesis, Appendices A to C. In addition, further
information and documention is contained in supplementary material, which is included
as Appendices D to F. The following is a summary of the most important findings in this
document.
Methodology
This study combines field mapping, structural analysis, palinspastic
reconstruction, mineral characterization via petrography and electron microprobe, U-Pb
geochronology, (U-Th)/He thermochronology, and compilations of pre-existing geologic
mapping to constrain formation of porphyry systems, and crustal extension in Arizona.
Original geologic mapping was used to identify the nature and timing of structural
features, as well as, the geometry and relative ages of different styles of hydrothermal
alteration in three study areas: the Tea Cup porphyry system, the Eagle Pass porphyry
system, and the Sheep Mountain porphyry system. These observations are combined with
data from pre-existing geologic maps to palinspastically reconstruct Oligo-Micoene
extension in an iterative manner. The resulting product constrains both the style of
extension and the zoning patterns of hydrothermal alteration in the porphyry systems.
Mineral compositions determined by electron microprobe are used to characterize
hydrothermal mineral assemblages, and the thermo- and geochronologic techniques are
used to place quantitative constraints on the timing of both porphyry system formation
and extension.
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Key results
Appendix A: “Domino-style” tilting in metamorphic core complexes: Evidence from
radial dikes in the Pinaleño Mountains, Arizona
In this appendix, geologic mapping in the Eagle Pass porphyry system and
stereographic analysis of its radial porphyry dike swarm are used to place new constraints
on the style of extension in the Pinaleño metamorphic core complex (MCC) of
southeastern Arizona. Three new U-Pb dates, coupled with field and petrographic
relationships, reveal that the porphyry system is the first well documented Oligocene
porphyry system in Arizona. A method for determining paleo-vertical in radial dikes
swarms is demonstrated and then used to show that both the footwall and hanging wall of
the Pinaleño MCC were homogeneously tilted ~83° SW during Oligo-Miocene
extension. Mapped patterns of hydrothermal alteration that are intimately associated with
the intrusion of the dike swarm also are consistent with significant southwesterly tilting
of footwall rocks. A previous interpretation of the Pinaleño MCC contends that the MCC
formed via isostatic upwarp of a strongly listric normal fault (Figure 5D), implying
different amounts of tilting in hanging wall and footwall rocks and folding of the footwall
rocks about a horizontal axis perpendicular to the extension direction; neither style of
deformation is recorded by the dike swarm. The constraints on footwall deformation
instead favor a “domino- style” model of MCC formation that produces similar amounts
of tilting in hanging wall and footwall rocks. A new interpretation for formation of this
MCC involves at least two independent sets of nearly planar normal faults that were
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sequentially superimposed (Fig. 5A-C). These results suggest that warping of normal
faults by localized isostatic uplift is not required for MCC formation.
Appendix B: Sodic-(calcic) alteration in two Arizona porphyry copper systems: Hybrid
hydrothermal systems of Laramide and mid-Tertiary ages
The distal expressions of hydrothermal alteration on the periphery of porphyry
systems vary significantly from system to system, including a diversity of distal alteration
types, intensity of distal alteration, and geometry of distal alteration patterns. Distal
alteration in porphyry systems, including sodic-calcic and propylitic, can host significant
base or precious metal mineralization, and the spatial distribution of distal hydrothermal
alteration can be used as a vector toward the center of the system.
In this appendix the flanks and cores the Laramide Tea Cup and Oligocene Eagle
Pass porphyry copper systems in Arizona are examined here using U-Pb geochronology,
as well as field and petrographic studies, to better characterize sodic (-calcic) and iron
oxide-rich alteration found in porphyry systems. New U-Pb ages of zircons from Tea Cup
reveal that the porphyry system dates from between ~72 and 70 Ma. Sodic assemblages
at Tea Cup and Eagle Pass contain quartz, albite, chlorite, and epidote, whereas sodiccalcic assemblages found only at Tea Cup contain actinolite, andesine, epidote and, in
areas of leaching of quartz, local garnet. Feldspar-destructive, sulfide-poor, iron oxiderich alteration intensely developed at Tea Cup is characterized by the assemblage quartz
+ chlorite + albite ± specular hematite.
Previously documented occurrences of these alteration styles in the Yerington
district, Nevada, at the Ann-Mason deposit and the Yerington mine, and at Sierrita-
26
Esperanza in the Pima district, Arizona, provide a basis of comparison for the new work.
Sodic (-calcic) alteration at the Tea Cup is developed 2 - 4 km outboard from the most
intense potassic alteration at paleodepths ranging from ~6 - 8 km. Iron oxide-rich
alteration developed structurally higher at paleodepths of ~2 - 4 km. Sodic (-calcic)
alteration at Eagle Pass is most intense 3 - 6 km outboard from the most intense potassic
alteration across 4 km of paleodepth, and a spatially and mineralogically distinct zone of
sodic alteration occurs in the immediate footwall of the Eagle Pass fault.
The diverse manifestations of distal hydrothermal alteration in porphyry systems
can be rationalized if all porphyry systems are conceptually regarded as hybrid
hydrothermal systems: a magmatic-hydrothermal portion best developed in the proximal
or core region, and a non-magmatic portion dominated by externally derived fluids of
various compositions on the flanks (Fig. 6). The non-magmatic portion may be weakly
developed to intense, and the associated alteration patterns may range spatially from
completely outboard of the magmatic-hydrothermal alteration products in certain systems
to intimately interfingering with or overprinting the magmatic-hydrothermal products in
other systems. When dilute meteoric external fluids, which are characteristic of temperate
climates, are circulated, propylitic alteration develops on the periphery. When saline
brines, which are characteristic of arid regions, are convected on the periphery of a
porphyry system, sodic (-calcic) alteration forms as the fluid descends on the warming
path. After the externally-derived fluids eventually turn toward the surface, iron oxiderich alteration (with or without metals other than Fe, such as Cu and Au) forms at shallow
structural levels on the cooling path. Nonetheless, the sodic (-calcic) and iron oxide-rich
27
alteration also can be developed without being associated with a magmatic-hydrothermal
system as long as there is a thermal drive for fluid circulation, as likely occurred along
the Eagle Pass fault and in many IOCG systems worldwide.
Appendix C: “Filling in a gap in the Laramide porphyry belt: Porphyry prospects near
Wickenburg, Arizona, with district- and arc-scale restorations of Tertiary extension”
This study examines the effects of Tertiary extension on the geometry of porphyry
deposits of the Laramide magmatic arc of southwestern North America at the district and
arc scales. Building upon previous work, we combine results from reconnaissance scale
mapping of hydrothermal alteration, rock types, and structures, to provide a district-scale
cross section and associated palinspastic reconstruction through a poorly understood
segment of the Laramide magmatic arc near Wickenburg, Arizona. Extension at the scale
of the magmatic arc is quantified using a compilation of the amount of tilting recorded by
Tertiary sedimentary and volcanic rocks across the modern expression of the Laramide
magmatic arc. Extension is then restored across the arc to reveal the geometry of the
porphyry belt prior to extension.
At the district scale, cross cutting relationships between normal faults, and tilting
of hanging wall and footwall rocks indicate that five sets of nearly planar normal faults
are superimposed upon one another in the study area. The normal faults initiated at angles
between 60 and 70° and rotated to angles as low as 20° during slip. The amount of
displacement on the largest faults is no greater than 4 - 6 kilometers. A fault-by-fault
palinspastic reconstruction of displacement along the various normal faults reveals the
28
presence of two spatially distinct hydrothermal systems sourced from different cupolas of
a Late Cretaceous pluton (Fig. 7). Hydrothermal alteration zones from greisen to potassic
to transitional greisen-potassic assemblages from deep to shallow structural levels. The
reconstruction also reveals two exploration targets centered on potassic alteration in two
porphyry systems that are now covered by younger Tertiary and Quaternary rocks.
Igneous source rock compositions, and styles of alteration suggest that the prospects may
be porphyry molybdenum systems of the Mo-Cu subclass, similar to previously identified
nearby porphyry resources.
At the scale of the Laramide porphyry belt, a compilation of strikes and dips of
Tertiary units is utilized to delineate post-porphyry mineralization extensional domains
across the porphyry belt. Extension is quantified by calculating the β factor in each
extensional domain, and an arc-scale reconstruction reveals the pre-extension geometry
of the Laramide porphyry belt. This arc-scale reconstruction reveals that the Laramide
porphyry displayed a variably well defined axis, approximately 100 km wide prior to
extension with gaps and clusters of deposits along the 700-km strike length of the arc
(Fig. 8). The majority of porphyry deposits occur within the axis of the arc, but others lie
in forearc or rear-arc settings. The geometry of the porphyry belt related to the Laramide
arc, once extension is restored, closely resembles other magmatic arcs and associated
porphyry belts formed at convergent oceanic-continental plate boundaries.
29
FIGURE CAPTIONS
Figure 1. Location map depicting selected ore deposits which lie in the Basin and Range
province of western North America. MCC = metamorphic core complex.
Figure 2. Schematic cross section showing a typical pattern of hydrothermal alteration in
a porphyry copper system.
Figure 3. Three models proposed to explain the link between upper-crustal and midcrustal extension in the Basin and Range province. A. Extension accommodated along a
“detachment” fault which initiates slip at a dip angle of < 30° (after Wernicke, 1985). B.
Extension accommodated along a strongly listric “detachment” fault that is up-warped by
isostasy during extension (after Spencer, 1984). C. Extension accommodated along two
sets of planar normal faults which rotate to shallower dips during extension.
Figure 4. Index maps of porphyry deposits in southwestern North America. The Tea Cup,
Eagle Pass, and Sheep Mountain study areas are indicated by bolded and italicized text.
Figure 5. A-C: Three-stage model for the formation of the Pinaleño MCC. A: Eagle Pass
fault (EPF) breaks at a high angle to the surface and begins tilting to lower angles during
extension. B: Pinaleño detachment fault (PDF) and another fault break also at high
angles, cutting the abandoned Eagle Pass fault, and begin tilting to lower angles during
continued extension. C: Modern cross section through Pinaleño MCC. D: Cross section
30
through Pinaleño MCC after Naruk (1987) using ‘rolling hinge’ model for MCC
formation, which predicts different amounts of hanging wall and footwall tilting in the
MCC that is not supported by new evidence presented here. QTg = Quaternary and
Tertiary gravels; Tu= Tertiary volcanic and sedimentary rocks; YX = Proterozoic rocks,
shades in purple reflect the depth of the rocks prior to extension.
Figure 6. Diagram depicting variation in peripheral styles of alteration in composite
porphyry systems created by variation in external fluid compositions. A: Propylitic
alteration is generated by circulating fresh external fluids. B: Sodic (-calcic) and ironoxide rich alteration is created by circulating saline fluids derived from ancient evaporitebearing sedimentary rocks. C: Sodic (-calcic) and iron-oxide rich alteration is created by
circulating saline fluids derived from modern evaporite-bearing sedimentary rocks.
Figure 7. Panels depicting the palinspastic reconstruction of a district-scale cross section
through the Sheep Mountain porphyry system. A. Modern cross section. B. Restoration of
the 5th set of normal faults. C. Restoration of the 4th set of normal faults. D. Restoration
of the 3rd set of normal faults. E. Restoration of the 2nd set of normal faults. The fault in
this set strikes nearly perpendicular to the line of section. The true orientation of this fault
prior to slip was 110°, 60° SW. F. Restoration of the 1st set of normal faults.
Figure 8. Comparison of porphyry systems of the reconstructed Laramide magmatic arc
to other porphyry belts and magmatic arcs. A. The reconstructed location of porphyry
31
systems of the Laramide magmatic arc. B. Porphyry copper systems of Miocene-Early
Pliocene magmatic arc of central Chile (after Sillitoe and Perelló, 2005). C. The
Quaternary Cascade magmatic arc of northwestern North America (after Hildreth, 2007),
showing major volcanic centers. Note the change in scale from panels A and B to panel
C.
32
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Figure 1.
42
Figure 2.
43
Figure 3.
44
Figure 4.
45
Figure 5.
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Figure 6.
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Figure 7.
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Figure 8
49
APPENDIX A: “DOMINO-STYLE” TILTING IN METAMORPHIC CORE
COMPLEXES: EVIDENCE FROM RADIAL DIKES IN THE PINALEÑO
MOUNTAINS, ARIZONA
Phillip A. Nickerson*
Eric Seedorff
Lowell Institute for Mineral Resources
Department of Geosciences
University of Arizona
1040 East Fourth Street
Tucson, Arizona 85721-0077, USA
To be submitted to Lithosphere
50
ABSTRACT
Geologic mapping and stereographic analysis of a radial porphyry dike swarm in
the footwall of the Pinaleño metamorphic core complex (MCC) of southeastern Arizona
place constraints on competing interpretations for formation of MCCs. Three new U-Pb
dates confirm that the dikes are Oligocene in age (~26.5 Ma). A method for determining
paleo-vertical in radial dikes swarms via stereographic analysis on a π diagram is
demonstrated and then used to show that both the footwall and hanging wall of the
Pinaleño MCC were homogeneously tilted ~83° SW during Oligo-Miocene extension.
Mapped patterns of hydrothermal alteration that are intimately associated with the
intrusion of the dike swarm also are consistent with significant southwesterly tilting of
footwall rocks. A previous interpretation of the Pinaleño MCC contends that the MCC
formed via isostatic upwarp of a strongly listric normal fault, implying different amounts
of tilting in hanging wall and footwall rocks and folding of the footwall rocks about a
horizontal axis perpendicular to the extension direction; neither style of deformation is
recorded by the dike swarm. The constraints on footwall deformation instead favor a
“domino- style” model of MCC formation that produces similar amounts of tilting in
hanging wall and footwall rocks. A new interpretation for formation of this MCC
involves at least two independent sets of nearly planar normal faults that were
sequentially superimposed. These results suggest that warping of normal faults by
localized isostatic uplift is not required for MCC formation.
51
INTRODUCTION
Metamorphic core complexes (MCCs) are widespread in highly extended
continental and oceanic crust (e.g., Verdel et al., 2007; John and Cheadle, 2010).
Constraints placed on the geometry, timing, and style of deformation of rocks in the
footwall of MCCs place important limitations on the applicability of competing models
for formation of MCCs (Roberts and Yielding, 1994). For instance, if a MCC were
formed only via slip on an initially low-angle normal fault (e.g., Wernicke, 1981), rocks
in the footwall of the MCC would experience minimal tilting or folding during
exhumation. If isostatic warping of a strongly listric normal fault were the principal
mechanism (i.e. the “rolling-hinge” model, Wernicke, 1992), rocks in the footwall would
be folded about a horizontal axis perpendicular to the extension direction (Spencer,
1984). If “domino-style” faulting (e.g., Proffett, 1977; Davis, 1987) were the principle
process (Wong and Gans, 2008), the amount of tilting of footwall and hanging wall rocks
would be similar.
Magmatic-hydrothermal systems (dikes, stocks, and associated hydrothermal
features) developed in the Basin and Range province (e.g., Seedorff et al., 2008) offer a
powerful set of constraints on the magnitude, geometry, and timing of extensional
features. For example, the orientations of porphyry dikes can be used to constrain
structural deformation of crystalline rocks (Wong and Gans, 2008). Also, mapped
patterns of hydrothermal alteration can be used as markers in a structural column because
vertical and lateral zoning patterns in porphyry systems, though variable between
deposits, are nonetheless reasonably predictable (e.g., Sillitoe, 2010).
52
In this study, the magmatic-hydrothermal system associated with a pre-extension
radial porphyry dike swarm exposed in the footwall of the Pinaleño MCC in southeastern
Arizona was mapped, analyzed, and compared with other key localities. The results
expand the utility of radial dike swarms in the structural analysis of deformation in
crystalline rocks and are then used to test several competing models for MCC formation.
PINALEÑO MCC
The footwall of the Pinaleño MCC (Fig. 1A) is bounded on the west by the Eagle
Pass fault and on the east by the Pinaleño detachment fault (Davis, 1980; Naruk, 1987;
Kruger and Johnson, 1994). Mylonitic fabrics, produced by northeast-southwest
extension, are only present on the eastern margin of the MCC structurally below the
Pinaleño detachment fault (Naruk, 1987). In its current orientation, the Eagle Pass fault
dips gently (12° SW) and separates Tertiary rocks in the hanging wall that dip 80-85° SW
from Proterozoic crystalline rocks in the footwall (Fig. 1A). Kinematic indicators show
that fault motion was up dip to the northeast. The fault was first mapped as a thrust fault
(Blacet and Miller, 1978) but was reinterpreted by Davis and Hardy (1981) as a normal
fault that has been tilted through horizontal. Naruk (1987) argues that this tilting was the
result of isostatic uplift during the formation of the Pinaleño MCC and that the Eagle
Pass fault is the warped, up-dip, expression of the Pinaleño detachment fault.
Alternatively, Lister and Davis (1989) suggested that the geometry of the Pinaleño
detachment fault was nearly planar and that the Pinaleño MCC formed by the dominolike “shear zone” model of Davis (1983, 1987). Subsequent studies in this MCC have
53
favored the Naruk (1987) interpretation (i.e., Kruger and Johnson, 1994; Long et al.,
1995).
Porphyry Dike Swarm
The Eagle Pass dike swarm is exposed in the footwall of the MCC (Fig 1A, 1D).
The composition of dikes in the swarm varies from rhyolitic porphyry, to quartz latitic
porphyry, to andesitic porphyry, in order of decreasing abundance. One dike from the
swarm yielded a K-Ar age of 24.66 ± 0.60 Ma (Shafiqullah et al., 1980). However, the KAr age may record the exhumation of the dike swarm during Oligo-Miocene extension,
not the age of intrusion of the dike.
To better constrain the magmatic age of the dike swarm, U-Pb zircon
geochronology by laser ablation multicollector inductively coupled plasma mass
spectrometry (LA-MC-ICPMS) was conducted at the University of Arizona LaserChron
Center. Methods are discussed in Appendix A.1. Three dikes were selected for analysis;
one rhyolite porphyry dike cut by quartz veins (Fig. 2A), one unaltered andesite porphyry
dike (Fig. 2B), and one quartz latite porphyry dike (Fig. 2C) containing secondary biotite
and chalcopyrite (e.g., indicators of potassic alteration and copper mineralization).
Results show that the rhyolite dike intruded at 26.46±0.11 Ma, the andesite dike at
26.7±1.2 Ma, and the quartz latite dike at 26.3±1.2 Ma. The ages represent the first well
documented occurrence of a post-Laramide (80-50 Ma) porphyry system in Arizona. The
ages of the dikes also place a maximum age for the initiation of normal faulting in the
MCC of ~26.5 Ma, as the dikes are cut by the Eagle Pass fault.
54
Dike Orientations and Their Use as a Paleo-Vertical Indicator
Orientations of dikes within radial dike swarms have been used to determine
paleo-stress fields during dike emplacement (Nakamura, 1976; Muller and Pollard,
1977). Paleo-stress fields are determined using fundamentals of rock mechanics (Pollard,
1987) which state that the least principal stress (σ3) is orientated perpendicular to the
plane of the dike, and the principal and intermediate stress (σ1 and σ2 respectively) are
perpendicularly oriented somewhere within the plane of the dike. Anderson’s (1942)
theory of dike’s and sills observes that the solid-liquid interface at the surface of the earth
is unable to support shear stress; therefore, at near surface conditions the principal
stresses must be oriented perpendicular or parallel to the earth’s surface (neglecting
impacts from topography). Thus, dikes are vertical at the surface when either σ1 or σ2 are
vertical. Near a magma chamber, principal stresses are oriented such that σ1 is
perpendicular to the wall of the magma chamber (Roberts, 1970). As a dike propagates
toward the surface its path will adjust to any changes in the orientations σ1, σ2, and σ3
(e.g. Muller and Pollard 1977). When dikes intrude above a magma chamber with a
magma pressure greater than the regional stress field, as in the porphyry forming
environment (e.g., Koide and Bhattacharji, 1975), changes in the orientations of σ1, σ2,
and σ3 along an individual dike’s path are minimal, producing a nearly planar vertical
dike (e.g.; Suppe 1985, p 225).
The attitudes of individual dikes can be used to characterize the geometry of the
collective swarm of dikes (Fig. 3) and can provide an indicator of the paleo-vertical
direction at the time of the intrusion of the dikes. If dikes are thought to have intruded
55
with vertical or nearly vertical dips, the intersections of the dikes within a swarm will be
vertical or near-vertical lines. The lines of intersection are determined by measuring the
orientations of dikes from within a swarm. The orientation can then be plotted
stereographically to determine their mean intersection (π axis) which constitutes a mean
paleo-vertical indicator at the time of intrusion of the dikes. To demonstrate the
technique, π axes were calculated for the dike swarms from localities where the amount
(if any) of post-emplacement deformation is well constrained.
The first example is the Spanish Peaks, Colorado, dike swarm (Fig. 4A), where
most of the nearly 500 exposed dikes dip vertically, and only a few dip less than 80°
(Odé, 1957). Due to the lack of any geologic evidence for post-emplacement
deformation, the Spanish Peaks dike swarm is considered to be untilted. The distribution
of dike attitudes on the π diagram suggests a symmetrical radial dike pattern (Fig. 3A).
The line representing the intersection of the planes of the dikes, equal to the π axis on a π
diagram, is nearly vertical (plunge of 88°; Fig. 4A), confirming that the π axis is an
effective measurement of paleo-vertical.
The second example is from the Yerington district of western Nevada, where the
Ann-Mason porphyry dike swarm is known to be tilted ~90° to the west-northwest
(Proffett, 1977). Here, the π axis has been tilted from vertical 88° west-northwest to an
orientation of 02/110 (Fig. 4B). This orientation lies in the extension direction of the
Yerington district and is interpreted to demonstrate that the paleo-vertical indicator in the
dike swarm records the same west-northwest tilting observed in strata of similar age and
by paleomagnetism (Geissman et al., 1982; Proffett and Dilles, 1984). When rotated to
56
their pre-tilting orientations, the distribution of the dikes in the Ann-Mason swarm (Fig.
4C) suggests a knotted radial dike pattern (Fig. 3B).
For the Pinaleño MCC, this technique reveals a π axis oriented 07/055 (Fig. 4E).
This orientation plots in the extension direction of the Pinaleño MCC and indicates that
the Eagle Pass dike swarm in the footwall of the MCC has been tilted (83° SW) a similar
amount as the most tilted Tertiary hanging wall rocks (~80°-85° SW; Fig. 4D). When the
dike data are rotated to restore paleo-vertical indicator to vertical (Fig. 4F), the dikes
exhibited a knotted radial pattern (Fig. 2B), consistent with the variation documented in
the dips of the dikes (Fig. 1A; Fig. 1D) but inconsistent with a sheeted pattern (Fig. 3C).
Folding of footwall rocks
The orientations of the Eagle Pass dikes can also be used to determine if footwall
rocks were folded during MCC formation as proposed by Naruk (1987). The southern
cluster of dikes within the main dike swarm (near dip marker of 62° SE in Fig. 1A) all
dip to the southeast at ~60°. If these dikes represented rocks in the southwestern limb of a
northwest-southeast striking antiform (as proposed by Naruk, 1987), the strike of these
dikes would diverge to the north as they traverse the MCC. This systematic deviation is
not observed over the 7 km strike length of the dikes (Fig 1A).
Hydrothermal Alteration
Zoning patterns in hydrothermal alteration are created by changes in the pressure,
temperature, and composition of hydrothermal fluids as they circulate in and adjacent to
intrusions (Seedorff et al., 2005) and can be used to constrain deformation in crystalline
rocks (Fig. 5A). Where hydrothermal alteration patterns are observed to progress from
57
deeper styles to shallower styles across a fault block, the direction and relative amount of
tilting of the porphyry system can be determined.
In the Pinaleño MCC the general distribution of hydrothermal alteration was
mapped, revealing systematic patterns (more detailed description and analysis of mineral
assemblages and phases is given in Appendix B). Potassic alteration developed proximal
to the dike swarm, and its intensity dissipates to the north and south (Fig. 5B). Sodiccalcic alteration developed ~5 km distal to the potassic alteration to the northwest and
southeast (i.e., perpendicular to the extension direction). Near the fault zone, sodic
alteration characterized by the assemblage quartz-chlorite-albite-specular hematite
alteration is superimposed upon the other styles of alteration. The localization of the
quartz-chlorite-albite-specular hematite alteration along the fault zone as previously
identified by Davis and Hardy (1981), coupled with the fact that it overprints other styles
of alteration, suggests that this alteration style was genetically associated with the Eagle
Pass fault and thus is unrelated to the ~26.5 Ma porphyry system.
The observed relationship between hydrothermal alteration zoning patterns and
the extension direction is similar to what has been documented in tilted porphyry systems
in Arizona (i.e., sodic-calcic and sodic alteration developed distal to potassic alteration
only perpendicular to the extension direction; Seedorff et al., 2008; Stavast et al., 2008;
Nickerson et al., 2010) and corroborates the hypothesis that the footwall of the Pinaleño
MCC is significantly tilted to the southwest.
58
INTERPRETATION OF OLIGOCENE REGIONAL STRESS PATTERNS IN
SOUTHEASTERN ARIZONA
The northeast-southwest preferential strike direction of dikes in the Eagle Pass
dike swarm has interesting implications for the Oligo-Miocene regional stress pattern in
southeastern Arizona. Throughout Arizona, Oligocene and Miocene dikes are observed to
have a strong northwest-southeast preferential strike direction; whereas, Laramide aged
dikes (~75-55Ma) are known to have a strong northeast-southwest preferential strike
direction (Heidrick and Titley, 1982). Regional stress patterns are known to control dike
orientations, because except under isotropic stress conditions, the strikes of dikes run
perpendicular to σ3 (Pollard, 1987). Thus, the strong correlation of dike strike direction
with age in Arizona is thought to be a manifestation of the change from northwestsoutheast compression in the Late Cretaceous-Early Tertiary, to northwest-southeast
extension in the Oligocene and Micoene (Heidrick and Titley, 1982).
The orientation of regional stress in southeastern Arizona can be examined by
constraining the onset of extension. Less than 40 km to the southwest on the western
slope of the Galiuro Mountains (Fig. 1C), and 80 km to the northeast near Morenci,
Arizona, northeast-southwest extension is known to have begun by 35 Ma (Dickinson,
1991) and 29 Ma (Ferguson et al., 2000), respectively. As described above, dikes
intruding under these stress conditions would strike northwest-southeast, perpendicular to
the strike of Dikes in the Eagle Pass dike swarm.
Thus, the new U-Pb ages for the Eagle Pass dike swarm (Fig. 2) can be
interpreted to suggest that regional stress fields varied widely over just tens of km during
59
the late Oligocene in southeastern Arizona. Furthermore, the data indicate that the Eagle
Pass dike swarm intruded under a stress regime similar to the Laramide episode of
northeast-southwest compression (Heidrick and Titley, 1982). In fact, when the
orientations of the dikes are rotated so that the paleo-vertical indicator is oriented
vertically (Fig. 4E), the orientations match very closely what is observed in magmatichydrothermal features from the Laramide Safford district (Dunn, 1978) 50 km to the east
(see Appendix B Fig. 5), an area for which there is no evidence of post-Laramide tilting.
IMPLICATIONS FOR THE FORMATION OF THE PINALEÑO MCC
Both the paleo-vertical indicator preserved in the radial dike swarm, and the
documented zoning patterns in hydrothermal alteration associated with the late Oligocene
porphyry copper system in the footwall of the Pinaleño MCC indicate that the hanging
wall and the footwall of the MCC were tilted congruently during MCC formation. These
results require the amount of down-dip curvature on the Eagle Pass fault to be minimal,
which matches predictions of a “domino-style” model of MCC formation and controverts
the involvement of listric faulting in the formation of this MCC.
A reinterpretation of the formation of the Pinaleño MCC is needed to respect the
new evidence for congruent hanging wall and footwall tilting. It is proposed that the
Pinaleño MCC formed by the superposition of two major sets of normal faults in a
“domino-style” model (Fig. 6A-C). Whereas faults within each set are loosely
kinematically linked to one another, the two fault sets were discrete in time and not
kinematically linked. The transition from nearly horizontal, untilted strata to significantly
tilted rocks (“breakaway zone”) on the eastern side of the Galiuro Mountains is formed
60
by the superposition of two footwall synclines that are related to each fault set (Fig. 6AC). The Eagle Pass fault achieved its current orientation by first tilting to lower angles
during slip, and then by passively tilting in the hanging wall of a fault in the subsequent
set. The second set of faults includes the Pinaleño detachment fault, and an unnamed fault
which is covered by Tertiary and Quaternary gravels. A fault in the location of the
unnamed fault has been imaged seismically (Kruger and Johnson, 1994). The Pinaleño
detachment fault cuts and offsets the Eagle Pass fault, and the mylonites of the Pinaleño
MCC are located in the footwall of both major normal faults. The new interpretation
incorporates previous constraints placed on the geometry and magnitude of normal
faulting in the Pinaleño MCC from seismic reflection (Kruger and Johnson, 1994) and
shear strain (Naruk, 1987) analyses.
DISCUSSION
Subsequent to the identification of MCCs as manifestations mid-crustal extension
(Crittenden et al., 1980), geologists have attempted to pinpoint what geologic processes
are critical to MCC formation. The “rolling hinge” model (e.g., Wernicke, 1992) that has
been widely applied to explain the formation of continental and oceanic MCCs globally
(e.g. Verdel et al., 2007; Kapp et al. 2008; John and Cheadle, 2010), including the
Pinaleño MCC (Naruk, 1987) requires several kilometers of isostatic uplift to be focused
over an area ~10-20 km wide in the footwall of detachment faults. Deformation of this
type would fold rocks in the footwall of MCCs and create differential tilting between
hanging wall and footwall rocks.
61
Evidence presented above for the Pinaleño MCC argues against such deformation.
In additions recent seismic studies in the Catalina-Rincon MCC, Arizona (Arca et al.,
2010), and numerous lines of geologic and thermochronologic evidence in the Sierra
Mazatán MCC, Mexico (Wong and Gans, 2008) demonstrate that narrowly focused
isostatic uplift was not important in the formation of these MCCs either.
Without question thinning of the upper- and mid-crust to the degree observed in
MCCs would be isostatically compensated in some manner, but evidence from these
three MCCs suggests that isostatic compensation must have occurred over a much wider
area. Such a scenario implies that the assumption of Airy isostacy in MCC formation
(e.g. Spencer, 1984) is not valid, and instead indicates that the upper crust possesses some
finite amount of flexural strength (Kusznir and Ziegler, 1992) even while undergoing
severe extension. Future work in all MCCs should attempt to place constraints on
footwall deformation and understand the implications, both geometric and mechanical,
for SMCC formation.
CONCLUSIONS
Geologic constraints placed on the geometry, timing, and style of deformation in
the Pinaleño MCC indicate that rocks in the hanging wall and footwall of the MCC were
tilted similar amounts during formation of the MCC. The “domino-style” model for MCC
formation appropriately replicates the uniform tilting of hanging wall and footwall
blocks. This work suggests that more constraints can be placed on the footwall geology
of MCC using geologic techniques, especially the examination of paleo-vertical
indicators preserved in dike swarms and mapping of hydrothermal alteration. These
62
results taken together with recent work in other MCCs suggest that warping of normal
faults by localized isostatic uplift is not an essential mechanism required for MCC
formation.
ACKNOWLEDGMENTS
The manuscript benefitted from earlier reviews by M. D. Barton and G. H. Davis.
Conversations with D. A. Johnson and D. J. Maher were also helpful. Financial support
of this project came from a Society of Economic Geologists Hugh E. McKinstry student
research award and Science Foundation Arizona.
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Figure 1. A: Geologic map of the northern portion of the Pinaleño MCC including
endpoints of cross section A-A’ through the dike swarm. EPF = Eagle Pass fault;
PDF=Pinaleño detachment fault. B: Location map of MCCs in western North America.
C: Location of cross section B-B’ in Fig. 5. Dashed box is area shown in Fig. 1A. D.
Cross section oriented perpendicular to the Eagle Pass dike swarm. A-A’ located in Fig.
1A.
Figure 2. Best age results for U-Pb geochronology of zircons from three dikes in
the Eagle Pass radial dike swarm. A. Rhyolite porphyry dike. Location: 32°45'18.25"N,
110° 8'9.21"W. B. Andesite porphyry dike. Location: 32°45'18.25"N, 110° 8'9.21"W. C.
Quartz latite porphyry dike. Location: 32°45'20.17"N, 110° 7'21.67"W.
Figure 3. Idealized geometries of steeply-dipping dike swarms in map view. A.
Symmetrical radial dikes. B. Knotted radial dikes. C. Sheeted dikes. Radial dikes of A
and B intersect in a vertical line; sheeted dikes of C do not intersect.
Figure 4. Contoured poles to planes of dikes and bedding. All stereonets are equal
area plots. Contour intervals are per 1% area. Black circle = π axis (i.e., the average
intersection of the planes) unless otherwise noted. A. Orientation of dikes in the Spanish
Peaks dike swarm. Data from Smith (1978). B. Orientation of dikes in the Ann-Mason
dike swarm at Yerington. Dashed line = plane to π axis. Data from Dilles (1983). C.
Orientation of Ann-Mason dikes with paleo-vertical indicator rotated to vertical D.
Orientation of the most steeply dipping sedimentary and volcanic rocks in the hanging
wall of the Eagle Pass fault. Here the black circle = pole to mean plane. E. Orientation of
dikes in the footwall of the Eagle Pass fault. Dashed line = plane to π axis. Both hanging
70
wall and footwall rocks show similar amounts of tilting (compare pole to mean plane in
panel D to π axis in panel E). Both lines were vertical prior to extension. F. Orientation of
dikes in the Pinaleño MCC with π axis rotated to vertical.
Figure 5 A: Schematic cross section showing a typical pattern of sericitic,
potassic, and sodic-calcic hydrothermal alteration in a porphyry copper system. Dashed
grey line is the proposed surface exposure in the Pinaleño MCC. Dashed brown lines
indicate areas were sodic-calcic alteration may be superimposed on potassic alteration in
a porphyry setting. B: Mapped pattern of hydrothermal alteration in the Pinaleño MCC;
compare with distribution of rocks and structures of Fig. 1A.
Figure 6. Three-stage model for the formation of the Pinaleño MCC. Dashed line
marks a structural horizon at 12 km depth prior to extension. A: Eagle Pass fault (EPF)
breaks at a high angle to the surface and begins tilting to lower angles during extension.
B: A new fault set breaks at high angles (PDF= Pinaleño detachment fault). The PDF cuts
the now dormant Eagle Pass fault, and begins tilting to lower angles during continued
extension. Label 1: Rocks above and below the Eagle Pass fault are rotated such that they
take the form of a hanging wall anticline and footwall syncline. C: Present day cross
section through Pinaleño MCC. Label 2. Rocks in the footwall of this unnamed inferred
fault are rotated such that they take the form of a footwall syncline. Label 3. Rocks
previously rotated in the footwall of the Eagle Pass fault are further tilted during slip on
the unnamed fault. D: More detailed cross section from the Galiuro Mountains to the
Pinaleño Mountains. Location of the line of section indicated by dashed lines in Panel C.
Abbreviations: QTg = Quaternary and Tertiary gravels; Tu= Tertiary volcanic and
71
sedimentary rocks; YX = Proterozoic rocks, shades in purple reflect the depth of the
rocks prior to extension.
Figure 7. A: Cross section through Pinaleño MCC after Naruk (1987) using
“rolling-hinge” model for MCC formation, which predicts different amounts of hanging
wall and footwall tilting in the MCC that is not supported by new evidence presented
here. The dashed line marking rocks originally at 12 km depth has been added to the
original figure. B: New model for the formation of the Pinaleño MCC. The new model
replicates the structural features of the previous model, but also honors the new data
suggesting similar hangingwall and footwall tiling in the MCC. Rock labels same as
Figure 6.
72
Figure 1.
73
Figure 2.
74
Figure 3.
75
Figure 4.
76
Figure 5.
77
Figure 6.
78
Figure 7.
79
APPENDIX A.1
Zircon crystals were extracted from samples by traditional methods of crushing
and grinding, followed by separation with a Wilfley table, heavy liquids, and a Frantz
magnetic separator. Samples were processed such that all zircons were retained in the
final heavy mineral fraction. A split of these grains (generally 50-100 grains) were
selected from the grains available and incorporated into a 1” epoxy mount together with
fragments of our Sri Lanka standard zircon. The mounts were sanded down to a depth of
~20 microns, polished, imaged, and cleaned prior to isotopic analysis.
U-Pb geochronology of zircons was conducted by laser ablation multicollector
inductively coupled plasma mass spectrometry (LA-MC-ICPMS) at the Arizona
LaserChron Center (Gehrels et al., 2008). The analyses involve ablation of zircon with a
New Wave UP193HE Excimer laser (operating at a wavelength of 193 nm) using a spot
diameter of 30 microns. The ablated material is carried in helium into the plasma source
of a Nu HR ICPMS, which is equipped with a flight tube of sufficient width that U, Th,
and Pb isotopes are measured simultaneously. All measurements are made in static
mode, using Faraday detectorswith 3x1011 ohm resistors for 238U, 232Th, 208Pb206
Pb, and discrete dynode ion counters for 204Pb and202Hg. Ion yields are ~0.8 mv per
ppm. Each analysis consists of one 15-second integration on peaks with the laser off (for
backgrounds), 15 one-second integrations with the laser firing, and a 30 second delay to
purge the previous sample and prepare for the next analysis. The ablation pit
is ~15 microns in depth.
80
For each analysis, the errors in determining 206Pb/238U and 206Pb/204Pb result in a
measurement error of ~1-2% (at 2-sigma level) in the 206Pb/238U age. The errors in
measurement of 206Pb/207Pb and 206Pb/204Pb also result in ~1-2% (at 2-sigma level)
uncertainty in age for grains that are >1.0 Ga, but are substantially larger for younger
grains due to low intensity of the 207Pb signal. For most analyses, the cross-over in
precision of206Pb/238U and 206Pb/207Pb ages occurs at ~1.0 Ga.
204
Hg interference with 204Pb is accounted for measurement of 202Hg during laser
ablation and subtraction of 204Hg according to the natural 202Hg/204Hg of 4.35. This Hg is
correction is not significant for most analyses because our Hg backgrounds are low
(generally ~150 cps at mass 204).
Common Pb correction is accomplished by using the Hg-corrected 204Pb and
assuming an initial Pb composition from Stacey and Kramers (1975). Uncertainties of
1.5 for 206Pb/204Pb and 0.3 for 207Pb/204Pb are applied to these compositional values based on
the variation in Pb isotopic composition in modern crystal rocks.
Inter-element fractionation of Pb/U is generally ~5%,
whereas apparent fractionation of Pb isotopes is generally <0.2%. In-run analysis of
fragments of a large zircon crystal (generally every fifth measurement) with known age
of 563.5 ± 3.2 Ma (2-sigma error) is used to correct for this fractionation. The uncertainty
resulting from the calibration correction is generally 1-2% (2-sigma) for both 206Pb/207Pb
and 206Pb/238U ages.
Concentrations of U and Th are calibrated relative to our Sri Lanka zircon, which
contains ~518 ppm of U and 68 ppm Th.
81
Locations of samples are shown in Table 1 and analytical data are reported in
Table 2. Uncertainties shown in these tables are at the 1-sigma level and include only
measurement errors. Inheritance was tested in the samples by examining both the core
and tip of each zircon where possible. Ages older than Oligocene were interpreted to
represent inheritance in the samples. Many of these ages are Proterozoic in age, which
would be expected due to the Proterozoic age of the country rock in the study area.
The resulting interpreted ages are shown on weighted mean diagrams using the
routines in Isoplot (Ludwig, 2008) (Fig. 2). The weighted mean diagrams show the
weighted mean (weighting according to the square of the internal uncertainties), the
uncertainty of the weighted mean, the external (systematic) uncertainty that corresponds
to the ages used, the final uncertainty of the age (determined by quadratic addition of the
weighted mean and external uncertainties), and the MSWD of the data set.
REFERENCES
Gehrels, G.E., Valencia, V., Ruiz, J., 2008, Enhanced precision, accuracy, efficiency, and
spatial resolution of U-Pb ages by laser ablation-multicollector-inductively
coupled plasma-mass spectrometry: Geochemistry, Geophysics, Geosystems, v.
9, Q03017 doi:10.1029/2007GC001805.
Ludwig, K., 2008, Isoplot 3.6: Berkeley Geochronology Center Special Publication 4, 77
p.
82
Stacey, J.S., and Kramers, J.D., 1975, Approximation of terrestrial lead isotope evolution
by a two-stage model: Earth and Planetary Science Letters, v. 26, p. 207-221.
83
TABLE 1. Location of U-Pb geochronology samples
Sample
Latitude
Longitude
EP 017d
32°45'18.25"N
110° 8'09.21"W
EP 017e
32°45'18.25"N
110° 8'09.21"W
EP 038b
32°45'20.17"N
110° 7'21.67"W
84
TABLE 1. U-Pb geochronologic analyses
Isotope ratios
Analysis
U
206Pb
U/Th
206Pb*
±
207Pb*
±
206Pb*
Apparent ages (Ma)
±
error
206Pb*
±
207Pb*
±
206Pb*
±
Best
age
±
(ppm)
204Pb
207Pb*
(%)
235U*
(%)
238U
(%)
corr.
