Orogenic Gold Deposits_Groves

http://www.ruf.rice.edu/~ctlee/cali/GrovesOrogenicGold.pdf

Ore Geol Geology ogy Revi Reviews ews 13 Ž1998. 7–27

Orogenic gold deposits: A proposed classification in the context of their crustal distribution distribution and rela relations tionship hip to other gold depos deposit it types D.I. Groves a

a, )

, R.J. Goldfarb b, M. Gebre-Mariam

a,c

, S.G. Hagemann a , F. Robert

d

Centre for Teaching and Research in Strategic Mineral Deposits, Department of Geology and Geophysics, Uni Õersity of Western Australia, Nedlands, WA 6907, Australia b U.S. Geological Sur Õey, Box 25046, Mail Stop 973, Den Õer Federal Center, Den Õer, CO 80225, USA c Wiluna Gold Mines Limited, 10 Ord St., West Perth, WA 6005, Australia d Geological Sur Õey of Canada, 601 Booth St., Ottawa, Ont., Canada K1A OE8

Received 20 March 1997

Abstract

The so-called ‘mesothermal’ gold deposits are associated with regionally metamorphosed terranes of all ages. Ores were formed during compressional compressional to transpr transpressiona essionall deform deformation ation processes at converge convergent nt plate margins in accretion accretionary ary and collisional orogens. In both types of orogen, hydrated marine sedimentary and volcanic rocks have been added to continental margins mar gins dur during ing tens to som somee 100 mil million lion year yearss of coll collisi ision. on. Sub Subduct ductionion-rela related ted ther thermal mal even events, ts, epis episodi odicall cally y rais raising ing geotherm geot hermal al grad gradient ientss with within in the hydr hydrated ated accr accretio etionary nary sequ sequence ences, s, init initiate iate and driv drivee long long-di -distan stance ce hyd hydroth rotherm ermal al flui fluid d migration. The resulting gold-bearing quartz veins are emplaced over a unique depth range for hydrothermal ore deposits, with gold deposition from 15–20 km to the near surface environment. On the basis of this broad depth range of formation, the term ‘mesothermal’ is not applicable to this deposit type as a whole. Instead, the unique temporal and spatial association of this deposit type with orogeny means that the vein systems are best termed orogenic gold deposits. Most ores are post-orogenic with respect to tectonism of their immediate host rocks, but are simultaneously syn-orogenic with respect to ongoing deep-crustal, subduction-related thermal processes and the prefix orogenic satisfies both these conditions. On the basis of their depth of formation, the orogenic deposits are best subdivided into epizonal Ž- 6 km., mesozonal Ž6–12 km. an and d hypozonal Ž) 12 km km. clas classes ses.. q 1998 Elsevier Science B.V. All rights reserved. Keywords: orogenic gold deposits; lode-gold mineralisation; ore formation; terminology; nomenclature

1. Introduction

This thematic issue of Ore Geology Re Õiews includes a wide variety of papers on a single type of )

Corresponding Correspondi ng author. Tel.: q61-9-380266 61-9-3802667; 7; fax: q61-93801178.

quartz–carbonate lode-gold deposit. The deposit type in th this is is issu suee alo alone ne is re refe ferr rred ed to as sy syno noro roge geni nic, c, turbidite-ho turbid ite-hosted, sted, mesoth mesothermal ermal and Archa Archaean ean lodegold. gol d. Thi Thiss ref reflec lects ts the pro prolif lifera eration tion of suc such h ter terms ms throughout throug hout the econo economic mic geolo geology gy literat literature ure during the last ten years and a subsequent increase in confusion for the readers. For example, is a synorogenic

0169-1368r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 1 6 9 - 1 3 6 8Ž 9 7 . 0 0 0 1 2 - 7

