Fault Surface Maps: Three-dimensional Structural Reconstructions
and Their Utility in Exploration and Mining
Eric Seedorff*, Carson A. Richardson, and David J. Maher
Lowell Institute for Mineral Resources, Department of Geosciences, University of Arizona, 1040 East 4th Street, Tucson, Arizona 85721-0077
ABSTRACT
Mineral deposits that have been dismembered and tilted by syn- or post-mineral
IDXOWV FDQ EH VWUXFWXUDOO\ UHFRQVWUXFWHG WR DFKLHYH VFLHQWL¿F DQG SUDFWLFDO REMHFWLYHV
)DXOWVXUIDFHPDSVDUHSODQYLHZSURMHFWLRQVRIWKHJHRORJ\RIWKHIRRWZDOODQGKDQJLQJ
ZDOOVXUIDFHVRIDIDXOWVKRZLQJURFNXQLWVIDXOWVDQGRWKHUIHDWXUHV+HUHZHGHVFULEH
KRZWRFRQVWUXFWIDXOWVXUIDFHPDSVKRZWRSUHVHQWWKHPHI¿FLHQWO\LQSXEOLFDWLRQVDQG
KRZWRXVHWKHPWRPDNHWKUHHGLPHQVLRQDOVWHSZLVHVWUXFWXUDOUHFRQVWUXFWLRQVUHVWRULQJWKHKDQJLQJZDOOPDSDJDLQVWWKHIRRWZDOOPDS$UHDVRIFRPSOH[JHRORJ\FRQWDLQLQJ
PXOWLSOHJHQHUDWLRQVRIIDXOWVZLWKGLIIHULQJVOLSGLUHFWLRQVHVSHFLDOO\EHQH¿WIURPWKHXVH
RIIDXOWVXUIDFHPDSVIRUWKUHHGLPHQVLRQDOUHFRQVWUXFWLRQV:KHUHWKHUHDUHDGHTXDWH
JHRORJLFPDUNHUVDQGWKUHHGLPHQVLRQDOFRQWUROWKHUHVWRUDWLRQUHVXOWVLQQXPHURXVVOLS
YHFWRUVDFURVVWKHIDXOWVXUIDFHIURPZKLFKWKHPDJQLWXGHRIVOLSLQWKHSODQHRIWKHIDXOW
FDQEHFDOFXODWHGIRUHDFKYHFWRU$GGLWLRQDOJHRORJLFFRQVWUDLQWVDUHUHTXLUHGWRDVVHVV
WKHDPRXQWRIWLOWLQJWKDWRFFXUUHGFRQFXUUHQWZLWKVOLSRQHDFKJHQHUDWLRQRIIDXOWV7R
achieve a three-dimensional structural reconstruction of an area, the restoration process
LVUHSHDWHGIURP\RXQJHVWWRROGHVWIDXOWVZRUNLQJEDFNZDUGLQWLPH
2OGHUIDXOWVDSSHDUDVVLQJOHOLQHVFRPPRQO\NQRZQDVFXWRIIOLQHVRQERWKWKH
IRRWZDOO DQG KDQJLQJ ZDOO VXUIDFHV RI \RXQJHU IDXOWV )DXOWV WKDW PRYHG V\QFKURQRXVZLWKWKHIDXOWVXUIDFHEHLQJPDSSHGHJVSOD\VRIWKHVDPHIDXOWDSSHDUDVD
VLQJOHEUDQFKOLQHWUDFHLQWKHVDPHSRVLWLRQLQERWKIRRWZDOODQGKDQJLQJZDOOPDSV
<RXQJHUFURVVFXWWLQJIDXOWVDSSHDUDVJDSVLQWKHIDXOWVXUIDFHVRIROGHUIDXOWVWKDW
DUHLGHQWLFDOO\SRVLWLRQHGRQIRRWZDOODQGKDQJLQJZDOOPDSVDQGWKHJDSVZLGHQLQ
WKHGLUHFWLRQRILQFUHDVLQJGLVSODFHPHQWRUGHFUHDVLQJGLSRIWKH\RXQJHUIDXOW([DPSOHVIURPQRUPDOIDXOWVLQWKH5RELQVRQDQG<HULQJWRQPLQLQJGLVWULFWV1HYDGDLOOXVWUDWHWKHGLIIHULQJDSSHDUDQFHVRIIDXOWVXUIDFHPDSVRIHDUO\JHQHUDWLRQVRIIDXOWV
YHUVXVODWHUJHQHUDWLRQVRIIDXOWV7KHW\SHVRIPRYHPHQWWKDWDFKLHYHDUHVWRUDWLRQ
GLIIHUGHSHQGLQJRQZKHWKHUWKHSRUWLRQRIDQRUPDOIDXOWEHLQJUHVWRUHGLVQHDURU
IDUIURPHLWKHUWLSZKHUHWKHGLVSODFHPHQWGLPLQLVKHVWR]HUR1HDUWLSUHJLRQVFRPmonly display an important rotational component pinned near the tip, whereas midIDXOWUHJLRQVDUHGRPLQDWHGE\DGRZQGLSWUDQVODWLRQDOFRPSRQHQW
)DXOWVXUIDFHPDSVSURYLGHDQHI¿FLHQWPHWKRGIRUSRUWUD\LQJWKHORFDWLRQVDQG
W\SHV RI WKUHHGLPHQVLRQDO JHRORJLF FRQWUROV WKHUHE\ DOORZLQJ UHDGHUV WR VHH PRUH
FOHDUO\ZKHUHJHRORJLFLQWHUSUHWDWLRQVDUHZHOOFRQVWUDLQHGYHUVXVORRVHO\FRQVWUDLQHG
E\ WKH DYDLODEOH GDWD 7KLV DOORZV XVHUV WR HYDOXDWH WKH YDOLGLW\ RI D SURSRVHG UHconstruction better, to develop and evaluate alternative hypotheses more easily, and
WRGLVSHQVHZLWKXQYLDEOHDOWHUQDWLYHVPRUHUHDGLO\6WUXFWXUDOUHFRQVWUXFWLRQVKLVWRULFDOO\ KDYH OHG WR GLVFRYHULHV RI RIIVHW FRQWLQXDWLRQV RI NQRZQ RUHERGLHV DQG RI
QHZRUHERGLHV8VHRIIDXOWVXUIDFHPDSVIRUUHFRQVWUXFWLRQVIDFLOLWDWHVDPRUHWKUHH
GLPHQVLRQDODSSURDFKWRPLQHUDOH[SORUDWLRQLQFRPSOH[O\IDXOWHGUHJLRQVVXFKDV
FHUWDLQSDUWVRIWKH%DVLQDQG5DQJHSURYLQFH
.H\ :RUGV Fault surface map, Structural reconstruction, Yerington district, Robinson
district, Basin and Range province
*E-mail: seedorff@email.arizona.edu
1179
1180
INTRODUCTION
Eric Seedorff, Carson A. Richardson, and David J. Maher
as the Basin and Range province (e.g., Proffett, 1977; Wilkins
and Heidrick, 1995; Maher, 2008; Seedorff et al., 2008), and
Structural reconstructions attempt to undo the effects of this deformation provides the opportunity to explore for strucsecondary deformations that distort the primary geometry of turally offset targets. Balanced structural reconstructions test
rock units. In shallow continental extension, the principal de- the feasibility of subsurface interpretations of structural geomformations are normal faulting and to a much lesser degree dis- etry (e.g., Proffett, 1977; Nickerson et al., 2010). This approach
tributed strains between faults. Structural reconstructions play has led to the discovery of displaced extensions of veins during
DVLJQL¿FDQWUROHLQDGGUHVVLQJFHUWDLQVFLHQWL¿FDQGSUDFWLFDO underground drift advance, such as in the Wright-Hargreaves
REMHFWLYHV5HFRQVWUXFWLRQVFDQUHYHDOVRPHWKLQJRIVFLHQWL¿F mine (Hopkins, 1940). Likewise, district-scale exploration
interest, such as tectonic and structural processes that lead to programs have discovered tilted and fault-bound fragments of
extension of the crust (e.g., Gans and Miller, 1983; Colgan et large porphyry copper systems, such as Kalamazoo, Arizona
al., 2010), the original geometry of calderas (e.g., Colgan et (Lowell, 1968; Lowell, 1991) and the Ann-Mason deposit,
al., 2008), and the original geometry and scale of ore-forming Yerington district, Nevada (Proffett, 1977; Proffett and Dilles,
systems and the processes that formed them (e.g., Shaver and 1984; Hunt, 2004). Similar approaches have been applied sucMcWilliams, 1987; Seedorff, 1991; Dilles and Proffett, 1995; cessfully in the petroleum industry, particularly to establish hyStavast et al., 2008). Likewise, reconstructions can have im- drocarbon migrations pathways across faults (Allan, 1989).
plications for exploration and production (e.g., Maher, 2008;
Our purpose is to offer one way in which the traditional
Nickerson et al., 2010).
two-dimensional, cross-sectional approach to structural reImportant challenges in achieving an actual structural re- constructions can be adapted to more of a three-dimensional
construction of deformation, however, are the completeness of approach by utilizing plan-view projections of fault surfaces.
subsurface geological constraints available to delimit fault ge- We restrict our attention to normal faults formed in areas of
ometry and displacement. Moreover, faults in three dimensions continental extension (e.g., Roberts and Yielding, 1994). Fault
can be non-planar, and displacements can show gradients along surface maps consist of information plotted on layers, which
strike. Challenges also lie in conveying and applying the results can be either physical or digital, with restoration of a geologic
of reconstructions such as to reveal the extent of the geologic map of the hanging wall surface against a geologic map of the
constraints available, to test the validity of the reconstruction it- footwall surface. Fault surface maps are particularly useful for
self, and to move toward three-dimensional reconstructions, in structural reconstructions where multiple, crosscutting sets of
the face of what can seem to be blurry distinctions between the normal faults have differing slip directions. We claim that fault
geologic facts and interpretations that underlie reconstructions. VXUIDFHPDSVDOVRSURYLGHDQHI¿FLHQWPHDQVRISRUWUD\LQJWKH
Two-dimensional structural reconstructions for cross sec- locations and types of three-dimensional data available, which
tions oriented parallel to the slip direction are the principal permit users to understand the nature of the constraints betmeans used to test geometric validity, which is also known as ter. In turn, this allows users to evaluate better the validity of
balance and derives from conservation of volume (Dahlstrom, a proposed reconstruction hypothesis, to develop and evaluate
1969). A balanced cross section purports to maintain material alternative hypotheses more easily, and to dispense more readbalance between the deformed state and the restored (initial) ily with new but unviable proposals.
state. With restrictive assumptions, then area balance and line:H EHJLQ E\ EULHÀ\ UHYLHZLQJ KLVWRULFDO DSSURDFKHV WR
length balance can substitute for material balance. These tests structural reconstructions and then describe a multi-layer apFDQ EH DSSOLHG WR LQWHUSUHWDWLRQV RI VSHFL¿F DUHDV HJ %DOO\ proach to constructing fault surface maps. We illustrate selected
et al., 1966; Dahlstrom, 1969; Elliott, 1983; Groshong, 1989; characteristics of fault surface maps in areas of complex exNunns, 1991; Buchanan, 1996), but they also can be used to test tensional deformation with examples of normal faults in the
geometric validity of kinematic models of deformation, such Robinson and Yerington mining districts of Nevada. These exas those that have been presented for metamorphic core com- amples also illustrate the application of fault surface maps to
plexes and other products of continental extension in the Ba- (1) district-scale exploration for structurally offset pieces of ore
sin and Range province (e.g., Proffett, 1977; Davis and Coney, bodies and untested new ore bodies, and (2) operational issues
1979; Wernicke, 1981; Davis, 1983; Miller et al., 1983; Buck, such as ore control, geometallurgy, and slope stability in com1988; Lister and Davis, 1989).In principle, only geometrically plexly faulted settings where faults juxtapose variably mineralbalanced cross sections are retained as possibly valid inter- ized and altered rocks.
pretations, whereas cross sections that fail to balance must be
revised or rejected because they could not possibly be correct HISTORICAL APPROACHES TO STRUCTURAL
'DKOVWURP,QSUDFWLFHKRZHYHUVLWHVSHFL¿FLQWHUSUH- RECONSTRUCTIONS
tations and kinematic models commonly are employed before
their geometries are tested adequately for balance.
Structural reconstructions undo the effects of fault offsets
Syn- and post-mineral normal faults have dismembered and any distributed strains (commonly folds) in blocks between
and tilted ore-forming systems in certain geologic terrains such faults. By convention, the footwall block is usually assumed to
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
EH¿[HGDQGWKHKDQJLQJZDOOEORFNLVPRYHGVRDVWRHOLPLQDWH
fault offset. The most common form of structural reconstruction is a two-dimensional cross-sectional reconstruction; with
limited exceptions, they are accurate and viable when oriented
parallel to the slip direction (e.g., Dahlstrom, 1969). In areas of
complex geology containing multiple generations of faults with
widely differing slip directions, the cross-sectional technique
cannot be used in a straightforward manner for reconstructions,
nor can it be used to display continuous changes in magnitude
and direction of slip of a fault along strike. These situations
warrant a three-dimensional approach.
Fault-surface map reconstructions, in contrast, are a threedimensional restoration technique, described below, that utilizes plan-view projections of a three-dimensional fault surface.
Although structure contours are widely used throughout geology, the addition of geologic maps of the footwall and hanging
wall surfaces to make fault surface maps generally have not
been addressed in structural geology textbooks and laboratory
manuals of the last century, nor in books on applied structural
geology for exploration geologists (e.g., Badgley, 1959). The
usage of fault surface maps in the mineral industry, at least locally, dates back more than a half century to determine fault offsets of major veins (e.g., Hopkins, 1940), and McKinstry (1948,
SDOOXGHVWRWKHPEULHÀ\LQDWH[WERRNRQPLQLQJJHRORJ\
Nonetheless, few economic geologists have been exposed to
fault surface maps, and the latter are without mention in the
current economic geology literature aside from some recent applications (e.g., Keeler, 2010; Schottenfeld, 2012; Richardson,
2014). Fault surface maps are in more routine use today in the
petroleum industry (Tearpock and Bischke, 2003, Chapter 7.6),
where they are known as fault cutoff maps (e.g., Needham et
al., 1996). Superimposed maps of the hanging wall and footwall surfaces are known as Allan diagrams (after Allan, 1989;
Groshong, 2006, p. 229). Nonetheless, fault surface maps also
are uncommonly used in the petroleum geology literature.
1181
abrupt change in lithology or alteration within the fault core. In
the authors’ experience in the Basin and Range province, mixing of lithologic or alteration types—even where faults have a
wide breccia zone—tends to be limited to true widths of centimeters to a few meters. The position of the fault surface is
placed at the midpoint of the zone with mixed characteristics.
The use of the more general term fault surface, rather than fault
plane, is a recognition that the geometry of many faults is somewhat irregular, commonly curviplanar. In our view, the presence or absence of normal drag or reverse drag in the damage
zone around faults is irrelevant to making of the fault surface
maps, although it might be important for constructing cross sections across faults or interpreting the total amount of extension
in the region.
Mineral deposits and mining districts offer the advantage
of potentially offering an abundance of three-dimensional data
collected across and along faults (e.g., Kloppenburg et al.,
2010). The two principal means of acquiring such data are geologic mapping and drill logging, although other sources (e.g.,
VHLVPLF UHÀHFWLRQ LPDJHV DOVR PD\ RIIHU XVHIXO LQIRUPDWLRQ
Geologic maps can be made of exposures at the present-day or
pre-mining topographic surface, of man-made exposures along
major infrastructure routes such as haul roads and underground
haulage ways, and of underground drift faces and shovel advances in open-pit mines (e.g., Brimhall et al., 2006). Maps can
show the trace of the fault, the elevation along its trace, and
the characteristics of the immediate footwall and hanging wall.
