Major Gold Deposits SillitoeCordillera2008

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IntroductionGOLD DEPOSITS occur at numerous localities along the fulllength of the North and South American Cordillera, fromAlaska in the north to Patagonia in the south. The Cordillerahas a long and colorful gold-mining history dating back to the16th century, since when the cumulative production plus cur-rent reserves of the yellow metal total >1,000 Moz (30,000metric tons), ~20 percent of the known global total. Today, sixof the top 20 gold-producing countries of the world are lo-cated there. Cordilleran gold is contained in a spectrum of widely recognized and well-documented ore deposit types(e.g., Robert et al., 2007; Fig. 1; Table 1) generated in a vari-ety of tectonomagmatic settings, a situation in marked con-trast to the majority of tin or copper resources, which in the

western Americas are hosted almost exclusively by single de-posit types (e.g., Turneaure, 1971; Sillitoe and Perelló, 2005).Most of the major Cordilleran gold deposits and belts areMesozoic or Cenozoic in age (Table 2), although it should beremarked that the major Homestake deposit in South Dakota,

not considered further herein, is Paleoproterozoic and part of the cratonic basement to the North American Cordillera(Slaughter, 1968; Fig. 2).

This analysis incorporates all gold belts and isolated de-posits in the western Americas that are estimated to contain≥ 10 Moz (>~300 t) of gold (Fig. 2; Table 2), an approach thatprobably takes account of at least three-quarters of the re-gion’s gold endowment. Only gold concentrations withdemonstrated economic potential or a reasonable chance of commercial production are considered. By-product gold inbase metal and silver deposits is ignored, although gold-rich

Special Paper:

Major Gold Deposits and Belts of the North and South American Cordillera:Distribution, Tectonomagmatic Settings, and Metallogenic Considerations

RICHARD H. SILLITOE

27 West Hill Park, Highgate Village, London N6 6ND, England

AbstractA compilation of economically viable gold concentrations containing≥ 10 Moz in the North and South

American Cordillera reveals the existence of 22 discrete belts in addition to five major isolated deposits, mostformed over the last 150 m.y. The gold concentrations are attributed to eight widely recognized deposit types,of which porphyry, sediment-hosted, and high-sulfidation epithermal are economically the most important.Individual gold belts are typically several tens to hundreds of kilometers long, dominated by single deposittypes, and metallogenically active for relatively brief periods (<5–20 m.y.).

Many of the gold belts and major isolated deposits were generated under extensional or transtensional tec-tonic conditions in either arc or back-arc settings. Nevertheless, the two main high-sulfidation epithermal goldbelts were generated in thickening or already-thickened crust during low-angle subduction. Eight other goldbelts or districts also accompanied compression or transpression, with two of them, the main orogenic goldbelts, occupying fore-arc sites. There is a strong suggestion that the preeminent Cordilleran gold concentra-tions formed either during or immediately following prolonged contraction. The major gold deposits and beltsoccur along the craton edge as well as in adjoining accreted terranes, but almost all are of postaccretionary tim-ing. Many of the gold belts and isolated deposits were localized by crustal-scale faults or lineaments, which may be either parallel or transverse to the Cordilleran margin.

The gold concentrations accumulated during active subduction, commonly in close spatial and temporalassociation with intermediate to felsic, medium- to high-K calc-alkaline igneous rocks. By contrast, the low-sulfidation epithermal gold deposits accompany bimodal volcanic pulses of calc-alkaline, tholeiitic, or alkalineaffinity. However, a gold-alkaline rock association is uncommon. A genetic link between gold mineralizationand coeval magmatism is widely accepted for most of the deposit types, the exceptions being the sediment-hosted and orogenic gold deposits.

Notwithstanding the small cumulative extent of the gold concentrations relative to the entire Cordilleranmargin, there is a marked tendency for two or more belts or isolated deposits of different ages and genetic typesto occur in close proximity within relatively restricted arc (including fore- and back-arc) segments. In the caseof the western United States, for example, six belts and four isolated major deposits make up a particularly

prominent cluster. If fortuity is discounted, this clustering or pairing of gold concentrations must imply a pre-disposition of certain arc segments to gold mineralization. An analogous situation is evident for other metals,particularly copper and tin. The reason for the recurrent generation of major deposits and belts dominated by one or more metals remains uncertain, although heterogeneously distributed metal preconcentrations, favor-able redox conditions, or other parameters somewhere above the subducted slab, between the mantle wedgeand upper crust, are widely contemplated possibilities. Elucidation of the reason(s) for this metallogenicinheritance at the scale of limited arc segments poses an important and challenging series of research questionsas well as being critical to the planning of potentially successful greenfield exploration programs.

E-mail: [email protected]

©2008 Society of Economic Geologists, Inc.Economic Geology, v. 103, pp. 663–687



porphyry copper deposits are included if either the value of the contained gold roughly equals or exceeds that of the cop-

per, or the gold endowment is metallogenically outstanding(e.g., Bingham Canyon, Utah; Pebble, Alaska; Fig. 2). The in-dividual gold belts are defined by either single or several oredeposit types, one of which tends to predominate, and weregenerated during relatively restricted metallogenic epochs,most of which have been reasonably well defined by isotopicdating (Table 2).

The paper summarizes the distribution and tectonomag-matic settings of the principal gold concentrations in the western Americas (including the Caribbean region) and,thereby, highlights the preeminent tectonic and associatedigneous activity that controlled and influenced gold depositformation here over the last 150 m.y. or so. Tectonomagmaticaspects are emphasized over deposit-scale physicochemical

conditions and mechanisms throughout this discussion. Thepaper is organized by gold deposit type, although skarn de-posits are not considered further in view of their relatively minor contribution (Table 1) and typical close association with other intrusion-related deposit types. A prefatory sec-tion provides a brief summary of gold deposit types and theirrelative economic importance in the American Cordillera. Aconcluding synthesis of the tectonomagmatic settings forgold and comparisons with the main Cordilleran copper andtin belts provides the basis for comment on broader metal-logenic issues, particularly the concepts of provinciality and

inheritance. Finally, some suggestions for future research areoffered.

Gold Deposit TypesThe western American Cordillera contains most of the

world’s economically important gold deposit types (Fig. 1;Table 1). The gold deposits are attributable to five broad cat-egories: epithermal deposits in shallow volcanic environ-ments; porphyry copper-gold or gold-only deposits in the sub- volcanic environment; sediment-hosted (or Carlin-type)deposits in nonmetamorphosed, carbonate-rich sedimentary sequences; pluton-related deposits in deeper, but still epi-zonal intrusive environments; and orogenic deposits in meta-morphic rocks, commonly assignable to greenschist facies.

Some investigators currently subdivide the epithermaldeposits of both vein and disseminated styles into high-, in-

termediate-, and low-sulfidation types, as defined by miner-alogic criteria (Hedenquist et al., 2000; Sillitoe and Heden-quist, 2003; Table 1). The porphyry deposits are typically large and always in the form of stockworks, whereas the sed-iment-hosted deposits are predominantly disseminated instyle and controlled by a combination of faults and receptivestratigraphy. The pluton-related deposits range from veinsand vein swarms to stockworks, but include other styles(Thompson et al., 1999; Lang and Baker, 2001; Fig. 1). Thepluton-related deposits are divisible into two distinct classesdepending on the redox state (e.g., Ishihara, 1977) of their

664 RICHARD H. SILLITOE

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V V V V V V V V V V V V

V V V V V V V V V V V V

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V

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Low-sulfidationepithermal Au

Volcanicrocks

Limestone

Limestone

Turbidite

km0

1

5

10

Greenstone

Orogenic lode Au

Shear zoneGranitoid

Oxidized orreduced felsicequigranular

intrusion

Carbonaceous +calcareous siltstone

Sediment-hostedAu

Porphyry Cu-Au/Au(±skarn)

Porphyryintrusion

Inferredfelsic

intrusion

Pluton-relatedAu (±skarn)

Dike

g -su a onepithermal Au

Intermediate-sulfidationepithermal Au

Placer Au

Volcanicrocks

FIG. 1. Schematic geologic settings and interrelationships of the principal gold deposit types in the North and South Amer-ican Cordillera, inspired by Robert et al. (2007). The approximate depth scale is logarithmic. Selected deposit characteristicsare summarized in Table 1. Note that placer gold is most commonly derived by erosion of orogenic and pluton-relateddeposits.



genetically related plutons: deposits related to relatively re-duced, magnetite-poor (and commonly ilmenite-bearing) in-trusions contain minor amounts of lithophile elements but noappreciable base metals (Thompson et al., 1999), whereasthose with oxidized, magnetite-bearing intrusions containmodest amounts of base metals (Table 1). The orogenicdeposits are typically in the form of quartz veins and vein ar-rays. Clearly, depth of erosion is a cogent control on the dis-tribution of outcropping gold deposit types. For example,

many epithermal deposits are removed once erosional depthsexceed 1 km (Sillitoe, 1993; Fig. 1) whereas orogenic gold de-posits are only exposed once erosion has reached paleodepthsranging from 3 to 15 km (Goldfarb et al., 2001).

The perceived role of magmatism as a source of the gold-bearing fluids responsible for the different deposit types is farfrom straightforward. Porphyry and pluton-related gold de-posits are generally accepted to be products of dominantly magmatic fluids derived from subjacent parental intrusions,and a similar—albeit generally more distant—magmatic con-nection is now widely accepted for epithermal deposits (e.g.,

Sillitoe and Hedenquist, 2003; Table 1). However, continueddiscussion surrounds the origin of sediment-hosted gold de-posits, with heated meteoric, metamorphic, and diluted mag-matic fluids preferred by different investigators (see Munteanet al., 2004). Orogenic gold deposits are widely considered tolack a close genetic association with intrusions (Goldfarb etal., 2001), although both deeply sourced metamorphic andmagmatic fluids remain viable alternatives (Table 1). It shouldbe cautioned, however, that distinction between pluton-re-

lated and orogenic gold deposits is commonly not straightforward because both typically formed from dilute, CO2-rich flu-ids as a consequence of their relatively deep settings (Sillitoeand Thompson, 1998; Groves et al., 2003). A case in point isthe Pataz-Parcoy belt in northern Peru (Fig. 2), which is as-signed herein to the oxidized pluton-related category becauseof the close association of the quartz veins with porphyrydikes, but considered as orogenic by others (Haeberlin et al.,2004). Of course, if pluton-related and orogenic gold deposits were both products of magmatic fluids, the distinction wouldbecome largely arbitrary anyway.

