Tectonic setting of synorogenic gold deposits of the Pacific Rim

Ore Geology Reviews 13 Ž1998. 185–218

Tectonic setting of synorogenic gold deposits of the Pacific Rim R.J. Goldfarb a

a,)

, G.N. Phillips b, W.J. Nokleberg

c

U.S. Geological SurÕey, Box 25046, DenÕer Federal Center, DenÕer, CO 80225, USA b Great Central Mines Limited, 1 Coppin St., East MalÕern 3145, Vic., Australia c U.S. Geological SurÕey, 345 Middlefield Road, Menlo Park, CA 94025, USA Received 1 February 1997

Abstract More than 420 million oz of gold were concentrated in circum-Pacific synorogenic quartz lodes mainly during two periods of continental growth, one along the Gondwanan margin in the Palaeozoic and the other in the northern Pacific basin between 170 and 50 Ma. These ores have many features in common and can be grouped into a single type of lode gold deposit widespread throughout clastic sedimentary-rock dominant terranes. The auriferous veins contain only a few percent sulphide minerals, have gold:silver ratios typically greater than 1:1, show a distinct association with medium grade metamorphic rocks, and may be associated with large-scale fault zones. Ore fluids are consistently of low salinity and are CO 2-rich. In the early and middle Palaeozoic in the southern Pacific basin, a single immense turbidite sequence was added to the eastern margin of Gondwanaland. Deformation of these rocks in southeastern Australia was accompanied by deposition of at least 80 million oz of gold in the Victorian sector of the Lachlan fold belt mainly during the Middle and Late Devonian. Lesser Devonian gold accumulations characterized the more northerly parts of the Gondwanan margin within the Hodgkinson–Broken River and Thomson fold belts. Additional lodes were emplaced in this flyschoid sequence in Devonian or earlier Palaeozoic times in what is now the Buller terrane, Westland, New Zealand. Minor post-Devonian growth of Gondwanaland included terrane collision and formation of gold-bearing veins in the Permian in Australia’s New England fold belt and in the Jurassic-Early Cretaceous in New Zealand’s Otago schists. Collision and accretion of dozens of terranes for a 100-m.y.-long period against the western margin of North America and eastern margin of Eurasia led to widespread, latest Jurassic to Eocene gold veining in the northern Pacific basin. In the former location, Late Jurassic and Early Cretaceous veins and related placer deposits along the western margin of the Sierra Nevada batholith have yielded more than 100 million oz of gold. Additional significant ore-forming events during the development of North America’s Cordilleran orogen included those in the Klamath Mountains region, California in the Late Jurassic and Early Cretaceous; the Klondike district, Yukon by the Early Cretaceous; the Nome and Fairbanks districts, Alaska, and the Bridge River district, British Columbia in the middle Cretaceous; and the Juneau gold belt, Alaska in the Eocene. Gold-bearing veins deposited during the Late Jurassic and Early Cretaceous terrane collision that formed the present-day Russian Far East have been the source for more than 130 million oz of placer gold. The abundance of gold-bearing quartz-carbonate veins throughout the Gondwanan, North American and Eurasian continental margins suggests the migration and concentration of large fluid volumes during continental growth. Such volumes could be released during orogenic heating of hydrous silicate mineral phases within accreted marine strata. The common temporal association between gold veining and magmatism around the Pacific Rim reflects these thermal episodes.

)

Corresponding author.

0169-1368r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 1 6 9 - 1 3 6 8 Ž 9 7 . 0 0 0 1 8 - 8

186

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

Melting of the lower thickened crust during arc formation, slab rollback and extensional tectonism, and subduction of a slab window beneath the seaward part of the forearc region can all provide the required heat for initiation of the ore-forming processes. q 1998 Elsevier Science B.V. All rights reserved. Keywords: lode-gold mineralisation; syn-orogenic; Pacific Rim; ore-forming processes

1. Introduction A key feature of many metasedimentary rockhosted gold deposits is their spatial and temporal association with collisional orogens and, because of this, we refer to such deposits in this paper as synorogenic gold deposits. The widespread distribution of these deposits throughout the accreted terranes of western North America suggests a direct association between continental growth and ore genesis ŽBarley et al., 1989; Kerrich and Wyman, 1990.. Gold ores have formed both in interior orogens developed between large land masses during continent– continent collision Ž i.e, Appalachian – Caledonian, Hercynian, Uralian. and in peripheral orogens built during subduction of oceanic crust along continental margins Ži.e., Cordilleran, Tasman.. Most significant is the fact that collisional tectonism

can eventually trigger crustal heating events and such heat is critical for devolatilization reactions and ore fluid formation ŽPowell et al., 1991; Phillips, 1991; Goldfarb et al., 1993.. Simultaneously with or soon after the heating, transform movements along major crustal fault zones may also be critical to the ore-forming process, leading to relaxation of regional compressive forces and enhanced crustal-scale permeabilities. Unlike Archaean gold vein deposits, synorogenic gold lodes of Phanerozoic age are predominantly hosted by oceanic sedimentary rocks. In many Phanerozoic belts, however, subordinate mafic volcanic rocks are interbedded with slates and graywackes. This reflects contemporaneous sedimentation and oceanic arc or ridge volcanism prior to collision. The magmatic roots to such arc volcanism are rarely observed in suture zones, appearing as

Fig. 1. Major synorogenic gold districts along the Pacific plate margin.

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

minor mafic andror ultramafic plutonic bodies. In most auriferous slate belts, felsic to intermediate intrusive bodies occur within a few tens of kilometres of the gold lodes. Modern dating methods have shown significant temporal overlap, suggesting the intrusions and the gold to be products of a single, large-scale crustal thermal event. These syn- to postcollision plutons, as well as the gold veins, can occur in the continental margin fore-arc region, further inboard in the magmatic arc, or, less commonly, a few tens of kilometres landward of the arc. Synorogenic gold deposits, often referred to as mesothermal deposits despite a wide range in P–T of ore formation, are widely-distributed in accreted terranes that were deformed along the circum-Pacific margin ŽFig. 1.. More than 420 million oz of gold have been recovered from quartz vein and related placer deposits in this region, with greatest production equally divided between the North American Cordillera, the Russian Far East and northeastern China, and the Tasman fold belt of eastern Australia ŽFig. 2.. These regions contain most of the world’s recognized Phanerozoic gold resources associated with synorogenic lodes Žthe one main exception being the upper Palaeozoic deposits along the southern side of the Angara craton in central Asia.. The ores are ultimately the product of two extensive diachronous periods of deformation along what were

187

or had recently been growing continental margins. These main periods of Pacific rim orogenesis include the Palaeozoic tectonism along the southeastern Gondwanan margin and the Middle Jurassic to Early Tertiary plate collisions in the northern Pacific basin. The detailed study of how gold formation relates to regional tectonism for some of the youngest lodes located in Alaska ŽGoldfarb et al., 1997. is a key to helping decipher the tectonic controls on genesis of older Phanerozoic ores. In the following summary, we describe the most accepted tectonic settings, the metamorphic and igneous histories and the published dates of gold veining for the more important circum-Pacific synorogenic deposits. Much of the detail is focused on the relatively well-studied Middle Jurassic to Early Eocene ore districts formed in the accreted terranes of western North America ŽTable 1.. A briefer summary of the Early to middle Cretaceous eastern Eurasian gold districts ŽTable 2. reflects the limited available information from that region of the Pacific margin. Similar geologic features are described that characterize the mainly Palaeozoic lode districts of eastern Australia and South Island, New Zealand ŽTable 2.. Comparisons and contrasts between the regions are evaluated in a final discussion to better establish significant relationships between gold veining and orogenesis.

Fig. 2. Relative production from synorogenic lodes and related placer deposits of the Pacific rim.

Major districts

Kodiak, Nuka Bay, Moose Pass, HopeSunrise, Girdwood, Pt Wells, Pt Valdez, Chichagof Berner’s Bay, Eagle River, Juneau, Snettisham, Windham Bay

Willow Creek

Valdez Creek

Bridge River, Coquihalla

Areaa

Southern coast, AK

Juneau gold belt, SE AK

Talkeetna Mts., south-central AK

Maclaren glacier metamorphic belt, south-central AK

SW B.C.

Pioneer, Bralorne, Carolin

Valdez Creek placer deposit

Independence

Alaska– Juneau, Treadwell, Kensington

Chichagof, HirstChichagof, Granite, Cliff

Major mines

4.3 Ž0.6 .

minor

minor

0.5

minor

minor

6.8 Ž ) 5.0 .

0.6

0.1

Placer production Ž m. oz Au .

0.9

Lode production Žreserves. Žm. oz Au .

L Pz-E Mz basinal rocks, arc rocks, and ophiolites of Bridge River and Cadwallader terranes

J-K flysch of the Kahiltna terrane; E Tert plutons

L Pz schist of the Peninsular terrane; L K tonalite

J-K flysch of the Gravina belt; Perm metabasalt; Tr phyllite and metagabbro of Taku terrane; mid-K monzodior

L K turbidities of the Chugach terrane; E Tert plutons

Host rocks b

Table 1 Main tectonicrgeochronological features of synorogenic gold deposits of the Cordilleran orogen, western Pacific Rim

91 – 86

63 – 57

66, 57 Ž? .

56 – 53

57 – 49

Age of veining Ž Ma.

270, 91 – 43

78, 70, 66 – 54

79 – 66

100 – 90, 70 – 60 Žtonalite sill belt., 60 – 50 Žnorthern Coast batholith .

60 – 50

Age of spatially associated magmatism ŽMa .

Yalakom

Valdez Creek shear zone; Denali

Castle Mountain Ž? .

subsidiary faults to the Sumdum and Fanshaw systems

Chichagof district s Border Ranges and Queen Charlotte; other districts s small brittle to ductile faults and joints

Associated fault zones

with onset of s-s

orthogonal collision of Wrangellia, but possibly coeval

oroclinal bending of AK; possible dextral s-s; uplift of flysch belt

subduction of Chugach terrane; possible s-s during oroclinal bending of AK

change from orthogonal to oblique subduction; uplift of orogen core along eastern side of gold belt

ridge subduction; s-s at Chichagof

Coeval tectonism

12

4,9,20

13

8,15

7,10,21

References c

188 R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

Council– Solomon, Fairhaven – Kougarok

Mother Lode, East Gold Belt, West Gold Belt, Alleghany, Grass Valley

French-Gulch, Deadwood

Klondike, Cassiar, Cariboo

Atlin, Stewart Lake

Seward Peninsula, NW AK

Sierra Foothills, central CA

Klamath Mts, northern CA

Omenica Geanticline, Yukon and B.C.

Northern and central B.C.

minor

0.3 Ž5.5 .

Atlin placer fields

Klondike placer fields

3.5

minor

)1

Jamestown, 35 Ž15 . Hammonton, Columbia, Jackson–Plymouth, Folsom

Nome placer deposits

Fort Knox, Ryan Lode, True North

1

) 12

3.5

65

6

) 11

Perm-Tr ophiolite of the Cache Creek terrane

E Pz pericratonic and miogeoclinal strata of Kootenay and Cassiar terranes; L Pz ophiolite of Slide Mtn. terrane; Perm metafelsic volcanics of Yukon– Tanana terrane

complex group of Pz-J oceanic arcs and accretionary prisms

mid-Pz-J argillite, graywacke, chert, and oceanic volcanic rocks of the northern Sierra, Merded River, Sullivan Creek, and Foothills terranes

E Pz phyllite of the Seward terrane

E Pz quartzite and schist of the Yukon – Tanana terrane; mid K diorite

177 – 135

G 147, F 136

170–165

172–162

G 140 – 130 180 – 190

150 – 80

108 – 82

105 – 85, 80 – 65, 55 – 50

144 – 141, 127–108

109

92 – 85, 77

perhaps regional-scale thrust faults in Klondike

Soap Creek – Siskiyou

Melones, Bear Mountains, and other steeply-dipping thrust faults

high-angle normal faults and extensional joint sets

Stockwork veins and shears; regional association with NEtrending s-s faultzones between Denali and Tintina faults

outboard collision of the YukonTanana terrane

postcollisional thermal reequilibration

rapid shifts in convergence velocities

seaward-stepping of subduction zone at 150–140 Ma; onset of rapid, orthogonal subduction at 120 Ma

slab rollback and regional extension

subduction of Gravina flysch belt during collision of Wrangellia

2

1,16,18,19

5

3,11

6

14,17

c

b

Areas: AK s Alaska, CA s California, B.C.s British Columbia. Host rocks: E s early, L s late, Pz s Palaeozoic, Mz s Mesozoic, K s Cretaceous, Tert s Tertiary, Js Jurassic, Tr s Triassic, Perm s Permian. References: Ž1 . Andrew et al. Ž1983 .; Ž2 . Ash et al. Ž1996.; Ž3. Bohlke and Kistler Ž1986.; Ž4. Davidson et al. Ž1992 .; Ž5 . Elder and Cashman Ž1992 .; Ž6 . Ford and Snee Ž1996 .; Ž7 . Goldfarb et al. Ž1986 .; Ž8 . Goldfarb et al. Ž1991 .; Ž9 . Goldfarb et al. Ž1997 .; 10. Haeussler et al. Ž1995 .; Ž11 .. Landefeld Ž1988 .; Ž12 . Leitch et al. Ž1991 .; Ž13 . Madden-McGuire et al. Ž1989 .; Ž14 . McCoy et al. Ž1997 .; Ž15 . Miller et al. Ž1994 .; Ž16 . Mortensen Ž1990 .; Ž17 . Mortensen et al. Ž1996 .; Ž18 . Rushton et al. Ž1993 .; Ž19 . Sketchley et al. Ž1986 .; Ž20 . Smith Ž1981 .; Ž21 . Taylor et al. Ž1994 ..

a

Fairbanks, Circle, Fortymile– Eagle, Kantishna

East-central AK

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218 189

190

Table 2 Main tectonicrgeochronological features of synorogenic gold deposits of the eastern Pacific Rim Major districts

Lode production Žreserves. Žm. oz. Au.

