The Jackson-Lawton-Bowman Normal Fault System
and Its Relationship to Carlin-type Gold Mineralization,
Eureka District, Nevada
Aryn K. Hoge, Eric Seedorff*, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
Lowell Institute for Mineral Resources, Department of Geosciences, University of Arizona, 1040 East Fourth Street,
Tucson, Arizona 85721-0077, USA
ABSTRACT
The Eureka district hosts mid-Cretaceous (~106 Ma), igneous-related, polymetallic carbonate replacement deposits that have subsequently been overprinted by
Eocene(?) Carlin-type gold mineralization, including the Archimedes deposit. This
study presents (1) results of new Anaconda-style outcrop geologic map of a structurally complex area measuring 4.5 km2 in the northern part of the Eureka district along
the Jackson-Lawton-Bowman normal fault system, (2) structural reconstructions of
Tertiary normal faults, as well as (3) reconnaissance trace-element and stable isotopic
analyses in an attempt to differentiate between alteration associated with the midCretaceous and Eocene(?) events. The study evaluates the possible relationship of the
Jackson fault system to Carlin-type gold.
The Jackson fault, which has been proposed as a structural control for both styles
of mineralization, extends the length of the Eureka district (21 km). The normal fault
system dismembers folds of the Eureka culmination, which involves lower Paleozoic
carbonate and clastic rocks. Evidence from structural reconstructions suggests that
the north-striking Jackson branch and north-northwest striking Lawton branch have
dismembered an anticline-syncline pair that is interpreted to have formed by faultpropagation folding concurrent with movement on the Champion thrust fault in the
Early Cretaceous in the Eureka portion of the central Nevada thrust belt. Beginning
at the southern edge of the district, the Jackson fault zone is composed of a series of
overlapping, steeply (~70°) east-dipping, north-striking fault segments for ~3.8 km.
Farther north, the main fault splits into at least three closely spaced, roughly parallel
branches, which also dip steeply eastward. The Buckeye fault is likely a fourth branch
of the Jackson normal fault system.
Contraction and growth of the Eureka culmination occurred concurrent with
deposition of the synorogenic Early Cretaceous Newark Canyon Formation at ~116
Ma (Aptian). Mid-Cretaceous intrusions were emplaced and associated carbonatehosted ores formed at ~106 Ma (Albian, i.e., late Early Cretaceous), or ~10 m.y. after
contractional deformation. The fact that the northwest-striking, down-to-the-north
Ruby Hill normal fault cuts and offsets mid-Cretaceous mineralization and is in turn
cut and offset by the Jackson branch effectively precludes the possibility that the
-DFNVRQ IDXOW DFWHG DV D FRQGXLW IRU PLG&UHWDFHRXV PDJPDWLFK\GURWKHUPDO ÀXids. Carlin-type mineralization at Archimedes is structurally controlled, but by the
older, west-northwest striking, down-to-the-north Blanchard and Molly faults. The
Eocene(?) Carlin-type overprint on Cretaceous base-metal mineralization in the
northern Eureka district may have enriched the tenor of gold mined from carbonate
replacement deposits.
Soil analyses in the northern Eureka district show subtle Au and As anomalies
adjacent to the compound portion of the Jackson fault, and the trace of the fault
broadly coincides with a belt of carbonate replacement ore mined in the late 1800s,
*E-mail: seedorff@email.arizona.edu
967
968
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
ZKLFKLVDOORULQSDUWRIPLG&UHWDFHRXVDJH0DSSHGDOWHUDWLRQSDWWHUQVMDVSHURLG
PDUEOHEOHDFKLQJDQGVDQGLQJRIFDUERQDWHVZKLFKVSDWLDOUHODWLRQVKLSVDQGLVRtopic studies suggest are related to the Cretaceous magmatic-hydrothermal system,
nonetheless show no relationship to the Jackson fault. The Jackson-Lawton-Bowman
normal fault system postdates and offsets not only the carbonate-hosted ores but also
Carlin-type gold mineralization and is likely a mid-Cenozoic fault system. It thus has
no genetic relationship to either the mid-Cretaceous or Eocene mineralizing systems
but may be responsible for preserving both systems on the eastern side of the area.
This study underscores the challenge of identifying structural controls on Carlin-type
mineralization prior to or beyond the extent of mining-related exposures, especially in
structurally complex areas where there is imperfect exposure and where there may be
partial spatial overlap between Carlin-type and other mineralizing systems.
Key Words: Carlin-type gold; carbonate replacement mineralization, structural
reconstruction, Eureka district, normal faults
INTRODUCTION
The Eureka district is located at the southern terminus of
the Cortez or Battle Mountain-Eureka trend (Figure 1). The
Production from Carlin-type gold deposits in Nevada dom- district has been extensively explored for lead, silver, and zinc
inates the United States gold industry (73% of the U.S. total) since the discovery of rich, gossanous polymetallic carbonate
and has made the state the sixth-largest gold producer in the replacement and skarn deposits in 1864 (Hague, 1883, 1892;
world (Nevada Bureau of Mines and Geology, 2011). Many Curtis, 1884; Binyon, 1946). Like many carbonate replacement
Carlin-type deposits, which have been mined since the early deposits (e.g., Titley, 1993), this mineralization has a clear
V EXW ZHUH ¿UVW UHFRJQL]HG DV D QHZ GHSRVLW W\SH EHJLQ- magmatic-hydrothermal origin, with links to Mo-Cu minerning in the 1960s (Hausen and Kerr, 1968), are now under- alization, small skarns, quartz and greisen veins in intrusions
stood to have strong structural as well as stratigraphic controls dated at ~106 Ma (Nolan, 1962; Nolan and Hunt, 1968; Vi(e.g., Teal and Jackson, 2002). The genesis of Carlin-type gold kre, 1998; Mortensen et al., 2000; Hastings, 2008; Seedorff et
deposits has been the subject of much research and debate al., this volume, a). Carlin-type gold was mined underground
(Radtke, 1985; Bagby and Berger, 1985; Bakken and Einau- at the Windfall deposit as early as 1908. Although Carlin-type
di, 1986; Sillitoe and Bonham, 1990; Seedorff, 1991; Kuehn ore constituted only a minor portion of historic production, it
and Rose, 1992, 1995; Ilchik and Barton, 1997; Stenger et al., quickly became the focus of modern exploration in the Eureka
1998; Hofstra and Cline, 2000; Thompson et al., 2002; Emsbo district following the discovery of the Archimedes orebody by
et al., 2003; Cline et al., 2005; Muntean et al., 2011), the bulk Homestake in 1993 (Dilles et al., 1996; Russell, 1996; MargoRIZKLFKLVGHYRWHGWRGH¿QLQJDQGFRQVWUDLQLQJJHRFKHPLFDO lis, 1997).
and thermal conditions at the time of ore formation in order
The genesis of Carlin-type mineralization is far less certain
WRGHWHUPLQHVRXUFHVRIPHWDOVÀXLGVDQGKHDW)HZHUVWXGLHV but is interpreted by some workers as having a non-magmatic
have focused on understanding the pre- and syn-mineralization hydrothermal origin (Seedorff, 1991; Ilchik and Barton, 1997;
structural controls at the deposit scale (i.e., why some faults Emsbo et al., 2000) and having formed in the late Eocene (Hofare mineralized, whereas others are not; one exception is Yigit stra et al., 1999; Tretbar et al., 2000; Arehart et al., 2003; Cline
et al., 2003). Moreover, published structural reconstructions of et al., 2005). Steeply dipping normal faults have been cited as
Carlin-type deposits are few, despite the fact that post-miner- primary or secondary structural controls in a number of Carlinalization faults have undoubtedly dismembered some gold de- type deposits (Volk et al., 1996; Teal and Jackson, 2002; Yigit et
posits of the Carlin and Battle Mountain-Eureka trends, albeit al., 2003), although the exact nature of the association remains
to a smaller degree than is exhibited by the porphyry centers of unclear. Deposits are commonly elongate parallel to high-angle
the Yerington and Robinson districts (Proffett, 1977; Proffett faults (Cline et al., 2005), and gold mineralization is commonand Dilles, 1984; Seedorff et al., 1996; Gans et al., 2001). This ly localized at structural intersections. Individual deposits are
study describes pre- and post-mineralization structural controls crudely aligned at the regional scale along “trends” up to 150
on Carlin-type gold mineralization in the northern Eureka min- km in length (Roberts, 1966), leading a number of workers to
ing district of east-central Nevada and attempts a structural propose deep crustal structural controls on gold mineralization
reconstruction of extensional deformation to gain insight into (Cunningham, 1988; Shawe, 1991; Grauch et al., 1995, 2003;
the pre-extensional geometry of the district, following earlier Tosdal et al., 2000).
contractional deformation.
In the Eureka district, Carlin-type mineralization occurs
Jackson normal fault system, Eureka district
969
Figure 1. Location map for the Eureka district, showing county boundaries (dashed lines), major roads (solid lines), major
WRZQVVTXDUHVDQG&DUOLQW\SHJROGGHSRVLWVFLUFOHV0RGL¿HGIURP'LOOHVHWDO
along a pronounced north-south trend (Figure 2), and the gold
system is in part superimposed on the mid-Cretaceous carbonate replacement system. Moreover, portions of both mineralizing systems have been affected by supergene alteration and remobilization of materials, which further obscures the temporal
relationship between rocks, faults, and hypogene mineralization, as supergene solutions can deposit materials in rocks that
ZHUHGHSRVLWHGDIWHUK\SRJHQHPLQHUDOL]DWLRQDQGFDQ¿OOIDXOWV
that cut and offset hypogene mineralization. These types of
complexities probably contribute to the uncertain—even contradictory—interpretations of the relative ages of events previ-
ously reported (e.g., Nolan, 1962; Dilles et al., 1996) and provide a continuing challenge. There has been much speculation
as to which high-angle faults may have acted as feeder channels
for gold mineralization (Dilles et al., 1996; unpublished Homestake Mining Company reports; unpublished Hamburg Ridge
Joint Venture report), but the bulk of it, including the Archimedes deposit and the Windfall, Rustler, and Paroni mines, lies on
or parallel to the strike of a complex normal fault zone known
as the Jackson-Lawton-Bowman fault system, or the Jackson
fault zone. This fault system can be traced from west of the
Windfall mine 21 km to the north, where several of its branches
970
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
run through the Ruby Hill area and, eventually, the Archimedes
pit. The Jackson fault zone has also been suggested as a potential ore control for carbonate replacement mineralization in
the district; Nolan (1962) noted that it “coincides with the belt
of most intense mineralization in the Eureka district” and “the
Jackson zone probably acted as a channelway.”
This study uses an integrated approach to clarify the structure of the northern portion of the Jackson fault zone, where
the fault is compound and poorly exposed, with the purpose
of attempting to distinguish between alteration products of the
Cretaceous event from those of the late Eocene(?) event and
WRDVVHVVWKHSRVVLEOHVLJQL¿FDQFHRIWKH-DFNVRQIDXOWWRJROG
mineralization. A reconnaissance isotopic study indicates that
the analyzed materials likely have a magmatic-hydrothermal
RULJLQ7KHLQWHJUDWLRQRIUHVXOWIURP¿HOGPDSSLQJVWUXFWXUDO
DQDO\VLVDQGLVRWRSLFVWXG\¿QGVQRFRPSHOOLQJJHQHWLFUHODtionship between the Jackson normal fault system and Carlintype gold mineralization.
METHODS
Figure 2. Geologic map of the Eureka district, after Nolan (1962), showing the
trace of the Jackson-Lawton-Bowman normal fault system highlighted in blue.
Dashed lines represent the inferred trace of the fault under cover. Red circles =
Cretaceous carbonate replacement deposits. Yellow circles = Carlin-type gold
deposits.
Lithology, structure, and alteration were mapped at 1:2000
scale over an area of 3 km by 1.5 km along the northern, compound portion of the Jackson-Lawton-Bowman normal fault
V\VWHP XVLQJ D PRGL¿HG YHUVLRQ RI WKH $QDFRQGD PDSSLQJ
method (Einaudi, 1997; Brimhall et al., 2006). This area of 4.5
km2 is complexly faulted but offers only fair exposure of outcrops.
The Anaconda method of mapping outcrops uses various
color codes for rock type, alteration, veins, ore minerals, and
limonites applied to successive overlays. Although the method
was originally devised by Anaconda geologists at Butte, Montana, El Salvador, Chile, and Yerington, Nevada, to map igneous rocks and alteration in porphyry environments, it was easily
PRGL¿HGWRPDSFDUERQDWHURFNV/LWKRORJ\YHLQVIDXOWVDQG
other structures were plotted on a base map. Pervasive alteraWLRQ LH VLOLFL¿FDWLRQ VDQGLQJ RI GRORPLWH HWF ZDV SORWWHG
RQD¿UVWRYHUOD\DQGR[LGDWLRQSURGXFWVRIRUHPLQHUDOVZHUH
plotted on a second overlay.
Several simple and low-cost techniques were employed
WR VXSSOHPHQW ¿HOG PDSSLQJ 6RLO VDPSOHV ZHUH WDNHQ DORQJ
two east-west transects across the trace of the Jackson fault to
LGHQWLI\SRWHQWLDOJROGDQRPDOLHVUHODWHGWRÀXLGÀRZDORQJWKH
fault. Fourteen surface samples were selected for stable isotopic
analysis of carbon and oxygen; calcite and dolomite were sampled from veins and wall rock in altered and unaltered rocks to
LQYHVWLJDWHWKHQDWXUHDQGLVRWRSLFHIIHFWVRIK\GURWKHUPDOÀXLGV
RQKRVWURFNVDQGWRLGHQWLI\DUHDVRIKLJKHUÀXLGÀRZ)LIWHHQ
polished thin sections were examined using a Nikon Eclipse
LV100 petrographic microscope in order to better constrain the
mineralogy and alteration paragenesis of altered rocks. Newly
collected data were integrated with data drawn from existing
publications and unpublished internal reports.
A district-scale cross section for the northern part of the Eu-
Jackson normal fault system, Eureka district
reka district was constructed using surface and drill hole data.
The geometry of four key faults in the area was determined
from structure contours to constrain their true dips and apparent
dips in cross section. Stratigraphic separation diagrams were
drawn to illustrate changes in the displacement of the Jackson
fault zone along its length from the southern boundary of the
district to the Archimedes pit, north of which it disappears under cover, and to gain insight into the temporal relationship between the Jackson fault and other structural features. A stepwise
reconstruction of a district-scale cross section was attempted to
obtain a view of the pre-extensional geometry of the northern
Eureka district.
971
stone with local sandy and silty interbeds and abundant stringers
of black chert, and the upper Bullwhacker member, characterized as a tan, platy limestone with shaly/sandy partings (Nolan,
1962). The Pogonip Group includes the basal Goodwin Formation, overlying Ninemile Formation, and uppermost Antelope
Valley Formation. The Goodwin Limestone, host to the bulk
of gold mineralization at the Archimedes deposit (Dilles et al.,
1996), has three members. Shaly and fossiliferous at its base,
the Lower Goodwin member (Og1) is best characterized as a
medium-grained massive limestone with sparse bedded of chert
nodules and fragments (Hastings, 2008). It grades into a thinly
(2–10 cm) bedded silty micrite known as the Lower Laminated
member (Ogll). This laminated member is in turn overlain by
REGIONAL GEOLOGIC FRAMEWORK
WKH8SSHU*RRGZLQPHPEHU2JZKLFKFDQEHLGHQWL¿HGRQ
the basis of its medium to thick bedding and conspicuous chert
Stratigraphy
content (locally as high as 20%; Hastings, 2008).
The upper part of the stratigraphic section, beginning in the
The stratigraphic section exposed in the Eureka district Mississippian with the Chainman Shale and Diamond Peak Forconsists of a thick section of Early Cambrian to Early Creta- mation (Nolan, 1962), includes carbonaceous silts, sands, and
ceous carbonate and clastic rocks that have been intruded or conglomerates that record the deposition of clastic sediments
overlain by numerous intrusive plugs, stocks, dikes, sills, lava into a large foreland basin developed along the eastern margin
ÀRZVDQGWXIIVUDQJLQJIURP&UHWDFHRXVWR2OLJRFHQHLQDJH of the Roberts Mountain allochthon during the Antler orogeny
(Figure 3). The northern part of the district exposes only the (Poole, 1974). Rocks of the Roberts Mountain allochthon are
Cambrian and Ordovician part of the stratigraphic section (Fig- absent in the Eureka district but crop out several kilometers to
ure 4). The characterization provided below summarizes more the northwest (Figure 5). The Pennsylvanian-Permian section
detailed descriptions by earlier workers (Hague, 1892; Nolan et consists of limestone and conglomerate of the Ely Limestone
al., 1956; Nolan, 1962) and emphasizes those units which are and Carbon Ridge Formation (Nolan, 1962; Long et al., 2014).
demonstrated ore hosts in the Eureka district.
