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Purpose of TripIGNEOUS-RELATED hydrothermal systems constitute the mostvaried type of geologic environment, ranging in tectonic set-ting from spreading centers to collisional belts, in depth fromthe surface to the deep crust, and in sources of materials frompurely magmatic to largely external. They comprise perhapsthe single most important ore-forming environment, yet mostigneous systems lack economically significant mineralization.This variety is attributable to igneous factors such as volatilecontent and its evolution from the intrusion, and to externalfactors that include depth of emplacement, host rocks, tec-tonic environment, and structural setting, which control per-meability and access of external fluids to the crystallized in-trusion and its contact aureole.

This field trip examines three large but markedly differentintrusion-centered hydrothermal systems in the westernGreat Basin of California and Nevada (Fig. 1, Table 1). Eachexample represents a major group of these systems world-wide. The field emphasis will be on examining mass transferfeatures—such as mechanisms for igneous emplacement, de-gassing of magmatic-aqueous fluids, and fracturing and duc-tile deformation—that allow variation from near-lithostatic tohydrostatic conditions, incursion of nonmagmatic fluids intothe high-temperature environment, and hydrothermal alter-ation, vein deposition, and wall-rock replacement via aqueous

fluids. The broader questions of metallogenic provinces andprocesses will be raised as a context for the specific sites ex-amined. The overall emphasis of this trip will be on docu-menting and understanding the dynamics of igneous-relatedhydrothermal systems.

This guidebook contains 10 papers that review the charac-teristics of these three systems and provide four independentand detailed guides, one for each day of the trip.

Trip route

The trip begins and ends in Reno, Nevada, and the route isillustrated on the cover and frontispiece of this guidebook.The first afternoon includes a drive from Reno to Bishop,California, via U.S. Highway 395, with a stop overlookingMono Lake and the eastern front of the Sierra Nevada. Thesecond day will be spent at Birch Creek in the southernWhite Mountains, which is located just east of Bishop in east-ern California (see Barton, 2000a, b). Following the BirchCreek visit, we will drive to Yerington, Nevada, via Bishopand Bridgeport, California. The next two days are spent in theYerington district, examining first the igneous history and ig-neous-hosted hydrothermal systems (see Dilles and Proffett,1995, Dilles et al., 2000b, and Lipske and Dilles, 2000). Thenext day, at Yerington, will focus on metamorphism and meta-somatism in the aureole (Einaudi, 2000) followed by a driveto Lovelock, Nevada. The final day we will tour central partsof the Humboldt mafic complex (see Johnson and Barton,2000a, b), returning to Reno in the evening.

Contrasting Styles of Intrusion-Associated Hydrothermal Systems—A Preface

MARK D. BARTON,† DAVID A. JOHNSON,Center for Mineral Resources, Department of Geosciences, University of Arizona, Tucson, Arizona 85721

JOHN H. DILLES,Department of Geosciences, Wilkinson Hall 104, Oregon State University, Corvallis, Oregon 97331

MARCO T. EINAUDI,Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305

AND DAVID A. JOHNSON

Center for Mineral Resources, Department of Geosciences, University of Arizona, Tucson, Arizona 85721

AbstractIntrusion-related hydrothermal systems represent a large variety of geologic environments that in some cases

form large metallic mineral deposits. The deposits examined in this trip represent the spectrum from systemsdominated by magmatic fluid (Birch Creek, California and Yerington, Nevada) to those systems in which in-trusions serve as heat engines to drive convectively circulating brines derived from sedimentary rocks (Hum-boldt, Nevada). In these examples, nonmagmatic fluids are largely excluded from more deeply emplaced in-trusions in a compressive environment, and the hydrothermal composition and ores (e.g., granite W-F, Cuporphyry and skarn) are dictated by the composition of the magma and its mechanism of crystallization andaqueous fluid generation. Magmatic fluids are less important in the shallow crustal ore environment, but ap-parently contribute to acidic alteration zones located vertically above source intrusions. Using Humboldt as anexample, we propose that the Fe oxide Cu-Au ores in the shallow environment require an abundant source ofsedimentary brines (typical of evaporitic environments), high fracture permeability (promoted by an exten-sional setting) to allow aqueous fluid flow and dike emplacement, and shallowly emplaced intrusions to serveas heat sources.