Placer production Žm. oz. Au.

Host rocks c

Age of veining ŽMa. c

Age of spatially associated magmatism ŽMa. c

Coeval tectonismc

Referencese

Yana-Kolyma belt Central part, Russian northeast

Omchak

8a

)130 a

L Pz-mid-Mz turbidities of the Kolyma–Omolon terrane

135–100

144–134, 120–80

increased collisional rates between Eurasia and Izanagi plates in E K; slab rollback and extension in mid-K

5,9,12–14

Verkhoyansk belt, western part and Allakh–Yun, southern part, Russian northeast

Carb.-J. passive margin sedimentary rocks

mid-K

mid-K

increased collisional rates between Eurasia and Izanagi plates

12,13

Chukotka belt, northern part, Russian northeast

numerous continental margin and oceanic terranes

opening of the Canada basin and terrane collision in mid-K; slab rollback and extension in mid-K

12,13

Selemdzha–Kerbi, northwestern part, Russian southeast

accretionary prism made up of Tukuringra–Dzhagdi and Galam terranes

L K subduction and collision

12,13

subduction-related basement uplift?; onset of extension?

6,11,17,20

NE China

Shangdong, Jianchanggouliang, Jinchangyu

) 30 b

Archaean gneisses and schists, L Pz-L Tr granitoids

130–120 d

L Pz-L Tr, 165–150, 130–120

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

Area

Macres Flat

New England fold belt, eastern Australia

Gympie, Hillgrove ) 4Ž1.

Lachlan fold belt, SE Australia

Bendigo, Ballarat, 32 Castlemaine, Stawell, Hill End

Hodgkinson– Broken River and Thomson fold belts, NE Australia

Hodgkinson Charters Tower, Ravenswood

9

Westland, South Island, New Zealand

Reefton

2.5 Ž1.

a

1Ž1.

)8

48

)5

Perm-L Tr turbidities of Torlesse and Caples terranes

J-E K

none

collisional deformation

10

Carb-Perm turbidities and granites of WandillaTablelands and Gympie terranes

Perm-E Tr

306–280, 255–245, E Tr

subduction and accretion; uplift?

2,7,18

Ord-E Dev flysch

L Sil-E DevŽ?., M Dev-E Carb

410–390, 370–360

intraplate thinskinned deformation; perhaps subductionrelated

1,16,19

Camb-Dev flysch, M Ord-M Dev granitoids

Sil-Dev, L Carb

M Ord-M Dev, L Carb-E Perm

intraplate thinskinned deformation; perhaps subductionrelated

3,15,19

Ord sandstone, siltstone, and shale

Pz

370-310

uncertain

4,8

Estimate for entire Russian Far East. Estimate for production and reserves. c Host rock and ages: E searly, M s middle; L s late; Pz s Palaeozoic, Mz s Mesozoic, CambsCambrian, OrdsOrdovician, Dev s Devonian, SilsSilurian, Perm s Permian, Tr s Triassic, Js Jurassic, K sCretaceous, CarbsCarboniferous. d Some of the northeast China deposits are definitely older and probably Hercynian. e References: Ž1. Arne et al. Ž1996.; Ž2. Ashley et al. Ž1994.; Ž3. Coney Ž1992.; Ž4. Cooper and Tulloch Ž1992.; Ž5. Eremin et al. Ž1994.; Ž6. Geological Survey of Canada Ž1991.; Ž7. Gilligan and Barnes Ž1990.; Ž8. Goldfarb et al. Ž1995.; Ž9. Goryachev Ž1994.; Ž10. McKeag and Craw Ž1989.; Ž11. Nie and Wu Ž1995.; Ž12. Nokleberg et al., 1994b; Ž13. Nokleberg et al. Ž1996.; Ž14. Parfenov et al. Ž1996.; Ž15. Peters and Golding Ž1989.; Ž16. Phillips and Hughes Ž1996.; Ž17. Poulsen and Mortensen Ž1993.; Ž18. Scheiber Ž1996.; Ž19. Solomon and Groves Ž1994.; Ž20. Wang et al. Ž1996.. b

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

Otago, South Island, New Zealand

191

192

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

2. Tertiary synorogenic gold deposits of the Pacific Rim The youngest economically significant gold ores hosted in regionally metamorphosed terranes of the Pacific Rim are those of the southern Alaska forearc ŽFig. 3.. Gold-bearing veins, now exposed in dis-

tricts throughout the Chugach and Kenai Mountains ŽFig. 4b. and Alexander Archipelago ŽFig. 4a., were emplaced within turbidities of a 2000-km-long accretionary prism between 57 and 49 Ma ŽGoldfarb et al., 1986; Taylor et al., 1994; Haeussler et al., 1995.. More productive districts, such as near Juneau, are located a few hundred kilometres landward of the

Fig. 3. Distribution of synorogenic gold districts within the Alaskan Cordillera. Absolute dates for veining in some districts are listed, as determined by a number of workers using K–Ar and Žor. 40Arr39Ar methods on hydrothermal micas. Generalized composite terranes after Plafker and Berg Ž1994..

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

prism. They occur adjacent to or are hosted by parts of the continental margin magmatic arc, and they formed between 66 and 53 Ma ŽGoldfarb et al., 1993..

193

2.1. Gulf of Alaska accretionary prism Subduction-related tectonics during the earliest Tertiary along the southern Alaska continental mar-

Fig. 4. Gold districts within the Southern margin composite terrane and adjacent parts of the Wrangellia terrane. Ža. Deposits of the Chichagof district in southeastern Alaska. Žb. Gold districts in the Kenai and Chugach Mountains of south-central Alaska.

194

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

gin, and along the northeasternmost part of the Pacific basin, led to the emplacement of widespread gold veins in a near-trench environment. Alaska itself is composed of more than fifty lithotectonic terranes of predominantly oceanic character ŽJones et al., 1987; Monger and Berg, 1987.. By the Late Cretaceous, most of these terranes were amalgamated and had already been accreted to the northwestern corner of the North American continent. Subsequently, during the Palaeocene and earliest Eocene, tectonism in the southern half of Alaska was driven by dextral-oblique to orthogonal convergence of both the Kula and Farallon plates with the North America plate. The convergence included emplacement of the outermost part of the Chugach terrane against and below the southern Alaska margin ŽPlafker and Berg, 1994.. This accretionary complex, predominantly Late Cretaceous to Palaeocene deep sea fan deposits, was highly deformed during early Tertiary collision and underthrusting. The Chugach terrane is bounded on its landward side by the steeply-dipping Border Ranges fault system ŽFigs. 3 and 4.. This crustal-scale thrust fault system separates the Chugach terrane from older rocks of the inboard Wrangellia composite terrane. A similar fault system, the early Eocene contact fault system ŽFig. 4b., separates the Chugach terrane from slightly younger turbidities of the Prince William terrane that are exposed along the continental margin of south-central Alaska. However, in southeastern Alaska, the seaward boundary to the Chugach terrane has been dominated by dextral translation along the Queen Charlotte–Fairweather fault system ŽFig. 3. perhaps since early Eocene ŽPlafker and Berg, 1994.. As described below, this difference in structural setting along the length of the accretionary complex likely played a major role in determination of the relative size of synorogenic gold vein systems. An early Tertiary high-T, low-P metamorphic event within the Chugach terrane ŽHudson and Plafker, 1982. generated magmas and fluids, with the latter being directly responsible for the turbiditehosted gold–quartz lode systems in the Chugach– Kenai Mountains of south-central Alaska ŽGoldfarb et al., 1986; Fig. 4b. and Alexander Archipelago of southeastern Alaska ŽTaylor et al., 1994; Fig. 4a.. The event coincides with the final collisional defor-

mation of the allochthonous terrane, but predates the onset of regional uplift by about 5 m.y. ŽPlafker et al., 1989.. The little documented postaccretionary, strike-slip movement on the major terrane-bounding, thrust-faulted suture zones in south-central Alaska limited crustal permeabilities along these major structures. Synorogenic fluid flow was, therefore, diffuse over a broad area of fracture networks between the suture zones, rather than focussed into and migrating up the large faults. The resulting small, gold-bearing occurrences are widespread, but generally subeconomic in south-central Alaska. Where developed, lodes and placers of the Kodiak, Nuka Bay, Hope-SunriserMoose Pass, Girdwood, Port Wells and Port Valdez districts ŽFigs. 3 and 4b. have a combined production of only 250,000 oz of Au. In contrast, in the southeasternmost part of the Chugach terrane, orogen-parallel transcurrent motion along terrane-bounding faults likely accompanied the Eocene thermal event. Such tectonism would have increased permeabilities along the major faults and in subsidiary fault zones between the faults. Resulting large fluid discharges could account for the 800,000 oz of gold recovered from the two main vein systems of the Chichagof and Hirst–Chichagof deposits ŽFig. 4a.. There is a general west to east younging of both 60- to 50-Ma flysch-melt plutons and 57- to 49-Ma synorogenic gold veins along the entire 2000-km length of the Chugach complex. This delineates migration of an active slab window ŽBradley et al., 1993, 1994; Haeussler et al., 1995. or young crust adjacent to an inactive window ŽRick Saltus, oral commun., 1996.. Where igneous rocks and veins both occur in a district, veins always cut the plutons and suggest hydrothermal mineralization was perhaps a few million years younger than magmatism. Subduction of a slab window in oceanic crust migrating downward beneath the base of the prism, likely a part of the spreading Kula–Farallon spreading ridge, is hypothesized to have contributed to anomalous heating of the prism that composed the outer forearc ŽHaeussler et al., 1995.. It is possible, however, that the gravity spreading along such a topographic rise may have stopped once the ridge neared the trench. Nevertheless, simple heat conduction from the underthrusting of hot, young oceanic lithosphere has the

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

potential for significantly increasing geothermal gradients at the base of the overlying accretionary prism ŽMolnar and England, 1995. 2.2. Near-arc and within-arc deposits of southern Alaska Simultaneous with early Tertiary gold formation along the continental margin of Alaska were the final stages of magmatic arc development and major gold-veining episodes a few hundred kilometres inboard from the margin ŽGoldfarb et al., 1993, 1997.. The arc is dominated by Late Cretaceous through early Eocene subduction-related batholiths that now predominate within the higher elevations of the Talkeetna Mountains, Alaska Range and Coast Mountains. Productive gold-bearing veins formed along the seaward margin of the arc between about 66 Ma and 53 Ma ŽFig. 3, No. 33, 34, 2, 8, 15, 32 and 35.. Most were formed in sedimentary rock-dominant terranes within 5–10 km of the arc rocks; some formed within felsic to intermediate calc-alkaline batholiths of the arc itself, about 5–10 m.y. after crystallization of igneous host rocks. 2.2.1. Juneau gold belt The 200-km-long Juneau gold belt in southeastern Alaska ŽBerner’s Bay, Eagle River, Juneau, Snettisham and Windham Bay districts of Fig. 3. has yielded about seven million oz of gold and still contains substantial resources. The deposits of the belt occur within a few kilometres of the Fanshaw and Sumdum thrust faults, steeply-dipping structures that separate rocks of the Yukon–Tanana terrane, the composited Taku and Wrangellia terranes, and the Gravina overlap assemblage immediately west of the Coast batholith ŽFig. 5.. Rocks in these terranes were regionally metamorphosed to lower greenschist and subgreenschist facies during mid-Cretaceous and older deformational episodes above the subducting Farallon plate ŽHimmelberg et al., 1991.. Thrusting along the two closely-spaced faults ceased at 83–71 Ma, but then stepped to the Coast shear zone generally located a few kilometres eastward ŽGehrels, 1998.. Ductile deformation along this latter steep structure, which cuts both sutures near the north end of the Juneau gold belt, occurred between 71 and 59 Ma. The deformation included rapid regional uplift

195

of the orogen core to the east of the Coast shear zone ŽGehrels, 1998., an area now exposing the immense Coast batholith. Deformation along the Coast shear zone was accompanied by the deep Ž4–7.5 kb; i.e., McClelland et al., 1991 and Gehrels et al., 1992. emplacement of a 700-km-long belt of 5–10-km-thick tonalite sills at about 70–60 Ma. Sill emplacement was immediately followed by voluminous 60 to 50 Ma magmatism to the east that formed the shallower Ž3–4 kb; i.e., McClelland et al., 1991. north part to the Coast batholith. Most significantly, latest Cretaceous to Palaeocene sill emplacement was accompanied by an 8-km-wide Barrovian metamorphism extending westerly to the two thrust faults ŽFig. 5; Himmelberg et al., 1991.. The fluid volumes generated during this high-T episode are hypothesized to have migrated into and along these faults, and deposited the gold in veins at 7–15 km depth within greenschist facies units of the Barrovian sequence ŽGoldfarb et al., 1997.. This 56–53 Ma fluid flow event occurred simultaneously with a major change in regional stress fields ŽGoldfarb et al., 1991.. The model requires a period of at least five million years between initial pore fluid generation and subsequent vein precipitation. 2.2.2. Valdez Creek district A tectonic scenario similar to that observed in the Juneau gold belt also characterizes the gold-rich Maclaren glacier metamorphic belt. This metamorphic belt is located along the southern side of the Denali fault system in south-central Alaska. Auriferous lodes are widespread throughout the greenschist facies units of the belt and have been eroded to yield the 500,000 oz of gold recovered from placers in the Valdez Creek district ŽFig. 3, No. 33; Fig. 6.. The belt formed within the Jurassic to mid-Cretaceous strata of the Kahiltna flysch basin. The basin was closed by middle Late Cretaceous time during convergence between the Yukon–Tanana terrane to the north and the subducting Wrangellia terrane to the south, with the latter being carried northward on the recently-formed Kula plate ŽPlafker and Berg, 1994.. Melt-enhanced deformation ŽHollister and Crawford, 1986. of the pelitic rocks between 78 and 68 Ma, perhaps due to the continued subduction from the south, was recorded within a major deep-crustal

196

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

ductile shear zone, the 4–5-km-thick Valdez Creek shear zone ŽDavidson et al., 1992.. During this period, at depths of 25–40 km, a 1-km-thick tonalite sill was emplaced at 78 Ma within the shear zone

and the 70 Ma Susitna batholith crystallized along the zone’s eastern edge ŽDavidson et al., 1992.. A steep Barrovian sequence was overprinted on the flysch at 78 Ma, extending from the sill seaward Žto

Fig. 5. Gold deposits of the Juneau gold belt, southeastern Alaska. Listed dates include 40Arr39Ar measurement on hydrothermal micas Žfrom Goldfarb et al., 1997. and U–Pb ages of adjacent batholith Žfrom Gehrels et al., 1992 and Gehrels, 1998..