8

D.I. Gro Ões et al. r Ore Geology Re Õiew iewss 13 (199 1998 8) 7–27

Mother-lo Mother -lode de typ typee gol gold d dep deposi ositt dif differ ferent ent fro from m an Archae Arc haean an gol gold-o d-only nly typ typee or fro from m a mes mesothe otherma rmall greenstone–gold type? Many researchers working on such deposits would recognize these as essentially a vari va riet ety y of su subty btype pess of a si sing ngle le de depo posi sitt ty type pe,, i.e i.e.. epigenetic, epigen etic, struc structurally turally-host -hosted ed lodelode-gold gold vein systems in metamorphic metamorphic terranes terranes ŽKerri Kerrich, ch, 1993.. However, eve r, the consiste consistent nt usa usage ge of a sin single gle and wid widely ely-accepted classification term for this deposit type as a whole is clearly warranted. ‘Mesothermal’ is such a term that has been widely adopted during the last ten years, yea rs, but is a ter term m tha that, t, as originally originally define defined d by Lindgren Lindgr en Ž1933. for deposi deposits ts formed formed at about about 1.2–3.6 km, is more applicable applicable to sedime sedimentary ntary rock-hosted rock-hosted ‘Carlin-type’ deposits and the gold porphyry rskarn environment enviro nment ŽPoulse Poulsen, n, 1996. . A pri princip ncipal al aim of this introduc introductor tory y pap paper er is to present and justify a unifying classification for these lode-gold lode-g old deposits. An attempt is made to place these so-called ‘mesothermal’ deposits into a broader class thatt emp tha emphas hasize izess the their ir tec tecton tonic ic set setting ting and time of formati for mation on rel relativ ativee to oth other er gold deposit deposit type types. s. A second aim is to review briefly their more significant defining features in the light of current inconsistent termino ter minology logy and the rec recogn ognitio ition n tha thatt this dep deposi ositt group may form over a wider range of crustal depths and te tempe mpera ratur tures es tha than n co common mmonly ly re recog cogniz nized ed ŽGroves, 1993; Hagemann and Ridley, 1993; GebreMariam et al., 1995.. The term orogenic is introduced and justified as a term to replace ‘mesothermal’ and other descriptors for this deposit type. It is also sugges sug gested ted tha thatt the ter terms ms epizonal , mesozonal and hypozonal be used to reflect crustal depth of gold deposition within the orogenic group of deposits.

2. Def Definit inition ion of soso-cal called led mes mesoth otherm ermal al gold deposits

The so-called so-called ‘mesothermal’ ‘mesothermal’ gold deposits deposits ŽTable 1. ar aree a dis distin tinct ctive ive type type of gold depos deposit it wh whic ich h is typifie typ ified d by man many y con consis sistent tent features features in spa space ce and time. These have been summarized in a variety of comprehens compr ehensive ive ore-d ore-deposi epositt model descr descriptions iptions that includ inc ludee Bohlke Bohlke Ž198 1982 2., Colvine Colvine et al. Ž198 1984 4., Berger Berger Ž19 . Ž . Ž 1986 86 , Gr Grov oves es and Fo Fost ster er 19 1991 91 , Ne Nesb sbitt itt 19 1991 91., Hodg Ho dgso son n Ž19 1993 93. an and d Robe Robert rt Ž19 1996 96.. Kerri Kerrich ch Ž19 1993 93 .