SPECIAL PAPER: MAJOR GOLD BELTS OF THE NORTH AND SOUTH AMERICAN CORDILLERA 665

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TABLE 1. Key Features of Main Gold Deposit Types in the American Cordillera

Contributionto totalCordilleran Principal Characteristic

Gold deposit gold endow- mineralization accompanying Typical Typical proximaltype ment (%)1 style(s) elements host rocks alteration type(s) Ore fluid Reference

Stockwork, Andesitic to

High-sulfidation disseminated, dacitic volcanic Mixed magmatic- Simmonsepithermal Au 16 veins, breccias Cu, As, Ag rocks + basement Advanced argillic meteoric et al. (2005)

Intermediate- Andesiticsulfidation Veins, Ag, Zn, Pb, Cu, to dacitic Intermediate Mixed magmatic- Simmonsepithermal Au 6 stockwork As, Sb, Mn volcanic rocks argillic ± adularia meteoric et al. (2005)

Low-sulfidation Veins, Felsic and basaltic Intermediate Mixed magmatic- Simmonsepithermal Au 6 disseminated As, Sb, Zn, Pb volcanic rocks argillic ± adularia meteoric et al. (2005)

Alkalic low-sulfidation Disseminated, Alkaline Intermediate Simmonsepithermal Au 3 veins Te, V, F volcanic rocks argillic ± adularia Magmatic et al. (2005)

Quartz dioriteto granodiorite Potassic, inter-

Porphyry Stockwork + porphyry stocks mediate argillic,Cu-Au 20 disseminated Mo + wall rocks sericitic Magmatic Sillitoe (2000)

Diorite to quartzdiorite stocks + Potassic, inter- Vila andPorphyry Au 2 Stockwork Cu, Mo wall rocks mediate argillic Magmatic Sillitoe (1991

Irregular tostrata-bound As, Bi, Te or Meinert

Skarn Au 4 replacements Cu, Zn, Pb Carbonate rocks Calc-silicate Magmatic et al. (2005)

Reduced pluton- Sheeted veins, As, Bi, Te, Felsic plutons + Alkali feldspar, Thompsonrelated Au 5 stockworks W, Mo wall rocks sericitic Magmatic et al. (1999)

Oxidized pluton- Sheeted veins, Felsic plutons + Alkali feldspar,related Au 4 stockworks Zn, Pb, Cu, Mo wall rocks sericitic Magmatic Sillitoe (1991)

Mixed magmatic-Sediment- Impure Decalcification, meteoric, meteoric, Clinehosted Au 21 Disseminated As, Sb, Hg, Tl carbonate rocks silicification or metamorphic et al. (2005)

Greenschist-facies Sericite Metamorphic Veins, metavolcano- (Cr mica)- and/or deep- Goldfarb

Orogenic Au 13 stockworks As, Te sedimentary rocks carbonate seated magmatic et al. (2005)

1 Based on production and/or reserves plus resources (measured + indicated categories), as listed in Table 2




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TABLE 2. Summary Characteristics of Principal Gold Belts and Isolated Deposits in the American Cordillera1

Gold belt/ Au content Preeminent Main (subsidiary) Mineralization Regional Related Syntheticdeposit (Moz)2 deposit(s) Au deposit type(s) age, Ma tectonic setting magmatic rocks reference(s)

Reduced calc- Hart et al. (2002),Kuskokwim Donlin Reduced Back-arc alkaline stocks Goldfarbbelt, Alaska 23 Creek pluton-related 71–65 transpression and dikes et al. (2004)

Uncertain, pos- Calc-alkaline BouleyPebble, Alaska 82 Pebble Porphyry Cu-Au ~90 sible compression stocks and sills et al. (1995)

Fairbanks-Tombstone belt, Reduced calc- McCoy et al.Alaska-Yukon Fort Knox, Reduced Back-arc alkaline stocks (1997), HartTerritory 29 Pogo pluton-related 104; 93-91 weak extension and plutons et al. (2002)

Klondike Early-Middle Localized exten- Rushton et al.distric t, Yukon Klondike Jurassic (?) sion following (1993), MacKenzieTerritory 13 placers Orogenic (<178) compression None et al. (2007)

Calc-alkaline Goldfarb et al.Juneau belt, Forearc plutons in nearby (1988, 1997), Mil-Alaska 12 Kensington Orogenic 56–53 transpression batholith ler et al. (2000)

Independence Low-magnitude Calc-alkalinetrend, Nevada 14 Jerritt Canyon Sediment-hosted ~42–36 extension dikes Cline et al. (2005)

Getchell trend, Low-magnitude Calc-alkalineNevada 35 Twin Creeks Sediment-hosted ~42–36 extension dikes Cline et al. (2005)

Cline et al.Carlin trend, Low-magnitude Calc-alkaline (2005), Ressel andNevada 105 Goldstrike Sediment-hosted ~42–36 extension felsic dikes Henry (2006)

Battle Mountain- Calc-alkalineEureka trend, Pipeline, Sediment- Low-magnitude felsic stocksNevada 57 Cortez Hills hosted (skarn) ~42–36 extension + dikes Cline et al. (2005)

Northern Nevada Low-sulfidation Tholeiitic basalt-rift, Nevada 11 Midas epithermal 16–14 Backarc extension rhyolite volcanics John (2001)

Initiation ofPorphyry Cu-Au extension or High-K calc-

Bingham Bingham (skarn, sediment termination of alkaline stocks Babcock

district, Utah 55 Canyon hosted) 39–37 compression and volcanics et al. (1995)Round Mountain, Round Low-sulfidation Calc-alkaline HenryNevada 14 Mountain epithermal 26 Extension volcanics et al. (1996)

Intermediate-sulfidation(low-sulfidation, Calc-alkaline

Walker Lane, Comstock high-sulfidation) volcanics andNevada 47 Lode epithermal 21–4 Transtension stocks John (2001)

Calc-alkaline Böhlke andSierra Foothills Forearc plutons in Kistler (1986),belt, California 100 Mother Lode Orogenic 135–115 transpression nearby batholith Marsh et al. (2007)

Transition fromcompression

Alkaline low- to backarc Bimodal alkaline Kelley et al.

Cripple Creek, Cripple sulfidation (Rio Grande volcanics and (1998), RampeColorado 30 Creek epithermal 31.6–28.4 rift) extension minor intrusions et al. (2005)

Sierra Madre Intermediate- Calc-alkaline Albinson et al.Occidental, Tayoltita, sulfidation volcanics and (2001), CamprubíMexico 22 El Oro epithermal 36–27 Extension stocks et al. (2003)

Pueblo Viejo, Kesler et al.Dominican High-sulfidation Inferred calc- (1981), SillitoeRepublic 24 Pueblo Viejo epithermal ~77–62 Extension (?) alkaline stock et al. (2006)

González (2001),Segovia belt, Oxidized Oxidized calc- AngloGoldColombia 24 Frontino pluton-related ~160 Extension alkaline plutons Ashanti (2007)



Epithermal, porphyry, and sediment-hosted deposits ac-count for three-quarters of Cordilleran gold endowment(Table 1). Sediment-hosted deposits clearly dominate in west-ern North America, whereas high-sulfidation epithermaldeposits are preeminent in the Andes, including theCaribbean region (Fig. 2; Table 2). These types are followedin importance by orogenic and pluton-related deposits if ap-preciable quantities of derivative placer gold are included(Fig. 2). Individually, the low- and intermediate-sulfidationepithermal as well as the skarn-type deposits make only mod-est contributions to the total Cordilleran gold inventory.

Tectonomagmatic Settings

High-sulfidation epithermal gold depositsThe Cajamarca-Huaraz belt in northern Peru and El

Indio-Maricunga belt in northern Chile, each ~400 km long,and the Pueblo Viejo district in the Dominican Republic arethe three main concentrations of large high-sulfidation ep-ithermal gold deposits in the American Cordillera (Fig. 2;Table 2), although smaller examples occur in the WalkerLane, Nevada (Goldfield, Paradise Peak; Fig. 3) and Sierra

Madre Occidental, Mexico gold belts, and elsewhere. Thelarge, high-sulfidation deposits are hosted by either volumi-nous, long-lived volcanic complexes of medium-K andesitic-dacitic-rhyolitic composition (e.g., Yanacocha, northern Peru;Longo and Teal, 2005) or basement rocks unaffected by ap-preciable contemporaneous volcanism (e.g., Pascua-Lama,northern Chile-Argentina: Bissig et al., 2001; Pueblo Viejo,Dominican Republic: Sillitoe et al., 2006).

Both the Cajamarca-Huaraz and El Indio-Maricunga beltsoccur within the two late Miocene to Recent, amagmatic, flat-slab segments of the central Andes defined by Barazangi and

Isacks (1976). However, the temporal and, hence, genetic re-lationships between the major high-sulfidation gold depositsand the slab flattening and eventual cessation of magmatismare not everywhere the same.

In the Cajamarca-Huaraz belt, the oldest major high-sulfi-dation gold deposits (e.g., Alto Chicama, Pierina), along withthe porphyry copper-gold deposits at Minas Conga and CerroCorona (Fig. 4), were formed from ~17 to 14 Ma (Noble andMcKee, 1999; Gustafson et al., 2004) during a noncompres-sive interval between the Quechua I (19.5–17 Ma) andQuechua II (~9 Ma) tectonic pulses (Noble and McKee,


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Porphyry Au(intermediate-sulfidation Calc-alkaline

Middle Cauca Colosa, epithermal, volcanics and Cediel

belt, Colombia 16 Marmato porphyry Cu-Au) 8–6 Transpression stocks et al. (2003)Sillitoe et al.

55–43 (1982), Anglo-Chocó belt, (porphyry Cu- Calc-alkaline Gold AshantiColombia 10 Placers Uncertain Au prospects) Probably extension stocks (2007)

Fruta del Intermediate- Calc-alkalineZamora belt, Norte, sulfidation volcanics, stocks, FontbotéEcuador 23 Nambija epithermal (skarn) ~155–146 Transtension and plutons et al. (2004)

Oxidized calc-Pataz-Parcoy Oxidized alkaline plutons Haeberlinbelt, Peru >10 Pataz pluton-related 314–312 Compression and dikes et al. (2004)

Medium- toCajamarca- High-sulfidation high-K calc- Noble and McKeeHuaraz belt, epithermal Episodic alkaline volcanics (1999), LongoPeru 86 Yanacocha (porphyry Cu-Au) 17–8.4 compression and stocks and Teal (2005)

El Indio: Medium- toEl Indio- High-sulfidation ~10–6.2 high-K calc- Kay et al. (1994),Maricunga belt, Pascua-Lama, epithermal Maricunga: Postcompression alkaline volcanics Bissig et al.Chile 81 El Indio (porphyry Au) 23–21; 12–10 relaxation and stocks (2001, 2003)

Porphyry Cu-AuFarallón (intermediate- High-K calc-Negro district, Bajo de la sufidation Initiation of alkaline stocks Sasso andArgentina 19 Alumbrera epithermal) 8–4.9 compression and volcanics Clark (1998)

Patagonian Calc-alkalineprovince, Cerro Low-sulfidation rhyolite-basalt SchalamukArgentina-Chile 15 Vanguardia epithermal ~160–150 Back-arc extension volcanics et al. (1997)

1 Gold belts and isolated deposits listed from north to south (Fig. 2)2

Production and/or reserves plus resources (measured + indicated categories)

TABLE 2. (Cont.)

Gold belt/ Au content Preeminent Main (subsidiary) Mineralization Regional Related Syntheticdeposit (Moz)2 deposit(s) Au deposit type(s) age, Ma tectonic setting magmatic rocks reference(s)



1999). In contrast, development of the giant Yanacocha high-sulfidation gold district spanned the 13.6 to 8.2 Ma interval(Longo and Teal, 2005), temporally closer to the final cessa-tion of magmatism in the Peruvian flat-slab segment at ~4 Ma(Noble and McKee, 1999). A change at Yanacocha from dom-inantly andesitic volcanism to emplacement of small volumesof highly oxidized, dacitic to rhyolitic magma at 9.8 Ma(Longo and Teal, 2005) may chart an advanced stage of slabflattening, contraction, and crustal thickening.

The major high-sulfidation gold deposits in the El Indio-

Maricunga belt (Pascua-Lama, Veladero, and El Indio-Tambo) formed from ~10 to 6.2 Ma (Jannas et al., 1999; Bis-sig et al., 2001; Charchaflié et al., 2007), after andesitic volcanism in the segment had ceased (Kay et al., 1999) andcompressive tectonism had migrated eastward (Bissig et al.,2003; Charchaflié et al., 2007). The gold mineralization ac-companied volumetrically minor silicic magmatism (cf.Yanacocha district) in tectonically thickened crust at high el-evations during flat-slab subduction (Kay and Mpodozis,2001, 2002; Bissig et al., 2003). However, the upper crustmay have been weakly extended in places at the time of gold

mineralization as a result of gravitational instability conse-quent upon the high elevation (e.g., Veladero: Charchafliéet al., 2007).