Mesozoic rocks are largely absent in the area but are repreSedimentary rocks in the district provide a nearly com- sented by the Early Cretaceous Newark Canyon Formation (Noplete record of deposition from the Cambrian through the lan et al., 1956). The unit consists of conglomerate, mudstone,
late Mississippian (Dilles et al., 1996). The lower portion of DQGOLPHVWRQHWKDWFRQWDLQIRVVLO¿VKRVWUDFRGVDQGQRQPDULQH
the section, from the Cambrian Prospect Mountain Quartzite mollusks (MacNeil, 1939; Fouch et al., 1979). The Newark
through the Devonian Devils Gate Limestone, is dominated &DQ\RQ)RUPDWLRQLVLQWHUSUHWHGWRKDYHIRUPHGLQÀXYLDODQG
by shelf carbonate rocks inferred to have originally been part lacustrine settings (Vandervoort and Schmitt, 1990). A detrital
of an eastward-thinning wedge of miogeoclinal sedimentary zircon date from the Upper Conglomerate member yielded a
rocks (Nolan et al., 1956). Carbonaceous shales and sandstones maximum age of 120.7 ± 3.2 Ma, and zircons from a waterlain
are locally interspersed among the limestones and dolostones pyroclastic fall deposit from the Upper Carbonaceous member
of the lower Paleozoic section, which host the majority of the yield a U-Pb concordia age of 116.1 ± 1.6 Ma (Druschke et al.,
mineralization (Figure 4). The Eldorado Dolomite, host to the 2011), indicating that the unit is Aptian (Long et al., 2014). The
bulk of the carbonate replacement ores at Ruby Hill and else- Newark Canyon Formation has been interpreted as having been
where, is composed of ~760 m of massive, coarsely crystalline deposited in a piggyback basin on the eastern limb of the Eubluish-gray dolomite and limestone. The Eldorado Dolomite reka culmination as it grew during development of the central
is succeeded by the Geddes Limestone, Secret Canyon Shale, Nevada thrust belt at ~116 Ma (Druschke et al., 2011; Long et
and Hamburg Dolomite. The Hamburg Dolomite, host to both al., 2014). The age of the Newark Canyon Formation thus indicarbonate replacement orebodies and to the Carlin-type miner- cates that growth of the culmination preceded emplacement of
alization at the Windfall, Rustler, and Paroni mines, consists of the mid-Cretaceous intrusions and their associated carbonate300 m of dark gray, massive limestone with dolomite horizons. hosted ores at ~106 Ma by ~10 m.y.
Although the Hamburg Dolomite occurs roughly 300 m stratiThe district also contains local exposures of a younger congraphically above the Eldorado Dolomite, it is lithologically glomerate, with an age bracketed between Late Cretaceous and
similar (Nolan, 1962; Hastings, 2008).
Eocene (Long et al., 2014).
Carlin-type gold mineralization at Archimedes occurs in
the Cambrian Windfall Formation and the overlying Ordovician Igneous rocks
Pogonip Group. The Windfall Formation is subdivided into two
members: the lower Catlin member, made up of massive limeIgneous activity in the heart of the Eureka district occurred
972
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
Figure 3. Geologic map of the Eureka district, showing the map area (outlined in red) and the branches of the Jackson-Lawton-Bowman normal fault system, after Nolan (1962). Solid blue line represents the main branch of the Jackson fault; dot-dashed lines represent the Jackson and Lawton branches; and the dashed line represents the Jackson/Holly fault. Solid black line is section 104000N.
Jackson normal fault system, Eureka district
973
Figure 4. Stratigraphic column of Cambrian–Ordovician rocks in the Eureka district, with unit descriptions, thicknesses, and the locality of the measured
sections from which unit thicknesses were taken.
974
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
)LJXUH6LPSOL¿HGWHFWRQLFPDSRI1HYDGDVKRZLQJORFDWLRQVRIPDMRU3Dleozoic (Roberts Mountain and Golconda) and Mesozoic (Luning-Fencemaker,
central Nevada, and Sevier) thrust systems, as well as Cordilleran metamorphic
core complexes (solid black). Belts of Carlin-type gold deposits shown in gray.
Box outlines limit of Figure 1. Based on Cline et al. (2005) and Long et al.
(2012).
in at least two discrete periods, mid-Cretaceous and mid-Cenozoic (Blake et al., 1975; Mortensen et al., 2000). In addition, there are Jurassic and Late Cretaceous intrusions nearby.
A large Jurassic intrusion crops out ~12 km to the northeast at
Whistler Mountain (159.5 ± 3.3 Ma, U-Pb zircon, Mortensen
et al., 2000). Late Cretaceous (~86 Ma), strongly peraluminous
granitoids are present ~10 km due south at Rocky Canyon and
~12 km to the southwest at McCullough Butte (Barton, 1982,
1987; Long et al., 2014; Barton et al., unpub. data). Although
some of the mid-Cenozoic dates originally were regarded as
early Oligocene, all of them now are late Eocene considering
that the currently accepted age of the Eocene-Oligocene boundary is 33.9 Ma (Walker et al., 2013).
The largest and ostensibly oldest igneous unit in the district
LVWKH*UDYH\DUG)ODWLQWUXVLRQZKLFKZDV¿UVWLQWHUFHSWHGEHneath alluvium during the drilling campaign that led to the dis-
covery of Archimedes. Due to intense intermediate argillic and
propylitic alteration, the primary mineralogy of the intrusion is
uncertain. It consists primarily of quartz and variably altered
SODJLRFODVH SKHQRFU\VWV LQ D ¿QHJUDLQHG HTXLJUDQXODU SODgioclase-dominated groundmass (Dilles et al., 1996; Hastings,
2008). Primary ferromagnesian minerals are not preserved; sericite, kaolinite, calcite, chlorite, epidote, and pyrite are common alteration products (Dilles et al., 1996). Textural variations
observed by Dilles et al. (1996) suggest that the intrusion may
have been emplaced in multiple phases. Mortensen et al. (2000)
reported a U-Pb zircon age of 106.2 ± 0.2 Ma for the Graveyard
Flat intrusion. The “Archimedes pluton,” which has an imprecise U-Pb zircon age determination of 105 ± 5 Ma (Mortensen
et al., 2000), may be related to the Graveyard Flat intrusion.
The Bullwhacker sill occurs west of the Graveyard Flat intrusion. It dips gently east underneath the Archimedes pit and
has been interpreted to merge with the Graveyard Flat intrusion
at depth. Although the sill was characterized as an “andesite
porphyry” by Langlois (1971), it has been strongly sericitically
altered; feldspar phenocrysts have been replaced by kaolinite ±
sericite ± calcite. Remnant biotite and hornblende phenocrysts
occur in less altered samples; quartz phenocrysts are common.
The groundmass texture is uncertain, and the relict mineralogy
suggests that the rock was most likely granodiorite porphyry.
Mortensen et al. (2000) report a U-Pb zircon age of 106.8 ± 1.2
Ma on the Bullwhacker sill.
The Cretaceous Ruby Hill or Mineral Hill stock, a granodiorite, is exposed immediately south of Ruby Hill (Figures 3,
6). Nolan (1962) and Vikre (1998) have attributed carbonate
UHSODFHPHQW PLQHUDOL]DWLRQ DW 5XE\ +LOO WR ÀXLG FLUFXODWLRQ
related to emplacement of the Ruby Hill stock. There are numerous preexisting K-Ar ages with scattered results (Table 2
of Vikre, 1998), whereas 40Ar/39Ar dating of igneous biotite
and alteration muscovite yields ages of ~105–108 Ma (Vikre,
0RUWHQVHQHWDOUHSRUWDGH¿QLWLYH83E]LUFRQ
age of 106.0 ± 1.6 Ma.
As evident above, the U-Pb zircon ages on mid-Cretaceous
intrusive rocks that are interpreted as crystallization ages by
Mortensen et al. (2000) are all within error of one another at
~106 Ma, increasing the likelihood that the rocks have a consanguineous origin. The ages of the intrusive rocks correspond
to the Albian stage in the lattermost Early Cretaceous epoch
(Walker et al., 2013). The intrusions are spatially and temporally associated with carbonate replacement deposits (Nolan,
1962; Langlois, 1971; Vikre, 1998); thus, the age of carbonate
replacement mineralization in the district is also ~106 Ma.
A second, younger period of magmatic activity is evident
based on radiometric dating of late Eocene extrusive volcanic
rocks in the district, which include the Pinto Peak and Target
+LOOUK\ROLWHÀRZGRPHFRPSOH[HVWKH5DWWR6SULQJVUK\RGDcite, and the Richmond Mountain andesite. These were dated
by Blake et al. (1975) by K-Ar methods that yielded ages between 37 and 33 Ma. Five 40Ar/39Ar dates from step heating
experiments on biotite, hornblende, and plagioclase pheno-
Jackson normal fault system, Eureka district
975
Figure 6. District-scale geologic cross section 104000N through Mineral Hill, looking north. Dip indicators on or projected into cross section shown near present
surface. Projections at depth are based on the surface geology and the few drill holes shown on the section, including presence of a pluton at depth (unlabeled).
No vertical exaggeration. Location of line of section shown on Figures 3 and 7 (see later restoration of this section). Faults on the cross section are assigned to
¿YHVHWVRUJHQHUDWLRQVRIIDXOWVDQHDUO\WRSWRWKHHDVWUHYHUVHIDXOWDQHDUO\ZHVWGLSSLQJVHWRIQRUPDOIDXOWVWZRVXEVHTXHQWHDVWGLSSLQJQRUPDOIDXOWVDQG
a younger west-dipping set of normal faults.
crysts by Long et al. (2014) yield the plateau ages that range
IURPWR0DZLWKıHUURUVUDQJLQJIURPWR
0.21 Ma. In addition, a single-crystal 40Ar/39Ar sanidine date on
rhyolite lava from the Pinto Peak dome yields an age of 36.69
± 0.04 Ma (Long et al., 2014). Late Eocene volcanic rocks
overlie Carlin-type gold ore hosted by Paleozoic rocks at both
the Rustler and East Archimedes pits, implying shallow depths
of gold deposition and perhaps constraining their ages (C.D.
Henry, written commun., 2014; Barton et al., unpub. data). The
implications of radiometric dates on volcanic rocks for the age
of Carlin-type ores remains problematic in some cases because
it remains to be determined whether anomalous metal contents
and clay alteration in the volcanic rocks are of hypogene or
supergene origin (C.D. Henry, written commun., 2014; Barton
et al., 2015). At this time, the most likely age of the Carlin-type
gold deposits in the district is 36–38 Ma, i.e., late Eocene by the
time scale of Walker et al. (2013).
Geologic structure
Hague (1892) divided the Eureka district into structural
blocks, the dominant features of which are large, roughly northsouth trending, fault-bounded antiforms. The most well known
of these is now referred to as the Eureka culmination, in which
the oldest rocks in the stratigraphic section (Cambrian Prospect
Mountain Quartzite) sit at the highest elevation in the district
on Prospect Peak, surrounded by younger strata at lower elevations (Figure 3). Later workers (Nolan, 1962; Nolan et al.,
1971; Nolan et al., 1974) mapped folds and thrust faults within
these blocks, including the Hoosac fault, which has since been
interpreted by various workers as either a thrust fault (Taylor et
al., 1993; Lisenbee et al., 1995; Long, 2012) or a normal fault
(Hague, 1883; Nolan et al., 1974; Long et al., 2014; this study).
Considering that the Eureka district is located just kilometers from the easternmost exposures of the Roberts Mountains
allochthon (Dilles et al., 1996), contractional deformation in
the district, lacking other constraints, might be attributed to the
emplacement of the allochthon in the mid-Paleozoic (Figure
5). Orogenic deposits of Early Cretaceous age, however, have
been tied to contractional deformation in the Eureka district.
Conglomerates of the Newark Canyon Formation (Vandervoort
and Schmidt, 1990) yield U-Pb zircon ages of 116–121 Ma
(Druschke et al., 2011; Long et al., 2014). Although the presence of some mid-Paleozoic deformation probably cannot be
precluded, the thrust faults that were originally described by
Nolan (1962) subsequently have been grouped into the Eureka
thrust belt, were later correlated with the Garden Valley thrust
system, have become part of what is now known as the central Nevada thrust belt (Figure 5), which in turn has been tied
to the Sevier orogeny (Speed, 1983; Speed et al., 1988; Bart-
976
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
ley and Gleason, 1990; Armstrong and Bartley, 1993; Taylor
et al., 1993, 2000; Druschke et al., 2011; Long et al., 2014).
As emphasized by Bartley and Gleason (1990), the present-day
distance between the central Nevada thrust belt and the Sevier
thrust front of ~350 km (Figure 5) is substantially greater than
the Cretaceous distance, which was probably ~200 km (e.g.,
Gans, 1987), because of subsequent extensional deformation.
The kinematic history of the Sevier fold-and-thrust belt
(Armstrong, 1968) in the type area of western Utah during the
Early Cretaceous has been a matter of debate (e.g., Armstrong,
1968; Wiltschko and Dorr, 1983; Heller et al., 1986; DeCelles,
&RQJORPHUDWLF ÀXYLDO GHSRVLWV RI WKH .HOYLQ &HGDU
Mountain, and San Pitch Formations in Utah and the Gannett Group in Wyoming, which are Lower Cretaceous (Katich,
1951; Stokes, 1952; Simmons, 1957; Thayn, 1973; Kirkland,
1992; Tschudy et al., 1984; Witkind et al., 1986; Weiss et al.,
2003; DeCelles and Burden, 1992), have characteristics of typical foredeep deposits (DeCelles and Currie, 1996) and were
sourced from the west-southwest (Furer, 1970; Lawton, 1982,
1985; DeCelles, 1986; DeCelles and Burden, 1992; DeCelles
et al., 1993; Lawton et al., 1997; Mitra, 1997; Currie, 1997,
2002). These data suggest that initial displacement on thrusts of
the classic Sevier belt in Utah had begun by Early Cretaceous
(DeCelles and Coogan, 2006). Aptian deformation within the
Eureka district in the hinterland of the Sevier thrust belt is coeval with emplacement of the Canyon Range thrust in western
Utah but postdates initiation of the Sevier belt in western Utah
by 10–30 m.y. and thus represents out-of-sequence deformation
(Long et al., 2014).
The ages of deformation suggest that the type Sevier thrust
belt and the central Nevada thrust belt systems overlapped in
time and thus may be kinematically linked. There is evidence in
the Snake Range of eastern White Pine County for contractional
deformation of mid-Jurassic and Late Cretaceous ages (Miller
et al., 1988), but the ages of rocks that crop out at the base of the
early Cenozoic unconformity and the uniformly low Conodont
Alteration Indices (CAI) for a given stratigraphic horizon indicate that most of east-central Nevada was not breached by major thrust faults and thus was a relatively undeformed area in the
hinterland of the type Sevier belt in Utah and southern Nevada
(Armstrong, 1968; Gans and Miller, 1983; Gans et al., 1990;
Long, 2012). The thrust systems in central Nevada and western
Utah instead could be largely separate, west-rooted thrust systems that eventually merge to the south near Las Vegas (Figure
5). Alternatively, they could be kinematically linked by a large,
EHGGLQJSDUDOOHO ÀDW WKDW SDVVHV EHQHDWK HDVWFHQWUDO 1HYDGD
(e.g., Figure 22-15 of Speed et al., 1988).
The challenge in this study is to attempt to decipher the nature and relative ages of various structures in the northern Eureka district, given that (1) some contractional structures might
be mid-Paleozoic in age and some are almost certainly Early
Cretaceous in age, (2) at least small-scale structures might be
associated with emplacement of the late Early Cretaceous Ruby
Hill stock broadly synchronous with deposition of base met-
als during carbonate replacement mineralization, and (3) there
surely are one or more generations of extensional faults in the
district, before, concurrent with, or after Carlin-type gold mineralization, and various episodes of supergene weathering.