summar summ ariz izes es ma many ny of th thee st step epss th that at le led d to th thes esee evolvi evo lving ng mod modern ern-da -day y mod models els.. A uni unifyi fying ng tec tectoni tonicc theme has recently been evaluated by workers such as Wyman Wyman and and Kerrich Kerrich Ž198 1988 8 ., Barley Barley et al. Ž198 1989 9 ., Hodgson Hodgso n and Hamilton Ž1989., Kerrich Kerrich and Wyman Ž199 . Ž 1990 0 , Kerrich Kerrich and Cassi Cassidy dy 199 1994 4 . and Goldf Goldfarb arb et al. Ž199 1998 8 - this issue issue. . 2.1. Geological characteristics 2.1.1. Geology of host terranes Perhaps Perha ps the single most consis consistent tent characteristic characteristic of the dep deposi osits ts is the their ir con consis sisten tentt ass associ ociatio ation n with deformed metamorphic terranes of all ages. Observationss fro tion from m thr throug oughou houtt the wor world’ ld’ss pre preser served ved Archaean cha ean gre greens enstone tone bel belts ts and mos mostt rec recent entlyly-act active ive Phanerozoic metamorphic belts indicate a strong association of gold and greenschist facies rocks. However, some significant deposits occur in higher metamorphi mor phicc gra grade de Arc Archae haean an ter terran ranes es Že.g e.g.. McC McCuai uaig g et al., 1993. or in lowe lowerr meta metamor morphic phic grade grade domains domains within the metamorphic belts of a variety of geological ages. In the Archaean Archaean of Wes Wester tern n Aus Austra tralia, lia, a number num ber of syn synmeta metamor morphi phicc dep deposi osits ts ext extend end into Ž gran gr anul ulite ite fa faci cies es ro rock ckss Gr Grov oves es et al al., ., 19 1992 92.. Pr Preemetamorphic protoliths for the auriferous Archaean greenstone green stone belts are predo predominant minantly ly volcan volcano-plu o-plutonic tonic terran ter ranes es of oce oceani anicc bac back-a k-arc rc bas basalt alt and fel felsic sic to mafic maf ic arc roc rocks. ks. Cla Clastic stic mar marine ine sed sedimen imentar tary y roc rockkdomin do minan antt te terr rran anes es th that at we were re met metam amor orph phos osed ed to graywa gra ywacke cke,, arg argilli illite, te, sch schist ist and phy phyllit llitee hos hostt mos mostt younger ores, and are important in some Archaean terranes terra nes Že.g. Slave Province, Province, Canada Canada.. 2.1.2. Deposit mineralogy These The se dep deposi osits ts are typ typifie ified d by qua quartz rtz-do -domina minant nt vein systems with F 3–5% sul sulfid fidee minerals minerals Žmain mainly ly . Fe-sul Fesulfid fides es and F 5–15% carbonate minerals. Al bite, white mica or fuchsite, chlorite, scheelite and tourmaline are also common gangue phases in veins in greenschist-facies host rocks. Vein systems may be continuous along a vertical extent of 1– 2 km with little litt le cha change nge in mine mineral ralogy ogy or gol gold d gra grade; de; min minera erall zoni zo ning ng do does es oc occu cur, r, ho howe weve ver, r, in so some me de depo posi sits ts.. Gold:si Gold :silve lverr ratios ratios rang rangee from from 10 Žnor normal mal. to 1 Žles lesss common. , with ore in places being in the veins and elsewhere elsewh ere in sulfid sulfidized ized wallrocks. wallrocks. Gold grades are

D.I. Gro Ões et al. r Ore Geology Re Õiews 13 (1998) 7–27

relatively high, historically having been in the 5–30 grt range; modern-day bulk mining methodology has led to exploration of lower grade targets. Sulfide mineralogy commonly reflects the lithogeochemistry of the host. Arsenopyrite is the most common sulfide mineral in metasedimentary country rocks, whereas pyrite or pyrrhotite are more typical in metamor phosed igneous rocks. In fact, the Salsigne gold deposit in Cambrian sedimentary rocks of the French Massif Central is the world’s largest producer of arsenic ŽGuen et al., 1992.. Gold-bearing veins exhibit variable enrichments in As, B, Bi, Hg, Sb, Te and W; Cu, Pb and Zn concentrations are generally only slightly elevated above regional backgrounds. 2.1.3. Hydrothermal alteration Deposits exhibit strong lateral zonation of alteration phases from proximal to distal assemblages on scales of metres. Mineralogical assemblages within the alteration zones and the width of these zones generally vary with wallrock type and crustal level. Most commonly, carbonates include ankerite, dolomite or calcite; sulfides include pyrite, pyrrhotite or arsenopyrite; alkali metasomatism involves sericitization or, less commonly, formation of fuchsite, biotite or K-feldspar and albitization and mafic minerals are highly chloritized. Amphibole or diopside occur at progressively deeper crustal levels and car bonate minerals are less abundant. Sulfidization is extreme in BIF and Fe-rich mafic host rocks. Wallrock alteration in greenschist facies rocks involves the addition of significant amounts of CO 2 , S, K, H 2O, SiO2 " Na and LILE. 2.1.4. Ore fluids Ores were deposited from low-salinity, near-neutral, H 2 O–CO 2 " CH 4 fluids which transported gold as a reduced sulphur complex. Fluids associated with this gold deposit type are notable by their consistently elevated CO 2 concentrations of G 5 mol%. 18 Typical d O values for hydrothermal fluids are about 5–8 per ml in the Archaean greenstone belts and about 2 per ml higher in the Phanerozoic gold lodes. 2.1.5. Structure There is strong structural control of mineralization at a variety of scales. Deposits are normally sited in