Drill holes offer comparable information at points where the
KROHVSLHUFHWKHIDXOWVXUIDFHWKRXJKWKHFRQ¿GHQFHLQFRUUHlating data between holes and with other exposures generally
decreases with distance from the drill hole collar and with increasing distance between holes. Whether the data from drill
hole piercements represent different observations along a single fault—rather than miscorrelation of potentially unrelated
faults—is an interpretation that must be repeatedly tested, such
as by various means of structural analysis, by stratigraphic
CONSTRUCTION OF FAULT SURFACE MAPS
thickness criteria, or with new exposures of the fault.
A wide variety of geologic data from maps and drill holes
'H¿QLWLRQVDQGGDWDLQSXWV
can be displayed on layers of fault surface maps. The data can
include the elevation of the fault, stratigraphic and intrusive
Faults are discontinuities where there is offset by shear dis- units, lithologic and textural variations within the units, strucplacement. The focus here is on faults that have a major normal tural features, characteristics of the fault zone (e.g., tectonic
component of slip, but the principles apply to all types of faults. breccias and gouge), and hydrothermal features. Structural
The presence or absence of a fault on a map is in part a function features include older, synchronous, and younger faults. Older
of the scale of observation and documentation. The maps pre- faults will show as single traces in different (offset) positions in
sented here ignore faults with offsets of less than ~10 m.
the footwall and hanging wall surfaces of younger faults. Faults
Faults typically consist of a zone of deformation (e.g., Da- that moved synchronous with the fault surface being mapped
vis et al., 2004, Figure 4; Berg and Skar, 2005, Figure 2; Wib- (e.g., splays of the same fault) will show as a single branch-line
berley et al., 2008), commonly consisting of a fault core where trace in the same position in both footwall and hanging wall
most of the displacement is accommodated and an enclosing maps (e.g., Walsh et al., 1999). Younger, crosscutting faults will
damage zone of deformed rock (e.g., Caine et al., 1996; Kim show as paired traces that constitute an offset. For normal sepaet al., 2004; Micklethwaite, 2011). The entire fault zone may ration faults, offsets create gaps in the fault surfaces of older
be tens of meters or more in true width. The fault surface is de- faults that must be closed (restored) before restoring the older
¿QHGKHUHIRUWKHSXUSRVHRIPDNLQJIDXOWVXUIDFHPDSVE\DQ fault. Those gaps are identically positioned on footwall and
1182
Eric Seedorff, Carson A. Richardson, and David J. Maher
hanging wall maps and widen in the direction of increasing displacement or decreasing dip of the younger fault. Hydrothermal
features include alteration minerals or types, ore and gangue
minerals, mineralogic assemblages and associations, as well as
assays for ore, by-product, and deleterious elements.
Over the life of a mine, the volume of rock that is well
GH¿QHGE\GULOOKROHVDOVRWHQGVWRPLJUDWHGRZQZDUGDQGRXWZDUGDVH[SORUDWLRQDQGRUHGH¿QLWLRQFRQWLQXH,QODUJHGHSRVits, this can result in as much as 2–3 km of vertical exposure
(Seedorff et al., 2005). The spatial distribution of the data on a
fault surface map reveals the abundance, or paucity, of geologic
control on the position and characteristics of the fault.
may be useful also to make a preliminary structure contour map
RIWKHIHDWXUHVWKDWVHHPWRGH¿QHWKHIDXOW,QRXUH[SHULHQFH
the surface contour maps at this stage of investigation tend to
be undulatory. Later work commonly reveals that the actual
fault surface consists of both a gently dipping fault and smaller,
crosscutting faults that were unrecognized during the preliminary analysis. After distinguishing between the gently dipping
fault and the later, smaller-offset faults, the seemingly undulatory fault surface of the gently dipping fault may be much more
planar than it appeared initially.
Preliminary structural analysis of faults and fault sets
After completion of the preliminary structural analysis of
faults and fault sets, maps of individual fault surfaces can be
constructed. More detailed map scales permit representation
RI ¿QHU JHRORJLF GHWDLOV DQG UHVROXWLRQ RI VPDOOHU RIIVHWV RQ
faults. Nonetheless, use of numerous overlapping or quilt-like,
stitched together maps can be unwieldy and may impede understanding of the overall area. Alternatively, maps of multiple
scales can be utilized for different purposes. If only one scale is
employed, as a rule of thumb for physical restoration exercises
we recommend selecting a map scale such that the area of interest will approximate the size of a standard drafting table, as
compilation may need to use mylar of similar dimensions, and
SUHVHQWDWLRQ RI ¿QDO UHVXOWV PD\ UHTXLUH SORWWLQJ RQ SDSHU RI
standardized widths.
It is useful to assemble universal base maps that apply to
all faults, such as topography of the pre-mining surface, current
topography, generations of pit topography, and drill hole collar
maps with total depth elevations. Other information is most easily attributed on a fault-by-fault basis using multiple layers. A
geologically defensible strategy for beginning to construct fault
surface maps is to begin with the seemingly youngest faults and
work backward in time to the oldest faults, which may miniPL]HHUDVXUHDQGPRGL¿FDWLRQ,QRXUH[SHULHQFHKRZHYHUWKH
process is highly iterative regardless of approach. Alternatively,
one may choose instead to begin with faults for which there are
the best, most numerous, or most widespread data, and then
gradually address faults for which there is greater uncertainty
regarding their location, relative age, etc.
Fault surface maps consist of information plotted on four
(or more) layers: (1) data, (2) structure contours, (3) footwall
geology; and (4) hanging wall geology. Separation of information onto layers, either physical or digital, keeps the observational constraints and interpretations separated and distinguishDEOHDQGHDVHVWKHWDVNRIPRGL¿FDWLRQRUHUDVXUH$OOOD\HUVFDQ
EHUHSURGXFHGWRGLVSOD\WKH¿QDOUHVXOWVRUWKHLQIRUPDWLRQRQ
OD\HUV DQG FDQ EH VXSHULPSRVHG RQ PRGL¿HG YHUVLRQV RI
layers 3 and 4 to save space, as is done in this paper. Layers or
sheets preferably are uniform in size and have a consistent survey grid, so that geologic maps and the various layers for each
fault and for different faults can be easily compared. It is useful
not to place more than one fault on each layer, for each layer to
An analysis of the structure of a region, district, deposit, or
prospect precedes construction of fault surface maps, because
the latter requires at least a hypothesis about where faults are
SUHVHQWKRZPDQ\IDXOWVPLJKWKDYHVXI¿FLHQWVOLSWRZDUUDQW
more detailed work, and how earlier faults may have been offset by younger faults.
7KH¿UVWVWHSIRUWKLVDQDO\VLVLVWRFRPSLOHDPDSRUVHWRI
maps that contains the best available information on the geology of the area of interest, with particular attention to continuity of faults along strike and crosscutting relationships between
different faults (i.e., relative ages). Second, the observed fault
segments should be assigned to individual faults, with each
seemingly distinct fault assigned a different name and color.
Faults of similar strikes, dips, and relative crosscutting relationships might also be grouped into sets of faults (e.g., Proffett,
1977; Westaway, 1991), in which case faults in the same set
may be assigned similar colors (e.g., varying shades of blue for
different faults of one set, varying shades of green for faults of
a second set, etc.). When there is considerable evidence that
faults assigned to the same fault set—a descriptive term—were
active more or less contemporaneously, sets of faults then may
be regarded as constituting sequential fault generations—a temporal and potentially genetic assignment (e.g., Maher, 2008;
Nickerson et al., 2010; Richardson and Seedorff, this volume).
The aforementioned exercise effectively creates a physical or digital overlay of the geologic map, showing the various
faults or sets of faults highlighted in different colors. The resulting assignments of fault segments to individual, named faults
then become the basis for generating fault surface maps. In
practice, these assignments are part of a long, iterative process,
DVDVVLJQPHQWVDUHUH¿QHGRYHUWLPHDVWKHVWUXFWXUDODQDO\VLV
continues, as new data are generated (e.g., from new mapping
or drill holes), and as hypotheses are tested. The more complex the structure in the area of interest and the less mature
the understanding of it, then the more extensive the subsequent
PRGL¿FDWLRQVDUHOLNHO\WREH7KHDVVLJQPHQWVDUHSDUWLFXODUO\
tentative for faults that have gentle dips and that crop out only
locally yet are laterally extensive beneath the surface or have
been eroded overhead. For the preserved parts of such faults, it
Construction of layers for fault surface maps
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
cover the same map area at the same scale, and for layers to be
labeled consistently, including the name of the fault, the type of
layer, the date created, the names of the geologists who made
WKHPDSDQGWKHGDWHVPRGL¿HGDVZHOODVDNH\WRFRORUVDQG
symbols.
7KH ¿UVW OD\HU FRQVWUXFWHG RI DQ\ JLYHQ IDXOW LV WKH GDWD
layer, which contains the observations. The surface traces of
the fault over its mapped extent are shown, with measurements
on the strike and dip of the fault and kinematic indicators (e.g.,
slickenlines), if available. Additional information can be added
as desired, such as characteristics of the damage zones on either
side of the fault. Along the fault trace, points are marked and labeled where major elevation contours cross the fault. Locations
where each drill hole pierces the fault also are marked (e.g.,
with a black dot) and typically are labeled with four pieces of
information for each hole: (1) the number of the drill hole (e.g.,
D117), (2) the elevation of the fault in that drill hole, (3) the
lithology or map unit in the immediate footwall of the fault,
and (4) the lithology or map unit in the immediate hanging wall
of the fault. Data from drill holes that nearly pierced the fault
may also be included, as they also constrain the position of the
fault to be beyond the end of the drill hole. Where a fault has
subsequently been intruded by a dike, then both the dike and the
lithologies or map units on either side of the dike (and fault) are
noted, as well as the estimated position of the fault zone prior
to intrusion by the dike.
The second layer constructed is the structure contour layer.
Data relevant to the elevation of the fault from drill holes and
surface traces of the fault are transferred from the data layer, and
an interpretation of the structure contours is drawn using sound
geologic reasoning for interpolations and extrapolations. Structure contours generated solely by machines run the danger of
being geologically unreasonable where data are sparse, which
commonly include the edges of the map. Attempting to make
the faults as simple and as close to planar as the data points
will allow tends to be a good strategy. The line type used (e.g.,
VROLGGDVKHGGRWWHGVKRXOGFRQYH\WKHOHYHORIFRQ¿GHQFHLQ
the interpreted position of the contours, whether interpolated on
the basis of numerous, closely spaced constraints, extrapolated
beyond the limit of constraints, or projected beneath or through
younger rocks, respectively. Gaps and offsets in the contours
result if the fault was cut and offset by a younger fault, creating
gaps in the fault surface. Consequently, generation of a structure contour map for a fault generally is an iterative process, as
interpretations from one fault are reconciled with those of other
faults nearby.
The third layer is the footwall geologic map. Boundaries
between rock units (depositional, faulted, or intrusive) will
appear on the footwall geologic map as traces that are called
cutoffs. There will be a matching cutoff (in some form) present on the hanging wall geologic map in a displaced down-dip
position for normal-separation faults that have not rotated past
horizontal. Unconformity, fault, and intrusive cutoffs may show
other cutoffs terminating against them, and these intersections
1183
create piercing points on the footwall and hanging wall maps
WKDWFDQEHXVHGWRGH¿QHQHWVOLSYHFWRUVRQWKHIDXOWVXUIDFH
(see below). By overlaying the footwall layer on the data layer,
the subset of data that are relevant to the geology of the footwall
can be transferred to the third layer using standard colors assigned to the various lithologies. The data include the geology
of the rocks in the immediate footwall of the mapped surface
traces of the fault and data from drill holes that pierce the fault,
with some consideration given to holes that nearly reach the
fault surface. The contacts between different lithologies (unconformities, depositional, intrusive, or related to other faults)
then are interpolated or extrapolated, marked with the appropriate symbols (e.g., wavy lines for unconformities), ideally with
PHDQV WR FRQYH\ WKH FRQ¿GHQFH LQ WKHLU LQWHUSUHWHG SRVLWLRQV
(see above). The interpretations also are guided by other geologic constraints that may exist (e.g., well documented thicknesses of stratigraphic units).
The fourth layer is the hanging wall geologic map, constructed using the same methodology as the footwall geological
map but using data relevant to the geology of the immediate
hanging wall of the fault.
If data are available regarding alteration types, ore and
gangue minerals, and assays for ore, by-product, and deleterious
elements, then the approach to developing the third and fourth
layers can be repeated numerous times to generate pairs of footwall and hanging wall layers for each of these types of information. These data commonly create crude, i.e., larger diameter
piercing points, although metal zoning patterns in some cases
SURGXFH¿QHVFDOHSDWWHUQVWKDWPDNHH[FHOOHQWSLHUFLQJSRLQWV
All of these data potentially can be used for restoration, and in
principle each should be consistent with restorations based on
lithology and structure. Patterns made of hydrothermal features
are particularly valuable for restorations where there are large
volumes of uniform host rocks (e.g., hypidiomorphic granular
granitoid). Nonetheless, reconstructions may not use data that
has changed during or after fault movement. For example, Cu
assays may be used for reconstruction, but only those assays in
rocks where Cu was not redistributed by supergene processes
during or after fault movement.
Reconstructions
Methodology
The methodology of constructing fault surface maps for a
short segment of a simple normal fault is illustrated in Figure
1. Figure 1a shows a block diagram of the fault cutting three
stratigraphic units and a crosscutting igneous body. Figures 1b
and 1c show conventional map and cross sectional views, respectively. Figures 1d and 1e show surface projections of the
footwall and hanging wall geology, respectively, i.e., fault surface map.
The amount and direction of slip is determined by restoring
the hanging-wall block relative to the footwall block in the direction opposite to the slip direction, pinning geologic markers
1184
Eric Seedorff, Carson A. Richardson, and David J. Maher
Figure 1. Construction of a geologic fault surface map. (a) Perspective view of block diagram; (b) map view of surface of blocks and exposed fault
surface; (c) cross section oriented normal to strike of fault, showing vertical projection of footwall and hanging-wall traces onto horizontal map surface;
(d) surface projection of the footwall geology, showing piercing points in footwall; (e) surface projection of the hanging wall geology; piercing points
are shown for hanging wall (solid) and footwall (dashed) sides of the fault surface. Vectors pointing toward hanging wall show horizontal projection of
slip, i.e., heave component, indicated by offset of piercing points. Reconstruction vectors would be same length but would point in the opposite direction as slip vector, i.e., toward footwall. Elevation difference between head and tail of heave gives throw component. Total slip = sqrt(heave2WKURZ2).
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
or cutoffs in the hanging wall to offset equivalents of the same
markers or cutoffs in the footwall (Figure 1e). For most normal faults, the hanging wall is restored up the direction of dip
(Figure 1); however, for normal faults that have been rotated
through horizontal (“overturned” normal faults), the hangingwall block will be restored down the current dip, but nonetheless opposite the slip direction (e.g., Nickerson et al., 2010).
(Analogous relationships exist for tilted reverse and strike-slip
faults.) Depending on the geometry of the geologic units and
the data available to constrain the positions of contacts in the
hanging wall and footwall, the reconstruction may be nonunique, permitting a range of solutions. Ideally, the reconstruction yields a unique slip vector or a unique family of slip vectors. Multiple slip vectors are necessary to characterize a fault if
the amount and direction of slip varies along strike because the
hanging wall has not only translated relative to the footwall, but
also rotated relative to the footwall. The fault surface method,
LQSULQFLSOHSHUPLWVGLVSOD\RIDQLQ¿QLWHQXPEHURIVOLSYHFtors on the plane of the fault.