Recently presented alteration and lithogeochemical evi-dence suggests that the Pueblo Viejo high-sulfidation gold de-posits in the Dominican Republic were generated as part of aregionally extensive Late Cretaceous to Paleogene vol-canoplutonic arc (e.g., Lebrón and Perfit, 1994) rather thanbeing genetically related to the hosting bimodal volcanic suc-cession of island-arc tholeiite composition and Early Creta-

ceous age (Sillitoe et al., 2006). The tectonic regime that prevailed in the Late Cretaceous to Paleogene arc, defined by both calc-alkaline intrusive and extrusive rocks, remains to bedefined, although extensional conditions are a distinct possi-bility given the inferred existence of a broadly contempora-neous back-arc basin (Mann et al., 1991).

Cross-arc zones of Miocene tectonomagmatic activity, up toseveral tens of kilometers wide, appear to have localized theAlto Chicama and Yanacocha high-sulfidation gold deposits inthe Cajamarca-Huaraz belt. In the case of Yanacocha, Quiroz(1997), followed by Turner (1999) and Longo and Teal


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Fairbanks-Tombstone beltRPR20(9)

KlondikeORO(13)

Juneau beltORO 12 HomestakeORO 40

Bingham districtPCu, skarn,sedh 55

Cripple CreekLS30 Pueblo Viejo

HS24

Getchell trendSEDH 35

Independence trendSEDH14

Carlin trendSEDH 105

Sierra Foothills beltORO 35(65)

Walker LaneLS, IS, hs, sedh 47

North Nevada riftLS11

Round MountainLS14 Segovia belt

OPR13(11)

Cajamarca-Huaraz beltHS, pCu, ls79(7)

Pataz-Parcoy beltOPR>10

El Indio-MaricungabeltHS, pAu81 Farallón

Negro districtPCu, is19Patagonian province

LS15

Pacific Ocean

1 2 0 °

1 0 5 °

9 0 °

7 5 °

6 0 °

4 5 °

1 3 5 °

1 5 0 °

1 7 5 °

45°

30°

15°

0°

15°

30°

45°

60°

1000 km1000 km

Kuskokwim beltRPR 20(3)

PebblePCu 82

Sierra Madre OccidentalLS, IS22

Battle Mountain-Eurekatrend SEDH, skarn57

Middle Cauca belt

PAu, is, pCu15(1)

Chocóbelt(10)

Zamora beltIS, skarn 22(1)

Miocene

Oligocene

Eocene

Late Cretaceous

Jurassic

Carboniferous

Proterozoic

SEDH Sediment hostedORO OrogenicRPR Reduced pluton relatedOPR Oxidized plutonrelatedPCu Porphyry Cu-AuPAu Porphyry Au

SKARNSkarnHS High-sulfidation epithermalIS Intermediate- sulfidation epithermalLS Low-sulfidation epithermal

(NB Abbreviations for major deposit typesin upper case)

57(5) Contained Au (placer Au),in million oz

Early Cretaceous

FIG. 2. Principal gold belts and isolated major deposits in the North and South American Cordillera. The box for each belt

shows the gold deposit type(s) (abbreviated names in black), the gold content expressed as million ounces (in red), and thegeneral age (color of box). Data from multiple sources, including Table 2 and references therein.



(2005), defined the 200-km-long, northeast-striking, Chi-cama-Yanacocha structural corridor, which encompasses the25-km-long alignment of volcanic and hydrothermal centersat Yanacocha as well as nearby high-sulfidation gold and por-phyry copper-gold deposits (Fig. 4a). An apparently similar,but northwest-striking basement feature is present in the ElIndio part of the El Indio-Maricunga belt, with the 6-km-longPascua-Veladero trend coincident with its northern margin(Bissig et al., 2001; Charchaflié et al., 2007; Fig. 4b). A com-parable transverse structure was also recently proposed as alocalizing influence on the Goldfield high-sulfidation gold de-posit in the Walker Lane (Berger et al., 2005).

Low-sulfidation epithermal gold depositsTwo of the less important gold belts in the western Ameri-

cas, the Patagonian province in southern Argentina and con-tiguous Chile and the Northern Nevada rift in Nevada, aredominated by low-sulfidation epithermal deposits. The Walker Lane in western Nevada and Sierra Madre Occiden-tal belt in Mexico also contain several additional examples(Fig. 2; Table 2). The Patagonian province and Walker Lanecover extensive areas, ~200,000 km2 in the case of the former, which encompasses the easternmost foothills of the Southern

Andes (Esquel deposit) besides the extra-Andean Somuncuraand Deseado massifs (Cerro Vanguardia deposit; Fig. 5a). Incontrast, the Northern Nevada rift is >500 km long and 4 to 7km wide, but is paralleled westward by other similar coinci-dent gravity and magnetic trends (Ponce and Glen, 2003; Fig.5c). The most important concentrations of low-sulfidationepithermal gold in the western Americas, however, are theisolated Round Mountain, Nevada (Fig. 3) and CrippleCreek, Colorado (Fig. 2) deposits, which are of disseminatedand subordinate vein type and vein and subordinate dissemi-nated type, respectively, rather than exclusively vein systemsas in the Patagonian province, Northern Nevada rift, Walker

Lane, and Sierra Madre Occidental (Table 2).The two low-sulfidation epithermal-dominated belts, thePatagonian province and Northern Nevada rift, possess anumber of tectonomagmatic similarities. Compositionally bi-modal, rhyolite and basalt-basaltic andesite volcanic suitescharacterize both belts, but rhyolite dominates the formerprovince whereas basalt is volumetrically preeminent in thelatter (Kay et al., 1989; Pankhurst et al., 1998; John, 2001).The silicic component in Patagonia constitutes oxidized, per-aluminous, medium- to high-K calc-alkaline ignimbrites,defining an ash-flow caldera province (Kay et al., 1989;


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Oregon Idaho

California Arizona

Utah

120° 112°

GREATBASIN

Nevada

Oregon Idaho

California Arizona

Utah

120° 112°

GREATBASIN

Nevada

National

Sleeper

Twin Creeks

Getchell

Ivanhoe

Jerritt Canyon

Gold Quarry

CarlinPost / Betze

Buckhorn

Reno

Comstock Lode

ParadisePeak

Goldfield

Bodie

Alleghany

MotherLodedistrict

Salt Lake City

Barneys Canyon

BinghamMercur

INDEPENDENCETREND 14

UINTA AXISCARLINTREND

105

BATTLE MNT-EUREKA TREND

57

NORTHERNNEVADA RIFT

10

WALKER LANE47

GETCHELLTREND

35

Sr i =< 0.706

120° 112°

40°

Sr i => 0.706

250 km250 kmPorphyry Cu-AuSkarnSediment-hosted AuOrogenic AuLow-sulfidation AuIntermediate-sulfidation Au-AgHigh-sulfidation Au ± Ag

Deposit Type

55

Midas

CopperCanyondistrict

Pipeline-Cortez Hills

Mule Canyon

ROUNDMOUNTAIN

14

GrassValley

SIERRAFOOTHILLS BELT

35 (65)

Early Cretaceous

Metallogenic Belt Age

Eocene

Miocene (20 – 4 Ma)

Miocene (16 – 14 Ma)

Oligocene (26 Ma)

32°

PacificOcean

32°

PacificOcean

40°40°

FIG. 3. Major gold belts and isolated major deposits in the Great Basin and surrounding regions of the western UnitedStates, showing their ages and gold contents (numbers beneath belt names). The number in parenthesis is placer gold con-tent. Several important deposits in each belt, assigned to deposit types, are also marked. Data from multiple sources, in-cluding Table 2 and references therein. Dot-dash line shows the initial87Sr/ 86Sr = 0.706 isopleth (Sri) for Meso-Cenozoic plu-tonic rocks (after Kistler, 1991), which is inferred to mark the western craton margin. Inset marks the position of the GreatBasin physiographic province, mentioned in the text



Pankhurst et al., 1998). In contrast, the rhyolites of theNorthern Nevada rift comprise volumetrically restricteddomes and dikes that are chemically reduced and plot in thetholeiitic field (John, 2001). The silicic volcanic rocks areinferred to be products of lower-crustal anatexis in responseto mafic underplating (Pankhurst and Rapela, 1995; John,2001).

In concert with the bimodal volcanic association, both thegold belts were generated during extension in back-arc set-tings while subduction-related arc magmatism was active far-ther west. The Chon Aike rhyolites accumulated in a series of regionally continuous, north-northwest–striking half grabens, which underwent reactivation during the low-sulfidation ep-ithermal gold mineralization and accompanying final-stage

(<160 Ma) volcanism in the western parts of the province(Pankhurst et al., 2000; Ramos, 2002). The Northern Nevadarift and similar parallel structures farther west, all under-pinned by mafic dike swarms (Zoback et al., 1994; Ponce andGlen, 2003), were the sites of low-sulfidation epithermal goldmineralization during a short interval (16–14 Ma) at the endof the early rift-related volcanism (John, 2001).

The Chon Aike rhyolite province and Northern Nevada riftare both products of mantle plume activity: the Discovery-Shona-Bouvet group of plumes for the former and the incep-tion of the Yellowstone hotspot for the latter (Riley et al.,

2001; Zoback et al., 1994; Glen and Ponce, 2002; Fig. 5b, c).The Patagonian gold province is located at the paleo-Pacificmargin of Gondwana and—along with the partially time-equivalent Karoo and Ferrar flood basalt provinces (Fig.5b)—formed during rifting preparatory to South AtlanticOcean opening and breakup of western Gondwana(Pankhurst et al., 1998, 2000; Riley et al., 2001). In contrast,the Northern Nevada rift aborted before any separation of the North American plate could take place.

The low-sulfidation epithermal gold deposits in the WalkerLane (e.g., Bodie) along with the Round Mountain deposit just to the east (Fig. 3) are associated with rhyolitic centers,including a major ash-flow caldera at Round Mountain(Henry et al., 1996). The Walker Lane is a dextral transten-

sional belt (Stewart, 1988), whereas extension prevailed at 26Ma when the Round Mountain deposit was formed and inthe Sierra Madre Occidental during the Oligocene (El Orolow-sulfidation epithermal deposit). Cripple Creek, locatedalong the eastern margin of the North American Cordillera(Fig. 2), has a very different magmatic affiliation, being partof a diatreme complex related to bimodal phonolite-alkalinelamprophyre rocks (Kelley et al., 1998). The alkaline mag-matic activity may be related to small degrees of mantlemelting triggered by the transition, between 40 and 35 Ma(Chapin and Cather, 1994), from Laramide compression to


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Fault

High-sulfidation epithermal Au±Ag

Deposit type

Intermediate-sulfidation epithermal Au

Porphyry Cu-Au

Reverse fault

Transverse fault / lineament

Structural corridor limits

0

km

100

km10

a b

Pascua-Lama

El Tambo

El Indio

Río del Medio

Veladero

70° 00’ W

29° 30’ S

78° 30’ W

6° 00’ S

Tantahuatay

Cerro Corona

Yanacocha district

SipanMinas Conga

El Galeno

FIG. 4. Examples of arc-transverse structures and their relationships to gold and copper-gold deposits in the two mainhigh-sulfidation epithermal gold belts of the American Cordillera. The arcs trend roughly perpendicular to the transversestructures. a. Northeast-striking Chicama-Yanacocha structural zone in the Cajamarca-Huaraz belt, northern Peru (afterQuiroz, 1997, and Longo and Teal, 2005). b. Northwest-striking structural zone in the El Indio part of the El Indio-Mari-cunga belt, northern Chile (after Bissig et al., 2001 and Charchaflié et al., 2007).



the extensional regime that culminated in opening of the RioGrande rift (Kelley et al., 1998; Rampe et al., 2005).

Intermediate-sulfidation epithermal gold depositsIntermediate-sulfidation epithermal deposits, mostly of

vein type, make important contributions to the 600-km-long Walker Lane in Nevada (Comstock Lode; Fig. 3), the750-km-long Sierra Madre Occidental belt in Mexico (Tay-oltita), the 100-km-long Zamora belt in southern Ecuador(Fruta del Norte), and the 300-km-long Middle Cauca belt inColombia (Marmato; Fig. 6). All these deposits are closely as-sociated with medium- to high-K calc-alkaline volcanism, which ranges from andesitic in the Comstock Lode area (Cas-tor et al., 2005) to voluminous rhyolitic ignimbrites in theSierra Madre Occidental (McDowell and Clabaugh, 1979;Ferrari et al., 2007).