9

second or third order structures, most commonly near large-scale Žoften transcrustal. compressional structures. Although the controlling structures are commonly ductile to brittle in nature, they are highly variable in type, ranging from: Ža . brittle faults to ductile shear zones with low-angle to high-angle reverse motion to strike-slip or oblique-slip motion; Ž b. fracture arrays, stockwork networks or breccia zones in competent rocks; Žc. foliated zones Žpressure solution cleavage. or Žd . fold hinges in ductile turbidite sequences. Mineralized structures have small syn- and post-mineralization displacements, but the gold deposits commonly have extensive down-plunge continuity Žhundreds of metres to kilometres.. Extreme pressure fluctuations leading to cyclic fault-valve behavior ŽSibson et al., 1988. result in flat-lying extensional veins and and mutually cross-cutting steep fault veins that characterize many deposits Že.g. Robert and Brown, 1986.. 2.2. Tectonic setting and timing of ‘mesothermal’ ein emplacement

Õ

The so-called ‘mesothermal’ gold deposits ŽTable 1. occupy a consistent spatialrtemporal position ŽFig. 1., having formed during deformational processes at convergent plate margins Žorogeny . irrespective of whether they are hosted in Archaean or Proterozic greenstone belts or Proterozoic and Phanerozoic sedimentary rock sequences Že.g. Barley and Groves, 1992; Kerrich and Cassidy, 1994 .. The placing of these deposits in a plate tectonic setting was a logical outgrowth of the acceptance of plate tectonic theory in the early 1970’s. Guild Ž1971. initially discussed the ‘‘ orogen-associated endogenic mineral deposits of Mesozoic and Tertiary age on the sites of Cordilleran-type Žcontinent rocean. collisions’’. Sawkins Ž1972. noted, soon after, how both these Circum-Pacific gold ores and spatially associated felsic magmas were probable products of subduction-related tectonism. Just as significant was Sawkins Ž1972. observation that Archaean gold lodes in the Superior Province, Canada, may have some relationship to the southward younging of igneous ages, interpreted as being reflective of a seawardmigrating trench. It would be, however, another sixteen years Žcf. Wyman and Kerrich, 1988. before workers would follow-up on this important concept


10

; o 4 9 t p 9 o 1 t , y m d o i r s f s a , C d r d e e n a d r o h c e i r r r e a K s e c m i n o r f v o r d P e i . f s i d e g o a m l y b l m t e r a s p s a s t n k a c n o i r m c o i d h p k r o c o r m a t e y r a m t n n e i m s i e d c e n i s v c i o r n p a e d c l o o g r e e m g n o s u o y m d o r f n s a s p l t i h e s b n e o i n t a o t l e r s n c e e i r n g o t n c e t a e a t h n c a r c i n A f i o n l y i t g a i n i s a m r d m o n a e f r f n o o a i s e t g a e a n m a g r r r n o f e s t i a n t i s e r e v o c n H i d l . n o i g 8 , c 9 e 9 i 1 l n b e , . a t g o l e a h r t o e t f f o r o 1 g b a m n f e i l d o t l b m a i o t o T T G b Ž

g r u b n e k c n a 5 l 9 B 9 , 1 7 s 8 i e 9 1 v a i D t r d u C n a

, b 1 9 9 1 4 9 . 9 l a 1 . t e l a t b r a e r f e d l l l o i G M

. l a t e e r i u G c M n e d 9 d a 8 9 M 1

g n i f o w o n r g o h i t t c u a e d b n e u b s e g g n d i r i u r g d n g i d n i a m n e s i i e r r v p s p

e g n a h g e g c n u i n ; i m q n r i i s l i u b e d h o v p l r g l i o i o n t s m l r f u a a o t n d t e o e n g e m o c n n m e a h t e i g r c r v o a o e l r p r m v n a o m r o e B f c

l a g n n s i l c i n n i o t e e r o v - n o f n o y i t t s c e u ; s a d n k b o s u a s d g r n l d a i n r A f a u o w a d n e g i o s g n t n i i d e m n n r k i e e c f c v b a o