238U*
(Ma)
235U
(Ma)
207Pb*
(Ma)
(Ma)
(Ma)
EP 017D 1C
212
46400
1.7
11.2709
1.7
1.1318
17.2
0.0925
17.2
1.00
570.4
93.7
768.6
93.2
1398.2
31.7
1398.2
31.7
EP 017D 1T
544
300090
5.2
11.0776
0.4
2.9355
1.4
0.2358
1.3
0.95
1365.0
16.3
1391.1
10.5
1431.3
8.3
1431.3
8.3
EP 017D 2C
320
7275
2.0
20.6222
18.1
0.0764
18.5
0.0114
3.9
0.21
73.3
2.8
74.8
13.3
123.3
428.6
73.3
2.8
EP 017D 3T
283
4231
1.9
24.3784
41.3
0.0243
43.0
0.0043
12.2
0.28
27.6
3.4
24.4
10.4
-286.3
1091.9
27.6
3.4
EP 017D 4C
156
42913
4.2
10.6470
0.9
3.2274
2.5
0.2492
2.3
0.93
1434.4
30.0
1463.8
19.4
1506.6
17.1
1506.6
17.1
EP 017D 5C
299
4845
0.5
1.3681
4001.9
0.3930
4001.9
0.0039
13.0
0.00
25.1
3.3
336.5
NA
0.0
1589.0
25.1
3.3
EP 017D 6C
218
98580
1.3
10.9945
1.0
3.1314
3.1
0.2497
2.9
0.95
1436.9
37.5
1440.4
23.6
1445.6
18.2
1445.6
18.2
EP 017D 6T
300
126179
1.3
11.0116
0.7
3.1349
1.0
0.2504
0.7
0.70
1440.4
8.6
1441.3
7.4
1442.7
13.1
1442.7
13.1
EP 017D 7C
475
282996
1.9
9.8943
0.4
4.0266
1.8
0.2889
1.8
0.98
1636.3
25.7
1639.6
14.8
1643.8
7.2
1643.8
7.2
EP 017D 9C
223
112663
2.4
10.1921
0.7
3.4606
5.9
0.2558
5.9
0.99
1468.4
77.2
1518.3
46.7
1588.6
13.0
1588.6
13.0
EP 017D 10T
384
455
0.6
23.7621
34.3
0.0230
34.7
0.0040
5.4
0.16
25.5
1.4
23.1
7.9
-221.5
885.8
25.5
1.4
EP 017D 11C
288
106965
2.0
11.0715
0.8
2.9062
2.4
0.2334
2.2
0.94
1352.1
26.9
1383.5
17.8
1432.3
15.8
1432.3
15.8
EP 017D 12C
189
3931
0.5
9.9549
48.7
0.0572
51.8
0.0041
17.6
0.34
26.6
4.7
56.5
28.5
1632.5
968.3
26.6
4.7
EP 017D 13C
20
8803
1.0
10.6689
6.6
2.7422
7.6
0.2122
3.9
0.50
1240.4
43.6
1340.0
56.9
1502.7
124.9
1502.7
124.9
EP 017D 14C
23
14665
1.1
11.1561
2.2
3.0765
3.0
0.2489
2.0
0.68
1432.9
25.6
1426.8
22.6
1417.8
41.5
1417.8
41.5
EP 017D 14T
24
13330
1.1
10.9079
3.7
3.1949
4.8
0.2528
3.1
0.65
1452.7
40.6
1455.9
37.2
1460.7
69.5
1460.7
69.5
EP 017D 15C
102
105897
1.4
9.9106
1.5
3.8992
2.1
0.2803
1.4
0.68
1592.7
19.7
1613.5
16.7
1640.8
28.1
1640.8
28.1
EP 017D 17T
229
1747
0.4
17.3649
76.9
0.0328
78.0
0.0041
12.8
0.16
26.5
3.4
32.7
25.1
514.1
2047.9
26.5
3.4
EP 017D 18C
183
1367
0.7
10.5284
102.5
0.0552
103.0
0.0042
10.1
0.10
27.1
2.7
54.5
54.8
1527.7
21.9
27.1
2.7
EP 017D 19T
570
6350
0.5
21.0800
28.5
0.0287
28.9
0.0044
5.1
0.18
28.3
1.4
28.8
8.2
71.3
689.2
28.3
1.4
EP 017D 20C
694
439
0.3
22.6986
22.0
0.0251
22.3
0.0041
3.5
0.16
26.6
0.9
25.1
5.5
-107.6
546.6
26.6
0.9
EP 017D 21C
34
25136
1.3
10.9826
3.1
3.1615
4.3
0.2518
2.9
0.69
1447.9
38.2
1447.8
33.1
1447.7
59.3
1447.7
59.3
EP 017D 22T
191
1541
0.5
7.9846
144.4
0.0699
145.0
0.0040
13.2
0.09
26.0
3.4
68.6
96.4
2032.2
126.1
26.0
3.4
EP 017D 22T2
117
1448
0.3
6.5470
58.8
0.0886
61.4
0.0042
17.4
0.28
27.1
4.7
86.2
50.7
2376.8
1122.7
27.1
4.7
EP 017D 23C
224
1905
0.4
13.4285
32.5
0.0449
34.4
0.0044
11.4
0.33
28.2
3.2
44.6
15.0
1054.2
671.5
28.2
3.2
EP 017E 1C
2953
18797
0.9
21.5161
11.0
0.0265
11.2
0.0041
2.1
0.18
26.6
0.5
26.6
2.9
22.4
265.1
26.6
0.5
EP 017E 2C
5223
27095
0.8
21.3609
3.3
0.0263
3.3
0.0041
0.5
0.14
26.2
0.1
26.4
0.9
39.8
78.6
26.2
0.1
EP 017E 3C
5731
34936
0.6
21.1227
2.8
0.0268
2.9
0.0041
1.0
0.33
26.4
0.3
26.8
0.8
66.5
66.2
26.4
0.3
85
EP 017E 3T
3158
7845
0.9
20.7528
9.1
0.0276
9.7
0.0042
3.3
0.34
26.7
0.9
27.7
2.6
108.4
215.9
26.7
0.9
EP 017E 4C
5093
27319
0.5
21.3187
3.2
0.0265
3.3
0.0041
0.9
0.28
26.4
0.2
26.6
0.9
44.5
75.7
26.4
0.2
EP 017E 5C
5000
31010
0.7
20.9426
4.8
0.0273
5.1
0.0042
1.9
0.37
26.7
0.5
27.4
1.4
86.9
113.1
26.7
0.5
EP 017E 6C
4961
44815
0.7
21.0631
3.8
0.0274
4.0
0.0042
1.3
0.31
26.9
0.3
27.4
1.1
73.2
91.4
26.9
0.3
EP 017E 7C
2929
6794
1.0
21.1598
8.1
0.0269
8.4
0.0041
2.2
0.27
26.5
0.6
26.9
2.2
62.4
192.9
26.5
0.6
EP 017E 8C
4321
5887
0.6
21.4210
2.5
0.0259
5.0
0.0040
4.3
0.87
25.9
1.1
26.0
1.3
33.1
59.6
25.9
1.1
0.3
EP 017E 9C
5983
49193
0.6
21.2579
2.8
0.0265
3.1
0.0041
1.2
0.41
26.3
0.3
26.6
0.8
51.3
67.1
26.3
EP 017E 10C
3741
24652
0.7
21.0362
3.0
0.0269
3.2
0.0041
1.2
0.38
26.4
0.3
27.0
0.9
76.3
70.6
26.4
0.3
EP 017E 11C
5149
72618
0.6
21.1808
5.5
0.0262
5.7
0.0040
1.7
0.29
25.9
0.4
26.3
1.5
60.0
130.7
25.9
0.4
EP 017E 12C
6142
43279
0.6
21.6115
2.4
0.0256
3.1
0.0040
1.9
0.62
25.8
0.5
25.7
0.8
11.8
57.8
25.8
0.5
EP 017E 12T
5986
43381
0.6
21.1893
3.6
0.0265
7.0
0.0041
6.0
0.85
26.2
1.6
26.6
1.8
59.1
87.0
26.2
1.6
EP 017E 13C
6414
32190
0.5
20.4154
3.1
0.0295
4.2
0.0044
2.9
0.67
28.1
0.8
29.5
1.2
147.0
73.6
28.1
0.8
EP 017E 14T
5276
41898
0.7
21.0984
4.4
0.0265
4.6
0.0041
1.0
0.23
26.1
0.3
26.6
1.2
69.3
105.5
26.1
0.3
EP 017E 15C
3021
19189
0.8
22.1222
8.4
0.0253
8.7
0.0041
2.2
0.26
26.1
0.6
25.3
2.2
-44.7
204.7
26.1
0.6
EP 017E 16C
3051
16390
0.9
21.0663
6.7
0.0264
6.8
0.0040
1.1
0.16
26.0
0.3
26.5
1.8
72.9
158.8
26.0
0.3
EP 017E 17T
6012
36359
0.6
21.3112
3.9
0.0264
4.4
0.0041
1.9
0.43
26.2
0.5
26.4
1.1
45.4
93.7
26.2
0.5
EP 017E 18C
5967
38074
0.5
21.6152
2.7
0.0271
3.1
0.0042
1.6
0.51
27.3
0.4
27.1
0.8
11.4
63.9
27.3
0.4
EP 017E 19C
4058
42710
0.6
20.9604
4.8
0.0279
5.2
0.0042
2.0
0.39
27.3
0.5
27.9
1.4
84.8
114.5
27.3
0.5
EP 017E 20C
4788
49994
0.5
22.0775
4.2
0.0260
4.2
0.0042
0.4
0.09
26.8
0.1
26.0
1.1
-39.7
102.7
26.8
0.1
EP 017E 21C
5286
54458
0.7
21.0176
2.9
0.0273
3.2
0.0042
1.3
0.40
26.8
0.3
27.3
0.9
78.4
68.8
26.8
0.3
EP 017E 22C
3256
24681
1.1
21.1700
3.8
0.0265
4.0
0.0041
1.1
0.27
26.1
0.3
26.5
1.0
61.2
90.7
26.1
0.3
EP 017E 23C
3287
9898
0.8
21.3422
4.8
0.0265
5.1
0.0041
1.6
0.32
26.3
0.4
26.5
1.3
41.9
115.5
26.3
0.4
EP 017E 24C
6397
61217
0.5
20.8097
2.4
0.0299
5.3
0.0045
4.7
0.89
29.0
1.4
29.9
1.6
102.0
57.7
29.0
1.4
EP 038B-1C
192
752
1.2
31.7667
66.4
0.0179
67.4
0.0041
11.5
0.17
26.5
3.0
18.0
12.0
-1013.4
2194.1
26.5
3.0
EP 038B-2C
292
1389
0.9
25.7960
53.7
0.0223
54.8
0.0042
10.9
0.20
26.8
2.9
22.4
12.1
-432.5
1507.3
26.8
2.9
EP 038B-3C
238
3070
1.1
24.4464
122.4
0.0227
122.6
0.0040
7.0
0.06
25.9
1.8
22.8
27.7
-293.4
1510.8
25.9
1.8
EP 038B-4C
210
1540
0.9
21.5033
59.7
0.0233
61.7
0.0036
15.8
0.26
23.4
3.7
23.4
14.3
23.9
1567.9
23.4
3.7
EP 038B-5C
198
1152
1.0
-1.2738
3225.1
-z0.4492
3225.2
0.0042
9.3
0.00
26.7
2.5
-605.6
NA
0.0
870.9
26.7
2.5
EP 038B-8C
158
1308
1.4
21.0842
86.0
0.0264
87.4
0.0040
15.7
0.18
25.9
4.1
26.4
22.8
70.9
2672.4
25.9
4.1
EP 038B-9C
293
3464
1.1
17.5417
43.8
0.0315
44.5
0.0040
8.3
0.19
25.8
2.1
31.5
13.8
491.8
1011.2
25.8
2.1
EP 038B-10C
133
848
1.0
-1.2437
759.4
-0.4565
759.6
0.0041
17.5
0.02
26.5
4.6
-619.1
NA
0.0
992.3
26.5
4.6
EP 038B-11C
198
1257
0.9
6.2955
176.1
0.0858
176.4
0.0039
11.5
0.07
25.2
2.9
83.6
142.5
2443.4
256.1
25.2
2.9
EP 038B-13C
293
2458
0.8
33.6180
57.9
0.0160
59.3
0.0039
12.4
0.21
25.0
3.1
16.1
9.5
-1185.1
1928.8
25.0
3.1
86
EP 038B-15C
147
1399
0.9
18.9318
84.9
0.0314
87.1
0.0043
19.2
0.22
27.8
5.3
31.4
27.0
321.1
2511.4
27.8
5.3
EP 038B-16C
196
1410
1.0
13.6952
67.9
0.0425
68.7
0.0042
10.5
0.15
27.1
2.8
42.2
28.4
1014.4
1585.9
27.1
2.8
EP 038B-18C
398
2632
1.2
18.1560
86.7
0.0308
86.9
0.0041
6.3
0.07
26.1
1.6
30.8
26.3
415.4
2584.0
26.1
1.6
EP 038B-19C
310
2467
1.1
33.6761
54.3
0.0171
54.8
0.0042
7.6
0.14
26.9
2.0
17.3
9.4
-1190.4
1790.9
26.9
2.0
EP 038B-20C
640
12737
1.3
10.6677
1.6
0.4806
4.0
0.0372
3.6
0.92
235.4
8.4
398.5
13.1
1502.9
29.9
235.4
8.4
EP 038B-21C
195
1301
0.9
24.1574
37.8
0.0237
41.1
0.0042
16.2
0.40
26.7
4.3
23.8
9.7
-263.2
988.6
26.7
4.3
EP 038B-22C
418
4069
1.0
19.0175
34.6
0.0302
35.4
0.0042
7.6
0.21
26.8
2.0
30.2
10.5
310.9
809.6
26.8
2.0
EP 038B-23C
450
3858
0.6
31.6983
49.1
0.0180
49.8
0.0041
8.6
0.17
26.7
2.3
18.2
9.0
-1007.0
1534.4
26.7
2.3
EP 038B-24C
192
2199
0.9
9.8477
111.8
0.0590
112.4
0.0042
11.4
0.10
27.1
3.1
58.2
63.6
1652.6
48.4
27.1
3.1
87
1.
2.
Analyses with >10% uncertainty (1-sigma) in 206Pb/238U age are not included.
Analyses with >10% uncertainty (1-sigma) in 206Pb/207Pb age are not included, unless
206Pb/238U age is <500 Ma.
3. Best age is determined from 206Pb/238U age for analyses with 206Pb/238U age <900
Ma and from 206Pb/207Pb age for analyses with 206Pb/238Uage > 900 Ma.
4. All uncertainties are reported at the 1-sigma level, and include only measurement errors.
5. Systematic errors are as follows (at 2-sigma level): [sample 1: 2.5% (206Pb/238U) &
1.4% (206Pb/207Pb)]
6. Analyses conducted by LA-MC-ICPMS, as described by Gehrels et al. (2008).
7. U concentration and U/Th are calibrated relative to Sri Lanka zircon standard and are
accurate to ~20%.
8. Common Pb correction is from measured 204Pb with common Pb composition
interpreted from Stacey and Kramers (1975).
9. Common Pb composition assigned uncertainties of 1.5 for 206Pb/204Pb, 0.3 for
207Pb/204Pb, and 2.0 for 208Pb/204Pb.
10. U/Pb and 206Pb/207Pb fractionation is calibrated relative to fragments of a large Sri
Lanka zircon of 563.5 ± 3.2 Ma (2-sigma).
11. U decay constants and composition as follows: 238U = 9.8485 x 10-10, 235U = 1.55125
x 10-10, 238U/235U = 137.88.
12. Weighted mean plots determined with Isoplot (Ludwig, 2008).
88
APPENDIX B: SODIC-(CALCIC) ALTERATION IN TWO ARIZONA PORPHYRY
COPPER SYSTEMS: HYBRID HYDROTHERMAL SYSTEMS OF LARAMIDE AND
MID-TERTIARY AGES
Phillip A. Nickerson*
Mark D. Barton
Eric Seedorff
Lowell Institute for Mineral Resources
Department of Geosciences
University of Arizona
1040 East Fourth Street
Tucson, Arizona 85721-0077, USA
To be submitted to Economic Geology
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ABSTRACT
The flanks and cores the Laramide Tea Cup and Oligocene Eagle Pass porphyry
copper systems in Arizona are examined here using U-Pb geochronology, as well as field
and petrographic studies, to better characterize sodic (-calcic) and iron oxide-rich
alteration found in porphyry systems. New U-Pb ages of zircons from Tea Cup reveal
that the porphyry system dates from between ~72 and 70 Ma. Sodic assemblages at Tea
Cup and Eagle Pass contain quartz, albite, chlorite, and epidote, whereas sodic-calcic
assemblages found only at Tea Cup contain actinolite, andesine, epidote and, in areas of
leaching of quartz, local garnet. Feldspar-destructive, sulfide-poor, iron oxide-rich
alteration intensely developed at Tea Cup is characterized by the assemblage quartz +
chlorite + albite ± specular hematite.
Previously documented occurrences of these alteration styles in the Yerington
district, Nevada, at the Ann-Mason deposit and the Yerington mine, and at SierritaEsperanza in the Pima district, Arizona, provide a basis of comparison for the new work.
Sodic (-calcic) alteration at the Tea Cup is developed 2 - 4 km outboard from the most
intense potassic alteration at paleodepths ranging from ~6 - 8 km. Iron oxide-rich
alteration developed structurally higher at paleodepths of ~2 - 4 km. Sodic (-calcic)
alteration at Eagle Pass is most intense 3 - 6 km outboard from the most intense potassic
alteration across 4 km of paleodepth, and a spatially and mineralogically distinct zone of
sodic alteration occurs in the immediate footwall of the Eagle Pass fault.
The diverse manifestations of distal hydrothermal alteration in porphyry systems
can be rationalized if all porphyry systems are conceptually regarded as hybrid
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hydrothermal systems: a magmatic-hydrothermal portion best developed in the proximal
or core region, and a non-magmatic portion dominated by externally derived fluids of
various compositions on the flanks. The non-magmatic portion may be weakly developed
to intense, and the associated alteration patterns may range spatially from completely
outboard of the magmatic-hydrothermal alteration products in certain systems to
intimately interfingering with or overprinting the magmatic-hydrothermal products in
other systems. When dilute meteoric external fluids, which are characteristic of temperate
climates, are circulated, propylitic alteration develops on the periphery. When saline
brines, which are characteristic of arid regions, are convected on the periphery of a
porphyry system, sodic (-calcic) alteration forms as the fluid descends on the warming
path. After the externally-derived fluids eventually turn toward the surface, iron oxiderich alteration (with or without metals other than Fe, such as Cu and Au) forms at shallow
structural levels on the cooling path. Nonetheless, the sodic (-calcic) and iron oxide-rich
alteration also can be developed without being associated with a magmatic-hydrothermal
system as long as there is a thermal drive for fluid circulation, as likely occurred along
the Eagle Pass fault and in many IOCG systems worldwide.
INTRODUCTION
Sodic (-calcic) and iron oxide-rich hydrothermal alteration are essential
components of iron-oxide copper gold (IOCG) deposits (Barton and Johnson, 1996,
2000; Williams et al., 2005). Sodic (-calcic) and iron oxide-rich hydrothermal alteration,
however, also have been documented in some porphyry copper deposits (e.g., Yerington,
Nevada; Carten, 1986; Sierrita-Esperanza, Arizona; Stavast et al., 2008; Ridgeway;
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Wilson et al., 2003). Where documented in porphyry copper systems, sodic (-calcic)
alteration is commonly developed at deep and distal positions, whereas iron oxide-rich
hydrothermal alteration generally is developed distally at shallow levels (Carten, 1986;
Dilles and Einaudi, 1992; Dilles et al., 2000; Barton et al., 2005).
Although some workers remain skeptical of the origin of sodic(-calcic) alteration
in porphyry systems (e.g., Bouzari and Clark, 2006; Sillitoe, 2010), in the most
extensively studied porphyry systems that exhibit sodic (-calcic) and iron oxide-rich
alteration, geologic and isotopic evidence indicates that the fluids were externally-derived
saline brines that were drawn towards, and circulated by, magmatic heat sources (Dilles
et al., 1992, 1995; Battles and Barton, 1995). Thus, the overall hydrothermal system can
be regarded as composite, with a core formed from magmatic-hydrothermal fluids and
fringes formed from externally-derived fluids. Deciphering the source of the brine that
led to sodic (-calcic) and iron oxide-rich alteration is useful to the exploration geologist
as these styles of alteration can be used as vectors toward mineralization, especially in
porphyry systems that were tilted by post-ore faults (Nickerson et al., 2010). Moreover,
iron oxide-rich alteration, although not necessarily well mineralized, can contain
significant copper-gold mineralization (e.g., Pumpkin Hollow, Yerington district,
Nevada; Battles and Barton, 1995).
This paper examines the Tea Cup and Eagle Pass porphyry copper systems in
Arizona (Fig. 1), which have been significantly tilted by sets of rotated normal faults,
exposing the roots and flanks of the systems. The original work at Tea Cup builds on
early work by Cornwall (1982) and more recent studies by Barton et al. (2005) and
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Nickerson et al. (2010). The work at Eagle Pass builds on earlier geologic mapping and
structural interpretation by work by Blacet and Miller (1978), Davis and Hardy (1981),
and Naruk (1986) but represents the first description of hydrothermal alteration in the
area.
Sodic (-calcic) and iron oxide-rich hydrothermal alteration are well exposed on
the flanks of the Tea Cup and Eagle Pass porphyry systems, as well as along the footwall
of one of the Tertiary normal faults. Geologic mapping, electron microprobe analyses,
and U-Pb geochronology are combined with previous palinspastic reconstructions to
characterize the hydrothermal mineral assemblages, their timing, and the spatial
distribution of these alteration types over ~5 km of paleodepth in the systems. The
observations are then compared and contrasted with other localities, and the synthesis
reveals two distinct situations in which sodic (-calcic) and iron oxide-rich alteration can
be spatially associated with porphyry systems. In the first, sodic (-calcic) and iron oxiderich alteration are broadly contemporaneous with porphyry-related magmatism and the
other of which was serendipitously superimposed on a portion of a porphyry system
during extension-related exhumation of the porphyry system.
GEOLOGIC SETTING
The porphyry copper deposits of Arizona include some of the best studied
porphyry systems in the world and have been the focus of over a century of scientific
study (Ransome, 1903; Titley and Hicks, 1966; Titley, 1982a; Pierce and Bolm, 1995).
However, the new ages on porphyry copper systems in Arizona (Seedorff et al., 2005a;
Stavast, 2006; Nickerson and Seedorff, Appendix A), as well as the recognition and
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description of the flanks and roots of these complex hydrothermal systems (Seedorff et
al., 2008; Stavast et al., 2008; Nickerson et al., 2010), continue to advance the
understanding of these porphyry copper systems.
The Tea Cup (Fig. 2) and Eagle Pass (Fig. 3) porphyry systems, which are the
focus of this study, are located in southeastern Arizona in the heart of the porphyry
copper belt of southwestern North America (Fig. 1). Nearby porphyry copper districts
include Ray (Phillips et al., 1974), Globe-Miami (Peterson, 1962), Superior (Hammer and
Peterson, 1968; Manske and Paul, 2002), Poston Butte (Nason et al., 1982), Christmas
(Koski and Cook, 1982), Pima (Barter and Kelly, 1982; Jansen, 1982; Titley, 1982c;
Aiken and Baugh, 2007), Safford (Robinson and Cook, 1966; Dunn, 1978; Langton and
Williams, 1982), and Morenci (Moolick and Durek, 1966; Enders et al., 2006).
Exploration for porphyry copper deposits in the region has ebbed and flowed in tandem
with copper prices (Lowell, 1978; Paul and Manske, 2005), with times of intense
exploration occurring mainly in the late 19th and middle 20th centuries. The discovery of
the Resolution deposit near Superior in the mid-1990s has renewed the interest of both
junior and major mining companies in the region.
As opposed to the well documented occurrences of sodic (-calcic) alteration on
the continental margin of North America where plutons intruded into the thick sequence
of sedimentary and volcanic rocks (Dilles et al., 2000), the Laramide (~80-50 Ma) and
younger magmatism in Arizona intruded a thin (~2 km) cratonal section of sedimentary
rocks (Titley, 1982b). As summarized by Dickinson (1989), the metamorphic basement
of southeastern Arizona consists of the Mesoproterozoic Pinal Schist (ca. 1.7 Ga). These
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crystalline rocks were intruded at 1.6 Ga by arc plutons of the Madera Diorite and at 1.4
Ga by widespread anorogenic granitic plutons known at Tea Cup as the Ruin Granite
(Cornwall and Krieger, 1975a, b) and at Eagle Pass as the Laurel Canyon Granodiorite
(Simons, 1964). The 1.4 Ga anorogenic plutons are host to the largest volume of
hydrothermal alteration observed in both localities. Before 1.1 Ga, the basement was
beveled and unconformably overlain by approximately 1 km of dominantly siliciclastic
sedimentary rocks of the Proterozoic Apache Group and Troy Quartzite. Near the time of
deposition of the Troy Quartzite, the siliciclastic sedimentary sequence and the
underlying crystalline rocks were intruded by diabase sheets, sills, and dikes that are
dated at ~1.1 Ga (Shride, 1967; Wrucke, 1989). The diabase sheets are most abundant in
sedimentary rocks of the Apache Group and in the upper one km of the underlying
crystalline rocks (Howard, 1991). The Proterozoic strata of the Troy Quartzite and
Apache Group are disconformably overlain by approximately 1.0-1.5 km of Paleozoic
strata, mainly carbonate rocks. Where preserved, evaporite-bearing beds are present in
the uppermost part of the Paleozoic section in Permian strata (Blakey and Knepp, 1989).
During Laramide time, regional contraction produced basement-cored uplifts
similar to those of the central Rocky Mountains (Davis, 1979), and a large magmatic arc
was built on the western margin of the North American plate (Drewes, 1976; Dickinson
and Snyder, 1978; Dickinson, 1989). The arc formed between about 84 and 61 Ma and
shows an overall progression to more felsic compositions over time (Cornwall, 1982;
Lang and Titley, 1998; Seedorff et al., 2005a). Contraction clearly postdates early (~8580 Ma) relatively mafic magmatism (Willden, 1964). Porphyry copper formation is
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related to somewhat younger (~75-55 Ma) arc magmatism of intermediate to silicic
composition (Titley, 1982b; Lang and Titley, 1998), which, in the cases of at least certain
deposits, postdates reverse faulting (Seedorff et al., 2005a; Barton et al., 2005).
A period of tectonic quiescence and erosion characterized the post-Laramide
period until Oligocene or early Miocene time (Dickinson, 1991), when magmatism and
extension took hold in much of the region formerly occupied by the Laramide arc (Coney
and Reynolds, 1978). Magmatism produced the bimodal Galiuro Volcanics exposed in
the Galiuro Mountains and the Eagle Pass porphyry dike swarm in the northern Pinaleño
Mountains (Nickerson and Seedorff, Appendix A). Large-magnitude extension
dismembered and tilted porphyry systems and formed the Catalina-Rincon and Pinaleño
metamorphic core complexes (Davis, 1980). Extension and magmatism continued
through the Miocene, but by 15 Ma was of lesser magnitude and was more silicic,
respectively. In many cases sedimentation accompanied extension in the newly formed
basins. Post-extension, Tertiary and Quaternary gravels were deposited to form
widespread pediment surfaces on older rocks (Dickinson, 1991). Today, the landscape is
undergoing incision as the pediment surfaces are exhumed by down-cutting along the
Gila River (Richard and Spencer, 1997).
GEOCHRONOLOGY
In this study, U-Pb geochronology was utilized to test a hypothesis that the Red
Hills dike swarm is part of the Laramide Tea Cup porphyry system (Barton et al., 2005;
Seedorff et al., 2005a). U-Pb zircon geochronology by laser ablation multicollector
inductively coupled plasma mass spectrometry (LA-MC-ICPMS) was conducted on for
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samples at the University of Arizona LaserChron Center (Fig. 8A-E). Methods are
discussed in Appendix E.
Tea Cup system
Samples were collected in and around the Tea Cup porphyry system to further
constrain the timing of magmatism. Previous work by Barton et al. (2005) and Seedorff et
al. (2005a) demonstrated that the composite Tea Cup pluton intruded over a period of two
m.y. between ~74-72 Ma. Samples from the previous work (GB 202, GB 203) were dated
again in this study, as were additional samples of dikes that crop out west of the Tea Cup
pluton near the Red Hills prospect (Fig 2). The source intrusion of the dikes has there
been a topic of speculation (Richard and Spencer, 1997). Nickerson et al. (2010)
proposed, on the basis of similar mineralogy and a palinspastic structural reconstruction,
some of the dikes were sourced from the biotite granite phase of the Tea Cup pluton.
Results corroborate (Fig 4) this hypothesis as the ages yielded from both the
pluton (GB 202: 71.1 ± 1.9 Ma; GB 203: 70.53 ± 0.73) and the dikes near the Red Hills
(SP 100: 71.94 ± 0.73 Ma) fall within the 2σ error of one another. It is important to note
that the samples GB 202 and 203 previously dated by Seedorff et al. (2005a) yielded ages
~ 2 m.y. younger in this study. An explanation for this discrepancy has not been
identified at this time. Sample SP 103 (70.1 ± 1.5 Ma) was collected from a muscovitebearing quartz latite dike intruding the biotite granite phase of the Tea Cup pluton, which
is known to be sourced from the muscovite-biotite granite phase of the Tea Cup pluton.
Sample SP 102 (67.5 ± 2.9 Ma) was collected from a 50-m wide granite porphyry dike
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five km north of the Red Hills, and its age indicates it postdates the intrusion of the Tea
Cup pluton.
Eagle Pass system
U-Pb geochronology was previously conducted on the Eagle Pass dike swarm
(Nickerson and Seedorff, Appendix A), yielding intriguing results. Ages from three dikes
of different composition fell within 2σ error of one another at 26.5 Ma. Sulfide-bearing
potassic alteration is hosted in one of the dated porphyry dikes, indicating that the Eagle
Pass represents the first porphyry system in Arizona with a well documented postLaramide age. Furthermore, the northeast-southwest strike of the porphyry dikes, which
has been shown to be a hallmark of Laramide porphyry systems (Heidrick and Titley,
1982), is also prominently displayed in the Oligocene dike swarm (Fig. 5A-B). The
observed preference in strike direction shown in Laramide porphyry dikes (e.g., Safford:
Fig. 5C) in Arizona has been attributed to a strong regional northeast-southwest
compressional stress field during the Laramide (Heidrick and Titley, 1982). The same
preferential strike direction of the Oligocene dikes suggests that near Eagle Pass a
Laramide regional stress patterns prevailed until the onset of extension in Arizona, which
in this region began after 26.5 Ma (Nickerson and Seedorff, Appendix A).
HYDROTHERMAL ALTERATION ASSEMBLAGES
Field and petrographic studies were conducted to constrain the mineralogy,
timing, and spatial relationships of hydrothermal alteration in the study areas. Alteration
terminology follows that of Seedorff et al. (2005b, 2008). At both Tea Cup and Eagle
Pass, two types of feldspar-stable alteration are prevalent (Table 1). The core of the
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hydrothermal system is defined by porphyry copper-style potassic alteration, whereas,
sodic (-calcic) is developed in a distal position. In addition, iron oxide-rich, feldspardestructive alteration is intensely developed in the Tea Cup porphyry system.
Tea Cup system
Hydrothermal alteration in the Tea Cup porphyry system is described in several
previous studies (Barton et al., 2005; Nickerson et al., 2010) and is summarized in the
following text and in Figures (6-8 and Tables 1-5. Potassic alteration, which is typified by
secondary biotite and/or K-feldspar plus quartz veins, formed in three distinct centers,
each focused on a different phase of the composite Tea Cup pluton, which evolved to
more felsic compositions with time. The oldest and most intense potassic alteration
exposed in the study area is located near the cupola of the hornblende-biotite
granodiorite, immediately west of the Kelvin prospect (Figs. 2, 6), where steeply dipping,
east-west striking, sulfide-poor veins (Fig 7B) of quartz-K-feldspar, biotite, quartz, and
magnetite-quartz locally reach up to 5 vol% abundance in outcrop. A younger, distinct
area of widespread potassic alteration is centered just east of Mount Grayback near the
cupola of the biotite - muscovite ± garnet granodiorite (the youngest phase of the pluton),
where it takes the form of steeply dipping east-west striking (Fig. 7C) quartz +K-feldspar
+ muscovite ± biotite ± sulfide veins associated with aplitic to pegmatitic phases of the
two-mica granite. Locally, vein abundance reaches ~1-3 vol%. Finally, to the west, weak
to moderate potassic alteration occurs at the Red Hills prospect, where secondary,
shreddy textured biotite and steeply dipping east-west striking (Fig. 7D) quartz ± Kfeldspar ± pyrite ± chalcopyrite veins (Fig. 3) reach ~1 vol% in abundance. As noted
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above, Nickerson et al. (2010) proposed, and new U-Pb age dates corroborate (Fig 4A),
that the potassic alteration exposed in the Red Hills is associated with the intrusion of the
intermediate aged biotite granite phase of the Tea Cup pluton.
Greisen-style alteration, which by definition is characterized by the presence of
coarse-grained muscovite, consists of muscovite ± pyrite ± quartz that is widely
developed west of Mount Grayback in the biotite - muscovite ± garnet granodiorite and,
rarely, in the hornblende-biotite granodiorite located 1-2 km west of the Tea Cup cupola
(Figs. 2, 6). Greisen locally forms narrow muscovite-rich veinlets, whereas other zones
have widths of tens of centimeters. The character of the greisen varies along strike from
solely muscovite-rich alteration envelopes to quartz + sulfide–rich cores with muscoviterich envelopes; locally, both have outer envelopes of K-feldspar (Seedorff et al., 2008).
In contrast to the K-silicate and greisen alteration that are centrally located in the
hydrothermal systems, sodic, sodic-calcic, and rare calcic assemblages are locally present
to the north and are widespread to the south of the zone of most intense potassic
alteration near the cupola of the hornblende-biotite granodiorite (Figs. 2, 6). Sodic
assemblages contain quartz, albite, chlorite, and epidote, whereas sodic-calcic
assemblages contain actinolite, andesine, epidote and, in areas of leaching of quartz, local
garnet (Fig. 8A; Barton et al., 2005; Seedorff et al., 2008). At the eastern margin of the
most intense sodic (-calcic) alteration, a potassium feldspar-stable, quartz-destructive
assemblage of chlorite, actinolite, epidote, titanite is developed locally.
Feldspar-destructive, sulfide-poor, iron oxide-rich alteration is intensely
developed in the Ruin Granite near the eastern margin of the Tea Cup pluton and east of
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the Red Hills prospect (Figs. 2, 6). The sulfide-poor nature of this type of feldspardestructive alteration, like the aforementioned sodic-calcic alteration,is characteristic of
IOCG systems (e.g., Barton and Johnson, 2000; Williams et al., 2005). Steeply-dipping
east-west striking veins of specular hematite + chlorite + quartz ± magnetite ± pyrite
(Figs. 8B-C) reach several vol% in abundance, and locally areas of quartz + specularite
hematite completely destroy preexisting texture. Zones of chlorite ± quartz alteration
surround the most intense areas of sulfide-poor sericite-bearing alteration.
Eagle Pass system
Original, reconnaissance-scale mapping of hydrothermal alteration in the Eagle
Pass porphyry system reveals that hydrothermal alteration is zoned in a symmetric pattern
centered on the Oligocene Eagle Pass dike swarm (Figs. 3, 9). Three types of porphyry
dikes were identified during field mapping and are described below in order of
decreasing abundance: 1) Granite porphyry dikes with an aphanitic light gray
groundmass of quartz and K-feldspar, 10% 2-4 mm quartz phenocrysts, 10% 1-2mm
plagioclase phenocrysts, 5% 1-3 mm K-feldspar phenocrysts, and 1% 1-2 mm biotite
phenocrysts. 2) Quartz monzonite dikes with a gray fine-grained groundmass of
plagioclase and K-feldspar, 10% 1-3 mm plagioclase phenocrysts, 10% 1-4 mm Kfeldspar phenocrysts, 5% 1 mm biotite phenocrysts, 1% 2 mm hornblende phenocrysts,
and 1% 1-2 mm quartz phenocrysts. 3) Quartz diorite dikes with an aphanitic dark gray
groundmass of biotite, plagioclase, and quartz, 30% 1-3 mm plagioclase phenocrysts, and
5% 1-2 mm biotite phenocrysts.
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Potassic alteration is most intensely developed within meters of the porphyry
dikes at the southwestern end of the dike swarm, where it is characterized by secondary
biotite, the addition of magnetite, and local areas of 1 vol% quartz ± sulfide veins. The
vast majority of the potassic hydrothermal alteration at Eagle Pass is hosted in the
Proterozoic units; however, the Oligocene dikes are locally cut by quartz - pyrite ±
chalcopyrite veins. The intensity of potassic alteration decreases to the northwest and to
the southeast of the center of the dike swarm. Quartz ± sulfide veins are absent outside
the dike swarm; however, secondary biotite and magnetite are present as far as 1 km from
the dike swarm.
Sodic (-calcic) alteration is developed ~2 km distal to potassic alteration and
within a zone approximately ~1 km from and parallel to the Eagle Pass fault (Fig. 9).
Near the fault zone, sodic (-calcic) alteration is characterized by the assemblage quartz +
chlorite + albite ± specular hematite (Fig. 8D). This assemblage overprints potassic
alteration (chlorite replaces biotite, albite replaces oligoclase) developed in Proterozoic
units but is only locally developed in the finer grained and less permeable Oligocene
porphyry dikes. Tertiary andesite lava flows in the hanging wall of the Eagle Pass fault
are predominantly unaltered, with the exception of sporadic specular hematite veins.
North and south of the Eagle Pass dike swarm, sodic (-calcic) alteration is characterized
by the destruction of quartz and the assemblage albite + chlorite + actinolite + epidote ±
titanite ± hematite (Figs. 8E, 8G). Sodic (-calcic) alteration is most intensely developed
north of the dike swarm, west of the contact between the Pinal Schist and Laurel Canyon
Granodiorite (Fig. 9). Porphyry dikes do not crop out in this area; however, some
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northeast-southwest striking quartz + epidote veins are truncated by the porphyry dikes
two kilometers to the south. Whether those veins are directly associated with the intense
sodic (-calcic) alteration to the north is uncertain. West of the most intense sodic (-calcic)
alteration, a potassium feldspar-stable, quartz-destructive assemblage of chlorite,
actinolite, epidote, and titanite is locally developed (Fig. 8F).
COMPOSITIONS OF HYDROTHERMAL MINERALS
Electron microprobe analysis of compositions of feldspar, mica, chlorite,
amphiboles, and epidote from the Tea Cup and Eagle Pass porphyry systems were
conducted on the Cameca SX 50 and Cameca SX 100 instruments. The beam diameter
for analysis of all minerals except plagioclase was five μm, whereas the diameter for
plagioclase varied from five to fifteen μm.
Tea Cup system
Minerals formed during potassic, sodic (-calcic), iron oxide-rich, and greisen
alteration, as well as compositions of minerals from fresh Ruin Granite, were analyzed
with the electron microprobe. Results are shown in Tables 2-4. Plagioclase compositions
from sodic (-calcic) alteration in the Ruin Granite vary from An19 to An01 and in the Tea
Cup pluton vary from An17 to An01. Mg/(Mg+Fe) ratios for biotite and chlorite replacing
biotite found in potassically altered rocks range from 0.49 to 0.55 in the Ruin Granite and
from 0.55 to 0.60 in porphyry dikes. Compositions of white micas from iron oxide-rich
alteration at the Red Hills prospect range from 46 to 48 wt% SiO2. White micas in
greisen alteration contain 0.0 to 0.37 wt% F, and SiO2 contents vary from 45-49 wt%.
When compositions of minerals in the same alteration type are examined as a function of
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paleodepth or distance from the center of the hydrothermal systems, no systematic
patterns in composition are revealed for plagioclase, biotite, chlorite, or white mica.
Eagle Pass system
The composition of igneous minerals in the Laurel Canyon Granodiorite, as well
as, minerals from sodic (-calcic) and potassic assemblages from Eagle Pass were
analyzed with the electron microprobe. Plagioclase compositions from sodic (-calcic)
alteration hosted in the Laurel Canyon Granodiorite north of the Eagle Pass dike swarm
range from An23 to An01. Plagioclase from sodic (-calcic) alteration near the Eagle Pass
fault are albitic, with compositions ranging from An04 to An00. Feldspar compositions
from the potassium feldspar-stable, quartz-destructive assemblage of chlorite + epidote +
titanite average An01 and Or95, respectively. Amphiboles present in sodic (-calcic)
alteration are actinolitic in composition (Leake, 1997).
Compositions of biotite and chlorite replacing biotite hosted in potassically
altered Laurel Canyon Granodiorite showed elevated Mg/(Mg+Fe) ratios (0.50-0.59)
compared to chlorite present in sodic (-calcic) alteration (0.24-0.48). Figure 10 illustrates
this distinction by comparing Mg/(Mg+Fe) versus lateral distance from the center of the
dike swarm. A clear pattern is discernible, where higher Mg/(Mg+Fe) ratios in mafic
alteration minerals occur closer to the center of the dike swarm in potassic alteration and
lower ratios were measured in sodic (-calcic) alteration on the periphery of the dike
swarm.
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Gains and losses in sodic alteration
The combination of electron microprobe analysis and modal mineralogy of fresh
and sodicly-altered assemblages at Tea Cup and Eagle Pass allows for the estimation of
gains and losses of chemical constituents in sodic alteration. Table 5 compares the SiO2,
CaO, Na2O, K2O, Fe2O3, and FeO contents ofr fresh and sodicly-altered samples. Majorelement compositions (in oxide wt%) of quartz, titanite, magnetite, ilmenite, and hematite
were calculated from idealized mineral formulas, as these phases were not analyzed by
electron microprobe in this study. The densities of idealized mineral phases (Nesse, 2000)
were used to covert modal mineralogy (vol%) into masses (wt%). Thus, the results shown
here should be considered estimates of the major-element contents of samples but not a
substitute for whole-rock analyses. All sodicly-altered samples show increases in Na2O
and CaO contents and decreases in K2O contents when compared to their fresh
equivalents. In addition, samples MW Spec Hem and TC 010’ show significant decreases
in SiO2 contents, and sample MW Spec Hem shows a significant increase in Fe2O3
content.
COMPARISON OF SODIC (-CALCIC) AND GREISEN HYDROTHERMAL
ALTERATION ASSEMBLAGES AT TEA CUP AND EAGLE PASS WITH OTHER
LOCALITIES
The Tea Cup and Eagle Pass localities are compared to well documented
examples of sodic -(calcic) and iron oxide-rich hydrothermal alteration in Tables 6 and 7
and Figure 11. Previous workers showed that examples of sodic (-calcic) alteration in the
western North America were predominantly Jurassic events (Battles and Barton, 1995;
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Dilles et al., 1995), with a few younger exceptions. However, results of this study and
related work by Seedorff et al. (2008) indicate that less voluminous sodic (-calcic)
alteration may be a widespread feature of many Laramide porphyry districts in Arizona in
which deep levels are exposed. This study extends that observation to the mid-Tertiary,
as it is now clear that Eagle Pass is an Oligocene porphyry system, and it, too, exhibits
sodic (-calcic) alteration. In addition, the tectonic setting of the porphyry systems does
not appear to be a limiting factor in the formation of sodic (-calcic) alteration, as the
Oligocene Eagle Pass porphyry system developed during a period of slab rollback as
opposed to an arc setting (Table 7).
Sodic (-calcic) mineral assemblages in the various porphyry systems exhibit some
differences. For instance, plagioclase compositions in the Arizona systems are more
albitic, and the mineral assemblages at Eagle Pass and Sierrita-Esperanza contain fewer
calcium-rich minerals (Fig. 11) than the sodic (-calcic) occurrences at Ann-Mason and
Yerington. Furthermore, the potassium feldspar-stable, quartz-destructive chlorite +
epidote + titanite assemblage documented at Tea Cup and Eagle Pass does not appear to
have a close counterpart in the other systems.
The vertical distribution of alteration varies among the systems is shown in Table
6. At Ann-Mason and the Yerington mine, there is a progression from more calcic
assemblages at depth to more sodic assemblages at shallower levels, which is interpreted
to represent the evolution of hydrothermal fluid compositions with time (e.g., Dilles et
al., 2000). A change in assemblages with depth is not as pronounced in the Arizona
systems (Table 6), particularly at Tea Cup where the most calcic (andradite-bearing)
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assemblage is located structurally higher than garnet-absent assemblages. Despite spatial
complexities that may be the result of the superposition of multiple episodes of sodic(calcic) alteration forming events, Figure 11 illustrates that deeper alteration assemblages
typically were stable at higher activity ratios of Ca2+/(H+)2 than shallower assemblages. If
hydrothermal fluids are assumed to flow upwards, this suggests that hydrothermal fluids
at each locality follow a similar geochemical path from higher to lower activity ratios of
Ca2+/(H+)2 with time.
Evidence for vertical zoning from sodic (-calcic) alteration at depth to shallow
iron oxide-rich alteration is clearly discernible in the Tea Cup porphyry system, where
sodic (-calcic) alteration forms at paleodepths of 6 - 8 km and iron-oxide rich alteration
forms at 2 - 4 km (Table 7). At Ann-Mason and the Yerington mine, however, the iron
oxide-rich alteration is absent in the Singatse Range, where sodic (-calcic) alteration is
well developed, but iron oxide-rich alteration is well developed in structurally higher
positions exposed to the west in the neighboring Buckskin Range (Dilles et al., 2000). At
Eagle Pass, hematite veins are superimposed directly upon sodic (-calcic) assemblages
north of the Eagle Pass dike swarm and crosscut sodic (-calcic) alteration in the
immediate footwall of the Eagle Pass fault.
Documented examples of greisen style alteration in porphyry copper systems are
sparse (Seedorff et al., 2005b, 2008); however, electron microprobe analyses of white
micas (Stavast, 2006) from the Ruby Star Granodiorite (Pima district) and Schultze
Granite (Globe-Miami district) provide a basis for comparison of white mica mineral
compositions at Tea Cup (Table 8). White micas from all three greisen localities are
107
muscovite and have less that 0.10 wt% F. The samples vary by several weight percent
SiO2 and FeO but display no other major compositional heterogeneities.
ORIGIN OF SODIC (-CALCIC) AND IRON OXIDE-RICH ALTERATION
Using observations from Tea Cup and Eagle Pass and the results of the
comparison to other well studied occurrences of sodic (-calcic) and iron oxide-rich
alteration in porphyry systems, hypotheses are put forward to explain the occurrences of
sodic (-calcic) and iron-oxide alteration found in the study areas (Figs. 12-13). The
results are then generalized to yield two models (14 A,B) for the formation of sodic (calcic) and iron oxide-rich alteration in porphyry and extensional settings Key
components of the models are the source of the fluids and transition from sodic (-calcic)
to iron oxide-rich alteration.
Source of fluids
Based on stable isotopic and geologic evidence, Dilles and Einaudi (1992) and
Dilles et al. (1992, 1995, 2000) argued that the source of fluids that caused sodic (-calcic)
alteration in the Yerington batholith was hypersaline formation water. Although stable
isotopic data are not available for Tea Cup, previous workers at Tea Cup (Barton et al,
2005; Nickerson et al., 2010) also argue for a non-magmatic fluid source for sodic (calcic) and iron oxide-rich alteration. In addition, spatial and temporal evidence at Eagle
Pass argues against a magmatic source, as sodic (-calcic) alteration near the Eagle Pass
fault postdates the Eagle Pass dike swarm (the only plausible nearby magmatic source),
and the most widespread sodic (-calcic) alteration increases in intensity several
kilometers distant from the Eagle Pass dike swarm.