† Corresponding author: e-mail, barton@geo.arizona.edu

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I-80

95

395

95

50

50

208338

50

395

266

6Mono Lake

Lake Tahoe

Walker Lake

Pyramid Lake

Lovelock

FallonReno

Yerington

Carson City

Bridgeport

Bishop

Big Pine

Fernley

Hawthorne

N

0 100kilometers

0 100miles

Nevada

California

Cal

ifor

nia

Nev

ada

Cenozoic

Mesozoic intrusions

Other pre-Cenozoic

BirchCreek

Yerington

Humboldt

Yerington

BirchCreek

Late-Klithophile-elementsystems

JurassicFe or Cusystems

• Yerington

Humboldt•

>10%

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0-10%>10%

0-10%

0-10%

0-10%

0-10%

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>50%

>50%

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B.

Jurassicintrusions

(volume fraction)

Cretaceousintrusions

(volume fraction)

Birch •Creek

A.

FIG. 1. A. Field trip route and location of Birch Creek, Yerington, and Humboldt districts in the western Great Basin. B.Regional distribution of Jurassic and Cretaceous magmatic rocks, field trip locations, and are locations of similar occurrencesmentioned in the text.

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TABLE 1. Comparison of Systems

Birch Creek Yerington Humboldt

Type Lithophile-element greisen, skarn and vein Cu porphyry and skarn; Fe oxide Cu-Au) Fe oxide (Cu) replacement, skarn and vein breccia and vein

Age 82 Ma (U-Pb, Ar-Ar) 168–169 Ma (U-Pb) 165–170 Ma (U-Pb, K-Ar)

Tectonics Mildly compressive; pluton strongly Pluton moderately deforms aureole and roof; Extensional setting controls and structure deforms aureole; late dikes and veins radial? neutral to weak SW-NE extension controls emplacement of gabbro into

NW-striking porphyry dikes and veins upper crust; basalt dike swarms oriented NW-SE.

Size of Dispersed skarns within 1 km, veins to Skarns within 1.5 km, veins to ca. 3 km; Replacement bodies near hydrothermal ca. 5 km; ca. 10 to 20 km3 strongly altered ca. 50 to 150 km3 strongly altered volcanic-intrusive contact, veins to system ca. 2.5 km, rare skarns within 0.5

km; >550 km3 strongly altered.

Size of igneous ca. 4 × 5 km; vertical not known, ca. 12 × 15 km × >6 km vertical ca. 35 × 40 km by 4 km vertical systems likely >5 km (>100 km3 stock) (>1000 km3 batholith) (approx. 2500 km3 complex)

Igneous Water-rich, peraluminous biotite-muscovite Metaluminous, hydrous hornblende-pyroxene Hornblende(-olivine) gabbros and compositions granodiorite to granite quartz monzodiorite to hornblende-biotite basalts with low water contents

granite

Igneous evolution Several major pulses of magma from Emplaced initially as many compositionally Emplaced intially as separate multiple sources in expanding pluton similar pulses; evolved with time to large, centers coalescing with time to

broadly homogeneous, deep magma body form a large plutonic mass; separate eruption centers as dike swarms

Hydrothermal Igneous host: multiple pulses of high-T Igneous host: multiple centers of high-T Igneous host: multiple centers of alteration K-feldspar stable quartz veins, then more K-silicate alteration with broadly coeval high-T Na-Ca alteration with

dispersed greisens Na-Ca alteration; shallow environs dominated coeval lower T Na-Ca and Na by moderate-T sericite, pyrophyllite alteration in shallow environs