0 5 – 6 6

0 6 – 0 7 , t e r C d i m

5 m 2 t d i s – n 9 y e t t l 2 l a a a 2 a i – 4 t d i c m s t , 3 n o g a o a s a 0 3 u p 1 S s a m M 3 m b a t a

5 9 9 1 . l a t e r e l s s u e a H

.

.

. s f e R . n o r h c o e G

Ž

. Ž

Ž

.

.

Ž

Ž

.

Ž

6 9 9 1 e e n S d n a d r o F

.

1 9 9 1 . l a t e h c t i e L

.

Ž

7 9 9 1 . l a t e y o C c M

.

Ž

Ž

n o l y i s r i l l a e o c d h n t d a i r l a e o n h w t a a r a e b s r e t t g a s n i i l a o r l C n u e g d f o o i g n t r s n a a i e n m g W i a e f t r o v o s f

n ; o ; t n d a o r i s a r c n f w e o a t d e x s s k e n a l c o m t a n o k i n o r n i o t f s d i e o e r g e s s e c u o r c n n h i a a e t t p g r n M i n n o n o o c 0 i i n m o t 1 g c t 1 e n a u e k u i – v d n Y 0 i b 2 n e m n n y u 1 s s v u i

r s c n i t i a e v m ; g a k c m a l b T a l l n o o r h i g t i g b e a h n o r l r s m f g o d n c r i i f r n a h u m p d n o k r o i g 0 n s m i n 5 n e t – a i t e x 0 e v e 4 m

c i s s a r u J

c i s s a r u J

e l d d i M i – c y s s l a r a r u E J

, t s n i a 0 h i 3 2 1 c 8 v o s – e – r r u 8 0 l a 7 1 b 0 1 B

0 5 – 6 6

, l l , i h t s t e r 0 8 i l o C 6 4 h d – – t i 0 0 a m 7 6 b

6 6 – 4 7

3 4 – 1 9 , 0 7 2

0 9 – 5 9

2 8 – 8 0 1

c i o s z f o o e n e t a a e a l r g s r o e M a A h t P

s u o e c a t e r C . L

s u o e c – a t e n r a C i m d r e i P m

c i o z o e l a P e t a L

– c c c i i i o o o z z z o o o y y l e l s e l t r l e a e a a r a a L P e M E P

f g n o i e i n a g e M A v

F

9 4 – 7 5

3 5 – 7 5

6 6

6 8 – 1 9

7 7 , 7 8 – 2 9

9 0 1

, s r p e l p p A u . , a s W , o s R e p y t . p l a t M a n I

a k s a l y r A a . n S h o , c a i t g r m u e s i h c C c a r p

t , l e b d l o a g k s u a a e l A n . u S J

- a k h e t k s e u a r l s A C o , l t w c a o i l r r t l t i i s n W d e c

a W i S b , m r e u v l i o R C e s g h i d t i r i r B B

t s a a e k s a , l s k A n l a a b t r r i a n F e c

W N , a e k s m a o l N A

t a n o i t a n i m a l e d b a l s d e z i s e h a t o M p y 5 h 4

s t n e v e t n a t r o p m i r e h t O

c i h p r o s m t a t e a e n M v e M .

Ž

0 ; t s 6 i – h 0 s 0 9 c 4 , e u – 5 l 1 4 b 4 4 .

Ž

.

.

.

.

Ž

Ž

.

Ž

.

Ž

.

e c n i v o r P

3 3

Ž

Ž

.

.