Pre-Cenozoic structural relief
Several lines of evidence suggest that the Eureka district
ZDV DQ DUHD RI ORFDOO\ VLJQL¿FDQW WRSRJUDSKLF UHOLHI SULRU WR
the initiation of Basin and Range-style extension. A recent Paleogene paleogeologic or subcrop map (Long, 2012) indicates
that the area between the northern Pancake Range and Eureka
has undergone 3–6 km of exhumation since the late Eocene;
calculated exhumation values decrease to ~2 km north of Eureka. Stable isotope paleoaltimetric analyses have returned
į18OSMOW values as negative as –14 to –16 per mil from calcite
in the limestones of the Cretaceous Newark Canyon Formation
from its type locality in Newark Canyon (J. Quade, pers. commun., 2013; Snell et al., 2014), which correspond to a minimum
elevation of 2–3 km. The Newark Canyon values are corroborated by isotopic data from the distal, meteoric water parts of
the 86 Ma McCullough Butte hydrothermal system that yield
į'a±SHUPLOHTXLYDOHQWWR±SHUPLOį18OSMOW (Barton
et al., 2015). Thermal alteration index (TAI) values from amorphous kerogen in carbonate rocks of the Windfall Formation
DQG3RJRQLS*URXSUDQJHIURPWRLQGLFDWLQJWKDWSDOHRtemperatures in these rocks ranged from ~65 to120°C (Homestake Mining Company unpublished report; Staplin, 1977;
Dutton, 1980). Assuming a typical geothermal gradient of
ƒ&NP7$,YDOXHVRI±LQGLFDWH±NPRIEXULDO
Such data suggest that the Eureka district was an area of
VLJQL¿FDQW UHOLHI E\ WKH (DUO\ &UHWDFHRXV +RZHYHU DV QRWHG
by Long et al. (2014), timing of contractional structures in the
district remains poorly constrained due to varying interpretations of individual features and overprinting by complex extensional structures, including the Jackson-Lawton-Bowman fault
system.
RESULTS
Lithology and structure
A generalized geologic map of the Eureka district is presented in Figure 7 that highlights the locations of the major
faults and the district-scale cross section. A new 1:2000-scale
Anaconda-style outcrop geologic map of an area of 4.5 km2
was made along the Jackson-Lawton-Bowman fault zone (Figures 8–11), extending along the fault from the historic workings
at Ruby Hill for 3 km south to east of the Sterling tunnel. Rock
types and lithology are shown in Figures 8 and 10. Structure
contour maps also were generated for the major faults in the
map area (Figure 12).
The geology of the northern Eureka district is described
here in terms of the district’s major structural features, which
Jackson normal fault system, Eureka district
977
Figure 7. Bedrock geologic map of the northern Eureka district, showing locations of the Sharp, Champion, Lawton, Jackson, Buckeye, Silver Connor, Ruby Hill,
DQG+RRVDFIDXOWVPRGL¿HGDIWHU1RODQ*UD\EROGOLQHUHSUHVHQWVFURVVVHFWLRQ1
strike either roughly north-south (the Sharp fault, the Eureka
culmination, the Jackson-Lawton-Bowman fault zone, and the
Hoosac fault), northwest-southeast (the Ruby Hill fault), or
northeast-southwest (the Silver Connor fault). The Sharp and
Hoosac faults lie outside the area of 1:2000 scale mapping for
this study but are included in a 4-km transect for construction
of a district-scale cross section (Figure 6) that is used for a subsequent structural reconstruction.
erly striking, west-dipping normal faults in the footwall of the
Cave Canyon fault that probably are older (e.g., Dugout fault
of Nolan, 1962) and that contain Au- and Sb-bearing jasperoid.
There are other west-dipping faults in the district, including at
least one small-displacement fault in the Archimedes deposit
(Dilles et al., 1996).
The Sharp fault is poorly exposed over much of its trace,
but Nolan (1962, p. 25) reported dips of 55–60°, and his map
shows that the fault has a northern tip with several splays that
Sharp fault
dip 48–72°W. On the cross section (Figure 6), the Sharp fault
The Sharp fault is the intermediate member of a set of three, is shown with an apparent dip of ~64°. The Sharp fault places
QRUWKZHVWVWHSSLQJZHVWGLSSLQJQRUPDOIDXOWVWKDWGH¿QHWKH 'HYRQLDQ'HYLOV*DWH/LPHVWRQHLQWKHÀRRURI6SULQJ9DOOH\
Eureka district’s western edge (Figures 6, 7). From south to against the Lower Cambrian rocks that make up the western
north, the set consists of the Cave Canyon, Sharp, and Spring ÀDQNRIWKH(XUHNDFXOPLQDWLRQRQ3URVSHFW5LGJHDQG0LQHUDO
Valley faults (Nolan, 1962). These faults cut alluvium and are Hill. The Devils Gate Limestone in eastern Spring Valley adinterpreted by most workers (e.g., Nolan, 1962) to be related to jacent to the Sharp fault is thick-bedded and somewhat poorly
Basin and Range-age extension, although there are other north- exposed. The Cambrian Prospect Mountain Quartzite and El-
978
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
Figure 8. Anaconda-style outcrop map of the northern Jackson fault zone showing lithology, structure, and veins.
Jackson normal fault system, Eureka district
Figure 9. Anaconda-style outcrop map of the northern Jackson fault zone showing alteration.
979
980
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
Figure 10. Anaconda-style outcrop map of the southern Jackson fault zone showing lithology, structure, and veins.
GRUDGR'RORPLWHRQWKHZHVWHUQÀDQNRIWKHFXOPLQDWLRQVWULNH brian Prospect Mountain Quartzite (Figure 3, 7); it is a regionroughly north-south and have moderate to steep westerly dips al structure with a strike length of ~100 km, the existence of
(35–60°).
which has been corroborated by Paleogene erosion patterns
(Long, 2012; Long et al., 2014). In the Mineral Hill area in
Eureka culmination and the Champion fault
the northern Eureka district, folds have been dismembered by
7KH (XUHND FXOPLQDWLRQ LV D ZHOOGH¿QHG QRUWKVRXWK crosscutting normal faults (Figure 6), and the map pattern of
trending anticlinal crest that includes Prospect Ridge and Min- the culmination consists of a core of Cambrian carbonate rocks,
eral Hill and that is marked by extensive exposures of Cam- ZKLFKDUHÀDQNHGWRWKHHDVWDQGZHVWE\WKH/RZHU&DPEULDQ
Jackson normal fault system, Eureka district
Prospect Mountain Quartzite (Figure 7). The carbonate rocks
in the core are folded into a syncline with the stratigraphically
youngest Hamburg Dolomite in the center and stratigraphically
ROGHVW(OGRUDGR'RORPLWHGH¿QLQJWKHHGJHV)LJXUH)ROGing appears to be spatially associated with the Champion fault,
a west-dipping reverse fault (Figures 6, 7). Structure contours
on the Champion fault indicate that it dips 23° to 43°W, steepening from south to north.
981
Moving from the western edge of the cross section toward
the center of the fold, the dips of the rocks over a short distance roll over from shallow easterly dips, through near-vertical dips, to overturned, moderate westerly dips in the core of
Hamburg Dolomite (Figure 6). Thus, the western limb of this
dismembered syncline, referred to in this study as the Mineral
Hill syncline, is overturned. The Cambrian Prospect Mountain
4XDUW]LWHRQWKHZHVWHUQÀDQNRIWKH0LQHUDO+LOOV\QFOLQHGLSV
Figure 11. Anaconda-style outcrop map of the southern Jackson fault zone showing alteration.
982
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
Figure 12. Structure contours on selected normal faults in the northern Eureka district. (a) Champion fault;
(b) Buckeye fault; (c) Jackson fault; and (d) Lawton fault. The north-south grid lines are spaced 2 km apart.
Jackson normal fault system, Eureka district
983
moderately steeply (55–60°) to the west. The Prospect Moun- Hoosac fault
WDLQ4XDUW]LWHRQWKHHDVWHUQÀDQNRIWKHV\QFOLQHLVLQWHQVHO\
The Hoosac fault is perhaps the most controversial strucfractured and oxidized; no reliable bedding surfaces have been ture in the Eureka district. Originally described by Hague
LGHQWL¿HGGXULQJWKLVRUDQ\SUHYLRXVVWXGLHV
(1883), its trace is currently mapped from Hoosac Mountain at
the southern boundary of the district north through the town of
Jackson-Lawton-Bowman normal fault system
(XUHND7KHIDXOWLVEXULHGE\ODYDÀRZVDQGWXIIVRUDOOXYLXP
The Jackson-Lawton-Bowman normal fault system runs for almost its entire length. The one exception is on Hoosac
the length of the Eureka district. It is mapped as a single fault 0RXQWDLQ ZKHUH LW ZDV ¿UVW GHVFULEHG 7KXV LWV LQWHUSUHWHG
strand from the southern edge of the district north to the Eureka trace north of the mountain is based on the estimated location
tunnel, at which point the strand diverges into the Jackson and of juxtaposed rocks of the Ordovician Hanson Creek Formation
Lawton branches (Figures 3, 7). Due to its tendency to form and Permian Carbon Ridge Formation. The Hoosac fault has
topographic depressions, the fault is poorly exposed along its been interpreted as both a contractional feature (Nolan, 1962;
OHQJWKDQGKDVEHHQLGHQWL¿HGSULPDULO\EDVHGRQWKHMX[WDSR- Taylor et al., 1993; Lisenbee et al., 1995) and an extensional
sition of younger units in the hanging wall (down to the east) feature (Hague, 1883; Nolan et al., 1974; Long et al., 2014).
against older units on Prospect Ridge and Mineral Hill. Just Hoosac Mountain is outside the map area for this study, but the
south of the map area of this study Nolan (1962) recorded steep Hoosac fault is critical to district-scale structural reconstruceasterly dips of 70–72° on the fault. At the southern end of the tions. The apparent dip shown in the cross section of Figure 6
map area, the northern continuation of the Jackson fault splits is 60°E.
into two branches; the Jackson branch continues to the north,
and the Lawton branch (Zulu Canyon fault of Vikre, 1998) Ruby Hill fault
YHHUVVOLJKWO\WRWKHQRUWKHDVWDORQJWKHÀRRURI=XOX&DQ\RQ
The Ruby Hill fault is a northwest-striking structure that
Structure contours on the Jackson branch indicate dips that forms the northeastern boundary of Ruby Hill (Nolan, 1962).
range from ~23° to 36°E, with an apparent dip in the cross sec- Nolan (1962) shows three dip measurements on the northeasttion of 27°E (Figure 12c), similar to the dip shown on the cross ern side of Ruby Hill, from north to south, of 70°, 62°, and
section (Figure 6). Structure contours on the Lawton branch in- 60°NE. The fault drops Cambrian Hamburg Dolomite in the
dicate that the southern end dips at ~40°E, whereas the northern hanging wall against Cambrian Eldorado Dolomite in the footend dips at only ~12°E, with an apparent dip in the cross section wall, omitting at least 300 m of stratigraphic section and offof 20°E (Figure 12d). The hanging wall of the Jackson branch setting Cretaceous carbonate replacement mineralization. The
consists of a continuous panel of Cambrian–Ordovician carbon- Eureka Corporation sunk the FAD shaft 1941 in order to exploit
ate and clastic rocks that dip to the east; dips are steepest close mineralization in the hanging wall of the Ruby Hill fault but,
to the fault and gradually shallow to the east. The footwall of famously, was forced to abandon the project after encountering
the Jackson branch consists of intensely fractured and oxidized high volumes of groundwater when the shaft pierced another
Cambrian Prospect Mountain Quartzite, which dips moderately fault, the Martin fault, which parallels the Ruby Hill fault (e.g.,
to the east. The Lawton branch contains west-dipping Secret Nolan and Hunt, 1968). As the Ruby Hill fault continues to the
Canyon Shale, Geddes Limestone, and Eldorado Dolomite in southeast, it is cut and offset ~400 m to the south by the Jackson
the hanging wall; in its footwall is the Hamburg Dolomite, branch. This timing relationship (i.e., the Ruby Hill fault cutwhich makes up the core of the Mineral Hill syncline.
ting mid-Cretaceous mineralization and, in turn, being cut by
the Jackson fault) is one of the few broad constraints on the age
Buckeye fault
of the Jackson fault system.
Between the Lawton branch to the west and the Jackson
branch to the east is a third structure, the Buckeye fault (Fig- Silver Connor fault
ure 6), which has historically been interpreted as the roof thrust
The Silver Connor fault, which is well exposed on Prosof a duplex known as the Ruby Hill thrust zone. The Buckeye pect Ridge, strikes N40°E and dips ~80°SE. Like the Ruby Hill
fault juxtaposes the east-dipping Prospect Mountain Quartzite fault, it juxtaposes the Hamburg Dolomite against the Eldorado
in the footwall of the Jackson branch against the moderately Dolomite; however, the Ruby Hill fault is down to the northwest-dipping Secret Canyon, Geddes, and Eldorado units in the east and the Silver Connor fault is down to the southeast. The
hanging wall of the Lawton branch. Close examination of the Silver Connor fault also appears to be cut by the Jackson fault
map pattern shows that this fault cuts down section and thus is to the northeast, where the Jackson and Lawton branches come
more likely a fourth branch of the Jackson normal fault system. together; however, exposure is poor and the offset portion of the
At its southern end, the Buckeye fault has a dip of 25°NE mea- Silver Connor fault could not be found east of this intersection.
sured in outcrop. Structure contours on the fault indicate that it
has a true dip of ~20–25° to the east or northeast, with an ap- Alteration types and distribution
parent dip of ~16°E in the cross section (Figure 12b), which is
similar to the dip shown on the cross section (Figure 6).
Figures 9 and 11 show the distribution of alteration in the
984
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
PDSDUHDZKLFKIDOOVLQWRIRXUEURDGFDWHJRULHVVLOLFL¿FDWLRQ
marble and hornfels, bleaching, and sanding.
6LOLFL¿FDWLRQ
6LOLFL¿FDWLRQ RU WKH UHSODFHPHQW RI FDUERQDWH PLQHUDOV
with silica, is a common alteration type in Carlin-type deposits but also occurs in a variety of other hydrothermal systems
/RYHULQJ,QWKH(XUHNDGLVWULFWVLOLFL¿FDWLRQLVIRXQG
in various forms: (1) as true “jasperoid,” the total replacement
of a carbonate rock outcrop with silica, (2) as “nodular” jasperoid, or the partial replacement of carbonate rock with silica
in seemingly irregular patches, (3) as jasperoid veins, which
can be centimeters to tens of centimeters thick and tend to be
strongly oxidized (Figure 13a); and (4) as “spiderweb silica,” or
thin, randomly-oriented veinlets of silica cutting across otherwise unaltered carbonate rock (Figure 13b).
In the Eureka district, jasperoid may be hematite-bearing
or hematite-absent. Hematitic jasperoid tends to be intensely
EUHFFLDWHG VPDOO PP WR FP VFDOH KLJKO\ DQJXODU VLOLFL¿HG
clasts make up ~75–80% of the rock and are chaotically distributed in an equally siliceous matrix. In thin section, complex
crosscutting relationships are observed. Multiple generations of
tiny silica veinlets crosscut the rocks; in some cases, silica veinlets are terminated at clast boundaries, whereas in other cases
the veinlets cut both clast and matrix, suggesting that silica was
FRQWLQXDOO\ÀRRGLQJWKHURFNDVLWZDVEHLQJEUHFFLDWHG)LJXUH 1RQKHPDWLWLF MDVSHURLG LV HTXDOO\ ZHOO VLOLFL¿HG EXW
is dark gray and exhibits no brecciation, although any primary
depositional textures that may have been present are destroyed.
Figures 9 and 11 show the distribution of alteration types
in the map area. Hematitic jasperoid (including spiderweb silica,
jasperoid veins, and nodular jasperoid as well as massive jasperoid) is the dominant type; non-hematitic jasperoid was found
RQO\DVÀRDWRQDKLVWRULFPLQHGXPSLQWKH&DPEULDQ+DPEXUJ
Dolomite near the Hamburg–Dunderberg contact. Hematitic jasperoid, by contrast, is common in the northern part of the district,
where it is best developed on Mineral Hill, and in the limestone
of the Ordovician Pogonip Group east of the historic Jackson
mine. Map patterns show that hematitic jasperoid is gradational in intensity. Narrow, elongate cores of massive brecciated
jasperoid outcrop are surrounded by wider zones of nodular
jasperoid, which are in turn surrounded by a zone of jasperoid
veins; most distal to the core is a zone of spiderweb silica.
Marble and hornfels
Marble in the Eureka district consists of coarse- to very
coarse-grained, recrystallized calcite. It may be bleached white
or retain the gray to blue-gray color of the original unrecrystallized carbonate rock. In general, the coarsest textures of marble
occur where the rock is also bleached. Spatially, the distribution
of marble is limited to the Hamburg Dolomite west of the Lawton branch on Mineral Hill, where it is abundant; the presence
of marble in this area can be attributed to heating by intrusion
of the Mineral Hill stock.