108
The interpretation of the formation of sodic (-calcic) alteration in the Yerington
district (Dilles and Einaudi, 1992; Dilles et al., 1992, 1995, 2000) predicts that sodic (calcic) alteration should occur wherever granitic heat sources are emplaced into
sedimentary-volcanic sections containing trapped saline or hyper-saline fluids, provided
that sufficient fracture permeability is available. Geologic observations confirm that such
conditions are met in the Yerington district, Nevada, and at Sierrita-Esperanza in the
Pima district, Arizona (Stavast, 2006). However, evaporite-bearing sedimentary units due
not crop out near the Tea Cup and Eagle Pass localities. Unconformities between Tertiary
and Proterozoic rocks at Tea Cup (Nickerson et al., 2010) and between Cretaceous and
Proterozoic rocks at Eagle Pass (Simons, 1964) demonstrate that Permian evaporatebearing sedimentary rocks that are regionally observed in southeastern Arizona are
presently absent at Eagle Pass. The denudation is most likely the result of erosion during
or following Laramide contraction, which created basement-cored uplifts (Davis, 1979)
prior to the onset of Laramide magmatism (Drewes, 1976). At Tea Cup, however, the
Permian evaporite-bearing sedimentary rocks may still have been present during the
intrusion of the Tea Cup pluton at 71 Ma, preserved in a footwall syncline east of the
reverse faults documented at Tea Cup (Fig. 12A-B). The nature of Laramide reverse
faulting in the vicinity of Eagle Pass is poorly understood, but a geologic setting similar
to Tea Cup also is plausible at Eagle Pass prior to large-magnitude Oligo-Miocene
extension (Fig. 13A), given the stratigraphic evidence for reverse faulting (i.e.,
Cretaceous strata deposited unconformably on Proterozoic rocks, with omission of ages
of rocks of intervening ages, which are present regionally). Hence, evaporites may have
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been present in nearby country rocks during formation of the porphyry systems at all of
the above localities in question.
As noted above, there are two distinct areas of sodic (-calcic) alteration at Eagle
Pass, and the occurrence that is spatially associated with the Eagle Pass fault is shown by
crosscutting relationships to be younger than they Eagle Pass dike swarm (Fig. 13A-D),
and (U-Th)/He dates indicate that it formed at 18.95 ± 0.12 Ma (Appendix F). The lack
of a observable relationship to any exposed magmatism and the close spatial relationship
shared with the Eagle Pass fault suggests that this occurrence of sodic (-calcic) alteration
is genetically related to the Eagle Pass fault and fluid flow accompanying crustal
extension. Broadly similar occurrences of syn- or post-slip chlorite- and iron oxide-rich
hydrothermal alteration associated with normal faults previously was documented in the
Colorado River Extensional Corridor (e.g., Spencer and Welty, 1986). There, saline
fluids are hypothesized to be derived from evaporite basins that formed
contemporaneously with normal faulting in an arid environment (Beane et al., 1986;
Wilkins et al., 1986; Roddy et al., 1988), consistent with association of saline fluid
inclusions with these deposits and formation of widespread halite deposits at about this
time in many parts of Arizona (Scarborough, 1989). A syn-extensional volcanic
fanglomerate nearly 4500 m thick rests in the hanging wall of the Eagle Pass fault (Davis
and Hardy, 1981). Although evaporite beds are not a primary feature in the fanglomerate
section exposed at the surface, it is likely that evaporite beds could have formed in the
geologic environment in which the fanglomerate was deposited (Fig.13 C). Alternatively,
saline formation waters could have been derived from circulation through late Paleozoic
110
evaporite beds, i.e., possibly the same source as the older sodic (-calcic) alteration on the
periphery of the Eagle Pass dike swarm (Fig. 13B).
Relationship of sodic-(calcic) alteration to iron oxide-rich alteration
Large volumes of sodic (-calcic) alteration are commonly spatially associated
with iron oxide-rich alteration in IOCG systems; however, a genetic relationship between
the two styles of hydrothermal alteration is controversial (Williams et al., 2005).
Proponents of a magmatic model for the formation of IOCG deposits suggest that both
styles of alteration have a magmatic source (e.g., Perring et al., 2000). The general
independence of different types of IOCG systems from specific magmatic compositions,
akin to what is observed in other magmatic-hydrothermal ore deposits (e.g., porphyry
deposits; Seedorff et al., 2005b), as well as, paleoclimate correlations, geochemical
arguments based on solubilities, and correlation with known evaporites led Barton and
Johnson (1996) to suggest an evaporitic source model for IOCG deposits. In the
evaporitic source model, sodic (-calcic) alteration results from warming of saline fluids as
they are drawn towards an igneous heat source. Along the warming path, Na and Ca are
precipitated and Fe, Si, K, Cu, and Au are removed. IOCG mineralization is suggested to
result from the cooling of these fluids at shallower structural levels along a cooling path
were Fe, Si, H+, ±K, ±S, ±Cu, and ±Au are precipitated (Barton and Johnson, 1996,
2000).
As previously described, an evaporitic source for sodic (-calcic) and iron oxiderich alteration is suggested by spatial and temporal geologic evidence at Tea Cup and
Eagle Pass. When the predicted flow paths of warming and cooling fluids of the
111
evaporitic source model (Barton and Johnson, 1996) are compared to the palinspastic
reconstruction of sodic (-calcic) and iron oxide-rich alteration at Tea Cup, the predicted
patterns of element transport are observed. At the other localities considered in Table 7
iron oxide-rich alteration is not observed. However, iron oxide-rich alteration and
mineralization is abundant at shallower structural levels in other parts of the Yerington
district (e.g., Buckskin mine, Gibson, 1988; Dilles et al., 2000).
DISCUSSION
Hybrid hydrothermal systems
There is a long history of debate between the Plutonists and the Neptunists about
the origin of fluids in hydrothermal systems, including in porphyry deposits (e.g.,
Seedorff et al., 2005b, p. 287). In many cases, the sources of fluids and metals in
porphyry systems have been viewed as virtually entirely magmatic (e.g., Sales, 1954;
Westra and Keith, 1981; Sillitoe, 1995b), whereas another end-member was that plutons
served mainly as thermal drives for circulation of external fluids (e.g., Norton, 1978,
1982). In the last three or four decades, the prevailing view has called for an essential role
for magmatism with a variable, generally subordinate role for external fluids (e.g.,
Gustafson and Hunt, 1975; Gustafson, 1978), a consensus that has edged even closer to
the magmatist end member in more recent years (e.g., Hedenquist and Lowenstern,
1994).As a result, all porphyry systems can be regarded conceptually as hybrid
hydrothermal systems (Fig. 15 A-C): a magmatic-hydrothermal portion best developed in
the proximal or core region, and a non-magmatic portion dominated by externally derived
fluids on the flanks. The magmatic-hydrothermal portion is always well developed; it is
112
an essential and defining characteristic of the porphyry deposit type. The non-magmatic
portion is variably developed and has more diverse expressions because the
characteristics of the non-magmatic portion are subject to more variables.
The products of magmatic-hydrothermal fluid are more regular and predictable
because the magmatic-hydrothermal fluid tends to overwhelm other influences in and
near a mineralizing intrusion, and all of the components necessary for making a deposit
are derived from the same, magmatic source: (1) the aqueous fluid involved in all aspects
of alteration-mineralization; (2) ligands, such as Cl, S, and O, necessary to complex the
metals, and (3) the elements necessary to precipitate the metals, such as S. The
components that will be transported by the fluid will largely be governed by such factors
as temperature and the total chlorinity and total sulfur content of the fluid (e.g., Fig. 15 of
Barton, 1996; Reed, 1997). The fact that the magmatic-hydrothermal fluid is initially in
equilibrium with the igneous rocks, however, causes a first-order relationship between
magma composition and metal content (Seedorff et al., 2005b). The diversity of products
of magmatic-hydrothermal fluid results from differences in factors of second-order
importance, such as the level of emplacement of the system and the chemical and
physical characteristics of the wall rocks.
External fluids, in contrast, generally produce hydrothermal products that are
much less regular and predictable because at least two and commonly all three of the
above components that are necessary for making a deposit originate from different
sources (Barton, 1996). Furthermore, a magma body, if present, may serve as a thermal
drive for fluid circulation yet may not contribute any of the three necessary components,
113
as in many IOCG deposits (e.g., Barton and Johnson, 1996, 2000). As in the magmatichydrothermal case, the components that will be transported by the fluid will largely be
governed by such factors as temperature and the total chlorinity and total sulfur content
of the fluid, but the composition of potential external fluids is more diverse. The external
fluid could be a fluid at the surface (e.g., dilute, oxygenated groundwater, a moderately
saline, moderately reduced lake water, a brine in a salar or playa, or seawater; Barton and
Johnson, 2000, plot these compositions); in many of these cases, the composition of the
fluid is at least indirectly controlled by climate, which in turn is a function of factors such
as latitude and orographic features (Barton and Johnson, 1996). Alternatively, the
external fluid could be a basinal fluid or formation water. Finally, it could be a surface or
basinal fluid whose composition was significantly shifted by interaction with wall rocks
(e.g., evaporite beds) along the flow path of the external fluid, i.e., a dilute meteoric fluid
could become a saline brine. As emphasized by Barton (1996), these differences will
impact (1) the expected alteration-mineralization patterns and (2) the ligands available to
transport metals. Because reduced sulfur necessary to precipitate sulfide minerals is not
necessarily present in the external fluid, the availability of (3) reduced sulfur or some
other type of chemical trap at the site of ore deposition may be required for formation of
an orebody. In spite of the inherent geochemical elegance of surficial and basinal fluid
systems, these systems are conceptually less straightforward than magmatichydrothermal systems because the factors that govern metal transport and deposition are
largely independent variables, as opposed to being inextricably linked, as they are for
magmatic-hydrothermal systems. Therefore, the hydrothermal products of external, non-
114
magmatic fluid flow in and around porphyry systems should consist of diverse types of
mineral assemblages and of variable intensity.
One type of mineral assemblage that can form on the periphery due to circulation
of external fluids is propylitic alteration. Propylitic alteration develops when dilute
meteoric or formation waters are circulated (Fig. 15A), as at Bingham (Bowman et al.,
1987) and Bajo de la Alumbrera (Proffett, 2003). In contrast, when saline brines are
convected on the periphery of a porphyry system (Fig. 15B-C), sodic (-calcic) alteration
develops at depth on the warming path, and iron oxide-rich alteration develops at shallow
structural levels on the cooling path of the externally derived fluids. When this type of
peripheral alteration is developed on the fringe of a porphyry system, an IOCG deposit
can develop on the flanks of or considerably distal to a porphyry system (Dilles et al.,
2000), as is weakly to moderately developed at Tea Cup (this study) and intensely
developed at Pumpkin Hollow in the Yerington district (Ohlin, 2010). If other
compositions of external fluids are involved, then additional variations on the theme of
porphyry deposits as variably hybrid systems are possible (e.g., Seedorff and Barton,
2004, p. 16). Although other factors can also be significant, to a first approximation dilute
meteoric waters at the surface typify temperate climates, and saline waters typify arid
climates (e.g., Barton and Johnson, 1996).
The non-magmatic portion of a porphyry system may be weakly developed (e.g.,
Robinson: Maher, 1996), moderately developed (Tea Cup: this study), to intensely
developed (e.g., Yerington mine: Carten, 1986); and the associated alteration patterns
may range spatially from largely outboard of the magmatic-hydrothermal alteration
115
products in certain systems (e.g., Bajo de la Alumbrera: Proffett, 2003) to intimately
interfingering with or overprinting the magmatic-hydrothermal products in other systems
(e.g., Ann-Mason: Dilles and Einaudi, 1992).
Even in known porphyry districts, not all of the sodic-calcic alteration necessarily
formed contemporaneously with the magmatic-hydrothermal portion of the hydrothermal
system; indeed, some of the sodic-calcic alteration at Eagle Pass formed on the flanks of
the porphyry system, but the sodic (-calcic) alteration along Eagle Pass fault is
demonstrated by superposition to be younger than the dike swarm and synchronous with
post-ore extensional dismemberment. Thus, the sodic-calcic alteration along the Eagle
Pass fault is genetically unrelated to, yet partially superimposed on, the porphyry system.
This relationship also has analogs in other porphyry systems: the Ajo porphyry copper
system in western Arizona, which formed during the Laramide at ~63 Ma, is adjacent to a
large zone of intense sodic-calcic alteration that affected the Cardigan Peak pluton in the
early Miocene (20-23 Ma) and contains abundant saline fluid inclusions (Cox and Ohta,
1984; Hagstrum et al., 1987; Cox et al., 2006). Thus, the origin of distal alteration types
present at each porphyry system must be judged on the geologic and geochemical merits
of its individual characteristics, and each system should be explored accordingly.
Implications for exploration
The use of observed patterns in hydrothermal alteration as a vector towards
porphyry mineralization has yielded exploration success for economic geologists in the
past (e.g., San Manuel-Kalamazoo, Lowell, 1968). However, most discoveries have
resulted from a top-down or side-in exploration approach, and use of vectors from the
116
bottom-up to ore bodies is a relatively recent advance (e.g., Maher et al., 2005; Maher,
2008; Seedorff et al., 2008), which has the possibility to yield significant finds in tilted
terrains such as southwestern North America (Maher, 2008; Nickerson et al., 2010).
Further study is required to hone this new approach to exploration in tilted
terrains (e.g., Seedorff et al., 2008); however, results here indicate the composition of
external fluids play a primary role in the manifestation of distal hydrothermal alteration
in porphyry copper systems. Thus, the presence of intense sodic (-calcic) alteration
should not be considered more prospective for porphyry copper formation than the
presence of propylitic alteration. However, sodic-calcic and iron oxide-rich hydrothermal
alteration are distinctive, and an understanding of their genetic implications (i.e., deep
and shallow levels, respectively, on the periphery of a porphyry copper system) could
prove useful when exploring in tilted terrains.
Mineralization directly associated with iron oxide-rich alteration is another
possible exploration target in composite porphyry systems. The best example of such a
deposit is Pumpkin Hollow in the Yerington district (measured and indicated resource of
531 M tons containing 0.55% Cu, 0.003 oz/t Au opt, and 0.079 oz/t Ag; TetraTech,
2010). In the Red Hills prospect at Tea Cup, mineralized iron oxide-rich alteration is
superimposed upon mineralized potassic alteration. The combination of the two styles of
mineralization produced a low-grade large-tonnage resource (450 million tonnes of 0.1%
Cu; Williams and Forrester, 1995). However, in IOCG systems there are many
occurrences of sodic (-calcic) and iron oxide-rich hydrothermal alteration but few
economic deposits. This may result from the systems having an effective mechanism of
117
metal transport (i.e., the circulation of heated brines) but commonly an ineffective
mechanism for metal precipitation mechanism (Barton and Johnson, 2000). A similarly
high ratio of occurrences to deposits should be expected in the composite porphyry
system environment. However, where a source of sulfur and an effective mechanism for
metal precipitation is present (i.e., carbonate rocks at Pumpkin Hollow), the resulting
mineralization can be economically significant.
SUMMARY AND CONCLUSIONS
Results of U-Pb geochronology, geologic mapping, petrographic study, and
electron microprobe analyses, constrain the possible origins of sodic (-calcic) alteration in
two Arizona porphyry copper systems. Spatial and temporal constraints, combined with
previous isotopic studies that indicate that the sodic (-calcic) and iron oxide-rich
alteration formed from externally derived saline fluids, suggest that these porphyry
systems are hybrid hydrothermal systems, in which magmatic fluids dominated the center
of the system and external fluids circulated peripherally. Conceptually, all porphyry
systems may be regarded as hybrid hydrothermal systems with an essential, usually
overwhelmingly dominant magmatic-hydrothermal contribution. The composition of
external fluids and wall rocks are proposed to control the manifestation of distal
alteration styles, which, to a first approximation, correlate with climate—propylitic
alteration forming from dilute meteoric fluids that characterize temperate climates, and
sodic (-calcic) alteration forming from saline brines that are most available in arid
climates. Sodic (-calcic) and iron oxide-rich alteration are genetically related to one
another, with the former forming on the warming path, and the latter forming on the
118
cooling path of saline hydrothermal fluids. Extension in arid climates, without the
requisite need for coeval plutons as the drive for fluid circulation, is another means of
producing sodic (-calcic) and iron oxide-rich alteration. Saline fluids derived from highly
saline surface waters in evaporite basins developed in half-grabens were warmed by an
elevated geothermal gradient and convected up highly porous and permeable normal
faults.
ACKNOWLEDGMENTS
We would like to thank K. Dominick for assistance at the Michael J. Drake
Electron Microprobe Laboratory (University of Arizona). Financial support for this
project came from two awards from the Society of Economic Geologists student research
fund, NSF Grant EAR08-38157 to Mark D. Barton, Science Foundation Arizona and the
industry sponsorship of the Lowel Institute for Mineral Resources, and Bronco Creek
Exploration. Some of the samples used in this study were collected and initially examined
by Tyler Vandruff, Eric Flesch, and Bill Stavast.
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TABLE 1. Hydrothermal alteration assemblages
Alteration
type
Potassic
Location
Tea Cup
Added and recrystallized minerals1
Quartz + k-feldspar + biotite(Phg# 49-55) + magnetite
+ muscovite ± pyrite ± chalcopyrite ±
molybdenite
Greisen
Tea Cup
Muscovite ± pyrite ± quartz ± molybdenite
Quartz ± orthoclase
Sodic
Tea Cup
Albite(An# 0-4) + chlorite + epidote ± titanite
± Quartz ± magnetite ±
orthoclase
Sodiccalcic
Tea Cup
Albite/oligoclase(An# 1-19) + epidote + actinolite +
titanite ± andradite
± Oligoclase
FeOx rich
Tea Cup
Specular hematite + chlorite + quartz ±
muscovite/alumino-celadonite ± magnetite ± pyrite
Quartz ± orthoclase
Potassic
Eagle
Pass
Quartz + k-feldspar + biotite(Phg# 50-59) + magnetite
± pyrite ± chalcopyrite
Quartz ± orthoclase ± biotite ±
magnetite
Sodic
(+qtz)
Eagle
Pass
Quartz + albite(An# 0-4) + chlorite + epidote
Quartz ± magnetite
Sodic
(-qtz)
Eagle
Pass
Albite/oligoclase(An# 1-23) + epidote ± clinochlore ±
actinolite ± specular hematite ±
muscovite/alumino-celadonite
± Quartz ± orthoclase
Relict Minerals2
Quartz ± orthoclase ± biotite ±
magnetite
An# = anorthite component in plagioclase; Phg# = phlogopite component in biotite
1
Minerals listed in order of abundance
2
Minerals occurring in trace amounts not considered
134
TABLE 2. Representative feldspar compositions.
Sample
SP
SP
SP 123
TC
number
035
035
kspar1
011
plg1
plg2
kspar2
TV08
07
plg2
EP
086
kspar3
EP
086
plg1
EP
038c
kspar2
MW
NACA2
plg1
Location
Tea
Cup
Tea
Cup
Tea
Cup
Tea
Cup
Tea
Cup
Eagle
Pass
Eagle
Pass
Eagle
Pass
Eagle
Pass
Alteration
assemblage
fresh
fresh
potassic
sodic
calcic
fresh
fresh
potassic
sodic
plag
plag
plag
plag
kspar
Replacing
Host rock
Yg
Yg
Yg
Yg
Yg
Yg
Yg
Yg
Yg
SiO2
64.54
64.54
64.35
64.54
62.76
63.34
65.30
64.72
67.61
TiO2
0.01
0.01
0.00
0.02
0.00
18.64
22.89
18.87
20.62
Al2O3
22.25
22.25
18.80
18.81
23.41
0.00
0.00
0.03
0.06
Cr2O3
0.00
0.00
0.01
0.00
0.00
0.00
0.00
0.00
0.05
Fe2O3
0.00
0.00
0.05
0.11
0.19
0.08
0.00
0.39
0.00
FeO
0.03
0.03
0.00
0.00
0.00
0.00
0.03
0.00
0.00
MgO
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
MnO
0.04
0.04
0.00
0.01
0.00
0.00
0.00
0.01
0.00
CaO
3.47
3.47
0.03
0.02
4.32
0.00
3.65
0.00
0.85
Na2O
9.70
9.70
1.33
0.89
9.27
0.77
10.21
0.72
11.60
K2O
0.17
0.17
14.65
15.05
0.20
15.20
0.13
15.43
0.10
F
0.00
0.00
0.00
0.08
0.00
0.30
0.00
0.25
0.00
Cl
0.00
0.00
0.00
0.00
0.00
0.00
0.01
0.00
0.01
100.21
100.21
99.23
99.48
100.15
98.20
102.22
100.32
100.90
Or#
0.01
0.94
0.96
0.00
0.00
0.93
0.01
0.93
0.01
An#
0.16
0.00
0.03
0.00
0.06
0.00
0.16
0.00
0.04
0.07
0.96
Total
End Member
Ab#
0.83
0.06
0.01
0.99
0.94
0.07
0.83
Yg = Ruin granite at Teac Cup and the Laurel Canyon granodiorite at Eagle Pass.
135
TABLE 3. Representative mica and chlorite compositions.
Sample
EP
EP 022b bt1
EP 034
TC 008
number
024
chl2
bt1
bt1
SP 123
bt2
TC 011
chl1
SP 079
ser2
Location
Eagle
Pass
Eagle Pass
Eagle Pass
Tea Cup
Tea Cup
Tea Cup
Tea Cup
Alteration
Assemblage
fresh
potassic
sodic after
potassic
fresh
potassic
sodic
sericitic
Mineral
name
annite
phlogopite
clinochlore
phlogopite
phlogopite
clinochlore
aluminoceladonite
biotite
shreddy
biotite
biotite
biotite
vein
Yg
Yg
Yg
Yg
Yg
Yg
Yg
SiO2
35.50
37.31
26.15
35.71
35.56
29.98
46.64
TiO2
3.41
1.98
0.10
2.81
3.00
0.00
0.28
Al2O3
14.55
17.03
18.73
17.37
14.69
19.03
28.64
Cr2O3
0.01
0.00
0.04
0.00
0.01
0.00
0.01
Fe2O3
5.36
3.81
4.55
4.19
4.28
2.04
1.16
FeO
19.28
13.70
23.19
15.10
15.42
10.39
4.16
MgO
7.73
11.56
13.71
9.66
11.75
23.87
2.54
Replacing
Host Rock
MnO
0.46
0.35
0.56
0.61
0.34
1.89
0.03
CaO
0.00
0.00
0.02
0.00
0.00
0.08
0.00
Na2O
0.21
0.03
0.01
0.05
0.10
0.01
0.20
K2O
9.39
9.74
0.00
9.52
9.44
0.07
10.49
H2O
3.48
3.62
11.18
3.38
3.53
12.07
4.12
F
0.55
0.64
0.00
0.99
0.57
0.13
0.44
Cl
0.09
0.03
0.01
0.04
0.08
0.01
0.01
Subtotal
100.02
99.80
98.23
99.44
98.80
99.56
98.72
O=F+Cl
-0.25
-0.28
0.00
-0.43
-0.26
Total
99.77
99.52
98.23
99.01
98.54
Yg = Ruin granite at Tea Cup and the Laurel Canyon granodiorite at Eagle Pass.
-0.06
-0.19
99.50
98.53
136
TABLE 4. Representative epidote and amphibole compositions.
Sample
MW
MW
MW
TV07 08 TC 010'
number
SPECHEM NACA3 NACA3
ep2
ep2
ep1
ep1
act1
TC 006
amph2
Location
Eagle Pass
Eagle
Pass
Eagle
Pass
Tea Cup
Tea
Cup
Tea Cup
sodic
sodic
sodic
calcic
sodic
sodic
epidote
epidote
actinolite
epidote
epidote
actinolite
Replacing
kspar
vein
biotite
kspar
quartz
biotite
Host rock
Yg
Yg
Yg
Yg
Yg
Yg
SiO2
38.26
37.25
51.37
37.08
38.40
50.44
TiO2
0.03
0.02
0.05
0.08
0.01
0.64
Al2O3
23.18
22.00
4.11
22.88
25.28
4.87
Cr2O3
0.00
0.00
0.00
0.03
0.00
0.01
Fe2O3
13.06
15.42
2.54
14.04
9.96
4.90
FeO
0.20
0.00
11.79
0.52
0.60
8.47
MgO
0.00
0.00
14.21
0.00
0.00
14.79
MnO
0.20
0.07
0.34
0.51
0.59
0.81
CaO
23.11
23.15
12.59
22.82
23.28
11.72
Na2O
0.00
0.00
0.48
0.05
0.00
0.96
K2O
0.00
0.00
0.15
0.00
0.00
0.37
H2O
1.88
1.87
1.86
1.80
1.90
2.08
F
0.00
0.00
0.41
0.15
0.01
0.00
Cl
0.01
0.01
0.04
0.00
0.01
0.00
Subtotal
99.94
99.78
99.92
99.95
100.04
100.07
O=F+Cl
0.00
0.00
-0.18
-0.06
0.00
0.00
Total
99.94
99.78
99.74
99.89
100.03
100.07
Alteration
assemblage
Mineral
Name
Yg = Ruin granite at Tea Cup and the Laurel Canyon granodiorite at Eagle Pass.
137
TABLE 5. Modal mineralogy and oxide weight% of alteration
types.
Sample
EP 024
MW
MW Spec
TC 008
number
NaCa2
Hem
Location
TC 010'
Eagle Pass
Eagle Pass
Eagle Pass
Tea Cup
Tea Cup
fresh
sodic
sodic
fresh
sodic
Quartz
40
39
0
38
3
Oligoclase
30
0
0
30
0
Albite
0
48
70
0
65
Orthoclase
21
0
0
23
0
Biotite
7
0
0
7
0
Muscovite
0
0
3
0
3
Chlorite
Epidote
0
0
4
8
0
4
0
0
17
11
Actinolite
0
0
0
0
0
Titanite
0
1
1
0
1
Magnetite
1
0
0
1
0
Ilmenite
1
0
0
1
0
Hematite
0
0
22
0
0
100
100
100
100
100
Alteration
assemblage
Total
Sample weight% oxide
SiO2
75
76
51
75
59
CaO
1.0
2.3
1.1
1.0
2.9
Na2O
3.1
5.6
8.0
3.1
7.7
K2O
3.9
0.0
0.2
4.3
0.3
Fe2O3
1.1
3.3
23
1.0
1.5
FeO
2.1
1.0
0.4
1.8
2.0
138
TABLE 6. Compilation of sodic (-calcic) mineral assemblages versus depth from localities in the western United States.
Tea Cup porphyry
system, Kelvin-Riverside
district, central Arizona4
Eagle Pass porphyry
system, Klondyke
district,
southeastern
Arizona5,6
Paleodepth
(km)
Ann-Mason deposit, Yerington
district, western Nevada1
Yerington mine, Yerington
district, western Nevada2
Sierrita-Esperanza
deposit, Pima
district, southern
Arizona3
1
Olg/Ab+Chl+Verm+Rt±Tnt±Py±Qtz
; Ab+Chl+Ser+Rt+Py(±Tm±Verm);
Ab+Tm+Rt+Py±Chl±Ser
Not exposed
Not exposed
Not exposed
Not exposed
2
Olg/Ab+Chl+Verm+Rt±Tnt±Py±Qtz
; Ab+Chl+Ser+Rt+Py(±Tm±Verm);
Ab+Tm+Rt+Py±Chl±Ser
Qtz+Olg/And+Tnt+Rt+Apt±Ep
; Qtz+Olg+Tnt+Apt+Act±Ep
Not exposed
Hem+Qtz+Chl+Ser±Mt±
Py
Not exposed
3
Ep+Tnt±Olg/Ab±Qtz±Act±Bi±Ser±
Py(±Chl±Rt)
Qtz+Olg/And+Tnt+Rt+Apt±Ep
; Qtz+Olg+Tnt+Apt+Act±Ep;
Qtz+Ab+Rt+Apt+Chl+Ep+Py+
Ser+Cal;
Qtz+Alb+Tnt+Apt+Chl+Act+E
p±Py+Ser
Not exposed
Hem+Qtz+Chl+Ser±Mt±
Py;
Mt+Qtz+Chl+Ser±Hem±
Py
Not exposed
4
Olg/And+Tnt+Qtz±Rt;
Olg/Ab+Act+Qtz+Tnt+Ep(±Py);
Olg/Ab+Qtz+Tnt+Ep+Act(±Chl);
Ep+Tnt±Olg/Ab±Qtz±Act±Bi±Ser±
Py(±Chl±Rt)
Qtz+Ab+Rt+Apt+Chl+Ep+Py+
Ser+Cal;
Qtz+Alb+Tnt+Apt+Chl+Act+E
p±Py+Ser
Ab+Chl+Act+Ep
(Qtz destroyed)
Not exposed
Chl+Ep+Tnt (Qtz
destroyed Kspar
stable)
5
Olg/And+Tnt+Qtz±Rt;
Olg/Ab+Act+Qtz+Tnt+Ep(±Py);
Olg/Ab+Qtz+Tnt+Ep+Act(±Chl)
Not exposed
Ab+Chl+Act+Ep
(Qtz destroyed)
Not exposed
Ab+Chl+Act+Ep±
Tnt (±Qtz
destroyed)
6
Olg/And+Tnt+Qtz±Rt;
Olg/Ab+Act+Qtz+Tnt+Ep(±Py);
Olg/Ab+Qtz+Tnt+Ep+Act(±Chl)
Not exposed
Ab+Chl+Act+Ep
(Qtz destroyed)
Chl+Ep+Tnt (Qtz
destroyed Kspar stable);
Alb+Chl+Ep+Anr±Act
Ab+Chl+Act+Ep±
Tnt±Hem (±Qtz
destroyed)
139
1
7
Not exposed
Not exposed
Ab+Chl+Act+Ep
(Qtz destroyed)
Ab+Chl+Act+Ep±Sph
(Qtz destroyed)
Ab+Chl+Act+Ep±S
ph±Hem (Qtz
destroyed)
8
Not exposed
Not exposed
Ab+Chl+Act+Ep
(Qtz destroyed)
Ab+Chl+Act+Ep±Sph
(Qtz destroyed)
Ab+Chl+Act+Ep±S
ph±Hem (Qtz
destroyed)
From Dilles and Eunaudi (1992). 2From Carten (1986). 3From Stavast (2006). 4From this study. 5From this study. 6Absolute paleodepth not constrained;
Mineral abbreviations: Act = actinolite, Alb = albite, And = andesine plagioclase, Anr = andradite, Apt, apatite, Bt = biotite, Cal = calcite, Chl = chlorite, Ep =
epidote, Hb = hornblende, Hem = hematite, Mt = magnetite, Olg = oligoclase, Py = pyrite, Rt = rutile, Ser = sericite, Tnt = titanite, Tm = tourmaline, Verm =
vermiculite, Qtz = quartz.
140
TABLE 7. Geologic setting of sodic (-calcic) alteration occurrences in the western United States
Location
Ann-Mason, Yerington
district, Nevada1
Age of
alteration
Jurassic
Intrusive rocks
Granite, granite
porphyry dikes
Wall rocks
Quartz
monzodiorite
Tectonic
environment
Recently
emergent arc
Source of
salinity
Jurassic
evaporites
Yerington mine,
Yerington District,
Nevada2
Jurassic
Granite, granite
porphyry dikes
Quartz
monzodiorite
Recently
emergent arc
Jurassic
evaporites
Sierrita-Esperanza,
Pima district, Arizona3
Laramide
Granodiorite
Granite,
carbonates
Continental
arc
Permian
evaporites
Tea Cup porphyry
system, KelvinRiverside district,
southeastern Arizona4
Laramide
Biotite
hornblende
granodiorite and
biotite granite
Granite
Continental
arc
Permian
evaporites?
Eagle Pass porphyry
system, Klondyke
district, southeastern
Arizona5
Oligocene
Granite, quartz
Granite,
Slab rollback
Permian
monzonite, and
granitic
magmatism
evaporites?
quartz diorite
gneiss
porphyry dikes,
composite
pluton?
1
From Dilles and Eunaudi (1992). 2From Carten (1986). 3From Stavast (2006). 4From this study. 5From this
study.
141
TABLE 8. Representative vein muscovite compositions
from greisen alteration
Sample
number
DM04 670
Schultze1
TV125
Ruby Star2
SP 114
Tea Cup3
Mineral
Name
Muscovite
Muscovite
Muscovite
SiO2
50.40
47.99
46.20
TiO2
.25
0.26
0.46
Al2O3
29.02
28.21
29.97
Cr2O3
0.02
Fe2O3
1.08
FeO
3.19
5.59
3.88
MnO
0
0.15
0.11
MgO
2.23
2.11
1.82
CaO
.10
0.11
0.02
BaO
0
0.08
Na2O
.16
0.24
0.25
K2O
10.23
10.32
10.51
SO3
0.00
0.02
P 2O 5
0.00
0.00
F
0.01
0.03
0.08
Cl
0.00
0.00
0.00
H2O
4.38
4.20
4.31
Subtotal
100.01
99.32
98.70
O=F+Cl
-0.01
-0.01
-0.03
Total
100.00
99.31
98.67
2
3
1From Stavast (2006). From Stavast (2006). From this study.
142
Fig. 1. Geologic map of south-central Arizona showing the study area, nearby
porphyry copper deposits, the Catalina core complex, the Pinaleño core complex, and the
Tortilla Mountains (geology from Reynolds, 1988).
Fig. 2. Geologic map of the Tea Cup area. The map is based on new mapping and
previous work by Schmidt (1971), Cornwall and Krieger (1975a and 1975b), Bradfish
(1979), Richard and Spencer (1997), and Barton et al. (2005a).
Fig. 3. Geologic map of the Eagle Pass area. A. Geologic map of the northern
portion of the Pinaleño metamorphic core complex including endpoints of cross section
A-A’ through the dike swarm. EPF = Eagle Pass fault; PDF=Pinaleño detachment fault.
B. Location of cross section B-B’ in Fig. 12D. Dashed box is area shown in Fig. 1A. C.
Cross section oriented perpendicular the Eagle Pass dike swarm. A-A’ located in Fig. 1A.
Fig 4. U-Pb geochronology. The 206Pb/238U zircon ages for rock samples collected
from the Tea Cup pluton and Red Hills dike swarm. Sample location located in Appendix
E (Table 1). A. SP 100 Red Hills dike collected near the Red Hills prospect. B. SP 102
granite porphyry dike located 5 km north of the Red Hills prospect. C. SP 103 muscovitebearing quartz latite dike intruding the Tea Cup pluton. D. Collected from the muscovitebiotite granite phase of the Tea Cup pluton. E. GB 202 collected from the hornblendebiotite granodiorite phase of the Tea Cup pluton.
Fig 5. Stereonets for Eagle Pass dikes and Safford veins. A. Orientation of dikes
in the Pinaleño MCC. Dashed line = plane to beta axis. B. Orientation of dikes in the
Pinaleño MCC with beta axis rotated to vertical, i.e., the proposed orientation of the dikes
143
prior to tilting. C. Mineralized veins found in dike rocks in the Kennecott area of the
Laramide aged Safford district; after Dunn (1978).
Fig. 6. Map illustrating the distribution of hydrothermal alteration in the Tea Cup
area.
Fig. 7. Equal area plot stereonets of Laramide hydrothermal features in the study
area. A. Compilation all strike and dip measurements of veins and porphyry dikes from
the Tea Cup porphyry system. B. Orientations of veins and porphyry dikes from the
oldest hydrothermal system sourced from the biotite-hornblende granodiorite. C.
Orientations of veins and porphyry dikes from the middle-aged hydrothermal system
sourced from biotite granite. Alteration crops out in and around the Red Hills prospect.
D. Orientations of veins and porphyry dikes from the youngest hydrothermal system
sourced from the biotite-muscovite±garnet granite near Mount Grayback.
Fig. 8. Photographs of rock slabs showing hydrothermal alteration at Tea Cup (AC) and Eagle Pass (D-G). A. Albite-epidote-chlorite±garnet sodic (-calcic) alteration of
the Ruin Granite on the southeastern flank of the Tea Cup pluton B. Quartz vein
surrounded by coarse-grained muscovite in the biotite-muscovite±garnet granodiorite
west of Mount Grayback. C. Specular hematite-quartz vein in the Red Hills prospect. D.
Quartz-chlorite-albite±specular hematite alteration hosted in the Laurel Canyon
granodiorite. Sample located ~100 m from the Eagle Pass Fault. Alteration is interpreted
to be considerably younger than the porphyry system (see text) and to be associated with
the normal faulting. E. Albite+chlorite +epidote ±actinolite±titanite alteration hosted in
the Laurel Canyon granodiorite. Sample located north of the Eagle Pass dike swarm.
144
Alteration is interpreted to be associated with the intrusion of the dike swarm. F.
Chlorite+epidote+titanite, quartz destructive, K-feldspar stable alteration hosted in the
Laurel Canyon granodiorite. G. Specular hematite+quartz alteration hosted in the Laurel
Canyon granodiorite; K-feldspar is altered to albite.
Fig 9. Mapped pattern of hydrothermal alteration near the Eagle Pass dike swarm
of Oligocene age.
Fig 10. Zoning pattern observed in Mg/(Mg+Fe) ratio in biotite and chlorite from
Eagle Pass.
Fig 11. Log(aCa2+/a2H+) versus log(aMg2+/a2H+) for 400° C, 500 bars, for the system
CaO-MgO-Al2O3-SiO2-HCl-H2O, showing boundaries of stability fields of plagioclase
compositions An5, An23, An35; epidote solid solution (SS) given by mole fraction Fe-endmember component X(Ca2Fe3Si3O12(OH)), grossular-andradite (grandite) garnet solid
solution, and K-feldspar (after Dilles et al., 1995). Mineral assemblages from AnnMason, Yerington, Tea Cup, Eagle Pass, and Sierrita-Esperanza are plotted on the
diagram. The dashed arrow indicates how fluids are interpreted to have evolved from
more calcic to less calcic with time.
Fig 12. Two models depicting the generation of sodic-calcic alteration. A. Sodiccalcic alteration generated on the periphery of a porphyry system. Fluids are derived from
evaporite deposits and circulated by a magmatic heat source. B. Sodic-calcic alteration
generated along a normal fault. Fluids are derived from evaporite deposits and circulate
up the porous and permeable fault zone. Fluids are heated by the warm upper crust
commonly observed in extension tectonic settings.
145
Fig 13. Reconstructed cross section for Tea Cup system. A. Hypothetical
Laramide geologic cross section (after Nickerson et al., 2010) depicting the composite
Tea Cup pluton intruding a basement-cored uplift. Thick black lines represent the modern
surface. Maroon lines mark the paleosurface at 73 Ma and 25 Ma. Q = Undifferentiated
Quaternary deposits; Tc = Tertiary conglomerate; Ts= Oligo-Miocene sedimentary rocks;
Kmbg = biotite-muscovite±garnet granodiorite; Kbg = biotite granite; K = hornblendebiotite granodiorite; Khbg = biotite-hornblende quartz monzodiorite; P = Paleozoic
sedimentary rocks; Ya = Proterozoic Apache Group; Yr = Proterozoic Ruin Granite. B.
Reconstruction of hydrothermal alteration. Yellow arrows illustrate a proposed fluid flow
path for the external saline fluids that produced sodic (-calcic) and iron-oxide rich
alteration at Tea Cup. No vertical exaggeration.
Fig 14. Sequential time panels depicting possible origin of the two sodic (-calcic)
alteration events at Eagle Pass. One has a magmatic heat source, and one is related to
extension. Qu = undifferentiated Quaternary rocks; Tv = Tertiary volcanic rocks; Tep =
Oligocene Eagle Pass pluton (inferred; the pluton is not exposed at the surface); Kc =
Cretaceous conglomerate; Plz = Paleozoic rocks including dolomite and evaporite
bearing units; Yag; Proterozoic Apache Group; Ylc = Proterozoic Laurel Canyon
granodiorite. A. Sodic (-calcic) alteration formed forms during the intrusion and cooling
of the Eagle Pass pluton (the magmatic source of the Eagle Pass dike swarm). B.
Generation of fault related sodic (-calcic) alteration option 1. Slip on the Eagle Pass fault
dismembers the Eagle Pass pluton. Sodic (-calcic) alteration forms as saline formation
waters derived from Paleozoic dolomite and evaporite bearing units (Plz) are circulated
146
up the fault. C. Generation of fault related sodic (-calcic) alteration option 2. Slip on the
Eagle Pass fault dismembers the Eagle Pass pluton. Sodic (-calcic) alteration forms as
saline formation waters derived from Tertiary evaporite bearing units (Tc) are circulated
up the fault. D. Modern cross section B to B’. Cross section endpoints shown on Fig. 1B.
Fig 15. Diagram depicting variation in peripheral styles of alteration in composite
porphyry systems created by variation in external fluid compositions. A. Propylitic
alteration is generated by circulating fresh external fluids. B. Sodic (-calcic) and ironoxide rich alteration is created by circulating saline fluids derived from ancient evaporitebearing sedimentary rocks. C. Sodic (-calcic) and iron-oxide rich alteration is created by
circulating saline fluids derived from modern evaporite-bearing sedimentary rocks.
147
Figure 1.
148
Figure 2.
149
Figure 3.
150
Figure 4.
151
Figure 5.
152
Figure 6.
153
Figure 7.
154
Figure 8.
155
Figure 9.
156
Figure 10.
157
Figure 11.
158
Figure 12.
159
Figure 13.
160
Figure 14.
161
Figure 15.
162
APPENDIX C: DISMEMBERED PORPHYRY SYSTEMS NEAR WICKENBURG,
ARIZONA: DISTRICT-SCALE RECONSTRUCTION WITH AN ARC-SCALE
CONTEXT
Phillip A. Nickerson*
Eric Seedorff
Lowell Institute for Mineral Resources
Department of Geosciences
University of Arizona
1040 East Fourth Street
Tucson, Arizona 85721-0077, USA
To be submitted to Economic Geology
163
ABSTRACT
This study combines results from reconnaissance-scale mapping of hydrothermal
alteration, rock types, and structures to provide a district-scale cross section and
associated palinspastic reconstruction of an area near Wickenburg, Arizona, that contains
previously undescribed Laramide (~70 Ma) porphyry systems. Extension at the district
scale in this poorly understood segment of the Laramide porphyry belt is placed in an arcscale context by using a compilation of tilt measurements on Tertiary sedimentary and
volcanic rocks to make a new estimate of the geometry of the Laramide porphyry belt of
southwestern North America prior to extension.
Crosscutting relationships between normal faults and tilting of hanging wall and
footwall rocks indicate that the study area contains five sets of nearly planar normal faults
superimposed upon one another. Geologic relationships demonstrate that the normal
faults initiated at angles between 60 and 70° and rotated to angles as gentle as 20° during
slip. The amount of displacement on the largest faults is no greater than 4 - 6 km. A faultby-fault palinspastic reconstruction of displacement reveals a total of ~160% northeastsouthwest extension across the study area and implies the presence of two, spatially
distinct hydrothermal systems sourced from different cupolas of a Late Cretaceous
pluton. Hydrothermal alteration is zoned from greisen to potassic to transitional greisenpotassic assemblages from deep to shallow structural levels. The reconstruction is used to
identify two exploration targets centered on potassic alteration in two porphyry systems
that are now covered by younger Tertiary and Quaternary rocks. Igneous source rock
compositions and styles of alteration suggest that the prospects may be porphyry
164
molybdenum systems of the Mo-Cu subclass, similar to previously identified nearby
porphyry resources.
A compilation of strikes and dips of Tertiary units in various extensional domains
astride the Laramide porphyry belt of southwestern North America is utilized create a
reconstruction of the porphyry belt. The resulting interpretation of the pre-extension
geometry of the Laramide porphyry belt displays a variably well defined axis,
approximately 100 km wide prior to extension with gaps and clusters of deposits along
the 700-km strike length of the arc, with the majority of porphyry deposits along the axis
but with others in fore-arc or rear-arc settings. The interpreted pre-extensional
geometrylosely resembles that of other porphyry belts and magmatic arcs formed at
convergent oceanic-continental plate boundaries.