Ž

Ž

c i o z y o l e r l a a E P


, 6 9 8 9 1 9 9 . 1 l a l . t e a t g e r b e r b a e f l k d l o o N G

.

.

Ž

Ž

s n e t e a d e l e w p s t a i e e b g r c s a n n a i e t z a I g r n d i r e n u c a n d e n g a g r i n e s i v a n r i u e n o v c E s u o – c e c i a s t s e a r r u C J y l e t a r a L E

0 8 – 4 4 1

, 6 8 r e 9 1 d l 2 E r e , 9 l 9 t 1 s 8 8 i 9 K 1 n d a m n l a d e h s f e a e C k l d h n d o a B L n a

.

e , i 6 N 9 , 9 6 1 9 . 9 l a 1 t e l . l l a u t e b g m n 7 9 u r a 9 T W 1

.

.

Ž

Ž

.

Ž

.

Ž

.

Ž

Ž

9 8 9 1 w a r C d n a g a e K c M

.

Ž

11

, 0 , 9 9 9 1 8 . , 6 9 1 l a 5 9 t . 9 9 l 1 9 a e u 1 . t l e a e a t n k t e o i l e v h e a i c h r u t o n e o a t B C M S .

, 3 9 9 1 6 . 9 l a 9 1 t e l . a n o t t e h s h u s R A

.

.

Ž

Ž

, 4 9 9 1 6 . 9 9 l a 1 t e r e y i e b l e h s h c A S

.

.

Ž

Ž

, 4 6 9 9 9 1 9 . 1 l a l . t e a t e r e w g r r e e B D

.

.

Ž

Ž

.

Ž

.

.

Ž

Ž

Ž

g n n i i r o u s n d e f e t x o e m ; e u l l g a m a p s n t o t s i e i l a t i s e t n l m a l a l g a m o g m d c n t i s e r n o z a i p u i d s n e f a h g o h n i s t o t e n n i e a p y s n v Y h o

t n e f m o e c , g a l d n i i p d p p n a m p r a e e t s f h o e c t i d t n r e l o a e s g h r t n w a o e a v b e s a n a a M o c d a l M 0 v a e 0 2 n N 1 4 o ; 1 h g a o r – c h r n t i 0 5 e r e r 1 t o S

n o i t t a s a m l r n t o i u f g o e r h d a g l m u a o n n r i o a h t i s n l y l a l w e o c d k f i l o n o g d G n i i g n o n i o e r e l v p a

n n o o i t i t c a u z d i n l b y a s u r ; s e s n i e d n m g r a a d a n g n o w o i n i t a s l e e e o r s t o c a d c c m a e g k r e b f g n o d i n l n s u u i o o e n y c v e t

f o g n d o o l i r a e p n o l i t a n c i u f d o b a t u i s l d e d a r t t a n l a s u e r n A o n g i n t r i e r t n e i c e c s v a a e

n a i n y n c o r s e i l H i l f o o c t e r n u e t n i u s t n r o a c e – n t s t n e i n s i o t p e n d o c

n a e a h c r A

y l r a E s – u c o e i c s a s t a e r r u J C

s u – c o e i c s a s t a e r r u J C y y l l r a r a E E

– i c c i s s s s a r a i u r J T y l e t a r a L E

c i s s a i r T – n a i m r e P

– n s u i a o r e m r f e i n P o y b l e t a r a r a L C E

0 4 3 – 0 5 3

0 6 1 – 0 9 1

y l r a E , , 0 8 5 4 c 2 2 i s – – s a 6 5 i 0 5 r 3 2 T

1 6 2 – 1 7 2 , 0 1 3

0 2 3 – 0 6 3

– c i c o z i s y o s l e i a r a l a r E P T

– s u o r e f i n n a o i b m r a r e C P

– n a n a i c i i r b v o m r a d C O

– c i c o z i o o z r o e y t e o l e t l a r r a a L P e P

y l r a E – n c a i i s s m a r r e i P T

– s n u i a o r m e f r e i n P o y b l e t a r a r a L C E

a ; 0 0 i l 1 i f 2 f a 3 m s e i r s s t – h " s 0 o a 0 a n e 4 0 B M 3 M 3 C

d . n a E l , i g l a n t e l a E b r s w d t e l u o N f A

l d a n t s a r t n i n , a e c s o u t p a s t t i e n n k e d u e c r b j a a u z i s M U d a A