Figure 13. Photographs of alteration in outcrop. (a) Hematite-bearing jasperoid
vein, ~30 cm thick, in the Goodwin Formation. (b) Hematite-bearing spiderweb
silica in marble on Mineral Hill.
There are limited exposures of a dense, hard, gray-green
laminated hornfels in the Clarks Spring member of the Secret
Canyon Shale (originally, a thinly-bedded limestone with yellow-tan argillaceous partings) on the heavily vegetated eastern
wall of Zulu Canyon. This hornfels is separated from the mar-
Jackson normal fault system, Eureka district
ble on Mineral Hill by the Lawton branch. However, porphyritic dike material (10–15% hornblende and ~20% plagioclase
phenocrysts in a dark gray, aphanitic groundmass) can be found
ORFDOO\LQÀRDWRQWKHHDVWHUQZDOORIWKHFDQ\RQ7KHKRUQIHOV
observed in the Secret Canyon Formation may be related to the
intrusion of this dike.
Bleaching
Bleaching of carbonates is common in the Eureka district,
DVGLVFUHWHSDWFKHVRUHORQJDWH¿QJHUV,QWKHQRUWKHUQSDUWRI
the map area, bleaching of marble occurs on the southern end
of Mineral Hill; bleached marble appears to grade out into unbleached marble and eventually into unaltered carbonate rock.
In the northern map area, patches of bleached rock also trend
northeast-southwest through the Hamburg Dolomite, the Windfall Formation, and the Pogonip Group, coinciding with the
trace of the Ruby Hill fault. In the southern part of the map
area, bleaching is prominent in the Hamburg Dolomite, where
it essentially demarcates the fault contact between the Hamburg
and Eldorado Dolomites (Figures 9, 11). Perhaps more than any
other alteration type, bleaching appears to be fault-controlled;
it is often, but not always, spatially associated with jasperoid.
985
dense rock” to dolomitic sand seems to be the result of hydroWKHUPDOÀXLGVGLVVROYLQJLQWHUVWLWLDOFDOFLXPFDUERQDWHWKDWFHments dolomite grains, because unsanded Hamburg Dolomite
commonly reacts vigorously with hydrochloric acid but sanded
Hamburg Dolomite does not. The areal extent of sanding in the
map area is small; it occurs only as small, discrete patches in the
Hamburg Dolomite west of the Jackson branch and also in the
Hamburg Dolomite on Mineral Hill.
Geochemical analyses
Whole-rock trace-element analysis of jasperoid
Three surface samples of jasperoid were submitted for
whole-rock analysis using the complete package analysis of
ALS Labs (includes 14 lithophile elements by lithium metaboUDWHIXVLRQ;UD\ÀXRUHVFHQFHRU,&3$(6DQGHOHPHQWV
by lithium borate fusion and ICP-MS). The samples were also
analyzed for gold.
Non-hematitic jasperoid samples SC-001a and SC-001b
were collected from a mine dump in the Hamburg Dolomite
RQWKHQRUWKHDVWHUQÀDQNRI+DPEXUJ5LGJHZHVWRI*RRGZLQ
Canyon, at the contact between the Hamburg Dolomite and
Dunderberg Shale. This is the only locality in the map area
Sanding
where non-hematitic jasperoid was observed. Farther south in
Sanding of dolomite is important in the Eureka district. the district, the Hamburg–Dunderberg contact is host to CarlinSanding is spectacularly exposed in the Hamburg Dolomite at type mineralization at the Paroni, Windfall, and Rustler mines.
the Paroni, Rustler, and Windfall pits, where Carlin-type gold Scorodite, a common secondary mineral resulting from the
was mined along the Hamburg–Dunderberg contact, and, there- oxidation of arsenic-bearing minerals, was observed on fracfore, appears to be important to the development of Carlin-type ture surfaces. Sample SC-002 was collected from a brecciated,
deposits in the district. In his description of this alteration in the hematitic jasperoid outcrop in the Ordovician Goodwin LimeHamburg Dolomite, Nolan noted that the “hard dense rock that stone just east of Austin Canyon, an area that was considered to
is normally characteristic of the Hamburg has been converted be one of the most prospective for Carlin-type mineralization
to a dolomite ‘sand,’ which can be easily scraped and broken EDVHG RQ OLWKRORJ\ DEXQGDQW VLOLFL¿FDWLRQ DSSDUHQW VWUXFWXUDO
E\DSLFNDOWKRXJKLWLVVXI¿FLHQWO\FRPSDFWWRPDLQWDLQQHDUO\ ground preparation (due to its proximity of the intersection of the
vertical walls” (Nolan, 1962, p. 44). The conversion of “hard Jackson branch with the Ruby Hill fault), arsenic and gold anomalies in historic soil samples, and a paucity of historic drilling.
Table 1 shows the concentrations of precious and base metals in the three jasperoid samples, as well as concentrations of
“Carlin-suite” trace elements (As, Tl, Hg, Sb, and Ba) and trace
elements that are typically considered igneous-related (Bi, Li,
Ni, and W). Sample SC-002, the hematitic jasperoid, contains
low concentrations of Au, Ag, base metals, and trace elements
and is essentially barren. By contrast, samples SC-001a and
6&E FRQWDLQHG DQG SSP$X DQG VLJQL¿FDQWO\
elevated concentrations of As, Tl, Hg, Sb, and Ba. However,
these two samples also contained elevated concentrations of
base metals and igneous-related trace elements.
Figure 14. Photomicrograph of brecciated, hematite-bearing jasperoid. Sample
SC-002 from the Goodwin Formation east of Austin Ridge in plane-polarized
OLJKW DQJXODU FODVWV RI LQWHQVHO\ VLOLFL¿HG OLPHVWRQH VRPH ZLWK FKDOFHGRQLF
silica rims, crosscut by multiple generations of silica veinlets.
Stable isotope analysis
A small number (n = 14) of surface samples were collected
and analyzed for carbon and oxygen isotopes. Samples included both visually altered and unaltered limestone and dolomite
wall rock as well as veins hosted by the Eldorado Dolomite,
Hamburg Dolomite, and Pogonip Group (Table 1). For this
986
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
Table 1. TRACE-ELEMENT CONCENTRATIONS OF SELECTED JASPEROID SAMPLES.
Sample ID
Au
(ppm)
Ag
(ppm)
As
(ppm)
Ti
(ppm)
Hg
(ppm)
Sb
(ppm)
Ba
(ppm)
Cu
(ppm)
Pb
(ppm)
Zn
(ppm)
Bi
(ppm)
Li
(ppm)
Ni
(ppm)
W
(ppm)
SC-001a
SC-001b
SC-002
0.207
0.09
0.005
> 100
> 100
0.02
7320.0
6550.0
83.3
3.05
3.00
0.43
60.50
48.50
0.41
61.10
59.10
1.09
160
130
50
79.1
68.1
1.4
5140
4530
3
6300
6260
7
0.08
0.07
0.03
41.2
37.5
5.4
17.9
15.3
2.2
1.7
1.2
0.8
study, isotopic compositions of samples from a wide range of
alteration types across the Eureka district were calculated and
compared with compositions calculated by previous studies for
fresh and unaltered sedimentary and igneous rock. Rather than
determining the extent to which isotopic exchange has occurred
EHWZHHQRUHÀXLGVDQGURFNVLQNQRZQPLQHUDOL]HG]RQHVHJ
Hastings, 2008), which would require a large and closelyspaced data set, the goal of this investigation was to capture
some of the variability in isotopic signatures associated with
ÀXLGURFNLQWHUDFWLRQVLQGLIIHUHQWW\SHVRIK\GURWKHUPDOV\VWHPVHJPDJPDWLFÀXLGVDVVRFLDWHGZLWKVNDUQIRUPDWLRQDQG
carbonate replacement deposits, as well as lower-temperature
PHWHRULFRUPL[HGÀXLGVWKDWPD\KDYHEHHQDVVRFLDWHGZLWKWKH
formation of the Carlin-type system at Archimedes).
)LJXUHVKRZVWKHUDQJHRIį18OSMOW compositions for
a variety of rocks in the Eureka district, including mid-Cretaceous igneous intrusions, quartz-base metal veins, jasperoid,
mineralized limestone and calcite veins at Archimedes, unalWHUHG FDUERQDWH URFN DQG VHGLPHQWDU\ FKHUW į18OSMOW com-
positions for mid-Cretaceous igneous rocks range from 7–10‰
(Vikre, 1998); by contrast, visually unaltered Hamburg Dolomite (this study) and sedimentary chert (Barton and Ilchik,
1995, unpublished internal report to Homestake Mining ComSDQ\ KDYH į18OSMOW ranging from ~20 to 25‰. As is typical of many Carlin-type deposits, mineralized wall rock from
WKH$UFKLPHGHVGHSRVLWH[KLELWVDUDQJHRIį18OSMOW, from 12
to 20‰ (Hastings, 2008). Material collected from skarn adjaFHQW WR WKH *UDYH\DUG )ODW LQWUXVLRQ DQG IURP VLOLFL¿HG URFN
with high Au grade near the Blanchard fault, which postdates
the intrusion, exhibit similar degrees of depletion, further indicating that Carlin-type mineralization is associated with a
post-Cretaceous hydrothermal system entirely separate from
the magmatic-hydrothermal system that produced the polymetallic carbonate replacement mineralization (Hastings, 2008).
Samples of limestone from the Pogonip Group collected east of
$XVWLQ&DQ\RQ7DEOH)LJXUHKDYHį18OSMOW of ~18‰,
whereas samples from sparry calcite veins in this location have
į18OSMOW of ~8–9‰.
INTERPRETATIONS
Stratigraphic separation on the Jackson-Lawton-Bowman
normal fault system
Figure 15. Variation in oxygen isotope values for altered and unaltered igneous and sedimentary rocks in the Eureka district. From right to left, symbols in black represent values for: visually unaltered Hamburg Dolomite and
sedimentary chert; Pogonip Group wall rock and calcite veins from the Archimedes deposit; Pogonip Group (Goodwin Formation) wall rock and calcite
veins from outside the mine site, west of Austin Ridge; jasperoid; quartz-base
metal veins; and Cretaceous intrusive rocks. Symbols in red represent calcuODWHG LVRWRSLF FRPSRVLWLRQV RI D ÀXLG LQ HTXLOLEULXP ZLWK .TS DW ƒ& DQG
300°C; based on empirical quartz–H2O fractionation curve from Taylor (1979).
Notes:
*Vikre, 1998;
**Barton and Ilchik, 1995, unpublished internal report to Homestake Mining
Company;
***Hastings, 2008.
Stratigraphic separation diagrams plot the stratigraphic
unit in both the footwall and hanging wall of a fault against the
distance along the trace of the fault (Woodward et al., 1989).
Although stratigraphic separation diagrams are most commonly
employed in fold-and-thrust belts to interpret the behavior and
geometry of thrust faults (e.g., DeCelles and Coogan, 2006),
they can also be used in extensional settings to illustrate the displacement geometry associated with normal faults (e.g., Chapman et al., 1978). Stratigraphic separation diagrams are particularly useful tools for identifying and illustrating individual fault
segments in complex normal fault systems, which commonly
have multiple displacement maxima and minima (Schlische,
1995), and in settings in which compressional structures have
been overprinted by later extension, such as the Eureka district.
Normal faults omit stratigraphic section and slide younger
rocks down against older rocks. Therefore, on a stratigraphic
separation diagram the curve representing the hanging wall of
the fault should be located above the curve representing the
footwall of the fault if stratigraphic separation is “normal.” A
reversal of this pattern, known as a separation anomaly (i.e.,
footwall curve above hanging wall curve) suggests that either
Jackson normal fault system, Eureka district
the fault has changed from a normal fault to a thrust fault or that
the fault cuts an older structure (Groshong, 2006). Displacement along normal faults is greatest near the center of the fault
and decreases to zero at the tips (e.g., Walsh and Watterson,
1991), resulting in a synclinal geometry in the hanging wall
and a stratigraphic separation pattern resembling a smile. Normal faults commonly tilt as they move, and the mid-fault regions of faults, which are the areas of greatest slip, tend to have
shallower dips than near the ends where slip diminishes to zero
(Schlische, 1995).
Figure 16a shows stratigraphic separation from south to
north along the Jackson fault system in the southern half of
the Eureka district, where the fault zone is mapped as a single
strand. From the measured starting point at the southern edge
of the district, stratigraphic separation gradually decreases from
500 m to tens of meters at roughly 4 km from the starting point,
indicating that the segment is closing to the north toward a fault
tip. The large amount of stratigraphic separation at the measured
starting point and the absence of a corresponding southern tip
suggest that the Jackson fault system extends southward out of
the Eureka district. There is a short gap in the mapped trace
of the Jackson fault 4 km north of the starting point, further
indicating a zone of low displacement that marks the boundary
between two faults where the rocks on the hanging wall side of
the fault are older than rocks on the footwall side. Rather than
indicating a sudden switch in the slip direction of the fault (i.e.,
from down-to-the-east to down-to-the-west displacement), this
separation is interpreted to mark the point at which the Jackson
fault cuts the older Eureka culmination.
Figure 16b shows stratigraphic separation along the trace
of the Jackson branch, from the FAD shaft to the northern
boundary of the district. From 0 to 0.5 km north of the FAD
shaft, separation is ~200 m. From 0.5 to 1.25 km north of the
FAD shaft there is an abrupt, short separation anomaly where
the Jackson branch is mapped as having rocks of the Bullwhacker member of the Cambrian Windfall Formation in its
hanging wall and Lower Ordovician Goodwin member (Og1)
in its footwall, suggesting that either a) there is a small thrust
“slice” of Cambrian Bullwhacker in this location, or that b) the
unit in the hanging wall of the Jackson branch has been mismapped. This separation anomaly also marks the point at which
the Holly fault splits from the Jackson branch, with the Jackson
branch continuing on to the northeast and the Holly fault splaying out to the northwest. North of this junction, separation is
normal to the northernmost extent of the fault trace.
6LJQL¿FDQFHRIWKH+RRVDFIDXOW
The Hoosac fault has been interpreted to be both a contractional feature (e.g., Nolan, 1962; Taylor et al., 1993; Lisenbee
et al., 1995) and an extensional feature (e.g., Hague, 1883; Nolan et al., 1974; Long et al., 2014). The Hoosac fault is located
outside the map area but on the eastern side of the district-scale
cross section (Figure 6).
987
Nolan’s (1962) map of the Eureka district shows the type
exposure of the Hoosac fault on Hoosac Mountain as consisting
of Ordovician Eureka Quartzite to the east, in the footwall, and
Cretaceous Newark Canyon Formation to the west, in the hanging wall. As mapped, this juxtaposition constitutes a youngeron-older relationship or stratigraphic omission that is suggestive of a normal fault. Nolan (1962, p. 25), however, considered
the overall sinuosity of the fault’s trace to be more compatible
with a “thrust fault of moderate to low dip,” seems to have
deemed Hague’s (1883) interpretation of the fault as having
more than 3.5 km of normal offset unlikely, and asserted that
“a thrust fault would be structurally in accord with the nature of
faulting throughout the district.” By contrast, Long et al. (2014)
describe a series of stratigraphic omissions on Hoosac Mountain and suggest that earlier thrust interpretations be abandoned
in favor of a normal fault system interpretation.
Reconnaissance investigations support the original interpretation of Hague (1883) and the more recent interpretations
by Long et al. (2014), rather than the thrust interpretation, mainly because the original juxtaposition of units as described by
Nolan (1962) is indicative of stratigraphic omission and, therefore, a normal fault. There is simply not enough “room” for
WKHHQWLUHVWUDWLJUDSKLFVHFWLRQWREHSUHVHQWZLWKRXWVLJQL¿FDQW
stratigraphic omission. Between 80 and 250 m of limestone of
the Pogonip Group, dipping 43–48°E, is present on the western
ÀDQNRI+RRVDF0RXQWDLQDERYHWKH5XVWOHUSLW$OWKRXJKDQ
unfaulted section of the Pogonip Group has not been measured
anywhere in the Eureka district, Nolan et al. (1956) estimated
that roughly 490 m of limestone of the Pogonip Group is present in the “somewhat faulted” section in Goodwin Canyon and
that roughly 600 m are present on the northern side of Windfall
&DQ\RQ7KHUHIRUHLWDSSHDUVWKDWDVLJQL¿FDQWSRUWLRQRIWKH
Pogonip Group has been faulted out on Hoosac Mountain.