INTRODUCTION
In southwestern North America, the Cenozoic Basin and Range extensional
province is superimposed upon many types of ore deposits (Fig. 1), including the
numerous porphyry systems of the Laramide (80-50 Ma) magmatic arc. The Laramide
magmatic arc contains some of the best studied porphyry systems in the world (e.g.,
Titley and Hicks, 1966; Titley, 1982a; Pierce and Bolm, 1995) (Fig. 2). However, few
previous studies consider the effect that post-mineralization normal faulting has had on
spatial relationships at the deposit scale (e.g., Lowell, 1968; Wilkins and Heidrick, 1995;
Stavast et al., 2008) or the scale of the magmatic arc (Richard, 1994). The superposition
of normal faults and porphyry systems creates challenges and benefits for the study of
both extensional and hydrothermal processes. For example, challenges can arise where
165
hydrothermal alteration destroys critical structural markers and where key parts of ore
bodies are dismembered by normal faults. Benefits of this juxtaposition arise when
products of one of the geologic processes help constrain aspects of the other process. For
example, predictable patterns in hydrothermal alteration zoning can be used as structural
markers (Nickerson et al., 2010), which may better constrain structural reconstructions
and, in turn, aid in better discriminating between different styles of extension. In addition,
deep levels of ore forming systems can be exhumed in the footwall of normal faults and
examined at the surface to better constrain ore forming processes (Carten, 1986; Dilles
and Einaudi, 1992; Seedorff et al., 2008).
Regional-scale reconstructions commonly subdivide regions into extensional
domains and then restore extension in each of the extended domains. At the arc-scale,
such reconstructions can aid in understanding tectonic processes (e.g., McQuarrie and
Wernicke, 2005) or, as attempted here and earlier by Richard (1994) using an alternative
method, the original distribution of porphyry deposits along a magmatic arc.
This study focuses on a poorly understood segment of the Laramide porphyry
copper belt near the town of Wickenburg in central Arizona (Fig. 3) and provides the first
public documentation of porphyry systems in the area, i.e., notwithstanding company
reports. Previous detailed mapping of rocks types and structural geology (Peterson, 1985;
Capps et al., 1986, Stimac et al., 1987; Powers, unpublished map) is combined with
original, reconnaissance-scale mapping of hydrothermal alteration and examination of
areas critical to a structural interpretation of the area, which were made possible by
helicopter-assisted access. The data for rock types, structure, and alteration are used to
166
make a structural analysis of the area, including a palinspastic reconstruction of the
Oligo-Miocene extension. The reconstruction demonstrates that extension was produced
by five super-imposed sets of normal faults, and the district-scale reconstruction is used
to identify two new porphyry exploration targets centered on potassic alteration. The
results from the Wickenburg area are placed in an arc-scale context by using the
equations of Jackson and McKenzie (1983) to generate a new estimate of the original,
pre-extensional distribution of porphyry deposits along the Laramide arc.
LOCATION AND GEOLOGIC SETTING
Location
The study area is located ~70 km northwest Phoenix, Arizona, and ~10 km east of
Wickenburg Arizona (Fig. 3). The study area, ~250 km2 in size, includes portions of the
Wickenburg, Buckhorn, Hieroglyphic, and Bradshaw Mountains, as well as Sheep
Mountain. Mining districts in the study area include the White Picacho and Sheep
Mountain districts. Four-wheel drive roads provide access to the Wickenburg, Buckhorn,
and Hieroglyphic Mountains. Access to steep and rugged terrain of Sheep Mountain and
the Bradshaw Mountains is limited, where helicopter support greatly facilitated geologic
mapping.
Laramide porphyry copper province
Porphyry deposits in Arizona are some of the best studied deposits in the world
(e.g., Seedorff et al., 2005a), and many have been productive mines for over a century
(e.g., Miami, Inspiration, Ray, and Morenci; Parsons; 1933) (Fig. 2). Nearly all porphyry
deposits in Arizona formed during Laramide time (~80-50 Ma) when northeast-directed
167
subduction of the Farallon plate beneath the North American plate produced a northwestsoutheast striking magmatic arc (Titley, 1982b; Lang and Titley, 1998). The district-scale
portion of this study examines a segment of the Laramide arc located between the GlobeMiami district and the Bagdad deposit, within which an economic deposit has yet to be
identified (Fig. 2).
Extension in western Arizona
The study area lies between the highly extended Harcuvar and Harquahala
metamorphic core complexes to the west and the Bradshaw Mountains to the east (Fig.
3), which lie within the Basin and Range extensional province. Three competing models
have emerged to explain the relationships between low-angle mylonitic fabrics that are
observed in mid-crustal metamorphic core complexes and the brittle normal faults that
are exposed in the upper crust of western Arizona and throughout the Basin and Range
province.
The first model proposes that the low-angle features are normal faults that
initiated at low angles, have tens of km of displacement (Wernicke, 1981, 1985; John,
1987), and eventually expose mylonitic rocks at the surface as extension proceeds (Fig.
4A). A second model and its variations, known as the rolling hinge model, suggests that
strongly listric normal faults with tens of km of displacement can be folded by isostatic
uplift during extension to expose mylonitic fabrics at the surface (Spencer, 1984; Buck,
1988; Wernicke and Axen, 1988) (Fig. 4B). The first two models contend that a master
fault in extensional systems serves as a detachment into which smaller scale faults sole,
thereby transferring their displacement.
168
The final model (Fig. 4C) puts forth that a set of “domino–style” faults breaks at
high angles (60°-70°) and rotates to low angles during extension (Proffett, 1977; Davis,
1983). When the faults rotate to low angles (~20-30°), slip on the faults becomes
kinematically unfavorable (Anderson, 1951), and a new set of faults forms at high angles.
Mylonitic rocks in the down-dip toes of abandoned faults, now tilted to low anlges, can
be brought to the surface (Davis 1983, 1987), especially if the process is repeated by
movement on multiple, crosscutting sets of faults.
Previous workers in the Vulture Mountains, ~10 km west of the study area (Fig.
3) proposed that southwest dipping, listric normal faults were responsible for the
observed repetition of steeply dipping (up to ~85°) Tertiary sedimentary and volcanic
rocks exposed in the Vulture Mountains, as well as for the slightly less tilted (up to ~65°)
Tertiary sedimentary and volcanic rocks exposed in the study area (Rehrig et al., 1980) .
However, subsequent detailed geologic mapping in the study area (Capps et al., 1986;
Stimac et al., 1987) at 1:24,000 scale revealed that normal fault geometries are nearly
planar and that higher angle faults cut lower angle faults. Determining the style of
extension in the district-scale study area is essential to creating the district-scale
reconstruction. Thus, predictions of the two competing models for extension regarding
the geometries of the normal faults, and deformation in the hanging walls and footwalls
of the normal faults are tested below. Constraints include the amounts of tilting and
amount of offset observed of structural markers and structure contour maps illustrating
the shapes of the fault planes.
169
Rock types
Previous geologic maps are heavily utilized in this study for the distribution of
rock types, although new mapping and field checking influenced the interpretation of the
nature of various contacts (e.g., unconformity, fault, intrusive, stratigraphic), and the
structural interpretations and distribution of alteration products are entirely the product of
this study. Geologic maps at 1:24,000 scale of the Wickenburg, southern Buckhorn, and
northwestern Hieroglyphic Mountains (Stimac et al., 1987), the western Hieroglyphic
Mountains (Capps et al., 1986), the Buckhorn Creek area (Peterson, 1985), and the
vicinity near Sheep Mountain (Powers, unpublished map) were compiled and generalized
to produce Figure 5.
Rocks in the study area consist of Proterozoic amphibolite, gneiss, schist, granite,
and pegmatite, intruded by Late Cretaceous granite, and overlain by late Oligocene and
Miocene volcanic rocks (Fig 5.) (Stimac et al., 1987). Proterozoic, Paleozoic, and
Mesozoic sedimentary rocks, which are locally important ore hosts in some Laramide
porphyry deposits (e.g., Resolution, Manske and Paul, 2002), have been denuded in the
study area. Most likely the denudation occurred during Laramide or Sevier uplift in the
Late Cretaceous (Flowers et al., 2008).
The metamorphic Proterozoic rocks exposed in the study area belong to the
Yavapai Supergroup (DeWitt et al., 2008). In the Bradshaw Mountains (Fig. 3), the
Yavapai Supergroup displays a consistent north-south striking moderate to steeply
dipping lineation. Variations in the lineation are used later in this study to constrain
Tertiary deformation in the metamorphic rocks. Late Cretaceous granite, dated at 68.4
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Ma (K/Ar) 10 km west of the study area in the Vulture Mountains (Rehrig et al., 1980),
crops out predominantly in the western half of the study area (Fig. 5). The granite is
porphyritic to equigranular in texture containing 30-40% orthoclase, 20-30% plagioclase,
20-30% quartz, 3-5% biotite, 1-2% magnetite, and up to 5% sphene, zircon, and other
accessory minerals (Stimac et al., 1987).
The crystalline Proterozoic and Cretaceous rocks are overlain by Tertiary units,
which include siliciclastic sedimentary rocks, volcanic rocks, debris flows, and
conglomerates. The oldest Tertiary unit is a red to brown conglomerate containing
pebble- to boulder-sized clasts of older crystalline rocks and some volcanic rocks. The
conglomerate is similar in appearance to the synextensional red-bed conglomerates of the
Whitetail and Cloudburst Formations in southeastern Arizona (Dickinson, 1991). The
conglomerate unit varies in thickness from 1 m to 10’s of m and consistently has steep
dips of ~55° - 75° to the northeast.
Approximately one to two kilometers of Tertiary volcanic and sedimentary rocks
overlie the basal Tertiary conglomerate. The geologic map and cross section in Figure 6
depicts a portion of this sequence. Tertiary volcanic and sedimentary rocks have not been
dated in the study area. However, volcanism in the nearby Vulture Mountains (Fig. 3) is
known to have occurred between ~25-15 Ma. The oldest volcanic unit is a basaltic lava
flow that in some places is interbedded with the basal conglomerate (Fig. 6). Above the
basalt, rhyolite lava flows and tuffs of the San Domingo Volcanics occur in the western
half of the study area. The Morgan City Rhyolite, Spring Valley Rhyolite, and Castle
Creek Volcanics occupy a similar stratigraphic position in the eastern half of the study
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area (Capps et al., 1986; Stimac et al., 1987). Dacite to rhyodacite lava flows and tuffs
make up the structurally higher Hells Gate Volcanics. Resting unconformably above the
Hells Gate Volcanics are interbedded basalts, tuffs, volcanic megabreccias, and debris
flow deposits with nearly horizontal bedding attitudes. Northwest striking and steeply
dipping felsic and mafic dikes locally intrude the crystalline basement and the Tertiary
volcanic rocks. The youngest Tertiary unit is a brown colored, consolidated to semiconsolidated conglomerate. A thin layer of Quaternary-Tertiary gravels locally covers the
conglomerate.
ECONOMIC GEOLOGY
The study area contains mineralization that is related to several genetic types of
deposits and formed at distinctly different times (DeWitt et al., 2008; this study). Gold
and copper associated with volcanogenic massive sulfide systems are hosted in
metamorphosed Proterozoic rocks. Pegmatite dikes of Proterozoic age have been
investigated for their beryllium and lithium potential (Jahns, 1952; London and Burt,
1978). Epithermal style mineralization is locally hosted in Tertiary volcanic rocks. Many
of the washes in the study area produced and continue to produce gold in placer deposits
hosted in Tertiary and Quaternary gravels. Just west of the study area in the Vulture
Mountains, the Vulture mine produced 340,000 ounces of gold and 260,000 ounces of
silver between 1863 and 1942 (White, 1989). Mineralization consists of native gold and
electrum hosted in Proterozoic and Cretaceous crystalline rocks and is interpreted to be
genetically related to a Cretaceous dike (Spencer et al., 2004).
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Several porphyry systems near the study area of Laramide age have yielded
identified resources but no significant past or current production. The largest resource is
the Copper Basin prospect, which is located 20 km north of the study area in the Silver
Mountain mining district of the southern Bradshaw Mountains (Fig. 3). This prospect,
which is distinct from the Copper Basin district described by Johnston and Lowell (1961)
that is located farther north near Prescott (Fig. 2), takes its name from the amphitheatershaped basin in which it lies, which was named by soldiers stationed nearby at Fort
Misery at the end of the 19th century (Tognoni, 1969). Chalcopyrite and molybdenite are
exposed at the surface in Copper Basin, as well as spectacular Cu-oxide seeps in the
drainages. Drilling conducted in the late 1960’s and early 1970’s produced a resource
estimate of one billion tons of 0.16% Cu and 0.031% MoS2 based on eight drill holes
(unpublished Asarco report, 1974).
Near Sheep Mountain (Fig. 5), two porphyry prospects have been identified. On
the eastern flank of Sheep Mountain, a resource containing 40 million tons of 1.6% Cu
and 0.04% MoS2 have been defined at the Sheep Mountain East prospect (Ullmer, 2007).
The mineralization lies underneath ~700 m of Tertiary volcanic and sedimentary rocks.
Molybdenite from drill core at the prospect has been dating the Re-Os technique at 70.34
± 0.36 Ma (R. Powers, written comm., 2012).
Approximately 5 km to the west of Sheep Mountain East is the Sheep Mountain
West prospect, where several outcrops of intensely altered Proterozoic granite are
exposed in tilted fault blocks (Fig 5.). The altered Proterozoic rocks are unconformably
overlain by Tertiary volcanic and sedimentary rocks. Several drill holes have been drilled
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in the last decade exploring for supergene mineralization, but a significant resource has
not been identified.
HYDROTHERMAL ALTERATION
Hydrothermal alteration was mapped at reconnaissance scale across the study area
(Fig. 7). Three important styles of alteration have been identified: greisen, potassic, and
transitional greisen-potassic. The term greisen is used here to describe hydrothermal
alteration assemblages where coarse-grained (> 0.5 mm) white mica is an important
constituent (e.g., Shaver, 1991; Seedorff et al., 2005a). Where greisen occurs in porphyry
copper systems, it occurs at deep levels of the system, generally beneath the level of the
orebodies and beneath the most intense potassic alteration and well below the level where
sericitic alteration develops (Seedorff et al., 2005a, 2008); in contrast, greisen can occur
in porphyry molybdenum deposits of the Mo-Cu subclass in and above orebodies and the
most intense potassic alteration, in a position that would be analogous for the position of
sericitic alteration in many porphyry copper systems (Shaver, 1991; Seedorff et al.,
2005a).
Greisen
Hosted within the Cretaceous granite (Fig. 8A), northeast-striking veins of quartz
+ muscovite + pyrite ± chalcopyrite ± K-feldspar (Fig. 8B) commonly compose 1-5% of
outcrops in the central Wickenburg Mountains (Fig. 7). Locally, greisen veins +
envelopes are so intense that they constitute up to 20 vol% of outcrops. Vein fillings
range from 1 - 50 mm wide and have envelopes 5 - 50 mm wide. White mica grains
ranges in size from 0.5 - 5 mm and are found in both the vein filling and alteration halo.
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Quartz in the vein filling is commonly milky white in color. Sulfides are found
predominantly in the vein filling but also in the alteration halo. They range in size from
1-15 mm and have a pyrite to chalcopyrite ratio of approximately 10:1. K-feldspar is
rarely found in the greisen veins, where it comprises <1% of the vein filling.
Potassic
In Buckhorn Creek west of Sheep Mountain (Fig. 7), northeast-striking veins of
quartz + K-felsdspar ± white mica ± pyrite ± chalcopyrite with biotite envelopes cut
Yavapai Schist (Fig. 8C). Veins vary in size from 1-15 mm wide with alteration halos
<10 mm wide. Quartz is the dominant mineral in the vein filling (~65%), accompanied by
K-feldspar (~20%), white mica (~10%), and sulfides (~5%; pyrite >> chalcopyrite).
White mica ranges in size from 0.1-2 mm. The veins increase in abundance to the
northeast until they reach an abundance of 5 vol% before they are unconformably
covered by Tertiary volcanic rocks.
Transitional greisen-potassic
This classification is used here with the meaning of Shaver (1991), who first
described this coarse-grained white mica-bearing style of alteration at the Hall (Nevada
Moly) deposit, Nevada, where it overlies potassic alteration and is regarded as a coarsegrained analogue of sericitic alteration (Shaver, 1991). At Sheep Mountain (Fig. 7), veins
of quartz + K-feldspar ± white mica ± sulfide (1-5 mm wide) are cut by quartz + Kfeldspar + white mica + sulfide veins (1-5 mm wide) with white mica halos (<5 mm
wide; Fig 8D). The vein density is intense in several areas, where it comprises 5-10 vol%
of outcrops. White mica varies in size from 0.1-1 mm. Envelopes surrounding the quartz
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in the vein filling of both vein types conspicuously change between white mica and Kfeldspar along strike.
STRUCTURAL GEOLOGY
The repetition of structural markers in the study area (i.e., Tertiary sedimentary
and volcanic units, the Tertiary-Proterozoic unconformity, contacts between Proterozoic
units, and styles of hydrothermal alteration), was determined by previous studies to be the
result of movement on Tertariy (~25-15 Ma) normal faults (Rerhig et al., 1980; Peterson,
1985; Capps et al., 1986; Stimac et al., 1987). By scrutinizing crosscutting relationships
between the normal faults exposed in the study area, relative ages can be determined,
which is critical to constraining the style of deformation and is necessary for
subsequently grouping faults into sets or generations.
Examination of the normal faults in map view reveals that five distinct sets of
Tertiary normal faults are present in the study area (Fig. 9). Faults within each set have
similar strikes and dips and exhibit common crosscutting relationships. Unless they
significantly influence the map pattern, faults determined to have less than 500 m of
offset are not shown on the geologic map (Fig. 5) and were not assigned to a set of faults
(Fig. 9). Many dozens of such small-offset normal faults were identified in previous work
across the study area (e.g., Stimac et al., 1987; Fig. 6).
Set 1: Two faults from this set crop out at the surface in the Wickenburg Mountains (Fig.
9.), the Wickenburg Mountains fault and the Mount Vernon Fault. These faults have
sinuous expressions at the modern surface produced by the intersections of their presentday gentle dips with the modern topography in the study area. A structure contour map
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(Fig. 10) reveals that the Wickenburg Mountains fault and the Mount Vernon fault have
azimuths of ~125 and dip ~4° to the southwest. Across 4 km of down-dip exposure on the
Wickenburg Mountains fault (Fig. 10B), the fault dip decreases only slightly from 5.1° to
3.3° (curvature of 0.5°/km). The structure contour map also reveals a northeast-southwest
striking trough in the plane of the Mount Vernon fault. Such “mullion” features are
commonly observed in low-angle normal faults (e.g., John, 1987; Wong and Gans, 2008).
Set 2: The northeast-southwest striking faults in this set strike nearly perpendicular to
faults in all other sets. One fault from this set is exposed in the central portion of the
study area, where it has a measured dip in outcrop of 45° to the southeast (Fig. 9). This
fault places Tertiary volcanic and sedimentary rocks on Proterozoic rocks. To date we
have not identified a structural marker that tightly constrains displacement on this fault.
Set 3: Faults from this set crop out across the study area. They strike with an azimuth of
~150 and have dips measured in outcrop that range from ~40-50° to the southwest. Ten
faults from this set are shown in the map. Typical offsets on faults from this set are
approximately one km. The Castle Creek fault (Fig. 9), which bounds the west side of
Sheep Mountain, and the Trilby Wash fault belong to this set.
Set 4: Members of the second youngest set of faults have an azimuth of ~150 and dip
steeply to the southwest at ~60-70°. Dozens of faults from this set crop out across the
study area (Stimac et al., 1987); however, few have significant amounts of offset and
only four are shown on Figure 9. The fault with the largest offset is the Buckhorn Creek
fault (Fig. 9), which has 1.5 km of slip in the central portion of the study area.
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Set 5: Faults belonging to the youngest set have azimuths of ~330 and dip steeply to the
northeast at ~70°. Faults from this set are more common in the eastern half of the study
area, and only two are depicted on Figure 9. An example is the Evans Butte fault (Fig. 9),
which bounds the western side of the valley west of Sheep Mountain and exhibits ~500 m
of offset.
STRUCTURAL INTERPRETATION AND PALINSPASTIC RECONSTRUCTION OF
NORMAL FAULTS
As previously mentioned, earlier work (Stimac et al., 1987) in a portion of the
study area concluded that there is no kinematic linkage between the different sets of
normal faults described above and that individual normal faults are nearly planar in
geometry (Fig. 6)). Original observation and compilation of crosscutting relationships
between normal faults across the entire study area (Fig. 9) and structure contour maps of
normal faults (Fig. 10) are combined with an analysis of Tertiary tilting shown below to
interpret the style of extension in the study area. The interpretation provides the means to
palinspastically reconstruct Tertiary extension in a 20-km long cross section through the
study area.
Tertiary tilting
The consistent ~65° northeasterly dip of the oldest Tertiary rocks and of the
Tertiary-Proterozoic unconformity (Fig. 5) is consistent with slip on and concurrent
tilting of the southwest dipping normal faults. Orientations of foliation in the Proterozoic
Yavapai Schist can constrain the magnitude of Tertiary tilting of crystalline rocks in the
study area. The orientation of foliation in the Yavapai Schist regionally is commonly
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consistent over distances of 10’s of km (e.g., DeWitt et al., 2008). Thus any changes
observed in the orientation of foliation are likely the result of deformation subsequent to
the Proterozoic foliation-forming event. The most probable candidate for reorienting
foliation is Tertiary extension.
Foliation measurements of the Yavapai Schist in the Wickenburg Mountains,
which have been highly extended (Stimac et al., 1987), are compared to foliation
measurements of the Yavapai Schist 20 km to the north in the Bradshaw Mountains (Fig.
3). An area for which there is no evidence for significant Tertiary extension and tilting
(Rehrig et al., 1980; DeWitt et al., 2008). Measurements of foliation in the two areas are
compared in contoured equal area stereographic projection in Figures 11A and 11B, and
the average foliation varies significantly between the two areas. To further test the
hypothesis that the rigid body rotation was caused by tilting associated with Tertiary
extension, the foliation data from the Wickenburg Mountains are rotated 65° clockwise
about a horizontal axis trending 150° (Fig. 11C). This rotation would restore the amount
of Tertiary tilting recorded by the attitude of the Tertiary-Proterozoic unconformity and
by dips on Tertiary volcanic and sedimentary rocks across the study area. The mean plane
of the rotated Wickenburg Mountain foliation data (Fig. 11C) plots very close to the
mean plane of the foliation data from the unextended Bradshaw Mountains, strongly
suggesting that the Yavapai Schist and other Proterozoic rocks record the same
magnitude of Tertiary tilting observed in the Tertiary-Proterozoic unconformity and
Tertiary volcanic and sedimentary rocks across the study area.
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Style of extension
As mentioned above, debate surrounds the style of extension in the study area
(i.e., listric versus more planar, “domino-style” normal faults). Predictions of the
competing models are outlined here and tested against observations in the study area.
Listric normal faults produce different amounts of hanging-wall and footwall tilting
during fault slip as rocks in the hanging wall are transported down a curved fault plane.
Where multiple listric normal faults are active, the dip of beds in the hanging walls of
successive fault blocks in the transport direction should show progressively steeper dips
(e.g., Ramsay and Huber, 1987, p. 520). Observations in map view (Fig. 3) and
stereographic analysis (Fig. 11A-C) are not consistent with prediction listric fault
geometry. The Yavapai Schist, Tertiary-Proterozoic unconformity, and the oldest Tertiary
volcanic and sedimentary rocks in the study area are all tilted ~65° to the northeast during
Tertiary extension. This observation requires curvature on fault planes in the study area to
be minimal. Furthermore, where significant down-dip exposure of fault planes allows for
the determination of fault curvature at the surface (Fig. 10), it is indeed calculated to be
quite low (0.3°/km). Taken together, evidence in the study area controverts the
involvement of listric normal faults in extension and suggests that extension was
accommodated by superimposed sets of nearly planar, “domino-style” faults.
Interpretation of the normal faults
The grouping of the Tertiary normal faults into fault sets, each with a distinct
relative age, suggests that each set can be viewed as sequential generations of faults.
Hence, each generation is defined as a set of similarly oriented faults that moved more or
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less contemporaneously during specific time windows, as evidenced by their consistent
crosscutting. As the normal faults within a given set cut and extended the crystalline and
supracrustal rocks in the study area, the dip of the active fault planes rotated to lower
angles. Once the fault planes of a fault set rotated to angles that were kinematically
unfavorable for slippage (less than ~30°; Anderson, 1951), a new fault set with new fault
planes formed, and faults of the new set cut and progressively rotated the older fault sets
and any contained geologic elements, including porphyry systems. This repeated
sequence of events produced a cumulative northeastward tilting of ~65° as evidenced by
the present-day dips of the oldest Tertiary volcanic and sedimentary rocks, the dips of
Proterozoic-Tertiary unconformity, and change in foliation observed in the Yavapai
Schist between local extended and unextended terrains.
Approach to restoring movement on normal faults
Figures 12 and 13 show palinspastic reconstruction of the 20-km long cross
section in the study area and an interpretation of that reconstruction. Displacement along
the normal faults was removed in sequential order, from the youngest to the oldest
generation of normal faults (panels A through F in Fig. 12), as determined by dip
measurements and relative ages. The magnitude of slip on individual faults was
constrained using structural markers, including the Proterozoic-Tertiary unconformity,
contacts between various lithologies of Proterozoic metamorphic rocks, Tertiary volcanic
stratigraphy, and hydrothermal alteration assemblages. Tertiary sedimentary and volcanic
rocks were rotated to horizontal in the time slice of the reconstruction when they were
deposited.
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Due to the significant percentage of crystalline rocks in the study area, and thus
the paucity of structural markers in certain areas, a number of uncertainties remain in the
restoration. The three-dimensional shape of the igneous bodies is unknown; thus the form
chosen here is based on relationships that are plausible considering constraints imposed
by restoration of hydrothermal alteration patterns (Fig. 13B). As previously mentioned,
dips measurements are not available on some faults, either from this study or previous
work, due to lack of exposure. In these cases, crosscutting relationships were used to
assess the generation to which such faults belonged, and then dips measured from other
faults of the same fault set were used.
Examination of the district-scale reconstruction
The palinspastic reconstruction reveals a total of ~160% northeast-southwest
extension across the study area (Fig. 13A). The magnitude of northwest-southeast
directed extension is not constrained. The reconstruction implies the presence of two,
spatially distinct hydrothermal systems sourced from different cupolas of a Late
Cretaceous pluton (Fig. 13A). The Cretaceous pluton intrudes metasedimentary and
metavolcanic rocks in the west and metaplutonic rocks in the east. Potassic and
transitional potassic-greisen hydrothermal alteration exposed at Buckhorn Creek and
Sheep Mountain appear to be sourced from the easternmost cupola of the pluton, whereas
the greisen alteration hosted in Late Cretaceous granite in the Wickenburg Mountains is
part of a separate hydrothermal system centered on the western cupola of the pluton (Fig
13B). Hydrothermal alteration is zoned upward from greisen to potassic to transitional
greisen-potassic assemblages (Fig. 13B).
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Exploration targets
Leading up to and subsequent to the discovery of the Kalamazoo orebody
(Lowell, 1968), knowledge and understanding of post-mineralization Tertiary extension
in the Laramide porphyry province began to change exploration strategies. Tilted and
dismembered orebodies were eventually recognized to be common features in the Basin
and Range province (e.g., Proffett, 1977; Shaver and McWilliams, 1987; Seedorff, 1991;
Seedorff et al., 1996), and Wilkins and Heidrick (1995) suggested that orebodies in the
Basin and Range province should be assumed to be faulted and tilted until proven
otherwise. During the past decade, the importance of tilting of orebodies across the Basin
and Range province has continued to be emphasized by numerous workers (e.g., p. 276277 of Seedorff et al., 2005a; Maher, 2008; Stavast et al., 2008; Nickerson et al., 2010)
and is again demonstrated here.
Despite at least two drilling campaigns in the 1960’s and 2000’s, economic
mineralization has not yet been located at the Sheep Mountain West prospect. The
palinspastic reconstruction demonstrates that sulfide-bearing transitional greisen-potassic
alteration at Sheep Mountain and potassic alteration at Buckhorn Creek are both pieces of
a larger dismembered porphyry system. Potassically altered pieces of the same porphyry
system are shown to be “structurally covered” (Corn an Ahern, 1994) by Tertiary
volcanic and sedimentary rocks west of Sheep Mountain in the modern cross section (Fig.
12A). To our knowledge, this target has not been tested with a drill hole but significant
mineralization could be associated with potassic alteration.
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Additionally, it is likely that intense greisen alteration exposed in the Wickenburg
Mountains is the expression of a porphyry system (Maher, 2008; Seedorff et al., 2008;
Stavast et al., 2008). Whether the intensity of greisen alteration has any correlation to the
development of structurally higher levels of potassic and sericitic alteration, including
sulfide mineralization, remains uncertain. However, outcrops in the Wickenburg
Mountains demonstrate that significant magmatic fluids were released at least locally
from that portion of the Late Cretaceous pluton. Structurally higher levels that may
contain porphyry mineralization are not located in the line of section but may lie
underneath Quaternary and Tertiary cover southwest of the study area.
The targets generated by the district-scale palinspastic reconstruction provide an
example of a geologically based method for exploring beneath post-mineralization cover
rocks. In the Laramide porphyry province, geologically driven exploration underneath
post-mineralization cover has yielded several discoveries (e.g., Kalamazoo, Lowell,
1968; Resolution, Paul and Manske, 2005). Continued exploration in the province should
incorporate structural interpretations when designing exploration programs that may also
involve geophysical and geochemical techniques.
CLASSIFICATION OF PORPHYRY SYSTEMS NEAR WICKENBURG
Because an orebody has not been located in the study area, it is speculative to
classify the two indentified porphyry systems based on an economically dominant metal.
However, deposit classes are at least partially constrained by compositions of igneous
source rocks and may display some distinctive styles of hydrothermal alteration (Seedorff
et al., 2005a). For example, porphyry Au deposits are normally associated with dioritic
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host rocks, whereas porphyry W and Sn deposits are associated with rhyolitic and
rhyodacitic source rocks, respectively.
The granitic composition of the inferred Late Cretaceous source rocks for the
porphyry systems in the study area (Figs. 13A-B) may be indicative of porphyry
molybdenum deposits of the quartz monzonitic-granitic porphyry Mo-Cu or granitic
porphyry Mo subclasses (Seedorff et al., 2005a). Nonetheless, porphyry Cu-(Mo)
deposits in the Globe-Miami district (Fig. 2) are sourced from the Schultze Granite,
which is compositionally similar (Stavast, 2006; Maher, 2008) to the Late Cretaceous
granite in the study area. The conspicuous absence of large numbers of porphyry dikes in
the study area is also commonly observed in porphyry Mo-Cu systems (e.g., Hall
(Nevada Moly), Shaver, 1991; Buckingham, Loucks and Johnson, 1992). The transitional
greisen-potassic style of alteration documented on Sheep Mountain is perhaps suggestive
of a porphyry Mo-Cu system as well, because the only other well documented instance of
this distinctive style of high-level alteration is the Hall (Nevada Moly) porphyry Mo-Cu
system (Shaver, 1991).
The high Mo contents observed in the nearby porphyry resources at Sheep
Mountain East (0.04 % MoS2; Fig, 3) and Copper Basin (0.031% MoS2; Fig. 3) also are
suggestive of porphyry Mo-Cu affinities. Together, this evidence suggests that the
porphyry systems identified here are perhaps part of a cluster of porphyry Mo-Cu
systems located in the middle of what was previously thought to be a large gap in the
Laramide porphyry belt (Titley, 1982b).
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ARC-SCALE RECONSTRUCTION OF TERTIARY EXTENSION IN THE
LARAMIDE PORPHYRY COPPER BELT
To better understand spatial relationships of porphyry deposits in the Laramide
porphyry copper belt, a preliminary regional scale reconstruction of Cenozoic extension
has been undertaken (Figs. 14-17), revisiting a topic addressed earlier by Richard (1994)
but using a different approach. The approach taken here is first described, and then,
compared to the previous work.
Methodology
A compilation of strikes and dips of the oldest pre- and syn-extension Oligocene
and Miocene sedimentary and volcanic strata across the porphyry belt serves as the data
for the reconstruction (Fig. 14). The tilting information recorded by the bedding attitudes
provides a basis for grouping regions where the magnitude of extension was similar.
These data are then adapted to estimate a β factor utilizing the equations of Jackson and
McKenzie (1983). The β factor is calculated using the following equation:
β=
sin 𝜃
sin 𝜃′
where θ is the dip of a normal fault at its inceptions, and θ’ is the dip of the normal fault
after fault motion ceases. Several assumptions are made in the calculations: (1) the dips
of syn- and post-extension Tertiary rocks record only the effects of Cenozoic extension;
(2) normal faults were tilted to lower angles by the same amount that Tertiary beds were
tilted to steeper dips; (3) single sets of faults accommodated a maximum of 30° of tilting;
(4) all extension was northeast-southwest directed; (5) tilting was unidirectional; and (6)
any post-Laramide strike-slip faulting did not significantly alter deposit locations. It is
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unlikely that these conditions are met across the entire region considered here; however,
the generalization of Cenozoic extension in this manner allows for a palinspastic
reconstruction of the porphyry systems of the Laramide porphyry copper belt that is more
representative of its original form than the current, post-extension distribution.
Using geometric considerations, Jackson and McKenzie (1983) demonstrated that
a normal fault which is back-tilted from 60° to 30° produces a β factor of 1.73, equivalent
to 73% extension. In the strike and dip compilation used here, dips of 0° to 30°, 30° to
60°, and 60° to 90° are grouped together. An average amount of extension was assigned
for each domain (Fig. 15), and a regional contour map of the magnitude extension was
created. Locations of porphyry deposits were restored to the northeast by removing the
cumulative amount of extension between the modern location of a deposit and the
unextended terrain outside the Basin and Range (either the Colorado Plateau or the
southern Rocky Mountains).
In addition to the uncertainties introduced from the assumptions made in its
construction, further uncertainties about the distribution of porphyry deposits arise from
their degree of preservation and the limited modern exposure of the porphyry copper belt.
Denudation prior to or during Tertiary extension in Arizona could have completely
eroded porphyry systems in the arc. Furthermore, Quaternary and Tertiary sedimentary
and volcanic rocks cover greater than 50 percent of the surface in the Basin and Range
province of Arizona (Reynolds, 1988). These younger rocks likely conceal additional
Laramide porphyry systems. Thus, the geometry of the exposed porphyry deposits of the
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Laramide magmatic arc in the reconstruction should be considered representative but not
absolute.
As previously mentioned, this study follows in the path of a previous arc-scale
reconstruction by Richard (1994). Central to both approaches were the process of
delineating extensional domains using tilting information recorded in Tertiary rocks and
restoring extension using the equations of Jackson and McKenzie (1983). However, the
two reconstructions differ in one important way. The earlier work averaged the dips of
Tertiary rocks to determine tilting within domains, as opposed to estimating tilting using
the dips of only the oldest pre- or syn-extension Tertiary rocks. By averaging the dips of
all Tertiary rocks, calculations of extension are influenced by rocks which only record a
portion of the extension with a domain. Thus, the earlier calculations significantly
underestimated the amount of extension.
Examination of the arc-scale reconstruction of the Laramide porphyry beltThe
Laramide porphyry copper belt is a manifestation of the Laramide magmatic arc of
southwestern North America (Titley, 1982b). Hence, when discussing the geometry of
the porphyry copper belt it is appropriate to call on terminology used to describe
magmatic features in continental arcs. It is important to consider, however, that the ages
of Laramide porphyry deposits span ~75-55 Ma (Titley, 1982b; Seedorff et al, 2005b).
Thus, the reconstruction of the porphyry belt shown here is a time-integrated product, not
a snapshot of arc magmatism.
The reconstructed distribution of porphyry deposits of the Laramide arc (Fig. 16,
17A) yields a variably well defined zone, with gaps and clusters of deposits along the 700
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km of strike length parallel to the Laramide plate margin. The apparent axis of the
porphyry copper belt (dashed in Figure 17A) extends from Mineral Park to Red
Mountain. Along-axis deposits lie between Mineral Park and Red Mountain. Forearc
deposits include Ajo, Cananea, and La Caridad, and rear-arc deposits include the Safford
district, Morenci, Tyrone, Chino, and Hillsboro. Along-axis spacing between the deposits
is variable. Deposits in the Globe-Miami, Safford. and Pima districts are separated by
only a few kilometers, whereas Sheep Mountain and Ajo are separated by an apparent
gap of more than 100 km along the axis of the magmatic arc.
Across-axis spacing of deposits is also highly variable. Resolution lies 20 km
from the deposits of the Globe-Miami district, but La Caridad is separated from Hillsboro
by 240 km. Casa Grande and Vekol, as well as deposits within the Globe-Miami and
Pima districts, are separated by less than 10 km across axis. In the Globe-Miami and
Pima districts, studies have shown that the clustering of deposits reflects in part the
dismemberment by Tertiary normal faults (Stavast, 2006; Maher, 2008; Stavast et al.,
2008). That is, the named deposits identified today were once parts of larger porphyry
systems, as is the case in the classic example of San Manuel-Kalamazoo (Lowell, 1968).
This reconstruction, using dips of Tertiary beds to make estimates of the amount
of extension, is a basis for comparison for future arc-scale structural reconstructions of
the porphyry belt. For example, a more precise and time-consuming approach would be
to perform fault-by-fault restorations, of the type employed here only in the Wickenburg
area, across the arc at numerous locations up and down the arc.
189
DISCUSSION
Style of extension in western Arizona
As introduced above, debate surrounds the style of extension in western Arizona,
and three competing models have been put forward (Fig. 4). Previous work in the Vulture
Mountains concluded that extension was accommodated on strongly listric normal faults
(Rerhig et al., 1980). Results shown here indicate that extension in the study area was
accommodated via normal faulting similar to the “domino-style” model of extension.
Whereas similar relationships observed in map pattern between faults, hanging wall
rocks, and footwall rocks do indicate a similar style of extension in the study area and the
Vulture Mountains, evidence within the study area precludes normal faults from having a
strongly listric geometry.
The principal difference observed between extended rocks in the Vulture
Mountains and the study area, is that rocks in the Vulture Mountains are more tilted
(~85° northeast). An increase in the amount of tilting in the Vulture Mountains can be
explained using the style of extension demonstrated in the study area if an additional set
of southwest dipping normal faults had been active there. Evidence for such a fault set
has been documented at the Vulture mine, where a normal fault has been back-tilted
through horizontal to a dip of 15° northeast overturned (Grubensky and Shipman, 2004).
This fault set has been tilted approximately an additional 20° to the southwest compared
to the low-angle faults exposed in the Wickenburg Mountains (Fig. 10), consistent with
the ~20° increase in tilting observed in the supracrustal rocks in the Vulture Mountains.
Thus, it is proposed here that both the Vulture Mountains and the study area were part of
190
a regional system of superimposed sets of rotating planar normal faults that
accommodated significant southwest-northeast extension between ~25 and 15 Ma.
The Harcuvar and Harquahala metamorphic core complexes are located
approximately 30 km west of the Vulture Mountains. The timing of extension in these
core complexes and in the study area was similar (~25-15 Ma, Rehig et al., 1980; Carter
et al., 2004). However, in the Harcuvar and Harquahala Mountains upper plate rocks
were transported to the northeast, opposite the transport direction observed in the study
area and in the Vulture Mountains (Spencer and Reynolds, 1990). Mylonitic rocks in the
core complexes are interpreted by Reynolds and Spencer (1985) to have formed during
slip on the Bullard detachment fault. According to Reynolds and Spencer (1985), the
Bullard fault initiated slip at a low angle (10°-20°), accommodated as much as 50 km of
slip, and captured the displacement of higher-angle faults that are interpreted to sole into
the detachment fault (Carter et al., 2004). This style of extension varies significantly from
was is observed in the study area, but has also been proposed to explain the formation of
the metamorphic core complexes further west in the Colorado River extensional corridor
in western Arizona and southeastern California (Howard and John, 1987; Lister and
Davis, 1989).
Metamorphic core complexes are known to be mid-crustal expressions of
extension (Davis, 1980). The lack of mylonitic fabrics exposed in the study area and the
Vulture Mountains suggests that normal faulting has only exposed the upper-crustal
expressions of extension in these areas. Currently, it is difficult to reconcile the different
styles of extension proposed here for upper-crustal rocks with models proposed for mid-
191
crustal extension in the nearby Harcuvar and Harquahala metamorphic core complexes
(Fig. 3). Further study is required to determine what factors control the different style of
extension in each area, or whether the proposed style of extension in the metamorphic
core complexes should be reconsidered.
Comparison of the scale and geometry of the Laramide magmatic arc to other arcs
Whereas exploration in the Laramide porphyry copper belt has evolved to
consider deposit-scale (e.g., Lowell, 1968; Wilkins and Heidrick, 1995), district-scale
(e.g., Stavast et al., 2008), and sometimes regional-scale extension (e.g., Maher, 2008),
little attention has been given to the effects of extension at the scale of the Laramide
porphyry belt (Richard, 1994), and a comparison of the pre-extension geometry of the
Laramide porphyry copper belt to magmatic features in other well studied arcs is lacking.
The length, breath, and spacing between porphyry centers in the reconstructed
Laramide porphyry copper belt is compared to other magmatic features in the prolific
central Chilean porphyry copper sub-belt in the Miocene-early Pliocene magmatic arc
(Sillitoe and Perelló, 2005) and the Quaternary Cascade volcanic arc of northwestern
North America (Hildreth, 2007) in Figure 17A-C. The magmatic features in each of the
arcs are distinctive. For example, as previously mentioned, the Laramide porphyry belt
spans about 20 million years of activity (~75-55 Ma, Lang and Titley, 1998; Seedorff et
al., 2005b) and was not necessarily stationary during that interval. The central Chilean
sub-belt—somewhat arbitrarily constrained in length—was active for about 12 million
years (16-4 Ma, Sillitoe and Perelló, 2005). The Quaternary portion of the Cascade arc
includes only its last two million years of activity (Hildreth, 2007), and this portion is not
192
yet sufficiently eroded to reveal much about its potential for porphyry mineralization
(e.g., John et al., 2005).
The length of the Laramide porphyry copper belt, at 700 km, is greater than the
400-km long Miocene-early Pliocene porphyry copper sub-belt of central Chile, but
shorter than the 1,250 km long chain of volcanic fields Quaternary Cascade arc. Spacing
between deposits (and volcanic fields) along strike is similar, with all three arcs having
area of clustered magmatic activity, as well as apparent gaps in magmatic activity greater
than 100 km. One clear difference is the breadth of the Laramide porphyry copper belt
south of Red Mountain, where it reaches a maximum width of 240 km. The maximum
across axis width between magmatic features in the other arcs is less than 150 km.
Clearly, there is no blueprint for magmatic features in convergent oceaniccontinental plate margin arc. Differences in the interaction between down-going slabs,
mantle wedges, and continental crust will make each arc distinctive. However, when
compared at the entire arc scale, differences in geometry between the reconstructed
Laramide magmatic arc (as revealed by the porphyry copper belt) and other arcs appear
to be minimal.
CONCLUSIONS
The effects of Tertiary extension on the geometry of Laramide porphyry systems
has been demonstrated at the district and porphyry belt scale. Original reconnaissance
mapping was combined with previous detailed mapping to serve as data for a 20 km long
palinspastic reconstruction. The reconstruction revealed that two porphyry-style
hydrothermal systems emanate from a Laramide aged pluton exposed in the study area.
193
Hydrothermal alteration is zoned from greisen at deeper levels, to potassic and
transitional greisen-potassic at higher levels. Five superimposed sets of normal faults,
which initially developed and high angles and then rotated to lower angles during
extension, dismembered the porphyry systems and buried potentially well-mineralized
fault blocks underneath Tertiary volcanic and sedimentary rocks. This upper-crustal style
of extension differs from mid-crustal models for extension in the nearby Harcuvar and
Harquahala metamorphic core complexes which formed contemporaneously. Further
study will be required to rectify the apparent inconsistency in the style of extension in the
region.
Extension at the scale of the Laramide porphyry belt was quantified using a
compilation strikes and dips documented in pre- and syn-extension rocks across the
porphyry belt. The tilting information recorded by the attitudes provides a basis to group
regions where the magnitude of extension was similar, and then is adapted to estimate β
factor . Tertiary extension was then restored quantitatively to reveal the pre-extension
geometry of the arc, where the majority of porphyry deposits clearly define a 100 km
wide axis, and others lie in fore-arc or rear-arc settings. The arc geometry, once extension
is restored, closely resembles other magmatic arcs formed at convergent oceaniccontinental plate boundaries demonstrating.