, d e t a l e r n a e c s p i o r a r u V E

, 0 7 1 2 1 1 – – 0 9 2 3 1 1

– c c i i n a o e e o z z l a o o d h e l e d s t r a a i e c L P m M A

5 3 , 0 1 h 8 h – t – t r 0 u 7 o 7 n 5 o 1 1 s

e n o n

– c i c o e z i l s o d e s a d i l a r u M P J

e t a L – n c a i i s s m i a r e r P T

.

.

Ž

Ž

0 0 1 – 5 3 1

s u o e c y a t l r r a e E C

t 8 8 0 r l 0 e e b 1 1 – – h t e 4 7 o 2 d 4 o 1 1 M l

t s a E r a F n a i s s u R

a e r . o E g E K d n a N n o l u , a d g s a n a n i n i n i a n h e h h S P C C

a s i l n l r i h t o h f t a i o m l a o a C f l a K r . , r s t e d i n S a M

Ž

.

s

.

Ž

y l r a E s – u c o e i c s s t a a e r r u J C

h t w u o e S N d , d , n o a g n a a l a l t e s O I Z

4 3 1 G

– 0 8 1

d h n s a i t i n r a o B i k b u r o m Y i r u l e t W n o S I C

a c i r f A n a – a i a M m i s 0 r e s u 5 P - r o 3 – ? r u a 0 8 n a L 3 i ; y n n o o b v i n e t o i D c u s i e d l t l a b u L s o c

. Ž

.

.

Ž

Ž


12

6 9 9 1 . l a t e l l e w o t S

.

. s f e R . n o r h c o e G

Ž

s t n e v e t n a t r o p m i r e h t O

d n a r T e – h t P o d a l i c r n e h a o g r h t c e g s i i m h l e n e A t g a v h t e o l r d r l e o o a c t N c a i l s n o i p u r c z s m o t r e r i e s s e n o p n a i e e e h p e v d P d

c i h p r o s m t a t e a e n M v e M

e t a d s ; u t L n o e n a r n e n e d a n a i i f s v i a c i e i e r g d n n v o r n o i o o e s d b v r a i w a o p r e C m l e O D

r , e y 0 e 9 m l 9 1 l a . D l a d t e n a k e i a t p 5 9 n o p e 9 K K 1

.

Ž

.

Ž

r e d t s n a o s F i p , l l i 6 9 h P 9 1 , 6 9 9 . 6 l 9 a 9 1 t 1 e s e e l . h g n a r u A t e H

.

.

Ž .

Ž

Ž

, 9 8 9 1 s g e n v o i r d l o G G d n a d n a n o s m r o 4 9 e l t e o 9 P S 1

.

Ž

.

Ž

e t a L n n e e i a w m t o t e r e b P d e n y t i l c r r u g a a E d b m o l d s a t n a k c n n e o a n i r i r t t u s n l o o i h c S

e g d a e n n n o i k a s - t a n d i n h o t g n i t ; i a t ? t i z c i n l l a e f r v e e n o n c i n ; o s m i t c c i d l u n o o d t g b c f u e s t o

7 7 3 – 5 1 4

– , l l o e i g w d a t n e e S B n n – 0 r 0 t u a 3 0 a o i n 4 r 4 l b a – l – e o v 0 l 0 a M e 6 4 B 1 4 D

d e n n i k s n i h t ; ? t n e v e n o s i t c c i n u o d b t c u s e t

, r 2 e 9 9 s y 6 9 1 n a K 9 r 1 d m e a n s s e a y r e K H k n e n d d y n o n a a a F C l s , , l e a 4 5 d m 9 s o 9 n h 9 9 A T 1 1

.

.

Ž

Ž

. .

Ž Ž

6 9 9 1 . l a t e s e d r i H

.