The interpretation here that the eastern third of the Eureka district is dominated by extensional features does not preclude the existence of a major thrust fault at depth, as has been
proposed by a number of workers (e.g., Lisenbee et al., 1995;
Lisenbee, 2001; Long et al., 2014).
Major fault blocks in present-day cross section
The district-scale cross section 104000N, which extends
4 km from west to east across northern Eureka district, can be
LQWHUSUHWHGLQWHUPVRI¿YHPDMRUIDXOWEORFNVDOWKRXJKLWDOVR
FRQWDLQVVHYHUDOVPDOOHUEORFNV)LJXUH7KH¿YHODUJHIDXOW
blocks are described from west to east.
7KH¿UVWEORFNWKH6SULQJ9DOOH\EORFNFRQVLVWVRI'HYRQLDQ'HYLOV*DWH/LPHVWRQHRQWKHÀRRURI6SULQJ9DOOH\LQWKH
hanging wall of the Sharp fault, juxtaposed against moderate to
steeply west-dipping Cambrian Prospect Mountain Quartzite in
the footwall of the fault (Figures 6, 7). This juxtaposition constitutes an omission of at least 2.4 km of stratigraphic section.
The second block, the Mineral Hill syncline block, contains a syncline with an overturned western limb consisting
988
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
Figure 16. Stratigraphic separation diagrams. Crosshatch pattern represents anomalous stratigraphic separation (i.e., the line representing the stratigraphic level of the hanging wall crosses the line representing the stratigraphic level of the footwall), which indicates that the fault either has cut an
older structure or switched from down-to-the-east to down-to-the-west offset. (a) Stratigraphic separation diagram for the main branch of the Jackson fault from the southern boundary of the Eureka district north to the vicinity of the Eureka tunnel, at which point the fault splays into the Jackson
and Lawton branches. (b) Stratigraphic separation diagram for the Jackson/Holly branch from north of the FAD shaft to north of the Archimedes pit.
Jackson normal fault system, Eureka district
of Cambrian carbonate rocks (Figures 6, 7). The syncline is
ÀDQNHG WR WKH ZHVW E\ &DPEULDQ 3URVSHFW 0RXQWDLQ 4XDUW]ite; the contact of the west-dipping quartzite with gently eastdipping Eldorado Dolomite in the nose of the syncline is an
older-on-younger relationship, suggesting the presence of a
contractional structure. Although the contact between the well
indurated Prospect Mountain Quartzite and Eldorado Dolomite
seems an unlikely slip surface, the Prospect Mountain Quartzite
RQ WKH ZHVWHUQ ÀDQN RI 3URVSHFW 5LGJH FRQWDLQV WKLQEHGGHG
siltstone and shale layers, which are well exposed in Cave Canyon and which could have accommodated a reverse fault. The
eastern boundary of this block is marked by the Lawton branch,
which juxtaposes moderately west-dipping Hamburg Dolomite
in its footwall against more steeply west-dipping Secret Canyon Shale and Geddes Limestone in its hanging wall.
The third block, the Lawton branch block, is a small block
bounded on the west by the Lawton branch and on the east by
the Prospect Mountain Quartzite (Figures 6, 7). In this block,
the stratigraphic order is reversed relative to the rocks in the
Mineral Hill syncline block; that is, the rocks young from east
to west rather than from west to east. Although the rocks in
the Lawton branch block might appear to be simply the eastern
limb of the Mineral Hill syncline, the fact that they are (1) in
fault contact with the syncline, omitting stratigraphic section,
and (2) dipping too steeply to the west to allow the full thickness of the Hamburg Dolomite to be present in the core of the
syncline, suggest that this block has been down-dropped by a
normal fault. Because the block is stratigraphically inverted relative to the western limb of the Mineral Hill syncline, it cannot
EHVRXUFHGIURPWKDWOLPEZLWKRXWVLJQL¿FDQWURWDWLRQ,QVWHDG
a more likely interpretation is that it was faulted from the western limb of the adjacent anticline of an anticline-syncline pair.
The fourth block, the Buckeye fault block, exposes gently
east-dipping Prospect Mountain Quartzite (Figures 6, 7). To the
west, the quartzite is in fault contact with the west-dipping Eldorado Dolomite in the Lawton branch block. To the east, the
quartzite is in fault contact with the moderately east-dipping
Clarks Spring member of the Secret Canyon Shale. The contact
between these two units historically has been interpreted as the
lowermost thrust fault of a duplex (Figure 6). As noted above,
the map pattern shows that this fault cuts down section, making
the thrust interpretation unlikely (Figure 16). This study, therefore, reinterprets the fault as a normal fault that juxtaposes Prospect Mountain Quartzite from the core of a fault-propagation
fold against the Eldorado Dolomite to the west, as explained
further below. Although only the Prospect Mountain Quartzite
is exposed at the surface (Figure 6), drill hole HRH-141 penetrated dramatically thinned Prospect Mountain Quartzite (6
m), Eldorado Dolomite (3 m), and Geddes Limestone (15 m)
in fault contact at depth. These fault slices are interpreted as
splays of the Jackson branch.
7KH ¿IWK EORFN WKH -DFNVRQ EUDQFK EORFN LV ORFDWHG
east of the Jackson branch and consists of a relatively unbroken
panel of moderately east-dipping beds, from the Clarks Spring
989
member of the Cambrian Secret Canyon Shale to the Permian
Carbon Ridge Formation. Anomalies in stratigraphic thicknesses (i.e., in the thickness of the Hamburg Dolomite) suggest
that small, previously unrecognized normal faults have omitted
stratigraphic thickness in this panel.
Crosscutting relationships, ages of events, and assessment
of structural controls for mineralization
This section summarizes the current understanding of the
sequence of geologic events in the district based on crosscutting
relationships and other information, which will be a basis for
a subsequent structural reconstruction, as well as the evidence
that certain faults did or did not serve as conduits for hypogene
mineralization in either the mid-Cretaceous or late Eocene(?)
events.
The host rocks in the district were deposited in the Cambrian and Ordovician. It is possible that some folds or thrust faults
are of mid-Paleozoic age, but the age of contraction and growth
of the Eureka culmination was concurrent with deposition of
the synorogenic Early Cretaceous Newark Canyon Formation
at ~116 Ma (Aptian) (Druschke et al., 2011; Long et al., 2014).
The Ruby Hill stock was emplaced and associated alteration
and carbonate-hosted base metal mineralization were formed
at ~106 Ma (Mortensen et al., 2000), which is Albian, i.e., late
Early Cretaceous, or ~10 m.y. after contractional deformation.
Workers in the northern Eureka district have entertained
K\SRWKHVHVWKDWPDQ\IDXOWVSRVVLEO\ZHUHFRQGXLWVIRUÀXLGV
that produced base-metal mineralization, yet it is now established that many of the faults clearly offset the Ruby Hill stock
and base-metal mineralization, as is also supported by data
from ground magnetics and drilling (e.g., Figures 2 and 3 of
Vikre, 1998). The northwest-striking, down-to-the-northeast
Ruby Hill normal fault, along with the Martin and perhaps the
2I¿FHIDXOWVLVRQHRIWKHHDUOLHVWQRUPDOIDXOWVWRFXWDQGRIIset the Ruby Hill stock and mid-Cretaceous carbonate-hosted
base metal mineralization. The Jackson branch cuts and offsets
the Ruby Hill fault; the Lawton branch cuts marble at Mineral
Hill (Figure 9) that is related to the intrusion of the Ruby Hill
stock (this study). Because the northwest-striking Ruby Hill
normal fault cuts and offsets mid-Cretaceous mineralization
and is in turn cut and offset by the Jackson branch, the Jackson
fault cannot have acted as a conduit for Cretaceous magmaticK\GURWKHUPDOÀXLGV7KHZHVWQRUWKZHVWVWULNLQJGRZQWRWKH
north Blanchard and Molly faults, which control Carlin-type
gold mineralization in the Archimedes pit (e.g., Dilles et al.,
1996), may be members of the same fault set as the Ruby Hill
fault and thus could be the same age. The age of Carlin-type
ores in the district may be late Eocene but remains somewhat
uncertain; although good radiometric dates on volcanic rocks
that exist, their relationship to the age of hypogene gold deposition in some cases requires further investigation (C.D. Henry,
written commun., 2014; Barton et al., 2015).
Mapped alteration patterns (jasperoid, marble, bleaching,
990
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
and sanding of carbonates), which spatial relationships and isotopic studies suggest are related to the Cretaceous magmatichydrothermal system, nonetheless show no relationship to the
Jackson fault (this study). This is consistent with the fact that
faults of the down-to-the-east Jackson fault system cut and offset the down-to-the-north faults that control Carlin-type gold
mineralization. The Jackson fault system is interpreted also as
post-ore in age relative to Carlin-type gold mineralization because it cuts and offsets the down-to-the-north faults. Structural
reconstructions (see below) suggest that the east-dipping Jackson normal fault system predates movement on the late Cenozoic, range-bounding, west-dipping Sharp fault, as the Sharp
fault cannot predate the Jackson fault because there would be
no logical source for the west-dipping, stratigraphically inverted rocks in the hanging wall of the Lawton branch (Figure 6).
Thus the Jackson fault system is probably mid-Cenozoic in age,
postdating the Ruby Hill, Blanchard, and Molly faults and predating the late Cenozoic Sharp fault.
may nearly be canceled out by back rotation by other sets. Unfortunately, there are few Tertiary rocks present in the district
to provide constraints on tilting and its association with certain
sets of faults. The Target Hill dome (~35.9 Ma, C.D. Henry,
written. commun., 2014) is a few km northeast of the map area,
but normal faulting and associated tilting may have preceded
and postdated its emplacement. It appears relatively upright and
intact, and associated pyroclastic rocks near the town of Eureka
dip only gently (12–20°) to the northeast, and dips that shallow might be primary dips. Hence, the net tilting is uncertain;
it might be gently northeast; it might be zero, or neither. In the
absence of evidence to the contrary, we assume it is negligible.
We also assume that all folding is related to contractional deforPDWLRQZKLFKLVDGHIHQVLEOH¿UVWDSSUR[LPDWLRQDOWKRXJKLQ
GHWDLOLWLVOLNHO\WREHLQFRUUHFWEHFDXVHVRPHÀH[XUDOEHQGLQJ
associated with normal faulting is likely (e.g., Seedorff et al.,
this volume, b).
If the net extensional tilting is negligible and no folding occurred during extension, then the attitudes of Paleozoic
District-scale structural reconstruction
rocks can be assumed approximately to represent their pre-extensional attitudes. Beds that are overturned (Figure 6), which
The cross section of Figure 6 is used to make a stepwise are widespread on the western side of the district (e.g., Nolan,
structural reconstruction of normal faulting in the northern Eu- 1962), thus were not overturned by extension-related tilting, as
reka district (Figure 17). To achieve a rigorous reconstruction, is the case in the Egan Range (Seedorff and Maher, 2002), but
the slip directions of all faults should be in the plane of the cross were overturned during earlier deformation. Syncline-anticline
section (e.g., Dahlstrom, 1969). This is unlikely to be strictly pairs with an overturned syncline in the footwall of the reverse
the case in this example, with numerous fault sets involved, fault are typical of fault-propagation folding but not fault-bend
although most of the faults strike nearly perpendicular to the folding (e.g., Shaw et al., 2005), so a reverse fault with a faultcross section (Figures7, 8, 10, 12). Thus, we use the cross sec- propagation fold should be the targeted structural architecture
WLRQRQO\WRPDNHD¿UVWSDVVGLDJUDPPDWLFUHFRQVWUXFWLRQ
for the restoration to achieve. For simplicity—which is war$VLJQL¿FDQWFKDOOHQJHFRPPRQWRPDQ\DUHDVZKHUHFRP- ranted given the paucity of constraints—we assume the presplex extensional deformation has been superimposed on con- ence of only one reverse fault, although having more than one
tractional deformation (e.g., Pape et al., 2015) is that the ge- reverse fault or a master reverse fault with several splays would
ometry following contraction is not tightly constrained. Some not be unreasonable in a contractional setting (e.g., Schmidt
of the considerations are: How many generations of normal and Perry, 1988).
faults are there, and how much tilting was associated with each
We then attempt to restore faults in a stepwise manner, begeneration of normal faults? Are the folds all formed during ginning with the youngest and ending with the oldest (Figure
contraction? Did contractional folds form by fault-propagation 17). Although we assume no net tilting, there may have been
folding, fault-bend folding, or some other mechanism? How considerable tilting associated with movement of any particular
many reverse faults are present?
generation of faults, so the attitudes of faults at various stages in
Although it is clear that the subsequent extensional struc- the reconstruction (Figure 17) are not necessarily representative
tures dismembered the contractional structures that formed the of their initial attitudes.
Eureka culmination, it is less clear how much tilting was asFour generations of faults (one reverse and three later sets
sociated with each generation of crosscutting normal faults and of normal faults) crop out in the cross section. To generate a
how much net tilting occurred during extension. Constraints on reasonable reconstruction following the above assumptions
the amount of tilting associated with each generation of faults without ignoring the lithologies and bedding attitudes in even
is necessary to restore movement on faults and to reconstruct the small fault fragments, it is necessary to include a fault that
the original orientations of the faults, but abundant pre-, syn- does not crop out at the surface in the line of section, which is
, and post-kinematic strata are needed to monitor tilting (e.g., QRWXQXVXDOLQUHFRQVWUXFWLRQLQYROYLQJIDXOWVZLWKVLJQL¿FDQW
Seedorff et al., this volume, b). Nonetheless, the net tilting re- offsets. This fault would belong to a set of faults that crops out
sulting from movement on all faults in the Eureka would not elsewhere in the area, from an early generation of down-to-theQHFHVVDULO\ EH VLJQL¿FDQW EHFDXVH IDXOWV RI YDULRXV SRODULWLHV west faults (Figure 6), such as the Dugout fault. The only fault
including both down-to-the-east and down-to-the-west normal VHWVWKDWLVVLJQL¿FDQWLQWKHQRUWKHUQ(XUHNDGLVWULFWWKDWLVQRW
faults are present, so the tilting related to individual faults sets represented in the cross section and reconstruction (Figures 6
Jackson normal fault system, Eureka district
)LJXUH'LDJUDPPDWLFVWHSZLVHUHVWRUDWLRQRIGLVWULFWVFDOHFURVVVHFWLRQ1WKURXJKWKHQRUWKHUQ(XUHNDGLVWULFWORRNLQJQRUWK7KH¿JXUH
shows the present cross section from Figure 6 and stepwise restoration of four, color-coded sets of normal faults, with locations of key faults and
positions of displaced present-day geologic surface labeled. Fifth stage shows Champion reverse fault and an associated fault-propagation fold. Note
that units beneath Cambrian Prospect Mountain Quartzite and above Mississippian Chainman Shale, including any synorogenic deposits, are omitted.
991
992
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
and 17) is the northeast-dipping set that includes the Ruby fault
and perhaps the Blanchard.
Figure 17 shows the stepwise restoration of faults on cross
section 104000, including where the present surface is located
during each step of the restoration. The younger west-dipping
normal faults (e.g., Sharp fault) appear to be the youngest fault
VHWDQGWKH\DUHUHVWRUHG¿UVW7KH6KDUSIDXOWKDVDQRIIVHWRI
~1.6 km in the plane of the cross section. Then the younger
set of east-dipping faults is restored, and the Hoosac fault has
an offset of ~1.0 km in the plane of the cross section. Then an
older, more gently dipping set of east-dipping faults is restored
(e.g., Jackson, Lawton, and Buckeye faults). Indeed, movement
on the faults of the Jackson normal fault system must predate
slip on the range-bounding Sharp fault; otherwise there would
be no logical source for the west-dipping, stratigraphically inverted rocks in the hanging wall of the Lawton branch. The
panel of east-dipping rocks in the hanging wall of the Jackson branch is restored to its pre-extension geometry by sliding
rocks in the hanging walls of the Lawton, Jackson, and Buckeye faults a total of ~3 km up dip (i.e., to the nose of the Eureka
culmination, from which they were sourced).
This results in the pre-extension structural architecture of
the district as a fault-propagation fold with an apparent offset
in cross section 104,000N of ~2.8 km formed by growth of the
&KDPSLRQIDXOW)LJXUHVKRZVDQHQODUJHPHQWRIWKH¿QDO
panel of Figure 17, with a possible view of the pre-erosional,
pre-extensional structural architecture of the district. The total
extension across this section is somewhat >100%.