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

the south. for 10 km ŽSmith, 1981.. Deformed metamorphic and igneous rocks began uplifting by 68 Ma and cooled below about 3008C by 62 Ma ŽDavidson et al., 1992.. Additional magmatism and the synorogenic gold veining occurred during the uplift of the Kahiltna flysch. A series of dioritic bodies were emplaced between 66 and 54 Ma throughout the greenschist part of the metamorphic belt. Simultaneously, 63–57 Ma gold-bearing quartz veins ŽFig. 6. were deposited within the cooling diorites and flysch of the Valdez Creek shear zone ŽGoldfarb et al., 1993, 1996.. Veining was likely aided by the rapid reduction in lithostatic load during the Palaeocene, which would have induced hydrofracturing and thus increased local permeabilities within the deformed belt Žfor example, see Norris and Henley, 1976.. The importance to the ore-forming process of transpressive

197

motions along major crustal structures at this same time is uncertain. But, gold veining occurred during the onset, and near the axis, of the oroclinal bending of Alaska due to North America–Eurasia plate collision ŽPlafker and Berg, 1994.. The Denali fault system, immediately landward of the Susitna batholith, underwent major dextral strike-slip motion during the bending. Similarly, the Broxson Gulch thrust fault that comprises the suture between the Kahiltna and Wrangellia terranes a couple of kilometres seaward of the Valdez Creek gold district, also was the likely focus of Palaeocene strike-slip movement ŽNokleberg et al., 1994a.. 2.2.3. Willow Creek district More than 600,000 oz of gold were recovered from veins in the Willow Creek district of southcentral Alaska ŽFig. 3, No. 34., mainly from fissure

Fig. 6. Distribution of gold-bearing quartz veins of the Valdez Creek district south-central Alaska. Geology and metamorphic facies generalized from Smith Ž1981. and Davidson et al. Ž1992..

198

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

veins at the Independence mine. Unlike the Juneau gold belt and the Valdez Creek district, the ores of the Willow Creek district were almost entirely hosted within the magmatic arc rocks. Jurassic pelitic rocks of the Peninsular terrane, amalgamated prior to ac-

cretion within the Wrangellia composite terrane, were part of the southern Alaska continental margin and regionally metamorphosed to greenschist facies by middle Late Cretaceous. Kula plate subduction along a seaward trench led to accretion of the Chugach

Fig. 7. Distribution of synorogenic gold districts of the Canadian Cordillera. Absolute dates for deposits are listed, as determined by Leitch et al. Ž1991., Ash et al. Ž1996., Andrew et al. Ž1983., Rushton et al. Ž1993., Sketchley et al. Ž1986. and Goldfarb et al. Ž1995. using K–Ar and Žor. 40Arr39Ar methods on hydrothermal micas. Terranes generalized from Wheeler et al. Ž1991..

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

accretionary prism throughout the latter half of the Late Cretaceous. Dioritic to tonalitic plutons, emplaced from 79 to 72 Ma in response to the continued subduction, formed the Talkeetna Mountains batholith within the Peninsular terrane. Tonalitic host rocks were rapidly cooled below 3008C by about 70 Ma ŽCsejtey et al., 1978.. Gold veining occurred within the southern part of the batholith at 66 Ma ŽMadden-McGuire et al., 1989; Steve Harlan, unpubl. data.. As in the Valdez Creek district, ore formation post-dates thrusting within the accreted terrane. Underthrusting of the Chugach terrane beneath the Peninsular terrane did continue during ore formation ŽBurleigh, 1987., but gold veining clearly occurred relatively late during the subduction-related thermal event. Because of this, we speculate that veining might have been aided by the initiation of oroclinal bending in the Palaeocene. The Border Ranges thrust fault system ŽFig. 3. represents the suture between the Peninsular and Chugach terranes. Pavlis et al. Ž1988. indicate that its probable northernmost strand, the Castle Mountain fault located within 7 km of the gold veins, became inactive in the Late Cretaceous. Subsequently, unlike elsewhere along the Border Ranges thrust fault system in south-central Alaska, this northern strand may have been reactivated by strike-slip motion during the oroclinal bending ŽPavlis et al., 1988..

3. Mesozoic synorogenic gold deposits of the Pacific Rim The Mesozoic in the northern Pacific basin was dominated by Kula–Farallon plate convergence with North America on the east and Izanagi and Farallon plate collision with Eurasia on the west. In addition to terrane accretion, many thousands of kilometres of lithosphere were subducted below the continental margins. Synorogenic gold veining, predominantly in the Early and middle Cretaceous, was an inherent part of the growth of both continental masses. Simultaneously in the southern Pacific basin, a final stage of accretion and subduction along the Gondwanan margin temporally correlates with veining in the Haast schists on New Zealand’s South Island.

199

3.1. Mid-Cretaceous deposits of the northern North American Cordillera Two regions of the northern Cordillera are characterized by productive mid-Cretaceous gold concentrations. A broad belt across interior Alaska, including the rich placer fields of the Nome ŽFig. 3, No. 7 and 10. and Fairbanks ŽFig. 3, No. 9. regions, contains Alaska’s oldest gold vein deposits. A smaller area in the south part of southeastern Alaska and southwestern British Columbia includes the Bridge River district ŽFig. 7., the most productive synorogenic lode system within the Canadian Cordillera. 3.1.1. Interior Alaska In interior Alaska, mid-Cretaceous gold-veining and felsic magmatism were widespread near Fairbanks in the Yukon–Tanana terrane and near Nome in the Seward terrane. Although having undergone a great deal of Mesozoic translation, these continental marginrcarbonate platform sedimentary rock-dominant terranes were already part of the North American cratonic margin for at least 100 m.y. prior to ore deposition. The Council, Solomon, Fairhaven, and Kougarok districts near Nome on northwestern Alaska’s Seward Peninsula ŽFig. 3. have combined to yield about six million oz of gold from placer accumulations. Gold-bearing veins are very widespread, but are thin and discontinuous and thus lodes have typically been uneconomical. Historically, Fairbanks and adjacent smaller gold districts of east-central Alaska defined a major placer-producing region that yielded more than 11 million oz of gold from the undulating terrain between the Denali and Tintina fault systems. This part of the Yukon–Tanana terrane, however, has recently been recognized to contain large-tonnage, bulk-mineable stockwork gold systems Že.g., the Fort Knox deposit. hosted in or near early Late Cretaceous felsic to intermediate intrusions. The tectonic regime during the mid-Cretaceous hydrothermal events is problematic. Pavlis Ž1989. and Miller and Hudson Ž1991. indicate a broad extensional event across the northernmost Cordillera due to lithospheric thinning and increased heat flow. The hypothesized control is slab retreat or rollback of the subduction zone in the mid-Cretaceous northern Pacific basin. This large magnitude crustal exten-

200

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

sion event may have continued into the Russian Far East forming the Okhotsk–Chukotka magmatic belt. In northern Alaska, contractional deformation due to Farallon–North America plate convergence resulted in the 170–130 Ma Brookian orogenic event that occurred 20–60 million years before gold veining. Deformation included oceanic crust being thrust above the Palaeozoic and older continental margin pelitic rocks of what became the Seward Peninsula and Brooks Range. During the obduction of the oceanic rocks, the lower continental plate experienced a high-Prlow-T blueschist facies metamorphism with a subsequent greenschist facies overprint ŽTill and Dumoulin, 1994.. Postkinematic Barrovian metamorphism and associated mid-Cretaceous magmatism were restricted to a 250-km-long zone throughout the central and southeastern Seward Peninsula between 108 and 82 Ma ŽArmstrong et al., 1986; Amato et al., 1994.. The initiation of the thermal episode correlates in time with the Seward

Peninsula gold veining located 40–50 km to the south and west ŽFord and Snee, 1996.. We believe that it is more than coincidence that magmatism and Barrovian metamorphism in the Nome area were synchronous with veining. But the 40–50-km spacing between the veins and the thermal front remains difficult to explain. Trench rollback due to mid-Cretaceous opening of the Canada basin, with the North America and Eurasia plates advancing on the Farallon plate, is hypothesized as the cause of large-magnitude crustal extension and heating ŽRubin et al., 1995.. Most of the recognized gold-bearing veins on the Seward Peninsula are located within associated small normal faults ŽFord and Snee, 1996.. The lack of large, crustal-scale structures within the thermally upgraded part of the Seward Peninsula hindered significant focusing of ore fluids and prevented formation of high tonnage ore lodes. The tectonic setting for the mid-Cretaceous gold

Fig. 8. Fairbanks and other gold districts within metamorphosed sedimentary rocks of the Yukon–Tanana terrane, east-central Alaska and westernmost Yukon. Metamorphic facies after Dusel-Bacon et al. Ž1993..

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

ores of the Fairbanks and other districts within the Yukon–Tanana terrane of east-central Alaska is less clear; most recent geochronology suggests that the Fairbanks ores formed subsequent to the regional extension. Palaeozoic and older sedimentary and igneous rocks of the terrane were added to the continental margin and regionally metamorphosed to both blueschist and amphibolite facies between the Late Triassic and Middle Jurassic. Gold veining and related shallow-level ŽF 5 km., calc-alkaline magmatism did not begin for another 100 m.y. ŽMcCoy et al., 1997.. It is uncertain whether the veins and intrusions were products of the widespread extension within the Yukon–Tanana terrane ŽMiller and Hudson, 1991., or slightly younger and renewed subduction below an already thinned-crust ŽStanley et al., 1990.. In support of the latter, Pavlis et al. Ž1993. use argon cooling ages to argue that extension in the terrane ceased by 110 Ma, about 20 m.y. prior to ore deposition. Gold veining was roughly coeval with final docking of the Gravina flysch basin and Wrangellia terrane along the Denali fault system with northwardly-directed subduction continuing below the Yukon–Tanana terrane. Where hosted by the mid-Cretaceous intrusions, gold veins were generally emplaced within 2 m.y. of crystallization ŽMcCoy et al., 1997.. The 600-km-long by 100-km-wide belt of midCretaceous plutons and gold ores, although offset 450 km along the Tintina fault system, continues east of the Yukon–Tanana terrane and into the North America craton of Yukon ŽMortensen et al., 1996.. In Yukon, bulk-mineable gold deposits include the two million oz Dublin Gulch deposit. The deposits of the Canadian Cordillera indicate that processes of gold ore formation that impacted the allochthonous rocks of western North America may, in some cases, have continued inboard of the most landward suture zones. A more favourable structural setting in the Yukon–Tanana terrane relative to the Seward terrane may account for the large, economical lode targets in the former. Northeast-trending strike-slip faults cut the Yukon–Tanana terrane and link the extensive Tintina and Denali fault systems, and much of the gold and magmatism is linked along these ŽFig. 8; LeLacheur, 1991.. More than 400–450 km of dextral displacement on each of the two fault systems began

201

in the Late Cretaceous ŽNokleberg et al., 1985; Plafker and Berg, 1994. and the NE-trending faults across the enclosed terrane could be dilational products of such motion. No matter what their origin, the presence of these large fault zones crossing the terrane can not be ignored in attempting to understand the distribution of some of the newly discovered lode deposits in the Yukon–Tanana terrane. 3.1.2. Southwestern British Columbia and the south part of southeastern Alaska Whereas extension predominated in northwestern Alaska, and both extension and contraction were important in interior Alaska, contraction was clearly dominant during mid-Cretaceous gold formation along the continental margin to the southeast. The Middle Jurassic docking of the Yukon–Tanana terrane to North America to form much of what is now the eastern mainland of Alaska was accompanied by the docking of the juxtaposed Stikine terrane to form much of western British Columbia ŽPlafker and Berg, 1994.. At about the same time, two small and amalgamated terranes composed of late Palaeozoic–early Mesozoic basinal and arc rocks and Permian ophiolites, the Bridge River and Cadwallader terranes, were accreted to the seaward side of the Stikine terrane ŽRusmore, 1987.. Deformation within these terranes continued into the early Late Cretaceous because of the outboard accretion of the Wrangellia terrane. The suture between the terranes to the east and the Wrangellia terrane in the south part of southeastern Alaska and along the southern half of British Columbia is marked by the oldest synkinematic plutons of the Coast batholith. During the final stages of orthogonal convergence, immediately prior to the 85 Ma shift to a more northerly oblique convergence with the birth of the Kula plate ŽEngebretson et al., 1985., gold veining occurred on both sides of the south part of the batholith. More than four million oz of gold were recovered from the lodes of the Bridge River district that are hosted in rocks of the Bridge River and Cadwallader terranes about 10 km east of the south part of the Coast batholith ŽFig. 7.. The veins formed between 91 and 86 Ma along a series of strands of the terrane-bounding Yalakam thrust fault system ŽLeitch, 1990; Leitch et al., 1991.. Although the suture between the small host terranes and the Stikine