As noted above, the Walker Lane developed under dextraltranstensional conditions (Stewart, 1988) and the SierraMadre Occidental belt is part of an extensional arc, the south-ern continuation of the Basin and Range province of the west-ern United States (Henry and Aranda-Gomez, 1992; Staude

and Barton, 2001; Ferrari et al., 2007). Extension in the SierraMadre Occidental culminated in opening of the Gulf of Cali-fornia (Ferrari et al., 2007). Although not well studied, theLate Jurassic Zamora belt may have been extensional (Table2) prior to the onset of Late Cretaceous collision-related com-pression (Pratt et al., 2005). Generation of the Fruta delNorte deposit, the main product of this event, overlapped with subaerial graben formation, coarse clastic sedimentation,and nearby dacitic ash-flow eruption (Stewart and Leary,2007). The Middle Cauca belt lies along the Cauca-Romeralfault system, the site of a collisional suture, and appears to


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74° 70° 66° 62 °

40°

44°

48°

52°

PacificOcean

Atlantic

Ocean

Cerro Vanguardia

Cerro Bayo

Esquel

Gastre faultzone

Chon Aikevolcanicprovince

Au deposit

CHONAIKE

KAROOFERRAR

Antarctic

Africa

South America

East Antarctica

New Zealand

2000 km

CHONAIKE

KAROOFERRAR

Antarctic Peninsula

Africa

South America

East Antarctica

New Zealand

2000 km2000 km

40 °

48 °

128 ° 120 ° 112 °

South margin of Farallon

10 Ma

20 Ma

Nevada

National

Midas

IvanhoeMule CanyonBuckhorn

McDermittcaldera 16.5 Ma

Yellowstonehot spot

Columbia River

basalts

Northern Nevada rift axis

S i e

r r a

N e v a d

a

H i g h

e

PacificOcean

°

° ° °

Plate

C a s c a d

s e

500 km

500 km500 km

Manantial Espejo

Sleeper

a

c

b

FIG. 5. Geologic comparison of the Patagonian and Northern Nevada rift low-sulfidation epithermal gold belts and theirrelationship to hot spots. a. Outcropping Chon Aike Group volcanic rocks (from Riley et al., 2001) and main gold deposits inthe Patagonian province. b. Large Igneous Provinces (Chon Aike rhyolites and Karoo and Ferrar basalts) related to the Dis-covery-Shona-Bouvet plume group (from Riley et al., 2001). c. Northern Nevada rift and similar magnetic feature farther west (after Ponce and Glen, 2003; heavy dashed lines), main low-sulfidation epithermal gold deposits, present and approxi-mate initial (16.5 Ma caldera) positions of the Yellowstone hot spot, hot spot-related Columbia River Basalt Group, and west-ern graben of Snake River Plain (hachured lines). East-west lines along the Pacific coast show approximate southern marginof the Farallon plate that was being subducted beneath North America at the ages indicated (from John et al., 2000).



have been subjected to dextral transpression during theMiocene (Rossetti and Colombo, 1999; Cediel et al., 2003)—a prominent exception to the extensional or transtensionalsettings of the other major intermediate-sulfidation epither-

mal gold deposits.Porphyry copper-gold deposits

The three preeminent porphyry copper-gold deposits,Bingham Canyon in the Bingham district of Utah, Bajo de laAlumbrera in the Farallón Negro district of northwestern Ar-gentina, and Pebble in Alaska, dominate the major, isolatedgold concentrations rather than helping to define belts (Fig.2). However, relatively small porphyry copper-gold depositsalso contribute to the gold inventory of the Cajamarca-Huaraz belt in northern Peru (Figs. 2, 4a).

The Bingham and Farallón Negro districts occupy a super-ficially similar position at the landward extremity of theAmerican Cordillera (Fig. 2). Both are centered on high-Kcalc-alkaline porphyry stocks that have partially preserved co-eval volcanic edifices (Waite et al., 1997; Sasso and Clark,1998). Waite et al. (1997) also hypothesized a primitive maficalkaline contribution to the Bingham magmas because of

their unusual enrichment in chromium, nickel, and barium.In both districts, as well as at Pebble, the magmatic rockshave typical supra-subduction zone petrochemistry.

Bajo de la Alumbrera and other porphyry copper-gold de-posits and prospects in the Farallón Negro district were em-placed above a rapidly shallowing subduction zone during theinitiation of contractional tectonism, crustal shortening, andsurface uplift. The resulting high-angle reverse faults led toformation of the basement-cored blocks that characterize thenorthernmost Sierras Pampeanas structural province (Ramoset al., 2002). Uplift was initiated some time between 7.6 and6.0 Ma and is still ongoing (Ramos et al., 2002) while por-phyry copper-gold deposit generation at Bajo de la Alumbreraspanned the 8- to 6-m.y. interval (Harris et al., 2004, 2008).

The Bingham district occupies a broadly similar position inthe context of low-angle Laramide subduction, but ratherthan being linked to slab shallowing, like the Farallón Negrodistrict, it presaged slab steepening. Presnell (1997) relatedthe magmatism and ore formation to the initial onset of post-Laramide extension, although end-stage contraction, base-ment uplift, and basin sedimentation may still have been ac-tive (Dickinson et al., 1988).

Both districts lie along fundamental transverse tectono-magmatic discontinuities: the Farallón Negro district on aneast-northeast–striking feature, the Tucumán transfer zone,marking the southern limit of the Arequipa-Antofalla craton(Sasso and Clark, 1998) where it intersects a northwest-ori-ented, trans-Andean lineament (Chernicoff et al., 2002); and

the Bingham district on the east-northeast–striking Uinta axis(Fig. 3), the shallow manifestation of an Archean-Proterozoicsuture zone, at its confluence with other regional-scale struc-tural elements (Billingsley and Locke, 1941; Ericksen, 1976;Presnell, 1997). Kutina (1991) considered the Uinta axis to bepart of a mantle-penetrating structure that transgresses theentire Cordilleran margin.

The plate-tectonic setting of the mid-Cretaceous Pebbledeposit is much less certain, although both Goldfarb (1997)and Young et al. (1997) inferred a continental-margin arc set-ting, possibly during northward subduction beneath the pre- viously accreted Wrangellia superterrane. Crustal shortening,thickening, and uplift may have followed Wrangellia accretion(Nokleberg et al., 2005). The structural setting of Pebble re-

mains to be defined, although it does lie near the major,northeast-striking Lake Clark fault zone. The small porphyry copper-gold deposits in the Cajamarca-Huaraz belt, whichare broadly contemporaneous with the earliest high-sulfida-tion gold deposits (Noble and McKee, 1999; Longo and Teal,2005), appear to coincide with a noncompressive interval (seeabove).

Porphyry gold depositsSignificant porphyry gold deposits, distinguished by much

lower (e.g., <~0.25 %) copper contents than those defining


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ECUADOR

COLOMBIA

PANAMAVENEZUELA

75°W

75°W

0°

5°S

10°S

250 km

Angostura

SEGOVIABELT

13 (11)

ANTIOQUIABATHOLITH

3 (2)

MIDDLE CAUCA BELT15 (1)

Western craton edge

CHOCO BELT (10)

CALIFORNIADISTRICT

7

Segovia

Marmato

Colosa

Jurassic

Late Cretaceous-Early Tertiary

Miocene

Eocene (?)

Porphyry Au

Intermediate-sulfidation

Oxidized pluton related

Medellín

Bogotá

Cali

Deposit Type

Metallogenic Belt Age

FIG. 6. Principal gold belts and districts in the northern Colombian Andes,showing their ages and gold contents (numbers beneath belt names). Thenumbers in parentheses are placer gold contents. Note that the Antioquiabatholith and California districts, estimated to contain <10 Moz Au, are notdiscussed in the text. The approximate limit between continental crust to theeast and oceanic accreted terranes to the west is also shown. Data from mul-tiple sources, including Table 2 and references therein; and AngloGoldAshanti (2007).



the porphyry copper-gold category dealt with above, are con-fined to the Maricunga portion of the El Indio-Maricungabelt in northern Chile and the Middle Cauca belt in Colom-bia (Fig. 2). The Maricunga belt hosts porphyry gold depositsof two discrete ages (~24–21 and ~14–11 Ma; Sillitoe et al.,1991; McKee et al., 1994), both of which are closely associ-ated with fine-grained diorite to quartz diorite porphyry

stocks emplaced into andesitic stratovolcanoes. These mag-matic products have a medium- to high-K calc-alkaline affin-ity (Kay et al., 1994; Mpodozis et al., 1995). Porphyry goldformation in the Middle Cauca belt (Fig. 6) took place in as-sociation with porphyries of similar composition (R. H. Silli-toe, personal observations, 2007).

The trace element characteristics of magmatic rocks in theMaricunga belt suggest that during the earlier porphyry goldevent (Refugio deposit) a relatively thick crust was subjectedto regional extension as a consequence of the steep subduc-tion angle (Kay et al., 1999; Kay and Mpodozis, 2001, 2002).Slab flattening, contractional tectonism, crustal thickening,and magmatic quiescence followed from 20 to 18 Ma, butstress relaxation and mild extension were reimposed during

the later porphyry gold event responsible for the Marte,Lobo, and Cerro Casale deposits (Kay and Mpodozis, 2001,2002). At least the northern part of the Maricunga belt coin-cides with the transverse tectonomagmatic discontinuity thatinfluenced the localization of the Farallón Negro copper-golddistrict farther east (Sillitoe et al., 1991; Sasso and Clark,1998; see above).

The tectonic setting of the Middle Cauca belt (Fig. 6) at thetime of porphyry gold mineralization in the late Miocene (R.Padilla, pers. commun., 2007) is less precisely defined, al-though dextral transpression linked to accretion of the Baudóallochthonous oceanic terrane farther west in northwesternColombia certainly characterized much of the Miocene(Cediel et al., 2003; see above).

Sediment-hosted gold depositsThe Carlin, Cortez, Independence, and Battle Mountain-

Eureka gold trends in northern Nevada are defined by theonly major sediment-hosted gold deposits in the AmericanCordillera, although small deposits of this type are also partof the Bingham district, Utah, farther east (Fig. 3). The Car-lin, Cortez, and Independence trends have lengths of up toabout 130 km but widths of only 5 km, whereas the BattleMountain-Eureka trend is longer (320 km) as well as alsocontaining important skarn gold deposits (e.g., CopperCanyon district).

Only small volumes of coeval igneous rocks, chiefly minorfelsic dikes of high-K calc-alkaline affinity, accompany the

sediment-hosted gold deposits (Hofstra et al., 1999; Resseland Henry, 2006). The presence of these dikes in combina-tion with spatially related magnetic anomalies points to theexistence of an extensive subsurface plutonic complex be-neath the Carlin trend (Ressel and Henry, 2006). Areally ex-tensive volcanic fields accumulated at broadly the same timein nearby areas as part of the mid-Tertiary southward migra-tion of the volcanic front (Ressel and Henry, 2006).

There is general consensus that the sediment-hosted goldtrends of Nevada developed during a relatively short, lateEocene interval (~42–36 Ma) marked by the initiation of

low-magnitude extension (Hofstra and Cline, 2000; Cline etal., 2005), but prior to the large-scale crustal attenuation thatcharacterized the Great Basin during the Oligocene andMiocene. The late Eocene extension gave rise to several fault-bounded, fluviolacustrine basins as well as to reactivation ofsuitably oriented high- and low-angle faults in underlying Pa-leozoic rocks (Cline et al., 2005). At least some of the gold

trends may have acted as accommodation zones across whichextension histories differed (Tosdal and Nutt, 1999; Munteanet al., 2001). The contemporaneous extension and volcanismmay have been triggered by processes linked to removal of the shallowly inclined Farallon plate from the base of theNorth American lithosphere, its position during the preced-ing Laramide orogeny (Sonder and Jones, 1999); however,any volcanic products along the sediment-hosted gold trendshave been lost to erosion.