ACKNOWLEDGMENTS
We would like to thank Bronco Creek Exploration for logistical and financial
support of this project, including helicopter support at Sheep Mountain. Additional
financial support came from Science Foundation Arizona and an award from the Society
194
of Economic Geologists student research fund. Dave Maher and David Johnson
introduced us to the study area, and discussions in the field with Dave Maher and Doug
Kreiner were also helpful. Early reviews of this manuscript by Mark Barton and George
Davis greatly improved its quality.
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FIGURE CAPTIONS
Figure 1. Location map depicting selected ore deposits which lie in the Basin and Range
province of western North America. MCC = metamorphic core complex. Dashed box
indicates location of Figure 3.
Figure 2. Index map of porphyry deposits in the Laramide porphyry copper belt.
Modified from Titley, (1982b).
Figure 3. Genearalized geologic map of western Arizona showing location of the districtscale study area (dashed box) and nearby mountain ranges discussed in the text. MCC =
metamorphic core complex (geology from Reynolds, 1988).
Figure 4. Three models proposed to explain the link between upper-crustal and midcrustal extension in the Basin and Range province. A. Extension accommodated along a
“detachment” fault which initiates slip at a dip angle < 30° (after Wernicke, 1985). B.
Extension accommodated along a strongly listric “detachment” fault which is up-warped
by isostacy during extension (after Spencer, 1984). C. Extension accommodated along
two sets of planar normal faults which rotate to lower dips during extension (after
Dickinson, 1991).
204
Figure 5. Generalized geologic map across the study area depicting rock units, faults,
selected bedding orientations, and localities discussed in the text. Tertiary volcanic rocks
in the Hells Gate Formation and older units are grouped in the Tertiary lower volcanic
unit. Tertiary volcanic rocks younger than the Hells Gate Formation are grouped in the
Tertiary upper volcanic unit. Geology from Peterson (1985),_Capps et al. (1986), Stimac
et al. (1987) and Powers (unpublished map).
Figure 7. Geologic map and cross section D-D’, digitized from Stimac et al. (1987)
Figure illustrates the detailed pre-existing mapping of rock type and structural geology in
the district-scale study area. Location of map shown in Figure 6.
Figure 7. Reconnaissance map of hydrothermal alteration in the study area. Key for rock
units faded in the background is found in Figure 5.
Figure 8. Photographs of styles of veins and associated alteration in the study area. A.
Unaltered Cretaceous granite. B. Quartz-muscovite-pyrite±chalcopyrite±K-feldspar vein
hosted in Cretaceous granite; an example of greisen style alteration. B. Quartz+Kfeldsspar+white mica+pyrite±chalcopyrite vein with a biotite envelope cutting Yavapai
Schist at Buckhorn Creek; an example of potassic alteration. C. Quartz+K-feldspar±white
mica±sulfide veins cut by quartz+K-feldspar+white mica+sulfide veins with white mica
halos hosted in Proterozoic gneiss at Sheep Mountain West prospect. The crosscutting
vein is an example of the transitional greisen-potassic style of alteration.
Figure 9. Normal faults in the study area grouped into five sets, numbered from oldest to
youngest. Faults within each set have similar strikes and dips, as well as, common cross
cutting relationships.
205
Figure 10. Structure contour map of two faults from set one in the exposed in the
Wickenburg Mountains. A. Structure contour map with topography as a base layer. B.
Structure contour map with the hanging wall and footwall of each fault shaded. Dips are
calculated across two intervals on the southwestern low-angle fault, illustrating that the
dip of the faults changes only slightly over 6 km of nearly continuous down dip exposure.
The calculated curvature is 0.5°/km.
Figure 11. Contoured poles to planes of foliation measurements in the Yavapai Schist
depicted on stereonets using equal area lower hemisphere projections. A. Foliation
measurements in the Yavapai Schist from the unextended southern Bradshaw Mountains
20 km north of Sheep Mountain. Data from DeWitt et al. (2008). B. Foliation
measurements in the Yavapai Schist from the Wickenburg Mountains. Data from Stimac
et al. (1987). C. Rotation of the data in panel B 65° clockwise about a horizontal axis
striking 150°. The rotation restores Tertiary tilting in the study area. The rotated data
from the Wickenburg Mountains very closely match the data from the Bradshaw
Mountains, indicating that congruent amounts of tilting are recorded in the Yavapai
Schist, the Proterozoic-Tertiary unconformity, and Tertiary sedimentary and volcanic
rocks.
Figure 12. Panels depicting the palinspastic reconstruction of cross section A to A’.
Locations of endpoints and key to rock units are located on Figure 5. A. Modern cross
section. B. Restoration of the 5th set of normal faults. C. Restoration of the 4th set of
normal faults. D. Restoration of the 3rd set of normal faults. E. Restoration of the 2nd set
of normal faults. The fault in this set strikes nearly perpendicular to the line of section.
206
The true orientation of this fault prior to slip was 110°, 60° SW. F. Restoration of the 1st
set of normal faults.
Figure 13. An interpretive cross section constrained by the palinspastic reconstruction.
Unit legend the same as Figure 5. A. The interpretation is faded in the background, and
pieces of the reconstruction are shown in the foreground. Geographic locations discussed
in the text are indicated with thin lines. Two exploration targets are indentified which are
located directly above the two cupolas of the Cretaceous pluton. B. Interpretation of the
zoning patterns in hydrothermal alteration in the two hydrothermal systems identified in
the study area.
Figure 14. Compilation of strikes and dips of Tertiary sedimentary and volcanic rocks.
(rock units from Reynolds, 1988)
Figure 15. Domains of Cenozoic extension constrained by dip measurements in Tertiary
sedimentary and volcanic rocks (Fig. 14). Locations of porphyry deposits shown in the
background.
Figure 16. Index map of porphyry deposits in their present and restored location.
Figure 17. Comparison of porphyry systems of the reconstructed Laramide porphyry
copper belt to features in other magmatic arcs. A. The reconstructed location of porphyry
systems of the Laramide magmatic arc. B. Porphyry copper systems of Miocene-Early
Pliocene magmatic arc of central Chile (after Sillitoe and Perelló, 2005). C. The
Quaternary Cascade magmatic arc of northwestern North America (after Hildreth, 2007),
showing major volcanic centers. Note the change in scale from panels A and B to panel
C.
207
Figure 1.
208
Figure 2.
209
Figure 3.
210
Figure 4.
211
Figure 5.
212
Figure 6.
Figure 6 continued.
213
214
Figure 7.
215
Figure 8.
216
Figure 9.
217
Figure 10.
218
Figure 11.
219
Figure 12.
220
Figure 13.
221
Figure 14.
222
Figure 15.
223
Figure 16.
224
Figure 17.
225
APPENDIX D: ELECTRON MICROPROBE ANALYSIS OF FELDSPAR, SHEET
SILICATES, EPIDOTE, AND AMPHIBOLES FROM TEA CUP AND EAGLE PASS,
ARIZONA
Figure 1. Location map of samples from the Tea Cup porphyry system, Pinal County,
Arizona
Figure 2. Location map of samples from the Eagle Pass porphyry system, Graham
County, Arizona
226
Figure 1.
227
Figure 2.
228
Table 1. Location of Tea Cup eletron microprobe samples
Position
Sample #
(Lat/Lon hddd mm.mmm')
on Fig. 1
Sample Name
TV07 08
0
N33 04.165 W111 03.203
TC 004
1
N33 04.098 W111 03.798
TC 011
2
N33 04.029 W111 03.923
TC 010
3
N33 04.211 W111 03.974
TC 008
4
N33 04.001 W111 03.212
TC 009
5
N33 04.020 W111 03.164
TC 007
6
N33 04.015 W111 03.146
TC 001
7
N33 03.945 W111 03.600
TC 002
8
N33 04.071 W111 03.235
SP 004
9
N33 04.463 W111 03.879
SP 007
10
N33 04.423 W111 03.820
SP 009
11
N33 05.877 W111 01.109
SP 014
12
N33 06.024 W111 02.008
SP 017
13
N33 02.783 W111 11.522
SP 019
14
N33 02.350 W111 13.547
SP 020
15
N33 02.352 W111 13.504
SP 023
16
N33 02.335 W111 13.412
SP 025
17
N33 02.725 W111 13.199
SP 029
18
N33 01.880 W111 11.456
SP 032
19
N33 02.535 W111 11.493
SP 034
20
N33 02.929 W111 11.876
SP 035
21
N33 03.263 W111 12.121
SP 043
22
N33 05.041 W111 12.816
SP 048
23
N33 03.426 W111 12.948
SP 073b
24
N33 02.281 W111 11.059
SP 075
25
N33 02.773 W111 13.098
SP 079
26
N33 02.716 W111 13.075
SP 081
27
N33 02.670 W111 12.925
SP 092
28
N33 02.562 W111 13.162
SP 097
29
N33 02.391 W111 13.089
SP 114
30
N33 05.114 W111 04.773
SP 115
31
N33 05.128 W111 04.819
SP 123
32
N33 05.506 W111 02.282
229
Table 2. Location of Eagle Pass eletron microprobe samples
Location
Sample #
(Lat/Lon hddd mm.mmm')
on Fig. 2
Sample name
MW SPCHEM
0
N32 48.840 W110 07.354
MW 001
1
N32 48.392 W110 06.688
MW NACA2
2
N32 48.452 W110 06.804
MW NACA3
3
N32 48.612 W110 07.113
MW ALT5
4
N32 49.235 W110 07.808
FRS ORCLE
5
N32 47.738 W110 06.599
EP 005
6
N32 46.678 W110 07.598
EP 007
7
N32 46.448 W110 07.362
EP 006
8
N32 46.207 W110 07.336
EP 016
9
N32 45.198 W110 08.139
EP 017
10
N32 45.304 W110 08.153
EP 021
11
N32 45.531 W110 07.973
EP 022
12
N32 45.576 W110 07.934
EP 024
13
N32 48.212 W110 07.275
EP 033
14
N32 44.951 W110 07.830
EP 034
15
N32 44.968 W110 07.776
EP 035
16
N32 44.974 W110 07.751
EP 037
17
N32 44.994 W110 07.452
EP 038
18
N32 45.336 W110 07.361
EP 040
19
N32 43.295 W110 05.820
EP 042
20
N32 44.224 W110 05.923
EP 046
21
N32 43.114 W110 07.389
EP 070
22
N32 48.144 W110 10.096
EP 086
23
N32 46.466 W110 07.674
230
Table 3. Normalized microprobe data: feldspars from Tea Cup
SP 004
SP 007
SP 009
Sample number
kspar1 SP 004 plg1
plag2
SP 007 plg3 kspar2
Replacing
kspar
kspar
plag
Host rock
Yg
Yg
Yg
Yg
Kpd
SiO2
64.90
68.95
68.95
68.70
93.36
TiO2
0.00
0.00
0.00
0.00
0.04
Al2O3
18.02
19.42
19.63
19.46
3.01
Cr2O3
0.00
0.00
0.00
0.00
0.00
Fe2O3
0.07
0.00
0.00
0.00
0.00
FeO
0.00
0.00
0.03
0.00
0.13
MgO
0.00
0.00
0.00
0.00
0.00
MnO
0.00
0.00
0.01
0.00
0.00
CaO
0.00
0.12
0.42
0.34
0.07
Na2O
0.33
12.23
11.74
11.61
0.09
K2O
15.88
0.02
0.06
0.06
1.88
F
0.00
0.07
0.00
0.00
0.43
Cl
0.00
0.01
0.00
0.00
0.00
Total
99.20
100.79
100.85
100.18
98.83
Based on IV=4
Si (T)
3.01
3.00
2.99
3.00
3.85
Al (T)
0.99
1.00
1.01
1.00
0.15
Fe3+ (T)
0.00
0.00
0.00
0.00
0.00
Na (A)
0.03
1.03
0.99
0.98
0.01
K (A)
0.94
0.00
0.00
0.00
0.10
Ca (A)
0.00
0.01
0.02
0.02
0.00
Mg (A)
0.00
0.00
0.00
0.00
0.00
Ti (A)
0.00
0.00
0.00
0.00
0.00
Cr (A)
0.00
0.00
0.00
0.00
0.00
Mn (A)
0.00
0.00
0.00
0.00
0.00
F (X)
0.00
0.01
0.00
0.00
0.06
Cl (X)
0.00
0.00
0.00
0.00
0.00
O
8.00
7.99
8.00
8.00
7.94
End Member
Or#
An#
Ab#
0.95
0.01
0.04
0.97
0.00
0.03
0.00
0.01
0.99
0.00
0.02
0.98
0.91
0.03
0.06
SP 014
kspar2
Yg
65.18
0.02
17.92
0.00
0.00
0.00
0.00
0.00
0.00
0.88
15.23
0.00
0.04
99.27
3.02
0.98
0.00
0.08
0.90
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
0.92
0.00
0.08
231
Table 3. Normalized microprobe data: feldspars from Tea Cup
SP 020
Sample number SP 014 plg1 SP 017 plg1 SP 017 ser1 SP 019 plg1 kspar1
Replacing
plag
plag
plag
Host rock
Yg
Kpd
Kpd
Yg
Yg
SiO2
68.71
67.12
68.03
64.69
63.95
TiO2
0.00
0.04
0.04
0.00
0.03
Al2O3
19.37
20.02
20.04
19.24
18.12
Cr2O3
0.02
0.00
0.00
0.01
0.02
Fe2O3
0.00
0.00
0.00
0.00
0.03
FeO
0.02
0.00
0.04
0.12
0.00
MgO
0.00
0.02
0.00
0.00
0.00
MnO
0.02
0.03
0.00
0.02
0.00
CaO
0.32
0.17
0.28
2.74
0.00
Na2O
11.59
11.79
12.22
11.17
0.33
K2O
0.16
0.02
0.07
0.04
15.87
F
0.04
0.00
0.00
0.00
0.00
Cl
0.06
0.00
0.01
0.00
0.00
Total
100.28
99.21
100.74
98.03
98.35
Based on IV=4
3.00
2.96
2.97
2.96
3.00
Si (T)
1.00
1.04
1.03
1.04
1.00
Al (T)
0.00
0.00
0.00
0.00
0.00
Fe3+ (T)
0.98
1.01
1.03
0.99
0.03
Na (A)
0.01
0.00
0.00
0.00
0.95
K (A)
0.02
0.01
0.01
0.13
0.00
Ca (A)
0.00
0.00
0.00
0.00
0.00
Mg (A)
0.00
0.00
0.00
0.00
0.00
Ti (A)
Cr (A)
0.00
0.00
0.00
0.00
0.00
Mn (A)
0.00
0.00
0.00
0.00
0.00
F (X)
0.01
0.00
0.00
0.00
0.00
Cl (X)
0.00
0.00
0.00
0.00
0.00
O
7.99
8.00
8.00
8.00
8.00
End Member
Or#
An#
Ab#
0.01
0.02
0.98
0.00
0.01
0.99
0.00
0.01
0.98
0.00
0.12
0.88
0.97
0.00
0.03
SP 020
kspar2
Yg
64.26
0.00
18.18
0.01
0.00
0.00
0.00
0.01
0.00
1.09
15.02
0.00
0.01
98.58
3.00
1.00
0.00
0.10
0.89
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
0.90
0.00
0.10
232
Table 3. Normalized microprobe data: feldspars from Tea Cup
SP 020
SP 023
SP 023
SP 025
SP 025
Sample number
kspar3
kspar1
kspar2
kspar1
kspar2
Replacing
Host rock
Yg
Yg
Yg
Yg
Yg
SiO2
64.80
65.46
64.81
64.54
65.00
TiO2
0.00
0.07
0.00
0.01
0.00
Al2O3
18.43
18.52
18.43
18.42
18.32
Cr2O3
0.00
0.01
0.00
0.00
0.05
Fe2O3
0.12
0.13
0.00
0.04
0.00
FeO
0.00
0.00
0.02
0.00
0.00
MgO
0.00
0.01
0.00
0.00
0.00
MnO
0.00
0.00
0.00
0.00
0.00
CaO
0.00
0.00
0.00
0.00
0.00
Na2O
0.40
0.51
0.55
0.49
0.58
K2O
16.10
15.79
16.27
15.55
15.78
F
0.00
0.19
0.33
0.00
0.17
Cl
0.01
0.02
0.01
0.00
0.00
Total
99.87
100.62
100.28
99.05
99.83
Based on IV=4
2.99
2.99
3.00
2.99
3.00
Si (T)
1.00
1.00
1.00
1.01
1.00
Al (T)
0.00
0.00
0.00
0.00
0.00
Fe3+ (T)
0.04
0.05
0.05
0.04
0.05
Na (A)
0.95
0.92
0.96
0.92
0.93
K (A)
0.00
0.00
0.00
0.00
0.00
Ca (A)
0.00
0.00
0.00
0.00
0.00
Mg (A)
0.00
0.00
0.00
0.00
0.00
Ti (A)
Cr (A)
0.00
0.00
0.00
0.00
0.00
Mn (A)
0.00
0.00
0.00
0.00
0.00
F (X)
0.00
0.03
0.05
0.00
0.03
Cl (X)
0.00
0.00
0.00
0.00
0.00
O
8.00
7.97
7.95
8.00
7.97
End Member
Or#
An#
Ab#
0.96
0.00
0.04
0.95
0.00
0.05
0.95
0.00
0.05
0.95
0.00
0.05
0.95
0.00
0.05
SP 025 plg1
Yg
67.91
0.01
20.14
0.00
0.06
0.00
0.00
0.01
0.53
11.10
0.20
0.00
0.00
99.96
2.96
1.04
0.00
0.94
0.01
0.02
0.00
0.00
0.00
0.00
0.00
0.00
8.00
0.01
0.03
0.96
233
Table 3. Normalized microprobe data: feldspars from Tea Cup
SP 029
SP 032
Sample number
kspar1 SP 029 plg1 kspar1 SP 032 plg1 SP 032 plg2
Replacing
plag
plag
Host rock
Kpd
Kpd
Kpd
Kpd
Kpd
SiO2
63.98
99.51
64.05
67.60
59.68
TiO2
0.00
0.01
0.00
0.03
0.00
Al2O3
18.42
0.24
18.79
20.49
24.57
Cr2O3
0.02
0.02
0.00
0.00
0.03
Fe2O3
0.04
0.11
0.03
0.00
0.02
FeO
0.00
0.00
0.00
0.00
0.16
MgO
0.00
0.00
0.00
0.00
0.00
MnO
0.01
0.00
0.00
0.00
0.00
CaO
0.00
0.01
0.01
0.78
6.43
Na2O
0.28
0.02
0.54
11.29
7.51
K2O
15.83
0.01
15.69
0.23
0.70
F
0.00
0.06
0.00
0.05
0.00
Cl
0.01
0.01
0.00
0.00
0.00
Total
98.58
99.98
99.13
100.46
99.11
Based on IV=4
2.99
3.98
2.97
2.95
2.69
Si (T)
1.01
0.01
1.03
1.05
1.31
Al (T)
0.00
0.00
0.00
0.00
0.00
Fe3+ (T)
0.02
0.00
0.05
0.95
0.66
Na (A)
0.94
0.00
0.93
0.01
0.04
K (A)
0.00
0.00
0.00
0.04
0.31
Ca (A)
0.00
0.00
0.00
0.00
0.00
Mg (A)
0.00
0.00
0.00
0.00
0.00
Ti (A)
Cr (A)
0.00
0.00
0.00
0.00
0.00
Mn (A)
0.00
0.00
0.00
0.00
0.00
F (X)
0.00
0.01
0.00
0.01
0.00
Cl (X)
0.00
0.00
0.00
0.00
0.00
O
8.00
7.99
8.00
7.99
8.00
End Member
Or#
An#
Ab#
0.97
0.00
0.03
0.96
0.02
0.02
0.95
0.00
0.05
0.01
0.04
0.95
0.04
0.31
0.65
SP 035
plag3
Yg
64.83
0.00
18.02
0.02
0.00
0.05
0.01
0.00
0.00
0.64
15.73
0.13
0.00
99.38
3.01
0.99
0.00
0.06
0.93
0.00
0.00
0.00
0.00
0.00
0.02
0.00
7.98
0.94
0.00
0.06
234
Table 3. Normalized microprobe data: feldspars from Tea Cup
SP 043
Sample number SP 035 plg2 kspar1 SP 043 plg1 SP 043 plg2 SP 048 plg1 SP 048 plg2
Replacing
kspar
plag
plag
plag
Host rock
Yg
Yg
Yg
Yg
Yg
Yg
SiO2
64.54
65.03
69.18
67.70
68.63
68.00
TiO2
0.01
0.00
0.00
0.00
0.00
0.00
Al2O3
22.25
18.00
19.21
18.76
19.59
19.78
Cr2O3
0.00
0.00
0.00
0.00
0.01
0.00
Fe2O3
0.00
0.00
0.00
0.00
0.00
0.00
FeO
0.03
0.05
0.08
0.02
0.01
0.04
MgO
0.00
0.00
0.00
0.00
0.01
0.00
MnO
0.04
0.00
0.00
0.00
0.01
0.00
CaO
3.47
0.00
0.23
0.04
0.02
0.24
Na2O
9.70
0.67
11.64
11.72
11.80
12.10
K2O
0.17
15.74
0.13
0.09
0.03
0.09
F
0.00
0.01
0.00
0.00
0.30
0.07
Cl
0.00
0.00
0.01
0.00
0.00
0.00
Total
100.21
99.50
100.48
98.33
100.27
100.30
Based on IV=4
2.84
3.01
3.01
3.01
2.99
2.98
Si (T)
1.16
0.99
0.99
0.99
1.01
1.02
Al (T)
0.00
0.00
0.00
0.00
0.00
0.00
Fe3+ (T)
0.83
0.06
0.98
1.01
1.00
1.03
Na (A)
0.01
0.93
0.01
0.01
0.00
0.00
K (A)
0.16
0.00
0.01
0.00
0.00
0.01
Ca (A)
0.00
0.00
0.00
0.00
0.00
0.00
Mg (A)
0.00
0.00
0.00
0.00
0.00
0.00
Ti (A)
Cr (A)
0.00
0.00
0.00
0.00
0.00
0.00
Mn (A)
0.00
0.00
0.00
0.00
0.00
0.00
F (X)
0.00
0.00
0.00
0.00
0.04
0.01
Cl (X)
0.00
0.00
0.00
0.00
0.00
0.00
O
8.00
8.00
8.00
8.00
7.96
7.99
End Member
Or#
An#
Ab#
0.01
0.16
0.83
0.94
0.00
0.06
0.01
0.01
0.98
0.01
0.00
0.99
0.00
0.00
1.00
0.00
0.01
0.98
235
Table 3. Normalized microprobe data: feldspars from Tea Cup
SP 073b
SP 081
SP 081
Sample number
kspar1
kspar2 SP 081 plg1 SP 081 plg2
kspar1
Replacing
plag
plag
plag
Host rock
Yg
Yg
Yg
Yg
Yg
SiO2
64.28
64.49
64.29
68.16
68.56
TiO2
0.01
0.00
0.11
0.05
0.05
Al2O3
18.65
18.64
18.61
19.96
19.86
Cr2O3
0.00
0.00
0.02
0.00
0.02
Fe2O3
0.06
0.14
0.02
0.00
0.00
FeO
0.00
0.00
0.00
0.01
0.00
MgO
0.01
0.00
0.00
0.01
0.00
MnO
0.00
0.00
0.00
0.00
0.00
CaO
0.00
0.02
0.00
0.23
0.37
Na2O
0.97
1.08
0.78
11.81
11.55
K2O
15.08
15.39
15.45
0.15
0.09
F
0.08
0.00
0.00
0.14
0.00
Cl
0.00
0.00
0.00
0.00
0.00
Total
99.10
99.77
99.27
100.46
100.51
Based on IV=4
2.98
2.98
2.98
2.97
2.98
Si (T)
1.02
1.02
1.02
1.03
1.02
Al (T)
0.00
0.00
0.00
0.00
0.00
Fe3+ (T)
0.09
0.10
0.07
1.00
0.97
Na (A)
0.89
0.91
0.91
0.01
0.01
K (A)
0.00
0.00
0.00
0.01
0.02
Ca (A)
0.00
0.00
0.00
0.00
0.00
Mg (A)
0.00
0.00
0.00
0.00
0.00
Ti (A)
Cr (A)
0.00
0.00
0.00
0.00
0.00
Mn (A)
0.00
0.00
0.00
0.00
0.00
F (X)
0.01
0.00
0.00
0.02
0.00
Cl (X)
0.00
0.00
0.00
0.00
0.00
O
7.99
8.00
8.00
7.98
8.00
End Member
Or#
An#
Ab#
0.91
0.00
0.09
0.90
0.00
0.10
0.93
0.00
0.07
0.01
0.01
0.98
0.01
0.02
0.98
SP 097
kspar1
plag
Yg
63.58
0.01
18.30
0.00
0.11
0.00
0.01
0.00
0.00
0.64
15.41
0.00
0.01
98.06
2.98
1.01
0.00
0.06
0.92
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
0.94
0.00
0.06
236
Table 3. Normalized microprobe data: feldspars from Tea Cup
SP 114
SP 123
Sample number
kspar2 SP 114 plg1 SP 114 plg2 SP 115 plg1 kspar1
Replacing
plag
plag
Host rock
Yg
Yg
Yg
Yg
Yg
SiO2
64.93
66.59
69.11
66.46
64.35
TiO2
0.00
0.07
0.03
0.00
0.00
Al2O3
18.56
19.21
20.17
19.71
18.80
Cr2O3
0.00
0.02
0.00
0.01
0.01
Fe2O3
0.08
0.00
0.01
0.00
0.05
FeO
0.00
0.17
0.00
0.06
0.00
MgO
0.02
0.02
0.00
0.00
0.00
MnO
0.04
0.01
0.01
0.01
0.00
CaO
0.01
0.19
0.32
0.65
0.03
Na2O
0.76
11.48
11.59
11.29
1.33
K2O
15.34
0.09
0.10
0.10
14.65
F
0.00
0.23
0.00
0.06
0.00
Cl
0.01
0.01
0.00
0.05
0.00
Total
99.74
97.97
101.34
98.36
99.23
Based on IV=4
2.99
2.98
2.98
2.96
2.97
Si (T)
1.01
1.02
1.02
1.04
1.02
Al (T)
0.00
0.00
0.00
0.00
0.00
Fe3+ (T)
0.07
1.00
0.97
0.98
0.12
Na (A)
0.90
0.01
0.01
0.01
0.86
K (A)
0.00
0.01
0.01
0.03
0.00
Ca (A)
0.00
0.00
0.00
0.00
0.00
Mg (A)
0.00
0.00
0.00
0.00
0.00
Ti (A)
Cr (A)
0.00
0.00
0.00
0.00
0.00
Mn (A)
0.00
0.00
0.00
0.00
0.00
F (X)
0.00
0.03
0.00
0.01
0.00
Cl (X)
0.00
0.00
0.00
0.00
0.00
O
8.00
7.97
8.00
7.99
8.00
End Member
Or#
An#
Ab#
0.93
0.00
0.07
0.01
0.01
0.99
0.98
0.00
0.02
0.96
0.03
0.01
0.12
0.00
0.88
SP 123
plag1
kspar
Yg
62.47
0.00
23.98
0.00
0.00
0.18
0.00
0.03
5.11
8.99
0.26
0.10
0.00
101.08
2.75
1.25
0.00
0.77
0.01
0.24
0.00
0.00
0.00
0.00
0.01
0.00
7.99
0.01
0.24
0.75
237
Table 3. Normalized microprobe data: feldspars from Tea Cup
SP 123
SP 123
TC 001
TC 001
TC 004
Sample number
plg1
plg2
kspar1
plag2
plag3
Replacing
vein
vein
plag
Host rock
Yg
Yg
Khbg
Kpd
Kpd
SiO2
66.66
66.85
62.84
62.11
64.29
TiO2
0.00
0.01
0.01
0.04
0.03
Al2O3
21.02
21.15
24.16
24.20
18.77
Cr2O3
0.03
0.02
0.00
0.00
0.00
Fe2O3
0.04
0.19
0.02
0.00
0.00
FeO
0.00
0.00
0.00
0.06
0.07
MgO
0.00
0.01
0.00
0.00
0.00
MnO
0.03
0.02
0.01
0.02
0.02
CaO
1.48
1.39
5.26
5.38
0.01
Na2O
10.97
11.18
8.19
8.17
0.80
K2O
0.15
0.14
0.43
0.53
14.95
F
0.00
0.05
0.00
0.30
0.53
Cl
0.00
0.00
0.00
0.00
0.01
Total
100.39
100.98
100.91
100.68
99.26
Based on IV=4
2.91
2.91
2.75
2.74
2.97
Si (T)
1.08
1.09
1.25
1.26
1.03
Al (T)
0.00
0.01
0.00
0.00
0.00
Fe3+ (T)
0.93
0.94
0.70
0.70
0.07
Na (A)
0.01
0.01
0.02
0.03
0.88
K (A)
0.07
0.06
0.25
0.25
0.00
Ca (A)
0.00
0.00
0.00
0.00
0.00
Mg (A)
0.00
0.00
0.00
0.00
0.00
Ti (A)
Cr (A)
0.00
0.00
0.00
0.00
0.00
Mn (A)
0.00
0.00
0.00
0.00
0.00
F (X)
0.00
0.01
0.00
0.04
0.08
Cl (X)
0.00
0.00
0.00
0.00
0.00
O
8.00
7.99
8.00
7.96
7.92
End Member
Or#
An#
Ab#
0.01
0.07
0.92
0.01
0.06
0.93
0.02
0.26
0.72
0.00
0.16
0.83
0.92
0.00
0.08
TC 004
plag1
Khbg
57.58
0.00
26.95
0.00
0.15
0.00
0.00
0.00
8.69
6.35
0.18
0.13
0.00
99.97
2.57
1.42
0.00
0.55
0.01
0.42
0.00
0.00
0.00
0.00
0.02
0.00
7.98
0.01
0.43
0.56
238
Table 3. Normalized microprobe data: feldspars from Tea Cup
TC 006
TC 006
TC 008
TC 009
TC 009
Sample number
kspar1
plg1
kspar1
kspar1
kspar2
Replacing
Host rock
Khbg
Khbg
Yg
Yg
Yg
SiO2
65.16
64.21
64.98
64.52
64.60
TiO2
0.03
0.00
0.03
0.01
0.01
Al2O3
18.62
22.95
18.77
18.64
18.78
Cr2O3
0.00
0.00
0.00
0.00
0.01
Fe2O3
0.00
0.15
0.00
0.24
0.06
FeO
0.08
0.00
0.00
0.00
0.00
MgO
0.00
0.00
0.02
0.01
0.01
MnO
0.00
0.02
0.00
0.01
0.00
CaO
0.00
3.55
0.00
0.00
0.07
Na2O
0.98
9.03
0.94
0.33
0.78
K2O
15.40
0.23
15.44
15.81
14.50
F
0.25
0.42
0.38
0.05
0.00
Cl
0.00
0.00
0.00
0.00
0.00
Total
100.41
100.40
100.40
99.60
98.82
Based on IV=4
2.99
2.81
2.98
2.98
2.98
Si (T)
1.01
1.18
1.02
1.01
1.02
Al (T)
0.00
0.01
0.00
0.01
0.00
Fe3+ (T)
0.09
0.77
0.08
0.03
0.07
Na (A)
0.90
0.01
0.90
0.93
0.85
K (A)
0.00
0.17
0.00
0.00
0.00
Ca (A)
0.00
0.00
0.00
0.00
0.00
Mg (A)
0.00
0.00
0.00
0.00
0.00
Ti (A)
Cr (A)
0.00
0.00
0.00
0.00
0.00
Mn (A)
0.00
0.00
0.00
0.00
0.00
F (X)
0.04
0.06
0.06
0.01
0.00
Cl (X)
0.00
0.00
0.00
0.00
0.00
O
7.96
7.94
7.94
7.99
8.00
End Member
Or#
An#
Ab#
0.91
0.00
0.09
0.01
0.18
0.81
0.91
0.00
0.09
0.97
0.00
0.03
0.92
0.00
0.08
TC 009
kspar3
Yg
64.42
0.00
18.54
0.00
0.05
0.00
0.00
0.01
0.00
0.25
16.03
0.00
0.01
99.31
2.99
1.01
0.00
0.02
0.95
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
0.98
0.00
0.02
239
Table 3. Normalized microprobe data: feldspars from Tea Cup
TC 009
TC 009
TC 010'
TC 011
TC 011
Sample number
plg1
plg2
plg1
kspar1
plg1
Replacing
kspar
plag
plag
Host rock
Yg
Yg
Yg
Yg
Yg
SiO2
67.55
67.61
69.19
64.54
64.18
TiO2
0.00
0.00
0.04
0.02
0.05
Al2O3
20.53
20.14
19.92
18.81
23.27
Cr2O3
0.00
0.00
0.00
0.00
0.01
Fe2O3
0.41
0.04
0.00
0.11
0.00
FeO
0.00
0.00
0.06
0.00
0.14
MgO
0.00
0.00
0.01
0.00
0.00
MnO
0.01
0.00
0.00
0.01
0.02
CaO
1.15
0.62
0.07
0.02
4.07
Na2O
11.32
11.48
11.90
0.89
9.78
K2O
0.03
0.06
0.04
15.05
0.13
F
0.00
0.00
0.22
0.08
0.00
Cl
0.00
0.00
0.00
0.00
0.01
Total
101.00
99.96
101.36
99.48
101.65
Based on IV=4
2.94
2.96
2.98
2.97
2.80
Si (T)
1.05
1.04
1.02
1.02
1.20
Al (T)
0.01
0.00
0.00
0.00
0.00
Fe3+ (T)
0.95
0.97
1.00
0.08
0.83
Na (A)
0.00
0.00
0.00
0.88
0.01
K (A)
0.05
0.03
0.00
0.00
0.19
Ca (A)
0.00
0.00
0.00
0.00
0.00
Mg (A)
0.00
0.00
0.00
0.00
0.00
Ti (A)
Cr (A)
0.00
0.00
0.00
0.00
0.00
Mn (A)
0.00
0.00
0.00
0.00
0.00
F (X)
0.00
0.00
0.03
0.01
0.00
Cl (X)
0.00
0.00
0.00
0.00
0.00
O
8.00
8.00
7.97
7.99
8.00
End Member
Or#
An#
Ab#
0.00
0.05
0.95
0.00
0.03
0.97
0.00
0.00
0.99
0.92
0.00
0.08
0.01
0.19
0.81
TV08 07
plg1
Yg
66.83
0.00
21.32
0.00
0.00
0.03
0.00
0.00
1.25
11.25
0.03
0.59
0.00
101.05
2.91
1.09
0.00
0.95
0.00
0.06
0.00
0.00
0.00
0.00
0.08
0.00
7.92
0.00
0.06
0.94
240
Table 3. Normalized microprobe data: feldspars from Tea Cup
TV08 07
Sample number
plg2
Replacing
plag
Host rock
Yg
SiO2
62.76
TiO2
0.00
Al2O3
23.41
Cr2O3
0.00
Fe2O3
0.19
FeO
0.00
MgO
0.00
MnO
0.00
CaO
4.32
Na2O
9.27
K2O
0.20
F
0.00
Cl
0.00
Total
100.15
Based on IV=4
2.77
Si (T)
1.22
Al (T)
0.01
Fe3+ (T)
0.79
Na (A)
0.01
K (A)
0.20
Ca (A)
0.00
Mg (A)
0.00
Ti (A)
Cr (A)
0.00
0.00
Mn (A)
F (X)
0.00
Cl (X)
0.00
O
8.00
End Member
Or#
An#
Ab#
241
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 004
SP 004 ser1
SP 004 ser2
SP 009 ser1
chl1
clinochlore alumino-celadonite alumino-celadonite
muscovite
biotite
vein
vein
biotite
Yg
Yg
Yg
Kpd
33.60
50.41
45.63
50.80
0.01
0.00
0.01
0.45
18.73
25.37
24.46
28.87
0.02
0.01
0.01
0.02
2.41
1.23
1.71
0.67
12.27
4.42
6.14
2.42
16.13
2.16
6.27
1.95
0.38
0.10
0.12
0.01
0.86
1.10
1.03
0.31
0.11
0.44
0.01
0.06
0.47
4.67
2.82
9.27
11.72
4.27
4.14
4.42
0.34
0.00
0.00
0.16
0.01
0.10
0.08
0.01
97.07
94.29
92.43
99.40
-0.15
-0.02
-0.02
-0.07
96.92
94.26
92.41
99.33
3.39
3.52
3.29
3.39
0.61
0.48
0.71
0.61
1.62
1.60
1.36
1.66
2.43
0.22
0.67
0.19
1.04
0.26
0.37
0.13
0.18
0.06
0.09
0.03
0.03
0.01
0.01
0.00
0.00
0.00
0.00
0.02
0.00
0.00
0.00
0.00
0.70
0.85
0.49
0.95
0.02
0.06
0.00
0.01
0.06
0.42
0.26
0.79
0.09
0.08
0.08
0.02
0.82
0.44
0.66
0.18
0.11
0.00
0.00
0.03
0.00
0.01
0.01
0.00
7.89
1.99
1.99
1.97
242
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 009 ser2 SP 014
SP 014
SP 014
SP 017 bt1
chl1
chl2
kspr1
muscovite
annite
clinochlore muscovite alumino-celadonite
biotite
biotite
biotite
Kpd
Yg
Yg
Yg
Kpd
48.05
35.90
26.97
47.17
47.98
0.13
2.81
0.07
0.14
0.21
31.64
15.19
18.70
32.90
29.60
0.00
0.01
0.02
0.01
0.00
0.78
4.85
4.18
0.47
1.10
2.80
17.46
21.29
1.70
3.97
1.02
8.96
15.60
0.88
2.31
0.00
0.26
0.63
0.03
0.08
0.17
0.00
0.04
0.00
0.24
0.15
0.02
0.00
0.28
0.09
10.05
9.42
0.00
10.29
9.25
4.40
3.62
11.31
4.43
4.28
0.08
0.24
0.16
0.00
0.30
0.02
0.21
0.02
0.01
0.00
99.28
98.94
98.97
98.31
99.40
-0.04
-0.15
-0.07
0.00
-0.13
99.24
98.79
98.90
98.31
99.27
3.24
2.84
2.84
3.19
3.26
0.76
1.16
1.16
0.81
0.74
1.75
0.26
1.16
1.82
1.62
0.10
1.06
2.45
0.09
0.23
0.16
1.16
1.88
0.10
0.23
0.04
0.29
0.33
0.02
0.06
0.00
0.02
0.06
0.00
0.00
0.01
0.17
0.01
0.01
0.01
0.00
0.00
0.00
0.00
0.00
0.94
0.05
0.12
0.96
0.85
0.02
0.00
0.00
0.04
0.01
0.86
0.95
0.00
0.89
0.80
0.01
0.00
0.00
0.00
0.02
0.10
0.05
1.00
0.07
0.17
0.02
0.06
0.05
0.00
0.06
0.00
0.03
0.00
0.00
0.00
1.98
1.91
7.94
2.00
1.94
243
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 017 bt2
SP 017 ser2 SP 019 ser1 SP 019 ser2 SP 019 ser4
alumino-celadonite clinochlore muscovite clinochlore muscovite
biotite
biotite
biotite
biotite
Kpd
Kpd
Yg
Yg
Yg
45.72
33.91
47.13
31.02
49.03
0.15
0.72
0.24
0.13
0.05
30.02
22.00
34.16
21.39
31.25
0.00
0.02
0.00
0.01
0.00
1.07
3.02
0.52
3.19
0.52
3.85
15.42
1.87
16.27
1.89
2.69
10.58
1.03
14.96
1.40
0.10
0.48
0.03
0.45
0.00
0.12
0.39
0.04
0.11
0.27
0.08
0.10
0.59
0.04
0.11
8.82
1.89
9.42
0.89
9.53
4.31
12.10
4.21
11.78
4.32
0.00
0.07
0.61
0.49
0.30
0.01
0.01
0.00
0.00
0.02
96.93
100.71
99.85
100.75
98.68
0.00
-0.03
-0.26
-0.21
-0.13
96.93
100.68
99.60
100.54
98.55
3.18
3.35
3.14
3.10
3.29
0.82
0.65
0.86
0.90
0.71
1.64
1.91
1.83
1.61
1.77
0.28
1.56
0.10
2.22
0.14
0.22
1.27
0.10
1.36
0.11
0.06
0.22
0.03
0.24
0.03
0.01
0.04
0.00
0.04
0.00
0.01
0.05
0.01
0.01
0.00
0.00
0.00
0.00
0.00
0.00
0.79
0.93
0.93
0.52
0.96
0.01
0.02
0.08
0.01
0.01
0.78
0.24
0.80
0.11
0.82
0.01
0.04
0.00
0.01
0.02
0.20
0.70
0.12
0.87
0.15
0.00
0.02
0.13
0.15
0.06
0.00
0.00
0.00
0.00
0.00
2.00
7.98
1.87
7.85
1.93
244
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 020 bt1
SP 020 bt2
SP 020 bt3 SP 023 bt2 SP 023 ser1
muscovite
vein
Yg
46.26
0.32
30.67
0.00
0.80
2.90
1.62
0.05
0.03
0.21
9.68
4.29
0.08
0.00
96.91
-0.03
96.88
3.20
0.80
1.71
0.17
0.17
0.04
0.00
0.02
0.00
0.90
0.03
0.86
0.00
0.11
0.02
0.00
1.98
alumino-celadonite
biotite
Yg
45.13
0.42
30.37
0.02
1.28
4.61
1.79
0.03
0.00
0.12
10.27
4.28
0.07
0.01
98.40
-0.03
98.36
3.14
0.86
1.62
0.18
0.27
0.07
0.00
0.02
0.00
0.83
0.02
0.91
0.00
0.07
0.02
0.00
1.98
muscovite
biotite
Yg
47.47
0.01
31.06
0.00
0.79
2.83
2.13
0.06
0.01
0.11
10.22
4.39
0.06
0.01
99.14
-0.03
99.11
3.22
0.78
1.70
0.21
0.16
0.04
0.00
0.00
0.00
0.89
0.01
0.88
0.00
0.10
0.01
0.00
1.99
muscovite
biotite
Yg
45.60
0.20
32.86
0.00
0.75
2.70
1.00
0.00
0.00
0.32
11.00
4.35
0.07
0.02
98.87
-0.03
98.83
3.12
0.88
1.76
0.10
0.15
0.04
0.00
0.01
0.00
0.93
0.04
0.96
0.00
0.00
0.02
0.00
1.98
muscovite
biotite
Yg
47.64
0.42
31.25
0.01
0.81
2.90
1.67
0.06
0.00
0.30
10.75
4.46
0.00
0.00
100.27
0.00
100.27
3.20
0.80
1.68
0.17
0.16
0.04
0.00
0.02
0.00
0.92
0.04
0.92
0.00
0.04
0.00
0.00
2.00
245
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea CTable 4. Nor
SP 025 bt1
SP 029
SP 029
SP 032
SP 032 SP 034 ser1
chl1
chl1
chl1
chl2
muscovite clinochlore clinochlore clinochlore clinochlore muscovite
biotite
biotite
biotite
biotite
biotite
plag
Yg
Kpd
Kpd
Kpd
Kpd
Yg
45.97
28.29
27.62
27.49
27.51
47.73
0.08
0.01
0.04
0.03
0.17
0.12
29.21
19.26
21.29
19.59
19.49
31.43
0.01
0.01
0.00
0.00
0.01
0.00
1.18
3.00
3.04
3.42
3.30
0.93
4.24
15.32
15.51
17.46
16.81
3.36
1.62
19.76
20.02
19.23
18.98
0.83
0.02
0.77
0.65
0.43
0.36
0.04
0.03
0.06
0.06
0.06
0.06
0.00
0.21
0.02
0.02
0.05
0.03
0.16
10.43
0.07
0.00
0.06
0.15
10.50
3.96
11.48
11.71
11.60
11.64
4.34
0.66
0.48
0.48
0.25
0.00
0.18
0.03
0.01
0.02
0.02
0.00
0.01
97.64
98.54
100.46
99.69
98.51
99.65
-0.28
-0.20
-0.21
-0.11
0.00
-0.08
97.36
98.34
100.25
99.58
98.51
99.57
3.22
2.90
2.77
2.81
2.83
3.23
0.78
1.10
1.23
1.19
1.17
0.77
1.63
1.22
1.29
1.17
1.20
1.74
0.17
3.02
3.00
2.93
2.91
0.08
0.25
1.31
1.30
1.49
1.45
0.19
0.06
0.23
0.23
0.26
0.26
0.05
0.00
0.07
0.06
0.04
0.03
0.00
0.00
0.00
0.00
0.00
0.01
0.01
0.00
0.00
0.00
0.00
0.00
0.00
0.88
0.15
0.12
0.10
0.14
0.93
0.03
0.00
0.00
0.01
0.01
0.02
0.93
0.01
0.00
0.01
0.02
0.91
0.00
0.01
0.01
0.01
0.01
0.00
0.04
0.98
0.99
0.98
0.97
0.07
0.15
0.15
0.15
0.08
0.00
0.04
0.00
0.00
0.00
0.00
0.00
0.00
1.85
7.84
7.85
7.92
8.00
1.96
246
rmalized microprobe data: sheet silicates from Tea Cup.