Sed host: skarnoid, then multiple high-T Gt-Id-Px skarn, dispersed mod-T sheet Sed host: Gt-Px skarnoid, then Gt-Px skarn, Sed host: minor Fe skarn (Px silicate-rich skarns and veins late hydrous skarn; skarn); Na alteration in other

areas

Hydrothermal Episodic fluid evolution throughout Episodic fluid evolution during emplacement Episodic circulation of external evolution emplacement history history; most magmatic and external fluids late brines throughout emplacement

history

Host rocks Late Proterozoic and Early Cambrian Early to middle Mesozoic volcanic, clastic Early to middle Mesozoic carbonate and clastic rocks and carbonate rocks volcanic, clastic and carbonate

rocks

Enrichments W-F-Be-Zn-Pb-Ag(-Bi-Sn) Cu(Mo)-Ag, Fe-Cu-Au Fe(-Cu-Co-Ni)

Level of exposure ~8–10 km 0–6 km 0–4 km

Fluids 5–10% NaCl, CO2-bearing 5–70% NaCl, minor COs saline brines (15–40% NaCl)

Source of fluids Magma Magma (Cu porphyry / skarn) and External brines external brines (Fe-Cu-Au)

Economic Small W(-Be-F-Zn) skarns and Moderate-sized porphyry Cu district Large magnetite resource (>500 significance Zn-Pb-Ag-Au veins (6 Mt Cu); large magnetite resource (>200 Mt) Mt), small Cu prospects,

local Ni-Co-Ag-As-U veins

Abbreviations: Gt = garnet; Px = pyroxene; Id = idocrase; T = temperature; Sed = sedimentary

Value of detailed field work

Each area has a well-defined geologic story that comesfrom detailed field work by many investigators, performed atat multiple scales and aimed at understanding the geologicsystems, not just particular aspects. Combining observationsof deformation, magmatism, metamorphism, and metasoma-tism allows a complete picture to emerge.

For example, in the Yerington district, parallel studies initi-ated by Anaconda Company in the 1960s involved 1:600-scalemapping of the details of porphyry copper geology in the Yer-ington mine, while, at the same time, 1:4800- to 1:12,000-scale mapping was done of district geology and hydrothermalalteration features. Detailed studies at the Yerington mine al-lowed the identification of different hydrothermal alterationtypes, their sulfide assemblages, and their age relative to em-placement of porphyry intrusions. Six separate intrusions,each serving as a time line, were mapped within the intrusivecenter. Relative ages were determined via crosscutting rela-tionships of different vein types with one another and veincutoffs by porphyries. At the kilometer scale, mapping wasconducted on host rocks (Proffett and Dilles, 1984), hornfelsand skarn zonation in the contact aureole (see Einaudi, 2000),and on hydrothermal alteration of the Yerington batholith(Dilles et al., 2000b), and overlying volcanics (see Lipske andDilles, 2000). These broader studies allow understanding ofpost-mineral tilting that provides a 6 km-crustal cross sectionand igneous emplacement history and processes, as well as re-construction of kilometer-scale hydrothermal fluid flow pathsvia mineralogical zonation in alteration assemblages (e.g.,Dilles and Einaudi, 1992).

Similarly, at Birch Creek, mapping of veins and dikes at themeter scale is linked with kilometer-scale mapping to deter-mine the emplacement history of the granite pluton, contactmetasomatic zonation, and structural controls (see Barton,2000a, b). In the Humboldt system, the detailed timing ofbasaltic dike emplacement and hydrothermal alteration isrecorded via meter-scale mapping in mine workings, and othercritical, nonmineralized exposures. Kilometer-scale mappingwas completed to understand the complex-scale distributionand timing of sodium-rich hydrothermal alteration and ironoxide and copper sulfide mineralization. Together these ob-servations allow a reconstruction of the igneous complex andassociated kilometer-scale hydrothermal system.