202

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

terrane developed tens of millions of years earlier, Wrangellia terrane collision from the west led to continued east-verging backthrusting and deformation along these structural zones until about 85 Ma ŽRusmore and Woodsworth, 1991.. Subsequently, major dextral slip continued into the Tertiary ŽUmhoefer and Schiarizza, 1996.. Gold veining appears to have occurred near the end of contractional deformation, but the close temporal association with the onset of strike-slip motion could have been important. Less productive Ž150,000 oz of gold production and reserves. gold deposits of the Coquihalla district ŽFig. 7. located on the opposite side of the terrane-bounding fault system and 115 km to the south may mark an offset part of the same hydrothermal event ŽLeitch et al., 1991.. The 90 Ma ages for gold veining in the Ketchikan district ŽFig. 3, No. 17; 25,000 oz of Au produced. on the seaward side of the southern part of the Coast batholith ŽGoldfarb, unpublished data. indicate ore-forming processes occurred on both sides of the 100-km-wide batholith during docking of the Wrangellia terrane. 3.2. Middle Jurassic to Early Cretaceous deposits of western North America As the Atlantic Ocean opened at about 180 Ma, terrane collision and translation was initiated along the entire length of the Pacific margin of North America. This oldest portion of significant continental growth during Cordilleran orogenesis was accompanied by a number of major gold vein emplacement episodes over a 70-million-year-long period. Resulting gold deposits are located inboard of the subsequently emplaced batholiths of the Canadian Cordillera ŽFig. 7. and outboard of the syn- to postore Sierra Nevada batholith in the conterminous United States ŽFig. 9.. The latter gold systems, located in central California, have been the most productive goldfields of the Cordilleran orogen. 3.2.1. Canadian Cordillera The oldest synorogenic lodes documented in the North American Cordillera occur along the western margin of the Cache Creek terrane in northernmost and central British Columbia ŽFig. 7.. In the former of these two areas, about one million oz of gold were recovered from placer accumulations in the Atlin

district. The Cache Creek terrane consists of Permian and Triassic oceanic crust that was enclosed between the Stikine and Quesnel terranes in the Early Jurassic. These three terranes, as well as the Yukon– Tanana terrane to the north, were subsequently accreted to North America by about 180 Ma ŽNelson and Mihalynuk, 1993.. This final closure of the Anvil Ocean included westward obduction of the Cache Creek terrane over the Stikine terrane. Gold-bearing veins in the Atlin and Stewart Lake Žcentral British Columbia. areas were emplaced in the Cache Creek rocks within 10–15 m.y. of accretion and obduction ŽAsh et al., 1996.. Also between 172 and 162 Ma, felsic plutons derived from underthrust Stikine terrane rocks intruded the Cache Creek terrane-hosted gold districts ŽAsh et al., 1996; Mihalynuk et al., 1992.. In the Atlin area, the relatively undeformed nature of the igneous bodies ŽMihalynuk et al., 1992. indicates that veining clearly postdated local deformation. It is unclear how the localization of the lodes relates to the poorly-exposed thrust contact between the terranes. Veining and plutonism, though, might be ultimately related to outboard subduction and accretion of the Nisling assemblage Ža part of the pericratonic Yukon–Tanana terrane of Fig. 7. to the Stikine terrane in the late Middle Jurassic ŽCurrie and Parrish, 1993.. A second and more extensive gold veining episode occurred sometime between the Middle Jurassic and Early Cretaceous landward of or on the landward side of the Intermontane Superterrane Žthe amalgamated Quesnel, Stikine, Cache Creek and Yukon– Tanana terranes.. Veins in the Klondike, Cassiar and Cariboo districts ŽFig. 7. are hosted by pericratonic and displaced lower Palaeozoic miogeoclinal strata ŽKootenay and Cassiar terranes., obducted upper Palaeozoic oceanic crust of the Anvil Ocean ŽSlide Mountain terrane., and Permian schist with a metafelsic volcanic rock protolith ŽKlondyke Schist assemblage of the Yukon–Tanana terrane.. The veins of the Klondike district in Yukon–Tanana rocks in Yukon, correlated by some with Kootenay terrane rocks ŽWheeler et al., 1991., were eroded to form the more than ten million oz of gold recovered from placer accumulations. These gold deposits in the Kootenay, Cassiar and Yukon–Tanana terranes are scattered along the length of the Omenica Geanticline, the uplifted region be-

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

tween the accreted terranes and older North American craton. Deformation and metamorphism of rocks in the geanticline occurred during the Late Triassic and Early Jurassic collision of the Intermontane Superterrane; the deformed rocks were later uplifted in the Early Cretaceous ŽMortensen, 1990.. The veins in the geanticline all yield K–Ar dates on micas of about 140–130 Ma ŽAndrew et al., 1983; Rushton et al., 1993; Sketchley et al., 1986., but regional magmatism is well constrained to the Early Jurassic ŽJohnston et al., 1996.. These ore systems in the Omenica Geanticline are notable in that they are the only major Cordilleran gold vein systems that lack an obvious temporal association with magmatism. The lack of earliest

203

Cretaceous plutonism could be an indication of little thermal activity at this time. The 140–130 Ma dates on the veins could be the true age of mineralization, which was caused by rising isotherms over an extensive period of postthickening thermal reequilibration ŽRushton et al., 1993.. If this scenario is correct, veining would postdate deformation and magmatism by perhaps 40–50 m.y. It can not be ruled out, however, that the mica dates simply could record cooling from earlier vein emplacement near the end of deformation. Biotites from schists in this part of the Canadian Cordillera have typically yielded latest Jurassic to earliest Cretaceous K–Ar and Rb–Sr cooling ages, rather than metamorphic ages ŽJohnston et al., 1996..

Fig. 9. Late Jurassic to Early Cretaceous synorogenic gold deposits of the Sierra foothills and Klamath Mountains along the western margin of the conterminous United States. Farther inboard, Late Cretaceous gold-bearing veins in some of the allochthonous terranes adjacent to the Idaho batholith may also be associated with Cordilleran orogenesis. Terranes generalized from Silberling et al. Ž1992..

204

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

3.2.2. Conterminous United States As was much of the northern Cordillera, the southern part of the Cordillera comprising the western edge of the conterminous United States was also a passive margin throughout the early Palaeozoic. In the late Palaeozoic, magmatic arcs developed on oceanic crust, probably fringing a rifted North American margin ŽBurchfiel et al., 1992.. By the Early Triassic, long-term convergence and westward growth had begun along the Pacific margin of the conterminous United States with collision and accretion of the extensive northern Sierran–Klamath arc ŽSonomia.. These arc rocks have been termed the northern Sierra terrane Žor Shoo Fly Complex. and their eastern margin is now marked by the Sierra Nevada batholith. During a 50-m.y.-long period in the Early and Middle Jurassic, the Merced River Žor Calveras Complex., Sullivan Creek and Foothills terranes were emplaced as narrow strips along the western edge of the northern Sierra terrane in what are now the western foothills of the Sierra Nevada range in central California ŽFig. 9; Paterson and Sharp, 1991.. In the Late Jurassic, subduction stepped outward with accretion of the Franciscan melange that is now exposed in the California Coast Ranges and a magmatic arc began to develop landward on the previously accreted terranes. The presence of Late Jurassic sediments in the Great Valley forearc region indicates that uplift of the terranes was also beginning at this time. Ductile deformation and metamorphism of the accreted oceanic arcs occurred between 155 and 123 Ma ŽTobisch et al., 1989.. Plutons were emplaced in these accreted terranes between 151 and 115 Ma and also several tens of kilometres to the east as the Sierra Nevada batholith between 150 and 80 Ma; the bulk of the batholith was emplaced after 120 Ma. Magmatism is generally considered to be a consequence of the initiation of the Late Jurassic, east-dipping subduction system outboard of the accreted terranes and rift basins ŽBurchfiel et al., 1992.. The tectonic setting of gold deposits in what is now central California is remarkably similar to that of the Juneau gold belt in southeastern Alaska; that is, auriferous lodes are located within a series of extremely narrow accreted terranes and typically 10– 20 km seaward of a major Andean-type batholith ŽFig. 9.. Steeply-dipping thrust faults between the

terrane slivers in California, such as the mid-Jurassic Melones fault zone, are sites of extensive gold veining. But unlike the Alaskan example, timing of gold genesis throughout the Sierran foothills is poorly constrained. A few K–Ar and Rb–Sr dates from scattered deposits suggest that lodes in the Grass Valley district may have formed during early magmatism at 144 Ma Ž10 m.y. subsequent to the onset of regional uplift., and then from 125 to 110 Ma along terrane-bounding faults in some of the districts of the Mother Lode belt ŽBohlke and Kistler, 1986.. The lodes in the Jurassic accreted terranes have combined to yield about 35 million oz of gold. The age of gold veining in the northern Sierra terrane, the backstop to which other terranes were accreted in the Jurassic, is unknown. Although lode production in this innermost part of the forearc was relatively minor, most of the approximately 65 million oz of placer production was derived from here. The same Mesozoic terrane accretion event was continuous northward in rocks now exposed as the Klamath Mountains of northern California and southern Oregon. Two composite terranes of predominantly Palaeozoic island arc successions, the Eastern Klamath and the Central Metamorphic terranes, had been added to the North American margin by Early Triassic time ŽBurchfiel et al., 1992.. A complex group of Palaeozoic to mid-Mesozoic terranes consisting of far-traveled oceanic arcs and more locally derived accretionary prisms were accreted to these along the Siskiyou thrust fault system during the Middle and Late Jurassic. Outboard accretion of the Franciscan complex accompanied continued subduction in the Early Cretaceous. Magmatism was widespread on both sides of the Jurassic suture with the older composite terranes between 177 and 135 Ma ŽHacker et al., 1995.. Regional metamorphism and deformation along the suture also continued until about 135 Ma and was likely continuous with Cordilleran orogenesis to the south in the Sierran foothills ŽHarper et al., 1994.. However, unlike that of the Sierra Nevada range and its western foothills, voluminous magmatism in the Klamath Mountains did not continue through the remainder of the Cretaceous. About seven million oz of gold were recovered from the districts in the Klamath Mountains ŽFig. 9., half from lodes and half from associated placers.

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

Some gold veining is at least as old as 147 Ma, whereas other veining is probably younger than 136 Ma ŽElder and Cashman, 1992.. Most of the veining, irregardless of age, is concentrated in the backstop to the Middle Jurassic accretion. Danielson et al. Ž1990.

205

reported a K–Ar age of 396 Ma for gold veining in Devonian greenstone of the eastern Klamath terrane. This date is roughly coeval with precollisional earliest deformation and metamorphism of the terrane somewhere to the west of the Palaeozoic continental

Fig. 10. Major gold belts of northeastern Asia and tectonic map of the region generalized from Sengor and Natal’in Ž1996. and Nokleberg et al. Ž1994b, 1996..

206

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

margin, and much older than that of any of the other western North America gold ores. However, the K–Ar age is based on analysis of hydrothermal paragonite and it is unclear if the analyzed potassium was actually derived from the K-poor mica rather than inherited from older wall rocks. The far-field tectonic controls on latest Jurassic to Early Cretaceous gold formation in the southwestern part of the Cordillera are problematic. Landefeld Ž1988. suggested that the 100 km seaward stepping of the subduction zone between about 150 and 130 Ma was an important ore-forming trigger in the Mother Lode belt. Such a process was shown to induce a rise in geotherms up through the accreted terranes to the east. Elder and Cashman Ž1992. suggest 142–133 Ma changes in Farallon and North America plate velocities and in the related stress fields, were the ultimate control on earliest veining in the Klamath Mountains. They hypothesize an extremely low convergence rate during this time as significant for an increased geothermal gradient that drove hydrothermal circulation within upper plate rocks. Latest veins in the Klamath Mountains, however, were deposited during a period of accelerated subduction, renewed regional contraction, and thrust faulting at about 130 Ma ŽElder and Cashman, 1992.. In contrast to the Juneau gold belt, where major changes in plate convergence directions in the northern Pacific basin appeared important for ore genesis, these data from the southern Cordillera suggest solely changes in subduction velocities and convergence angles are adequate far-field controls on ore genesis. 3.3. Eastern Eurasia The major synorogenic gold deposits of the Russian Far East occur in five metallogenic belts ŽFig. 10. that include Yana–Kolyma, Chukotka, Verkhoyansk, Allakh–Yun and Selemdzha–Kerbi ŽNokleberg et al., 1996.. It remains difficult to get an estimate of tonnage for many of the mesothermal-type deposits in these gold belts, but Goryachev Ž1994. has estimated a combined past production of about 8 million oz lode gold and ) 130 million oz placer gold for these belts in the Russian Far East. Vein emplacement in all of the cited belts is mainly associated with Late Jurassic and Early Cretaceous collisional, deformational, and metamorphic events along the

northeastern Eurasia margin ŽNokleberg et al., 1994b.. The majority of the known lodes are hosted in greenschist facies turbidities comprising numerous accreted terranes. We speculate that the order-ofmagnitude increase in convergence rates between the Eurasian and Izanagi plates at about 135 Ma ŽEngebretson et al., 1985. was a driving force for the increased collision. The specifics and timing of ore genesis in the Russian Far East are still poorly understood. Upper Palaeozoic through middle Mesozoic turbidities of the Kular–Nera terrane of the Kolyma–Omolon composite ‘superterrane’ ŽNokleberg et al., 1994b, 1996. host the most economically significant lode ores in the Yana–Kolyma belt, mainly recognized in the deposits of the Omchak district. The gold-bearing veins of the belt formed between 135–100 Ma ŽEremin et al., 1994., during regional deformation associated with final accretion of the superterrane to the Eurasian craton margin. Widespread granite plutonism at 144–134 Ma accompanied the collision ŽParfenov et al., 1996.. Ore formation and magmatism continue landward into the Carboniferous to Jurassic passive margin sedimentary rocks of the Verkhoyansk and Allakh–Yun belts. Rocks of these belts were deformed along the 2000-km-long margin of the eastern Siberian platform ŽAngara craton. during the collision ŽZonenshain et al., 1990.. At the same time, opening of the Canada basin to the northeast formed the Arctic Ocean and led to collision of the Palaeozoic and early Mesozoic continental margin sedimentary rocks amalgamated into the Chukotka superterrane and of a number of smaller oceanic terranes with the Kolyma–Omolon superterrane ŽNokleberg et al., 1994b, 1996.. Gold-bearing veins of the Chukotka belt formed in some of these terranes during the middle Cretaceous ŽGoryachev, 1996. as the terranes were being deformed to generate the Anyuy fold belt ŽHarbert et al., 1990.. Major crustal extension emplaced the 120–80 Ma Okhotsk–Chukotka magmatic arc within parts of the Anyuy fold belt and Kolyma–Omolon superterrane during the final stages of accretion and deformation. Therefore, it is possible that the same tectonic event that ultimately controlled Albian gold veining near Nome and elsewhere on the Seward Peninsula of northwestern Alaska was also significant for ore formation in the Russian northeast.