Sample number SP 034 ser2 SP 034 ser3 SP 035 bt2
SP 035 chl1
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
muscovite
plag
Yg
45.54
0.41
30.74
0.01
1.07
3.84
1.58
0.07
0.00
0.30
10.83
4.14
0.43
0.00
98.95
-0.18
98.76
3.15
0.85
1.65
0.16
0.22
0.06
0.00
0.02
0.00
0.89
0.04
0.95
0.00
0.01
0.09
0.00
1.91
muscovite phlogopite
plag
Yg
Yg
46.87
36.63
0.10
3.14
30.10
15.74
0.00
0.02
1.21
3.93
4.36
14.15
0.93
10.64
0.04
0.60
0.00
0.01
0.13
0.05
10.28
9.46
4.25
3.16
0.19
1.46
0.00
0.00
98.48
98.98
-0.08
-0.62
98.40
98.36
3.24
2.85
0.76
1.15
1.69
0.29
0.10
1.23
0.25
0.92
0.06
0.23
0.00
0.04
0.01
0.18
0.00
0.00
0.90
0.11
0.02
0.01
0.91
0.94
0.00
0.00
0.08
0.05
0.04
0.36
0.00
0.00
1.96
1.64
alumino-celadonite
biotite
Yg
46.65
0.33
24.53
0.01
1.74
6.28
5.17
0.15
0.04
0.05
7.56
3.88
0.78
0.01
97.17
-0.33
96.84
3.29
0.71
1.33
0.54
0.37
0.09
0.01
0.02
0.00
0.63
0.01
0.68
0.00
0.31
0.17
0.00
1.83
247
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 035 ser1
SP 043
SP 043 SP 043 ser1 SP 048 bt1
chl1
chl2
alumino-celadonite clinochlore clinochlore muscovite muscovite
plag
biotite
biotite
vein
biotite
Yg
Yg
Yg
Yg
Yg
52.68
27.93
26.14
46.65
49.47
0.08
0.21
0.06
0.07
0.16
25.43
18.18
18.32
34.65
28.78
0.01
0.01
0.01
0.00
0.06
1.04
4.10
4.00
0.32
0.66
3.73
20.91
20.42
1.16
2.36
2.45
15.17
15.74
0.30
1.93
0.00
0.54
0.52
0.07
0.05
0.40
0.13
0.09
0.00
0.12
0.06
0.04
0.00
0.36
0.11
8.41
0.13
0.06
10.68
9.12
4.20
11.30
10.91
4.42
4.23
0.53
0.25
0.47
0.06
0.33
0.01
0.00
0.00
0.00
0.03
99.01
98.90
96.73
98.75
97.41
-0.22
-0.10
-0.20
-0.03
-0.15
98.79
98.80
96.53
98.72
97.27
3.55
2.93
2.82
3.14
3.37
0.45
1.07
1.18
0.86
0.63
1.56
1.19
1.14
1.89
1.69
0.25
2.38
2.53
0.03
0.20
0.21
1.84
1.84
0.07
0.13
0.05
0.32
0.32
0.02
0.03
0.00
0.05
0.05
0.00
0.00
0.00
0.02
0.00
0.00
0.01
0.00
0.00
0.00
0.00
0.00
0.93
0.21
0.11
0.99
0.94
0.01
0.01
0.00
0.05
0.01
0.72
0.02
0.01
0.92
0.79
0.03
0.01
0.01
0.00
0.01
0.24
0.96
0.98
0.04
0.18
0.11
0.08
0.16
0.01
0.07
0.00
0.00
0.00
0.00
0.00
1.89
7.92
7.84
1.99
1.93
248
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 048
SP 048
SP 073b
SP 073b
SP 073b
SP 073b
chl1
chl2
chl3
chl4
chl1
chl2
clinochlore clinochlore chamosite chamosite chamosite chamosite
biotite
biotite
vein
vein
vein
vein
Yg
Yg
Yg
Yg
Yg
Yg
26.43
26.09
24.74
24.41
26.21
23.30
0.10
0.00
0.03
0.01
0.02
0.02
19.47
20.20
19.69
19.07
17.13
20.71
0.02
0.03
0.01
0.00
0.00
0.01
3.68
3.71
5.15
5.05
4.57
5.56
18.77
18.92
26.26
25.74
23.28
28.36
14.32
14.85
8.19
8.54
6.52
8.15
1.13
1.20
0.99
1.02
1.52
1.13
0.09
0.05
0.09
0.11
0.31
0.03
0.00
0.00
0.03
0.08
0.09
0.05
0.00
0.05
0.32
0.11
0.92
0.07
10.79
11.03
10.69
10.45
10.13
10.73
0.59
0.35
0.00
0.18
0.09
0.08
0.00
0.01
0.01
0.01
0.02
0.04
95.39
96.48
96.20
94.76
90.80
98.24
-0.25
-0.15
0.00
-0.08
-0.04
-0.04
95.14
96.33
96.20
94.68
90.76
98.20
2.86
2.79
2.77
2.78
3.09
2.59
1.14
1.21
1.23
1.22
0.91
1.41
1.35
1.34
1.38
1.34
1.47
1.31
2.31
2.37
1.37
1.45
1.15
1.35
1.70
1.69
2.46
2.45
2.29
2.64
0.30
0.30
0.43
0.43
0.40
0.47
0.10
0.11
0.09
0.10
0.15
0.11
0.01
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.22
0.18
0.26
0.23
0.53
0.12
0.00
0.00
0.01
0.02
0.02
0.01
0.00
0.01
0.05
0.02
0.14
0.01
0.01
0.01
0.01
0.01
0.04
0.00
0.99
0.99
0.94
0.95
0.80
0.98
0.20
0.12
0.00
0.06
0.03
0.03
0.00
0.00
0.00
0.00
0.00
0.01
7.80
7.88
8.00
7.93
7.96
7.97
249
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 073b
SP 073b SP 075 ser1 SP 075 ser2 SP 075 ser3 SP 075 ser4
ser1
ser2
muscovite muscovite muscovite muscovite muscovite muscovite
biotite
biotite
biotite
plag
plag
plag
Yg
Yg
Yg
Yg
Yg
Yg
48.96
45.21
45.32
48.28
48.45
47.69
0.04
0.66
0.66
0.04
0.12
0.09
29.75
30.86
30.26
31.76
30.75
32.18
0.00
0.01
0.02
0.00
0.01
0.00
1.30
0.97
1.12
0.83
0.88
0.85
4.67
3.49
4.05
2.97
3.17
3.06
0.40
1.38
1.62
0.59
0.71
0.55
0.12
0.02
0.05
0.01
0.07
0.02
0.05
0.00
0.00
0.13
0.03
0.05
0.19
0.30
0.22
0.22
0.17
0.18
10.15
10.60
10.78
9.99
9.69
10.03
4.29
4.22
4.03
4.36
4.32
4.30
0.28
0.20
0.61
0.19
0.19
0.29
0.00
0.01
0.00
0.01
0.00
0.00
100.19
97.92
98.74
99.37
98.57
99.29
-0.12
-0.09
-0.26
-0.08
-0.08
-0.12
100.07
97.83
98.48
99.29
98.49
99.17
3.32
3.14
3.14
3.25
3.29
3.22
0.68
0.86
0.86
0.75
0.71
0.78
1.69
1.67
1.62
1.78
1.75
1.79
0.04
0.14
0.17
0.06
0.07
0.05
0.26
0.20
0.23
0.17
0.18
0.17
0.07
0.05
0.06
0.04
0.04
0.04
0.01
0.00
0.00
0.00
0.00
0.00
0.00
0.03
0.03
0.00
0.01
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.93
0.90
0.88
0.95
0.94
0.94
0.03
0.04
0.03
0.03
0.02
0.02
0.88
0.94
0.95
0.86
0.84
0.86
0.00
0.00
0.00
0.01
0.00
0.00
0.09
0.02
0.02
0.10
0.14
0.11
0.06
0.04
0.13
0.04
0.04
0.06
0.00
0.00
0.00
0.00
0.00
0.00
1.94
1.95
1.87
1.96
1.96
1.94
250
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 076 ser1 SP 076 ser2 SP 076 ser3 SP 076 ser4
SP 076 ser6
muscovite
plag
Yg
48.76
0.02
29.88
0.00
0.91
3.28
1.55
0.00
0.00
0.22
10.16
4.29
0.29
0.00
99.37
-0.12
99.25
3.30
0.70
1.69
0.16
0.19
0.05
0.00
0.00
0.00
0.92
0.03
0.88
0.00
0.09
0.06
0.00
1.94
muscovite
plag
Yg
48.96
0.02
29.98
0.00
0.84
3.01
1.32
0.01
0.00
0.22
10.34
4.43
0.00
0.00
99.13
0.00
99.13
3.31
0.69
1.70
0.13
0.17
0.04
0.00
0.00
0.00
0.95
0.03
0.89
0.00
0.08
0.00
0.00
2.00
muscovite
biotite
Yg
46.21
0.32
29.09
0.00
1.02
3.69
1.96
0.01
0.00
0.18
10.38
4.15
0.31
0.00
97.32
-0.13
97.19
3.23
0.77
1.62
0.20
0.22
0.05
0.00
0.02
0.00
0.89
0.02
0.92
0.00
0.05
0.07
0.00
1.93
muscovite
plag
Yg
46.61
0.07
33.07
0.01
0.78
2.82
1.24
0.00
0.00
0.28
10.52
4.36
0.20
0.00
99.97
-0.08
99.88
3.14
0.86
1.77
0.12
0.16
0.04
0.00
0.00
0.00
0.91
0.04
0.90
0.00
0.06
0.04
0.00
1.96
alumino-celadonite
plag
Yg
47.11
0.01
27.83
0.00
1.57
5.64
1.85
0.00
0.00
0.22
10.51
4.25
0.13
0.02
99.13
-0.06
99.07
3.27
0.73
1.55
0.19
0.33
0.08
0.00
0.00
0.00
0.85
0.03
0.93
0.00
0.04
0.03
0.00
1.97
251
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 079 ser1
SP 079 ser2
SP 079 ser3 SP 081 bt2 SP 081 ser1
muscovite
vein
Yg
47.48
0.17
29.70
0.00
0.89
3.19
1.40
0.03
0.03
0.24
9.99
4.19
0.32
0.01
97.64
-0.14
97.51
3.28
0.72
1.69
0.14
0.18
0.05
0.00
0.01
0.00
0.93
0.03
0.88
0.00
0.09
0.07
0.00
1.93
alumino-celadonite
vein
Yg
46.64
0.28
28.64
0.01
1.16
4.16
2.54
0.03
0.00
0.20
10.49
4.12
0.44
0.01
98.72
-0.19
98.53
3.23
0.77
1.56
0.26
0.24
0.06
0.00
0.01
0.00
0.86
0.03
0.93
0.00
0.05
0.10
0.00
1.90
muscovite
vein
vein
46.99
0.02
28.72
0.00
0.98
3.53
1.21
0.02
0.07
0.23
9.86
4.10
0.34
0.02
96.09
-0.15
95.94
3.30
0.70
1.68
0.13
0.21
0.05
0.00
0.00
0.00
0.93
0.03
0.88
0.00
0.08
0.08
0.00
1.92
muscovite
biotite
Yg
48.52
0.18
29.13
0.00
0.80
2.90
1.61
0.03
0.00
0.16
10.39
4.10
0.59
0.02
98.42
-0.25
98.17
3.32
0.68
1.67
0.16
0.17
0.04
0.00
0.01
0.00
0.95
0.02
0.91
0.00
0.07
0.13
0.00
1.87
muscovite
biotite
Yg
46.52
0.21
30.72
0.00
0.94
3.37
1.59
0.02
0.01
0.23
10.49
4.18
0.38
0.02
98.66
-0.16
98.50
3.20
0.80
1.68
0.16
0.19
0.05
0.00
0.01
0.00
0.90
0.03
0.92
0.00
0.05
0.08
0.00
1.92
252
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 092 ser1
SP 092 ser2 SP 092 ser3 SP 097 bt1
SP 097
chl1
alumino-celadonite muscovite muscovite phlogopite clinochlore
biotite
vein
vein
biotite
Yg
Yg
Yg
Yg
Yg
45.36
47.57
46.29
36.47
27.39
0.23
0.16
0.14
3.60
0.00
27.77
29.88
30.01
15.51
20.58
0.00
0.00
0.00
0.04
0.02
1.38
0.86
0.97
3.89
3.30
4.96
3.10
3.48
13.99
16.85
3.57
1.25
1.43
11.84
18.25
0.09
0.00
0.03
0.17
0.30
0.00
0.03
0.00
0.00
0.01
0.19
0.31
0.23
0.10
0.00
10.74
9.99
10.39
9.12
0.05
4.13
4.31
4.19
3.68
11.66
0.32
0.08
0.24
0.34
0.00
0.00
0.00
0.01
0.17
0.00
98.75
97.55
97.42
98.92
98.40
-0.14
-0.03
-0.10
-0.18
0.00
98.61
97.51
97.31
98.74
98.40
3.17
3.28
3.22
2.81
2.82
0.83
0.72
0.78
1.19
1.18
1.46
1.70
1.68
0.22
1.31
0.37
0.13
0.15
1.36
2.80
0.29
0.18
0.20
0.90
1.45
0.07
0.04
0.05
0.23
0.26
0.01
0.00
0.00
0.01
0.03
0.01
0.01
0.01
0.21
0.00
0.00
0.00
0.00
0.00
0.00
0.79
0.94
0.91
0.07
0.16
0.03
0.04
0.03
0.02
0.00
0.96
0.88
0.92
0.90
0.01
0.00
0.00
0.00
0.00
0.00
0.02
0.08
0.05
0.09
0.99
0.07
0.02
0.05
0.08
0.00
0.00
0.00
0.00
0.02
0.00
1.93
1.98
1.95
1.89
8.00
253
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 097 SP 097 ser1 SP 114 act1
SP 114 chl3
SP 114
chl2
kspar1
clinochlore phlogopite clinochlore alumino-celadonite muscovite
biotite
biotite
biotite
kspar
Yg
Yg
Yg
Yg
Yg
27.46
36.55
26.48
48.53
46.20
0.07
1.06
0.19
0.15
0.46
18.30
17.18
18.95
23.13
29.97
0.03
0.00
0.00
0.00
0.02
3.38
3.55
3.85
1.56
1.08
17.25
12.77
19.62
5.63
3.88
18.62
13.60
16.12
4.95
1.82
0.32
0.18
1.68
0.22
0.11
0.01
0.00
0.04
0.04
0.02
0.06
0.11
0.01
0.02
0.25
0.04
8.73
0.00
9.92
10.51
11.16
3.62
11.23
4.12
4.31
0.55
0.52
0.25
0.36
0.08
0.00
0.14
0.00
0.00
0.00
97.28
98.01
98.43
98.65
98.70
-0.23
-0.25
-0.11
-0.15
-0.03
97.05
97.76
98.32
98.50
98.67
2.88
2.81
2.80
3.39
3.19
1.12
1.19
1.20
0.61
0.81
1.15
0.36
1.16
1.30
1.62
2.91
1.56
2.54
0.52
0.19
1.51
0.82
1.73
0.33
0.22
0.27
0.21
0.31
0.08
0.06
0.03
0.01
0.15
0.01
0.01
0.01
0.06
0.02
0.01
0.02
0.00
0.00
0.00
0.00
0.00
0.12
0.00
0.10
0.76
0.88
0.01
0.02
0.00
0.00
0.03
0.01
0.86
0.00
0.88
0.92
0.00
0.00
0.00
0.00
0.00
0.98
0.13
0.99
0.11
0.04
0.18
0.13
0.08
0.08
0.02
0.00
0.02
0.00
0.00
0.00
7.82
1.86
7.92
1.92
1.98
254
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 115
SP 115 SP 115 ser1 SP 123 bt1 SP 123 bt2
SP 123
chl1
kspar1
kspar2
muscovite muscovite clinochlore phlogopite phlogopite clinochlore
kspar
kspar
biotite
kspar
biotite
vein
Yg
Yg
Yg
Yg
Yg
Yg
45.23
44.64
28.00
34.27
35.56
26.91
0.17
0.28
0.18
3.15
3.00
0.06
33.71
33.50
19.75
16.64
14.69
18.37
0.00
0.00
0.01
0.01
0.01
0.00
0.85
0.90
3.41
4.36
4.28
4.02
3.06
3.25
17.40
15.71
15.42
20.48
0.70
0.61
14.04
10.70
11.75
16.50
0.02
0.05
1.46
0.35
0.34
0.49
0.01
0.00
0.20
0.00
0.00
0.05
0.72
0.30
0.04
0.10
0.10
0.06
10.07
11.18
0.52
9.47
9.44
0.00
4.40
4.19
11.21
3.60
3.53
11.35
0.00
0.37
0.19
0.43
0.57
0.01
0.00
0.00
0.00
0.04
0.08
0.01
98.93
99.27
96.40
98.84
98.80
98.32
0.00
-0.16
-0.08
-0.19
-0.26
-0.01
98.93
99.11
96.32
98.64
98.54
98.31
3.08
3.06
2.97
2.69
2.79
2.84
0.92
0.94
1.03
1.31
1.21
1.16
1.79
1.77
1.44
0.24
0.15
1.12
0.07
0.06
2.22
1.25
1.38
2.60
0.17
0.19
1.54
1.03
1.01
1.81
0.04
0.05
0.27
0.26
0.25
0.32
0.00
0.00
0.13
0.02
0.02
0.04
0.01
0.01
0.01
0.19
0.18
0.01
0.00
0.00
0.00
0.00
0.00
0.00
0.91
0.92
0.37
0.01
0.00
0.11
0.10
0.04
0.01
0.02
0.02
0.01
0.88
0.98
0.07
0.95
0.95
0.00
0.00
0.00
0.02
0.00
0.00
0.01
0.03
0.00
0.90
0.03
0.04
0.98
0.00
0.08
0.06
0.11
0.14
0.00
0.00
0.00
0.00
0.01
0.01
0.00
2.00
1.92
7.94
1.89
1.85
7.99
255
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
SP 123 SP 123 ser1 TC 001 bt1 TC 001
TC 001
TC 002
chl2
chl1
chl2
chl1
clinochlore phlogopite phlogopite clinochlore clinochlore clinochlore
vein
biotie
biotite
biotite
vein
Yg
Yg
Kpd
Kpd
Kpd
Kpd
27.88
36.58
29.61
26.62
26.64
27.23
0.09
3.07
0.15
0.16
0.02
0.00
19.55
14.61
20.36
20.03
19.99
20.19
0.01
0.02
0.02
0.01
0.00
0.00
3.85
4.10
4.58
3.74
4.04
3.77
19.65
14.76
16.50
19.05
20.61
19.20
15.12
11.76
13.68
15.97
15.44
16.79
0.55
0.30
0.84
1.06
1.07
1.00
0.02
0.03
0.10
0.11
0.03
0.03
0.01
0.09
0.12
0.01
0.02
0.04
0.37
9.24
1.44
0.08
0.03
0.03
11.46
3.63
3.51
11.43
11.47
11.56
0.04
0.44
0.25
0.00
0.00
0.18
0.00
0.06
0.00
0.01
0.02
0.00
98.60
98.69
91.18
98.28
99.36
100.01
-0.02
-0.20
-0.11
0.00
0.00
-0.08
98.58
98.49
91.07
98.28
99.36
99.93
2.91
2.85
2.44
2.79
2.78
2.80
1.09
1.15
1.56
1.21
1.22
1.20
1.32
0.19
0.43
1.27
1.25
1.25
2.35
1.36
1.68
2.50
2.41
2.58
1.72
0.96
1.14
1.67
1.80
1.65
0.30
0.24
0.28
0.29
0.32
0.29
0.05
0.02
0.06
0.09
0.09
0.09
0.01
0.18
0.01
0.01
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.25
0.05
0.00
0.16
0.13
0.14
0.00
0.01
0.02
0.00
0.00
0.01
0.05
0.92
0.15
0.01
0.00
0.00
0.00
0.00
0.01
0.01
0.00
0.00
0.95
0.07
0.82
0.97
0.99
0.99
0.01
0.11
0.07
0.00
0.00
0.06
0.00
0.01
0.00
0.00
0.00
0.00
7.99
1.88
1.93
8.00
8.00
7.94
256
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
TC 002 TC 004 bt1 TC 004 bt2 TC 004 bt3 TC 004 TC 006 bt1
ser1
chl1
muscovite phlogopite phlogopite phlogopite clinochlore phlogopite
vein
biotite
Khbg
Khbg
Khbg
Khbg
Khbg
Kpd
47.25
36.47
37.22
36.89
27.13
37.74
0.26
3.53
3.14
3.08
0.07
3.39
31.15
14.47
14.34
14.25
18.78
14.53
0.00
0.03
0.02
0.00
0.00
0.00
0.77
4.04
4.09
4.24
3.62
3.73
2.77
14.52
14.74
15.27
18.46
13.43
1.93
11.88
11.80
11.41
16.71
13.14
0.11
0.94
0.90
0.94
1.52
0.53
0.06
0.00
0.01
0.06
0.05
0.01
0.42
0.08
0.13
0.04
0.00
0.11
10.33
9.31
9.19
9.07
0.09
9.67
4.43
3.69
3.86
3.59
11.38
3.61
0.00
0.33
0.00
0.52
0.00
0.71
0.00
0.10
0.10
0.08
0.03
0.02
99.48
99.38
99.55
99.44
97.83
100.63
0.00
-0.16
-0.02
-0.24
-0.01
-0.31
99.48
99.22
99.52
99.20
97.83
100.32
3.20
2.82
2.87
2.86
2.86
2.86
0.80
1.18
1.13
1.14
1.14
1.14
1.68
0.14
0.17
0.17
1.19
0.16
0.19
1.37
1.36
1.32
2.62
1.48
0.16
0.94
0.95
0.99
1.63
0.85
0.04
0.24
0.24
0.25
0.29
0.21
0.01
0.06
0.06
0.06
0.14
0.03
0.01
0.21
0.18
0.18
0.01
0.19
0.00
0.00
0.00
0.00
0.00
0.00
0.91
0.04
0.05
0.03
0.14
0.07
0.05
0.01
0.02
0.01
0.00
0.02
0.89
0.92
0.90
0.90
0.01
0.93
0.00
0.00
0.00
0.01
0.01
0.00
0.05
0.07
0.08
0.09
0.98
0.05
0.00
0.08
0.00
0.13
0.00
0.17
0.00
0.01
0.01
0.01
0.00
0.00
2.00
1.91
1.99
1.86
8.00
1.83
257
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
TC 008 bt1 TC 008 bt2 TC 009
TC 010' ser1
TC 011 bt1
chl1
phlogopite phlogopite clinochlore alumino-celadonite phlogopite
biotite
plag
Yg
Yg
Yg
Yg
Yg
35.71
36.41
32.76
50.17
36.86
2.81
2.10
0.00
0.05
3.63
17.37
16.82
16.91
24.36
13.88
0.00
0.02
0.03
0.03
0.03
4.19
4.14
2.10
1.14
3.81
15.10
14.90
10.72
4.09
13.73
9.66
10.01
20.56
4.20
12.96
0.61
0.64
1.04
0.12
0.56
0.00
0.06
0.52
0.48
0.02
0.05
0.10
0.06
0.30
0.08
9.52
9.29
0.01
8.09
9.29
3.38
3.25
11.88
4.18
3.67
0.99
1.26
0.00
0.36
0.42
0.04
0.04
0.02
0.01
0.04
99.44
99.04
96.61
97.59
98.99
-0.43
-0.54
0.00
-0.16
-0.19
99.01
98.51
96.61
97.43
98.80
2.77
2.83
3.31
3.46
2.85
1.23
1.17
0.69
0.54
1.15
0.36
0.38
1.32
1.43
0.11
1.12
1.16
3.09
0.43
1.49
0.98
0.97
0.91
0.24
0.89
0.25
0.24
0.16
0.06
0.22
0.04
0.04
0.09
0.01
0.04
0.16
0.12
0.00
0.00
0.21
0.00
0.00
0.00
0.00
0.00
0.09
0.08
0.43
0.83
0.04
0.01
0.02
0.01
0.04
0.01
0.94
0.92
0.00
0.71
0.91
0.00
0.01
0.06
0.04
0.00
0.05
0.06
0.93
0.21
0.07
0.24
0.31
0.00
0.08
0.10
0.00
0.01
0.00
0.00
0.01
1.75
1.69
8.00
1.92
1.89
258
Sample number
Mineral name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
Table 4. Normalized microprobe data: sheet silicates from Tea Cup.
TC 011
TV07 08
chl1
ser1
clinochlore chamosite
biotite
biotite
Yg
Yg
29.98
34.79
0.00
1.84
19.03
16.40
0.00
0.01
2.04
3.21
10.39
16.39
23.87
8.41
1.89
1.12
0.08
2.01
0.01
0.06
0.07
4.64
12.07
11.44
0.13
0.59
0.01
0.04
99.56
100.95
-0.06
-0.26
99.50
100.69
2.96
3.56
1.04
0.44
1.18
1.53
3.52
1.28
0.86
1.40
0.15
0.25
0.16
0.10
0.00
0.14
0.00
0.00
0.14
1.30
0.00
0.01
0.01
0.61
0.01
0.22
0.98
0.16
0.04
0.19
0.00
0.01
7.96
7.80
259
Table 5. Normalized microprobe data: epidote from Tea Cup
Sample
SP 004
SP 007
SP 007
SP 014
SP 029
SP 032
ep1
ep1
number
ep3
ep1
ep2
ep2
Mineral name epidote
epidote
epidote
epidote
epidote
epidote
Replacing
kspar
kspar
kspar
vein
kspar
plg
Host rock
Yg
Yg
Yg
Yg
Yg
Kpd
SiO2
38.10
37.53
37.31
37.75
37.37
36.76
TiO2
0.31
0.21
0.11
0.08
0.03
0.08
Al2O3
23.52
21.19
20.01
22.29
23.53
24.02
Cr2O3
0.00
0.01
0.00
0.01
0.00
0.03
Fe2O3
12.01
15.07
16.75
13.87
12.90
11.92
FeO
0.21
0.28
0.59
0.24
0.53
0.45
MgO
0.06
0.01
0.00
0.00
0.03
0.04
MnO
0.21
0.27
0.59
0.24
0.53
0.45
CaO
23.42
22.96
22.53
23.21
23.00
22.83
Na2O
0.00
0.00
0.00
0.00
0.00
0.00
K2O
0.00
0.02
0.00
0.01
0.00
0.00
H2O
1.81
1.82
1.85
1.87
1.81
1.69
F
0.16
0.07
0.00
0.00
0.15
0.37
Cl
0.01
0.00
0.00
0.01
0.00
0.00
Subtotal
99.81
99.43
99.74
99.56
99.89
98.63
O=F+Cl
-0.07
-0.03
0.00
0.00
-0.07
-0.16
Total
99.74
99.40
99.74
99.56
99.82
98.47
Si (T)
3.03
3.03
3.02
3.03
2.98
2.96
Al (T)
0.00
0.00
0.00
0.00
0.02
0.04
Al (Oct)
2.20
2.02
1.91
2.11
2.19
2.24
Mg (Oct)
0.01
0.00
0.00
0.00
0.00
0.01
Mn 2+ (Oct)
0.01
0.02
0.04
0.02
0.04
0.03
Mn 3+ (Oct)
0.00
0.00
0.00
0.00
0.00
0.00
Fe 3+ (Oct)
0.73
0.93
1.06
0.85
0.81
0.75
Ti (Oct)
0.02
0.01
0.01
0.00
0.00
0.00
Cr (Oct)
0.00
0.00
0.00
0.00
0.00
0.00
Na (A)
0.00
0.00
0.00
0.00
0.00
0.00
K (A)
0.00
0.00
0.00
0.00
0.00
0.00
Ca (A)
1.99
1.99
1.96
1.99
1.96
1.97
F (X)
0.04
0.02
0.00
0.00
0.04
0.09
Cl (X)
0.00
0.00
0.00
0.00
0.00
0.00
OH (X)
0.96
0.98
1.00
1.00
0.96
0.91
SP 097
ep1
epidote
kspar
Yg
36.90
0.12
23.65
0.08
12.71
0.48
0.11
0.48
22.56
0.00
0.00
1.79
0.15
0.01
99.04
-0.07
98.98
2.96
0.04
2.20
0.01
0.03
0.00
0.80
0.01
0.01
0.00
0.00
1.94
0.04
0.00
0.96
260
Table 5. Normalized microprobe data: epidote from Tea Cup
Sample
TV07 08 TC 001
TC 002
TC 009 TC 010' TC 010'
ep2
ep1
ep1
ep1
ep2
ep1
number
epidote
epidote
epidote
epidote
epidote
Mineral name epidote
kspar
vein
biotite
plag
quartz
quartz
Replacing
Yg
Kpd
Kpd
Yg
Yg
Yg
Host rock
37.08
37.16
36.77
37.32
38.40
37.73
SiO2
0.08
0.01
0.29
0.14
0.01
0.02
TiO2
22.88
23.98
23.08
20.65
25.28
20.51
Al2O3
0.03
0.00
0.00
0.01
0.00
0.00
Cr2O3
14.04
12.46
12.90
16.56
9.96
15.93
Fe2O3
0.52
0.40
0.38
0.34
0.60
0.67
FeO
0.00
0.06
0.05
0.00
0.00
0.00
MgO
0.51
0.40
0.37
0.33
0.59
0.66
MnO
22.82
22.88
22.70
22.90
23.28
22.36
CaO
0.05
0.04
0.04
0.07
0.00
0.03
Na2O
0.00
0.00
0.02
0.00
0.00
0.01
K2O
1.80
1.67
1.78
1.73
1.90
1.79
H2O
0.15
0.43
0.14
0.29
0.01
0.15
F
0.00
0.00
0.02
0.00
0.01
0.00
Cl
99.95
99.50
98.54
100.35
100.04
99.84
Subtotal
-0.06
-0.18
-0.06
-0.12
0.00
-0.06
O=F+Cl
99.89
99.32
98.48
100.23
100.03
99.78
Total
2.96
2.97
2.97
3.00
3.02
3.05
Si (T)
0.04
0.03
0.03
0.00
0.00
0.00
Al (T)
2.12
2.23
Al (Oct)
2.17
1.96
2.35
1.95
Mg (Oct)
0.00
0.01
0.01
0.00
0.00
0.00
Mn 2+ (Oct)
0.03
0.03
0.03
0.02
0.04
0.05
Mn 3+ (Oct)
0.00
0.00
0.00
0.00
0.00
0.00
Fe 3+ (Oct)
0.88
0.78
0.81
1.02
0.63
1.01
Ti (Oct)
0.00
0.00
0.02
0.01
0.00
0.00
Cr (Oct)
0.00
0.00
0.00
0.00
0.00
0.00
Na (A)
0.01
0.01
0.01
0.01
0.00
0.00
K (A)
0.00
0.00
0.00
0.00
0.00
0.00
Ca (A)
1.95
1.96
1.97
1.97
1.96
1.93
F (X)
0.04
0.11
0.04
0.07
0.00
0.04
Cl (X)
0.00
0.00
0.00
0.00
0.00
0.00
OH (X)
0.96
0.89
0.96
0.93
1.00
0.96
261
Table 6. Normalized microprobe data: amphibole from Tea Cup
Sample
SP 007 act2 SP 007 chl1 TC 006 amph1 TC 006 amph2
Mineral Name
actinolite
actinolite
actinolite
actinolite
Replacing
biotite
quartz
biotite
biotite
Host rock
Yg
Yg
Yg
Yg
SiO2
50.82
53.51
50.00
50.44
TiO2
0.64
0.06
0.59
0.64
Al2O3
4.86
1.96
5.21
4.87
Cr2O3
0.02
0.00
0.01
0.01
Fe2O3
5.54
3.50
5.40
4.90
FeO
7.62
7.62
8.44
8.47
MgO
15.18
13.96
14.50
14.79
MnO
0.82
4.57
0.81
0.81
CaO
11.68
11.71
11.61
11.72
Na2O
0.92
0.22
0.97
0.96
K2O
0.42
0.15
0.50
0.37
H2O
1.99
1.96
2.07
2.08
F
0.22
0.22
0.00
0.00
Cl
0.01
0.01
0.01
0.00
Subtotal
100.74
99.45
100.12
100.07
O=F+Cl
-0.10
-0.09
0.00
0.00
Total
100.65
99.36
100.12
100.07
Si (T)
Al (T)
Al (6)
Fe 3+ (6)
Ti (6)
Cr (6)
Mg (8)
Fe 2+ (8)
Mn (8)
Ca (8)
Na (A)
K (A)
vac.
F
Cl
OH
7.27
0.73
0.09
3.24
0.91
0.60
0.10
0.07
0.00
1.79
0.26
0.08
0.67
0.10
0.00
1.90
7.77
0.23
0.10
3.02
0.93
0.38
0.56
0.01
0.00
1.82
0.06
0.03
0.91
0.10
0.00
1.90
7.22
0.78
0.11
3.12
1.02
0.59
0.10
0.06
0.00
1.80
0.27
0.09
0.64
0.00
0.00
2.00
7.27
0.73
0.10
3.18
1.02
0.53
0.10
0.07
0.00
1.81
0.27
0.07
0.66
0.00
0.00
2.00
262
Table 6. Normalized microprobe data: amphibole from Tea Cup
Sample
TC 011 act1 TC 011 act2
Mineral Name
actinolite
actinolite
Replacing
biotite
biotite
Host rock
Yg
Yg
SiO2
48.97
51.46
TiO2
0.79
0.35
Al2O3
5.95
4.18
Cr2O3
0.01
0.04
Fe2O3
5.29
4.54
FeO
8.96
7.91
MgO
14.06
15.45
MnO
0.72
0.73
CaO
11.76
12.04
Na2O
0.99
0.53
K2O
0.51
0.29
H2O
1.96
1.92
F
0.21
0.35
Cl
0.03
0.00
Subtotal
100.21
99.80
O=F+Cl
-0.09
-0.15
Total
100.12
99.65
Si (T)
Al (T)
Al (6)
Fe 3+ (6)
Ti (6)
Cr (6)
Mg (8)
Fe 2+ (8)
Mn (8)
Ca (8)
Na (A)
K (A)
vac.
F
Cl
OH
7.10
0.90
0.12
3.04
1.09
0.58
0.09
0.09
0.00
1.83
0.28
0.10
0.63
0.09
0.01
1.90
7.40
0.60
0.11
3.31
0.95
0.49
0.09
0.04
0.00
1.86
0.15
0.05
0.80
0.16
0.00
1.84
263
Table 7. Normalized microprobe data: feldspars from Eagle Pass.
Sample
EP 005a EP 005a EP 005a
number
kspar1 kspar2
plg1
Replacing
Host Rock
Tpd
Tpd
Tpd
SiO2
64.60
65.02
66.74
Al2O3
18.85
18.73
21.65
TiO2
0.05
0.00
0.04
Cr2O3
0.00
0.03
0.01
Fe2O3
0.00
0.05
0.00
FeO
0.00
0.00
0.07
MgO
0.00
0.00
0.01
MnO
0.01
0.00
0.00
CaO
0.00
0.00
2.02
Na2O
0.85
1.23
11.23
K2O
15.28
14.78
0.17
F
0.08
0.00
0.00
Cl
0.00
0.00
0.00
Total
99.69
99.84
101.94
Based on IV=4
Si
2.98
2.98
2.89
Al
1.02
1.01
1.11
Fe3+
0.00
0.00
0.00
Na
0.08
0.11
0.94
K
0.90
0.87
0.01
Ca
0.00
0.00
0.09
Mg
0.00
0.00
0.00
Ti
0.00
0.00
0.00
Cr
0.00
0.00
0.00
Mn
0.00
0.00
0.00
F
0.01
0.00
0.00
Cl
0.00
0.00
0.00
O
7.99
8.00
8.00
End Member
Or #
0.92
0.89
0.01
An #
0.00
0.00
0.09
Ab #
0.08
0.11
0.90
EP 006
kspar1
EP 006
kspar2
EP 006
plg1
EP 007
kspar1
Yg
65.65
18.60
0.03
0.01
0.10
0.00
0.00
0.00
0.00
0.95
15.18
0.00
0.02
100.54
Yg
65.42
18.71
0.00
0.00
0.00
0.02
0.00
0.00
0.00
1.34
15.21
0.47
0.01
100.98
Yg
65.66
21.48
0.04
0.00
0.09
0.00
0.00
0.00
2.25
9.88
0.33
0.00
0.00
99.72
Tpd
64.63
18.36
0.00
0.01
0.00
0.18
0.00
0.00
0.00
0.47
15.80
0.39
0.00
99.68
2.99
1.00
0.00
0.08
0.88
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.99
1.01
0.00
0.12
0.89
0.00
0.00
0.00
0.00
0.00
0.07
0.00
7.93
2.88
1.11
0.00
0.84
0.02
0.11
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.99
1.01
0.00
0.04
0.93
0.00
0.00
0.00
0.00
0.00
0.06
0.00
7.94
0.91
0.00
0.09
0.88
0.00
0.12
0.02
0.11
0.87
0.96
0.00
0.04
264
Table 7. Normalized microprobe data: feldspars from Eagle Pass.
Sample
EP 007
number
plg1
Replacing
kspar
Host Rock
Tpd
SiO2
58.07
Al2O3
25.99
TiO2
0.00
Cr2O3
0.00
Fe2O3
0.28
FeO
0.00
MgO
0.01
MnO
0.00
CaO
7.80
Na2O
6.89
K2O
0.13
F
0.00
Cl
0.00
Total
99.15
Based on IV=4
2.61
Si
1.38
Al
0.01
Fe3+
0.60
Na
0.01
K
Ca
0.38
Mg
0.00
Ti
0.00
Cr
0.00
Mn
0.00
F
0.00
Cl
0.00
O
8.00
End Member
Or #
0.01
An #
0.38
Ab #
0.61
EP 016
kspar1
EP 016
plg1
EP 016
ser1
EP 017a EP 017a EP 017c
kspar1 kspar2
plg1
Yg
65.52
18.41
0.00
0.01
0.12
0.00
0.00
0.01
0.01
0.53
15.62
0.01
0.01
100.23
Yg
68.03
20.07
0.00
0.00
0.00
0.00
0.01
0.00
0.32
11.73
0.08
0.00
0.00
100.25
Yg
63.31
19.65
0.12
0.01
0.94
0.00
0.16
0.03
0.00
0.48
15.64
0.00
0.00
100.34
Tpd
65.43
18.80
0.05
0.00
0.00
0.08
0.00
0.01
0.06
1.71
14.19
0.46
0.01
100.60
Tpd
64.54
18.46
0.04
0.00
0.63
0.00
0.00
0.01
0.00
0.39
15.95
0.00
0.01
100.02
Tpd
55.74
27.65
0.04
0.02
0.32
0.00
0.02
0.01
9.78
5.59
0.30
0.00
0.00
99.47
3.00
0.99
0.00
0.05
0.91
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.97
1.03
0.00
0.99
0.00
0.02
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.90
1.07
0.03
0.04
0.91
0.00
0.01
0.00
0.00
0.00
0.00
0.00
8.00
2.98
1.02
0.00
0.15
0.83
0.00
0.00
0.00
0.00
0.00
0.07
0.00
7.93
2.97
1.00
0.02
0.03
0.94
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.52
1.47
0.01
0.49
0.02
0.47
0.00
0.00
0.00
0.00
0.00
0.00
8.00
0.95
0.00
0.05
0.00
0.01
0.98
0.96
0.00
0.04
0.84
0.00
0.15
0.96
0.00
0.04
0.02
0.48
0.50
265
Table 7. Normalized microprobe data: feldspars from Eagle Pass.
Sample
EP 017c
number
plg2
Replacing
Host Rock
Tpd
SiO2
62.54
Al2O3
23.27
TiO2
0.00
Cr2O3
0.00
Fe2O3
0.00
FeO
0.00
MgO
0.00
MnO
0.00
CaO
4.44
Na2O
8.64
K2O
0.08
F
0.00
Cl
0.00
Total
98.97
Based on IV=4
2.78
Si
1.22
Al
0.00
Fe3+
0.74
Na
0.00
K
Ca
0.21
Mg
0.00
Ti
0.00
Cr
0.00
Mn
0.00
F
0.00
Cl
0.00
O
8.00
End Member
Or #
0.00
An #
0.22
Ab #
0.78
EP 021
kspar1
Yg
65.62
18.61
0.02
0.01
0.06
0.00
0.01
0.00
0.00
0.53
15.71
0.15
0.00
100.66
EP 021
plg1
kspar
Yg
68.13
19.64
0.04
0.00
0.05
0.00
0.00
0.00
0.07
11.62
0.08
0.00
0.00
99.63
EP 022a EP 022b EP 022b EP 024
plg1
plg1
plg2
kspar1
plag
Yg
Yg
Yg
Yg
68.86
69.22
68.56
64.79
19.91
19.77
19.91
18.75
0.02
0.02
0.05
0.00
0.00
0.00
0.01
0.02
0.00
0.13
0.02
0.06
0.10
0.00
0.00
0.00
0.00
0.04
0.00
0.00
0.00
0.01
0.02
0.02
0.29
0.09
0.24
0.00
11.92
11.09
11.29
0.79
0.09
0.35
0.25
15.31
0.00
0.00
0.00
0.17
0.00
0.00
0.00
0.01
101.20 100.71 100.34
99.84
3.00
1.00
0.00
0.05
0.91
0.00
0.00
0.00
0.00
0.00
0.02
0.00
7.98
2.98
1.01
0.00
0.99
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.98
1.02
0.00
1.00
0.01
0.01
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.99
1.01
0.00
0.93
0.02
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.98
1.02
0.00
0.95
0.01
0.01
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.98
1.02
0.00
0.07
0.90
0.00
0.00
0.00
0.00
0.00
0.02
0.00
7.98
0.95
0.00
0.05
0.00
0.00
0.99
0.01
0.01
0.98
0.02
0.00
0.98
0.01
0.01
0.97
0.93
0.00
0.07
266
Table 7. Normalized microprobe data: feldspars from Eagle Pass.
Sample
EP 024
number
plg1
Replacing
Host Rock
Yg
SiO2
64.33
Al2O3
22.56
TiO2
0.00
Cr2O3
0.00
Fe2O3
0.00
FeO
0.05
MgO
0.00
MnO
0.01
CaO
3.46
Na2O
9.77
K2O
0.09
F
0.30
Cl
0.01
Total
100.45
Based on IV=4
2.83
Si
1.17
Al
0.00
Fe3+
0.83
Na
0.01
K
Ca
0.16
Mg
0.00
Ti
0.00
Cr
0.00
Mn
0.00
F
0.04
Cl
0.00
O
7.96
End Member
Or #
0.01
An #
0.16
Ab #
0.83
EP 033
plg1
EP 033
plg2
EP 034
plg1
EP 034 EP 035b EP 035b
plg2
kspar1
plg1
Yg
68.54
19.79
0.05
0.02
0.00
0.00
0.00
0.01
0.20
11.44
0.04
0.00
0.00
100.09
Yg
68.42
20.09
0.03
0.00
0.00
0.06
0.01
0.00
0.38
11.97
0.06
0.00
0.00
101.03
Yg
67.37
20.77
0.00
0.00
0.23
0.00
0.05
0.00
0.74
11.08
0.37
0.00
0.00
100.61
Yg
67.72
19.58
0.00
0.00
0.00
0.03
0.00
0.02
0.03
11.93
0.06
0.00
0.00
99.36
Yg
64.40
18.82
0.00
0.03
0.03
0.00
0.01
0.00
0.00
0.45
15.81
0.00
0.01
99.55
Yg
68.16
20.39
0.02
0.00
0.14
0.00
0.03
0.00
1.00
10.86
0.29
0.00
0.00
100.89
2.98
1.02
0.00
0.97
0.00
0.01
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.97
1.03
0.00
1.01
0.00
0.02
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.93
1.06
0.01
0.93
0.02
0.03
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.98
1.02
0.00
1.02
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.97
1.03
0.00
0.04
0.93
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.95
1.04
0.00
0.91
0.02
0.05
0.00
0.00
0.00
0.00
0.00
0.00
8.00
0.00
0.01
0.99
0.00
0.02
0.98
0.02
0.04
0.94
0.00
0.00
1.00
0.96
0.00
0.04
0.02
0.05
0.94
267
Table 7. Normalized microprobe data: feldspars from Eagle Pass.