Time-space relationships

Another common theme among these areas is the synthesisof the systems in a time-space framework (e.g., Barton, 2000,Dilles et al., 2000a; Einaudi, 2000: Johnson and Barton,2000). This time-space framework is built on detailed cross-cutting age relationships established at numerous locations onthe meter scale (e.g., via 1:600-scale mapping of mine facies),and the mapping of spatial distribution of mineral assem-blages and veins on the kilometer scale. One of the problemswith such an approach is that although relative ages can be es-tablished at one location, the dynamics of the hydrothermalsystem require that temperature, pressure, and hydrothermalfluid composition and flow direction vary considerably at anyone point over time. As a result, similar hydrothermal alter-ation and mineralization features at widely separated locations

may have formed at different times or through the reactionof rocks with different fluids. The time-space syntheses illus-trated herein represent our best attempts at understandingthe relations of spatially separated assemblages.

At Birch Creek, the relatively small size of the magmaticsystem allows a very detailed reconstruction of igneous andhigh-temperature events within the intrusions via observationand mapping of granite contacts, dikes derived from thesecontacts, and veins. However, only the highest temperaturemetasomatic features in the intrusion (vein-dikes andgreisens) may be traced to events in the contact aureole; tem-poral and spatial connections of these proximal fluids to thedistal and lower temperature vein environment are more ten-uous and based mainly on geochemical evidence (Barton,2000a). Central questions in the Birch Creek system are, Whyis the system poorly mineralized? Is it that level of exposureis too deep? Are the granites too unevolved? Or does the sys-tem lose volatiles in a semicontinuous fashion so as to pre-clude focused fluid flow and magmatic concentration of met-als and ligands?

At Yerington, the time-space evolution of events in thedeep, central porphyry copper environments (Dilles et al.,2000b) may be compared with evolution of hornfels and cop-per skarn in the contact aureole (Einaudi, 2000) and the hy-drolytic alteration of the volcanic environment (Lipske andDilles, 2000); the time-space evolution of the Fe oxide-Cu-Aureplacement and lode deposits such as the Lyon (PumpkinHollow) deposit are less well known. Efforts to link these spa-tially separated environments require inferences of fluid flowpaths that cannot be demonstrated directly (e.g., Proffett andDilles, 1995; Dilles et al., 2000a). Central questions to be ad-dressed in the field excursions, not yet resolved, include tem-poral linking of events in the batholith, contact aureole, andvolcanic environments, e.g.,What are the time-space links be-tween deep porphyry copper K silicate and sericitic alterationtypes with volcanic sericitic and advanced argillic alterationtypes? How does the timing of the formation of contact aure-ole hornfels, Cu skarn, and Fe oxide deposits relate to timingof events in the batholith? One proposal, presented hereinbut still not fully tested, is that sedimentary brines that tra-versed deep parts of the Yerington batholith to cause sodic-calcic alteration also discharged into the shallow parts of thebatholith and the contact aureole to produce Fe oxide Cu-Aulode and replacement deposits (Dilles et al., 2000a).

At Humboldt, time-space evolution is constructed on thebasis of detailed observations in intermediate level mine ex-posures along the roof of the gabbroic rocks and from less in-tensely studied deeper and shallower exposures. Here, thetemporal evolution is well understood in the mine environ-ment, but lateral and vertical spatial zonation on the kilome-ter scale is less constrained by sparse exposures and a limitedvertical (>1.5 km) interval in contiguous sections. As at theYerington porphyry copper deposit, the observations at Hum-boldt allow for detailed construction of a time-temperatureevolution within one mine area from basalt intrusion to high-temperature scapolite-hornblende metasomatism to moder-ate-temperature magnetite ore replacements, and finally,low-temperature albitic and carbonate-chlorite assemblages(Johnson, 2000; Johnson and Barton, 2000b). Geochemicalstudies grounded in the field relationships at Humboldt show

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that enormous quantities of metals are redistributed duringhydrothermal alteration. Where did they go? What do welearn from this system of the nature of brine-rock interactionwhere magmatic fluids are minor or absent?