Notwithstanding the incipiently extended crust during thelate Eocene, the aftermath of a complex history of much olderdeformation and intrusive activity had profound effects onsediment-hosted gold deposit localization. Particularly impor-tant ore-localizing sites are provided by the following: recep-

tive carbonate rock types juxtaposed with overlying, relativelyimpermeable siliciclastic units along low-angle, reverse faults,especially the Roberts Mountain thrust; structural culmina-tions formed by inversion of high-angle faults during Paleo-zoic contractional tectonism; and Mesozoic plutons thatcaused perturbation of the late Eocene stress field and helpedto focus fluid upflow (Cline et al., 2005 and referencestherein).

The gold trends of northern Nevada are located near the western margin of the North American craton (Fig. 3) and areinferred to reflect the basement fault fabric (Roberts, 1960).The northwest and northeast gold trends may follow funda-mental, crustal-scale faults that controlled Neoproterozoicrifting to form a passive continental margin as well as influ-

encing subsequent sedimentation, contractional deformation,magmatism, and hydrothermal activity (Tosdal et al., 2000;Crafford and Grauch, 2002; Grauch et al., 2003).

Orogenic gold depositsThe Sierra Foothills belt in California, including the Mother

Lode and Grass Valley districts plus a major contribution fromderivative placer deposits of Eocene and younger age (Lind-gren, 1911; Garside et al., 2005), is the premier orogenic goldconcentration in the American Cordillera (Fig. 2; Table 2). Itdwarfs the second- and third-largest orogenic gold concentra-tions, the Juneau belt in southeastern Alaska and Klondike dis-trict in the Yukon Territory, the latter dominated by Plio-Pleis-tocene placers derived from numerous, apparently small

orogenic gold veins (Rushton et al., 1993; Knight et al., 1999;Fig. 2; Table 2). The primary gold deposits comprise quartz veins and veinlet swarms, the largest of which in the SierraFoothills belt were exploited downdip for >1 km (Knopf,1929). The overall geologic settings of the Sierra Foothills andJuneau belts, 270 and 200 km long, respectively, but both nomore than 5 km wide, have many similarities, notwithstandingtheir appreciable age difference (see below). The Klondikeplacer district occupies an area of approximately 1,200 km2.

The Sierra Foothills and Juneau belts both occur on the western, fore-arc sides of Andean-type magmatic arcs defined


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by the major Sierra Nevada and Coast batholiths, respec-tively (Fig. 7). The deposits reveal intimate relationships tomajor fault zones, but no clear-cut connections to individualintrusions. Nonetheless, both belts were generated duringemplacement of the flanking calc-alkaline batholiths. New 40Ar/ 39Ar ages for gold mineralization in the Sierra Foothillsbelt suggest formation between ~135 and 115 Ma (Marsh et

al., 2007). Emplacement of the western parts of the SierraNevada batholith, immediately east of the Sierra Foothillsbelt (Fig. 7a), overlaps with this Early Cretaceous interval(Bateman, 1992). Moreover, just south of the gold belt, thebatholith transgresses the Sierra Foothills terrane, whichcontinues only as a series of contained roof pendants (e.g., Wolf and Saleeby, 1995; Fig. 7a), and subjacent plutons re-main a distinct possibility farther north where erosion level isshallower. Gold mineralization in the Juneau belt is dated at56 to 53 Ma, essentially coeval with Early Eocene (55 ± 2Ma) Coast batholith emplacement (Miller et al., 1994; Gold-farb et al., 1997). Gold introduction in the Klondike district,probably in the Early to Middle Jurassic (Table 2), was not

accompanied by any known intrusive activity (MacKenzie etal., 2007).

The primary orogenic gold mineralization of the SierraFoothills, Juneau, and Klondike is hosted by lithotectonic ter-ranes that underwent deformation and greenschist faciesmetamorphism during their accretion to the North Americancraton. The accretion events clearly predated the gold miner-

alization, by several tens of million years in the case of boththe Sierra Foothills and Juneau belts (e.g., Dickinson, 2004,2006). The gold deposits are hosted by steep, relatively minorbrittle faults and shears related to regionally extensive reversefault zones that display complex and incompletely understoodductile and brittle histories (e.g., Paterson and Wainger, 1991; Wolf and Saleeby, 1995). These structures are exemplified by the Melones fault zone (Fig. 7a), which contains abundantserpentinized ultramafic bodies and acts as a fundamentalcontrol to the Mother Lode and other deposits in the SierraFoothills belt (Knopf, 1929; Landefeld and Silberman, 1987;Böhlke and Kistler, 1986; Fig. 7a). These major fault zonesappear to be crustal-scale, terrane-bounding features active


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FIG. 7. Geologic comparison of the Sierra Foothills, California, and Juneau, Alaska, orogenic gold belts and their flankingbatholiths, taken from Böhlke and Kistler (1986) and Goldfarb et al. (1997). The gold deposits lie along terrane-boundingfault zones, abbreviated as follows: BMFZ, Bear Mountains fault zone; MFZ, Melones fault zone; FFZ, Fanshaw fault zone;SFZ, Sumdum fault zone.



during mid-Jurassic island-arc accretion responsible for theNevadan orogeny (e.g., Schweickert and Cowan, 1975; Pater-son and Wainger, 1991; Gehrels, 2000; Hildenbrand et al.,2000); however, fault initiation may have been as part of theCalifornia-Coahuila sinistral transform of Permo-Triassic age(Dickinson, 2006).

Miller et al. (1994, 2000) and Goldfarb et al. (1997) pro-posed that generation of the Juneau gold belt immediately followed the transition from orthogonal to oblique subductionof the Kula oceanic plate, an event that initiated dextral trans-pression along the controlling fault zones as well as concomi-tant uplift. A broadly similar scenario may be envisioned forthe origin of the Sierra Foothills gold belt, which is coeval with reinvigorated eastward subduction of the Farallonplate—following the Nevadan collisional orogeny—andbatholithic arc construction (Ernst et al., 2008). At that time,the major crustal-scale, gold-localizing faults may have beenreactivated in a dextral transpressive regime (Glazner, 1991).Accretion of the Yukon-Tanana terrane, host to the Klondikeplacer district, is an Early Jurassic event (e.g., Plafker and

Berg, 1994), with orogenic vein formation taking place duringlocalized extension that concluded the collision-inducedthrust stacking (MacKenzie et al., 2007; Table 2).

Reduced pluton-related gold depositsTwo temporally distinct belts of pluton-related gold de-

posits in the Yukon Territory and Alaska are commonly as-signed to the Tintina gold province (Flanigan et al., 2000;Hart et al., 2002; Nokleberg et al., 2005). The older is the470-km-long Tombstone belt, Yukon and its extension, dex-trally displaced ~430 km to the northwest, in the Fairbanksdistrict, Alaska, and the younger is the 550-km-long Kuskok- wim belt still farther west in Alaska (Fig. 2). Both belts arecharacterized by varied styles of gold mineralization, which

range from sheeted quartz veins in the apical parts of plutonsto distal disseminated, vein, and skarn-type mineralization within their hornfels aureoles (Newberry et al., 1995; McCoy et al., 1997; Thompson et al., 1999). Emplacement depth,ranging from 2 to 10 km, is an important control on exposeddeposit style (Thompson et al., 1999; Lang and Baker, 2001;Hart et al., 2002).

The deposits are related to small (<5 km across), felsic in-trusions, which are parts of areally more extensive plutonicsuites. The intrusive rocks are metaluminous to locally pera-luminous, calc-alkaline, isotopically evolved, and I-type(Newberry et al., 1995; McCoy et al., 1997; Aleinikoff et al.,2000; Hart et al., 2004); all of them are moderately reduced,broadly spanning the boundary between Ishihara’s (1977)

magnetite and ilmenite series (Thompson et al., 1999;Thompson and Newberry, 2000). Those in the Tombstonebelt are both magnetite and ilmenite poor (Hart et al., 2004).High Sri (>0.709) and δ 18O values suggest an appreciablecrustal contribution to the magmas (Hart et al., 2002). Al-though the intrusive rocks in the Fairbanks-Tombstone beltspan the ~110 to 88 Ma interval (Mortensen et al., 2000), themost important gold mineralization appears to cluster at 92 ±1 Ma (McCoy et al., 1997), except for the Pogo deposit, at104.2 ± 1.1 Ma (Selby et al., 2002). The Kuskokwim belt isappreciably younger, ~71 to 65 Ma (Hart et al., 2002).

Most investigators assign both parts of the Tintina goldprovince and its contained plutonic rocks to a subduction-re-lated arc on the basis of overall petrochemical characteristics(Newberry et al., 1995; Bundtzen and Miller, 1997; McCoy et al., 1997; Aleinikoff et al., 2000; Flanigan et al., 2000). Arcconstruction postdated Early Jurassic to mid-Cretaceous ter-rane accretion, contractional deformation, and metamor-

phism in southern Alaska. The Tombstone belt was gener-ated during north- to northwest-directed, low-magnitudeextension (Rubin et al., 1995; Rhys et al., 2003; Hart et al.,2004), whereas dextral transpression on the orogen-parallelIditarod-Nixon Fork fault was coincident with gold mineral-ization in the Kuskokwim belt (Bundtzen and Miller, 1997;Miller et al., 2002; Goldfarb et al., 2004).

Reconstruction of the Fairbanks-Tombstone belt, by restoring the ~430 km of Cenozoic dextral offset on theTintina fault, results in a broad, >400-km-wide magmatic arc(Flanigan et al., 2000) suggestive of relatively low-angle sub-duction (Plafker and Berg, 1994); moreover, the Fairbanks-Tombstone gold belt is confined to the landward periphery of the arc. Indeed, both the Fairbanks-Tombstone and Kusko-

kwim belts may be considered to occupy back-arc settings(Thompson et al., 1999; Fig. 2). Notwithstanding the inferredexistence of low-angle subduction, contractional tectonism isnot reported.

The relatively reduced nature of the host intrusions and, asa direct consequence, the auriferous fluids themselves areatypical of western American arc terranes and remain poorly understood. Nevertheless, it is tempting to suggest that eitherassimilation of material from the reduced, siliciclastic host-rock sequences—Neoproterozoic and Paleozoic in the Fair-banks-Tombstone belt and Late Cretaceous in the Kuskok- wim belt (McCoy et al., 1997; Thompson et al., 1999;Thompson and Newberry, 2000)—or contamination by re-duced fluids expelled from them played an influential chem-

ical role (Thompson et al., 1999; Thompson and Newberry,2000; Hart et al., 2002, 2004).

Oxidized pluton-related gold depositsThe principal gold deposits related to oxidized plutonic

rocks are located in the northern Central Cordillera of Colombia where they define the Segovia belt (Fig. 2; Table2). The Segovia belt (Fig. 6), about 300 km long and up to 75km wide, is dominated by quartz veins and vein swarms con-taining minor amounts of zinc, lead, and copper sulfides, al-though half of the gold production has come from derivativeplacers. Substantially smaller is the 160-km-long Pataz-Par-coy belt in northern Peru, where the auriferous, sulfide-richquartz veins also contain subsidiary quantities of zinc and

lead.Both belts occur within and around composite, calc-alka-line, metaluminous batholiths of I-type, magnetite series, andsubduction origin (González, 2001; Haeberlin et al., 2004).Compositionally, these equigranular plutons are similar to theporphyry stocks that host Cordilleran porphyry copper-goldand gold deposits (see above). The Segovia batholith, consid-ered to be of Late Jurassic age, is dominated by hornblendediorite and tonalite intrusions, whereas the Carboniferous(Mississippian) Pataz-Parcoy batholith comprises mainlytonalite and granodiorite (Haeberlin et al., 2004). The


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batholiths were emplaced into greenschist- to amphibolite-grade metasedimentary sequences, which accumulated alongthe edge of the Amazon craton during the Neoproterozoicand early Paleozoic (Cediel et al., 2003; Haeberlin et al.,2004).