Sample
EP 035b EP 037
number
plg2
plg1
Replacing
kspar
Host Rock
Yg
Tpd
SiO2
61.78
66.20
Al2O3
23.50
20.64
TiO2
0.00
0.00
Cr2O3
0.00
0.00
Fe2O3
0.02
0.00
FeO
0.00
0.13
MgO
0.00
0.00
MnO
0.01
0.00
CaO
4.80
1.39
Na2O
8.78
11.42
K2O
0.16
0.06
F
0.00
0.00
Cl
0.00
0.00
Total
99.06
99.83
Based on IV=4
2.76
2.92
Si
1.24
1.08
Al
0.00
0.00
Fe3+
0.76
0.98
Na
0.01
K
0.00
Ca
0.23
0.07
Mg
0.00
0.00
Ti
0.00
0.00
Cr
0.00
0.00
Mn
0.00
0.00
F
0.00
0.00
Cl
0.00
0.00
O
8.00
8.00
End Member
Or #
0.01
0.00
An #
0.23
0.06
Ab #
0.76
0.93
EP 038a EP 038a EP 038a EP 038a EP 038a
kspar1 kspar2
plg1
plg2
plg3
Tpd
63.81
18.69
0.00
0.03
0.03
0.00
0.00
0.00
0.00
0.59
15.67
0.00
0.00
98.82
Tpd
63.71
18.69
0.04
0.06
0.10
0.00
0.00
0.00
0.00
0.69
15.31
0.00
0.01
98.60
Tpd
76.31
14.81
0.17
0.00
0.28
0.00
0.04
0.03
1.98
6.51
0.17
0.00
0.00
100.30
Tpd
56.90
27.28
0.07
0.00
0.31
0.00
0.01
0.00
8.91
6.34
0.18
0.00
0.00
100.01
Tpd
57.28
26.32
0.02
0.00
0.43
0.00
0.01
0.00
8.17
6.83
0.11
0.00
0.00
99.18
2.97
1.03
0.00
0.05
0.93
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.97
1.03
0.00
0.06
0.91
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
3.24
0.75
0.01
0.54
0.01
0.09
0.00
0.01
0.00
0.00
0.00
0.00
8.00
2.55
1.44
0.01
0.55
0.01
0.43
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.58
1.40
0.01
0.60
0.01
0.40
0.00
0.00
0.00
0.00
0.00
0.00
8.00
0.95
0.00
0.05
0.94
0.00
0.06
0.01
0.14
0.84
0.01
0.43
0.56
0.01
0.40
0.60
268
Table 7. Normalized microprobe data: feldspars from Eagle Pass.
Sample
EP 038c EP 038c
number
kspar2
plg1
Replacing
plag
Host Rock
Yg
Yg
SiO2
64.72
58.77
Al2O3
18.87
25.01
TiO2
0.03
0.00
Cr2O3
0.00
0.00
Fe2O3
0.39
0.33
FeO
0.00
0.00
MgO
0.00
0.00
MnO
0.01
0.00
CaO
0.00
6.50
Na2O
0.72
7.43
K2O
15.43
0.26
F
0.25
0.00
Cl
0.00
0.00
Total
100.32
98.30
Based on IV=4
2.97
2.66
Si
1.02
1.33
Al
0.01
0.01
Fe3+
0.06
0.65
Na
0.90
K
0.01
Ca
0.00
0.31
Mg
0.00
0.00
Ti
0.00
0.00
Cr
0.00
0.00
Mn
0.00
0.00
F
0.04
0.00
Cl
0.00
0.00
O
7.96
8.00
End Member
Or #
0.93
0.02
An #
0.00
0.32
Ab #
0.07
0.66
EP 040
kspar 1
EP 040
kspar2
EP 040
plg3
plag
Yxm
67.23
20.29
0.04
0.02
0.03
0.00
0.01
0.02
0.38
11.09
0.33
0.00
0.00
99.44
EP 042
kspar1
Yxm
64.33
18.70
0.00
0.01
0.00
0.07
0.00
0.00
0.00
0.56
16.18
0.16
0.00
99.93
EP 040
plg2
kspar
Yxm
67.86
20.26
0.05
0.01
0.03
0.00
0.00
0.00
0.63
11.19
0.14
0.00
0.00
100.17
Yxm
64.97
18.55
0.00
0.00
0.01
0.00
0.00
0.01
0.00
0.46
15.66
0.07
0.01
99.71
2.99
1.01
0.00
0.04
0.92
0.00
0.00
0.00
0.00
0.00
0.01
0.00
7.99
2.98
1.02
0.00
0.05
0.96
0.00
0.00
0.00
0.00
0.00
0.02
0.00
7.98
2.96
1.04
0.00
0.95
0.01
0.03
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.95
1.05
0.00
0.94
0.02
0.02
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.97
1.02
0.00
0.05
0.93
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
0.96
0.00
0.04
0.95
0.00
0.05
0.01
0.03
0.96
0.02
0.02
0.96
0.95
0.00
0.05
Yxm
64.23
18.78
0.01
0.00
0.04
0.00
0.00
0.00
0.00
0.51
15.82
0.00
0.01
99.39
269
Table 7. Normalized microprobe data: feldspars from Eagle Pass.
Sample
EP 042
number
kspar2
Replacing
Host Rock
Yxm
SiO2
64.82
Al2O3
18.97
TiO2
0.00
Cr2O3
0.00
Fe2O3
0.00
FeO
0.00
MgO
0.00
MnO
0.00
CaO
0.00
Na2O
2.00
K2O
13.66
F
0.08
Cl
0.01
Total
99.52
Based on IV=4
2.97
Si
1.03
Al
0.00
Fe3+
0.18
Na
0.80
K
Ca
0.00
Mg
0.00
Ti
0.00
Cr
0.00
Mn
0.00
F
0.01
Cl
0.00
O
7.99
End Member
Or #
0.82
An #
0.00
Ab #
0.18
EP 042
plg1
EP 046
kspar2
EP 070
kspar1
EP 070
kspar2
EP 070
plg1
Yxm
67.02
20.12
0.00
0.00
0.02
0.00
0.00
0.00
0.67
11.04
0.07
0.00
0.00
98.94
EP 042
plg2
kspar
Yxm
67.58
19.84
0.00
0.01
0.00
0.03
0.00
0.00
0.46
11.58
0.11
0.00
0.00
99.62
Yg
65.21
18.34
0.00
0.01
0.12
0.00
0.00
0.00
0.00
0.38
16.23
0.01
0.00
100.31
Yg
64.69
18.59
0.04
0.02
0.00
0.07
0.00
0.00
0.00
0.74
15.54
0.32
0.02
99.90
Yg
64.71
18.58
0.05
0.02
0.27
0.00
0.00
0.02
0.00
0.41
16.14
0.02
0.04
100.23
Yg
69.34
19.82
0.00
0.03
0.04
0.05
0.01
0.00
0.21
11.76
0.15
0.00
0.02
101.42
2.95
1.05
0.00
0.94
0.00
0.03
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.97
1.03
0.00
0.99
0.01
0.02
0.00
0.00
0.00
0.00
0.00
0.00
8.00
3.00
1.00
0.00
0.03
0.95
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.98
1.02
0.00
0.07
0.91
0.00
0.00
0.00
0.00
0.00
0.05
0.00
7.95
2.98
1.01
0.01
0.04
0.95
0.00
0.00
0.00
0.00
0.00
0.00
0.00
7.99
2.99
1.01
0.00
0.98
0.01
0.01
0.00
0.00
0.00
0.00
0.00
0.00
8.00
0.00
0.03
0.96
0.01
0.02
0.97
0.97
0.00
0.03
0.93
0.00
0.07
0.96
0.00
0.04
0.01
0.01
0.98
270
Table 7. Normalized microprobe data: feldspars from Eagle Pass.
Sample
EP 070
number
plg3
Replacing
Host Rock
Yg
SiO2
69.00
Al2O3
19.41
TiO2
0.00
Cr2O3
0.02
Fe2O3
0.00
FeO
0.13
MgO
0.00
MnO
0.00
CaO
0.15
Na2O
11.72
K2O
0.17
F
0.00
Cl
0.00
Total
100.59
Based on IV=4
3.00
Si
1.00
Al
0.00
Fe3+
0.99
Na
0.01
K
Ca
0.01
Mg
0.00
Ti
0.00
Cr
0.00
Mn
0.00
F
0.00
Cl
0.00
O
8.00
End Member
Or #
0.01
An #
0.01
Ab #
0.98
EP 086
kspar1
EP 086
kspar2
EP 086
kspar3
EP 086
plg1
EP 086
plg2
EP 086
plg3
Yg
63.92
18.63
0.00
0.00
0.06
0.00
0.00
0.00
0.00
1.11
14.94
0.00
0.02
98.67
Yg
64.79
18.75
0.07
0.00
0.00
0.01
0.00
0.00
0.00
1.14
15.05
0.30
0.00
100.00
Yg
63.34
18.64
0.00
0.00
0.08
0.00
0.00
0.00
0.00
0.77
15.20
0.30
0.00
98.20
Yg
65.30
22.89
0.00
0.00
0.00
0.03
0.00
0.00
3.65
10.21
0.13
0.00
0.01
102.22
Yg
65.36
22.50
0.00
0.02
0.00
0.03
0.00
0.02
3.47
9.79
0.08
0.47
0.01
101.54
Yg
64.87
22.36
0.05
0.02
0.00
0.03
0.00
0.04
3.40
9.89
0.16
0.25
0.01
100.97
2.98
1.02
0.00
0.10
0.89
0.00
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.98
1.02
0.00
0.10
0.88
0.00
0.00
0.00
0.00
0.00
0.04
0.00
7.96
2.97
1.03
0.00
0.07
0.91
0.00
0.00
0.00
0.00
0.00
0.04
0.00
7.96
2.83
1.17
0.00
0.86
0.01
0.17
0.00
0.00
0.00
0.00
0.00
0.00
8.00
2.84
1.16
0.00
0.83
0.00
0.16
0.00
0.00
0.00
0.00
0.06
0.00
7.94
2.84
1.16
0.00
0.84
0.01
0.16
0.00
0.00
0.00
0.00
0.04
0.00
7.96
0.90
0.00
0.10
0.90
0.00
0.10
0.93
0.00
0.07
0.01
0.16
0.83
0.00
0.16
0.83
0.01
0.16
0.83
271
Table 7. Normalized microprobe data: feldspars from Eagle Pass.
Sample
EP 086 MW 001 MW 001 MW ALT5' MW NACA2 MW NACA3
number
plg4
plg1
plg2
plg1
plg1
plg1
Replacing
kspar
kspar
kspar
kspar
kspar
Host Rock
Yg
Yg
Yg
Yg
Yg
Yg
SiO2
61.91
68.33
69.14
66.65
67.61
67.27
Al2O3
24.35
19.71
19.67
21.06
20.62
21.00
TiO2
0.04
0.00
0.00
0.00
0.06
0.00
Cr2O3
0.00
0.00
0.01
0.00
0.05
0.00
Fe2O3
0.00
0.34
0.04
0.08
0.00
0.01
FeO
0.06
0.00
0.00
0.00
0.00
0.00
MgO
0.00
0.00
0.00
0.00
0.00
0.00
MnO
0.00
0.00
0.00
0.00
0.00
0.01
CaO
5.57
0.08
0.13
1.49
0.85
1.05
Na2O
8.61
11.52
11.12
10.78
11.60
11.18
K2O
0.21
0.00
0.06
0.12
0.10
0.09
F
0.00
0.00
0.00
0.00
0.00
0.00
Cl
0.00
0.00
0.00
0.00
0.01
0.01
Total
100.75
99.99
100.18
100.19
100.90
100.62
Based on IV=4
2.73
2.98
2.99
2.91
2.94
2.92
Si
1.27
1.01
1.00
1.08
1.06
1.08
Al
0.00
0.01
0.00
0.00
0.00
0.00
Fe3+
0.74
0.97
0.93
0.91
0.98
0.94
Na
0.01
0.00
0.00
0.01
0.01
0.00
K
0.26
0.00
0.01
0.07
0.04
0.05
Ca
0.00
0.00
0.00
0.00
0.00
0.00
Mg
Ti
0.00
0.00
0.00
0.00
0.00
0.00
Cr
0.00
0.00
0.00
0.00
0.00
0.00
Mn
0.00
0.00
0.00
0.00
0.00
0.00
F
0.00
0.00
0.00
0.00
0.00
0.00
Cl
0.00
0.00
0.00
0.00
0.00
0.00
O
8.00
8.00
8.00
8.00
8.00
8.00
End Member
Or #
0.01
0.00
0.00
0.01
0.01
0.00
An #
0.26
0.00
0.01
0.07
0.04
0.05
Ab #
0.73
1.00
0.99
0.92
0.96
0.95
272
Table 7. Normalized microprobe data: feldspars from Eagle Pass.
Sample
MW SPECHEM
number
plg1
Replacing
Host Rock
Yg
SiO2
68.71
Al2O3
19.80
TiO2
0.00
Cr2O3
0.00
Fe2O3
0.18
FeO
0.00
MgO
0.11
MnO
0.00
CaO
0.29
Na2O
11.42
K2O
0.10
F
0.00
Cl
0.00
Total
100.61
Based on IV=4
2.98
Si
1.01
Al
0.01
Fe3+
0.96
Na
0.01
K
0.01
Ca
0.01
Mg
Ti
0.00
0.00
Cr
Mn
0.00
F
0.00
Cl
0.00
O
8.00
End Member
Or #
0.01
An #
0.01
Ab #
0.98
273
Table 8. Normalized microprobe data: sheet silicates from Eagle Pass.
Sample number EP 005a EP 006 bt1 EP 006 bt2
EP 006 ser1
EP 007 bt1
bt1
Mineral Name
annite
annite
annite
alumino-celadonite phlogopite
Replacing
biotite
Host Rock
Tpd
Tpd
Tpd
Yg
Tpd
SiO2
36.72
37.36
36.98
46.41
38.11
TiO2
2.04
0.08
0.10
0.22
1.92
Al2O3
16.30
21.20
19.71
28.65
15.32
Cr2O3
0.00
0.01
0.01
0.00
0.13
Fe2O3
4.54
4.40
4.73
1.23
3.38
FeO
16.34
15.83
17.02
4.43
12.16
MgO
8.37
6.06
6.34
2.39
13.40
MnO
1.04
0.45
0.46
0.10
0.15
CaO
0.01
0.33
0.34
0.00
0.09
Na2O
0.08
0.09
0.04
0.12
0.02
K2O
9.48
3.43
4.19
10.48
8.23
H2O
3.05
3.80
3.58
4.12
3.89
F
1.60
0.00
0.37
0.40
0.00
Cl
0.05
0.00
0.02
0.02
0.04
Subtotal
99.62
93.01
93.88
98.58
96.86
O=F+Cl
-0.68
0.00
-0.16
-0.17
-0.01
Total
98.93
93.01
93.72
98.41
96.85
Si (T)
2.88
2.95
2.95
3.22
2.93
Al (T)
1.12
1.05
1.05
0.78
1.07
Al (Oct)
0.39
0.92
0.80
1.57
0.31
Mg (Oct)
0.98
0.71
0.75
0.25
1.53
Fe 2+ (Oct)
1.07
1.05
1.14
0.26
0.78
Fe 3+ (Oct)
0.27
0.26
0.28
0.06
0.20
Mn (Oct)
0.07
0.03
0.03
0.01
0.01
Ti (Oct)
0.12
0.00
0.01
0.01
0.11
Cr (Oct)
0.00
0.00
0.00
0.00
0.01
vacant (Oct)
0.10
0.02
0.00
0.85
0.05
Na (A)
0.01
0.01
0.01
0.02
0.00
K (A)
0.95
0.35
0.43
0.93
0.81
Ca (A)
0.00
0.03
0.03
0.00
0.01
vacant (A)
0.04
0.61
0.54
0.06
0.18
F (X)
0.40
0.00
0.09
0.09
0.00
Cl (X)
0.01
0.00
0.00
0.00
0.01
OH (X)
1.60
2.00
1.90
1.91
1.99
274
Table 8. Normalized microprobe data: sheet silicates from Eagle Pass.
Sample number EP 007 bt2 EP 016 bt1 EP 017a
EP 017a
EP 017c
EP 017c
bt1
bt2
bt1
bt2
Mineral Name phlogopite phlogopite phlogopite phlogopite phlogopite phlogopite
Replacing
biotite
biotite
biotite
biotite
Host Rock
Tpd
Yg
Tpd
Tpd
Tpd
Tpd
SiO2
38.45
38.67
37.16
37.59
36.14
36.15
TiO2
1.76
2.23
0.30
0.36
1.31
3.39
Al2O3
14.72
15.07
16.57
16.82
17.11
17.16
Cr2O3
0.85
0.01
0.00
0.00
0.00
0.00
Fe2O3
3.15
3.55
3.31
3.32
3.84
3.98
FeO
11.32
12.78
11.90
11.95
13.81
14.34
MgO
13.92
12.75
12.70
13.01
11.69
10.17
MnO
0.17
0.26
0.66
0.69
0.30
0.29
CaO
0.09
0.05
0.16
0.17
0.16
0.00
Na2O
0.00
0.12
0.05
0.11
0.04
0.10
K2O
7.73
9.57
8.11
8.31
9.45
9.22
H2O
3.71
3.57
2.88
2.98
3.57
3.87
F
0.39
0.79
1.98
1.88
0.59
0.00
Cl
0.04
0.02
0.02
0.02
0.01
0.06
Subtotal
96.31
99.43
95.78
97.20
98.01
98.72
O=F+Cl
-0.17
-0.34
-0.84
-0.80
-0.25
-0.01
Total
96.13
99.10
94.94
96.40
97.76
98.70
Si (T)
2.95
2.94
2.92
2.91
2.81
2.79
Al (T)
1.05
1.06
1.08
1.09
1.19
1.21
Al (Oct)
0.29
0.28
0.45
0.44
0.38
0.35
Mg (Oct)
1.59
1.44
1.49
1.50
1.36
1.17
Fe 2+ (Oct)
0.73
0.81
0.78
0.77
0.90
0.92
Fe 3+ (Oct)
0.18
0.20
0.20
0.19
0.22
0.23
Mn (Oct)
0.01
0.02
0.04
0.04
0.02
0.02
Ti (Oct)
0.10
0.13
0.02
0.02
0.08
0.20
Cr (Oct)
0.05
0.00
0.00
0.00
0.00
0.00
vacant (Oct)
0.04
0.11
0.03
0.03
0.05
0.11
Na (A)
0.00
0.02
0.01
0.02
0.01
0.01
K (A)
0.76
0.93
0.81
0.82
0.94
0.91
Ca (A)
0.01
0.00
0.01
0.01
0.01
0.00
vacant (A)
0.23
0.05
0.17
0.15
0.04
0.08
F (X)
0.09
0.19
0.49
0.46
0.15
0.00
Cl (X)
0.00
0.00
0.00
0.00
0.00
0.01
OH (X)
1.90
1.81
1.51
1.54
1.85
1.99
275
Table 8. Normalized microprobe data: sheet silicates from Eagle Pass.
Sample number
EP 017c ser1
EP 021 ser1
EP 021
EP 022a bt1
ser2
Mineral Name alumino-celadonite alumino-celadonite muscovite
phlogopite
Replacing
biotite
plag
plag
Host Rock
Tpd
Yg
Yg
Yg
SiO2
45.92
48.58
45.00
37.89
TiO2
0.58
0.08
0.03
1.35
Al2O3
28.95
27.32
33.83
15.23
Cr2O3
0.03
0.00
0.02
0.01
Fe2O3
1.19
1.23
0.94
4.16
FeO
4.28
4.44
3.40
14.98
MgO
2.52
2.33
0.46
11.06
MnO
0.03
0.03
0.00
0.38
CaO
0.04
0.00
0.00
0.11
Na2O
0.23
0.21
0.24
0.07
K2O
10.74
10.84
10.62
8.78
H2O
4.23
4.25
4.38
3.12
F
0.21
0.24
0.00
1.54
Cl
0.01
0.02
0.00
0.00
Subtotal
98.97
99.56
98.93
98.68
O=F+Cl
-0.09
-0.10
0.00
-0.65
Total
98.88
99.46
98.93
98.03
Si (T)
3.18
3.33
3.08
2.95
Al (T)
0.82
0.67
0.92
1.05
Al (Oct)
1.54
1.54
1.81
0.34
Mg (Oct)
0.26
0.24
0.05
1.28
Fe 2+ (Oct)
0.25
0.25
0.19
0.97
Fe 3+ (Oct)
0.06
0.06
0.05
0.24
Mn (Oct)
0.00
0.00
0.00
0.02
Ti (Oct)
0.03
0.00
0.00
0.08
Cr (Oct)
0.00
0.00
0.00
0.00
vacant (Oct)
0.85
0.90
0.90
0.05
Na (A)
0.03
0.03
0.03
0.01
K (A)
0.95
0.95
0.93
0.87
Ca (A)
0.00
0.00
0.00
0.01
vacant (A)
0.02
0.02
0.04
0.11
F (X)
0.05
0.05
0.00
0.38
Cl (X)
0.00
0.00
0.00
0.00
OH (X)
1.95
1.95
2.00
1.62
276
Table 8. Normalized microprobe data: sheet silicates from Eagle Pass.
Sample number EP 022a
EP 022a
EP 022a
EP 022b
EP 022b
EP 022b
bt2
bt3
bt4
bt1
ser1
ser2
Mineral Name phlogopite phlogopite phlogopite phlogopite muscovite muscovite
Replacing
biotite
biotite
biotite
plag
biotite
Host Rock
Yg
Yg
Yg
Yg
Yg
Yg
SiO2
36.70
37.47
37.79
37.31
47.37
47.61
TiO2
1.54
1.60
0.16
1.98
0.10
0.51
Al2O3
16.39
15.88
17.07
17.03
34.92
29.27
Cr2O3
0.03
0.02
0.00
0.00
0.00
0.00
Fe2O3
4.38
4.28
3.94
3.81
0.35
1.05
FeO
15.77
15.40
14.19
13.70
1.28
3.77
MgO
10.14
10.86
11.54
11.56
0.68
1.84
MnO
0.41
0.44
0.39
0.35
0.05
0.04
CaO
0.05
0.06
0.11
0.00
0.01
0.00
Na2O
0.05
0.07
0.08
0.03
0.27
0.20
K2O
9.23
9.15
8.23
9.74
9.93
10.55
H2O
3.77
3.76
3.60
3.62
4.47
4.39
F
0.15
0.25
0.59
0.64
0.08
0.00
Cl
0.03
0.01
0.01
0.03
0.01
0.01
Subtotal
98.63
99.25
97.72
99.80
99.52
99.24
O=F+Cl
-0.07
-0.11
-0.25
-0.28
-0.04
0.00
Total
98.56
99.15
97.47
99.52
99.48
99.24
Si (T)
2.86
2.89
2.92
2.84
3.15
3.25
Al (T)
1.14
1.11
1.08
1.16
0.85
0.75
Al (Oct)
0.37
0.34
0.48
0.37
1.88
1.61
Mg (Oct)
1.18
1.25
1.33
1.31
0.07
0.19
Fe 2+ (Oct)
1.03
0.99
0.92
0.87
0.07
0.22
Fe 3+ (Oct)
0.26
0.25
0.23
0.22
0.02
0.05
Mn (Oct)
0.03
0.03
0.03
0.02
0.00
0.00
Ti (Oct)
0.09
0.09
0.01
0.11
0.00
0.03
Cr (Oct)
0.00
0.00
0.00
0.00
0.00
0.00
vacant (Oct)
0.05
0.05
0.01
0.09
0.95
0.90
Na (A)
0.01
0.01
0.01
0.00
0.04
0.03
K (A)
0.92
0.90
0.81
0.95
0.84
0.92
Ca (A)
0.00
0.00
0.01
0.00
0.00
0.00
vacant (A)
0.07
0.08
0.17
0.05
0.12
0.05
F (X)
0.04
0.06
0.14
0.15
0.02
0.00
Cl (X)
0.00
0.00
0.00
0.00
0.00
0.00
OH (X)
1.96
1.94
1.86
1.84
1.98
2.00
277
Table 8. Normalized microprobe data: sheet silicates from Eagle Pass.
Sample number EP 024 bt1 EP 024 bt2 EP 024 bt3 EP 033
EP 033
EP 033
ser1
ser2
ser3
Mineral Name
annite
annite
annite
muscovite muscovite muscovite
Replacing
biotite
biotite
plag
plag
plag
Host Rock
Yg
Yg
Yg
Yg
Yg
Yg
SiO2
35.50
35.67
36.86
47.08
49.58
48.06
TiO2
3.41
2.63
0.42
0.29
0.23
0.15
Al2O3
14.55
15.41
19.55
29.82
27.84
28.91
Cr2O3
0.01
0.03
0.01
0.05
0.02
0.00
Fe2O3
5.36
5.29
4.56
0.90
1.08
1.03
FeO
19.28
19.06
16.41
3.23
3.88
3.71
MgO
7.73
8.31
6.38
1.60
2.13
2.09
MnO
0.46
0.24
0.49
0.05
0.02
0.02
CaO
0.00
0.07
0.20
0.00
0.00
0.02
Na2O
0.21
0.07
0.45
0.14
0.11
0.13
K2O
9.39
9.04
8.12
9.52
10.42
10.04
H2O
3.48
3.58
3.80
4.30
4.18
4.08
F
0.55
0.40
0.00
0.08
0.52
0.63
Cl
0.09
0.07
0.07
0.00
0.00
0.00
Subtotal
100.02
99.86
97.33
97.05
100.00
98.87
O=F+Cl
-0.25
-0.18
-0.02
-0.03
-0.22
-0.27
Total
99.77
99.68
97.31
97.02
99.78
98.61
Si (T)
2.83
2.82
2.89
3.26
3.36
3.29
Al (T)
1.17
1.18
1.11
0.74
0.64
0.71
Al (Oct)
0.19
0.26
0.70
1.69
1.58
1.62
Mg (Oct)
0.92
0.98
0.75
0.17
0.22
0.21
Fe 2+ (Oct)
1.28
1.26
1.08
0.19
0.22
0.21
Fe 3+ (Oct)
0.32
0.32
0.27
0.05
0.05
0.05
Mn (Oct)
0.03
0.02
0.03
0.00
0.00
0.00
Ti (Oct)
0.20
0.16
0.02
0.02
0.01
0.01
Cr (Oct)
0.00
0.00
0.00
0.00
0.00
0.00
vacant (Oct)
0.05
0.01
0.15
0.89
0.91
0.89
Na (A)
0.03
0.01
0.07
0.02
0.01
0.02
K (A)
0.95
0.91
0.81
0.84
0.90
0.88
Ca (A)
0.00
0.01
0.02
0.00
0.00
0.00
vacant (A)
0.01
0.07
0.10
0.14
0.08
0.10
F (X)
0.14
0.10
0.00
0.02
0.11
0.14
Cl (X)
0.01
0.01
0.01
0.00
0.00
0.00
OH (X)
1.85
1.89
1.99
1.98
1.89
1.86
278
Table 8. Normalized microprobe data: sheet silicates from Eagle Pass.
Sample number
EP 034
EP 034 chl2
EP 034 chl4
EP 035b bt1
chl1
Mineral Name clinochlore
clinochlore
chamosite
alumino-celadonite
Replacing
biotite
shreddy biotite
vein
biotite
Host Rock
Yg
Yg
Yg
Yg
SiO2
26.88
26.15
24.90
45.23
TiO2
0.06
0.10
0.03
0.29
Al2O3
18.56
18.73
20.85
29.41
Cr2O3
0.01
0.04
0.00
0.00
Fe2O3
4.52
4.55
4.88
1.30
FeO
23.02
23.19
24.89
4.67
MgO
13.56
13.71
11.14
2.22
MnO
0.62
0.56
0.65
0.07
CaO
0.02
0.02
0.01
0.00
Na2O
0.00
0.01
0.12
0.25
K2O
0.02
0.00
0.02
9.99
H2O
11.24
11.18
11.10
4.24
F
0.00
0.00
0.00
0.09
Cl
0.01
0.01
0.04
0.00
Subtotal
98.53
98.23
98.63
97.77
O=F+Cl
0.00
0.00
-0.01
-0.04
Total
98.52
98.23
98.62
97.73
Si (T)
2.87
2.81
2.69
3.16
Al (T)
1.13
1.19
1.31
0.84
Al (Oct)
1.20
1.17
1.34
1.59
Mg (Oct)
2.16
2.19
1.79
0.23
Fe 2+ (Oct)
2.05
2.08
2.25
0.27
Fe 3+ (Oct)
0.36
0.37
0.40
0.07
Mn (Oct)
0.06
0.05
0.06
0.00
Ti (Oct)
0.00
0.01
0.00
0.02
Cr (Oct)
0.00
0.00
0.00
0.00
vacant (Oct)
0.16
0.12
0.16
0.82
Na (A)
0.00
0.00
0.03
0.03
K (A)
0.00
0.00
0.00
0.89
Ca (A)
0.00
0.00
0.00
0.00
vacant (A)
0.99
1.00
0.97
0.07
F (X)
0.00
0.00
0.00
0.02
Cl (X)
0.00
0.00
0.01
0.00
OH (X)
8.00
8.00
7.99
1.98
279
Table 8. Normalized microprobe data: sheet silicates from Eagle Pass.
Sample number EP 035b chl1 EP 035b chl2 EP 035b ser1 EP 037 chl1 EP 037 ser1
Mineral Name
Replacing
Host Rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Fe 2+ (Oct)
Fe 3+ (Oct)
Mn (Oct)
Ti (Oct)
Cr (Oct)
vacant (Oct)
Na (A)
K (A)
Ca (A)
vacant (A)
F (X)
Cl (X)
OH (X)
clinochlore
shreddy biotite
Yg
27.26
0.11
17.90
0.01
4.23
21.55
15.77
0.60
0.01
0.01
0.00
11.26
0.22
0.00
98.93
-0.09
98.84
2.88
1.12
1.10
2.48
1.90
0.34
0.05
0.01
0.00
0.11
0.00
0.00
0.00
1.00
0.07
0.00
7.93
clinochlore
biotite
Yg
26.71
0.05
18.14
0.00
4.34
22.14
14.89
0.45
0.03
0.00
0.06
11.04
0.40
0.01
98.25
-0.17
98.08
2.85
1.15
1.14
2.37
1.98
0.35
0.04
0.00
0.00
0.12
0.00
0.01
0.00
0.99
0.14
0.00
7.86
muscovite
biotite
Yg
46.49
0.51
31.38
0.00
0.95
3.44
0.64
0.01
0.00
0.37
10.33
4.22
0.31
0.01
98.66
-0.13
98.53
3.19
0.81
1.73
0.07
0.20
0.05
0.00
0.03
0.00
0.94
0.05
0.90
0.00
0.05
0.07
0.00
1.93
clinochlore
biotite
Tpd
29.35
0.40
19.00
0.03
3.46
17.64
14.72
0.73
0.19
0.03
1.29
11.54
0.00
0.03
98.41
-0.01
98.40
3.05
0.95
1.38
2.28
1.53
0.27
0.06
0.03
0.00
0.44
0.01
0.17
0.02
0.80
0.00
0.00
8.00
muscovite
plag
Tpd
48.55
0.00
30.01
0.01
0.74
2.65
1.75
0.01
0.00
0.22
10.65
4.28
0.30
0.01
99.18
-0.13
99.06
3.29
0.71
1.69
0.18
0.15
0.04
0.00
0.00
0.00
0.95
0.03
0.92
0.00
0.05
0.06
0.00
1.94
280
Table 8. Normalized microprobe data: sheet silicates from Eagle Pass.
Sample number EP 038a
EP 038a
EP 038a
EP 038a
EP 038a
EP 038c
bt1
bt2
bt3
bt4
bt5
bt1
Mineral Name phlogopite phlogopite phlogopite phlogopite phlogopite phlogopite
Replacing
plag
biotite
biotite
biotite
Host Rock
Tpd
Tpd
Tpd
Tpd
Tpd
Yg
SiO2
36.29
35.49
36.67
36.17
37.09
38.30
TiO2
2.40
1.98
4.02
1.70
2.16
2.22
Al2O3
16.56
17.12
14.54
16.75
15.68
15.16
Cr2O3
0.03
0.06
0.04
0.00
0.01
0.00
Fe2O3
4.08
4.36
4.39
4.49
4.39
3.91
FeO
14.67
15.68
15.80
16.16
15.81
14.07
MgO
10.42
10.06
10.21
10.23
10.60
11.46
MnO
0.31
0.24
0.34
0.41
0.42
0.34
CaO
0.00
0.08
0.00
0.09
0.00
0.00
Na2O
0.09
0.00
0.07
0.09
0.14
0.04
K2O
9.52
9.16
9.22
9.14
9.30
9.37
H2O
3.61
3.51
3.62
3.70
3.75
3.73
F
0.51
0.65
0.41
0.32
0.26
0.35
Cl
0.02
0.03
0.15
0.03
0.03
0.03
Subtotal
98.50
98.40
99.50
99.29
99.62
98.99
O=F+Cl
-0.22
-0.28
-0.21
-0.14
-0.11
-0.16
Total
98.29
98.12
99.29
99.15
99.51
98.83
Si (T)
2.83
2.79
2.85
2.82
2.87
2.94
Al (T)
1.17
1.21
1.15
1.18
1.13
1.06
Al (Oct)
0.35
0.37
0.18
0.35
0.30
0.31
Mg (Oct)
1.21
1.18
1.18
1.19
1.22
1.31
Fe 2+ (Oct)
0.96
1.03
1.03
1.05
1.02
0.90
Fe 3+ (Oct)
0.24
0.26
0.26
0.26
0.26
0.23
Mn (Oct)
0.02
0.02
0.02
0.03
0.03
0.02
Ti (Oct)
0.14
0.12
0.24
0.10
0.13
0.13
Cr (Oct)
0.00
0.00
0.00
0.00
0.00
0.00
vacant (Oct)
0.09
0.03
0.09
0.02
0.05
0.10
Na (A)
0.01
0.00
0.01
0.01
0.02
0.01
K (A)
0.95
0.92
0.91
0.91
0.92
0.92
Ca (A)
0.00
0.01
0.00
0.01
0.00
0.00
vacant (A)
0.04
0.08
0.07
0.07
0.06
0.08
F (X)
0.12
0.16
0.10
0.08
0.06
0.09
Cl (X)
0.00
0.00
0.02
0.00
0.00
0.00
OH (X)
1.87
1.84
1.88
1.92
1.93
1.91
281
Table 8. Normalized microprobe data: sheet silicates from Eagle Pass.
Sample number EP 038c
EP 038c EP 040 bt2 EP 040 bt3 EP 040
EP 042
bt2
ser1
ser1
chl1
Mineral Name phlogopite muscovite muscovite muscovite muscovite chamosite
Replacing
plag
biotite
biotite
plag
biotite
Host Rock
Yg
Yg
Yxm
Yxm
Yxm
Yxm
SiO2
36.82
45.99
45.10
45.50
47.92
23.76
TiO2
3.17
0.51
0.20
0.37
0.14
0.02
Al2O3
15.12
30.39
29.14
31.83
29.63
19.03
Cr2O3
0.00
0.00
0.00
0.02
0.00
0.01
Fe2O3
4.20
1.11
0.93
1.25
0.96
5.16
FeO
15.12
3.99
3.36
4.49
3.45
26.29
MgO
10.65
1.80
1.31
0.07
1.66
8.08
MnO
0.33
0.05
0.10
0.13
0.01
2.10
CaO
0.00
0.02
0.02
0.00
0.05
0.06
Na2O
0.11
0.22
0.22
0.19
0.08
0.04
K2O
9.21
10.91
9.58
10.82
10.41
0.00
H2O
3.62
4.33
3.93
4.20
3.99
10.42
F
0.45
0.08
0.53
0.31
0.81
0.11
Cl
0.09
0.00
0.01
0.01
0.03
0.00
Subtotal
98.88
99.40
94.44
99.20
99.16
95.07
O=F+Cl
-0.21
-0.03
-0.23
-0.13
-0.35
-0.05
Total
98.67
99.36
94.21
99.06
98.81
95.03
Si (T)
2.86
3.16
3.23
3.14
3.28
2.72
Al (T)
1.14
0.84
0.77
0.86
0.72
1.28
Al (Oct)
0.25
1.62
1.69
1.73
1.66
1.29
Mg (Oct)
1.23
0.18
0.14
0.01
0.17
1.38
Fe 2+ (Oct)
0.98
0.23
0.20
0.26
0.20
2.52
Fe 3+ (Oct)
0.25
0.06
0.05
0.06
0.05
0.44
Mn (Oct)
0.02
0.00
0.01
0.01
0.00
0.20
Ti (Oct)
0.19
0.03
0.01
0.02
0.01
0.00
Cr (Oct)
0.00
0.00
0.00
0.00
0.00
0.00
vacant (Oct)
0.08
0.88
0.90
0.91
0.91
0.17
Na (A)
0.02
0.03
0.03
0.02
0.01
0.01
K (A)
0.91
0.96
0.88
0.95
0.91
0.00
Ca (A)
0.00
0.00
0.00
0.00
0.00
0.01
vacant (A)
0.07
0.01
0.09
0.02
0.08
0.98
F (X)
0.11
0.02
0.12
0.07
0.18
0.04
Cl (X)
0.01
0.00
0.00
0.00
0.00
0.00
OH (X)
1.88
1.98
1.88
1.93
1.82
7.96
282
Table 8. Normalized microprobe data: sheet silicates from Eagle Pass.
Sample number
EP 042
EP 046
EP 046
EP 070 EP 086 bt1 EP 086 bt2
kspar1
chl2
chl1
chl2
Mineral Name chamosite clinochlore muscovite chamosite
annite
annite
Replacing
biotite
vein
kspar
biotite
Host Rock
Yxm
Yxm
Yxm
Yg
Yg
Yg
SiO2
27.20
26.79
47.97
25.40
36.99
36.26
TiO2
0.06
0.06
0.16
0.09
2.02
1.70
Al2O3
17.01
20.60
31.70
19.79
14.53
14.11
Cr2O3
0.00
0.00
0.00
0.01
0.00
0.00
Fe2O3
5.10
4.34
0.76
5.60
4.57
4.72
FeO
26.02
22.13
2.75
28.54
16.44
16.99
MgO
6.23
13.43
1.06
5.79
8.92
9.10
MnO
1.04
0.18
0.01
0.35
0.41
0.36
CaO
1.04
0.02
0.03
0.07
0.18
0.27
Na2O
0.00
0.01
0.12
0.03
0.04
0.15
K2O
0.10
0.18
9.94
0.91
7.65
7.70
H2O
10.51
11.25
4.44
10.70
3.24
3.43
F
0.00
0.35
0.00
0.00
1.01
0.52
Cl
0.02
0.01
0.00
0.05
0.05
0.05
Subtotal
94.32
99.36
98.95
97.32
96.05
95.36
O=F+Cl
0.00
-0.15
0.00
-0.01
-0.44
-0.23
Total
94.32
99.21
98.95
97.31
95.61
95.13
Si (T)
3.10
2.81
3.24
2.84
2.97
2.95
Al (T)
0.90
1.19
0.76
1.16
1.03
1.05
Al (Oct)
1.39
1.36
1.76
1.46
0.35
0.30
Mg (Oct)
1.06
2.10
0.11
0.97
1.07
1.10
Fe 2+ (Oct)
2.48
1.94
0.16
2.67
1.10
1.16
Fe 3+ (Oct)
0.44
0.34
0.04
0.47
0.28
0.29
Mn (Oct)
0.10
0.02
0.00
0.03
0.03
0.02
Ti (Oct)
0.00
0.01
0.01
0.01
0.12
0.10
Cr (Oct)
0.00
0.00
0.00
0.00
0.00
0.00
vacant (Oct)
0.53
0.22
0.93
0.39
0.05
0.02
Na (A)
0.00
0.00
0.02
0.01
0.01
0.02
K (A)
0.01
0.02
0.86
0.13
0.78
0.80
Ca (A)
0.13
0.00
0.00
0.01
0.02
0.02
vacant (A)
0.86
0.97
0.13
0.85
0.19
0.15
F (X)
0.00
0.12
0.00
0.00
0.26
0.13
Cl (X)
0.00
0.00
0.00
0.01
0.01
0.01
OH (X)
8.00
7.88
2.00
7.99
1.74
1.86
283
Table 8. Normalized microprobe data: sheet silicates from Eagle Pass.
Sample number EP 086 bt3 EP 086 bt4 EP 086 bt5 MW NACA2
MW NACA2
chl1
chl2
Mineral Name
annite
phlogopite phlogopite
clinochlore
clinochlore
Replacing
biotite
biotite
biotite
Host Rock
Yg
Yg
Yg
Yg
Yg
SiO2
36.67
36.65
37.31
28.42
29.08
TiO2
2.32
1.85
1.14
0.06
0.05
Al2O3
13.91
13.44
14.29
16.06
15.33
Cr2O3
0.00
0.03
0.00
0.01
0.03
Fe2O3
4.56
4.69
4.61
4.65
4.69
FeO
16.40
16.88
16.61
23.71
23.92
MgO
8.66
9.50
9.42
14.69
14.10
MnO
0.42
0.41
0.38
0.65
0.58
CaO
0.24
0.19
0.20
0.07
0.20
Na2O
0.11
0.04
0.05
0.01
0.00
K2O
7.88
7.31
8.19
0.02
0.01
H2O
3.21
3.29
3.49
11.14
11.29
F
1.00
0.82
0.49
0.41
0.00
Cl
0.04
0.04
0.05
0.02
0.00
Subtotal
95.41
95.13
96.23
99.93
99.28
O=F+Cl
-0.43
-0.35
-0.22
-0.17
0.00
Total
94.98
94.78
96.01
99.75
99.27
Si (T)
2.98
2.98
2.99
3.01
3.09
Al (T)
1.02
1.02
1.01
0.99
0.91
Al (Oct)
0.31
0.27
0.35
1.01
1.01
Mg (Oct)
1.05
1.15
1.13
2.32
2.23
Fe 2+ (Oct)
1.11
1.15
1.11
2.10
2.12
Fe 3+ (Oct)
0.28
0.29
0.28
0.37
0.37
Mn (Oct)
0.03
0.03
0.03
0.06
0.05
Ti (Oct)
0.14
0.11
0.07
0.00
0.00
Cr (Oct)
0.00
0.00
0.00
0.00
0.00
vacant (Oct)
0.08
0.00
0.04
0.15
0.20
Na (A)
0.02
0.01
0.01
0.00
0.00
K (A)
0.82
0.76
0.84
0.00
0.00
Ca (A)
0.02
0.02
0.02
0.01
0.02
vacant (A)
0.15
0.22
0.14
0.99
0.98
F (X)
0.26
0.21
0.12
0.14
0.00
Cl (X)
0.00
0.01
0.01
0.00
0.00
OH (X)
1.74
1.78
1.87
7.86
8.00
284
Table 8. Normalized microprobe data: sheet silicates from Eagle Pass.
Sample number MW NACA3 ser1 MW SPECHEM ser1
Mineral Name alumino-celadonite
Replacing
biotite
Host Rock
Yg
SiO2
43.91
TiO2
0.00
Al2O3
29.87
Cr2O3
0.00
Fe2O3
1.24
FeO
4.45
MgO
4.91
MnO
0.06
CaO
0.09
Na2O
0.11
K2O
8.19
H2O
4.29
F
0.00
Cl
0.01
Subtotal
97.14
O=F+Cl
0.00
Total
97.14
Si (T)
3.06
Al (T)
0.94
Al (Oct)
1.52
Mg (Oct)
0.51
Fe 2+ (Oct)
0.26
Fe 3+ (Oct)
0.06
Mn (Oct)
0.00
Ti (Oct)
0.00
Cr (Oct)
0.00
vacant (Oct)
0.64
Na (A)
0.01
K (A)
0.73
Ca (A)
0.01
vacant (A)
0.25
F (X)
0.00
Cl (X)
0.00
OH (X)
2.00
phlogopite
plag
Yg
41.61
0.04
17.09
0.00
3.29
11.86
10.20
0.17
0.54
1.70
4.06
0.75
6.74
0.01
98.06
-2.84
95.21
3.16
0.84
0.69
1.15
0.75
0.19
0.01
0.00
0.00
0.20
0.25
0.39
0.04
0.31
1.62
0.00
0.38
285
Sample number
Mineral Name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Based on T+O+A=8
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Mn 2+ (Oct)
Mn 3+ (Oct)
Fe 3+ (Oct)
Ti (Oct)
Cr (Oct)
Na (A)
K (A)
Ca (A)
F (X)
Cl (X)
OH (X)
Table 9. Normalized microprobe data: epidote from Eagle Pass.