Comparison of SystemsThe Birch Creek, Yerington, and Humboldt intrusion-re-

lated hydrothermal systems have a common theme of hy-drothermal alteration centered on shallow crustal intrusions,but in detail they represent a spectrum from deep to shallow,from silicic to mafic magma composition, and from domi-nance by magmatic fluids to dominance by nonmagmaticbrines, respectively (Table 1).

Magmatic fluids

The magmatic end member is seen at Birch Creek, wherebiotite-muscovite granitoids were relatively deeply emplaced(ca. 10 km) in the Late Cretaceous into carbonate-clastic con-tinental shelf rocks in a compressional environment. Water-rich magma was emplaced as a series of discrete chemicallyunique pulses, and crystallized to yield abundant, Cl-F-richmagmatic aqueous fluids enriched in lithophile elements.

At Yerington and Humboldt, which are both part of a mid-dle Jurassic (170 to 165 Ma) magmatic event, host rocks in-clude volcanic rocks, clastic and carbonate sedimentary rocks,and evaporites. Both of these intrusions are emplaced shal-lowly (roofs at <1 to 2 km) but mapped to 6-km paleodepth.

The Humboldt mafic complex is dominated by an exten-sional tectonic environment that allowed basaltic magmas ac-cess to the shallow crust to form lavas, dike complexes, and alarge, volcano-plutonic complex. The tholeiitic basaltic mag-mas contained relatively low water contents, crystallized ashornblende (olivine) gabbro and produced, at most, minoramounts of relatively magmatic aqueous fluids.

Yerington is dominated by intermediate to silicic composi-tion, moderately water-rich quartz monzodiorite to granitemagmas that form a large differentiated batholith. Early mag-mas were emplaced as pulses that coalesced with time into alarge, deeper homogeneous magma chamber. Each intrusioncrystallized to hornblende and biotite-bearing granitoid andyielded Cl-rich magmatic aqueous fluids rich in sulfur, alkalis,and transition metals.

Hydrothermal features

Hydrothermal features differ greatly among the three envi-ronments, as reviewed below. The Birch Creek environmentcontains small-volume, very well developed, high-tempera-ture hydrothermal features characteristic of lithophile ele-ment-enriched systems closely linked to magmatic fluids.These include granite intrusions that are directly related toproximally emplaced aplite dikes, which grade out into abun-dant quartz veins and greisen alteration zones in granitichosts. In the contact aureole, Ca skarn and Mg skarn withweak W(-Be-F-Zn) mineralization and hornfels are devel-oped in strongly ductily deformed (folded, foliated) calcite,dolomite and clastic rocks within 1 km of the granite contact,and with small veins extending up to 5 km away.

In contrast, at Humboldt, there was little magmatic fluid,but large volumes of external, sedimentary-derived brines cir-culated through intermediate and shallow portions of the

complex. The complex comprises shallow gabbros, the basalticdike complex, and the overlying volcanic and sedimentaryrocks to produce an estimate of >900 km3 of sodic alteration(Johnson and Barton, 2000a). In the environment proximal todike swarms, alteration is dominated by high-temperaturescapolite-hornblende assemblages and later moderate-temperature massive iron oxide, whereas overlying rocks arealtered to albitic and carbonate-bearing assemblages.

Yerington forms a link between the two environments ex-posed at Birch Creek and Humboldt, and is intermediate insize and depth (ca. 100 km3 of altered rocks). The copper por-phyry and skarn environments were produced by saline mag-matic fluids associated with emplacement of granite porphyrydikes. Fracturing associated with magmatic fluids and dikeemplacement also allowed for access of external, sedimentarybrines to the Yerington batholith. These brines producedlarge quantities of deep (2- to 6-km depth) endoskarn, deepsodic-calcic plagioclase-actinolite and shallow propylitic (acti-nolite) alteration. In the latter environment and in the contactaureole, late and shallow Fe oxide Cu-Au deposits form thatare analogous to those at Humboldt. Discharge of magmaticfluids into the subvolcanic environment at Yerington pro-duced advanced argillic and sericitic alteration.