The amount and direction of slip can be measured or calculated from the reconstruction. The x-y component of slip,
the heave, can be measured from the length of the horizontal
component of the slip vector, i.e., its length on the fault surface
maps, which are horizontal projections. The z component of
slip is the difference in elevations of the piercing points on the
hanging-wall and footwall fault surfaces, which can be determined from the structure contours. The geologic constraints in
DJLYHQVHJPHQWRIWKHIDXOWPD\EHLQVXI¿FLHQWWRGHWHUPLQH
whether or by how much the direction and magnitude of slip
vary along strike; indeed, the rotational component of slip may
be undetectable without geologic markers that offer detailed
spatial resolution, coupled with closely spaced three-dimensional observational constraints.
Unique restorations generally involve one or more piercLQJSRLQWVZKLFKDUHJHRORJLFDOO\GH¿QHGSRLQWVLQWKHKDQJing wall that must have a corresponding, unique point in the
footwall (Figure 1e). Such points generally result from two
intersecting geologic surfaces (i.e., intersecting geologic conWDFWVLQVSDFHWKHUHE\GH¿QLQJDOLQH:KHUHDWKLUGVXUIDFH
the fault, cuts the line, two corresponding points on either side
of the fault (the piercing points) are produced. Nonetheless, the
geology of the hanging wall may be uniquely matched to the
geology of the footwall without involving piercing points if
rock units have distinctive shapes. Note that the reconstructions
are not driven by kinematic models of faults; this procedure
uses the geology of the fault surfaces, which are based on interpretations constrained by observations, such as geologic maps
and drill hole logs.
The geologic markers used to achieve the reconstruction
commonly are supracrustal strata that are part of a known stratigraphic sequence, but there are no restrictions on the types of
geologic features involved. For instance, these can include
crystalline rocks such as plutons and metamorphic rocks or
hydrothermal features, even though structural reconstruction
1185
software commonly is not designed to deal with them. Crystalline rocks also may contain numerous, though potentially
subtle, geologic features that provide markers for constraining
slip (e.g., Maher, 2008), including opportunities for generating
piercing points. Examples of such markers, including some that
are not routinely recorded on many quadrangle-scale geologic
maps, include: (1) sills and their feeder dikes; (2) mappable,
compositional or textural variants of plutons; (3) pegmatite and
aplite dikes and distinctive hydrothermal veins that may be associated with a pluton; and (4) distinctive textural or compositional variants within metamorphic rock units.
The geometries of faults, which are largely inherited from
their nucleation, growth, and linkage (e.g., Martel, 1999), have
consequences for developing a three-dimensional approach
to reconstruction. Over their full lengths, normal faults tend
to have characteristic geometries, although an area of interest
(e.g., a mining district) may cover only a small fraction of the
entire length of a given fault. For the case of an isolated normal
fault (Figure 2), its geometry is characteristic and simple, with
the opposite ends of the fault having tips where the displacement diminishes to zero (e.g., Muraoka and Kamata, 1983; Barnett et al., 1987; Walsh and Watterson, 1991; Schlische and Anders, 1996). The hanging wall has a gently synclinal geometry
between the tips, with the axis of the syncline oriented perpendicular to the fault and plunging toward it (Figure 2). The footwall has an even more subtly anticlinal geometry, with the axis
of the anticline oriented perpendicular to the fault and plunging
away from the fault. Real normal faults generally have more
irregular, sinuous traces at the surface than is shown in Figure
2. Recesses and salients in the surface trace correspond to the
troughs and ridges of fault-surface corrugations, respectively,
that plunge for many kilometers down dip.
The amount of displacement increases along the fault away
from each tip toward the point of maximum displacement (Figure 2); theoretically, the change in displacement with length
is non-linear, and maximum displacement occurs at the midpoint between the tips for isolated faults (Walsh and Watterson,
1989). For real normal faults, maximum displacement nonetheless tends to occur near the midpoint, and the maximum tilt of
both the hanging wall and footwall strata also occurs near the
midpoint (Figure 3), with both the displacement and tilt tapering to zero at the tips (Anders and Schlische, 1994). Moreover,
longer faults have greater displacements (e.g., Walsh and Watterson, 1987; Dawers and Anders, 1995), with a scaling relationship between displacement (D) and length (L) given by D f
Ln, where n is a small number likely to be 1 (Cowie and Scholz,
1992; Dawers et al., 1993). In practice, faults may have more
complex geometries and be segmented; moreover, nearby faults
commonly interact with one another and join over time (e.g.,
Childs et al., 1995; Hodgkinson et al., 1996; Cartwright et al.,
1996; Crider and Pollard, 1998; Peacock, 2002).
Implications for accuracy
The characteristic geometry of normal faults (Figure 2) has
1186
Eric Seedorff, Carson A. Richardson, and David J. Maher
Figure 2. Three-dimensional perspective view of an idealized, isolated normal fault from tip to tip, showing the point of maximum slip, the tips at either end of
WKHIDXOWZKLFKKDYH]HURVOLSDQGLQWHUYHQLQJUHJLRQ7KLVGLDJUDPDOVRLQFRUSRUDWHVÀH[XUDOGHIRUPDWLRQRIIDXOWVEORFNVZLWKÀH[XUDOUHERXQGRUXSOLIWRIWKH
KDQJLQJZDOODQGÀH[XUDOVXEVLGHQFHRIWKHIRRWZDOO0RGL¿HGIURP)RVVHQ)LJXUH$
multiple implications for how normal faults are restored and for
the accuracy of a reconstruction.
First, a purely rigid, up-dip translation of the hanging wall
surface relative to the footwall surface in principle is likely to
be in error. A purely translational reconstruction may be an
exceptionally good approximation for any relatively short segment of a fault (Figure 1e), especially if the region of interest
is far from a tip of the fault. This is expected because rotations
about horizontal axes that result in tilting of fault blocks are
clearly the dominant deformation in areas characterized by
domino-style extension. Nonetheless, an increase in displacement along the strike of a normal fault implies at least a minor
component of relative vertical-axis rotation between hanging
wall and footwall blocks (Figure 2). This effect is expected to
EHPRVWVLJQL¿FDQWQHDUDWLSRIDQRUPDOIDXOWDQGWKHQHWHIIHFW PLJKW EH PRVW VLJQL¿FDQW UHJLRQDOO\ ZLWKLQ DFFRPPRGDtion zones, where many faults typically are tipping out (e.g.,
Faulds and Varga, 1998).
Second, the direction of rotation of the hanging wall relative to the footwall must reverse as one crosses the point of
maximum displacement. Consequently, the accuracy of rigidbody approximations that employ both translational and rotational components will be increased if conducted separately on
opposite ends of the point of maximum displacement.
Third, additional assumptions may be required when reconstructing displacements near the tips of faults, especially in the
absence of closely spaced observational control. Strain extends
beyond the tip in the form of fractures and small folds (e.g., McGrath and Davison, 1995; Schlische, 1995; Walsh et al., 1999;
Crider and Peacock, 2004; d’Alessio and Martel, 2004), but the
amount of slip at the tip is zero (Figure 1). Figure 3 shows two
versions of near-tip behavior of a normal fault. Though omitting effects of strain beyond the tip, Figure 3a depicts non-rigid
behavior of the hanging-wall block, with a distinctly non-linear
increase in displacement as a function of distance from the tip.
Obviously, any rigid reconstruction—whether or not it involves
rotation—will be only an approximation if the change in slip
along strike is nonlinear. Alternatively, an assumption of linear
change in displacement along strike may be an acceptable approximation. The assumption of a linear decrease in displacement toward the tip and zero displacement beyond it implies
components of both translation and rotation of the hanging wall
relative to the footwall, with rotation of the hanging wall as a
rigid block about a pole of rotation located at the tip and ignoring effects of strain beyond the tip (Figure 3b).
Fourth, a rigid-body reconstruction also will be only an
approximation if penetrative deformation of either the hanging wall or footwall blocks occurs concurrent with slip. Penetrative deformation of both hanging wall and footwall are
LQKHUHQWLQWKHÀH[XUDOFDQWLOHYHUW\SHGHIRUPDWLRQHJ)LJure 1) that seems to characterize continental extension (e.g.,
Kusznir and Egan, 1990; Kusznir and Ziegler, 1992; Roberts
and Yielding, 1994). A perfect palinspastic reconstruction
must not only restore the slip but also remove the monoclinal
ÀH[XULQJWKDWDFFRPSDQLHGVOLS7KHRUHWLFDOFDOFXODWLRQVVXJgest that reconstructions assuming rigid domino-type behavLRUZLOORYHUHVWLPDWHWKHDPRXQWRIH[WHQVLRQLIÀH[XUDOFDQtilever-type deformation is involved (Westaway and Kusznir,
1993).
Fifth, the restoration process only backs out the movement
on the fault; even if the direction and amount of slip have been
determined quite rigorously (notwithstanding second-order
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
characteristics of normal faults, noted above), it does not generally return the fault surface to its original orientation prior to
the onset of faulting because normal faults commonly rotate or
tilt as they move (Thompson, 1960; Morton and Black, 1975;
:HUQLFNH DQG %XUFK¿HO *DQV HW DO -DFNVRQ
1987). Additional geologic constraints typically are required to
determine the original dip of the fault. For example, beddingto-fault angles of syntectonic sedimentary strata (Gawthorpe
DQG/HHGHUDQGRULHQWDWLRQVRIÀDWWHQHGSXPLFHLQSUH
WHFWRQLFLJQLPEULWHVDVKÀRZWXIIV²ZLWKDSSURSULDWHUHJDUG
for the likelihood of unreliable measurements due to differential compaction in paleovalleys with steep walls (e.g., Henry,
2008; Henry and Faulds, 2010)—can be used to determine how
each fault surface should be restored to its original dip (Proffett,
1977; Gonsior and Dilles, 2008; John et al., 2008). The origiQDOGLSRIWKHIDXOWLVRIVLJQL¿FDQWLQWHUHVWEHFDXVHWKHDQJOH
of initiation of normal faults in continental extensional tectonics is a persistent controversy (e.g., Gans et al., 1985; Jackson
and White, 1989; Lister and Davis, 1989; Roberts and Yielding, 1994; Wong and Gans, 2008), and structural reconstruction
is an important method for constraining initial dips of faults.
For many faults, the direction and amount of slip are well constrained, yet the constraints on the initial dips are nonetheless
poor.
To obtain a three-dimensional structural reconstruction
of an area, the reconstruction process proceeds backward in
1187
WLPH LH IURP \RXQJHVW WR ROGHVW IDXOWV 6LJQL¿FDQW HUURUV
in determining crosscutting relationships generally preclude
achieving a reconstruction that will balance. Hence, continual
testing of hypotheses regarding the relative ages of faults is
essential.
When restoring older faults, the gaps created by younger
FURVVFXWWLQJQRUPDOIDXOWV¿UVWPXVWEHFORVHG6PDOOHUURUVLQ
the amount and direction of slip will be introduced if the geometry of the older fault was deformed by offset on the younger
fault. Errors in the amount and direction of slip also will be
introduced if there was differential tilting of the older fault surface across the hanging wall and footwall blocks of the younger
fault, because tilting of the fault surface changes the dimensions
and geology of its surface projection. If the shape of the fault
surface, as illustrated by the structure contours, changes markedly on either side of the gaps created by offsets by younger,
crosscutting faults are closed, then care is required in calculating the direction and magnitude of slip.
It is unlikely that any palinspastic restoration mimics nature perfectly, because all methods make simplifying assumptions. Nonetheless, even imperfect restorations can lead to
greater geologic understanding. As the models become more
three-dimensional, however, the overall importance of the 3-D
effects in the natural processes becomes more apparent. Indeed,
a restoration cannot be achieved in some geologic settings without a satisfactory accounting of the 3-D effects.
)LJXUH3HUVSHFWLYHYLHZRIVLPSOL¿HGEORFNGLDJUDPVVKRZLQJPRYHPHQWWKDWPLJKWRFFXUQHDUWKHWLSRIDQRUPDOIDXOWD([DPSOHVKRZLQJQRQULJLGQRQ
linear) behavior of the hanging wall block relative to the footwall block, which resembles the case in Figure 1. (b) For comparison, an example with a simplifying
assumption that might be employed in a restoration in which the hanging-wall block is assumed to move rigidly with a linear displacement-length behavior. In
reality, such movement also would produce additional deformation beyond the tip of the fault (not shown). These two examples involve both translation and rotation of the hanging wall relative to the footwall.
1188
Eric Seedorff, Carson A. Richardson, and David J. Maher
EXAMPLES AND APPLICATIONS: TOPOLOGY AND
RECONSTRUCTION OF SUPERIMPOSED FAULT
GENERATIONS
magnitudes of slip than the younger faults that bound the major
blocks.
Selected post-mineral normal faults in the Liberty pit of the
Robinson district illustrate some of the diversity in topologies
The Robinson and Yerington districts, Nevada, provide of fault surface maps, even though a reconstruction of the postexamples of some of the diversity in topologies and character- mineral faulting of the district is still incomplete, so the results
istics of fault surface maps and applications of structural recon- shown are preliminary. For geologic context and location of the
structions to exploration and mining operations.
faults described below, Figure 4 shows an east-west cross section from Maher and Seedorff (2000) through the middle of the
Overview of Robinson district geology
Liberty pit with overlays showing rock types, alteration, and
structure.
The Robinson district, also known as the Ely porphyry copThe horizontal projection of the rock/alteration types and
per system, contains porphyry, skarn, carbonate replacement, structure of the footwall and hanging-wall surfaces is illustrated
and distal Au-Ag ores in the central Egan Range near the town for the Dexter, Alpha, and Liberty faults in Figures 5 through
of Ely in east-central Nevada. The Robinson district seemingly 7. Grid lines are labeled in the mine grid coordinates in feet
constitutes one, mid-Cretaceous porphyry copper center with (virtually no rotation from true north), but a metric scale bar is
early sills and several later mineralizing stocks (Seedorff et al., included. The rocks in certain areas are so intensely altered that
1996). The system was dismembered and variably tilted by late the determination of the protolith can be problematic; in such
Eocene normal faults that formed within a narrow absolute time rocks, reliable bedding attitudes generally were never mapped.
interval between ~37.60 and 36.68 Ma.
In some cases, bedding attitudes were measured at the surface
Robinson is a monzonitic porphyry Cu-(Mo-Au) system and can be projected down to the fault surface (dips shown in
LQWKHFODVVL¿FDWLRQVFKHPHRI6HHGRUIIHWDO7KHKRVW parentheses). Stratigraphic and intrusive contacts are shown in
rocks are carbonate and clastic units of the miogeocline of thin black lines; faults contacts are shown in thick colored lines.
western North America (e.g., Stewart, 1980), and those that Various lithologic/alteration types each have distinct colors, but
crop out in the district range in age from Devonian to Permian so, too, do the various faults, their associated dip symbols, and
(Bauer et al., 1966; Maher, 1996; Shaver and Jeanne, 1996). ODEHOV7KH GLVWULEXWLRQ RI DOWHUDWLRQ KDV EHHQ VLPSOL¿HG DQG
A batholithic intrusion that is the source of the stocks and sills certain alteration boundaries have been omitted unless they ilin the district, the Weary Flat pluton, has a U-Pb zircon LA- lustrate structural aspects that are the focus of this contribution.