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

Continuing to the south in the Russian Far East, gold veins of the Selemdzha–Kerbi metallogenic belt are hosted in the accretionary prism that includes rocks of the Tukuringra–Dzhagdi and Galam terranes ŽNokleberg et al., 1994b, 1996.. Veining in this region is located a few tens of kilometres seaward of the Precambrian Khingan–Bureya massif along the western side of the Sikhote–Alin–Sakhalin fold belt. Most of the 140–110 Ma lodes produced only a few tens of thousands of ounces of gold, but related placers have yielded more than 30 million oz of gold during the last seventy years ŽRatkin, 1995.. The fold belt is mainly comprised of terranes of Lower Cretaceous flysch deposited in back arc basins. It was deformed during Cretaceous subduction and collision of the Sikhote–Alin terrane ŽZonenshain et al., 1990.. Gold occurrences of the same age continue southward into the Archaean rocks of the eastern part of the north China craton ŽFig. 10., emplaced during what has been generally known in China as the Middle Jurassic through mid-Cretaceous Yanshanian orogen. These lodes, notably concentrated on the Shangdong Peninsula Ž) 20 million oz of gold; Yang et al., 1996. and in provinces north and northeast of Beijing, are China’s most productive gold producers. They are associated with Early Cretaceous plutons generally stated to be subduction-related ŽTian, 1992.. However, Wang et al. Ž1996. claim that by about 125 Ma, mantle plume activity initiated a 100-m.y.-long period of extension along the eastern Asian continental margin and the 126–120 Ma deposits of the Shangdong Peninsula overlap the onset of this tectonism. The Shangdong deposits are also spatially associated with eastern strands of the perhaps 5000-km-long Tan Lu wrench fault system that extends from the Yangtze River north to the Russian Far East ŽXu, 1993.. In the latter region, it may be associated with some of the gold deposits of the Selemdzha–Kerbi metallogenic belt. Xu Ž1993. noted more than 700 km of strike slip motion along the fault system since Late Jurassic. Similar ages for vein emplacement of 130–121 Ma have been determined in the Chifeng area of southeastern Inner Mongolia and western Liaoning province ŽGeological Survey of Canada, 1991; Trumbull et al., 1996.. The spatial relation with alkalic igneous phases ŽNie and Wu, 1995., the lack

207

of extensive alteration, consistent brittle nature of the host structures, Ag-rich nature of many of the ores, and the hosting of ores in inboard basement uplifts along the northern border of the craton are atypical of synorogenic lodes. These features have led some workers to suggest that these systems are more like the precious metal-bearing veins of the Colorado mineral belt rather than Cordilleran-type mesothermal veins ŽPoulsen et al., 1990.. But some deposits, including the Jinchangyu gold deposit in eastern Hebei Ž1.5 million oz of gold production and reserves., appear more like typical circum-Pacific synorogenic gold lodes ŽPoulsen and Mortensen, 1993.. It is uncertain as to how far to the west do these Cretaceous gold deposits continue across north China. Sulphide-poor gold vein deposits associated with alkalic igneous rocks extend 600 km west of Beijing to the Batou and Bayan Obo areas of western Inner Mongolia. Whereas some of these deposits and magmatic bodies to the west could also be products of Yanshanian orogenesis, many formed during the late Palaeozoic Hercynian orogeny ŽNie and Wu, 1995., as the Altaid Ocean was consumed between the colliding North China and Angara cratons. 3.4. Otago, South Island, New Zealand Turbidities of the Permian to Late Triassic Torlesse and Caples terranes along the eastern edge of New Zealand were the final tectonostratigraphic units added to the Gondwanan margin in the southwestern Pacific. Deformation and metamorphism of these terranes occurred during Early Jurassic to Early Cretaceous collision ŽBishop et al., 1985.. Subsequently uplifted and exposed auriferous greenschist facies rocks of the amalgamation, often termed the Haast schists, are mainly exposed in the southeastern part of South Island. Final accretion of the terranes to the continental margin took place in the mid-Cretaceous ŽBradshaw, 1994.. Despite the production of more than eight million oz of placer gold, lode production from the Haast schists has historically been negligible. However, during the last few years, mining of more than two million oz of proven reserves has begun in the Macres Flat belt of deposits. McKeag and Craw Ž1989. hypothesize that gold vein emplacement in the presently exposed Haast schists of the terranes

208

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

was continuous throughout much of the period of Jurassic and Early Cretaceous collisional deformation. Absolute dates are lacking for the major deposits in the schists of the South Island, but Adams and Graham Ž1993. have reported a range of Early Cretaceous dates for small auriferous veins in the Torlesse terrane near Wellington on the North Island. Like North America’s Klondike district, the Mesozoic gold deposits of New Zealand also lack a spatial association with coeval igneous rocks. Late Triassic to Early Jurassic arc magmatism is only recognized a few hundred kilometres west of the major gold lodes.

4. Palaeozoic synorogenic gold deposits of the Pacific Rim

during much of this orogeny through episodic periods of contraction and strike-slip movement. This eastward growth of the Indo-Australian plate margin included early through middle Palaeozoic development of the Lachlan, Thomson, and Hodgkinson– Broken River fold belts and middle to late Palaeozoic formation of the New England fold belt in what is now eastern Australia ŽFig. 11.. The early to middle Palaeozoic deformation also impacted rocks now exposed in northern Victoria Land, Antarctica and Westland, South Island, New Zealand. Significant goldfields developed during orogenesis within the Lachlan fold belt, with less productive provinces also recognized in the Hodgkinson–Broken River fold belt and Westland. 4.1. Lachlan fold belt

The Tasman Orogenic Belt formed along the eastern margin of Gondwanaland over a period of about 200 m.y. beginning in the Cambrian. Quartz-rich turbidite sequences were amalgamated and deformed

The Lachlan fold belt is part of the more extensive Tasman orogenic belt that comprises Australia on the eastern side of the suture with its Precambrian

Fig. 11. Gold provinces and major gold districts of eastern Australia generalized from Solomon and Groves Ž1994..

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

craton. The Lachlan fold belt includes a succession of Cambrian island-arc volcanic rocks Žmostly basalts. overlain by a thick and widespread Ordovician to Early Devonian flysch sequence representing a huge turbidite fan shed from the Ross–Delamerian orogen to the west. Plutonism in the belt was most abundant between 420 and 360 Ma, with distinct pulses near Stawell at 410–390 Ma and in central Victoria at 370–360 Ma ŽRamsay and VandenBerg, 1986.. The major period of Tabberabberan deformation Žgenerally assumed to be 386–378 Ma. was accompanied by mainly low-grade regional metamorphism, then followed rapidly by emplacement of dyke swarms, I-type and S-type plutonism, and acid volcanism in central Victoria ŽCollins and Vernon, 1992.. Carboniferous molasse-style sedimentary rocks, including red beds, are only mildly deformed. Unusual features of the Lachlan fold belt are its 800-km E–W width, widespread greenschist facies rocks with a paucity of higher-grade units, lack of Precambrian basement, similar structural levels exposed across the entire fold belt, and large volume of acid igneous rocks ŽConey, 1992.. Production from the Victorian sector of the Lachlan fold belt ŽFig. 11. has been outstanding on a world scale: ca. 80 million oz of Au, mostly mined prior to 1910. Forty percent has come from quartz vein deposits, and the rest from placer and palaeoplacer deposits that are traceable directly to known lodes, or at least to the more highly mineralized gold districts. There are twelve districts that have yielded at least one million oz of gold, with Bendigo Ž23 million oz., Ballarat Ž13 million oz. and Castlemaine Ž5.5 million oz. being the largest of these ŽPhillips and Hughes, 1995, 1996.. These three districts, most of the other one million ounce districts, and many of the smaller ones are within what has been informally termed the Ballarat zone of central Victoria. Other geological zones to the east and west of the Ballarat zone have considerably less gold, particularly in the far east and west. Essentially all primary gold has come from rocks that predate the Carboniferous, and virtually all rocks older than this age contain auriferous veins somewhere in the province. Major primary deposits are in black slates and mafic dykes, and together these Candror Fe- rich hosts contained veins that accounted for at least 75% of production ŽPhillips and Hughes,

209

1995, 1996.. Alteration surrounding deposits includes broad carbonate zones, muscovite or biotite envelopes, and narrow sulphide intervals close to gold. All deposits are structurally controlled, but the type of local hosting structure varies between goldfields and even within single fields. The major goldfields are characterized by a pronounced repetition of hosting structures. Regionally, deposits are spatially associated with major west-dipping reverse faults ŽCox et al., 1991.. A diachronous period of gold mineralization in Victoria can be constrained for deposits that occur in Devonian host rocks to being mainly Middle to Late Devonian in age, in part contemporaneous with the major Tabberabberan thermal and deformational event. For deposits in older host rocks, a similar age of mineralization is permissible but rarely demonstrated. Along the eastern edge of the Lachlan fold belt, in the Hill End goldfield of New South Wales, argon geochronology indicates some significant gold veining continued into the early Carboniferous ŽLu et al., 1996.. Arne et al. Ž1996. have recently used U–Pb data from Devonian igneous rocks and crosscutting relationships between these rocks and gold systems to suggest locally older ore deposition in the Lachlan fold belt. They argue that some of the gold occurrences in the Stawell area are likely Late Silurian to Early Devonian in age. Two distinct periods of synorogenic gold veining appear to characterize the north part of the Tasman orogenic belt – an economically significant Silurian–Devonian event and a less important Carboniferous event. Flysch units of Silurian to Devonian age in the Hodgkinson–Broken River fold belt ŽFig. 1. are host to Late Carboniferous gold–quartz veins of the Hodgkinson district ŽPeters et al., 1990.. These are very similar in many ways to the Victorian gold deposits, but have had only minor production. Although the deposits are hosted in flysch, they are surrounded by many of the posttectonic Carboniferous batholiths of the north Queensland magmatic province. The gold vein deposits of the Charters Tower– Ravenswood area Žlocated a few tens of kilometres south of the Hodgkinson–Broken River fold belt. have yielded 7.3 million oz of gold mostly from the Charters Tower district. They might mark a southern extension of the synorogenic gold deposits in the