Similar features-major differences

In comparison with the other systems, the greater depthand lower permeability of wall rocks at Birch Creek allowedmagmatic fluids to dominate and produce a relatively long-lived and high-temperature hydrothermal system that waslargely under lithostatic pressure conditions and distributedaround the top of an equidimensional granitic stock. The rel-atively F-rich and lithophile element metasomatic zones werethus directly produced by processes in the peraluminousmagma that led to separation of a magmatic aqueous fluid.Fluid flow was dominantly unidirectional away from uppercontacts of several stocks (Barton, 2000a, b; Fig. 2).

In contrast, in the extensional environment at Humboldt,basaltic dike emplacement dominated and was accompaniedby little magmatic fluid. Instead, extensional fractures al-lowed access of local saline groundwater (derived from sea-water and coeval evaporites) to the magmatic “heat engine,”which served to drive a very large nonmagmatic hydrothermalconvection system under broadly hydrostatic pressures. Thehigh temperature of the basaltic magmas, high permeability,and large source of fluids in porous upper crustal sedimentaryrocks contributed to the large size of the hydrothermal sys-tem. Where the sedimentary brines heated, they causedsodium metasomatism and extracted Fe and Cu, which weredeposited in discharge zones with declining temperature andwall-rock reaction.

At Yerington, the oxidized hydrous magmas generated chlo-ride, metal, and sulfur-rich fluids that produced Cu-Fe sul-fide mineralization in the high-temperature, proximal Cuporphyry and skarn environments. Due to shallower em-placement and a mildly extensional environment (comparedto deep and compressive environment at Birch Creek), mag-matic aqueous fluids generated extensive planar, steeply dip-ping fracture systems that focused fluid flow and porphyry dikeemplacement. The magmatic hydrothermal fluids generatedchlacopyrite-bornite-magnetite ores with biotite-orthoclase

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alteration in cupola regions of nonventing dike swarms. Thesesame fluids, possibly diluted with nonmagmatic fluids, as-cended, cooled rapidly, and acidified to create pyrite-richsericitic and advanced argillic alteration. External fluids hadaccess to the crystallizing batholith at early stages only nearthe outer contact, where they produced endoskarn and horn-fels in the contact aureole. Following the late magmatic hy-drofracturing event, external fluids passed through the cen-tral and deep parts of the batholith, heated to produce sodicalteration, and ascended and cooled to produce Fe oxide Cu-Au mineralization. The nonmagmatic alteration is analogous,but smaller in volume, to that observed at Humboldt.

Major IssuesThis field trip and guidebook are intended to stimulate

discussion of major unresolved issues, among them the fol-lowing:

• What underlies the variability in hydrothermal systems? Isit province versus process? Is it level of exposure?

The evidence reviewed herein suggests that all of these el-ements are important factors. The magmatic conditions lead-ing to generation of ores related to magmatic fluids has beendiscussed by Barton (1996), who concluded that magma com-position is the most important factor, but that regional crustalcomposition, tectonic setting, depth of emplacement, and theprocesses of (1) mineralogical control on fluid composition,and (2) the efficacy of magmatic processes in producing ore-forming aqueous fluids are also key. The hydrothermal sys-tems dominated by external fluids, in our view, are moreclearly controlled by high permeability, availability of a largesource of saline nonmagmatic fluids, and a heat engine. Keyquestions include the following: How are large permeabilitiesgenerated in the upper crust? Where do saline sedimentaryfluids occur in abundance in the upper crust? What are theconditions that favor shallow emplacement of intrusions?

• What systems produce important ores? Are large depositsdue to an optimal combination of all the factors above, or arecertain processes or features of critical importance?

Hot brine, of either magmatic or sedimentary origin, is theessential ore fluid that transports and precipitates ores; in thecase of sulfide ores, a sulfur source is also key. What is the rel-ative importance of fluid salinity and volume (i.e., metal-car-rying ability) compared to efficient mechanisms of ore pre-cipitation as governed by thermal gradients and host-rockcomposition and reactivity?

• What do we learn from “barren” systems?