ICP-MS date of 109.3±1.5 Ma (Seedorff et al., this volume). The geometry of faults is indicated by structure contour lines in
From west to east, the copper occurs principally in the Vet- feet that are identical on the footwall and hanging wall geologic
eran, Tripp, Liberty, Ruth, and Kimbley pits (e.g., Bauer et maps. The locations of reliable geologic control for these maps
al., 1966).
are shown by intensely colored dots (drill hole piercing locaPaleozoic and Tertiary strata in the northern Egan Range tions) and by very thick colored lines (the geology in the immestrike northerly and dip to the west because of tilting associated diate footwall and hanging wall along the mapped trace of the
with slip on several sets of east-dipping normal faults, whereas fault). Interpretations of lithologic/alteration types are shown
strata in the southern Egan Range strike northerly but dip to in fainter colors. Circles show reference points for restoration
the east, associated with slip on several sets of west-dipping of slip. Black vectors show the direction and magnitude of slip,
normal faults. The Robinson district is located in the central measured in the plane of the fault. Red arcs with exaggerated
Egan Range, where faults typical of the northern Egan Range curvature emphasize the sense of rotation for faults with an imare tipping out to the south and faults typical of the southern portant rotational component of slip (Figures 5b, 7b).
Egan Range are tipping out to the north. Thus the Robinson district occurs within a regional-scale extensional accommodation Fault surfaces of relatively young faults
zone that persists for tens of km north-south within the central
Egan Range (Seedorff et al., 1996; Gans et al., 2001; Seedorff
Figure 5 illustrates the horizontal projection of the geoland Maher, 2002).
ogy of the footwall and hanging-wall surfaces of the Dexter
The alignments of intrusions and mineralization across the fault. This fault illustrates characteristics of fault surface maps
district are the net result of slip on the numerous sets of post- of relatively young faults, i.e., faults from late generations of
mineral faults. The large open pits are bounded by relatively faults: the fault surface tends to contain many rock types and allate, post-mineral normal faults (e.g., Bauer et al., 1966; Wes- teration types in complex patterns, a wide range in bedding attitra, 1982; Seedorff et al., 1996; Gans et al., 2001), but each tudes with locally abrupt changes at boundaries between faults,
big fault block internally contains numerous other, mostly older a paucity of younger faults, and an abundance of older faults.
faults. Some of the older faults, including the Alpha fault deThe Dexter fault is a relatively young, east-dipping norscribed below, are gently dipping, do not crop out at the surface mal fault that cuts across the western end of the Liberty area in
within any one large fault block, and in some cases have greater the Robinson district. This fault is cut off at depth by the still
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
1189
Figure 4. East-west geologic cross section through the middle of the Liberty pit along section 102,900N, with overlays showing (a) rock type, (b) structure, (c)
alteration, and (d) copper grade. Note that many of the normal faults that dip steeply, both to the east and west, are cut off at depth by the gently dipping Footwall
East fault, yet the Footwall East fault in turn is cut and offset by younger faults such as the Liberty and Josie faults. From Maher and Seedorff (2000). Fault names
XVHGLQODWHU¿JXUHVDQGWKHJHRORJLFXQGHUVWDQGLQJRIWKH/LEHUW\DUHDKDYHHYROYHGVOLJKWO\VLQFHWKHVHFURVVVHFWLRQVZHUHPDGHHJ+XPEXJIDXOWQRWVKRZQ
KHUH%DOO3DUNIDXOWLQWKLV¿JXUHFRUUHVSRQGWR%HHKLYHIDXOW
younger Footwall East fault (Figure 4b); therefore, the northward and down-dip continuation of the Dexter fault must be
present somewhere in the footwall of the Footwall East fault
(not shown). As indicated by the structure contours, the Dexter
fault dips ~40–45°E and strikes nearly due north in the middle
of the Liberty pit but swings eastward further south (Figure 5),
whereas the Footwall East fault beneath it dips ~30°SE. The
Dexter fault everywhere places younger rocks on older rocks,
FRQ¿UPLQJWKDWLWLVDQRUPDOIDXOW
Relatively young faults generally cut and offset numerous older faults. The older faults that are cut by the Dexter
IDXOW $OSKD %HHKLYH &RSSHU )ODW 6XO¿GH (DVW (OGRUDGR
Champion, and High Grade Hanging Wall Splay faults) occur
as single, curving lines on both the footwall and hanging-wall
surface geologic maps, but their positions are offset between
the footwall and hanging wall (Figure 5). Among other geologic features, the older faults serve as geologic markers to
constrain the direction and magnitude of slip on the younger
fault. The Footwall East fault cuts off the Dexter fault to the
QRUWK DQG DW GHSWK 7KH 'H[WHU IDXOW LQ WKH ¿HOG RI YLHZ RI
Figure 5 also is cut by two younger faults (Humbug and Josie
faults), which also cut the Footwall East fault at depth. In any
fault surface map, younger faults occur in the same place in
the footwall and hanging-wall surfaces and create gaps in both
1190
Eric Seedorff, Carson A. Richardson, and David J. Maher
Figure 5. Preliminary fault surface maps for the Dexter fault in the Liberty pit, Robinson district. The Dexter fault is relatively young and its subsurface geometry
is well sampled by drill holes. (a) Footwall map. (b) Hanging wall map. Structure contours (gray) on both maps show that Dexter fault is corrugated and indicate
that overall it has a northerly strike and a moderate easterly dip of ~40–45°, extending from surface (green) to its down-dip truncation by the Footwall East fault
SLQNH[FHSWWRWKHVRXWKZKHUHWKHORFDWLRQRIWKH)RRWZDOO(DVWIDXOWLVXQFRQVWUDLQHG*HRORJLFPDSVRIVXI¿FLHQWTXDOLW\DQGGHWDLOGLGQRWH[LVWLQWKLVDUHD
so the only locations of reliable geologic control are intensely colored dots for drill hole piercements; interpretations of lithologic/alteration types around the drill
holes are shown in fainter colors. Older faults individually colored and labeled) are shown as colored lines; the locations of older faults are offset between the
hanging wall and footwall fault surface maps. Therefore, the older faults constrain the direction and magnitude of slip on the fault, as do other geologic markers.
The overturned dip symbol is used where the dip directions of the Alpha and Beehive faults are opposite to their interpreted slip directions. Two younger faults
(Humbug and Josie) crosscut the Dexter fault on these maps, and a third younger fault, the Footwall East fault, cuts off the Dexter to the north and dips under these
fault surfaces (see Figure 4). Younger faults occur in the same place in the hanging wall and footwall surfaces of the Dexter fault and create gaps in both the hangLQJZDOODQGIRRWZDOOIDXOWVXUIDFHPDSVLOOXVWUDWLQJWKHVXEVHTXHQWH[WHQVLRQ$OWKRXJKWKHJHRORJLFLQWHUSUHWDWLRQVUHTXLUHIXUWKHUUH¿QHPHQWWKHDSSUR[LPDWH
slip is shown by circular reference points in the hanging wall and footwall blocks. Geologic reference points are shown as circles. At southern end of map the slip
measured in the plane of the fault is ~95 ft (~29 m) N53E and increases to ~240 ft (~73 m) in a N66E direction at the northern end, producing a horizontal component of clockwise rotation of the hanging wall by ~2° relative to the footwall. Source of information; E. Seedorff et al. (unpub. data).
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
the footwall and hanging-wall fault surface maps. These gaps
illustrate the extension that was produced by subsequent faulting, and the gaps must be closed before determining the slip
on the older fault.
Regardless of relative age, faults with large magnitudes of
slip are most likely to create large discontinuities in metal grade
and metallurgical behavior, but late, small-offset faults such as
the Dexter also can create large discontinuities in places where
they cut and offset older, large-offset faults (e.g., Figure 4d).
Because late faults tend to be more continuous along strike and
down dip, they are especially critical for rock mechanics issues (e.g., pit slope stability and block caving behavior), even
if they have only small amounts of slip. Of course, it is not only
the characteristics of the faults (e.g., strike and dip, presence
of gouge, thickness of breccia), but also the characteristics of
the rocks (e.g., attitudes of bedding planes and joints, strength,
friability) that affect rock mechanics, as well as the angles of intersection of the various faults and other features (e.g., whether
they form wedges or buttresses).
Some of the contacts (fault, stratigraphic, intrusive, alteration) shown on the fault surface maps of the Dexter fault (Figure 5) are approximately planar, but many are highly irregular.
A few of the irregularities in contacts are the product of remaining imperfections in the three-dimensional geologic interpretations. A second factor leading to irregularities is that deformaWLRQDVVRFLDWHGZLWKPRYHPHQWRQ\RXQJHUIDXOWVHJÀH[XUH
of the hanging wall and footwall blocks near the fault surface)
can deform preexisting features, including older faults (seen
best for later example of the Alpha fault). Most irregularities,
however, result from a third factor: lines on these maps result
from intersection of two, irregular, curviplanar features (i.e., the
Dexter fault and the contact of interest), and that intersection—
and its horizontal projection—can be much more irregular than
the irregularities in either of the two surfaces that intersect. The
structure contours on the fault surface maps help remind users
of these geometric consequences.
The dip directions of older faults, which are taken from dip
measurements and structure contour maps of the older faults,
generally are far from perpendicular to the trace of the older
faults. This effect is produced on fault surface maps by the intersection of older fault surfaces with the surface of younger
faults, such as the Dexter. The effect is analogous to dip measurements on faults not being perpendicular to the trace of a
fault if the fault trace is changing elevation across a topographic
surface.
These preliminary footwall and hanging-wall fault surface
maps do not match perfectly because of remaining imperfections in the three-dimensional geologic interpretations, but slip
on the Dexter fault nonetheless can be estimated to a precision of ~10 m. The magnitude of slip on the Dexter fault at the
southern end of the map is ~95 ft (~29 m), and the magnitude of
slip increases to ~240 ft (~73 m) at the northern end (Figure 5),
resulting in a horizontal component of clockwise rotation of the
hanging wall relative to the footwall of ~2°.
1191
Fault surfaces of relatively old faults
Figure 6 shows preliminary fault surface maps for the Alpha fault in the Liberty pit east of the Kaboony fault and west
RIWKH6XO¿GH(DVWIDXOWH[HPSOLI\LQJFKDUDFWHULVWLFVRIIDXOWV
from relatively early fault generations: few rock types and alteration types present, generally regular changes in bedding dips
and typically of a limited range, abundance of younger faults,
and paucity of older faults.
The Alpha fault in the Liberty pit is a relatively old, gently
dipping fault that crops out on the western side of the Liberty pit
both north and south of the younger White Hill Rhyolite (Figure 6), and it continues into other parts of the Robinson district.
The Alpha fault is cut off to the north by the younger Footwall
East fault (Figure 6); therefore, the Alpha fault must continue
in the footwall of the Footwall East fault (not shown). Between
WKH\RXQJHU.DERRQ\DQG6XO¿GH(DVWIDXOWVWKH$OSKDIDXOW
has a narrow range in elevation, mostly between 7000 and 7250
ft, and dips in variable directions at moderate to shallow angles,
as indicated by the morphology of structure contours (Figure
6). The Alpha fault must be normal because it everywhere omits
stratigraphic section (e.g., a common relationship for the Alpha
IDXOW LQ WKH /LEHUW\ SLW LV YDULDEO\ VLOLFL¿HG 3HUPLDQ 5LE +LOO
Sandstone in the hanging wall, resting on Pennsylvanian Ely
Limestone altered to silica-pyrite and ore-related porphyry with
intense sericitic alteration in the footwall). For some time, the
VOLSGLUHFWLRQRIWKH$OSKDIDXOWZDVQRW¿UPO\NQRZQEXWWKH
fault surface maps here (Figure 6) demonstrate that the Alpha
fault is a top-to-the-east normal fault which may have originated as a steep, down-to-the-east normal fault.
Within the area shown by Figure 6, the Alpha does not cut
any older faults. The Alpha fault, however, is highly dismembered by numerous younger, crosscutting faults that displace
the Alpha fault (Kaboony, West Dexter, Dexter, Watson West,
:DWVRQ:DWVRQ(DVW6XO¿GH(DVW+XPEXJDQG-RVLHIDXOWV
plus the Footwall East fault that cuts it off to the north). Each
younger, crosscutting fault creates a gap in both the footwall
and hanging-wall fault surface maps for the Alpha fault (Figure
6), which must be closed to assess the amount and direction of
slip on the Alpha fault precisely. In the northern part of the Liberty pit, each of the small fragments of the Alpha fault dips back
to the west. At the southern end of the area, the Alpha fault assumes a more consistent southerly dip. The Alpha fault also appears to be less planar than many younger faults, and structure
contours suggest that this may have been caused by footwall
uplift and hanging wall subsidence related to movement on the
younger faults (Figure 6). Such deformation varies in magnitude along the strikes of the younger faults, causing warps and
wrinkles in the surface of the older, Alpha fault. Such deformation also passively rotates the Alpha fault surface. Where the
Alpha fault has been rotated through horizontal, the originally
east-dipping Alpha fault becomes an “overturned,” gently westdipping normal fault (Figures 4b and 6).
Bedding attitudes measured at the pre-mining surface in the
1192
Eric Seedorff, Carson A. Richardson, and David J. Maher
)LJXUH$3UHOLPLQDU\IDXOWVXUIDFHPDSVIRUWKH$OSKDIDXOWLQWKH/LEHUW\SLWHDVWRIWKH.DERRQ\IDXOWDQGZHVWRIWKH6XO¿GHIDXOW5RELQVRQGLVWULFW
exemplifying characteristics of faults from relatively early fault generations. (A) Footwall; (B) hanging wall. The locations of good geologic control are
shown by intensely colored dots (drill hole piercements). Other attributes are as described for Figure 6 and in the text. There are no older faults cut by the
Alpha in the area shown, but there are numerous crosscutting younger faults that create gaps in both the hanging wall and footwall fault surface maps that
must be closed before determining the slip on the Alpha fault. There is no overlap in the geology of the hanging wall and footwall fault surfaces, so the
amount of slip exceeds the length of a line in the slip direction across the illustrated view, but a preliminary indication of the slip is ~3–4 km in an easterly
direction. Source of information; E. Seedorff et al. (unpub. data).
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
1193
)LJXUH%3UHOLPLQDU\IDXOWVXUIDFHPDSVIRUWKH$OSKDIDXOWLQWKH/LEHUW\SLWHDVWRIWKH.DERRQ\IDXOWDQGZHVWRIWKH6XO¿GHIDXOW5RELQVRQGLVWULFW
exemplifying characteristics of faults from relatively early fault generations. (A) Footwall; (B) hanging wall. The locations of good geologic control are
shown by intensely colored dots (drill hole piercements). Other attributes are as described for Figure 6 and in the text. There are no older faults cut by the
Alpha in the area shown, but there are numerous crosscutting younger faults that create gaps in both the hanging wall and footwall fault surface maps that
must be closed before determining the slip on the Alpha fault. There is no overlap in the geology of the hanging wall and footwall fault surfaces, so the
amount of slip exceeds the length of a line in the slip direction across the illustrated view, but a preliminary indication of the slip is ~3–4 km in an easterly
direction. Source of information; E. Seedorff et al. (unpub. data).
1194
Eric Seedorff, Carson A. Richardson, and David J. Maher
KDQJLQJZDOORIWKH$OSKDIDXOWGH¿QHDVPDOOV\QFOLQH)LJXUH
6b). The fold is likely is a synextensional Tertiary fold formed
E\VXEVLGHQFHRIWKHKDQJLQJZDOORIWKHFRQFDYHZHVW6XO¿GH
East fault because the syncline roughly corresponds to a trough
LQWKHIDXOWVXUIDFHDQGSOXQJHVWRZDUGWKH6XO¿GH(DVWIDXOW
Single stratigraphic units are widespread in both the footwall and hanging-wall fault surface maps of the Alpha fault
(Figure 6). Bedding in the footwall dips ~20–30°SW (Figure
6a), and bedding in the hanging wall dips ~35°NE to ~35°SE
(Figure 6b). The dip of the Alpha fault is moderate to subhorizontal; hence, the angle between bedding and the fault is a small
to moderate angle. The following three geologic scenarios conceivably are consistent with small to moderate bedding-to-fault
angles. (1) The Alpha fault formed initially as a Tertiary, highangle normal fault but cut bedding in Paleozoic rocks at a low
angle because bedding was rotated to moderate or high angles
by Mesozoic contractional folding. The strike of the later fault
also would have been subparallel to the trend of the fold axis,
and the limb of the fold was steep enough such that the fault was
subparallel to bedding over distances comparable to the area of
Figure 6. (2) The Alpha fault formed initially as a high-angle
normal fault but cut bedding at low to moderate angles because
bedding was tilted to high angles by movement on one or more
earlier normal faults. (3) The Alpha fault formed initially as a
low-angle normal fault but Paleozoic rocks were gently dipping
because Mesozoic contractional deformation produced open
folds; thus the Alpha fault cut bedding in Paleozoic rocks at low
to moderate angles. This question remains unresolved pending
completion of a compelling three-dimensional structural reconstruction of the district, but district and regional-scale geologic
considerations suggest that hypothesis (2) is most likely and
that hypothesis (3) is least likely.