Reconstructions in the Eureka district might be improved
in the future by adopting a three-dimensional approach to reconstruction (e.g., Seedorff et al., this volume, b) and incorporating drill hole results in the district.
eral proximity of the samples to the Mineral Hill stock, and
the sparry (i.e., high-temperature) texture of the veins suggest
that the veins in this area also are the product of the Cretaceous
magmatic-hydrothermal system.
As Nolan (1962) noted, the Jackson-Lawton-Bowman
normal fault zone does spatially coincide with the belt of most
intense carbonate replacement mineralization in the district.
The exact timing of movement on the Jackson fault remains
poorly constrained. However, the fact that the Ruby Hill fault
cuts and offsets mid-Cretaceous mineralization and is in turn
cut and offset by the Jackson branch effectively precludes the
possibility that the Jackson fault acted as a conduit for CretaFHRXV PDJPDWLFK\GURWKHUPDO ÀXLGV 7KH VSDWLDO UHODWLRQVKLS
between Cretaceous mineralization and the fault system is,
therefore, most likely fortuitous and a function of exposure.
Carlin-type mineralization at Archimedes is structurally
controlled, but it is focused along the west-northwest striking,
down-to-the-north Blanchard and Molly faults. The Blanchard
DQG0ROO\IDXOWVKDYHVLJQL¿FDQWO\VPDOOHURIIVHWVaPLQ
both cases) than any branches of the Jackson fault system. The
prominent north-south alignment of Carlin-type mineralization
in the Eureka district, rather than being related to the Jackson
fault zone, is an effect of the strike of the stratigraphic contact between the Hamburg Dolomite and Dunderberg Shale,
which is host to gold mineralization at the Paroni, Windfall,
and Rustler pits. Whole-rock geochemical analysis of jasperoid
samples from the Hamburg-Dunderberg contact in the northern
SDUWRIWKHGLVWULFWVKRZWKDWLWDOVRORFDOL]HGJROGEHDULQJÀXids there, and in concentrations that one might expect from a
Carlin-type system (0.09–0.209 ppm). That samples from this
contact, which hosts gold-only mineralization at the Paroni,
Windfall, and Rustler mines, also contain elevated concentrations of base metals, Li, Ni, Be, and W in the northern Eureka
Controls on Carlin-type gold mineralization in the
GLVWULFWVXJJHVWVWKDW&DUOLQW\SHÀXLGVPD\KDYHWUDYHOHGDORQJ
northern Eureka district and implications for mineral
this contact, overprinting the Cretaceous base-metal mineralexploration
ization where it was present (i.e., largely in the northern part
of the district, proximal to the Mineral Hill stock) but forming
With the exception of carbonate bleaching, alteration in the monogenetic Carlin-type deposits in the southern Eureka disnorthern Eureka district shows no spatial association with the trict, spatially removed from the effects of the mid-Cretaceous
Jackson fault zone; most of the mappable alteration in this part system.
of the district appears to be spatially related to the mid-CretaNolan (1962) noted that the low-grade disseminated gold
ceous (~106 Ma) Mineral Hill stock (Figures 9, 11). Mapping deposits at the Windfall mine are “so distinctive that one might
and reconnaissance isotopic analyses suggests that alteration in suspect a different source (p. 30)” and also observed that all of
the limestones of Ordovician Pogonip Group just east of Aus- the historically mined deposits in the district, which varied in
tin Canyon (an area that might be considered one of the most tenor from mine to mine, tended to be relatively rich in gold and
prospective for Carlin-type mineralization based on lithology, arsenic. Titley (1993) compiled Cu, Pb, Zn, Ag, and Au grades
DEXQGDQWVLOLFL¿FDWLRQJHRFKHPLFDODQRPDOLHVLQVRLOVVWUXF- IRU ¿IW\WZR FDUERQDWHKRVWHG PDVVLYH VXO¿GH GHSRVLWV LQ WKH
tural ground preparation, and dearth of drilling) is most likely United States and Mexico. Although metal content varies from
related to the intrusion of the stock. Prominent hematitic jas- district to district, gold grades in the carbonate replacement
peroid outcrops in this area closely resemble jasperoids on the deposits in the Eureka district are conspicuously high (28.28
ÀDQNRI0LQHUDO+LOO&DOFLWHYHLQVLQWKLVDUHDDUHVSDUU\DQG g/t) relative to other locales. In the 42 districts whose ores conKDYHOLJKWį18O values relative to the host rock (Table 2; Figure tained measureable amounts of gold, the mean gold grade was
15) that closely resemble the compositions of mid-Cretaceous 3.16 g/t. It, therefore, is plausible that an Eocene (?) Carlin-type
intrusive rocks in the district. These depleted values, the gen- overprint on Cretaceous base-metal mineralization may have
Jackson normal fault system, Eureka district
993
)LJXUH'LDJUDPPDWLFUHFRQVWUXFWLRQRISUHH[WHQVLRQDOJHRPHWU\RIQRUWKHUQ(XUHNDGLVWULFW(QODUJHPHQWRI¿IWKSDQHORISUHYLRXV¿JXUHDIWHUIRUPDWLRQRI
fault-propagation fold associated with slip on Champion reverse fault. Other faults are normal faults that will form subsequently, shown in the future positions in
which they will appear. Units beneath Cambrian Prospect Mountain Quartzite and above Mississippian Chainman Shale, including any synorogenic deposits, are
not shown. Pluton at depth intersected by drilling (see Figure 6) and indicated by aeromagnetic data (Vikre, 1998).
994
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
7DEOH &$/&8/$7('į182$1'į13C VALUES FOR CALCITE AND DOLOMITE SAMPLES.
Sample ID
Material
Location
VPDB
VPDB
C std
dev
O std
dev
į18O
(SMOW)
calcite
SC001B
SC001-A
ET001
LHR01
TV1
ZC001
ZC002
ZC003
ZC004
TV1-V
SC003
SS01
SC003V2
SS01V
Dolomite blebs in Ce
Limestone - Ce with dolomite blebs
Dolomite - Ch
Dolomite - Ch
Ch - late calcite vein
Marble (sanded) - Ch
Dolomite - Ch
Marble - Ch
Dolomite - Ch
Late calcite vein - Ch
Limestone - Op
Limestone - Op
Sparry calcite vein in Op
Calcite vein in Op
Silver Connor
Silver Connor
Eureka Tunnel
Little Hamburg Ridge
Zulu Canyon/MH - Trav
Zulu Canyon/MH
Zulu Canyon/MH
Zulu Canyon/MH
Zulu Canyon/MH
Zulu Canyon/MH - Trav
Shadow Canyon
Soil sample line
Shadow Canyon
Soil sample line
2.44
2.24
0.92
–0.29
–1.63
–0.52
0.29
0.69
0.11
–6.52
1.64
–0.91
2.58
–0.16
–13.24
–14.02
–6.95
–8.74
–13.42
–13.38
–6.98
–10.91
–9.79
–14.79
–11.74
–12.38
–21.32
–20.11
0.01
0.04
0.01
0.02
0.01
0.01
0.02
0.01
0.03
0.03
0.01
0.02
0.04
0.02
0.05
0.09
0.06
0.08
0.01
0.02
0.04
0.03
0.03
0.06
0.02
0.02
0.03
0.02
17.21
16.4
23.7
21.85
17.02
17.07
23.67
19.61
20.76
15.61
18.76
18.09
8.88
10.13
į13C
į18O
į18O
(SMOW)
true
Mineral
16.41
15.6
22.9
21.85
17.02
17.07
23.67
19.61
19.96
15.61
17.96
18.09
8.88
9.33
dolomite
calcite
dolomite
dolomite
calcite
calcite
dolomite
calcite
dolomite
calcite
calcite
calcite
calcite
calcite
1RWHV5HSRUWHGIRUFDOFLWHSKRVSKRULFDFLGIUDFWLRQDWLRQDWƒ&VDPSOHVSLFNHGE\$U\Q.+RJH
enriched the tenor of gold mined from carbonate replacement
deposits in the northern Eureka district.
faults. Because many normal faults rotate or tilt as they move
(e.g., Jackson, 1987), in general this process does not return
the fault surface to its orientation relative to a paleohorizontal
DISCUSSION
reference frame prior to the onset of movement for each set
of faults, and additional geologic constraints typically are reThe nature of Early Cretaceous contractional deformation quired to determine the original dip of the fault (Seedorff et
al., this volume, b). Ideally, one has a series of dated geologic
The Eureka district has been affected by multiple periods units (e.g., volcanic or syntectonic sedimentary strata) that were
of deformation, including a major contractional event associat- deposited throughout the various deformation events, with beded with the central Nevada thrust belt (e.g., Nolan, 1962; Long ding-to-fault angles available for each so that the orientations
et al., 2014) and subsequently multiple sets of normal faults. of the faults relative to paleohorizontal can be determined as a
As noted by Pape et al. (2015), such areas generally require an function of time. The more limited the available geologic coniterative approach to producing a viable structural restoration, straints, however, the more the resulting interpretation is modZKHUHLQWKHSUHH[WHQVLRQDOPRGHOLVSURJUHVVLYHO\PRGL¿HGWR el-driven, yet controversies remain, for exmple, regarding the
SURGXFHDUHVWRUHGH[WHQVLRQDOVWUXFWXUDOJHRPHWU\WKDWVDWLV¿HV applicability of various models of continental extension (e.g.,
all of the available geologic constraints on the nature of all de- Wong and Gans, 2008; Wernicke, 2009).
formational events. The iterative approach, however, results in
The challenge in central Nevada in general and in the Eurea degree of internal circularity within the retrodeformable cross ka district in particular is that there are few such constraints on
section because the extensional structure and the pre-extension- paleohorizontal as a function of time; hence, explicit or implicit
al structural interpretations are not mutually independent, i.e., assumptions critically affect the resulting interpretation. Such a
uncertainties regarding the structure of both the extended and limitation is acknowledged for the structural interpretation prerestored states of the cross sections increase the number of po- sented here, particularly as it affects the geometry of the contentially valid retrodeformable cross sectional models. The un- tractional structure. Determination of whether fault-bend folds
FHUWDLQWLHVDUHPDJQL¿HGLIFRQVLGHUDEOHXQFHUWDLQWLHVDOVRH[- (e.g., Bartley and Gleason, 1990; Long et al., 2014) or faultLVWLQWKH¿HOGUHJDUGLQJWKHFURVVFXWWLQJUHODWLRQVKLSVEHWZHHQ propagation folds (this study) characterize the central Nevada
various structures, as is not uncommon in areas of considerable thrust belt—or both in different places—probably will depend
complexity and imperfect exposure.
LPSRUWDQWO\RQ¿QGLQJIXUWKHUFRQVWUDLQWVRQSDOHRKRUL]RQWDODV
Determining the amount and direction of slip in the nor- a function of time.
mal faults is determined by restoring the hanging-wall blocks
relative to the footwall blocks in the directions opposite to their Relative ages of magmatic-hydrothermal replacement ores
slip direction, pinning geologic markers in the hanging wall and contractional deformation
to offset equivalents of the same markers in the footwall. This
process, however, only backs out the movement on the normal
Since the advent of the theory of plate tectonics it has been
Jackson normal fault system, Eureka district
clear that many magmatic-hydrothermal systems—especially
porphyry copper deposits—form at convergent plate margins
(e.g., Sillitoe, 1972, 2010; Seedorff et al., 2005), yet the timing of local contractional deformation relative to the formation
RIPDJPDWLFK\GURWKHUPDOV\VWHPVKDVUHODWLYHO\IHZ¿UPGDWD
points (e.g., Potrerillos, Chile: Olson, 1989; Marsh et al., 1997)
anywhere in the world. Additional information on the timing
of deformation and formation of magmatic-hydrothermal systems would make it possible to assess exploration models calling on formation in areas removed from active contractional
deformation, such as in transtensional sites along arc-parallel
strike-slip faults (Tosdal and Richards, 2001; see also Richards
et al., 2001; Sapiie and Cloos, 2004), versus models inferring
ore formation during contraction (Sillitoe, 1998), especially in
relays or contractional accommodation zones (Skármeta et al.,
2003). Is the relative timing of deformation and magmatism
necessarily even that important to whether or not ore formation
will occur or the degree to which metals may be concentrated?
The Eureka district is one of several broadly contemporaneous magmatic-hydrothermal systems, including those in
the Robinson and White Pine districts, that formed in a backarc setting from ~98 and 111 Ma at a latitude of ~39º15cN in
east-central Nevada (Seedorff et al., this volume, a). The midCretaceous base metal replacement ores and related skarns and
greisen veins of the Eureka district (Nolan and Hunt, 1968;
Vikre, 1998), which constitute a Mo-Cu type of magmatic-hyGURWKHUPDOV\VWHPLQWKHFODVVL¿FDWLRQRI6HHGRUIIHWDO
contribute to the diversity of magmatism and associated mineralization in the Mesozoic Cordilleran arc (e.g., Barton, 1990,
1996). The integration of recent geochronological and structural studies (Mortensen et al., 2000; Long et al., 2014) indicates
that this magmatic-hydrothermal event occurred ~10 m.y. after
Early Cretaceous contractional deformation in the district, thus
SURYLGLQJ DQRWKHU ¿UP GDWD SRLQW LQ GDWLQJ WKH GLIIHUHQFH LQ
ages of contractional deformation and magmatic-hydrothermal
ore formation.
Syn-ore faults in Carlin-type deposits and their impact on
gold grade
Although Carlin-type deposits, are known for commonly
forming regional-scale “trends” (e.g., Hofstra and Cline, 2000),
the trends do not necessarily parallel major faults, and the faults
that control ore commonly are small-offset normal faults that
strike at high angles to the trend (Seedorff, 1991; see also comprehensive compilation, Tables A1 and A2, Cline et al., 2005).
The prominent north-south alignment of Carlin-type mineralization in the Eureka district, rather than being related to the
Jackson fault zone, instead is an effect of the strike of the stratigraphic contact between the Hamburg Dolomite and Dunderberg Shale, which is host to gold mineralization at the Paroni,
Windfall, and Rustler pits (Barton et al., 2015). In the northern part of the Eureka district, Carlin-type gold mineralization
at Archimedes is structurally controlled, focused along the
995
west-northwest striking, down-to-the-north faults such as the
Blanchard fault (Dilles et al., 1996), and similar controls exist
at deposits elsewhere in the district (e.g., Nolan, 1962). Faults
VXFKDVWKH%ODQFKDUGKRZHYHUKDYHVLJQL¿FDQWO\VPDOOHURIIset (~100 m) than any branches of the later Jackson fault system
(this study). As is known from other types of structurally controlled ore deposits and geothermal systems (e.g., Faulds et al.,
2011), small-offset faults, irrespective of age, may be more efIHFWLYHDWFLUFXODWLQJPLQHUDOL]LQJÀXLGVWKURXJKWKHVXUURXQGing rock due to their relatively high pore pressures. In contrast,
large-offset faults can act as “drains.”
The complexities of the geology of the Eureka district
highlight the challenge of identifying structural controls on
Carlin-type mineralization, particularly prior to or beyond the
extent of mining-related exposures where the exposure may be
limited and where there may be partial spatial overlap between
Carlin-type and other mineralizing systems. The challenge is
PDGHPRUHGLI¿FXOWZKHQWKHIDXOWVWKDWKDYHWKHPRVWFRQWURO
on gold grade have relatively small offsets, as is commonly the
case.
CONCLUSIONS
The northern part of the Eureka district hosts mid-Cretaceous (~106 Ma) base metal replacement ores and related
skarns and greisen veins that constitute a Mo-Cu type of magmatic-hydrothermal system, which was subsequently overprinted by Eocene(?) Carlin-type gold mineralization, including the
Archimedes deposit. An Eocene(?) Carlin-type overprint on
Cretaceous base-metal mineralization may have enriched the
tenor of gold mined from the carbonate replacement deposits.
The Jackson-Lawton-Bowman normal fault system extends the
length of the Eureka district for 21 km, and the Buckeye fault is
likely a fourth branch of the system. The fault system dismembers folds of the Eureka culmination. Structural reconstructions
suggest that in the northern part of the district the culmination
formed by fault-propagation folding, likely in the Early Cretaceous during development of the central Nevada thrust belt.