The Segovia batholith was emplaced under extensional tec-tonic conditions as part of the late Paleozoic through Jurassic

“Bolivar aulacogen” rifting and continental sedimentationevent in northwestern South America, which was linked toopening of the Caribbean basin (Cediel et al., 2003). Postcol-lisional crustal thickening and uplift characterized the Pataz-Parcoy belt during batholith emplacement and the subse-quent gold mineralization, which took place along a major,north-northwest–striking crustal lineament under conditionsof east-directed crustal shortening (Haeberlin et al., 2004).

Tectonomagmatic Synthesis

Tectonic associationsThe major gold deposits and belts in the western Americas

occur both along the craton margin and in some of the many

accreted terranes. However, all the major gold deposits andbelts were generated after their host terranes were accretedto the craton edge, a situation that contrasts with the preac-cretionary timing of some other Cordilleran mineral deposits(e.g., volcanogenic massive sulfides; McMillan, 1991; Mor-tensen et al., 2008). Nonetheless, the placer deposits thatconstitute the Chocó belt in the northern Colombian Andes(Fig. 6; Table 2) are likely to have been derived from preac-cretionary gold concentrations, although not necessarily fromthe porphyry copper-gold prospects that are the only signifi-cant deposit type currently known in the belt (Sillitoe et al.,1982; Table 2). The craton-hosted gold deposits and belts were formed independently of whether tectonic erosion, as inthe central Andes (Rutland, 1971), or accretion, as in much of

the North American Cordillera and northern Andes (Coney et al., 1980; Cediel et al., 2003), dominated at the continentaledge at the time of mineralization.

Many of the major Cordilleran gold deposits and belts were generated within active, subduction-related magmaticarcs, although back-arc and fore-arc environments are alsomineralized in places: the low-sulfidation epithermal and re-duced pluton-related gold deposits typically occur in backarcs, whereas the orogenic gold deposits are confined to forearcs (Figs. 2, 8). Approximately two-thirds of the major golddeposits and belts occupy a variety of extensional ortranstensional tectonic environments. Broadly contractionalsettings, consequent upon shallow subduction, appear to beless common at the times of major gold deposit formation,

although they host the largest high-sulfidation epithermalgold deposits in the Cajamarca-Huaraz and El Indio-Mari-cunga belts, the porphyry copper-gold deposits of the Faral-lón Negro district, and, rather less certainly, the BinghamCanyon and Pebble porphyry copper-gold deposits. TheMiddle Cauca belt in Colombia, Kuskokwim belt in west-central Alaska, and Sierra Foothills and Juneau orogenicgold belts were most likely generated during transpression,induced either by oblique subduction or, in the case of theMiddle Cauca belt, oblique terrane docking. Notwithstand-ing the prevalence of extension at the times of major gold

deposit and belt formation, the largest Cordilleran gold con-centrations (Fig. 2) either coincide with (Cajamarca-Huaraz, El Indio-Maricunga, and Sierra Foothills belts) orconclude or immediately follow (Bingham district and Car-lin and Battle Mountain-Eureka trends) long-standing con-tractional episodes. This observation may suggest that theconsequent crustal thickening and uplift may somehow have


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HS Au

P Cu -Au RPR Au

SEDH Au P Cu -Au

LS, IS,HS Au LS Au

ORO Au

batholithterrane-bounding

fault

rift

strike-slipfault

strike-slipfault

mantleplume

crustal-scalefault

a

b

c

d

e

FIG. 8. Cartoon sections showing generation of selected gold belts at dif-ferent times and places along the American Cordillera, all during active, east-directed subduction. a. Cajamarca-Huaraz high-sulfidation (HS) belt duringthe Miocene. b. Pebble porphyry (P) copper-gold deposit and Kuskokwim re-duced pluton-related (RPR) gold belt in west-central Alaska during the LateCretaceous. c. Sediment-hosted (SEDH) gold trends of Nevada and por-phyry (P) copper-gold, skarn, and sediment-hosted deposits of the Binghamdistrict, western United States during the Eocene. d. Walker Lane low-, in-termediate-, and high-sulfidation (LS, IS, HS) and Northern Nevada rift low-sulfidation (LS) gold belts, western United States during the mid-Miocene.e. Sierra Foothills orogenic (ORO) gold belt in California during the Early Cretaceous. See Figures 2 and 3 for belt and deposit locations.



been conducive to the formation of different types of majorgold concentrations.

Tectonic relaxation, extension, or transtension following con-tractional episodes responsible for crustal thickening accom-panied the generation of several of the gold belts and isolateddeposits. This extension was due to slab steepening followingLaramide low-angle subduction in the case of the Bingham

Canyon and Cripple Creek deposits and the sediment-hostedgold trends of Nevada, whereas tectonic relaxation consequentupon eastward migration of crustal compression prevailed inthe El Indio part of the El Indio-Maricunga belt (Charchafliéet al., 2007) and during generation of the younger Maricungaporphyry gold deposits in the El Indio-Maricunga belt (Kay etal., 1994). Exactly the opposite situation, the transition fromextension to contraction, prevailed when the Cajamarca-Huaraz belt and Farallón Negro district were formed. In con-trast, extensional collapse of overthickened crust produced by terrane accretion may have occurred in the reduced pluton-related Tombstone-Fairbanks belt of the Yukon and adjoiningAlaska.

These and some other porphyry, epithermal, sediment-

hosted, and orogenic gold deposits were generated duringmagmatic pulses that accompanied marked changes in tec-tonic regime, a scenario that has been considered to favormajor gold deposit generation elsewhere in the circum-Pa-cific region (Solomon, 1990; Richards, 1995; Sillitoe, 1997;Barley et al., 2002; Mungall, 2002; Garwin et al., 2005). Thetime gaps between major contractional episodes and the gold-related tectonic regimes may be minimal (e.g., Bingham dis-trict, sediment-hosted gold trends of Nevada) or amount to afew million (e.g., El Indio belt, Klondike) or even several tensof million years (e.g., Sierra Foothills and Juneau belts). How-ever, other major gold deposits in the western Americas arenot so readily correlated with tectonic change at the conver-gent margin, as exemplified by the epithermal deposits of the

Walker Lane and at Round Mountain in Nevada and Pueblo Viejo in the Dominican Republic. Elsewhere in the westernAmericas, the extension that was synchronous with gold min-eralization was not immediately preceded by a compressiveregime, as observed in the smaller gold concentrations of theSegovia belt of Colombia, the Patagonian province, and theNorthern Nevada rift.

Notwithstanding the fact that all gold mineralization is atleast partly structurally controlled, the positions of some of the deposits appear to have been influenced by fundamentalarc-parallel or arc-transverse fault zones or lineaments. Thelinkage between reactivation of terrane-bounding, brittle-ductile fault zones parallel to active arcs and the SierraFoothills and Juneau orogenic gold belts is widely appreci-

ated (Goldfarb et al., 2005), as are the arc-parallel transten-sional (e.g., Walker Lane) and, locally, transpressional faults(Kuskokwim belt, Middle Cauca belt) that were active duringgold mineralization elsewhere. Arc-transverse features areconsidered important in the Cajamarca-Huaraz high-sulfida-tion epithermal belt in northern Peru (Quiroz, 1997) andelsewhere, as well as in the localization of the isolated por-phyry copper-gold deposits in the Bingham and FarallónNegro districts. Deep-seated fault zones inherited from a lateNeoproterozoic rifting event are proposed as first-order con-trols on the sediment-hosted gold trends of Nevada (Tosdal et

al., 2000). Elsewhere, however, major gold concentrations,such as the isolated Pueblo Viejo and Cripple Creek epither-mal deposits and the Fairbanks-Tombstone pluton-relatedbelt, lack any recognized controlling structures of continen-tal-margin scale.

Magmatic associations

This review shows that a broad petrochemical spectrum of intrusive and/or volcanic rocks is temporally and spatially re-lated to the major gold deposits and belts in the AmericanCordillera. The most common magmatic rocks accompanyingthe gold mineralization events are undoubtedly parts of oxi-dized, magnetite-series, medium- to high-K calc-alkalinesuites. Porphyry copper-gold and gold, high- and intermedi-ate-sulfidation epithermal, and oxidized pluton-related de-posits are everywhere genetically related to such suites. Insharp contrast, the fractionated, calc-alkaline intrusions ge-netically linked to the reduced pluton-related gold depositsare themselves moderately reduced and span the ilmenite-magnetite series transition (Thompson et al., 1999). The low-sulfidation epithermal gold belts are alone in accompanying

compositionally bimodal volcanism, which is calc-alkaline inPatagonia (Pankhurst et al., 1998) but tholeiitic in the North-ern Nevada rift (John, 2001). Alkaline rocks are not abundantin the Cordilleran arc and back-arc environments, and theonly major gold concentration with this affiliation is the iso-lated Cripple Creek low-sulfidation epithermal deposit inColorado, where compositional bimodality is also evident(Kelley et al., 1998).

Sediment-hosted and orogenic gold deposits have lessclear-cut magmatic connections, as noted above, although thepremier belts of both deposit types do coincide spatially andtemporally with well-defined magmatic arcs. In the case of the sediment-hosted deposits in Nevada, minor felsic dikes were intruded during the gold mineralization and, on the

basis of the broadly coincident magnetic anomalies, appear tobe upward offshoots of an underlying plutonic complex (Res-sel and Henry, 2006). In contrast, the Sierra Foothills andJuneau orogenic gold belts lie along the western margins of major calc-alkaline batholiths, which may have transcrustalthicknesses as great as 35 km (Ducea, 2001). The intrusiverocks coeval with the sediment-hosted and orogenic goldbelts would offer a ready source for any magmatic contribu-tions to the respective ore-forming fluids or, alternatively,may simply have provided the thermal impetus required to ei-ther circulate or liberate nonmagmatic fluids (e.g., Jia et al.,2003; Ressel and Henry, 2006).

Comparison with copper and tin belts

Porphyry deposits containing co- or by-product goldand/or molybdenum completely dominate the copper inven-tory of the western Americas (e.g., Sillitoe and Perelló, 2005;Perelló, 2006). Like the gold deposits dealt with in this review, porphyry copper deposits are emplaced in a variety of tectonic settings, which range from extensional to contrac-tional. Furthermore, the three preeminent copper belts, innorthern Chile-southern Peru (42–31 Ma), central Chile(11–4 Ma), and southwestern North America (Laramide:74–52 Ma; Fig. 9), were generated during intervals of re-gional compression, crustal thickening, and rapid surface


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uplift and exhumation (Sillitoe, 1998; Cooke et al., 2005; Sil-litoe and Perelló, 2005; Perelló, 2006). These compressionalevents may be related to low-angle subduction of topograph-ically prominent, buoyant features such as aseismic ridges onthe downgoing oceanic plates in conjunction with subductionerosion of the fore arcs (e.g., Henderson and Gordon, 1984;Stern, 1991; Kay et al., 2005), although gravitational delami-nation of the lithospheric mantle has been proposed recently as a cause of the Laramide slab flattening (Wells and Hoisch,2008). Additional outstanding copper concentrations occur

in the isolated porphyry copper-gold deposits at BinghamCanyon and Pebble (Figs. 2, 9; see above), as well as the iso-lated, ~65 Ma (Lund et al., 2002) Butte porphyry copper-molybdenum deposit in Montana, also emplaced duringLaramide compression (e.g., Kalakay et al., 2001; Fig. 9). Nev-ertheless, a far greater percentage (>90%) of the copper thanof the gold (<50%; Table 2) is confined to contractional set-tings. In common with gold deposits, arc-transverse structuresare also considered important for porphyry copper localiza-tion by some investigators, particularly in the central Andesand southwestern North America (e.g., Richards, 2000).