210

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

north part of the Tasman Orogenic Belt ŽSolomon and Groves, 1994.. The veins at Charters Tower cut Middle Ordovician to Middle Devonian plutons within the deformed flysch, which is often termed the Thomson fold belt. Peters and Golding Ž1989. report a 408 " 30 Ma date for Charters Tower ore formation, roughly coeval with early gold formation in the Stawell area of the Lachlan fold belt. But, some of the gold in the area is definitely younger and of the same age as veins in the Hodgkinson district. In the Ravenswood district, 313–296 Ma veins cut an early Palaeozoic tonalite that intrudes an Ordovician sedimentary and volcanic rock sequence ŽSolomon and Groves, 1994.. Whereas the younger orogens of the northern Pacific basin were dominated by collision of multiple allochthonous terranes and largely crustal thickening, the Lachlan fold belt and its northern extensions, the Thomson and Hodgkinson–Broken River fold belts, were characterized by poorly understood intraplate thin-skinned tectonics ŽConey, 1992.. Shortening and folding were major components of deformation in the Tasman orogenic belt, but major uplift of deep crustal rocks did not occur. Many workers now argue for a subduction-related event beginning in the Middle Devonian during Pacific– Australian plate collision ŽPowell and Li, 1994; Collins, 1996.. But if such an event did occur, crustal response within the Lachlan fold belt was certainly quite different than within the slices of terranes along the North American Cordillera and northeastern Asia margin. 4.2. Buller terrane, Westland, New Zealand The outermost part of the Tasman orogenic belt throughout the early Palaeozoic was, in part, what are now the rocks of the Buller terrane that are exposed in the Westland area ŽFig. 1. along the western margin of South Island of New Zealand. These rocks were deformed and metamorphosed along the southeastern Gondwanan margin during the Silurian and Early Devonian and then were widely intruded by S-type granites during the Late Devonian through Carboniferous ŽCooper and Tulloch, 1992.. It is uncertain whether the widespread gold veins within the Buller terrane, including the productive lodes of the Reefton district Žabout 2.5 million oz of

gold., were emplaced during the magmatism or during earlier periods of deformation ŽGoldfarb et al., 1995.. The Late Cretaceous breakup of southern Gondwanaland further separated these Palaeozoic lodes from the other Palaeozoic gold systems of southeastern Australia. 4.3. New England Fold Belt The New England fold belt ŽFig. 11. is the youngest part of the Tasman orogenic belt. It developed during latest Devonian to Early Triassic accretion and subduction of oceanic arc and marine sedimentary rock-dominant terranes along the eastern side of the Lachlan and Thomson fold belts ŽGilligan and Barnes, 1990; Scheiber, 1996.. Within this part of the orogen, the Gympie deposits of southeastern Queensland have yielded 3.4 million ounces of gold from lodes in hosted in the Gympie terrane ŽKitch and Murphy, 1990., an accretionary prism of Permian rocks added to eastern Australia by the Middle Triassic ŽScheiber, 1996. along the seaward margin of the fold belt. The Gympie terrane was accreted to the Wandilla–Tablelands terrane, a turbidite-rich sequence that had originally collided with eastern Australia in the Late Carboniferous. The Wandilla– Tablelands terrane subsequently underwent Early Permian strike-slip movement prior to final collision in the Middle Permian ŽScheiber, 1996.. The terrane hosts the Hillgrove gold district, in northeastern New South Wales, comprised of a number of deposits with a combined historical production of 600,000 oz of gold ŽSuppel, 1975.. Veining in the New England fold belt is Permian to Triassic in age and thus appears to be somehow related to the final period of subduction and accretion along eastern Australia. Late Carboniferous plutons were emplaced in the Wandilla–Tablelands terrane during its initial collision with the continental margin and were deformed during the Middle Permian final collision. Immediately thereafter, at about 250 Ma, gold veining in the Hillgrove district occurred during regional uplift and perhaps along dilational zones between two major fault systems ŽAshley et al., 1994.. Age constraints are poor for veins in the outboard Gympie terrane, but most likely veins are coeval with Early Triassic dykes found in the region ŽKitch and Murphy, 1990..

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

211

Fig. 12. A variety of tectonic scenarios Žafter Goldfarb et al., 1993 and Haeussler et al., 1995. are associated with mid-crustal heating that eventually caused gold vein emplacement in the relatively young Alaskan part of the Pacific rim. ŽA. A few hundred kilometres landward of the Pacific margin, crustal thickening and melt-enhanced deformation are associated with Eocene ore formation during changes in regional stress fields. Adjacent to the margin, subduction of an oceanic ridge led to ore formation in the accretionary prism. ŽB. Mid- to Late Cretaceous extensional heating in interior Alaska led to 110 Ma gold vein emplacement near Nome in the Arctic Alaska composite terrane. Veining at 90 Ma near Fairbanks in the Yukon-Tanana terrane is related either to the final stages of the extension or subsequent, renewed convergence.

212

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

5. Discussion Goldfields of the circum-Pacific rim ŽFig. 1. have many features in common, and together define the world’s historically most productive region for the ‘gold-only’ slate belt type of deposit as defined by Phillips and Powell Ž1993.. Auriferous quartz veins are consistently distributed in pelitic and psammatic rock sequences that have been metamorphosed to low to medium grades. The more productive lodes are spatially associated with deep crustal, steep thrusts that, in many cases, are terrane boundaries. Adjacent to the first-order structures, relatively competent, older igneous rocks and relatively carbonaceous sedimentary rocks typically provide secondorder structural or chemical traps, respectively, for ore. Deposits are similar in that gold:silver ratios of most productive systems range from 1:1 to 10:1, deposits show great vertical continuity Ž1–2 km. despite limited surface exposure, and low-salinity ore fluids are consistently CO 2-rich and characterized by isotopically heavy hydrogen and oxygen compositions. Plutonism is often coeval with gold vein emplacement. But, with the exception of some intrusive bodies in east-central and south-central Alaska, the temporally associated magmatic rocks rarely host ore-bearing veins. For example, about 20 percent of the Lachlan fold belt is comprised of Palaeozoic granites, but none of the twenty largest Victorian lode producers are hosted by the granites ŽHughes et al., 1996.. In general, subduction and associated mountain building processes along the periphery of a continent include extensive mid-crustal fluid flow events leading to the generation of synorogenic gold veins. In the northern Pacific basin, such events characterized the period between 170 and 50 Ma along the growing margins of North America and Eurasia. In the southwestern Pacific, veining was concentrated along the active Gondwanan margin in the Devonian with lesser activity associated with Permian and Jurassic–Early Cretaceous collisions. Significant synorogenic gold lodes are lacking along the Andean margin of South America. This is, however, an eroding and not a growing margin, and therefore lacks abundant young allochthonous terranes in the very narrow zone between the trench and Andean arc. Perhaps this fact indicates that a key to ore

formation is a growing margin; i.e., one that contains a potential huge crustal fluid volume added into the margin within hydrous silicate mineral phases of the accreted marine strata that undergo subsequent dehydration when heated from below. Observations from the various districts around the Pacific Rim make it clear that there is no single type of tectonic process that provides the heat to drive the necessary volumes of fluid during continental growth. The onset of orogenic processes above a downgoing slab are crucial for gold genesis along a subductiondominated margin because very low heat flow typifies subduction zone environments Žcf. Hyndman and Lewis, 1995.. Most commonly along western North America, it is some type of Andean-style orogenesis above the subducting oceanic slab that causes the required steep rise in geothermal gradients ŽFig. 12.. The partial melting of asthenospheric mantle above the sinking slab initiates a series of thermal events that includes devolatilization of upper plate rocks previously added to the continental margin and the resultant hydrothermal fluid circulation. From the relatively detailed work in the Alaskan Cordillera, it is apparent that other processes such as subduction of a spreading ridge or an extensional period during slab rollback also can provide heat needed to initiate fluid flow and the resulting gold veining ŽFig. 12.. Relations from the North American Cordillera indicate that ore formation can occur on the seaward side of the subduction-related arc ŽJuneau gold belt, Mother Lode., directly within the magmatic arc rocks ŽWillow Creek., and on the landward side of the arc ŽBridge River.. Where there is a lack of temporal association with large-scale melting and magmatism, gold deposits are uncommon. But, the Klondike and other 140 Ma districts in western Canada and the Otago region of New Zealand seem to be exceptions. Although simply an increased thermal gradient following collisonal and overthrusting events could have induced metamorphic dehydration in these latter areas, a deep-seated heat source characterized by an abundance of unexposed intrusions is also certainly possible. In the Canadian case, the 140 Ma dates may also simply be cooling ages and ore formation might have occurred simultaneously with Early Jurassic magmatism. Data from the circum-Pacific goldfields indicate that subduction-related magmatism may predate, be

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

synchronous with, or postdate vein formation. Interpretation of detailed geochronology from the relatively young Alaskan ores indicates the same range of possibilities for regional uplift. Certainly when simultaneous, uplift can enhance fluid migration by reducing lithostatic loads. But data show gold vein emplacement can predate uplift by 5 m.y. ŽChugach–Kenai Mountains districts., occur during a broad period of regional uplift ŽJuneau gold belt., or postdate uplift by 5 m.y. ŽWillow Creek district.. The spatial associations between greenschist facies and gold vein emplacement in the narrow inverted Barrovian sequences of the Juneau gold belt and Valdez Creek district suggest ore genesis-related to metamorphic processes. The required periods of about 5 m.y. and 15 m.y., respectively, between metamorphic devolatilization and fluid focusing suggests a complex hydrologic history. Such a history is strongly influenced by the evolving crustal thermal structure that would vary from district to district, a structure whose understanding requires detailed numerical modeling specific for each district. Determination of absolute ages for the Mesozoic and Tertiary gold systems allow us to recognize timing relationships between tectonic processes and ore genesis during orogeny. Along the accretionary prism of southern Alaska, Tertiary veining coincident with the subduction of a ridge segment was essentially coeval with accretion and deformation of the host terrane. A more typical scenario may exist a few hundred kilometres inboard from accretionary prisms throughout the Cordilleran orogen. Deposits formed here in host rocks tens of millions of years after their accretion and the related initiation of deformation; i.e., at least 30–80 m.y. later in the Juneau gold belt, much of the Canadian Cordillera, the Sierra foothills, and the Klamath Mountains. Dating of mid-Cretaceous deposits in interior Alaska indicates that, in certain cases, gold veining can postdate accretion and associated deformation by more than 100 m.y. Host rocks for ores in east-central Alaska and northwestern Alaska had already cooled to relatively low temperatures and been uplifted to relatively shallow depths by the time of mid-Cretaceous crustal heating. Also, thrusting along sutures or zones of melt-enhanced deformation within the ore-host terranes ceased prior to veining. In most cases, however, slab subduction and un-

213

derthrusting continued beneath the earlier deformed terranes during veining. Ores are typically emplaced in or near orogen cores after back-stepping of the subduction zones along the growing continental margin Žcf. Landefeld, 1988.. Orogenic processes taking place at depth above a sinking slab and 100–200 km landward of the subduction zone, will still have a major impact on shallower rock sequences that already have undergone much of their deformation. Additionally, reconfiguration of plate subduction patterns could be important in the development of some of the larger gold districts in the overlying upper plate. For example, the onset of orogen-parallel tectonism during a more oblique Eocene convergence along southeastern Alaska or dramatic shifts in midMesozoic plate convergence rates along the western conterminous United States may have been critical for the formation of the Juneau and California gold fields, respectively. Gold veining is an inherent part of continental growth, whether by intraplate or interplate tectonics. As pointed out by Coney Ž1992., such contrasting tectonic styles characterize both the gold-rich Tasman and Cordilleran circum-Pacific orogens. The Tasman system consists of a single composite terrane in which deformation and magmatism were controlled by a subduction zone to the east. In contrast, western North America and eastern Eurasia were built through the collision and deformation of dozens of diverse terranes leading to widespread thrusting and the exposure of different crustal levels. Hence, it is the thermal regime and not a single tectonic style of the growing margins that played the major role in localizing the circum-Pacific gold ores.

Acknowledgements We thank David Groves and Ross Ramsey for suggesting the topic of this summary and for the opportunity to present much of the material at the meeting on ‘‘Mesothermal Gold: A Worldwide Connection’’, held in Perth during July, 1996. Discussions with Craig Hart, Larry Snee, Leslie Landefeld, Rick Saltus, Feng-Jun Nie, Tony Christie, Lance D. Miller, Dwight Bradley, Peter P. Haeussler, Roger Powell, Martin Hughes, Julian Vearncombe and Jonathan Law improved our understanding of the

214

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

Pac-Rim tectonics, metallogenesis, and geochronology in various geographic areas. Vladimir I. Shpikerman and Nikolai A. Goryachev ŽNortheast Science Center, Russian Academy of Sciences, Magadan. and Vladimir V. Ratkin ŽFar East Geological Institute, Russian Academy of Sciences, Vladivostok. provided critical information on the Russian Far East deposits. The manuscript has been greatly improved through the very constructive reviews by Rick Saltus, Byron Berger, Andy Wilde and an anonymous journal reviewer.

References Adams, C.J., Graham, I.J., 1993. K–Ar and Rb–Sr age studies of the metamorphism and quartz vein Au mineralisation on Terawhiti Hill, near Wellington, New Zealand. Chem. Geol. ŽIsotope Geosci. Sect.. 103, 235–249. Amato, J.M., Wright, J.E., Gans, P.B., Miller, E.L., 1994. Magmatically induced metamorphism and deformation in the Kigluaik gneiss dome, Seward Peninsula, Alaska. Tectonics 13, 515–527. Andrew, A., Godwin, C.I., Sinclair, A.J., 1983. Age and genesis of Cariboo gold mineralization determined by isotopic methods. B.C. Ministry of Energy, Mines and Petroleum Resources, Pap. 1983-1, pp. 305–313. Armstrong, R.L., Harakal, J.E., Forbes, R.B., Evans, B.W., Thurston, S.P., 1986. Rb–Sr and K–Ar study of metamorphic rocks of the Seward Peninsula and southern Brooks Range, Alaska. Geol. Soc. Am. Mem. 164, 185–203. Arne, D.C., Bierlein, F.P., McNaughton, N., Wilson, C.J.L., Morand, V.J., Ramsay, W.R.H., 1996. Timing of gold mineralisation in western and central Victoria. New constraints from SHRIMP II analysis of zircon grains from felsic intrusive rocks. In: Ramsay, W.R.H. ŽEd.., Sedimentary-hosted Mesothermal Gold Deposits. A Global Overview. Minerals Industry Research Institute, Univ. Ballarat, Abstr. vol., pp. 20–24. Ash, C.H., Reynolds, P.H., Macdonald, R.W.J., 1996. Mesothermal gold–quartz vein deposits in British Columbia oceanic terranes. New mineral deposit models of the Cordillera, B.C. Geol. Surv., 1996 Cordilleran Roundup Short Course, pp. O1-O32. Ashley, P.M., Cook, N.D.J., Hill, R.L., Kent, A.J.R., 1994. Shoshonitic lamprophyre dykes and their relation to mesothermal Au–Sb veins at Hillgrove, New South Wales, Australia. Lithos 32, 249–272. Barley, M.E., Eisenlohr, B.N., Groves, D.I., Perring, C.S., Vearncombe, J.R., 1989. Late Archean convergent margin tectonics and gold mineralization. A new look at the Norseman–Wiluna belt, western Australia. Geology 17, 826–829. Bishop, D.G., Bradshaw, J.D., Landis, C.A., 1985. In: Howell, D.G. ŽEd.., Tectonostratigraphic terranes of the circum-Pacific