Unraveling the structural complexities of the Eureka district remains a work in progress, but the series of superimposed
structural, intrusive, and hydrothermal events in the district
have been interpreted in this study as follows. Contraction and
growth of the Eureka culmination occurred concurrent with deposition of the synorogenic Early Cretaceous Newark Canyon
Formation at ~116 Ma, with the possibility that some contractional deformation is as old as mid-Paleozoic. Mid-Cretaceous
intrusions were emplaced and associated carbonate-hosted ores
formed at ~106 Ma, or ~10 m.y. after Early Cretaceous contractional deformation. Mapped alteration patterns, which spatial relationships and isotopic studies suggest are related to the
Cretaceous magmatic-hydrothermal system, nonetheless show
no relationship to the Jackson fault. Carlin-type mineralization
at Archimedes is structurally controlled, but by the older, westnorthwest striking, down-to-the-north Blanchard and Molly
996
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
faults. The Jackson-Lawton-Bowman normal fault system postdates and offsets not only the carbonate-hosted ores but also
Carlin-type gold mineralization. Structural reconstructions suggest that the east-dipping Jackson normal fault system nonetheless must predate slip on the late Cenozoic, range-bounding,
west-dipping Sharp fault; thus the Jackson is a mid-Cenozoic
fault system. The Jackson fault system has no genetic relationship to either the mid-Cretaceous or Eocene mineralizing
events, yet these series of down-to-the-east normal faults may
be responsible for preventing the erosion of and minimizing the
weathering of both the mid-Cretaceous base-metal replacement
ores and the higher levels of the Eocene(?) Carlin-type gold
ores on the eastern side of the northern Eureka district.
ACKNOWLEDGMENTS
:HDUHJUDWHIXOIRUWKH¿QDQFLDOVXSSRUWIRUWKLVVWXG\DQG
DVVRFLDWHG ¿HOG ZRUN E\ %DUULFN *ROG &RUSRUDWLRQ D VFKROarship from SRK Consulting, Inc., and by the University of
Arizona’s Titley Scholarship. Hoge would like to thank Pete
DeCelles for guidance and a thoughtful review of an earlier version of the manuscript and Jay Quade for conversations regarding paleoaltimetry. Hoge also thanks fellow graduate students
at the University of Arizona for their helpful discussions and assistance with various aspects of the project, particularly Simone
Runyon, and J.D. Mizer. Special thanks go to the Barrick Exploration staff at Ruby Hill, to Bob Loranger for his support of
the project; to Rodney Harney for his ever-cheerful attitude and
assistance in soil sampling; to Dave Schwarz for his thoughtprovoking discussions of regional structure; and, last but not
least, to Ron Kieckbusch, for giving me an excellent introduction to the geology of the Eureka district, answering my many
TXHVWLRQVKHOSLQJPHWR¿QGWKHKLVWRULFGDWD,QHHGHGLQDYHU\
FUDPSHGRI¿FHDQGDFWLQJDVDVRXQGLQJERDUGIRUP\WKLQNLQJ
out loud. The authors appreciate the comments from reviewers
and editors of the symposium volume.
REFERENCES
Arehart, G.B., Chakurian, A.M., Tretbar, D.R., Christensen, J.N., McInnes,
B.A., and Donelick, R.A., 2003, Evaluation of radioisotope dating of
Carlin-type deposits in the Great Basin, western North America, and
implications for deposit genesis: Economic Geology, v. 98, p. 235–248.
Armstrong, P.A., and Bartley, J.M., 1993, Displacement and deformation associated with a lateral thrust termination, southern Golden Gate Range,
southern Nevada, U.S.A.: Journal of Structural Geology, v. 15, p. 721–
735.
Armstrong, R.L., 1968, Sevier orogenic belt in Nevada and Utah: Geological
Society of America Bulletin, v. 79, p. 429–458.
Bagby, W.C., and Berger, B.R., 1985, Geologic characteristics of sediment-hosted, disseminated precious-metal deposits in the western United States,
in Berger, B.R., and Bethke, P.M., eds., Geology and geochemistry of
epithermal systems: Reviews in Economic Geology, v. 2, p.169–202.
Bakken, B.M., and Einaudi, M.T., 1986, Spatial and temporal relations between
wall rock alteration and gold mineralization, Main pit, Carlin gold mine,
Nevada, USA, in Macdonald, A.J., ed., Proceedings of Gold ’86, an
International Symposium on the Geology of Gold, Toronto, Canada, p.
388–403.
Bartley, J.M., and Gleason, G., 1990, Tertiary normal faults superimposed on
Mesozoic thrusts, Quinn Canyon and Grant Ranges, Nye County, Nevada, in Wernicke, B. P., ed., Basin and Range extensional tectonics
near the latitude of Las Vegas, Nevada: Geological Society of America
Memoir 176, p. 195–212.
%DUWRQ0'6RPHDVSHFWVRIWKHJHRORJ\DQGPLQHUDORJ\RIWKHÀXRrine-rich skarn at McCullough Butte, Eureka County, Nevada: Carnegie
Institution of Washington Year Book 81, p. 324–328.
Barton, M.D., 1987, Lithophile-element mineralization associated with Late
Cretaceous two-mica granites in the Great Basin: Geology, v. 15, p.
337–340.
Barton, M.D., 1990, Cretaceous magmatism, metamorphism, and metallogeny
in the east-central Great Basin, in Anderson, J.L., ed., The nature and
origin of Cordilleran magmatism: Geological Society of America Memoir 174, p. 283–302.
Barton, M.D., 1996, Granitic magmatism and metallogeny of southwestern
North America, in Brown, M., Candela, P.A., Peck, D.L., Stephens,
W.E., Walker, R.J., and Zen, E., eds., The Third Hutton Symposium
on the origin of granites and related rocks: Transactions of the Royal
Society of Edinburgh: Earth Sciences, v. 87, and Geological Society of
America Special Paper 315, p. 261–280.
Barton, M.D., Seedorff, E., and Ghidotti, G.A., 2015, Contrasting, variably
superimposed hydrothermal systems, Eureka mining district, northern
Fish Creek Range, Nevada [abs.]: Geological Society of Nevada, Symposium, Reno/Sparks, May 2015, Program with Abstracts Volume.
Blake, M.C., McKee, E.H., Marvin, R.F., Silberman, M.L., and Nolan, T.B.,
1975, The Oligocene volcanic center at Eureka, Nevada: U.S. Geological Survey Journal of Research, v. 3 p. 605–612.
Binyon, E.O., 1946, Exploration of the gold, silver, lead, and zinc properties,
Eureka Corporation, Eureka County, Nevada: U.S. Bureau of Mines Report of Investigation 3949, 18 p.
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.
Chapman, G.R., Lippard, S.J., and Martyn, J.E., 1978, The stratigraphy and
structure of the Kamasia Range, Kenya rift valley: Journal of the Geological Society of London, v. 135, p. 265–281.
Cline, J.S., Hofstra, A.H., Muntean, J.L., Tosdal, R.M., and Hickey, K.A., 2005,
Carlin-type gold deposits in Nevada: Critical geological characteristics
and viable models, in Hedenquist, J.W., Thompson, J.F.H., Goldfarb,
R.J., and Richards, J.P., eds., Economic Geology 100th Anniversary
Volume, p. 451–484.
Cunningham, C.G., 1988, The relationship between some disseminated gold
deposits, the western edge of the Precambrian craton, and paleothermal anomalies in Nevada, in Schafer, R.W., Cooper, J.J., and Vikre,
P.G., eds., Bulk mineable precious metal deposits of the western United
States: Geological Society of Nevada, Symposium, Reno/Sparks, April
1987, Proceedings, p. 35–48.
Currie, B.S., 1997, Sequence stratigraphy of nonmarine Jurassic-Cretaceous
rocks, central Cordilleran foreland-basin system: Geological Society of
America Bulletin, v. 109, p. 1206–1222.
&XUULH%66WUXFWXUDOFRQ¿JXUDWLRQRIWKH(DUO\&UHWDFHRXV&RUGLOOHUDQ
foreland-basin system and Sevier thrust belt, Utah and Colorado: Journal of Geology, v. 110, p. 697–718.
Curtis, J.S., 1884, Silver-lead deposits of Eureka, Nevada: U.S. Geologic Survey Monograph 7, 200 p.
Dahlstrom, C.D.A., 1969, Balanced cross sections: Canadian Journal of Earth
Sciences, v. 6, p. 743–757.
Jackson normal fault system, Eureka district
DeCelles, P.G., 1986, Sedimentation in a tectonically partitioned, nonmarine
foreland basin: The Lower Cretaceous Kootenai Formation, southwestern Montana: Geological Society of America Bulletin, v. 97, p. 911–931.
DeCelles, P.G., 2004, Late Jurassic to Eocene evolution of the Cordilleran
thrust belt and foreland basin system, western U.S.A.: American Journal
of Science, v. 304, p. 105–168.
DeCelles, P.G., and Burden, E.T., 1992, Sedimentology and sedimentary petrology of Jurassic-Cretaceous Morrison and Cloverly Formations in the
RYHU¿OOHGSDUWRIWKH&RUGLOOHUDQIRUHODQGEDVLQ%DVLQ5HVHDUFKY
p. 291–314.
DeCelles, P.G., and Coogan, J.C., 2006, Regional structure and kinematic history of the Sevier fold-thrust belt, central Utah: Implications for the
Cordilleran magmatic arc and foreland basin system: Geological Society of America Bulletin, v. 118, no. 7/8, p. 841–864.
DeCelles, P.G., and Currie, B.S., 1996, Long-term sediment accumulation in
the Middle Jurassic–early Eocene Cordilleran retroarc foreland basin
system: Geology, v. 24, p. 591–594.
DeCelles, P.G., Pile, H.T., and Coogan, J.C., 1993, Kinematic history of the
Meade thrust based on provenance of the Bechler Conglomerate at Red
Mountain, Idaho, Sevier thrust belt: Tectonics, v. 12, p. 1436–1450.
Dilles, P.A., Wright, W.A., Monteleone, S.E., Russell, K.D., Marlowe, K.E.,
Wood, R.A., and Margolis, J., 1996, The geology of the West Archimedes deposit: A new gold discovery in the Eureka mining district, Eureka
County, 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, p. 159–171.
Druschke, P.A., Hanson, A.D., Wells, M.L., Gehrels, G.E., and Stockli, D.F.,
2011, Paleogeographic isolation of the Cretaceous to Eocene Sevier
hinterland, east-central Nevada: Insights from U-Pb and (U-Th)/He detrital zircon ages of hinterland strata: Geological Society of America
Bulletin, v. 123, no. 5/6, p. 1141–1160.
Dutton, S.P., 1980, Petroleum source rock potential and thermal maturity, Palo
Duro basin, Texas: Texas Bureau of Economic Geology Geological Circular, v. 80, no. 10, 48 p.
Einaudi, M.T., 1997, Mapping altered and mineralized rocks: The “Anaconda
method”, Unpublished manuscript, 10 p.
(PVER 3 +RIVWUD$+ /DXKD ($ *ULI¿Q */ DQG +XWFKLQVRQ 5:
2ULJLQ RI KLJKJUDGH JROG RUH VRXUFH RI RUH ÀXLG FRPSRQHQWV
and genesis of the Meikle and neighboring Carlin-type deposits, northern Carlin trend, Nevada: Economic Geology, v. 98, p. 1069–1100.
Faulds, J.E., Hinz, N.H., and Coolbaugh, M.F., 2011, Structural investigations
RI *UHDW %DVLQ JHRWKHUPDO ¿HOGV $SSOLFDWLRQV DQG LPSOLFDWLRQV 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. 361–372.
Fouch, T.D., Hanley, J.H., and Forester, R.M., 1979, Preliminary correlation of
Cretaceous and Paleogene lacustrine and related nonmarine sedimentary and volcanic rocks in parts of the eastern Great Basin of Nevada
and Utah, in Newman, G.W., and Goode, H.D., eds., Basin and Range
Symposium: Rocky Mountain Association of Geologists, p. 305–312.
Furer, L.C., 1970, Nonmarine Upper Jurassic and Lower Cretaceous rocks of
western Wyoming and southeastern Idaho: American Association of Petroleum Geologists Bulletin, v. 54, p. 2282–2304.
Gans, P.B., 1987, An open-system, two-layer crustal stretching model for the
eastern Great Basin: Tectonics, v. 6, p. 1–12.
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., Repetski, J.E., Harris, A.G., and Clark, D.H., 1990, Conodont geothermometry of Paleozoic supracrustal rocks in the eastern Great Basin
997
[abs.]: Geology and ore deposits of the Great Basin: Geological Society
of Nevada, Symposium, Reno/Sparks, April 1990, Program with Abstracts, p. 103.
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.
Grauch, V.J.S., Jachens, R.C., and Blakely, R.J., 1995, Evidence for a basement feature related to the Cortez disseminated gold trend and implications for regional exploration in Nevada: Economic Geology, v. 90, p.
203–207.
Grauch, V.J.S., Rodriguez, B.D., and Wooden, J.L., 2003, Geophysical and isotopic constraints on crustal structure related to mineral trends in northcentral Nevada and implications for tectonic history: Economic Geology, v. 98, p. 269–286.
Groshong, R.H., Jr., 2006, 3-D structural geology, 2nd Edition: A practical
guide to quantitative surface and subsurface map interpretation: Berlin,
Springer, 400 p.
Hague, A., 1883, Abstract of report on the geology of the Eureka district, Nevada: U. S. Geological Survey 3rd Annual Report, p. 237–272.
Hague, A., 1892, Geology of the Eureka district, Nevada: U.S. Geological Survey Monograph 20 (with atlas), 419 p.
Hastings, M.H., 2008, Relationship of base-metal skarn mineralization to Carlin-type gold mineralization at the Archimedes gold deposit, Eureka,
Nevada: Unpublished M.S. thesis, University of Nevada, Reno, 111 p.
Hausen, D.M., and Kerr, P.F., 1968, Fine gold occurrence at Carlin, Nevada, in
Ridge, J.D., ed., Ore deposits of the United States, 1933–1967 (GratonSales Volume): New York, American Institute of Mining, Metallurgical,
and Petroleum Engineers, v. 2, p. 908–940.
Heller, P.L., Bowdler, S.S., Chambers, H.P., Coogan, J.C., Hagen, E.S., Shuster,
M.W., Winslow, N.S., and Lawton, T.F., 1986, Time of initial thrusting
in the Sevier orogenic belt, Idaho-Wyoming and Utah: Geology, v. 14,
p. 388–391.
Hofstra, A.H., Snee, L.W., Rye, R.O., Folger, H.W., Phinisey, J.D., Loranger,
R.J., Dahl, A.R., Naeser, C.W., Stein, H.J., and Lewchuk, M., 1999,
Age constraints on Jerritt Canyon and other Carlin-type gold deposits in
the western United States—relationship to mid-Tertiary extension and
magmatism: Economic Geology, v. 94, p. 769–802.
Hofstra, A.H., and Cline, J.S., 2000, Characteristics and models for Carlin-type
gold deposits, in Brown, P.E., and Hagemann, S.G.eds., Gold in 2000:
Reviews in Economic Geology, v. 13, p. 163–220.
Ilchik, R.P., and Barton, M.D., 1997, An amagmatic origin of Carlin-type gold
deposits, Economic Geology, v. 92, no. 3, p. 269–288.
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.
Katich, P.J., 1951, Recent evidence of Lower Cretaceous deposits in the Colorado Plateau: American Association of Petroleum Geologists Bulletin,
v. 35, p. 2093–2094.
.LUNODQG-,'LQRVDXUVGH¿QHDWZRIROG/RZHU&UHWDFHRXV]RQDWLRQRI
the Cedar Mountain Formation, central Utah [abs.]: Geological Society
of America Abstracts with Programs, v. 24, no. 6, p. 22.
Kuehn, C.A., and Rose, A.R., 1992, Geology and geochemistry of wall-rock
alteration at the Carlin gold deposit, Nevada: Economic Geology, v. 87,
p. 1697–1721.
Kuehn, C.A., and Rose, A.W., 1995, Carlin gold deposits, Nevada: Origin in
a deep zone of mixing between normally pressured and overpressured
ÀXLGV(FRQRPLF*HRORJ\YS±
Langlois, J.D., 1971, Hydrothermal alteration of intrusive igneous rocks in the
Eureka mining district, Nevada [M.S. thesis]: Tucson, University of
Arizona, 113 p.
998
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
Lawton, T.F., 1982, Lithofacies correlations within the Upper Cretaceous Indianola Group, central Utah, in Nielson, D.L., ed., Overthrust belt of
Utah: Utah Geological Association Publication 10, p. 199–213.
Lawton, T.F., 1985, Style and timing of frontal structures, thrust belt, central
Utah: American Association of Petroleum Geologists Bulletin, v. 69,
p. 1145–1159.
Lawton, T.F., Sprinkel, D., DeCelles, P.G., Mitra, G., and Sussman, A.J., 1997,
Thrusting and synorogenic sedimentation in the central Utah Sevier
thrust belt and foreland basin: Brigham Young University Geology
Studies, v. 42, part 2, p. 33–67.