The magnetite-series, medium- to high-K calc-alkalinemagmas responsible for copper deposit formation in the threepremier belts (e.g., Lang and Titley, 1998; Sillitoe andPerelló, 2005, and references therein) appear to have beenlargely confined to mid- to upper-crustal chambers becausethe synmineralization contraction inhibited widespread arc volcanism (e.g., Mpodozis and Ramos, 1990). The extremesize of the giant deposits that make major contributions tothese three copper belts may be directly related to the largesize of the parent magma chambers, which may be reasonably

assumed to fractionate efficiently and evolve larger volumesof magmatic fluid than do their smaller counterparts (Sillitoe,1998; Richards, 2003). However, such reasoning cannot beapplied to all the major gold deposits and belts, except per-haps for the principal high-sulfidation epithermal gold con-centrations, because, as noted above, many of them formedduring extension.

Nearly all Cordilleran tin resides in the Bolivian tin-silverbelt, which occupies a unique behind-arc position in the An-dean Cordillera, extending from southernmost Peru throughthe Eastern Cordillera of Bolivia to northwesternmost


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1 2 0 °

1 0 5 °

9 0 °

7 5 °

6 0 °

4 5 °

1 3 5 °

1 5 0 °

1 7 5 °

45°

30°

15°

0°

15°

30°

45°

60°

1000 km

Butte

Bingham

Pebble

SouthwesternNorth America

Gold

Copper

Northern Chile-southern Peru

Central ChileFarallónNegrodistrict

FIG. 9. Major copper and gold belts and isolated major deposits in the North and South American Cordillera. Note themutual exclusivity of the principal gold and copper concentrations, although the porphyry copper-gold deposits obviously contain major quantities of both metals. Gold belts and isolated major deposits identified in Figures 2 and 3.



Argentina (Ahlfeld, 1967; Turneaure, 1971; Fig. 10). Theintrusion-related veins were generated during three discreteepochs: 225 to 180 and 26 to 22 Ma in the northern part of the belt, and 20 to 12 Ma in the southern part (Grant et al.,1979; Clark et al., 1990; Sempere et al., 2002; Fig. 10). TheLate Triassic-Early Jurassic epoch was a product of crustalmelting induced by shoshonitic mafic melts generated in a

back-arc rift environment (Clark et al., 1990; Sempere et al.,2002). In contrast, the Miocene epochs took place under neu-tral to weakly extensional conditions in response to slab steep-ening (Clark et al., 1990), detachment of subcontinentallithospheric mantle, and inflow of hot asthenosphere; theseevents in the Eastern Cordillera of Bolivia took place some 5m.y. after the cessation of amagmatic crustal compression andthickening (Hoke and Lamb, 2007).

The tin mineralization is related to emplacement of peralu-minous, ilmenite-series, and locally S-type magmas (Sugaki etal., 1988; Clark et al., 1990; Lehmann et al., 1990) bearingsome similarities to those linked to the reduced pluton-related gold (and nearby major tungsten) deposits in the backarc of Alaska and the Yukon Territory (see above). In common

with the Alaskan and Yukon back-arc gold belts, a thick prismof reduced, siliciclastic marine sedimentary rocks of early Paleozoic age hosts the Bolivian tin-silver belt and seemslikely to have influenced the redox state of the crustally de-rived magmas, which were generated as a result of the deep

emplacement of mafic mantle melts (Lehmann et al., 1990;Redwood and Rice, 1997; Hoke and Lamb, 2007).

A noteworthy aspect of the distribution of the preeminentcopper and tin concentrations in the North and South Amer-ican Cordillera is their clear spatial separation from the majorgold belts (Fig. 9). Although the isolated giant porphyry cop-per-gold deposits at Bingham Canyon, Pebble, and Bajo de la

Alumbrera combine major quantities of the two metals, thismutual exclusivity suggests that the fundamental controls oncopper and gold belts are different. This mutually exclusivepattern of major gold and copper concentrations is furtheremphasized by the spatial separation of the major porphyry copper and high-sulfidation epithermal gold belts in the cen-tral Andes (Fig. 9), notwithstanding the well-documented factthat the latter deposit type typically forms above the formeras parts of single hydrothermal systems (Fig. 1; Sillitoe, 2000)Difference in erosion level alone does not seem to adequately explain this spatial separation of major gold and copper beltsbecause the known porphyry copper and copper-gold de-posits in the Cajamarca-Huaraz belt, including those beneaththe Yanacocha high-sulfidation gold deposits (Gustafson et

al., 2004; e.g., Fig. 4a), are all of low to moderate grade andprobably relatively small.

Metallogenic ConsiderationsThe 22 Phanerozoic gold belts and five isolated giant gold

deposits defined herein together occupy only a small propor-tion of the American Cordillera, perhaps <5 percent of itsarea (Fig. 2). This situation mirrors that for most metals, whereby the majority of the resources are concentrated in afew giant deposits and highly endowed belts (e.g., Singer,1995). Each Cordilleran gold belt was typically generated in<5 to 20 m.y. (Table 2; see above), with individual giant de-posits having lifespans of <0.5 to >5 m.y. (e.g., Henry et al.,1996; Harris et al., 2004, 2008; Longo and Teal, 2005). The

central Andean copper and tin belts (Fig. 10) are analogous inbeing constructed by one or more metallogenic epochs of comparable duration (11–20 m.y.).

All the major gold deposits and belts formed during sub-duction-related magmatic activity (Fig. 8), with each gold de-posit type tending to occupy a reasonably well-definedtectonomagmatic niche rather than occurring randomly.However, when taken together, the major gold deposits andbelts span a spectrum of tectonic settings and magma compo-sitions, although the largest concentrations formed eitherduring or immediately after major contractional episodes inassociation with calc-alkaline magmatism. Fundamental arc-parallel and arc-transverse faults and lineaments or abruptchanges in tectonomagmatic regime at the Cordilleran mar-

gin seem to have acted as localizers of some, but by no meansall, of the major deposits and belts. Another possibility, opti-mization of ore-forming physicochemical processes at the de-posit scale, can be invoked for at least some of the isolated,major deposits, but would fail to satisfactorily explain the ori-gin of the several deposits needed to define the individualgold belts. Therefore, although the spatial and temporal re-striction of the major belts and isolated deposits can be as-cribed to specific tectonomagmatic events, the overall distri-bution of the premier Cordilleran gold concentrations at theorogen scale remains enigmatic, because apparently similar


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La Paz

Salta

225-187 Ma26-22 Ma

Cu belts

Sn-Ag belt

21-12 Ma

43-32 Ma

8-5 Ma

66-52 Ma

135-110 Ma

Antofagasta

PacificOcean

Arequipa

0 500

km

20°

30°

70°

FIG. 10. Principal copper and tin belts of the central Andes, with forma-tional age ranges shown. The copper belts coincide with linear magmaticarcs, which migrated progressively eastward with time, whereas the compos-ite tin belt occupies an essentially fixed, behind-arc position. Taken fromGrant et al. (1979), Clark et al. (1990), and Sillitoe and Perelló (2005).



events elsewhere resulted in only relatively small or no golddeposits.

Perusal of Figure 2 (and Fig. 8) reveals that at least sixCordilleran arc (including fore- and back-arc) segments con-tain at least two gold belts or major isolated deposits, typically comprising different deposit types, formed at different timesunder different tectonomagmatic conditions. The Great

Basin and contiguous areas of the western United States andthe northern Andes of Colombia are perhaps the most strik-ing examples. The Great Basin and environs comprise acluster of six relatively short belts (Carlin, Getchell, and In-dependence sediment-hosted gold trends, Battle Mountain-Eureka sediment-hosted and skarn gold trend, Walker Laneepithermal gold belt, and Sierra Foothills orogenic gold belt),the Bingham district (Bingham Canyon porphyry copper-goldand nearby sediment-hosted gold deposits), and the isolatedRound Mountain epithermal gold and Cripple Creek alkalineepithermal gold deposits. To these gold concentrations may be added the Paleoproterozoic Homestake deposit (Fig. 2)and spatially associated, but subordinate Tertiary gold miner-alization (Paterson et al., 1988). In the Colombian Andes, the

three main belts are defined by pluton-related, porphyry andepithermal, and placer gold deposits, respectively, to whichmay be added two less important gold districts of completely different age to the three main belts (Fig. 6). The pairing orclustering of gold belts and isolated major deposits might bedismissed as fortuitous or, alternatively, ascribed to some fun-damental predisposition of the particular orogen segments

concerned to upper-crustal gold concentration. The closeproximity of both the major copper and the major tin belts inthe central Andes provides closely analogous situations (Fig.10). Explanations involving differences in erosion level andpreservation potential (see above) do not convincingly ac-count for the observed proximity of the metal-enriched andpoorly mineralized arc segments.

One of the more widely debated hypotheses for recurrentmetallic mineralization within relatively restricted orogensegments is inheritance from preexisting metal concentra-tions (e.g., Noble, 1970; Routhier, 1976). The site of any such available metal preconcentration is commonly assumedto be in the middle to upper crust (e.g., Titley, 1987; Hodg-son, 1993; Fig. 11), a concept inherent in the proposal thatmuch of the gold in the sediment-hosted trends of the GreatBasin came from subeconomic sedimentary-exhalative min-eralization in some of the late Paleozoic eugeoclinal hostrocks (Emsbo et al., 1999, 2006). Keith et al. (1991), how-ever, preferred the notion that crustal redox state, ratherthan crustal metal preconcentration, is the ultimate metallo-genic control, with reduced crust like that beneath much of

the Great Basin being conducive to repeated gold mineral-ization; by contrast, oxidized crust, as beneath southwesternNorth America, results in a dominance of copper mineral-ization. The likely role of carbonaceous sedimentary se-quences in the development of reduced magmas was al-luded to above for the Alaskan and Yukon pluton-relatedgold belts and Bolivian tin-silver belt.


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Au deposit

Crust

Subcontinentallithospheric

mantle

AsthenospherePartialmelting

of mantlewedge

Slabdehydration

Upper crust

Hypothetical Aupreconcentrations

Lower crust

Mafic underplate

Mantle wedge

M a n t l e f l o w

Oc e a n ic c r u s t

Sea level

FIG. 11. Cartoon section of a convergent margin to show possible sites of gold (or other metal) concentrations that may be tapped during the magmatism or transcrustal fluid flow responsible for upper-crustal mineralization. Alternatively, an-other chemical parameter, such as redox state, may influence metal availability. See text for further discussion.