region. Circum-Pacific Council for Energy and Mineral Resources, Earth Sciences Series, No. 1, Houston, pp. 515–521. Bohlke, J.K., Kistler, R.W., 1986. Rb–Sr, K–Ar, and stable isotope evidence for ages and sources of fluid components of gold-bearing quartz veins in the northern Sierra Nevada foothills metamorphic belt, California. Econ. Geol. 81, 296– 322. Bradley, D.C., Haeussler, P.J., Kusky, T.M., 1993. Timing of early Tertiary ridge subduction in southern Alaska. U.S. Geol. Surv., Bull. 2068, 163–177. Bradley, D., Haeussler, P., Kusky, R., Goldfarb, R., 1994. Near trench magmatism, deformation and gold mineralization during Paleogene ridge subduction in Alaska. SUBCON Conf., Catalina Island, CA, Abstr. vol., pp. 219-222. Bradshaw, J.D., 1994. Brook Street and Murihuku terranes of New Zealand in the context of a mobile South Pacific Gondwana margin. J. South Am. Earth Sci. 7 Ž3–4., 325–332. Burchfiel, B.C., Cowan, D.S., Davis, G.A., 1992. Tectonic overview of the Cordilleran orogen in the western United States. In: Burchfiel, B.C., Lipman, P.W., Zoback, M.L. ŽEds.., The Cordilleran Orogen. Conterminous U.S. Geol. Soc. Am., The Geology of North America, G-3: 407–479. Burleigh, R.E., 1987. A stable isotope, fluid inclusion and petrographic study of gold–quartz veins in the Willow Creek mining district, Alaska. Unpubl. M.Sc. thesis, Univ. Alaska, 246 pp. Collins, W.J., 1996. Tectonic setting of gold deposits in eastern Australia. In: Mesothermal Gold Deposits. A Global Overview. Univ. West. Aust., Publ. 27, 18–21. Collins, W.J., Vernon, R.H., 1992. Palaeozoic arc growth, deformation and migration across the Lachlan fold belt, southeastern Australia. Tectonophysics 214, 381–400. Coney, P.J., 1992. The Lachlan belt of eastern Australia and circum-Pacific tectonic evolution. Tectonophysics 214, 1–25. Cooper, R.A., Tulloch, A.J., 1992. Early Palaeozoic terranes in New Zealand and their relationship to the Lachlan fold belt. Tectonophysics 214, 129–144. Cox, S.F., Etheridge, M.A., Cas, R.A.F., Clifford, B.A., 1991. Deformational style of the Castlemaine area, Bendigo–Ballarat zone. Implications for evolution of crustal structure in central Victoria. Aust. J. Earth Sci. 38, 151–170. Csejtey, B., Jr. and 8 others, 1978. Reconnaissance geologic map and geochronology, Talkeetna Mountains quadrangle, northern part of Anchorage quadrangle, and southwest corner of Healy quadrangle, Alaska. U.S. Geol. Surv., Open-file Rep. 78-558A, 60 pp., scale 1:250,000. Currie, L., Parrish, R.R., 1993. Jurassic accretion of Nisling terrane along the western margin of Stikinia, Coast Mountains, northwestern British Columbia. Geology 21, 235–238. Danielson, J., Silberman, M.L., Shafiqullah, M., 1990. Age of mineralization of gold–quartz veins at the Reid mine, eastern Klamath terrane, Shasta County, northern California. Geol. Soc. Am. Abstr. Prog. 22 Ž3., 17. Davidson, C., Hollister, S.M., Schmid, S.M., 1992. Role of melt in the formation of a deep-crustal compressive shear zone. Tectonics 11, 348–359. Dusel-Bacon, C., Csejtey, B., Jr., Foster, H.L., Doyle, E.O.,

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218 Nokleberg, W.J., Plafker, G., 1993. Distribution, facies, ages, and proposed tectonic associations of regionally metamorphosed rocks in east- and south-central Alaska. U.S. Geol. Surv., Prof. Pap. 1497-C, 73 pp. Elder, D., Cashman, S.M. 1992, 1992. Tectonic control and fluid evolution in the Quartz Hill, California, lode gold deposits. Econ. Geol. 87, 1795–1812. Engebretson, D.C., Cox, A., Gordon, R.G., 1985. Relative motions between oceanic and continental plates in the Pacific basin. Geol. Soc. Am., Spec. Pap. 206, 64 pp. Eremin, R.A., Voroshin, S.V., Sidorov, V.A., Shakhtyrov, V.G., Pristavko, V.A., 1994. Geology and genesis of the Natalka gold deposit, Northeast Russia. Int. Geol. Rev. 36, 1113–1138. Ford, R.C., Snee, L.W., 1996. 40Arr39Ar thermochronology of white mica from the Nome district, Alaska. The first ages of lode sources to placer gold deposits in the Seward Peninsula. Econ. Geol. 91, 213–220. Gehrels, G.E., 1998. Geology and U–Pb geochronology of the western flank of the Coast Mountains between Juneau and Skagway, southeastern Alaska. In: McClelland, W.C. ŽEd.., Tectonics of the Coast mountains, southeastern Alaska and coastal British Columbia. Geol. Soc. Am. Spec. Pap., in press. Gehrels, G.E., McClelland, W.C., Samson, S.D., Patchett, P.J., Orchard, M.J., 1992. Geology of the western flank of the Coast Mountains between Cape Fanshaw and Taku Inlet, southeastern Alaska. Tectonics 11, 567–585. Geological Survey of Canada, 1991. Radiogenic age and isotopic studies. Geol. Surv. Can., Pap. 91-2: 252. Gilligan, L.B., Barnes, R.G., 1990. New England fold belt, New South Wales. Regional geology and mineralisation. In: Hughes, F.E. ŽEd.., Geology of the Mineral Deposits of Australia and Papua New Guinea. Australas. Inst. Min. Metall., Melbourne, pp. 1417–1423. Goldfarb, R.J., Leach, D.L., Miller, M.L., Pickthorn, W.J., 1986. Geology, metamorphic setting, and genetic constraints of epigenetic lode–gold mineralization within the Cretaceous Valdez Group, south-central Alaska. Geol. Assoc. Can. Spec. Pap. 32, 87–105. Goldfarb, R.J., Snee, L.W., Miller, L.D., Newberry, R.J., 1991. Rapid dewatering of the crust deduced from ages of mesothermal gold deposits. Nature 354, 296–298. Goldfarb, R.J., Snee, L.W., Pickthorn, W.J., 1993. Orogenesis, high-T thermal events, and gold vein formation within metamorphic rocks of the Alaskan Cordillera. Mineral. Mag. 57, 375–394. Goldfarb, R.J., Christie, T., Skinner, D., Haeussler, P., Bradley, D., 1995. Gold deposits of Westland, New Zealand and southern Alaska. Products of the same tectonic processes? In: Mauk, J. ŽEd.., PACRIM ’95. Symp. vol., pp. 239–244. Goldfarb, R.J., Miller, L.D., Leach, D.L., Snee, L.W., 1997. Gold deposits in metamorphic rocks in Alaska. In: Goldfarb, R.J., Miller, L.D. ŽEds.., Mineral Deposits of Alaska. Econ. Geol. Monogr. 9, 151–190. Goryachev, N.A., 1994. Mesothermal gold lode deposits of the Russian Far East. Alaska Miners Assoc., 1994 Annual Convention, Anchorage, Abstr. and Pap.

215

Goryachev, N., 1996. Geologic setting and evolution of Au-quartz deposits in the geological history of metallogenic province of Mesozoids, northeastern Asia. 30th IGC Abstr., vol. 1, Beijing, pp. 391. Hacker, B.R., Donato, M.M., Barnes, C.G., McWilliams, M.O., Ernst, W.G., 1995. Timescales of orogeny. Jurassic construction of the Klamath Mountains. Tectonics 14, 677–703. Haeussler, P.J., Bradley, D., Goldfarb, R., Snee, L., Taylor, C., 1995. Link between ridge subduction and gold mineralization in southern Alaska. Geology 23, 995–998. Harbert, W., Frei, L., Jarrard, R., Halgedahl, S., Engebretson, D., 1990. Paleomagnetic and plate-tectonic constraints on the evolution of the Alaskan–eastern Siberian Arctic. In: Grantz, A., Johnson, L., Sweeny, J.F. ŽEds.., The Arctic Ocean Region. Geol. Soc. Am., The Geology of North America, v. L, pp. 567–592. Harper, G.D., Saleeby, J.B., Heizler, M., 1994. Formation and emplacement of the Josephine ophiolite and the Nevadan orogeny in the Klamath Mountains, California–Oregon. UrPb zircon and 40Arr39Ar geochronology. J. Geophys. Res. 99, 4293–4321. Himmelberg, G.R., Brew, D.A., Ford, A.B., 1991. Development of inverted metamorphic isograds in the western metamorphic belt, Juneau, Alaska. J. Metamor. Geol. 9, 165–180. Hollister, L.S., Crawford, M.L., 1986. Melt-enhanced deformation. A major tectonic process. Geology 14, 558–561. Hudson, T., Plafker, G., 1982. Paleogene metamorphism of an accretionary flysch terrane, eastern Gulf of Alaska. Geol. Soc. Am. Bull. 93, 1281–1290. Hughes, M.J., Phillips, G.N., Gregory, L., 1996. Victorian gold. II. Large gold deposits and granites. Geol. Soc. Aust. Abstr. 41, 204. Hyndman, R.D., Lewis, T.J., 1995. Review. The thermal regime along the southern Canadian Cordillera Lithoprobe corridor. Can. J. Earth Sci. 32, 1611–1617. Johnston, S.T., Mortensen, J.K., Erdmer, P., 1996. Igneous and metaigneous age constraints for the Aishihik metamorphic suite, southwest Yukon. Can. J. Earth Sci. 33, 1543–1555. Jones, D.L., Silberling, N.J., Coney, P.J., Plafker, G., 1987. Lithotectonic terrane map of Alaska Žwest of the 141st Meridian.. U.S. Geol. Surv., Misc. Field Studies Map, MF-1874-A, scale 1:2,500,000. Kerrich, R., Wyman, D.A., 1990. The geodynamic setting of mesothermal gold deposits. An association with accretionary tectonic regimes. Geology 18, 882–885. Kitch, R.B., Murphy, R.W., 1990. Gympie gold field. In: Hughes, F.E. ŽEd.., Geology of the Mineral Deposits of Australia and Papua New Guinea. Australas. Inst. Min. Metall., Melbourne, pp. 1515–1518. Landefeld, L.A., 1988. The geology of the Mother Lode gold belt, Sierra Nevada Foothills metamorphic belt, California. Bicentennial Gold 88. Geol. Soc. Australas. Abstr. 22, 167–172. Leitch, C.H.B., 1990. Bralorne: A mesothermal, shield-type vein gold deposit of Cretaceous age in southwestern British Columbia. Can. Inst. Min. Metall. Bull. 83 Ž941., 53–80. Leitch, C.H.B., Van der Hayden, P., Godwin, C.I., Armstrong,

216

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

R.L., Harakal, J.E., 1991. Geochronometry of the Bridge River camp, southwestern British Columbia. Can. J. Earth Sci. 28, 195–208. LeLacheur, E.A., 1991. Brittle-fault hosted gold mineralization in the Fairbanks district, Alaska. Unpubl. M.Sc. thesis, Univ. Alaska, 167 pp. Lu, J., Seccombe, P.K., Foster, D., Andrew, A.S., 1996. Timing of mineralization and source of fluids in a slate-belt auriferous vein system, Hill End goldfield, NSW, Australia. Evidence from 40Arr39Ar dating and O- and H-isotopes. Lithos 38, 147–165. Madden-McGuire, D.J., Silberman, M.L., Church, S.E., 1989. Geologic relationships, K–Ar ages, and isotopic data from the Willow Creek gold mining district, southern Alaska. Econ. Geol. Monogr. 6, 242–251. McClelland, W.C., Anovitz, L.M., Gehrels, G.E., 1991. Thermobarometric constraints on the structural evolution of the Coast mountains batholith, central southeastern Alaska. Can. J. Earth Sci. 28, 921–928. McCoy, D., Newberry, R.J., Layer, P., DiMarchi, J.J., Bakke, A., Masterman, J.S., Minehand, D.L., 1997. Plutonic-related gold deposits of interior Alaska. In: Goldfarb, R.J., Miller, L.D. ŽEds.., Mineral Deposits of Alaska. Econ. Geol. Monogr. 9, 191–241. McKeag, S.A., Craw, D., 1989. Contrasting fluids in gold-bearing quartz vein systems formed progressively in a rising metamorphic belt: Otago Schist, New Zealand. Econ. Geol. 84, 22–33. Mihalynuk, M.G., Smith, M.T., Gabites, J.E., Runkle, D., Lefebure, D., 1992. Age of emplacement and basement character of the Cache Creek terrane as constrained by new isotopic and geochemical data. Can. J. Earth Sci. 29, 2463– 2477. Miller, E.L., Hudson, T.L., 1991. Mid-Cretaceous extensional fragmentation of a Jurassic-Early Cretaceous compressional orogen, Alaska. Tectonics 10, 781–796. Miller, L.D., Goldfarb, R.J., Gehrels, G.E., Snee, L.W., 1994. Genetic links among fluid cycling, vein formation, regional deformation, and plutonism in the Juneau gold belt, southeastern Alaska. Geology 22, 203–206. Molnar, P., England, P., 1995. Temperatures in zones of steadystate underthrusting of young oceanic lithosphere. Earth Planet. Sci. Lett. 131, 57–70. Monger, J.W.H., Berg, H.C., 1987. Lithotectonic terrane map of western Canada and southeastern Alaska. U. S. Geol. Surv., Misc. Field Studies Map, MF- 1874-B, scale 1:2,500,000. Mortensen, J.K., 1990. Geology and U–Pb geochronology of the Klondike district, west-central Yukon Territory. Can. J. Earth Sci. 27, 903–914. Mortensen, J.K., Murphy, D.C., Poulsen, K.H., Bremner, T., 1996. Intrusion-related gold and base metal mineralization associated with the early Cretaceous Tombstone plutonic suite, Yukon and east-central Alaska. New mineral deposit models of the Cordillera, B.C. Geol. Surv., 1996 Cordilleran Roundup Short Course, pp. L1-L13. Nelson, J.L., Mihalynuk, M.G., 1993. Cache Creek ocean. Closure or enclosure?. Geology 21, 173–176. Nie, F.-J., Wu, C.-Y., 1995. Gold deposits related to alkaline