The distribution of rock/alteration units coupled with bedding orientations in the footwall and hanging-wall maps for the
Alpha fault indicates that there is no overlap between the two
fault surface maps. Note that the hanging wall map contains
mostly Permian Rib Hill Sandstone (variably altered to silica-pyrite) and virtually no porphyry (Figure 6b), whereas the
footwall consists of an east-west trending band of sericitically
altered porphyry, > 300 m wide, bordered both to the north and
south by ~300-m wide zones of silica-pyrite alteration of Pennsylvanian Ely Limestone, grading outward to weaker alteration
and eventually into other rock units (Figure 6a). Therefore, the
Alpha fault has moved a volume of rock that formed somewhat outside the porphyry system and translated it down on
the intensely altered, centrally located but high-level part of the
porphyry copper system. The magnitude of slip on the Alpha
fault must exceed the length of a line in the slip direction across
the illustrated view, i.e., the magnitude of slip exceeds one km.
Alignment of the southwesterly dipping stratigraphic contact
between the Rib Hill Sandstone and Riepe Spring Limestone
in the footwall with the same contact in the hanging wall suggests that there is ~3–4 km of slip in an easterly direction on the
Alpha fault.
Fault surfaces in a near-tip setting
Figure 7 shows preliminary fault surface maps for the Liberty fault. The Liberty fault illustrates characteristics of fault
surface maps in the near-tip environment, including a major
rotational component of the hanging wall relative to the footwall. Like the Dexter fault, the Liberty fault is also relatively
young—indeed even younger than the Dexter—so it also shows
characteristics of other young faults.
The Liberty fault is a northeast-striking, southeast-dipping
normal fault that is exposed for ~1000 m of strike length on the
eastern end of the Liberty pit (Figures 4 and 7). Two vintages
of reliable geologic maps are available for this region of the
pit, one spatially offset from the other by mining progress; very
thick colored lines show the rock/alteration types along the two
mapped traces of the fault (Figure 7). Intensely colored dots
show the logged geology of drill hole piercements, which are
relatively few because the fault is relatively steep (requiring a
deep hole to penetrate it) and the copper grade drops quickly
with depth (obviating the need to drill many holes for ore delineation in this area). Because of the presence of a block cave
mine nearby, the Liberty fault was crossed by underground
drifts on the 6560 ft level south of 104,000N, in which the location of the Liberty fault was mapped (locations not shown
because of lack of corresponding data on rock/alteration types).
Fault locations at that elevation improve the control on structure contours along most of the illustrated portion of the fault,
which must continue further to the northeast.
The southwestern tip of the Liberty fault was mapped (unpublished 1958 Liberty pit map, Geology Department, Nevada
Mines Division, Kennecott Copper Corporation), with the fault
ending in a horsetail of small faults. Continuations of the Liberty fault to the southwest of the tip are shown on some maps
(e.g., Spencer, 1917), but careful attempts to trace the fault
VRXWKZHVWZDUGLQWKH¿HOGDQGWRGRFXPHQWFRPSHOOLQJRIIVHWV
in geologic markers (after accounting for other faults in the
DUHDLQGULOOKROHVFRQ¿UPWKDWWKHIDXOWWHUPLQDWHVZLWKLQWKH
pit as originally mapped and shown on Figure 7. The Liberty
fault picks up displacement northeastward, cutting and offsetting the Eureka fault immediately northeast of the northern rim
of the Liberty pit (Figure 7).
Measurements on the dip of the Liberty fault range from
45° to 70°SE (Figure 7). The steepest dips are near the southwestern termination of the fault, whereas to the northeast, over
the rest of its exposed length, typical dips are about 50° (Figure
7). The main Liberty fault has a nearly linear trace, but it has a
concave southeast footwall splay and a north-striking, concave
southeast, scooped-shaped hanging wall splay within ~600 m
of its southwestern tip. The Liberty Footwall Splay fault is subparallel to the main fault but is more irregular in strike and dips
65° to the southeast (not shown); the branch-line with the main
Liberty fault (i.e., where the Footwall Splay joins with the main
fault) is shown on the footwall geologic map (Figure 7a). The
Liberty Hanging Wall Splay fault, in contrast, swings abruptly
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
1195
Figure 7A. Preliminary fault surface maps for the Liberty fault on the eastern end of the Liberty pit, Robinson district, illustrating characteristics of fault surface
maps in the near-tip environment, including a major rotational component of the hanging wall relative to the footwall. (A) Footwall; (B) hanging wall. The locations of reliable geologic control for these maps are shown by intensely colored dots (drill hole piercements) and by very thick colored lines (the mapped trace of
the fault on two vintages of geologic maps during mining). Other attributes are as described for Figure 6 and in the text. The southwestern end of the Liberty fault
was mapped within the Liberty pit. The measured dips indicate that the fault dips to the southeast at moderate to steep angles; some of the dip orientations near
the southwestern tip of the Liberty fault are measured on small horsetails (not shown) off the main fault. Branch lines show how hanging-wall and footwall splays
joint with the main Liberty fault. There is no slip at the tip at the southwestern end of the fault; farther to the northeast, geologic interpretations require further
PRGL¿FDWLRQWRUH¿QHWKHDPRXQWDQGGLUHFWLRQRIVOLSRIYDULRXVSLHUFLQJSRLQWVDORQJWKHIDXOWVXUIDFH1RQHWKHOHVVRIIVHWVLQWKHFLUFXODUUHIHUHQFHSRLQWVDWWKH
northeastern end of the map indicate that the hanging wall point moved 227 m in the plane of the fault in a S40E direction relative to the footwall, producing a
horizontal component of clockwise rotation of the hanging wall by ~7° relative to the footwall. Restoring this movement causes the position of the Eureka fault and
other geologic markers in the hanging wall to match closely with corresponding markers in the footwall. Source of information; E. Seedorff et al. (unpub. data).
1196
Eric Seedorff, Carson A. Richardson, and David J. Maher
Figure 7B. Preliminary fault surface maps for the Liberty fault on the eastern end of the Liberty pit, Robinson district, illustrating characteristics of fault surface
maps in the near-tip environment, including a major rotational component of the hanging wall relative to the footwall. (A) Footwall; (B) hanging wall. The locations of reliable geologic control for these maps are shown by intensely colored dots (drill hole piercements) and by very thick colored lines (the mapped trace of
the fault on two vintages of geologic maps during mining). Other attributes are as described for Figure 6 and in the text. The southwestern end of the Liberty fault
was mapped within the Liberty pit. The measured dips indicate that the fault dips to the southeast at moderate to steep angles; some of the dip orientations near
the southwestern tip of the Liberty fault are measured on small horsetails (not shown) off the main fault. Branch lines show how hanging-wall and footwall splays
joint with the main Liberty fault. There is no slip at the tip at the southwestern end of the fault; farther to the northeast, geologic interpretations require further
PRGL¿FDWLRQWRUH¿QHWKHDPRXQWDQGGLUHFWLRQRIVOLSRIYDULRXVSLHUFLQJSRLQWVDORQJWKHIDXOWVXUIDFH1RQHWKHOHVVRIIVHWVLQWKHFLUFXODUUHIHUHQFHSRLQWVDWWKH
northeastern end of the map indicate that the hanging wall point moved 227 m in the plane of the fault in a S40E direction relative to the footwall, producing a
horizontal component of clockwise rotation of the hanging wall by ~7° relative to the footwall. Restoring this movement causes the position of the Eureka fault and
other geologic markers in the hanging wall to match closely with corresponding markers in the footwall. Source of information; E. Seedorff et al. (unpub. data).
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
southward from the main Liberty fault, forming an easterly facing scoop that dips ~40° east and terminates to the south (not
shown); the branch line with the main Liberty is shown on the
hanging-wall geologic map (Figure 7b).
The offset segments of the older Eureka fault, which occur
as a curving line on both the footwall and hanging wall Liberty fault surface geologic maps (Figure 7), provide a geologic
marker to restore slip on the southwestern end of the younger
Liberty fault. The restoration can be accomplished by rotation
of the hanging wall relative to the footwall about a rotation axis
near the tip, such that any point in the hanging wall makes an arc
UHODWLYHWRWKHIRRWZDOO7KHVOLSGLUHFWLRQLVGH¿QHGE\DYHFWRU
that joins the ends of the arc, which is oriented at ~S40°E, and the
length of the vector as measured in the plane of the fault, which
is the magnitude of slip on the Liberty fault, is ~ 745 ft (~230 m).
The horizontal component of clockwise rotation of the hanging
wall relative to the footwall is ~7° (Figure 7), or more than three
times the amount observed for the Dexter fault (Figure 5).
Overview of Yerington district geology
The Yerington district, located near the town of Yerington in western Nevada, contains porphyry copper, skarn, and
iron-oxide-copper-gold (IOCG) mineralization related to the
Middle Jurassic Yerington batholith. Mineralization is hosted
in the Yerington batholith and its Triassic to Jurassic wall rocks
(Dilles and Wright, 1988; Dilles et al., 2000). The district conWDLQVPXOWLSOHSRUSK\U\FRSSHUFHQWHUVZKLFKDUHFODVVL¿HGDV
quartz monzodioritic-granitic porphyry Cu-(Mo) systems in
the scheme of Seedorff et al. (2005). The Yerington district has
been structurally dismembered and rotated 60 to 90°, primarily
by three temporally distinct sets of east-dipping normal faults
since ~14 Ma (Proffett, 1977, 1979; Einaudi, 1977; Harris and
Einaudi, 1982; Dilles, 1987; Dilles and Einaudi, 1992; Dilles
and Gans, 1995; Barton and Johnson, 2000; Dilles et al., 2000).
Rocks of the Yerington batholith crop out over an east-west disWDQFHRIa±NP2OLJRFHQHDVKÀRZWXIIVWKDWZHUHGHSRVited horizontally upon a mid-Tertiary erosion surface are now
highly tilted (Figure 8), and distinct phases and porphyry dike
swarms, associated with a Jurassic batholith, provide abundant
markers to aid in reconstruction and indicate the district has
been extended more than 150% (Proffett and Proffett, 1976;
Proffett and Dilles, 1984; Runyon, 2013).
Two-dimensional structural reconstructions led to the discovery of the Ann-Mason deposit by the Anaconda Company
(Proffett, 1977; Proffett and Dilles, 1984; Hunt, 2004). Recent
drilling and exploration has further expanded the availability of
data in three dimensions and has allowed a 3-D reconstruction
of the Ann-Mason and Blue Hill area (Richardson, 2014; Richardson and Seedorff, this volume). Fault surface maps provide a
PHDQVWRUH¿QHWKHORFDWLRQRIH[SORUDWLRQWDUJHWV,QDUHDVVXFK
as Yerington where there are multiple discrete porphyry dike
swarms, fault surface maps and associated reconstructions also
allow one to test questions such as whether mineralization on
1197
two sides of a fault were contiguous prior to faulting. Both of
these possibilities can be addressed at Ann-Mason.
Ann-Mason deposit
The Ann-Mason deposit is a porphyry Cu-(Mo) deposit
associated with a swarm of granite porphyry dikes that presHQWO\ VWULNH DW a1ƒ: DQG GLS ƒ1 EXW LQ SUHWLOW FRQ¿JXration would have had a strike of ~N35°W and dipped ~90°
(Dilles, 1987; Dilles and Proffett, 1995; Dilles et al., 2000). The
ÀDQNVWRSDQGERWWRPRIWKHK\GURWKHUPDOV\VWHPDUHH[SRVHG
in the Ann-Mason fault block in the Singatse Range (Dilles and
Einaudi, 1992), as well as in the Buckskin Range to the west
(Lipske and Dilles, 2000; Dilles et al., 2000). The main part
of the Ann-Mason deposit is bound by two gently east-dipping
faults: the deposit is located in the footwall of the Singatse fault
and in the hanging wall of the Blue Hill fault (Figure 8). In addition, the deposit is cut by other, more steeply dipping faults.
Exploration opportunities exist in each place where the deposit
potentially is truncated by post-mineral faults.
Lateral continuations across fault blocks
As described above, the Ann-Mason ore body is truncated
above by the Singatse fault (Figure 8). The Singatse fault has
3.6 km of slip along its northern exposure and increases to 3.8
km of slip along its southern exposure directly above the AnnMason deposit (Figure 9) over a distance of 3.8 km (Richardson
and Seedorff, this volume). The minimal increase in slip along
strike is further constrained by the scoop-like geometry of the
Singatse fault, which limits the viable structural interpretations,
as large rotations involving north-south components would require much larger strains on the wall rocks (e.g., Needham et
al., 1996). The outermost limits of the Ann-Mason ore body are
projected to the footwall surface of the Singatse fault (Figure 9),
and the outline of the Ann-Mason ore body in the hanging wall
of the Singatse fault represents a potential exploration target.
The two generations of faults that postdate the Singatse fault
complicate the exercise, as these create gaps in the fault surface
maps (Figure 9) that have to be closed before reconstructing the
Singatse fault. These younger faults also dismember the outline
of the Ann-Mason ore body and generate a smaller target on the
HDVWHUQÀDQNVRIWKH6LQJDWVH5DQJHLQWKHKDQJLQJZDOOVRIWKH
Singatse fault and a younger, crosscutting fault, such that the
bulk of the hanging-wall projection is located directly beneath
the abandoned pit of the Yerington mine (Figure 9). The presence of the hanging-wall fragment of the Ann-Mason deposit
beneath the Yerington mine is somewhat coincidental and does
not indicate that the Ann-Mason deposit is related to the Yerington system; instead, each deposit is associated with separate, narrow dike swarms (each ~2 km in thickness) that dip 45°
N. The northern-most limit of the Ann-Mason fragment in the
hanging wall of the Singatse fault projects ~1.8 km SSW of the
Yerington pit at the modern surface.
Figure 8. Bent cross section through the Yerington district, oriented approximately east-west, looking north. Adapted from cross section A-Ac of Proffett and Dilles (1984).
1198
Eric Seedorff, Carson A. Richardson, and David J. Maher
Figure 9. Geologic fault surface map for the hanging wall of the Singatse fault, showing closure of gaps created by younger faults. The Singatse fault is cut by faults of two younger generations of faults.
(a) Map prior to closure of gaps created by the younger, crosscutting normal faults. (b) Map after closure of gaps. Arrows show displacement directions based on restoration of hanging wall map on top
of footwall map (not shown). From Richardson and Seedorff, this volume.