The lower crust or underlying subcontinental lithosphericmantle, including underplated mafic igneous rock producedby mantle melting and ultramafic to mafic restites or cumu-lates resulting from mantle-plume or lower-crustal melting,may offer a viable alternative site for either gold preconcen-tration or influential redox conditions (e.g., Noble, 1970; Fig.11). Lower- or subcrustal influences would be eminently fea-

sible given the ubiquitous petrochemical evidence for mantlecontributions to ore-related, arc and back-arc magmatism(e.g., Kelley et al., 1998; Riley et al., 2001; Richards, 2003;Hart et al., 2004; Kay et al., 2005; Hoke and Lamb, 2007) andgeophysical evidence for penetration of some gold-localizingfault zones and lineaments to deep crustal levels (e.g.,Hildenbrand et al., 2000; Grauch et al., 2003). Furthermore,the gold contents of porphyry copper deposits are completely independent of upper crustal structure and composition and,hence, most likely subcrustally imposed (e.g., Sillitoe andPerelló, 2005). Core et al. (2006) furnished evidence for a lo-calized, copper-enriched magma source, in either the deepcrust or subcontinental lithospheric mantle (Fig. 11), for theBingham Canyon porphyry copper-gold deposit, and further

suggested that similar, but areally more extensive copper pre-concentrations may have been tapped to form premier cop-per belts elsewhere. A tin-enriched segment of behind-arccrust (± upper mantle), extending eastward to the Rondôniantin province of contiguous Brazil (e.g., Dardenne andSchobbenhaus, 2001), has also been invoked beneath the Bo-livian tin-silver belt (Schuiling, 1967; Halls and Schneider,1988). However, the concept was refuted by Lehmann et al.(1990), who related the tin concentration to the reduced na-ture of the magmatism, a factor favoring tin (Sn2+) partitioninto the magmatic aqueous phase (Ishihara, 1978). Never-theless, acceptance of the latter hypothesis does not neces-sarily preclude the former when the trivial amounts of tinthroughout the rest of the American Cordillera are taken into

account.In both the Great Basin and contiguous regions of the west-ern United States and the northern Andes of Colombia, thegold deposits and belts are situated both at the craton edgeand in the adjoining accreted terranes of oceanic affinity (Sierra Foothills belt and Middle Cauca and Chocó belts, re-spectively; Figs. 3, 6). Similarly, the paired Kuskokwim goldbelt and giant Pebble porphyry copper-gold deposit in Alaska(Fig. 2) lie within different accreted terranes. Therefore, alower-crustal or subcontinental lithospheric mantle gold pre-concentration may not offer an adequate explanation for therecurrence of gold mineralization events unless the accretedterranes were originally rifted from the craton near their sitesof eventual accretion (Colpron et al., 2007) and/or overthrust

the continental margin along shallow-level décollements(Snyder et al., 2002). Kutina’s (1991) concept of ore depositlocalization by mantle-rooted, latitudinal discontinuities cut-ting across both the craton and accreted terranes fails to ade-quately explain the gold belts, most of which are oriented par-allel, not transverse, to the Cordilleran margin. Alternativeexplanations might include preexisting metal concentrationsin the mantle wedge (e.g., McInnes et al., 1999; Fig. 11) orhighly oxidized conditions, imposed by slab-derived aqueousfluids, conducive to efficient stripping of gold and copperfrom residual sulfides that are broken down in the mantle

wedge (e.g., Mungall, 2002). Furthermore, gold might be pref-erentially stripped under more oxidized mantle-wedge condi-tions than those that favor copper removal (Richards, 2005).

Although the gold and associated chalcophile and siderophilemetals in Cordilleran ore deposits are ultimately derived fromthe dehydration of subducted oceanic crust (e.g., Sillitoe,1972; Richards, 2003, 2005; Fig. 11), anomalously metal-rich

slab material cannot be convincingly invoked to explain highlygold endowed Cordilleran segments because such material would have had to have been intermittently subducted for120 to 150 m.y. to explain both the Great Basin and Colom-bian Andes provinces and even longer elsewhere (northernPeru: ~300 m.y.). Similarly, central Andean copper belts wereformed recurrently over a time span of 130 m.y. (Fig. 10).Nevertheless, protracted subduction of oceanic lithosphere,perhaps coupled with episodic erosion of the leading edge of the overthrust plate (e.g., Stern, 1991), may play a key role inthe progressive enrichment of metals in as well as above themantle wedge.

The complex and varied Precambrian and Phanerozoic his-tories of the American Cordillera and subjacent subcontinen-

tal lithospheric mantle and mantle wedge undoubtedly re-sulted in profound chemical heterogeneity. Notwithstandingthe effects of episodic and relatively localized delamination,and related processes (Menzies et al., 2007), the subconti-nental lithospheric mantle and overlying lower crust seemlikely to be the longest-lived and, hence, potentially most het-erogeneous parts of the crust-mantle system, particularly be-neath Archean cratons. Some of this chemical heterogeneity,in particular with regard to the highly siderophile elementslike gold, may even date from formation of the Earth’s coresome 4.5 billion years ago (Marty, 2008). Some aspect of theresulting chemical provinciality, whether it is in metal con-tent, redox state, or some other parameter, seems the mostlikely reason for the predisposition of certain arc segments to

repetitive epochs of gold mineralization. A redox control, im-posed in the mantle wedge (e.g., Richards, 2005), crust (Keithet al., 1991), or possibly somewhere in the subcontinentallithospheric mantle where oxidation state varies markedly (e.g., Haggerty, 1990), might explain the mutual exclusivity ofmajor gold and copper belts documented above (Fig. 9), as well as perhaps permitting the local co-concentration of thetwo metals under intermediate redox conditions. However,the effective upper-crustal concentration of gold in associa-tion with both oxidized and reduced magmas (see above) se-riously complicates comprehension of mechanisms that mightbe involved. Metal acquisition or redox imposition could beaccomplished by interaction of either magmas or, in the caseof amagmatic gold belts, deeply derived fluids (cf. Hodgson,

1993) with the lithosphere, particularly at times of stasis insubepizonal magma or fluid reservoirs. These subepizonalmagmas or fluids would, of course, have their own intrinsicmetal contents prior to any supplementation from externalsources.

General ConclusionsConsideration of Cordilleran gold belts along with the cen-

tral Andean copper and tin belts strongly suggests that certainupper-crustal segments are subjected to repeated concentra-tion of individual metals or metal suites, whereas adjoining


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segments are relatively poorly mineralized. The same metal-logenic provinciality is observed for gold and other metals worldwide in orogens as old as Archean (e.g., Robert et al.,2005). The processes involved appear to be inherently inde-pendent of tectonic and magmatic settings, which commonly differ between closely spaced metallogenic belts within re-stricted arc segments. Whether or not mantle or crustal metal

preconcentrations or other factors, such as specific redox con-ditions, are called upon, some fundamental predisposition of certain orogen segments with regard to particular metals ormetal suites seems inescapable.

This conclusion, if accepted, has profound implications forexploration because diligent search beyond the favorable oro-gen segments is unlikely to be rewarded by major gold dis-coveries. So the gold explorer may either focus attention onorogen segments containing two or more belts or isolatedgiant deposits, and therefore with proven metallogenic cre-dentials but almost certainly well explored, or try to definenew parts of the orogen predisposed to exceptional gold en-dowment. The latter course of action implies that the reasonfor the predisposition, perhaps the most critical as well as

intractable metallogenic research topic, can be successfully deciphered.

Future DirectionsClassification of the gold deposit types present in the

American Cordillera (and elsewhere), their defining alter-ation assemblages and mineralogy, the physicochemical char-acteristics of the fluids involved, and the timing of their for-mation are reasonably well documented. Nevertheless, thisreview underscores many aspects of Cordilleran gold metal-logeny that require additional investigation, with improvedunderstanding of genetic controls having a direct effect on ex-ploration at the regional scale.

Further clarification of the regional tectonic settings of

many of the major gold deposits and belts in the Cordillera would help to ascertain whether or not specific deposit typesoccupy unique upper-crustal tectonic niches or whether they may form across a spectrum of tectonic settings. Several of the more fundamental questions relate to the economically preeminent high-sulfidation epithermal, sediment-hosted,and orogenic categories: The largest high-sulfidation epither-mal gold deposits are restricted to the two central Andean arcsegments presently characterized by flat-slab subduction(Fig. 2). Is this fortuitous and unrelated to the modern slabconfiguration or does decreasing subduction angle somehow favor major high-sulfidation deposit formation, perhaps by al-lowing direct crustal input of slab-derived auriferous fluids(Bissig et al., 2003) or, as in the case of major porphyry cop-

per deposits, by inducing crustal compression and generationof large epizonal magma chambers capable of voluminousfluid discharge (Sillitoe, 1998)? Major sediment-hosted de-posits are largely responsible for definition of the four closely spaced gold trends in northern Nevada (Fig. 3), but such de-posits appear unimportant elsewhere in the AmericanCordillera. Is this a reflection of the role played by the deeply penetrating structures inherited from Neoproterozoic rifting(Tosdal et al., 2000) or are other processes involved? TheSierra Foothills belt is the only world-class orogenic gold con-centration in the American Cordillera, which is somewhat

surprising if such deposits are one of the hallmarks of accre-tionary tectonic settings (Goldfarb et al., 2001). Is the appar-ent absence of orogenic gold deposits from the Late Creta-ceous and Tertiary collisional collage of the northern Andes of Colombia and Ecuador (Cediel et al., 2003) due to insuffi-cient erosion to allow deposit exhumation (cf. Goldfarb etal., 2001) or to some other factor(s), such as absence of suit-

able deeply tapping fault zones and/or major associatedbatholiths?Additional detailed petrochemical studies of well-dated

magmatic suites associated with the major Cordilleran golddeposits and belts, like those carried out in the El Indio-Mar-icunga belt (Kay et al., 1994, 1999; Kay and Mpodozis, 2001),Patagonian province (Pankhurst et al., 1998; Riley et al.,2001), and Bingham district (Waite et al., 1997), would assist with assessment of any direct links between specific gold de-posit types and specialized magma chemistries or evolution-ary paths. In this regard, Richards and Kerrich (2007) show,contrary to recent proposals, that adakitic (high Sr/Y andLa/Yb) magmatism is unlikely to be a requirement for majorporphyry copper ± gold deposit genesis. Injection of mafic

magma into more felsic epizonal chambers has been pro-posed as an important step in the development of major por-phyry copper-gold deposits (e.g., Waite et al., 1997; Hattoriand Keith, 2001; Halter et al., 2004) and perhaps even the in-trusive rocks of the Carlin sediment-hosted gold trend(Ryskamp et al., 2008). Is similar magma mixing involved inthe formation of other major Cordilleran gold deposits andbelts? If so, it is important to systematically collect the sup-porting petrologic and petrochemical evidence, with a view todefining possible exploration criteria. Cordilleran gold beltsaccompany both oxidized and reduced magma suites, al-though the latter are restricted to the northern Cordillera of Alaska and the Yukon Territory. Is generation of reducedmagmas an exclusively upper-crustal process or can deeper

crustal or mantle redox controls, such as those proposed by Keith (1991) and Richards (2005), have an influence too? And why are the reduced magmatic rocks of the Bolivian tin-silverbelt so poor in gold mineralization? As described above, thelargest Cordilleran sediment-hosted and orogenic gold beltsare likely underlain by concealed plutons emplaced at thetime of mineralization. Is the gold derived from nonmagmaticsources, as currently preferred by most investigators, or couldit have been liberated during cooling of these deep intru-sions? An approach using lead isotopes may be applicable, asemployed recently to link the low-sulfidation epithermal goldof the Northern Nevada rift to mafic volcanic products of theYellowstone mantle plume (Kamenov et al., 2007).

Although these and numerous other tectonomagmatic

problems need our attention, the most fundamental ques-tions of all relate to the concepts of metallogenic inheritanceand provinciality as explanations for the metal distributionpatterns highlighted in this review and elsewhere, as a for-tuitous association seems an unsatisfactory explanation, par-ticularly to the avid explorationist. Perhaps the best long-term means of addressing this topic would be to routinely acquire analytical data for gold, copper, tin, and associatedmetals as well as information to determine the associatedredox conditions while conducting integrated tectonic, geo-chemical, and geophysical studies of the lower crust and


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upper mantle, like that recently synthesized by Karlstrom etal. (2005) for the Rocky Mountains region of the westernUnited States. The analytical data could be obtained fromoutcropping rocks in deeply eroded, high-grade metamor-phic terranes as well as from xenoliths of both upper mantleand lower crustal provenance. Such analytical data areneeded for both well-endowed and poorly mineralized belts

in order to properly define the nature and environment of any metal preconcentrations. Particular attention might be paidto high-grade terranes containing Precambrian mineraliza-tion in proximity to Phanerozoic belts defined by the samemetal(s), as exemplified by the Paleoproterozoic Homestakegold deposit in the context of the major Meso-Cenozoic golddeposits and belts in the western United States (Fig. 2).

These are just a few of the basic questions, and possible ap-proaches, which investigators may consider when identifyingresearch topics of merit.

AcknowledgmentsThe manuscript benefited from constructive reviews by Jeff

Hedenquist, Jay Hodgson, Pepe Perelló, Jeremy Richards,

and François Robert, all of whom are absolved of any directresponsibility for the opinions expressed.May 6, May 12, 2008

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