Lisenbee, A.L., 2001, Structure and stratigraphy of the Eureka area, Nevada,
in Miller, M.S., and Walker, J.P., eds., Structure and stratigraphy of the
Eureka, Nevada, area: Nevada Petroleum Society, 2001 Fieldtrip Guidebook, p. 51–66.
Lisenbee, A.L., Monteleone, S.R., and Saucier, A.E., 1995, The Hoosac thrust
and related faults, Eureka region, Nevada, in Hansen, M.W., Walker,
J.P., and Trexler, J.H., Jr., eds., Mississippian source rocks in the Antler
basin of Nevada and associated structural and stratigraphic traps: Nevada Petroleum Society, 1995 Fieldtrip Guidebook, p. 115–121.
Long, S.P., 2012, Magnitudes and spatial patterns of erosional exhumation
in the Sevier hinterland, eastern Nevada and western Utah, USA: Insights from a Paleogene paleogeographic map: Geosphere, v. 8, no. 4,
p. 881–901.
Long, S.P., Henry, C.D., Muntean, J.L., Edmondo, G.P., and Cassel, E.J., 2014,
Early Cretaceous construction of a structural culmination, Eureka, Nevada, U.S.A.: Implications for out-of-sequence deformation in the Sevier hinterland: Geosphere, v. 10, no. 3, p. 564–584.
Lovering, T.G., 1962, The origin of jasperoid in limestone: Economic Geology,
v. 57, pp. 861–889.
MacNeil, F.S., 1939, Fresh water invertebrates and land plants of Cretaceous
age from Eureka, Nevada: Journal of Paleontology, v. 13, p. 355–360.
Margolis, J., 1997, Gold paragenesis in intrusion-marginal sediment-hosted
gold mineralization at Eureka, Nevada, in Vikre, P.G., Thompson, T.B.,
Bettles, K.H., Christensen, O.D., and Parratt, R.L., eds., Carlin-type
JROGGHSRVLWV¿HOGFRQIHUHQFH6RFLHW\RI(FRQRPLF*HRORJLVWV*XLGHbook Series, v. 28, p. 213–221.
Marsh, T.M., Einaudi, M.T., and McWilliams, M., 1997, 40Ar/39Ar geochronology of Cu-Au and Au-Ag mineralization in the Potrerillos district,
Chile: Economic Geology, v. 92, p. 784–806.
Miller, E.L., Gans, P.B., Wright, J.E., and Sutter, J.F., 1988, Metamorphic history of the east-central Basin and Range province: Tectonic setting and
relationship to magmatism, in Ernst, W.G., ed., Metamorphism and
crustal evolution of the western United States (Rubey Volume VII):
Englewood Cliffs, New Jersey, Prentice Hall, p. 649–682.
Mitra, G., 1997, Evolution of salients in a fold-and-thrust belt: The effects of
sedimentary basin geometry, strain distribution and critical taper, in
Sengupta, S., ed., Evolution of geological structures in micro- to macroscales: London, Chapman and Hall, p. 59–90.
Mortensen, J.K., Thompson, J.F.H., and Tosdal, R.M., 2000, U-Pb age constraints on magmatism and mineralization in the northern Great Basin,
Nevada, in Cluer, J.K., Price, J.G., Struhsacker, E.M., Hardyman, R.F.,
and Morris, C.L., eds., Geology and Ore Deposits 2000: The Great
Basin and Beyond: Geological Society of Nevada, Symposium, Reno/
Sparks, May 2000, Proceedings, v. 1, p. 419–438.
Muntean, J.L., Cline, J.S., Simon, A.C., and Longo, A.A., 2011, Magmatichydrothermal origin of Nevada’s Carlin-type gold deposits: Nature
Geoscience, v. 4, no. 2, p. 122–127.
Nevada Bureau of Mines and Geology, 2011, The Nevada mineral industry
2010: Nevada Bureau of Mines and Geology Special Publication MI2010, 151 p.
Nolan, T.B., 1962, The Eureka mining district, Nevada: U.S. Geological Survey
Professional Paper 406, 78 p., map scale 1:12,000.
Nolan, T.B., and Hunt, R.N., 1968, The Eureka mining district, Nevada, in
Ridge, J.D., ed., Ore deposits of the United States, 1933–1967 (GratonSales Vol.): New York, American Institute of Mining Metallurgy Petroleum Engineers, v. 1, p. 966–991.
Nolan, T.B., Merriam, C.W., and Williams, J.S., 1956, The stratigraphic section
in the vicinity of Eureka, Nevada: U.S. Geological Survey Professional
Paper 276, 77 p.
Nolan, T.B., Merriam, C.W., and Brew, D.A., 1971, Geologic map of the Eureka quadrangle, Eureka and White Pine Counties, Nevada: U.S. Geological Survey Miscellaneous Investigations Series Map I-612, scale
1:31,680, 8 p.
Nolan, T.B., Merriam, C.W., and Blake, M.C., Jr., 1974, Geologic map of the
Pinto Summit quadrangle, Eureka and White Pine Counties, Nevada:
U.S. Geological Survey Miscellaneous Investigations Series Map I-793,
scale 1:31,680, 14 p.
Olson, S.F., 1989, The stratigraphic and structural setting of the Potrerillos porphyry copper district, northern Chile: Revista Geológica de Chile, v.
16, p. 3–29.
Pape, J.R., Seedorff, E., Baril, T.C., and Thompson T.B., 2015, Structural reconstruction and age of normal faults, Spruce Mountain district, Elko
County, Nevada: Economic Geology, in revision.
Poole, F.G., 1974, Flysch deposits of the Antler foreland basin, western United
States, in Dickinson, W.R., ed., Tectonics and Sedimentation: Society
of Economic Paleontologists and Mineralogists Special Publication 22,
p. 58–82.
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., and Dilles, J.H., 1984, Geologic map of the Yerington district, Nevada: Nevada Bureau of Mines and Geology, Map 77, scale
1:24,000.
Radtke, A.S., 1985, Geology of the Carlin gold deposit, Nevada: U.S. Geological Survey Professional Paper 1267, 124 p.
Richards, J.P., Boyce, A.J., and Pringle, M.S., 2001, Geologic evolution of the
Escondida area, northern Chile: A model for spatial and temporal localization of porphyry Cu mineralization: Economic Geology, v. 96, p.
271–305.
Roberts, R.J., 1966, Metallogenic provinces and mineral belts in Nevada: Nevada Bureau of Mines Report 13, pt. A, p. 47–72.
Russell, K.D., 1996, West Archimedes gold deposit, in Green, S.M., and Struhsacker, E.M., eds., Geology and Ore Deposits of the American Cordillera: Geological Society of Nevada Field Trip Guidebook Compendium,
1995, Reno/Sparks, v. 1, p. 316–319.
Sapiie, B., and Cloos, M., 2004, Strike-slip faulting in the core of the Central
Range of west New Guinea: Ertsberg mining district, Indonesia: Geological Society of America Bulletin, v. 116, p. 277–293.
Schlische, R.W., 1995, Geometry and origin of fault-related folds in extensional
settings: American Association of Petroleum Geologists Bulletin, v. 79,
no. 11, p. 1661–1678.
Schmidt, C.J., and Perry, W.J., Jr., eds., 1988, Interaction of the Rocky Mountain foreland and the Cordilleran thrust belt: Geological Society of
America Memoir 171, 582 p.
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, 1991, Proceedings, v. 1, p. 359–391.
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.
Jackson normal fault system, Eureka district
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., and Takaichi, M.L., this volume, a, 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.
Seedorff, E., Richardson, C.A., and Maher, D.J., this volume, b, Fault surface
maps: Three-dimensional structural reconstructions and their utility in
exploration and mining: Geological Society of Nevada, Symposium,
Reno/Sparks, May 2015.
Shaw, J.H., Connors, C.D., and Suppe, J., 2005, Seismic interpretation of contractional fault-related folds: American Association of Petroleum Geologists, Studies in Geology No. 53, 156 p.
Shawe, D.R., 1991, Structurally controlled gold trends imply large gold resources in Nevada 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, 1991, Proceedings, v. 1, p. 199–212.
Sillitoe, R.H., 1972, A plate tectonic model for the origin of porphyry copper
deposits: Economic Geology, v. 67, p. 184–197.
Sillitoe, R.H., 1998, Major regional factors favouring large size, high hypogene
grade, elevated gold content and supergene oxidation and enrichment of
porphyry copper deposits, in Porter, T.M., ed., Porphyry and hydrothermal copper and gold deposits—A global perspective, Perth, Australia,
30 November–1 December 1998, Conference Proceedings: Glenside,
South Australia, Australian Mineral Foundation, p. 21–34.
Sillitoe, R.H., 2010, Porphyry copper systems: Economic Geology, v. 105, p.
3–41.
Sillitoe, R.H., and Bonham, H.F., Jr., 1990, Sediment-hosted gold deposits:
Distal products of magmatic-hydrothermal systems: Geology, v. 18, p.
157–161.
Simmons, G.C., 1957, Contact of the Burro Canyon Formation with the Dakota
Sandstone, Slick Rock district: American Association of Petroleum Geologists Bulletin, v. 41, p. 2519–2529.
Skármeta, J., McClay, K.R., and Bertens, A., 2003, Structural controls on porphyry copper deposits in northern Chile: New models and implications
for Cu-Mo mineralization in subduction orogens [abs.]: Congreso Geológico Chileno, Actas, 10th, Concepción, (unpaginated).
Snell, K.E., Koch, P.L., Druschke, P.A., Foreman, B.Z., and Eiler, J.M., 2014,
High elevation of the “Nevadaplano” during the Late Cretaceous: Earth
and Planetary Science Letters, v. 386, p. 52–63.
Speed, R.C., 1983, Evolution of the sialic margin in the central-western United
States, in Watkins, J.S., and Drake, C.L., eds., Studies in continental
margin geology: American Association of Petroleum Geologists Memoir 34, p. 457–468.
Speed, R.C., Elison, M.W., and Heck, F.R., 1988, Phanerozoic tectonic evolution of the Great Basin, in Ernst, W.G., ed., Metamorphism and crustal
evolution of the western United States: (Rubey Volume VII): Englewood Cliffs, New Jersey, Prentice-Hall, p. 572–605.
Staplin, F.L., 1977, Interpretation of thermal history from color of particulate
organic matter: A review: Palynology, v. 1, p. 9–18.
999
Stenger, D.P., Kesler, S.E., Peltonen, D.R., and Tapper, C.J., 1998, Deposition
RIJROGLQ&DUOLQW\SHGHSRVLWV7KHUROHRIVXO¿GDWLRQDQGGHFDUERQation at Twin Creeks, Nevada: Economic Geology, v. 93, 201–215.
Stokes, W.L., 1952, Lower Cretaceous in the Colorado Plateau: American Association of Petroleum Geologists Bulletin, v. 36, p. 1766–1776.
Taylor, H.P., 1979, Oxygen and hydrogen isotope relationships in hydrothermal mineral deposits, in Barnes, H.L., ed., Geochemistry of Hydrothermal Ore Deposits, 2nd Edition: New York, John Wiley and Sons, p.
109–142.
Taylor, W.J., Bartley, J.M., Fryxell, J.E., Schmitt, J.G., and Vandervoort, D.S.,
1993, Tectonic style and regional relations of the Central Nevada thrust
belt, in Lahren, M.M., Trexler, J.H., Jr., and Spinosa, C., eds., Crustal
evolution of the Great Basin and the Sierra Nevada, Geological Society
of America Fieldtrip Guidebook: Reno, University of Nevada, Department of Geological Sciences, p. 57–96.
Taylor, W.J., Bartley, J.M., Martin, M.W., Geissman, J.W., Walker, J.D., Armstrong, P.A., and Fryxell, J.E., 2000, Relations between hinterland and
foreland shortening: Sevier orogeny, central North American Cordillera: Tectonics, v. 19, p. 1124–1143.
Teal, L., and Jackson, M.R., 2002, Geologic overview of the Carlin trend gold
deposits. in Thompson, T.B., Teal, L., and Meeuwig, R.O., eds., Gold
deposits of the Carlin trend: Nevada Bureau of Mines and Geology Bulletin 111, p. 9–19.
Tschudy, R.H., Tschudy, B.D., and Craig, L.C., 1984, Palynological evaluation
of the Cedar Mountain and Burro Canyon Formations, Colorado Plateau: U.S. Geological Survey Professional Paper 1281, 24 p.
7KD\Q *) 7KUHH VSHFLHV RI SHWUL¿HG GLFRW\OHGRQRXV ZRRG IURP WKH
Lower Cretaceous Cedar Mountain Formation of Utah [Ph.D. thesis]:
Provo, Utah, Brigham Young University, 43 p.
Thompson, T.B., Teal, L., and Meeuwig, R.O., eds., 2002, Gold deposits of the
Carlin trend: Nevada Bureau of Mines and Geology Bulletin 111, 204 p.
Titley, S.R., 1993, Characteristics of high-temperature, carbonate-hosted massive sulphide ores in the United States, Mexico and Peru, in Kirkham,
R.V., Sinclair, W.D., Thorpe, R.I., Duke, J.M., eds., Mineral deposit
modeling: Geological Association of Canada Special Paper 40, p. 585–
614.
Tosdal, R.M., and Richards, J.P., 2001, Magmatic and structural controls on
the development of porphyry Cu ± Mo ± Au deposits: Reviews in Economic Geology, v. 14, p. 157–181.
Tosdal, R.M., Wooden, J.L., and Kistler, R.W., 2000, Geometry of the Neoproterozoic continental break-up, and implications for location of Nevadan
mineral belts, in Cluer, J.K., Price, J.G., Struhsacker, E.M., Hardyman,
R.F., and Morris, C.L., eds., Geology and ore deposits 2000: The Great
Basin and beyond, Geological Society of Nevada, Symposium, Reno/
Sparks, May 2000, Proceedings, v. 1, p. 451–466.
Tretbar, D.R., Arehart, G.B., and Christensen, J.N., 2000, Dating gold deposition in a Carlin-type gold deposit using Rb/Sr methods on the mineral
galkhaite: Geology, v. 28, p. 947–950.
Vandervoort, D.S., and Schmitt, J.G., 1990, Cretaceous to early Tertiary paleogeography in the hinterland of the Sevier thrust belt, east-central Nevada: Geology, v. 18, p. 567–570.
Vikre, P.G., 1998, Intrusion-related polymetallic carbonate replacement deposits in the Eureka district, Eureka County, Nevada: Nevada Bureau of
Mines and Geology Bulletin 110, 52 p.
Volk, J.A., Lauha, E.A., Leonardson, R.W., and Rahn, J.E., 1996, Structural
geology of the Betze-Post and Meikle deposits, Elko and Eureka Counties, Nevada, in Green, S.M., and Struhsacker, E.M, eds., Geology and
ore deposits of the American Cordillera: Geological Society of Nevada
Field Trip Guidebook Compendium, 1995, Reno/Sparks, p. 180–194.
Walker, J.D., Geissman, J.W., Bowring, S.A., and Babcock, L.E., 2013, The
Geological Society of America Geologic Time Scale: Geological Society of America Bulletin, v. 125, p. 259–272.
1000
Aryn K. Hoge, Eric Seedorff, Mark D. Barton, Carson A. Richardson, and Daniel A. Favorito
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.
Weiss, M.P., McDermott, J.G., Sprinkel, D.A., Banks, R.L., and Biek, R.F.,
2003, Geologic map of the Chriss Canyon quadrangle, Juab and
Sanpete Counties, Utah: Utah Geological Survey Map M-185, scale
1:24,000.
Wernicke, B.P., 2009, The detachment era (1977–1982) and its role in revolutionizing continental tectonics, in Ring, U., and Wernicke, B. P., eds.,
Extending a continent: Architecture, rheology and heat budget: Geological Society of London Special Publication 321, p. 1–8.
Wiltschko, D.V., and Dorr, J.A., Jr., 1983, Timing of deformation in overthrust
belt and foreland of Idaho, Wyoming, and Utah: American Association
of Petroleum Geologists Bulletin, v. 67, p. 1304–1322.
Witkind, I.J., Standlee, L.A., and Maley, K.F., 1986, Age and correlation of
Cretaceous rocks previously assigned to the Morrison(?) Formation,
Sanpete–Sevier Valley area, central Utah: U.S. Geological Survey Bulletin 1584, 9 p.
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., 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.
Yigit, O., Nelson, E.P., Hitzman, M.W., and Hofstra, A.H., 2003, Structural
controls on Carlin-type gold mineralization in the Gold Bar district, Eureka County, Nevada: Economic Geology, v. 98, no. 6, p. 1173–1188.