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
1199
1200
Eric Seedorff, Carson A. Richardson, and David J. Maher
Likewise, the Ann-Mason ore body is truncated at depth by
the Blue Hill fault (Figure 8), and there is mineralized rock that
crops out on the footwall side of the Blue Hill fault, known as
the Blue Hill deposit. Although Dilles and Proffett (1995, Figure 1) present a reconstruction that suggests that both deposits
originated in the same porphyry dike swarm, most of the data
WKDWZHUHXVHGWRJHQHUDWHWKH¿JXUHLVXQSXEOLVKHG5LFKDUGson and Seedorff (this volume) test that hypothesis using fault
VXUIDFHPDSVZLWKWKHEHQH¿WRIGDWDGHULYHGIURPKROHVGULOOHG
E\(QWUpH*ROGPRUHUHFHQWO\DQGFRQ¿UPWKDWWKHSURMHFWLRQ
of the Ann-Mason dike swarm down to the Blue Hill fault does
indeed restore directly over the Blue Hill deposit and its associated dikes (Richardson and Seedorff, this volume). Thus, the
Blue Hill and the Ann-Mason deposits are genetically linked,
and Blue Hill indeed can be thought of, in pre-tilt position, as
the lateral continuation of the Ann-Mason porphyry system
(Dilles and Proffett, 1995).
Another swarm of porphyry dikes is present south of the
Ann-Mason dike swarm, and it could be associated with another center of porphyry mineralization, for which a few exploration holes have been drilled. This target is known variously as
Yerington West and Roulette (see Richardson and Seedorff, this
volume). The viability of this center as an exploration target
will be advanced by further delineation of the geology of the
Blue Hill fault surface.
As the Yerington district example demonstrates, fault surface maps provide an opportunity to generate exploration targets by transferring tightly constrained interpretations of the
geology across faults to where there may be little or no known
information, thereby making better informed decisions about
EURZQ¿HOGVH[SORUDWLRQIRUIDXOWRIIVHWIUDJPHQWV
mum displacement along strike (Elliott, 1983). The slip vector
at the point of maximum displacement represents the bisector
between the two fault tips, also known as Elliott’s (1976) “bow
and arrow” rule. Structural features plotted should be observDEOHLQWKH¿HOGLQVHLVPLFUHÀHFWLRQVDQGRULQGULOOFRUHZLWK
structural styles shown on the section matching those observed
on the ground, e.g., chevron and box folds not plotted as concentric folds (Woodward et al., 1989). Where data are sparse,
data from out of the cross section can be projected down plunge
(Mackin, 1950) into the cross section to provide additional
constraints. Reconstructions should aim to conserve volume,
which, with various simplifying assumptions, in 2-D translates
to conserving bed length and unit thickness (Dahlstrom, 1969;
Groshong, 1994; Judge and Allmendinger, 2011), as well as be
strain-compatible, geometrically valid, and internally consistent (Woodward et al., 1986; Buchanan, 1996). In sets of serial
cross sections, where one is attempting to assess changes along
strike, the amount of slip on any one fault between two closely
neighboring cross sections should not differ greatly nor should
there be changes in structural style; whereas, over longer distances across the fault system, displacement is transferred from
one fault to another (Dahlstrom, 1969).
These 2-D reconstructions show an amount of slip that is
determined by the choice of a line of cross section. Faults have
points of zero displacement at the tips and a point of maximum
displacement between them; between the point of maximum
displacement and the tips, the hanging wall should be rotating
about a vertical axis relative to the footwall. Additionally, the
line of section may cross multiple, superimposed fault generations with differing slip directions, where material will be
moving in and out of the one, chosen line of section, making it
unrestorable. The necessity for a more 3-D approach to strucDISCUSSION
tural reconstruction becomes apparent in the Robinson district.
Strata dip moderately west in the western part of the Robinson
Contrasting perspectives between 2-D and 3-D structural
district, but strata dip moderately to steeply east in the central
reconstructions
and eastern parts of the district. Thus rigid-body 2-D cross-sectional structural reconstructions cannot untilt strata on one side
Over the last half-century, rules and guides have been de- of the district without increasing the degree of tilting on the
veloped that govern 2-D, cross-sectional reconstructions to test opposite side of the district. A restoration of the tilting of beds
interpretations, either validating or dismissing them. This work cannot be achieved solely by rotations about horizontal axes.
was developed in contractional settings and have been widely Although horizontal-axis rotations characterize normal faults,
used in fold and thrust belts (e.g., Bally et al., 1966; Dahlstrom, an important component of vertical-axis rotation occurs near
1969; Mitra, 1992; Wilkerson and Dicken, 2001), but cross- tips. The abundant 3-D geologic data available in the Robinsectional reconstructions also have been applied in settings of son district, as depicted in the fault surface maps shown here,
continental extension (e.g., Proffett, 1977; Gibbs, 1983, 1984; UHTXLUHVVLJQL¿FDQWFRPSRQHQWVRIYHUWLFDOD[LVURWDWLRQIRUWKH
Wernicke et al., 1988; Smith et al., 1991; Seedorff, 1991; Col- Liberty fault and non-trivial components for other faults. The
gan et al., 2008; Nickerson et al., 2010). In the petroleum in- importance of vertical-axis rotations in the Robinson district is
GXVWU\WKHLQWHQWRISHUIRUPLQJWKLVWHGLRXVSURFHVVLV¿UVWWR consistent with the fact that strata within the central Egan Range
test targets conceptually before spending money, in an attempt commonly strike 20–50° from due north, which contrasts with
to avoid drilling dry holes. Faults can affect not only the forma- strikes observed north and south of the accommodation zone
tion of the trap, but also the migration path of hydrocarbons where typical strikes are northerly.
(Buchanan, 1996).
The technique described here, though not a volumetric
Cross sections are typically constructed parallel to the restoration, restores a 2-D image of the hanging wall against a
principal slip direction, preferably nearest to the point of maxi- 2-D image of its footwall and captures the third dimension via
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
structure contours of the fault surface. The examples offered
here demonstrate that fault surface maps are a useful technique
for reconstruction. Nonetheless, even this type of 3-D reconstruction may not result in a substantially improved structural
interpretation over a 2-D, cross-sectional reconstruction without considerable 3-D geologic control.
Asymmetry in amount and familiarity with geologic data
used in reconstructions
The advancement of science and its practical application
depend on making and presenting observations, constructing
hypotheses—ideally multiple working hypotheses, and using
geological reasoning to test the hypotheses to advance understanding (Chamberlin, 1890; Frodeman, 1995). Although
some workers view geologic maps as anachronistic (House
et al., 2013), the geologic map remains a fundamental means
of presenting geologic observations (Compton, 1985; Barnes
and Lisle, 2004), and cross sections and three-dimensional
block models are the principal means of presenting geologic
interpretations of the map area, especially in the disciplines of
structural and economic geology (e.g., Stevens, 2010; Davis et
al., 2012). Nonetheless, the basis for these interpretations—the
geologic map—contains an underlying element of interpretation (e.g., Coe et al., 2010). A map represents the modern, irregular, two-dimensional surface through a region that evolved
both in time and in three-dimensional space. The preserved
geology may lack any evidence for certain time intervals; the
degree of exposure in the map area may be imperfect; and critical contacts may be poorly exposed at the surface or may exist
only at depth. Thus a geologic map constitutes only a working,
testable hypothesis, so the impact on structural reconstructions
of data derived from maps and other inputs should be displayed
explicitly.
Many users of structural reconstructions, be they readers of
a journal article or managers in an exploration company, may
have neither the time nor the interest in evaluating the validity
of the interpretation. However, the small fraction of users who
have the most interest or have the most at stake in the success
or failure in using the reconstruction may want to perform “due
diligence” on the reconstruction. These consumers of geologic
interpretations in both science and industry, however, are at a
distinct disadvantage relative to the geologists who initially
offer the structural reconstruction because the users typically
have access to only a small fraction of the available data, or the
GDWDDUHLQDIRUPWKDWPDNHLWGLI¿FXOWIRUWKHXVHUVWRDVVHVV
their quality and to consider and test alternative interpretations.
The use of fault surface maps decreases this asymmetry in
NQRZOHGJH EHFDXVH IDXOW VXUIDFH PDSV DUH DQ HI¿FLHQW PHDQV
of presenting more of the data that constrain the structural
reconstructions, as shown in the illustrations above. This has
VHYHUDOLPSRUWDQWVFLHQWL¿FFRQVHTXHQFHV)LUVWLWKHOSVSHUPLW
the reader (and earlier reviewers and editors) to evaluate better
whether the reconstruction is potentially valid geologically and
1201
geometrically. Second, it makes it easier for the less informed
user to generate alternative hypotheses with the same data set,
LQFOXGLQJ FRPSHWLQJ UHFRQVWUXFWLRQV )LQDOO\ LW LV PRUH GLI¿cult for geologists who are less disposed to accept the interpretation resulting from a compelling reconstruction to reject the
interpretation, because it is apparent to readers that the interpretation is indeed well supported by a rich body of data. Hence
it becomes incumbent on the skeptics to develop an alternative
that is at least as viable. As a result, the improved transparency
in reconstructions is a feature of fault surface maps that makes
them an appealing alternative to 2-D reconstructions even
where 3-D data are sparse.
Exploration in 3-D
The areas where the concepts of palinspastic structural
reconstruction have been applied to district-scale exploration
programs, such as San Manuel-Kalamazoo, Arizona (Lowell,
1968; Lowell, 1991) and the Yerington district, Nevada (Proffett, 1977; Proffett and Dilles, 1984), are locales where the
faults with major displacement tend to have similar strike directions. Hence, 2-D reconstructions using cross sections are
accurate and effective means of structural reconstruction, and
the Ann-Mason examples shown here are a by-product of exSORUDWLRQWKDWEHQH¿WWHGIURP'VWUXFWXUDOUHFRQVWUXFWLRQV,Q
areas with more complicated extensional faulting, however, a
3-D approach is especially valuable, both to aid visualization of
the structure and to calculate the amounts and directions of slip
more rigorously.
The Robinson district is one of those regions with complex geometries of crosscutting normal faults (Seedorff et al.,
WKDWEHQH¿WVPRVWIURP'UHFRQVWUXFWLRQV,QGHHGWKH
reason that a 3-D structural reconstruction of normal faulting in
the Robinson district became a long-term goal for the Robinson project was to assess whether the district had any remaining exploration potential. So many holes had been drilled in
the Robinson district (>10,000) that its potential for growth in
ore reserves appeared to have been exhausted, save for favorable changes in metal prices and production costs. Without a
rigorous, geologically defensible 3-D reconstruction, however,
LW ZRXOG EH GLI¿FXOW WR DVVHVV WKH SRVVLELOLW\ WKDW PDWHULDO DW
minable grades and depths remains to be located. A 3-D model
could show the preserved and eroded portions of fault blocks
and the volumes of ore-grade material that was known (mined
out or in place) or that could reasonably be inferred. Restoration
RI D IDXOW RU IDXOWV WKDW LGHQWL¿HV WKH SURMHFWLRQ RI SUHVHUYHG
ore-grade material within an undrilled fault block would signify an area that would be especially prospective for mine-site
exploration.
Thus, 3-D reconstructions are valuable both in grass roots
H[SORUDWLRQDQGLQEURZQ¿HOGVH[SORUDWLRQZKHQDGGUHVVLQJWKH
potential of regions that exhibit complex extensional faulting,
and fault surface maps are useful for achieving these 3-D reconstructions.
1202
Eric Seedorff, Carson A. Richardson, and David J. Maher
Future developments
Many characteristics of faults described here cannot be
readily incorporated into reconstructions without use of computer software; however, these characteristics are currently not
well accommodated in the algorithms of commercially available structural reconstruction software programs. For example,
neither non-rigid, synkinematic deformation related either to
ÀH[XUDOFROODSVHRIWKHKDQJLQJZDOODQGUHERXQGRIWKHIRRWwall (Kusznir and Ziegler, 1992) nor along-strike changes in
WKHGLVSODFHPHQWSUR¿OH:DOVKDQG:DWWHUVRQDUHLQFRUporated easily. Indeed, the use of fault surface maps as inputs
for restoration into computer software also is not readily incorporated. In the meantime, structural reconstructions of fault
surface maps with adequate accuracy can be achieved manually
or with standard drafting software.
whether the reconstruction is valid and robust. Reconstructions
can play an important role in exploration for and exploitation of
ore deposits, and the use of fault surface maps can facilitate a
more three-dimensional approach to mineral exploration, especially in complexly faulted regions such as certain parts of the
Basin and Range province.
ACKNOWLEDGMENTS
Two of us (ES, DJM) started working on fault surface
maps in the early to mid-1990s at the Robinson project while
owned by Magma Copper Company. We appreciate discussions over the years with many people regarding fault surface
maps and the geology of the Robinson deposit with Pat Fahey,
Steve Shaver, Dick Breitrick, Rich Hasler, Richard Jeanne,
Larry James, and the mine and exploration staffs of Magma,
BHP, Quadra, QuadraFNX, and KGHM International, includCONCLUSIONS
ing Bridget Ball, Jim Biggs, Randal Burns, and Judd Fee. We
WKDQN4XDGUDIRU¿QDQFLDOVXSSRUWRIVRPHRIWKHZRUNWKDWOHG
Three-dimensional reconstructions of faults can be made
WRWKLVFRQWULEXWLRQWKURXJKWKHJRRGRI¿FHVRI3DW)DKH\(Qwith fault surface maps, which are plan-view projections of the
trée Gold sponsored CAR’s M.S. research and provided access
geology of the footwall and hanging-wall surfaces of a fault. A
to drill data in the Ann-Mason area of the Yerington district. We
four-layer strategy is used to develop fault surface maps. The
especially thank Tom Watkins and Norm Page of Entrée Gold
UHVXOWVFDQEHSUHVHQWHGHI¿FLHQWO\KRZHYHULQWZRSDQHOVWKDW
for their support and assistance. Over the years we value the
display interpretations of the geology of the hanging wall and
discussions about the geology of the Yerington district that we
footwall overlain on structure contours, as well as the sources
have had with John Dilles, Marco Einaudi, John Proffett, Mark
of geologic data for each panel—usually lines from geologic
Barton, and David Johnson, and more recently with Hank Ohmaps and points from drill hole piercements. Older faults will
lin, Korin Carpenter, and Simone Runyon. We thank Daniel A.
show as lines on fault surface maps of younger faults. In con)DYRULWRIRUKLVKXJHDVVLVWDQFHE\GUDIWLQJVRPHRIWKH¿JXUHV
trast, younger normal faults produce gaps in the fault surfaces
The many people who have challenged our interpretations of
of older faults, and the gaps widen in the direction of increasing
normal faults in places such as Robinson have helped motivate
displacement or decreasing dip of the crosscutting fault.
XVWRUH¿QHWKHPHWKRGSUHVHQWHGKHUHDVDPHDQVRIGHPRQThe movement of a fault is restored by matching the geostrating the geologic constraints by which we all seemingly
logic map of the hanging wall with the geologic map of the
will have to abide. We highly appreciate the detailed comments
footwall. Where there are adequate geologic markers and threereceived from formal and informal reviewers alike, Sean P.
dimensional control, numerous slip vectors across the fault surLong, Steven H. Lingrey, and Steven A. Shaver, each of whom
face result from the restoration, from which the magnitude of
brought the differing perspectives of someone with a tectonics
slip in the plane of the fault can be calculated for each vector.
and structural reconstruction background, a structural geology
In a given area, the type of movement exhibited by the fault
specialist in the petroleum industry, and an economic geologist
depends in part on whether the portion of a normal fault bewho is familiar with the Robinson and Yerington districts and
ing restored is near or far from either tip of the fault; near-tip
experienced in structural reconstructions of mineral deposits,
regions commonly display an important rotational component
respectively.
of movement, but mid-fault regions are dominated by downdip translation. Additional geologic constraints are required to
determine the amount of tilting that occurred concurrent with REFERENCES
slip. Three-dimensional structural reconstructions of areas are
achieved by stepwise repetition of the process from youngest Allan, U.S., 1989, Model for hydrocarbon migration and entrapment within
faulted structures: American Association of Petroleum Geologists Bulto oldest faults.
letin, v. 73, p. 803–811.