EP 022a EP 037 EP 038a MW SPECHEM MW NACA2
ep1
ep1
ep1
ep1
act1
epidote
epidote
epidote
epidote
epidote
kspar
vein
vein
kspar
vein
Yg
Tpd
Tpd
Yg
Yg
36.90
38.01
37.44
38.26
37.73
0.12
0.09
0.11
0.03
0.19
22.06
22.74
21.25
23.18
22.96
0.00
0.00
0.00
0.00
0.02
14.58
13.55
15.11
13.06
13.42
0.37
0.43
0.28
0.20
0.22
0.02
0.00
0.00
0.00
0.00
0.37
0.42
0.28
0.20
0.22
22.23
22.67
22.48
23.11
23.24
0.00
0.01
0.00
0.00
0.02
0.00
0.09
0.00
0.00
0.00
1.84
1.88
1.74
1.88
1.88
0.00
0.00
0.22
0.00
0.00
0.00
0.00
0.00
0.01
0.01
98.50
99.88
98.92
99.94
99.92
0.00
0.00
-0.09
0.00
0.00
98.50
99.88
98.83
99.94
99.92
3.00
0.00
2.11
0.00
0.03
0.00
0.92
0.01
0.00
0.00
0.00
1.94
0.00
0.00
1.00
3.03
0.00
2.14
0.00
0.03
0.00
0.84
0.01
0.00
0.00
0.01
1.94
0.00
0.00
1.00
3.04
0.00
2.03
0.00
0.02
0.00
0.94
0.01
0.00
0.00
0.00
1.96
0.06
0.00
0.94
3.04
0.00
2.17
0.00
0.01
0.00
0.80
0.00
0.00
0.00
0.00
1.97
0.00
0.00
1.00
3.01
0.00
2.16
0.00
0.01
0.00
0.82
0.01
0.00
0.00
0.00
1.99
0.00
0.00
1.00
286
Sample number
Mineral Name
Replacing
Host rock
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
Na2O
K2O
H2O
F
Cl
Subtotal
O=F+Cl
Total
Based on T+O+A=8
Si (T)
Al (T)
Al (Oct)
Mg (Oct)
Mn 2+ (Oct)
Mn 3+ (Oct)
Fe 3+ (Oct)
Ti (Oct)
Cr (Oct)
Na (A)
K (A)
Ca (A)
F (X)
Cl (X)
OH (X)
Table 9. Normalized microprobe data: epidote from Eagle Pass.
MW NACA3 MW ALT5' MW NACA2
ep1
ep1
EP1
epidote
epidote
epidote
vein
vein
vein
Yg
Yg
Yg
37.25
37.18
37.19
0.02
0.12
0.08
22.00
23.25
23.08
0.00
0.00
0.00
15.42
14.23
13.68
0.00
0.00
0.00
0.00
0.00
0.00
0.07
0.10
0.25
23.15
23.25
23.26
0.00
0.00
0.00
0.00
0.00
0.02
1.87
1.88
1.87
0.00
0.00
0.00
0.01
0.00
0.00
99.78
100.00
99.44
0.00
0.00
0.00
99.78
100.00
99.44
2.99
0.01
2.07
0.00
0.00
0.00
0.93
0.00
0.00
0.00
0.00
1.99
0.00
0.00
1.00
2.96
0.04
2.15
0.00
0.00
0.01
0.85
0.01
0.00
0.00
0.00
1.99
0.00
0.00
1.00
2.98
0.02
2.16
0.00
0.00
0.02
0.82
0.00
0.00
0.00
0.00
2.00
0.00
0.00
1.00
287
Table 10. Normalized microprobe data: amphibole from Eagle Pass.
Sample number
EP 007 act1
EP 086 act1
MW NACA3 MW NACA3
act2
act1
Mineral Name Alumino-actinolite Alumino-ferro-actinolite actinolite
actinolite
Replacing
biotite
biotite
biotite
biotite
Host rock
Tpd
Yg
Yg
Yg
SiO2
45.44
42.48
51.21
51.37
TiO2
1.96
1.54
0.03
0.05
Al2O3
9.86
8.64
4.05
4.11
Cr2O3
0.03
0.04
0.00
0.00
Fe2O3
4.49
5.05
2.61
2.54
FeO
7.18
18.13
11.57
11.79
MgO
14.24
7.20
14.37
14.21
MnO
0.20
0.82
0.34
0.34
CaO
11.32
11.16
12.54
12.59
Na2O
1.74
1.48
0.60
0.48
K2O
0.77
1.20
0.17
0.15
H2O
1.99
1.77
1.66
1.86
F
0.13
0.34
0.83
0.41
Cl
0.02
0.05
0.04
0.04
Subtotal
99.37
99.91
100.03
99.92
O=F+Cl
-0.06
-0.15
-0.36
-0.18
Total
99.31
99.75
99.67
99.74
Si (T)
6.61
6.55
7.45
7.46
Al (T)
1.39
1.45
0.55
0.54
Al (6)
0.30
0.13
0.14
0.17
Fe 3+ (6)
0.49
0.59
0.29
0.28
Ti (6)
0.21
0.18
0.00
0.01
Cr (6)
0.00
0.01
0.00
0.00
Mg (8)
3.09
1.66
3.12
3.08
Fe 2+ (8)
0.87
2.34
1.41
1.43
Mn (8)
0.02
0.11
0.04
0.04
Ca (8)
1.76
1.85
1.96
1.96
Na (A)
0.49
0.44
0.17
0.14
K (A)
0.14
0.24
0.03
0.03
vac.
0.37
0.32
0.80
0.84
F
0.06
0.17
0.38
0.19
Cl
0.01
0.01
0.01
0.01
OH
1.93
1.82
1.61
1.80
288
Table 10. Normalized microprobe data: amphibole from Eagle Pass.
Sample number
MW ALT5'
MW ALT5'
MW ALT5'
act1
act3
act2
Mineral Name
actinolite
actinolite
actinolite
Replacing
biotite
biotite
biotite
Host rock
Yg
Yg
Yg
SiO2
51.86
52.34
55.80
TiO2
0.06
0.04
0.04
Al2O3
3.26
3.76
1.75
Cr2O3
0.02
0.03
0.00
Fe2O3
2.04
1.52
0.01
FeO
10.71
10.78
9.03
MgO
15.14
15.61
17.81
MnO
0.15
0.18
0.26
CaO
12.36
12.72
12.79
Na2O
0.48
0.60
0.31
K2O
0.17
0.24
0.11
H2O
1.72
1.82
2.13
F
0.69
0.56
0.00
Cl
0.01
0.01
0.00
Subtotal
98.69
100.21
100.05
O=F+Cl
-0.29
-0.24
0.00
Total
98.39
99.97
100.05
Si (T)
7.58
7.53
7.87
Al (T)
0.42
0.47
0.13
Al (6)
0.14
0.16
0.16
Fe 3+ (6)
0.22
0.17
0.00
Ti (6)
0.01
0.00
0.00
Cr (6)
0.00
0.00
0.00
Mg (8)
3.30
3.35
3.74
Fe 2+ (8)
1.31
1.30
1.06
Mn (8)
0.02
0.02
0.03
Ca (8)
1.94
1.96
1.93
Na (A)
0.14
0.17
0.09
K (A)
0.03
0.04
0.02
vac.
0.83
0.79
0.89
F
0.32
0.26
0.00
Cl
0.00
0.00
0.00
OH
1.68
1.74
2.00
289
APPENDIX E: TEA CUP U-PB GEOCHRONOLOGY
Zircon crystals were extracted from samples by traditional methods of crushing
and grinding, followed by separation with a Wilfley table, heavy liquids, and a Frantz
magnetic separator. Samples were processed such that all zircons were retained in the
final heavy mineral fraction. A split of these grains (generally 50-100 grains) were
selected from the grains available and incorporated into a 1” epoxy mount together with
fragments of our Sri Lanka standard zircon. The mounts were sanded down to a depth of
~20 microns, polished, imaged, and cleaned prior to isotopic analysis.
U-Pb geochronology of zircons was conducted by laser ablation multicollector
inductively coupled plasma mass spectrometry (LA-MC-ICPMS) at the Arizona
LaserChron Center (Gehrels et al., 2008). The analyses involve ablation of zircon with a
New Wave UP193HE Excimer laser (operating at a wavelength of 193 nm) using a spot
diameter of 30 microns. The ablated material is carried in helium into the plasma source
of a Nu HR ICPMS, which is equipped with a flight tube of sufficient width that U, Th,
and Pb isotopes are measured simultaneously. All measurements are made in static
mode, using Faraday detectors with 3x1011 ohm resistors for 238 U, 232 Th, 208 Pb206
Pb, and discrete dynode ion counters for 204 Pb and202 Hg. Ion yields are ~0.8 mv per
ppm. Each analysis consists of one 15-second integration on peaks with the laser off (for
backgrounds), 15 one-second integrations with the laser firing, and a 30 second delay to
purge the previous sample and prepare for the next analysis. The ablation pit
is ~15 microns in depth.
290
For each analysis, the errors in determining 206 Pb/238 U and 206 Pb/204 Pb result in a
measurement error of ~1-2% (at 2-sigma level) in the 206 Pb/238 U age. The errors in
measurement of 206 Pb/207 Pb and 206 Pb/204 Pb also result in ~1-2% (at 2-sigma level)
uncertainty in age for grains that are >1.0 Ga, but are substantially larger for younger
grains due to low intensity of the 207 Pb signal. For most analyses, the cross-over in
precision of206 Pb/238 U and 206 Pb/207 Pb ages occurs at ~1.0 Ga.
204
Hg interference with 204 Pb is accounted for measurement of 202 Hg during laser
ablation and subtraction of 204 Hg according to the natural 202 Hg/204 Hg of 4.35. This Hg is
correction is not significant for most analyses because our Hg backgrounds are low
(generally ~150 cps at mass 204).
Common Pb correction is accomplished by using the Hg-corrected 204 Pb and
assuming an initial Pb composition from Stacey and Kramers (1975). Uncertainties of
1.5 for 206 Pb/204 Pb and 0.3 for 207 Pb/204 Pb are applied to these compositional values based on
the variation in Pb isotopic composition in modern crystal rocks.
Inter-element fractionation of Pb/U is generally ~5%,
whereas apparent fractionation of Pb isotopes is generally <0.2%. In-run analysis of
fragments of a large zircon crystal (generally every fifth measurement) with known age
of 563.5 ± 3.2 Ma (2-sigma error) is used to correct for this fractionation. The
uncertainty resulting from the calibration correction is generally 1-2% (2-sigma) for
both 206 Pb/207 Pb and 206 Pb/238 U ages.
Concentrations of U and Th are calibrated relative to our Sri Lanka zircon, which
contains ~518 ppm of U and 68 ppm Th.
291
Locations of the samples are shown in Table 1, and the analytical data
are reported in Table 2. Uncertainties shown in these tables are at the 1-sigma level and
include only measurement errors.
Inheritance was tested in the samples by examining both the core and tip of each
zircon where possible. Ages older than Oligocene were interpreted to represent
inheritance in the samples. Many of these ages are Proterozoic in age, which would be
expected due to the Proterozoic age of the country rock in the study area.
The resulting interpreted ages are shown on weighted mean diagrams using the
routines in Isoplot (Ludwig, 2008) (Fig. 2). The weighted mean diagrams show the
weighted mean (weighting according to the square of the internal uncertainties), the
uncertainty of the weighted mean, the external (systematic) uncertainty that corresponds
to the ages used, the final uncertainty of the age (determined by quadratic addition of the
weighted mean and external uncertainties), and the MSWD of the data set.
REFERENCES
Gehrels, G.E., Valencia, V., Ruiz, J., 2008, Enhanced precision, accuracy, efficiency, and
spatial resolution of U-Pb ages by laser ablation- multicollector-inductively
coupled plasma- mass spectrometry: Geochemistry, Geophysics, Geosystems, v.
9, Q03017, doi:10.1029/2007GC001805.
Ludwig, K., 2008, Isoplot 3.6: Berkeley Geochronology Center Special Publication 4, 77
p.
Stacey, J.S., and Kramers, J.D., 1975, Approximation of terrestrial lead isotope evolution
by a
two-stage model: Earth and Planetary Science Letters, v. 26, p. 207-221.
292
TABLE 1. Location of U-Pb geochronology samples
Sample
Latitude
Longitude
SP 100
33°02’33.6” N
111°13’07.5” W
SP 102
33°04’42.8” N
111°14’26.9” W
SP 103
33°05’31.0” N
111°04’11.9” W
GB 202
33°04' 16.3" N
111°06' 29.2" W
GB 203
33°05' 15.0" N
111°03' 06.9" W
293
TABLE 2. U-Pb geochronologic analyses
Isotope ratios
Analysis
U
206Pb
(ppm)
204Pb
U/T h
Apparent ages (Ma)
206Pb*
±
207Pb*
±
206Pb*
±
error
206Pb*
±
207Pb*
±
206Pb*
±
Best
age
±
207Pb*
(%)
235U*
(%)
238U
(%)
corr.
238U*
(Ma)
235U
(Ma)
207Pb*
(Ma)
(Ma)
(Ma)
SP102-1T
554
2084
3.5
25.9006
10.2
0.0544
10.3
0.0102
1.3
0.13
65.5
0.9
53.7
5.4
-443.2
269.7
SP102-1TC
374
44171
7.1
10.1237
0.4
3.7854
2.3
0.2779
2.3
0.99
1581.0
32.4
1589.7
18.8
1601.2
7.0
65.5
0.9
1601.2
SP102-2T
1184
5164
2.2
20.6269
4.7
0.0707
5.0
0.0106
1.6
0.33
67.8
1.1
69.3
3.3
122.8
110.4
67.8
7.0
1.1
SP102-2C
339
33256
0.7
10.9727
0.7
2.9485
1.3
0.2346
1.1
0.86
1358.8
14.0
1394.4
10.0
1449.4
12.7
1449.4
12.7
SP102-4T
487
1432
1.8
21.9176
6.7
0.0697
6.8
0.0111
1.1
0.16
71.0
0.8
68.4
4.5
-22.1
162.2
71.0
0.8
SP102-5TB
478
2086
3.2
24.3408
16.8
0.0632
17.1
0.0112
2.8
0.17
71.5
2.0
62.2
10.3
-282.4
431.0
71.5
2.0
SP102-5C
64
4292
1.4
11.4185
4.1
1.9761
7.9
0.1637
6.8
0.85
977.1
61.4
1107.4
53.6
1373.2
79.5
1373.2
79.5
SP102-11T
756
3194
2.1
21.5728
8.3
0.0733
8.3
0.0115
1.1
0.13
73.5
0.8
71.9
5.8
16.1
198.7
73.5
0.8
SP102-12T
501
1854
2.3
23.3944
7.1
0.0632
7.5
0.0107
2.4
0.31
68.8
1.6
62.3
4.5
-182.4
177.9
68.8
1.6
SP102-13T
343
2183
3.5
23.0149
11.9
0.0611
12.1
0.0102
1.7
0.14
65.5
1.1
60.3
7.1
-141.7
296.8
65.5
1.1
SP102-13C
109
791
1.4
33.3635
46.5
0.0458
46.6
0.0111
2.4
0.05
71.0
1.7
45.5
20.7
-1161.7
1496.8
71.0
1.7
SP102-13T B
427
1830
2.8
27.5381
12.5
0.0500
12.5
0.0100
0.8
0.06
64.1
0.5
49.5
6.0
-607.3
341.0
64.1
0.5
SP102-13C
158
12966
3.2
10.9774
1.4
2.5057
3.1
0.1995
2.7
0.90
1172.6
29.4
1273.7
22.2
1448.6
26.0
1448.6
26.0
GB0203-1T
336
1475
2.3
27.6397
19.4
0.0548
19.5
0.0110
2.0
0.10
70.4
1.4
54.1
10.3
-617.3
534.5
70.4
1.4
GB0203-2T
385
2581
2.3
23.8034
16.1
0.0625
16.1
0.0108
1.0
0.06
69.2
0.7
61.6
9.6
-225.9
406.5
69.2
0.7
GB0203-3T
634
2715
1.5
24.7508
9.6
0.0625
9.9
0.0112
2.4
0.24
72.0
1.7
61.6
5.9
-325.1
247.6
72.0
1.7
GB0203-4T
418
2105
2.3
24.7288
12.8
0.0618
13.0
0.0111
2.4
0.19
71.1
1.7
60.9
7.7
-322.8
329.9
71.1
1.7
GB0203-5T
457
2611
2.2
26.0598
9.4
0.0601
9.8
0.0114
2.5
0.26
72.9
1.8
59.3
5.6
-459.3
249.6
72.9
1.8
GB0203-6T
564
2301
1.9
24.7621
9.7
0.0614
10.0
0.0110
2.4
0.24
70.7
1.7
60.5
5.9
-326.3
248.9
70.7
1.7
GB0203-7T
420
2024
2.2
24.4885
12.2
0.0611
12.4
0.0109
1.9
0.15
69.6
1.3
60.2
7.2
-297.8
313.9
69.6
1.3
GB0203-8T
377
1790
2.9
25.4820
10.6
0.0581
10.7
0.0107
1.6
0.15
68.9
1.1
57.3
6.0
-400.5
277.1
68.9
1.1
1.0
GB0203-9T
451
3620
2.1
23.0475
13.6
0.0645
13.7
0.0108
1.5
0.11
69.1
1.0
63.5
8.4
-145.2
339.2
69.1
GB0203-10T
645
3799
1.8
21.3759
4.4
0.0705
4.7
0.0109
1.5
0.32
70.1
1.0
69.2
3.1
38.1
105.6
70.1
1.0
GB0203-11T
257
1244
2.8
26.4254
23.4
0.0579
23.5
0.0111
1.7
0.07
71.1
1.2
57.1
13.0
-496.3
629.5
71.1
1.2
GB0203-12T
403
2414
2.7
25.5956
15.3
0.0612
15.4
0.0114
1.7
0.11
72.8
1.2
60.3
9.0
-412.1
402.2
72.8
1.2
GB0203-13T
334
1476
2.5
29.3068
21.3
0.0535
21.4
0.0114
2.2
0.10
72.8
1.6
52.9
11.0
-779.9
608.0
72.8
1.6
GB0203-14T
351
3453
2.3
23.5910
12.1
0.0668
12.2
0.0114
1.0
0.08
73.3
0.7
65.7
7.7
-203.3
305.0
73.3
0.7
GB0203-15T
510
5247
1.9
20.6048
9.9
0.0719
10.0
0.0107
1.3
0.13
68.9
0.9
70.5
6.8
125.3
234.2
68.9
0.9
GB0203-16T
367
1813
2.3
24.8912
16.1
0.0607
16.2
0.0110
2.1
0.13
70.3
1.5
59.9
9.4
-339.7
416.1
70.3
1.5
GB0203-17T
418
2082
2.6
24.5240
16.9
0.0617
17.0
0.0110
2.1
0.12
70.3
1.4
60.8
10.1
-301.5
435.0
70.3
1.4
294
GB0203-18T
555
2847
1.7
25.3655
12.6
0.0591
12.8
0.0109
1.8
0.14
69.7
1.3
58.3
7.2
-388.6
329.9
69.7
1.3
GB0203-19T
384
2507
2.2
23.3687
21.3
0.0648
21.5
0.0110
2.5
0.12
70.4
1.7
63.8
13.3
-179.7
537.5
70.4
1.7
GB0203-20T
457
3568
2.1
24.6856
20.2
0.0616
20.2
0.0110
1.6
0.08
70.7
1.2
60.7
11.9
-318.4
521.8
70.7
1.2
SP100-1C
222
20336
2.1
11.0287
0.8
3.2721
2.0
0.2617
1.8
0.91
1498.7
24.2
1474.4
15.6
1439.7
16.2
1439.7
16.2
SP100-2C
418
23023
8.5
10.9802
0.7
3.0050
1.6
0.2393
1.4
0.89
1383.1
17.3
1408.9
11.9
1448.1
13.6
1448.1
13.6
SP100-4T
580
2116
2.9
21.8092
8.7
0.0722
9.0
0.0114
2.2
0.25
73.2
1.6
70.7
6.1
-10.1
210.5
73.2
1.6
SP100-5T
490
1455
3.2
21.7016
9.0
0.0697
9.2
0.0110
1.7
0.19
70.4
1.2
68.5
6.1
1.8
217.7
70.4
1.2
SP100-7T
874
3148
2.4
21.3921
8.2
0.0743
8.3
0.0115
1.2
0.15
73.9
0.9
72.8
5.8
36.3
196.6
73.9
0.9
SP100-13T
767
2392
3.6
22.6571
17.5
0.0687
17.6
0.0113
0.8
0.05
72.4
0.6
67.5
11.5
-103.1
433.9
72.4
0.6
SP100-15T
420
1732
3.3
20.2081
18.4
0.0753
18.5
0.0110
1.8
0.10
70.8
1.2
73.7
13.1
170.9
432.3
70.8
1.2
SP100-15C
320
33485
7.0
11.0198
0.7
3.1595
1.5
0.2525
1.3
0.89
1451.4
17.0
1447.3
11.3
1441.3
12.6
1441.3
12.6
SP100-17T
629
2960
2.9
24.8627
16.0
0.0615
16.1
0.0111
1.3
0.08
71.1
1.0
60.6
9.5
-336.7
414.5
71.1
1.0
SP100-19T
751
2960
2.9
22.1286
11.6
0.0698
11.7
0.0112
2.0
0.17
71.9
1.4
68.5
7.8
-45.4
281.7
71.9
1.4
SP100-23T
611
2340
3.5
25.8368
13.5
0.0594
13.7
0.0111
2.1
0.15
71.3
1.5
58.6
7.8
-436.7
357.1
71.3
1.5
SP100-24T
729
2422
2.6
21.4870
8.4
0.0693
9.2
0.0108
3.5
0.39
69.2
2.4
68.0
6.0
25.7
202.7
69.2
2.4
SP100-25C
139
10405
2.0
10.9099
0.9
3.1787
2.9
0.2515
2.8
0.95
1446.3
35.9
1452.0
22.5
1460.3
17.1
1460.3
17.1
SP100-26T
440
1839
4.4
26.4061
29.3
0.0584
29.3
0.0112
0.8
0.03
71.7
0.6
57.6
16.4
-494.3
792.0
SP100-26C
285
36626
4.5
10.9478
0.4
3.1677
0.9
0.2515
0.8
0.88
1446.3
10.1
1449.3
6.8
1453.7
7.9
SP103-1T
569
2221
2.1
24.2841
16.6
0.0633
16.7
0.0111
1.0
0.06
71.4
0.7
62.3
10.1
-276.5
425.8
71.7
0.6
1453.7
7.9
71.4
0.7
SP103-2T
452
1693
3.1
22.3991
13.3
0.0690
13.3
0.0112
1.0
0.07
71.9
0.7
67.8
8.7
-75.0
325.9
71.9
0.7
SP103-3T
1733
6503
7.0
19.9099
11.0
0.0729
11.0
0.0105
1.5
0.13
67.5
1.0
71.5
7.6
205.5
254.7
67.5
1.0
SP103-6T
411
1987
2.0
22.9376
22.5
0.0668
22.5
0.0111
1.1
0.05
71.2
0.7
65.6
14.3
-133.4
561.8
71.2
0.7
SP103-7T
531
2409
4.2
23.6806
16.5
0.0669
16.7
0.0115
2.4
0.14
73.7
1.7
65.8
10.6
-212.9
417.3
73.7
1.7
SP103-9T
593
2793
1.6
23.7847
14.7
0.0643
14.8
0.0111
1.3
0.09
71.1
0.9
63.3
9.1
-223.9
372.3
71.1
0.9
SP103-10T
676
2782
2.1
22.8659
11.8
0.0685
12.1
0.0114
2.6
0.22
72.9
1.9
67.3
7.9
-125.7
292.4
72.9
1.9
SP103-14T
411
1754
2.7
21.2957
22.5
0.0724
22.7
0.0112
3.1
0.14
71.6
2.2
70.9
15.6
47.1
544.4
71.6
2.2
SP103-17T
310
1093
7.0
24.5262
45.5
0.0617
45.6
0.0110
2.7
0.06
70.4
1.9
60.8
26.9
-301.8
1218.4
70.4
1.9
SP103-18T
1013
4386
5.3
22.7836
11.4
0.0629
11.6
0.0104
1.9
0.16
66.6
1.3
61.9
7.0
-116.8
282.5
66.6
1.3
SP103-19T
422
1395
2.4
22.2374
37.3
0.0686
37.6
0.0111
5.0
0.13
70.9
3.5
67.4
24.5
-57.3
936.4
70.9
3.5
SP103-20T
574
2345
1.8
25.1058
20.6
0.0609
20.7
0.0111
2.0
0.10
71.1
1.4
60.1
12.1
-361.8
538.2
71.1
1.4
SP103-22T
722
2979
2.0
20.6063
13.3
0.0723
13.8
0.0108
3.6
0.26
69.2
2.5
70.8
9.4
125.1
315.2
69.2
2.5
SP103-25T
619
2588
3.0
24.9157
29.2
0.0564
29.3
0.0102
1.2
0.04
65.4
0.8
55.8
15.9
-342.2
767.0
65.4
0.8
GB0202-1T
484
2419
2.9
19.0447
18.7
0.0825
19.2
0.0114
4.3
0.23
73.0
3.2
80.4
14.8
307.6
428.1
73.0
3.2
GB0202-2T
547
3555
2.0
21.2216
10.7
0.0699
11.2
0.0108
3.4
0.30
69.0
2.4
68.6
7.5
55.4
256.1
69.0
2.4
GB0202-3C
1322
11485
14.0
14.8926
9.6
0.1465
12.0
0.0158
7.1
0.59
101.2
7.1
138.8
15.5
842.4
200.7
101.2
7.1
GB0202-4T
951
3509
3.3
20.8842
10.1
0.0715
10.1
0.0108
1.1
0.11
69.5
0.8
70.2
6.9
93.5
239.0
69.5
0.8
GB0202-6T
393
1889
1.1
30.1605
28.0
0.0473
28.3
0.0104
4.4
0.15
66.4
2.9
47.0
13.0
-861.7
816.5
66.4
2.9
295
GB0202-6C
279
38033
3.2
11.1258
0.8
2.4492
2.4
0.1976
2.3
0.95
1162.6
24.5
1257.2
17.5
1423.0
14.9
1423.0
GB0202-8T
638
3514
12.7
20.7915
13.1
0.0708
13.8
0.0107
4.1
0.30
68.4
2.8
69.4
9.2
104.0
311.4
68.4
14.9
2.8
GB0202-9T
1144
5814
5.1
21.2041
4.8
0.0682
5.2
0.0105
2.1
0.40
67.2
1.4
66.9
3.4
57.3
114.7
67.2
1.4
296
1. Analyses with >10% uncertainty (1-sigma) in 206Pb/238U age are not included.
2. Analyses with >10% uncertainty (1-sigma) in 206Pb/207Pb age are not included,
unless 206Pb/238U age is <500 Ma.
3. Best age is determined from 206Pb/238U age for analyses with 206Pb/238U age
<900 Ma and from 206Pb/207Pb age for analyses with 206Pb/238Uage > 900 Ma.
4. All uncertainties are reported at the 1-sigma level, and include only measurement
errors.
5. Systematic errors are as follows (at 2-sigma level): [sample 1: 2.5%
(206Pb/238U) & 1.4% (206Pb/207Pb)]
6. Analyses conducted by LA-MC-ICPMS, as described by Gehrels et al. (2008).
7. U concentration and U/Th are calibrated relative to Sri Lanka zircon standard and
are accurate to ~20%.
8. Common Pb correction is from measured 204Pb with common Pb composition
interpreted from Stacey and Kramers (1975).
9. Common Pb composition assigned uncertainties of 1.5 for 206Pb/204Pb, 0.3 for
207Pb/204Pb, and 2.0 for 208Pb/204Pb.
10. U/Pb and 206Pb/207Pb fractionation is calibrated relative to fragments of a large
Sri Lanka zircon of 563.5 ± 3.2 Ma (2-sigma).
11. U decay constants and composition as follows: 238U = 9.8485 x 10-10, 235U =
1.55125 x 10-10, 238U/235U = 137.88.
12. Weighted mean plots determined with Isoplot (Ludwig, 2008).
297
APPENDIX F: (U- TH)/HE DATING OF HEMATITE FROM TEA CUP AND EAGLE
PASS
INTRODUCTION
Multiple varieties of hydrothermal hematite have been dated using the (U-Th)/He
system (Tables 1,2). While questions remain regarding fundamental aspects of this dating
system in hematite (e.g., closure temperature), specular and botryoidal hematite have
been demonstrated to retain helium over geologically significant periods of time (Lippolt
et al., 1993; Bahr et al; 1994), and geologically meaningful ages have been generated. For
example, dating of paragenetic hydrothermal specular hematite (specularite) and adularia
from Elba, Italy, yielded concordant (U-Th)/He and K-Ar ages respectively (Lippolt et
al., 1995). Hydrothermal botryoidal hematite from Schwarzwald, Germany, was dated by
Wernicke and Lippolt (1994) but yielded varying results.
In this study, samples of hematite from Tea Cup and Eagle Pass interpreted to
have formed during episodes of iron-oxide rich alteration, sodic (-calcic) alteration. and
supergene weathering were dated using the (U-Th)/He technique. Hematite was removed
from the samples with a “dremel” tool or by scratching them with a piece of steel. Pieces
of hematite were then picked and packed into Nb foil packets or tubes. Forty total
aliquots from nine samples, as well as six zircon standards, were then lased between three
and fifteen minutes using a Nd:YAG laser to extract He. The ratio of 4 He/3 He was
measured in a quadrupole mass spectrometer after a spike with a known amount of 3 He
298
was added. Re-extractions were performed until the re-extracted helium was less than the
five percent of the original helium extraction. Uranium and thorium were measured in
each aliquot by ICP-MS after dissolving them in a Parr bomb with a two-stage HF-HNO3
and HCl method and spiking them with known amounts of 233 U, 229 Th, and 147 Sm.
RESULTS
Tea Cup
Four samples of hematite were collected near the Red Hills prospect (Fig. 1) for
(U-Th)/He dating (Tables 1-2; Figure 2). Samples SP 076 and SP 092 are specular
hematite that is interpreted to have formed as part of iron oxide-rich alteration in the Tea
Cup porphyry system at ~71 Ma. Samples SP 079 and SP 097 contained hematite that
occurs in quartz veins containing oxidized sulfide minerals, which is interpreted to have
formed during a younger, supergene weathering event superimposed on earlier hypogene
potassic alteration.
The results of the (U+Th)-He dating of hematite from four samples are shown in
Table 2 and Figure 2. Aliquots from samples SP076, SP092, and SP097 showed
variations in their ages of greater than 10 m.y. Aliquots from sample SP079 yielded ages
within a range of four m.y. and a weighted average age of 14.4 ± 0.24 Ma.
Samples SP076, SP092, and SP097 yielded a wide variation in age, varying from
76 Ma (near the age of the porphyry system) to 10 Ma, with one extremely low-He
sample at 1 Ma. so Due to the variation, weighted averages are not reported for these
samples (Table 2). Results from SP 079 are much more consistent and provide a plausible
299
age for supergene alteration. The dates correspond approximately with the last stages of
normal faulting in the area at ~15 Ma (Richard and Spencer, 1997; Nickerson et al.,
2010). All the samples lie in the footwall of a normal fault which structurally denuded
overlaying rocks (Nickerson et al, 2010). Hematite in sample SP 079 was then produced
by the oxidation of Laramide aged potassic alteration which may have begun as when
extension ended.
Eagle Pass
Five samples of hematite were collected at Eagle Pass (Tables 1-2; Figures 3-4).
Samples EP 027 and EP 086 were collected from hematite veins hosted in sodic (-calcic)
alteration interpreted to have formed concurrently with the intrusion of the Eagle Pass
dike swarm at ~26.5 Ma (U-Pb; Appendix A). Sample EP 034 was collected from sodic
(-calcic) alteration interpreted to be assocatiated with slip on the Eagle Pass which began
after the intrusion of the Eagle Pass dikes (Appendix A). Sample EP 033 was collected in
the heart of the Eagle Pass dike swarm from sulfide-bearing potassic alteration that had
been affected by intense supergene weathering. Sample EP 069 was collected from a
shear zone between two Proterozoic units ~10 km northwest of the Eagle Pass dike
swarm.
In all the samples, ages from some aliquots yielded nearly reproducible ages. In
some cases the 4 He versus mol eU plots Figure 2 indicate irreproducibility may be the
result of excess 4 He in the aliquots. Samples EP 027 and EP 085 did not yield ages that
match the inferred age of the sodic (-calcic) alteration in which they are hosted (~26.5
Ma). Instead five aliquots from samples EP 027 yield a weighted average age of 13.2 ±
300
0.02 Ma. Aliquot EP 027_5 was omitted from the weighted average because it shows
anomalously low eU and an old age. Assuming that loss of U-Th is less likely than gain
of extraneous He in these samples, this sample is tentatively interpreted as
having“excess” 4 He (Figure 4B) . Sample EP 087 yielded also yielded a weighted
average age (10.49 ± 0.06 Ma) significantly younger than predicted 26.5 Ma age of the
sodic (-calcic). Aliquots from sample EP 034 yielded a range of ages that ~22 Ma and
~17 Ma, and a weighted average age of 18.93 ± 0.12. While not internally consistent, the
ages do provide a reasonable timing for slip along the Eagle Pass fault.
The onset of supergene weathering is not constrained at Eagle Pass, but the ages
yielded from four aliquots, which range from ~8-6 Ma, are geologically reasonable.
Aliquot EP 033_1 was not included in the weighted average because it has low eU and,
by comparison to other aliquots and with the assumption that gain of unsupported He is
more likely than loss of U-Th, likely contains may excess 4 He(Figure 4A). No geologic
constraints are able to be placed on the age of formation of hematite found in the shear
zone between two Proterozoic units where EP 069 was collected. The shear zone likely
formed as the result of deformation in the Proterozoic or during the Late CretaceousEarly Tertiary Laramide Orogeny. The weighted average age of 10.49 ± .06 Ma suggests
the hematite from this sample records anevent which post dates the formation of the shear
zone.
301
SIGNIFICANCE OF AGES
At both localities hematite (U-Th)/He ages of aliquots from the same sample
varied significantly. In some instances this may be the result of aliquots having contained
excess 4 He. Geologically plausible ages were obtained from hematite formed as the result
of supergene weathering (SP 079 and EP 033), and sodic (-calcic) alteration associated
with slip on the Eagle Pass fault (EP 034). Samples EP 027, EP 085, and EP 069 yielded
weighted averages between ~13-10 Ma that do not appear to coincide with the formation
of the hematite in each sample for reasons discussed above. The consistency of these ages
suggests that instead the hematite is recording a younger event, which may reflect
regional fluid flow or cooling. No known nearby magmatism was ongoing at this time.
The most likely cause of the ~13-10 Ma thermal event is tectonic denudation via normal
faulting. The timing of the youngest normal faulting that is not well constrained at Eagle
Pass but did occur in the Late Miocene in the nearby Catalina core complex (Davis et al.,
2004).
Going forward, the main uncertainties surrounding the interpretation of all the (UTh)/He ages spring from the lack of understanding of diffusive loss of He from hematite.
Results from this study indicate that (U-Th)/He ages from hematite record post- magmatic
events such as supergene weathering or cooling associated with exhumation. Further
analytical studies on the system, such as diffusion experiments, will be a necessary step
in determining the geologic significance of hematite (U-Th)/He ages.
302
REFERENCES
Bähr, R., Lippolt, H.J., and Wernicke, R.S., 1994, Temperature- induced 4He degassing
of specularite and botryoidal hematite: A 4He retentivity study: Journal of
geophysical research, v. 99, no. B9, p. 17695–17.
Davis, G.H., Constenius, K.N., Dickinson, W.R., Rodríguez, E.P., and Cox, L.J., 2004,
Fault and fault-rock characteristics associated with Cenozoic extension and corecomplex evolution in the Catalina-Rincon region, southeastern Arizona:
Geological Society of America Bulletin, v. 116, no. 1-2, p. 128–141.
Lippolt, H.J., Wernicke, R.S., and Boschmann, W., 1993, 4 He diffusion in specular
hematite: Physics and Chemistry of Minerals, v. 20, no. 6, p. 415–418.
Lippolt, H. J., Wernicke, R. S., and Bahr, R., 1995, Paragenetic specularite and adularia
(Elba, Italy): Concordant (U+Th)-He and K-Ar ages: Earth and Planetary Science
Letters, v 132, p. 43-51.
Nickerson, P.A., Barton, M.D., and Seedorff, E., 2010, Characterization and
reconstruction of multiple copper-bearing hydrothermal systems in the Tea Cup
porphyry system, Pinal County, Arizona, in Goldfarb, R.J., Marsh, E.E., and
Monecke, T., eds., The Challenge of Finding New Mineral Resources: Society of
Economic Geologists Special Publication 15, p. 299-316.
Richard, S. M., and Spencer, J. E., 1997, Geologic map of the North Butte area, central
Arizona: Arizona Geological Survery Open-File Report 97-4, scale 1:24,000, text
18 p.
303
Wenicke, R. S., and Lippolt, H. J., 1994, 4 He age discordance and release behavior of a
double shell botryoidal hematite from Schwarzwald, Germany: Geochimica et
Cosmochimica Acta, v 58, p. 421-329.
304
TABLE 1. Location and weighted average ages of (U-Th)/He samples fro m Tea Cup and Eagle Pass
Weighted
Average
(Ma)
Standard
Error
(Ma)
14.36
0.24
Sample
Location
Latitude
Longitude
SP 076
Tea Cup
33° 2'46.30"N
111°13'5.97"W
SP 079
Tea Cup
33° 2'42.89"N
111°13'4.57"W
SP 092
Tea Cup
33° 2'33.73"N
111°13'9.76"W
SP 097
Tea Cup
33° 2'23.49"N
111°13'5.42"W
EP 027
Eagle Pass
32°49'11.37" N
110° 6'42.72"W
13.39
0.10
EP 033
Eagle Pass
32°44'57.03" N
110° 7'49.89"W
7.46
0.60
EP 034
Eagle Pass
32°44'58.11" N
110° 7'46.61"W
18.95
0.12
EP 069
Eagle Pass
32°51'30.58" N
110°11'49.01"W
10.10
0.07
EP 085
Eagle Pass
32°48'49.30" N
110° 6'48.08"W
9.98
0.06
305
TABLE 2. (U-Th)/ He Isotopic Analysis from Tea Cup and Eag le Pass
4
Sample
Location
Hematite
source
SP076A
Tea Cup
FeOx rich alt
10.18
1.64
2.47
37.68
1.07
SP076B
Tea Cup
FeOx rich alt
9.91
1.67
1.12
42.28
1.21
SP076C
Tea Cup
FeOx rich alt
24.55
2.29
1.58
75.77
1.88
SP079A
Tea Cup
Supergene
16.94
5.98
10.43
16.58
0.48
SP079B
Tea Cup
Supergene
14.02
6.12
5.92
15.43
0.43
SP079C
Tea Cup
Supergene
29.46
16.06
15.38
12.37
0.36
SP092A
Tea Cup
FeOx rich alt
6.76
0.95
0.90
47.79
1.41
SP092B
Tea Cup
FeOx rich alt
6.28
1.47
1.15
29.78
0.99
SP092C
Tea Cup
FeOx rich alt
3.09
2.49
0.24
10.05
0.22
He
(ncc)
U (ng)
Th
(ng)
Raw age
(Ma)
±
(Ma)
SP097A
Tea Cup
Supergene
11.04
5.33
1.83
15.86
0.47
SP097B
Tea Cup
Supergene
0.03
0.24
0.03
1.00
0.05
SP097c
Tea Cup
Supergene
0.19
0.17
0.11
7.88
0.12
EP027_1
Eagle Pass
NaCa alt
0.29
0.15
0.14
13.05
0.22
EP027_2
Eagle Pass
NaCa alt
0.19
0.08
0.09
14.64
0.21
EP027_3
Eagle Pass
NaCa alt
0.82
0.40
0.37
14.12
0.20
EP027_4
Eagle Pass
NaCa alt
0.33
0.17
0.17
12.74
0.20
EP027_5
Eagle Pass
NaCa alt
0.22
0.03
0.03
48.73
0.68
EP027_6
Eagle Pass
NaCa alt
0.16
0.09
0.10
11.47
0.29
EP033_1
Eagle Pass
Supergene
1.00
0.56
0.13
13.97
0.24
EP033_2
Eagle Pass
Supergene
0.64
0.87
0.02
6.07
0.13
EP033_3
Eagle Pass
Supergene
0.71
0.84
0.12
6.78
0.12
EP033_4
Eagle Pass
Supergene
0.61
0.65
0.03
7.74
0.13
EP033_5
Eagle Pass
Supergene
1.19
1.15
0.03
8.57
0.15
EP033_6
Eagle Pass
Supergene
0.34
0.35
0.01
8.16
0.14
EP034_1
Eagle Pass
NaCa alt
1.73
0.57
0.58
20.08
0.28
EP034_2
Eagle Pass
NaCa alt
2.06
0.64
0.59
21.87
0.33
EP034_3
Eagle Pass
NaCa alt
3.40
1.42
0.40
18.69
0.43
EP034_4
Eagle Pass
NaCa alt
1.18
0.43
0.36
18.89
0.25
EP034_5
Eagle Pass
NaCa alt
1.45
0.67
0.24
16.59
0.34
EP034_6
Eagle Pass
NaCa alt
1.39
0.58
0.34
17.51
0.28
EP069_1
Eagle Pass
NaCa alt
0.19
0.07
0.35
10.40
0.14
EP069_2
Eagle Pass
NaCa alt
0.08
0.03
0.12
10.57
0.16
EP069_3
Eagle Pass
NaCa alt
0.10
0.03
0.21
10.96
0.15
EP069-5
Eagle Pass
NaCa alt
0.06
0.02
0.12
8.79
0.14
EP069-6
Eagle Pass
NaCa alt
0.11
0.04
0.22
10.02
0.14
306
EP085-1
Eagle Pass
NaCa alt
0.21
0.14
0.25
8.84
0.12
EP085-2
Eagle Pass
NaCa alt
1.59
0.56
1.32
15.17
0.21
EP085-3
Eagle Pass
NaCa alt
0.13
0.07
0.17
9.93
0.14
EP085-4
Eagle Pass
NaCa alt
0.14
0.07
0.15
10.52
0.15
EP085-5
Eagle Pass
NaCa alt
0.20
0.12
0.24
9.57
0.15
EP085-6
Eagle Pass
NaCa alt
0.11
0.07
0.14
8.91
0.16
307
Figure 1. Location map of (U- Th)/He samples at Tea Cup.
308
Figure 2. Moles of equivalent U (eU) vs mole of 4 He in Tea Cup samples. Red colored
samples are hematite derived from sodic (-calcic) alteration, and blue colored samples are
hematite derived from supergene alteration. Lines represent predicted moles of 4 He and
eU at for ages of 1 Ma, 10 Ma, 15 Ma, and 70 Ma.
309
Figure 3. Location map of (U- Th)/He samples at Eagle Pass. A: Geologic map of the
northern portion of the Pinaleño MCC including endpoints of cross section A-A’ through
the dike swarm. EPF = Eagle Pass fault; PDF=Pinaleño detachment fault. B: Location
map of MCCs in western North America. C: Regional location Map Dashed box is area
shown in Fig. 1A. D. Cross section oriented perpendicular the Eagle Pass dike swarm. AA’ located in Fig. 1A.
310
Figure 4. Moles of equivalent U (eU) vs mole of 4 He in Red Hills samples. Red colored
samples are hematite derived from sodic (-calcic) alteration or iron-oxide rich alteration,
and blue colored samples are hematite derived from supergene alteration. . Lines
represent predicted moles of 4 He and eU for ages of 1 Ma, 10 Ma, 15 Ma, and 20 Ma. A)
Data from all samples. B) Graph with axis values changed to highlight samples with
lower mol 4 He and mol eU values.
A)
B)