igneous rocks in the north China craton, People’s Republic of China. In: Pasava, J., Kribek, B., Zak, K. ŽEds.., Mineral Deposits: From their Origin to their Environmental Impacts. Proc. of the 3rd Biennial SGA Meeting, Prague. A.A. Balkema, Rotterdam, pp. 173–176. Nokleberg, W.J., Bundtzen, T.K., Dawson, K.M., Eremin, R.A., Goryachev, N.A., Koch, R.D., Ratkin, V.V., Rozenblum, I.S., Shpikerman, V.I., Frolov, Y.F., Gorodinsky, M.E., Khanchuck, A.I., Kovbas, L.I., Melnikov, V.D., Nekrasov, I.Ya., Ognyanov, N.V., Petrachenko, E.D., Petrachenko, R.I., Pozdeev, A.I., Ross, K.V., Sidorov, A.A., Wood, D.H., Grybeck, D., 1996. Significant metalliferous lode deposits and placer districts for the Russian Far East, Alaska, and the Canadian Cordillera. U.S. Geol. Surv., Open-File Rep. 96513-A, 385 pp. Nokleberg, W.J., Jones, D.L., Silberling, N.J., 1985. Origin and tectonic evolution of the Maclaren and Wrangellia terranes, eastern Alaska Range, Alaska. Geol. Soc. Am. Bull. 96, 1251–1270. Nokleberg, W.J., Parfenov, L.M., Monger, J.W.H., Baranov, B.V., Byalobzhesky, S.G., Bundtzen, T.K., Feeney, T.D., Fujita, K., Gordey, S.P., Grantz, A., Khanchuk, A.I., Natal’in, B.A., Natapov, L.M., Norton, I.O., Patton, W.W., Jr., Plafker, G., Scholl, D.W., Sokolov, S.D., Sosunov, G.M., Stone, D.B., Tabor, R.W., Tsukanov, N.V., Vallier, T.L., Wakita, Koji, 1994b. Circum-North Pacific tectono-stratigraphic terrane map. U.S. Geol. Surv., Open-File Rep. 94-714, 221 pp., 2 sheets, scale 1:5,000,000; 2 sheets, scale 1:10,000,000. Nokleberg, W.J., Plafker, G., Wilson, F.H., 1994a. Geology of south-central Alaska. In: Plafker, G., Berg, H.C. ŽEds.., The Geology of Alaska. Geol. Soc. Am., The Geology of North America, G-1, pp. 311–366. Norris, R.J., Henley, R.W., 1976. Dewatering of a metamorphic pile. Geology 8, 333–336. Parfenov, L.M., Fujita, K., Layer, P.W., Stone, D.B., 1996. Main tectonic units, events, and tectonic evolution of Mesozoic orogenic belts of northeast Russia. 30th IGC Abstr., vol. 1, Beijing, p. 217. Paterson, S.R., Sharp, W.D., 1991. Comparison of structural and metamorphic histories of terranes in the western metamorphic belt, Sierra Nevada, California. In: Sloan D., Wagner, D.L. ŽEds.., Geologic Excursions in Northern California: San Francisco to the Sierra Nevada. California Div. Mines and Geol., Spec. Publ. 109, pp. 113–130. Pavlis, T.L., 1989. Middle Cretaceous orogenesis in the northern Cordillera. A Mediterranean analog of collision-related extensional tectonics. Geology 17, 947–950. Pavlis, T.L., Monteverde, D.H., Bowman, J.R., Rubenstone, J.L., Reason, M.D., 1988. Early Cretaceous near-trench plutonism in southern Alaska. A tonalite–trondhjemite intrusive complex injected during ductile thrusting along the Border Ranges fault system. Tectonics 7, 1179–1199. Pavlis, T.L., Sisson, V.B., Foster, H.L., Nokleberg, W.J., Plafker, G., 1993. Mid-Cretaceous extensional tectonics of the Yukon–Tanana terrane, trans-Alaska crustal transect ŽTACT., east-central Alaska. Tectonics 12, 103–122. Peters, S.G., Golding, S.D., 1989. Geologic, fluid inclusion, and

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218 stable isotope studies of granitoid-hosted gold-bearing quartz veins, Charters Towers, northeastern Australia . Econ. Geol. Monogr. 6, 260–273. Peters, S.G., Golding, S.D., Dowling, K., 1990. Melange- and sediment-hosted gold-bearing quartz veins, Hodgkinson gold field, Queensland, Australia . Econ. Geol. 85, 312–327. Phillips, G.N., 1991. Gold deposits of Victoria: A major province within a Palaeozoic sedimentary succession. World Gold ’91, Cairns, pp. 237–245. Phillips, G.N., Hughes, M.J., 1995. Victorian gold: A sleeping giant. Soc. Econ. Geol. Newslett. 21, 1–13. Phillips, G.N., Hughes, M.J., 1996. The geology and gold deposits of the Victorian gold province. Ore Geol. Rev. 11, 255–302. Phillips, G.N., Powell, R., 1993. Link between gold provinces. Econ. Geol. 88, 1084–1098. Plafker, G., Berg, H.C., 1994. Overview of the geology and tectonic evolution of Alaska. In: Plafker G., Berg, H.C. ŽEds.., The Geology of Alaska. Geol. Soc. Am., The Geology of North America, G-1, pp. 989–1021. Plafker, G., Nokleberg, W.J., Lull, J.S., 1989. Bedrock geology and tectonic evolution of the Wrangellia, Peninsular, and Chugach terranes along the Trans Alaska Crustal Transect in the northern Chugach Mountains and southern Copper River basin, Alaska . J. Geophys. Res. 94, 4255–4295. Poulsen, K.H., Mortensen, J.K., 1993. Observations on the gold deposits of Eastern Hebei Province, China. In: Current Research, Part D. Geol. Surv. Can., Pap. 93-1D, pp. 183–190. Poulsen, K.H., Taylor, B.E., Robert, F., Mortensen, J.K., 1990. Observations on gold deposits in North China Platform. In: Current Research, Part A. Geol. Surv. Can., Pap. 90-1A, pp. 33–44. Powell, C.McA., Li, Z.X., 1994. Reconstruction of the Panthalassan margin of Gondwanaland. In: Veevers, J.J. ŽEd.., Permian–Triassic Pangean Basins and Foldbelts along the Panthalassan Margin of Gondwanaland. Geol. Soc. Am., Mem. 184, pp. 5–10. Powell, R., Will, T.M., Phillips, G.N., 1991. Metamorphism in Archaean greenstone belts. Calculated fluid compositions and implications for gold mineralization. J. Metamor. Geol. 9, 141–150. Ramsay, W.R.H., VandenBerg, A.H.M., 1986. Metallogeny and tectonic development of the Tasman fold belt system in Victoria. Ore Geol. Rev. 1, 213–257. Ratkin, V., 1995. Pre- and postaccretionary metallogeny of the southern Russian Far East. Res. Geol. Special Issue 18, 127– 133. Rubin, C.M., Miller, E.L., Toro, J., 1995. Deformation of the northern circum-Pacific margin. Variations in tectonic style and plate-tectonic implications. Geology 23, 897–900. Rushton, R.W., Nesbitt, B.E., Muehlenbachs, K., Mortensen, J.K., 1993. A fluid inclusion and stable isotope study of Au quartz veins in the Klondike district, Yukon Territory, Canada. A section through a mesothermal vein system. Econ. Geol. 88, 647–678. Rusmore, M.E., 1987. Geology of the Cadwallader Group and the

217

Intermontane- Insular superterrane boundary, southwestern British Columbia. Can. J. Earth Sci. 24, 2279–2291. Rusmore, M.E., Woodsworth, G.J., 1991. Coast Plutonic Complex. A mid- Cretaceous contractional orogen. Geology 19, 941–944. Scheiber, E., 1996. Geology of New South Wales. Synthesis. Geol. Surv. of New South Wales, Mem. Geol. 13Ž1., 295 pp. Sengor, A.M.C., Natal’in, B.A., 1996. Paleotectonics of Asia. Fragments of a synthesis. In: Yin, A., Harrison, M. ŽEds.., The Tectonic Evolution of Asia. Cambridge University Press, Cambridge, pp. 486–640. Silberling, N.J., Jones, D.L., Monger, J.W.H., Coney, P.J., 1992. Lithotectonic terrane map of the North American Cordillera. U.S. Geol. Surv., Misc. Invest. Map Series, I-2176, scale 1:5,000,000. Sketchley, D.A., Sinclair, A.J., Godwin, C.I., 1986. Early Cretaceous gold–silver mineralization in the Sylvester allochthon, near Cassiar, north central British Columbia. Can. J. Earth Sci. 23, 1455–1458. Smith, T.E., 1981. Geology of the Clearwater Mountains, southcentral Alaska. Alaska Div. Geol. Geophys. Surv., Rep. 60, 72 pp. Solomon, M., Groves, D.I., 1994. The geology and origin of Australia’s mineral deposits. Oxford Monogr. Geol. Geophys. 24, 951 pp. Stanley, W.D., Labson, V.F., Nokleberg, W.J., Csejtey, B. Jr., Fisher, M.A., 1990. The Denali fault system and Alaska Range of Alaska. Evidence for suturing and thin-skinned tectonics from magnetotellurics. Geol. Soc. Am. Bull. 102, 160–173. Suppel, D.W., 1975. Nambucca block. In: Markham, N.L., Basden, H. ŽEds.., The Mineral Deposits of New South Wales. Geol. Surv. New South Wales, Sydney, pp. 428–447. Taylor, C.D., Goldfarb, R.J., Snee, L.W., Gent, C.A., Karl, S.M., Haeussler, P.P., 1994. New age data for gold deposits and granites, Chichagof mining district, SE Alaska. Evidence for a common origin. Geol. Soc. Am. Abstr. Prog. 26, A140. Tian, Z.Y., 1992. The Mesozoic–Cenozoic East China rift system. Tectonophysics 208 Ž1–3., 341–363. Till, A.B., Dumoulin, J.A., 1994. Geology of Seward Peninsula and Saint Lawrence Island. In: Plafker, G., Berg, H.C. ŽEds.., The Geology of Alaska. Geol. Soc. Am., The Geology of North America, G-1, pp. 141–152. Tobisch, O.T., Paterson, S.R., Saleeby, J.B., Geary, E.E., 1989. Nature and timing of deformation in the Foothills terrane, central Sierra Nevada, California. Its bearing on orogenesis. Geol. Soc. Am. Bull. 101, 401–413. Trumbull, R.B., Hua, L., Lehrberger, G., Satir, M., Wimbauer, T., Morteani, G., 1996. Econ. Geol. 91, 875–895. Umhoefer, P.J., Schiarizza, P., 1996. Latest Cretaceous to early Tertiary dextral strike-slip faulting on the southeastern Yalakom fault system, southeastern Coast Belt, British Columbia. Geol. Soc. Am. Bull. 108, 768–785. Wang, L.G., Luo, Z.K., McNaughton, N.J., Groves, D.I., Huang, J.Z., Miao, L.C., Guan, K., Liu, Y.K., 1996. SHRIMP U–Pb

218

R.J. Goldfarb et al.r Ore Geology ReÕiews 13 (1998) 185–218

in zircon studies of plutonic rocks from the Jiaodong Peninsular, Shangdong Province, China. Constraints on crustal and tectonic evolution and gold metallogeny. In: Mesothermal Gold Deposits. A Global Overview. Univ. West. Aust., Publ. 27, 34–38. Wheeler, J.O., Brookfield, A.J., Gabrielse, H., Monger, J.W.H., Tipper, H.W., Woodsworth, G.J., 1991. Terrane map of the Canadian Cordillera. Geol. Surv. Can., Map 1713A, scale 1:2,000,000.

Xu, J. ŽEd.., 1993. The Tanchung–Lujiang wrench fault system. John Wiley and Sons, Chichester, 279 pp. Yang, S., Su, S., Du, C., Zhou, M., 1996. Discussion on metallogenic patterns of large and super-large gold mineral deposits in Jiaodong Peninsula, Shandong, China. 30th IGC Abstr., vol. 2, Beijing, p. 784. Zonenshain, L.P., Kuzmin, M.I., Natapov, L.M., 1990. Geology of the USSR: A plate-tectonic synthesis. Am. Geophys. Union, Geodyn. Ser. 21, 242 pp.