We believe we learn a lot! One can choose to look at thebest locations, where there are large vertical exposures, freshrocks, more complete magmatic histories, a simpler sequenceof hydrothermal events, etc., and may be able to see detailsthat are tough (if not impossible) to find in major districtswhere multiple hydrothermal events, surface weathering ofsulfide and consequent supergene alteration, and complexityand size of the system make for difficult understanding.

REFERENCESBarton, M.D., 1996, Granite magmatism and metallogeny of southwestern

North America: Transactions of the Royal Society of Edinburgh: EarthSciences, v. 87, p. 261–280.

——2000a, Overview of the lithophile element-beraring magmatic-hydro-thermal system at Birch Creek, White Mountains, California: Society ofEconomic Geologists Guidebook Series, v. 32, p. 9–26.

——2000b, Field trip day 1: Birch Creek, White Mountains, California: So-ciety of Economic Geologists Guidebook Series, v. 32, p. 27–43.

Dilles, J.H., and Einaudi, M.T., 1992, Wall-rock alteration and hydrothermalflow paths about the Ann-Mason porphyry copper deposit, Nevada—a 6km vertical reconstruction: Economic Geology, v. 87, p. 1963–2001.

Dilles, J.H., and Proffett, J.M., 1995, Metallogenesis of the Yeringtonbatholith, Nevada, in Pierce, F.W. and Bolm, J.G., eds., Porphyry CopperDeposits of the American Cordillera: Arizona Geological Society Digest20, p. 306–315.

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10 k

m

Magmatic fluids

External fluids

Intrusion:Fluid Source &“Heat Engine”

Horizontal scales from 2 - 20 km

Yeringtonexposures

Humboldtexposures

Birch Creekexposures

FIG. 2. Sources of fluids and scales of hydrothermal alteration in some intrusion-related hydrothermal systems, showingcontrasting proportions of magmatic and nonmagmatic fluids in shallow (A) and deep (B) environments (modified from John-son, 2000).

A B

Dilles, J.H., Einaudi, M.T., Proffett, J.M., and Barton, M.D., 2000a, Overviewof the Yerington porphyry copper district: Magmatic to nonmagmaticsources of hydrothermal fluids, their flow paths, alteration affects onrocks, and Cu-Mo-Fe-Au ores: Society of Economic Geologists Guide-book Series, v. 32, p. 55–66.

Dilles, J.H., Proffett, J.M., and Einaudi, M.T., 2000b, Field Trip Day 2: Mag-matic and hydrothermal features of the Yerington batholith with emphasison the porphyry Cu-(Mo) deposit in the Ann-Mason area: Society of Eco-nomic Geologists Guidebook Series, v. 32, p. 67–89.

Einaudi, M.T., 2000, Skarns of the Yerington district, Nevada: A triplog andcommentary with applications to exploration: Society of Economic Geolo-gists Guidebook Series, v. 32, p. 101–125.

Johnson, D.A., 2000, Comparative studies of iron-oxide mineralization: GreatBasin: Unpublished Ph.D. dissertation, University of Arizona, 451 p.

Johnson, D.A., and Barton, M.D., 2000a, Field trip day 4: Buena Vista Hills,Humboldt mafic complex, western Nevada: Society of Economic Geolo-gists Guidebook Series, v. 32, p. 145–162.

——2000b, Time-space development of an external brine-dominated ig-neous-driven hydrothermal system: Humboldt mafic complex, westernNevada: Society of Economic Geologists Guidebook Series, v. 32, p. 127–143.

Lipske, J.L., and Dilles, J. H., 2000, Advanced argillic and sericitic alterationin the subvolcanic environment of the Yerington porphyry copper district,Buckskin Range, Nevada: Society of Economic Geologists Guidebook Se-ries, v. 32, p. 91–99.

Proffett, J.M., Jr., and Dilles, J.H., 1984, Geologic map of the Yerington dis-trict, Nevada: Nevada Bureau Mines Geologic Map 77, scale 1:24,000.

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