Areas of complex geology containing multiple generations
Anders, M.H., and Schlische, R.W., 1994, Overlapping faults, intrabasin highs,
RIIDXOWVZLWKGLIIHULQJVOLSGLUHFWLRQVHVSHFLDOO\EHQH¿WIURPWKH
and the growth of normal faults: Journal of Geology, v. 102, p. 165–180.
use of fault surface maps for three-dimensional reconstructions. Badgley, P.C., 1959, Structural methods for the exploration geologist and a seNonetheless, fault surface maps are effective even in areas of
ries of problems for structural geology students: New York, Harper and
less complex faulting at portraying the locations and types of
Brothers, 280 p.
three-dimensional geologic controls, which aids in assessing Bally, A.W., Gordy, P.L., and Stewart, G. A., 1966, Structure, seismic data, and
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
orogenic evolution of southern Canadian Rocky Mountains: Bulletin of
Canadian Petroleum Geology, v. 14, p. 337–381.
Barnes, J.W., and Lisle, R.J., 2004, Basic geological mapping, 4th edition:
Chichester, John Wiley and Sons, Ltd., 184 p.
Barnett, J.A.M., Mortimer, J., Rippon, J.H., Walsh, J.J., and Watterson, J.,
1987, Displacement geometry in the volume containing a single normal
fault: American Association of Petroleum Geologists Bulletin, v. 71, p.
925–937.
Barton, M.D., and Johnson, D.A., 2000, Alternative brine sources for Feoxide(-Cu-Au) systems: Implications for hydrothermal alteration and
metals, in Porter, T.M., ed., Hydrothermal iron oxide copper-gold and
related deposits—A global perspective: Glenside, South Australia, Australian Mineral Foundation, p. 43–60.
Bauer, H.L., Jr., Breitrick, R.A., Cooper, J.J., and Anderson, J.A., 1966, Porphyry copper deposits in the Robinson mining district, Nevada, in Titley, S.R., and Hicks, C.L., eds., Geology of the porphyry copper deposits, southwestern North America: Tucson, University of Arizona Press,
p. 232–244.
Berg, S.S., and Skar, T., 2005, Controls on damage zone asymmetry of a normal
fault zone: Outcrop analyses of a segment of the Moab fault, SE Utah:
Journal of Structural Geology, v. 27, p. 1803–1822.
Brimhall, G.H, Dilles, J.H., and Proffett, J.M., Jr., 2006, The role of geologic
mapping in mineral exploration, in Doggett, M.D., and Parry, J.R., eds.,
Wealth creation in the minerals industry: Integrating, science, business,
and education: Society of Economic Geologists Special Publication 12,
p. 221–241.
Buchanan, J.G., 1996, The application of cross-section construction and validation within exploration and production: A discussion, in Buchanan,
P. G., and Nieuwland, D. A., eds., Modern developments in structural
interpretations, validation and modeling: Geological Society of London
Special Publication 99, p 41–50.
Buck, W.R., 1988, Flexural rotation of normal faults: Tectonics, v. 7, p. 959–
973.
Caine, J.S., Evans, J.P., and Forster, C.B., 1996, Fault zone architecture and
permeability structure: Geology, v. 24, no. 11, p. 1025–1028.
&DUWZULJKW-$0DQV¿HOG&DQG7UXGJLOO%'7KHJURZWKRIQRUPDO
faults by segment linkage, in Buchanan, P.G., and Nieuwland, D.A.,
eds., Modern developments in structural interpretation, validation and
modelling: Geological Society of London Special Publications 99, p.
163–177.
Chamberlin, T.C., 1890, The method of multiple working hypotheses: Science,
v. 15, no. 366, p. 92–96.
Childs, C., Watterson, J., and Walsh, J.J., 1995, Fault overlap zones within developing normal fault systems: Geological Society of London Journal,
v. 152, p. 535–549.
&RH$/$UOHV7:5RWKHU\'$DQG6SLFHU5$*HRORJLFDO¿HOG
techniques: London, Wiley-Blackwell and The Open University, 336 p.
Colgan, J.P., John, D.A., Henry, C.D., and Fleck, R.J., 2008, Large-magnitude
Miocene extension of the Eocene Caetano caldera, Shoshone and Toiyabe Ranges, Nevada: Geosphere, v. 4, no. 1, p. 107–130.
Colgan, J.P., Howard, K.A., Fleck, R.J., and Wooden, J.L., 2010, Rapid middle
0LRFHQHH[WHQVLRQDQGXQURR¿QJRIWKHVRXWKHUQ5XE\0RXQWDLQV1Hvada: Tectonics, v. 29, no. 6, TC6022, doi:10.1029/2009TC002655.
&RPSWRQ55*HRORJ\LQWKH¿HOG1HZ<RUN:LOH\S
Cowie, P.A., and Scholz, C.H., 1992, Displacement-length scaling relationship
for faults: Data synthesis and discussion: Journal of Structural Geology,
v. 14, p. 1149–1156.
Crider, J. G., and Peacock, D. C. P., 2004, Initiation of brittle faults in the upper
FUXVW$UHYLHZRI¿HOGREVHUYDWLRQV-RXUQDORI6WUXFWXUDO*HRORJ\Y
26, p. 691–707.
Crider, J.G., and Pollard, D.D., 1998, Fault linkage: Three-dimensional me-
1203
chanical interaction between echelon faults: Journal of Geophysical
Research, v. 103, p. 24,373–24,391.
Dahlstrom, C.D.A., 1969, Balanced cross sections: Canadian Journal of Earth
Sciences, v. 6, p. 743–757.
d’Alessio, M.A., and Martel, S.J., 2004, Fault terminations and barriers to fault
growth: Journal of Structural Geology, v. 26, p. 1885–1896.
Davis, G.H., 1983, Shear-zone model for the origin of metamorphic core complexes: Geology, v. 11, p. 342–347.
Davis, G.H., and Coney, P.J., 1979, Geologic development of the Cordilleran
metamorphic core complexes: Geology, v. 7, p. 120–124.
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 core-complex evolution in the Catalina-Rincon region,
southeastern Arizona: Geological Society of America Bulletin, v. 116,
p. 128–141.
Davis, G.H., Reynolds, S.J., and Kluth, C.F., 2012, Structural geology of rocks
and regions, 3rd Edition: New York, John Wiley and Sons, 839 p.
Dawers, N.H., and Anders, M.H., 1995, Displacement-length scaling and fault
linkage: Journal of Structural Geology, v. 17, p. 607–614.
Dawers, N.H., Anders, M.H., and Scholz, C.H., 1993, Growth of normal faults:
Displacement-length scaling: Geology, v. 21, p. 1107–1110.
Dilles, J.H., 1987, Petrology of the Yerington batholith, Nevada: Evidence for
HYROXWLRQRISRUSK\U\FRSSHURUHÀXLGV(FRQRPLF*HRORJ\YS
1750–1789.
Dilles, J.H., and Einaudi, M.T., 1992, Wall-rock alteration and hydrothermal
ÀRZSDWKVDERXWWKH$QQ0DVRQSRUSK\U\FRSSHUGHSRVLW1HYDGD²$
6-km vertical reconstruction: Economic Geology, v. 87, p. 1963–2001.
Dilles, J.H., and Gans, P.B., 1995, The chronology of Cenozoic volcanism and
deformation in the Yerington area, western Basin and Range and Walker
Lane: Geological Society of America Bulletin, v. 107, p. 474–486.
Dilles, J.H., and Proffett, J.M., Jr., 1995, Metallogenesis of the Yerington batholith, Nevada, in Pierce, F.W., and Bolm, J.G., eds., Porphyry Copper
Deposits of the American Cordillera: Arizona Geological Society Digest 20, p. 306–315.
Dilles, J.H., and Wright, J.E., 1988, The chronology of early Mesozoic arc magmatism in the Yerington district, Nevada, and its regional implications:
Geological Society of America Bulletin, v. 100, p. 644–652.
Dilles, J.H., Einaudi, M.T., Proffett, J.M., Jr., and Barton, M.D., 2000, Overview of the Yerington porphyry copper district: Magmatic to nonmagPDWLF VRXUFHV RI K\GURWKHUPDO ÀXLGV7KHLU ÀRZ SDWKV DQG DOWHUDWLRQ
effects on rocks and Cu-Mo-Fe-Au ores, in Dilles, J.H., Barton, M.D.,
Johnson, D.A., Proffett, J.M., Jr., and Einaudi, M.T., eds., Part I. Contrasting styles of intrusion-associated hydrothermal systems: Society of
Economic Geologists Guidebook Series, v. 32, p. 55–66.
Einaudi, M.T., 1977, Petrogenesis of the copper bearing skarn at the Mason
Valley mine, Yerington district, Nevada: Economic Geology, v. 72, p.
769–795.
Elliott, D., 1976, The energy balance and deformation mechanisms of thrust
sheets: Royal Society of London Philosophical Transactions, A, v. 283,
p. 289–312.
Elliott, D., 1983, The construction of balanced cross-sections: Journal of Structural Geology, v. 5, p. 101.
Faulds, J. E., and Varga, R. J., 1998, The role of accommodation zones and
transfer zones in the regional segmentation of extended terranes, in
Faulds, J. E., and Stewart, J. H., eds., Accommodation zones and transfer zones: The regional segmentation of the Basin and Range province:
Geological Society of America Special Paper 323, p. 1–45.
Fossen, H., 2010, Structural geology: Cambridge, United Kingdom, Cambridge
University Press, 463 p.
Frodeman, R., 1995, Geological reasoning: Geology as an interpretive and
1204
Eric Seedorff, Carson A. Richardson, and David J. Maher
historical science: Geological Society of America Bulletin, v. 107, p.
960–968.
Gans, P.B., and Miller, E.L., 1983, Style of mid-Tertiary extension in eastcentral Nevada, in Nash, W.P., and Gurgel, K.D., eds., Geological excursions in the overthrust belt and metamorphic core complexes of the
Intermountain region: Utah Geological Mineral Survey Special Studies
59, p. 107–139.
Gans, P.B., Miller E.L., McCarthy, J., and Ouldcott, M.L., 1985, Tertiary extensional faulting and evolving ductile-brittle transition zones in the
northern Snake Range and vicinity: New insights from seismic data:
Geology, v. 13, p. 189–193.
Gans, P.B., Seedorff, E., Fahey, P.L., Hasler, R.W., Maher, D.J., Jeanne, R.A.,
and Shaver, S.A., 2001, Rapid Eocene extension in the Robinson district, White Pine County, Nevada: Constraints from 40Ar/39Ar dating:
Geology, v. 29, p. 475–478.
Gawthorpe, R.L., and Leeder, M.R., 2000, Tectono-sedimentary evolution of
active extensional basins: Basin Research, v. 12, p. 195–218.
Gibbs, A.D., 1983, Balanced cross-section construction from seismic sections
in areas of extensional tectonics: Journal of Structural Geology, v. 5, p.
153–160.
Gibbs, A.D., 1984, Structural evolution of extensional basin margins: Journal
of the Geological Society, v. 141, p. 609–620.
Gonsior, Z.J., and Dilles, J.H., 2008, Timing and evolution of Cenozoic extensional normal faulting and magmatism in the southern Tobin Range,
Nevada: Geosphere, v. 4, p 687–712.
Groshong, R.H., Jr., 1989, Half-graben structures: Balanced models of extensional fault-bend folds: Geological Society of America Bulletin, v. 101,
p. 96–105.
Groshong, R.H., Jr., 1994, Area balance, depth to detachment, and strain in
extension: Tectonics, v. 13, p. 1488–1497.
Groshong, R.H., Jr., 2006, 3-D structural geology: A practical guide to quantitative surface and subsurface map interpretation, 2nd Edition: Berlin,
Springer-Verlag, 400 p.
Harris, N.B., and Einaudi, M.T., 1982, Skarn deposits in the Yerington district,
Nevada—metasomatic skarn evolution near Ludwig: Economic Geology, v. 77, p. 877–898.
+HQU\ &' $VKÀRZ WXIIV DQG SDOHRYDOOH\V LQ QRUWKHDVWHUQ 1HYDGD
Implications for Eocene paleogeography and extension in the Sevier
hinterland, northern Great Basin: Geosphere, v. 4, p. 1–35.
+HQU\&'DQG)DXOGV-($VKÀRZWXIIVLQWKH1LQH+LOO1HYDGD
paleovalley and implications for tectonism and volcanism of the western Great Basin, USA: Geosphere, v. 6, p. 339–369.
Hodgkinson, K.M., Stein, R.S., and King, G.C.P., 1996, The 1954 Rainbow
Mountain-Fairview Peak-Dixie Valley earthquakes: A triggered normal
faulting sequence: Journal of Geophysical Research, v. 101, p. 25,459–
25,471.
Hopkins, H., 1940, Faulting at the Wright-Hargreaves mine with notes on
ground movements: Transactions of the Canadian Institute of Mining
and Metallurgy, v. 43, p. 685–707.
House, P.K., Clark, R., and Kopera, J. P., 2013, Overcoming the momentum
RIDQDFKURQLVP$PHULFDQJHRORJLFPDSSLQJLQDWZHQW\¿UVWFHQWXU\
world, in Baker, V.R., ed., Rethinking the fabric of geology: Geological
Society of America Special Paper 502, p. 103–125.
Hunt, J.P., 2004, Society of Economic Geologists Silver Medal for 2003 Citation of John M. Proffett: Economic Geology, v. 99, p. 1817–1818.
Jackson, J.A., 1987, Active normal faulting and crustal extension, in Coward,
M.P., Dewey, J.F., and Hancock, P.L., eds., Continental extensional tectonics: Geological Society of London Special Publication 28, p. 3–17.
Jackson, J.A., and White, N.J., 1989, Normal faulting in the upper continental
crust: Observations from regions of active extension: Journal of Structural Geology, v. 11, p. 15–36.
John, D.A., Henry, C.D., and Colgan, J.P., 2008, Magmatic and tectonic evolution of the Caetano caldera, north-central Nevada: A tilted, mid-Tertiary
eruptive center and source of the Caetano Tuff: Geosphere, v. 4, p.
75–106.
Judge, P.A., and Allmendinger, R.W., 2011, Assessing uncertainties in balanced
cross sections: Journal of Structural Geology, v. 33, p. 458–467.
Keeler, D.A., 2010, Structural reconstruction of the Copper Basin area, Battle
Mountain district, Nevada: Unpublished M. S. thesis, Tucson, University of Arizona, 92 p.
Kim, Y.-S., Peacock, D.C.P., and Sanderson, D.J., 2004, Fault damage zones:
Journal of Structural Geology, v. 26, p. 503–517.
Kloppenburg, A., Grocott, J., and Hutchinson, D., 2010, Structural setting and
synplutonic fault kinematics of a Cordilleran Cu-Au-Mo porphyry mineralization system, Bingham mining district, Utah: Economic Geology,
v. 105, p. 743–761.
Kusznir, N.J., and Egan, S.S., 1990, Simple-shear and pure-shear models of extensional sedimentary basin formation: Application to the Jeanne d’Arc
basin, Grand Banks of Newfoundland, in Tankard, A.J., and Balkwill,
H.R., eds., Extensional tectonics and stratigraphy of the North Atlantic
margins: American Association of Petroleum Geologists Memoir 46, p.
305–322.
Kusznir, N.J., and Ziegler, P.A., 1992, The mechanics of continental extension
DQG VHGLPHQWDU\ EDVLQ IRUPDWLRQ $ VLPSOHVKHDUSXUHVKHDU ÀH[XUDO
cantilever model: Tectonophysics, v. 215, p. 117–131.
Lipske, J.L., and Dilles, J.H., 2000, Advanced argillic and sericitic alteration in
the subvolcanic environment of the Yerington porphyry copper system,
Buckskin Range, Nevada, in Dilles, J.H., Barton, M.D., Johnson, D.A.,
Proffett, J.M., Jr., and Einaudi, M.T., eds., Part I. Contrasting styles of
intrusion-associated hydrothermal systems: Society of Economic Geologists Guidebook Series, v. 32, p. 91–99.
Lister, G.S., and Davis, G.A., 1989, The origin of metamorphic core complexes
and detachment faults formed during Tertiary continental extension in
the northern Colorado River region, U.S.A.: Journal of Structural Geology, v. 11, p. 65–94.
Lowell, J.D., 1968, Geology of the Kalamazoo orebody, San Manuel district,
Arizona: Economic Geology, v. 63, p. 645–654.
Lowell, J.D., 1991, How the Kalamazoo was found, in Hollister, V.F., ed., Porphyry copper, molybdenum, and gold deposits, volcanogenic deposits
PDVVLYH VXO¿GHV DQG GHSRVLWV LQ OD\HUHG URFN 6RFLHW\ IRU 0LQLQJ
Metallurgy, and Exploration, Case Histories of Mineral Discoveries, v.
3, p. 29–30.
Mackin, J.H., 1950, The down-structure method of viewing geologic maps:
Journal of Geology, p. 55–72.
Maher, D.J., 1996, Stratigraphy, structure, and alteration of igneous and carbonate wall rocks at Veteran Extension in the Robinson (Ely) porphyry
copper district, Nevada, in Coyner, A.R., and Fahey, P.L., eds., Geology and ore deposits of the American Cordillera: Geological Society of
Nevada Symposium, Proceedings, Reno/Sparks, Nevada, April 1995, v.
3, p. 1595–1621.
Maher, D.J., 2008, Reconstruction of middle Tertiary extension and Laramide
porphyry copper systems, east-central Arizona: Unpublished Ph. D. thesis, University of Arizona, 328 p.
Maher, D.J., and Seedorff, E., 2000, Post-mineral structure of the Liberty area,
Robinson (Ely) porphyry copper district, White Pine County, Nevada
[abs.]: Geological Society of America Abstracts with Programs, v. 32,
no. 7, p. A232–A233.
Martel, S. J., 1999, Mechanical controls on fault geometry: Journal of Structural Geology, v. 21, p. 585–596.
McGrath, A.G., and Davison, I., 1995, Damage zone geometry around fault
tips: Journal of Structural Geology, v. 17, p. 1011–1024.
McKinstry, H. E., 1948, Mining geology: New York, Prentice Hall, 680 p.
Fault surface maps: Three-dimensional structural reconstructions and their utility in exploration and mining
Micklethwaite, S., 2011, Fault-induced damage controlling the formation of
Carlin-type ore deposits, in Steininger, R.C., and Pennell, W.M., eds.,
Great Basin evolution and metallogeny: Geological Society of Nevada,
Symposium, Reno/Sparks, May 2010, Proceedings, v. 1, p. 221–231.
Miller, E.L., Gans, P.B., and Garing, J., 1983, The Snake Range décollement:
An exhumed mid-Tertiary ductile-brittle transition: Tectonics, v. 2, p.
239–263.
Mitra, G., 1992, Balanced structural interpretations in fold and thrust belts, in
Mitra, G., and Fisher, G.W., eds., Structural geology of fold and thrust
belts: Baltimore, Johns Hopkins University Press, p. 53–77.
Morton, W.H., and Black, R., 1975, Crustal attenuation in Afar, in Pilger, A.,
and Rösler, A., eds., Afar depression of Ethiopia, International Symposium on the Afar region and related rift problems, Proceedings, Inter8QLRQ&RPPLVVLRQRQ*HRG\QDPLFV6FLHQWL¿F5HSRUW6WXWWJDUW(
Schweizerbart’sche Verlagsbuchhandlung, p. 55–65.
Muraoka, H., and Kamata, H., 1983, Displacement distribution along minor
fault traces: Journal of Structural Geology, v. 5, p. 483–495.
Needham, D.T., Yielding, G., and Freeman, B., 1996, Analysis of fault geometry and displacement patterns, in Buchanan, P.G., and Nieuwland,
D.A., eds., Modern developments in structural interpretation, validation
and modeling: Geological Society of London Special Publication 99,
p. 189–199.
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.,
0DUVK((DQG0RQHFNH7HGV7KHFKDOOHQJHRI¿QGLQJQHZPLQeral resources: Global metallogeny, innovative exploration, and new
discoveries: Society of Economic Geologists Special Publication 15, p.
299–316.
Nunns, A.G., 1991, Structural restoration of seismic and geologic sections in
extensional regimes: American Association of Petroleum Geologists
Bulletin, v. 75, p. 278–297.
Peacock, D.C.P., 2002, Propagation, interaction and linkage in normal fault systems: Earth-Science Reviews, v. 58, p. 121–142.
Proffett, J.M., Jr., 1977, Cenozoic geology of the Yerington district, Nevada,
and implications for the nature and origin of Basin and Range faulting:
Geological Society of America Bulletin, v. 88, no. 2, p. 247–266.
Proffett, J.M., Jr., 1979, Ore deposits of the western United States—A summary, in Ridge, J.D., ed., Papers on mineral deposits of western North
America, The International Association on the Genesis of Ore Deposits,
Fifth Quadrennial Symposium, Proceedings, v. II: Nevada Bureau of
Mines and Geology Report 33, p. 13–32.
Proffett, J.M., Jr., and Dilles, J.H., 1984, Geologic map of the Yerington district, Nevada: Nevada Bureau of Mines and Geology, Map 77, scale
1:24,000.
3URIIHWW-0-UDQG3URIIHWW%+6WUDWLJUDSK\RIWKH7HUWLDU\DVKÀRZ
tuffs of the Yerington district, Nevada: Nevada Bureau of Mines and
Geology Report 27, 28 p.
Richardson, C.A., 2014, Reconstruction of normal fault blocks in the Ann-Mason and Blue Hill areas, Yerington district, Nevada: Unpublished M. S.
thesis, Tucson, University of Arizona, 107 p.
Richardson, C.A., and Seedorff, E., this volume, Reconstruction of normal fault
blocks in the Ann-Mason and Blue Hill areas, Yerington district, Nevada: Geological Society of Nevada, Symposium, Reno/Sparks, May
2015, Proceedings, in press.
Roberts, A.M., and Yielding, G., 1994, Continental extensional tectonics, in
Hancock, P. L., ed., Continental deformation: Oxford, Pergamon Press,
p. 223–250.
Runyon, S.E., 2013, Contrasting Fe oxide-rich mineralization in the Yerington
district, Nevada: Unpublished M. S. thesis, Tucson, University of Arizona, 94 p.
1205
Schlische, R.W., 1995, Geometry and origin of fault-related folds in extensional
settings: American Association of Petroleum Geologists Bulletin, v. 79,
p. 1661–1678.
Schlische, R.W., and Anders, M.H., 1996, Stratigraphic effects and tectonic
implications of the growth of normal faults and extensional basins, in
Beratan, K. K., ed., Reconstructing the history of Basin and Range extension using sedimentology and stratigraphy: Geological Society of
America Special Paper 303, p. 183–203.
Schottenfeld, M. T., 2012, Structural analysis and reconstruction of the southern end of the Pumpkin Hollow deposit, Yerington district, Nevada: Unpublished M. S. thesis, University of Arizona, 50 p. plus unpaginated
¿JXUHVDQGDSSHQGLFHV
Seedorff, E., 1991, Magmatism, extension, and ore deposits of Eocene to Holocene age in the Great Basin—Mutual effects and preliminary proposed
genetic relationships, in Raines, G.L., Lisle, R.E., Schafer, R.W., and
Wilkinson, W.H., eds., Geology and ore deposits of the Great Basin:
Geological Society of Nevada, Symposium, Reno/Sparks, April 1990,
Proceedings, v. 1, p. 133–178.
Seedorff, E., and Maher, D.J., 2002, Overview of the geology of the central
Egan Range, in Ehni, W.J., and Faulds, J.E., eds., Detachment and attenuation in eastern Nevada and its application to petroleum exploration: Nevada Petroleum Society Guidebook, v. 17, p. 139–147.
Seedorff, E., Hasler, R.W., Breitrick, R.A., Fahey, P.L., Jeanne, R.A., Shaver,
S.A., Stubbe, P., Troutman, T.W., and Manske, S.L., 1996, Overview
of the geology and ore deposits of the Robinson district, with emphasis
on its post-mineral structure, in Green, S.M., and Struhsacker, E.M.,
eds., Geology and ore deposits of the American Cordillera, Great Basin
porphyry deposits: Geological Society of Nevada Field Trip Guidebook
Compendium, 1995, Reno/Sparks, p. 87–91.
Seedorff, E., Dilles, J.H., Proffett, J.M., Jr., Einaudi, M.T., Zurcher, L., Stavast,
W.J.A., Johnson, D.A., and Barton, M.D., 2005, Porphyry deposits:
Characteristics and origin of hypogene features, in Hedenquist, J.W.,
Thompson, J.F.H., Goldfarb, R.J., and Richards, J.P., eds., Economic
Geology 100th Anniversary Volume, p. 251–298.
Seedorff, E., Barton, M.D., Stavast, W.J.A., and Maher, D.J., 2008, Root zones
of porphyry systems: Extending the porphyry model to depth: Economic Geology, v. 103, p. 939–956.
Seedorff, E., Barton, M.D., and Takaichi, M.L., this volume, East-west swath of
mid-Cretaceous intrusions in east-central Nevada: U-Pb geochronology
and metallogeny: Geological Society of Nevada, Symposium, Reno/
Sparks, May 2015, in preparation.
Shaver, S.A., and Jeanne, R.A., 1996, The geology and evolution of the weakly
Au-(Cu)-mineralized far eastern side of the Robinson mining district,
Ely, Nevada, in Coyner, A.R., and Fahey, P.L., eds., Geology and ore
deposits of the American Cordillera: Geological Society of Nevada
Symposium, Reno/Sparks, April 1995, Proceedings, v. 3, p. 1623–1637.
Shaver, S.A., and McWilliams, M.O., 1987, Cenozoic extension and tilting recorded in Upper Cretaceous and Tertiary rocks at the Hall molybdenum
deposit, northern San Antonio Mountains, Nevada: Geological Society
of America Bulletin, v. 99, no. 3, p. 341–353.
Smith, D.L., Gans, P.B., and Miller, E.L., 1991, Palinspastic restoration of Cenozoic extension in the central and eastern Basin and Range province
at latitude 39 - 40º N, in Raines, G.L., Lisle, R.E., Schafer, R.W., and
Wilkinson, W.H., eds., Geology and ore deposits of the Great Basin:
Geological Society of Nevada, Symposium, Reno/Sparks, April 1990,
Proceedings, v. 1, p. 75–86.
Spencer, A.C., 1917, The geology and ore deposits of Ely, Nevada: U. S. Geological Survey Professional Paper 96, 189 p., map scale 1:30,000.
Stavast, W.J.A., Butler, R.F., Seedorff, E., Barton, M.D., and Ferguson, C.A.,
2008, Tertiary tilting and dismemberment of the Laramide arc and related hydrothermal systems, Sierrita Mountains, Arizona: Economic
Geology, v. 103, p. 629–636.
1206
Eric Seedorff, Carson A. Richardson, and David J. Maher
Stevens, R.A., 2010, Mineral exploration and mining essentials: Port Coquitlam, British Columbia, Pakawau GeoManagement Inc., 322 p.
Stewart, J.H., 1980, Geology of Nevada: Nevada Bureau of Mines and Geology
Special Publication 4, 136 p.
Tearpock, D.E., and Bischke, R.E., 2003, Applied subsurface geological mapping: with structural methods, 2nd Edition (e-book): Upper Saddle
River, New Jersey, Prentice Hall, 822 p.
Thompson, G.A., 1960, Problem of late Cenozoic structure of the Basin Ranges: International Geological Congress, 21st, 1960, Pt. 18, Copenhagen,
1960, p. 62–68.
Walsh, J.J., and Watterson, J., 1987, Distribution of cumulative displacement
and seismic slip on a single normal fault surface: Journal of Structural
Geology, v. 9, p. 1039–1046.
Walsh, J.J., and Watterson, J., 1989, Displacement gradients on fault surfaces:
Journal of Structural Geology, v. 11, p. 307–316.
Walsh, J.J., and Watterson, J., 1991, Geometric and kinematic coherence and
scale effects in normal fault systems, in Roberts, A.M., Yielding, G., and
Freeman, B., eds., The geometry of normal faults: Geological Society of
London Special Publication 56, p. 193–203.
Walsh, J.J., Watterson, J., Bailey, W.R., and Childs, C., 1999, Fault relays, bends
and branch-lines: Journal of Structural Geology, v. 21, p. 1019–1026.
Wernicke, B.P., 1981, Low-angle normal faults in the Basin and Range province: Nappe tectonics in an extending orogen: Nature, v. 291, p. 645–
648.
:HUQLFNH %3 DQG %XUFK¿HO %& 0RGHV RI H[WHQVLRQDO WHFWRQLFV
Journal of Structural Geology, v. 4, p. 105–115.
Wernicke, B.P., Axen, G.J., and Snow, J.K., 1988, Basin and Range extensional
tectonics at the latitude of Las Vegas, Nevada: Geological Society of
America Bulletin, v. 100, p. 1738–1757.
Westaway, R., 1991, Continental extension on sets of parallel faults: Observational evidence and theoretical models, in Roberts, A.M., Yielding,
G., and Freeman, B., eds., The geometry of normal faults: Geological
Society of London Special Publication 56, p. 143–169.
Westaway, R., and Kusznir, N. J., 1993, Fault and bed ‘rotation’ during continental extension: Block rotation or vertical shear? Journal of Structural
Geology, v. 15, no. 6, p. 753–770.
Westra, G., 1982, Alteration and mineralization in the Ruth porphyry copper
deposit near Ely, Nevada: Economic Geology, v. 77, p. 950–970.
Wibberley, C.A.J., Yielding, G., and di Toro, G., 2008, Recent advances in the
understanding of fault zone internal structure: A review, in Wibberley,
C.A.J., Kurz, W., Imber, J., Holdsworth, R.E., and Collettini, C., eds.,
The internal structure of fault zones: Implications for mechanical and
ÀXLGÀRZSURSHUWLHV*HRORJLFDO6RFLHW\RI/RQGRQ6SHFLDO3XEOLFDWLRQ
299, p. 5–33.
Wilkerson, M.S., and Dicken, C.L., 2001, Quick-look techniques for evaluating two-dimensional cross sections in detached contractional settings:
American Association of Petroleum Geologists Bulletin, v. 85, p. 1759–
1770.
Wilkins, J., Jr., and Heidrick, T.L., 1995, Post-Laramide extension and rotation of porphyry copper deposits, southwestern United States, in Pierce,
F.W., and Bolm, J.G., eds., Porphyry copper deposits of the America
Cordillera: Arizona Geological Society Digest 20, p. 109–127.
Wong, M.S., and Gans, P.B., 2008, Geologic, structural, and thermochronologic
constraints on the tectonic evolution of the Sierra Mazatán core complex,
Sonora, Mexico: New insights into metamorphic core complex formation: Tectonics, v. 27, no. 4, TC4013, doi:10.1029/2007TC002173.
Woodward, N.B., Gray, D.R., and Spears, D.B., 1986, Including strain data in
balanced cross-sections: Journal of Structural Geology, v. 8, p. 313–324.
Woodward, N.B., Boyer, S.E., and Suppe, J., 1989, Balanced geological cross
sections: An essential technique in geological research and exploration:
Washington, D. C., American Geophysical Union, Short Course in Geology, v. 6, 132 p.