Ž

; s d e t g u n n i e n d r n r i v e t u a t e n d e e a l o v g s n e c r n r i n k u o n c e b o u m o i r r E s e s s f o l h s o f t e a c e g s r f n e p n o n i e r i e t i a s s o n u r a s e q n M u b d s n a r i o e r s 0 t n h a a l 9 i t t c a i s l 6 a e g a p n m 1 i n n u a r a m o l q c h i i o l r n i t l r i f e g e h e n e b e o p t r u v o d v Ž

.

.

.

Ž

.

Ž

s o t u o n r m d i a f e s i y e t i t c l i l a a n i a v o i c m o t b e o g a r a s a t d r a a p S s a m M L O C

6 1 3 , 0 7 3 – 0 8 3

c i s o f e z o n o t a e e a r s l g o r a M e A h t P

– n a n a i c i i r b v o m r a d C O

.

Ž

.

Ž

f g n o i e i n a g e M A v

4 9 2 – 3 4 3

2 6 3 – 0 8 3

e c n i v o r P

, s n a i n h c r a e l h a A t p u o p S S A U

a v o N , a m a u i t g e o c M S

.

Ž

d e u n i t n o c 1 e l b a T

.

Ž

Ž

0 7 7 1 – 0 7 8 1

, 0 9 0 6 3 3 – – 5 1 0 7 4 3

s u – o n r , a n f e i a i c e i e i n l l n v o d d o o b d d v i d r i e r a M O M D C

4 3 8 1 – 0 9 8 1

, 8 0 8 5 1 0 2 2 – – 5 6 8 1 1 1 2 2

n a n i a c i i n v y o o l v d r r a e O E D

– n a n a i n i o r u v l e i S D

c i o z o y r e l t r o a r E P

; 0 s 5 c e r 1 i a y r 2 n t n e e s l – a t g c c n h 5 n l j i a 8 s g u 1 o a i o d l v 2 a b s y

0 , 6 ? 3 – 0 5 6 1 4 4

e s t a u L o r e , f 0 i 3 n o " b r 8 a 0 4 C

0 2 7 1 – 7 0 8 1

0 0 1 2 t u o b a

E S , i a a l i r a r o t t c s i u V A

E N , d n a a l l s i a n r e t e u s u Q A

l n a r o s t n d u e c , a H n d s e n g a n a o a r T r o C

f o r n – t e i e o l s e t r a o F b s a v e n I – ’ a a a i n d i n m e k i a t r r h i o u B G C B

. Ž

.

Ž

.

Ž


0 , 9 9 1 9 8 . 9 a 1 l . t e l a n t e a n h d s a i t r s g k a l o r a K B

, 6 9 l 9 1 n l a g l . n a u m o a t e e D g c t a M n e H K d d n , n a 5 a 6 t t 9 9 n n e 9 e 9 1 K K 1

d n r e a n n o l a o 5 p h 9 S c a 9 1 d L c t n a a d M e m a a , t s h 5 a m 9 l r b 9 e 1 A H

s d e e n n a i n r a o , r r i t t e l t s t e s s i o l s n l b u m o t c s e f o c o i r h g e h y t o l c n r i m s f e r u r o g o u n a e a o d p t ; f l o i n n o K s s e o o i g i e r t t o e n h a a i t t h z r z t s n i i u l l i a t m t a a u r r r h r e s o i e c o n d f h p i n i n o m m a t w i m

d l m u s i o h c p r g n o i n m i a t e v e d m e n n i o ; e a e r g t s a a t d n g o t n s c i l e y g o l o r n c u o e o o y b p

e m i g e r n o i t c u d b u s 2 1 g 7 2 n o y l . b y . d e t m a - i t 0 i 0 n 1 i

.

.

Ž

Ž

.

Ž

.

.

Ž

Ž

.

Ž

.

Ž

, , 3 6 9 9 9 9 1 1 6 r l . 9 9 e 1 p a t i e P e l . d i r a n t a h e s r y u e b t r y s n o a i F D V

. .

Ž Ž

.

Ž

h c i r , l . r e 4 n e a t K 9 d e u , 9 r l 1 4 C l e 9 y d w 9 d n o 1 i a s P s n , h a o c C s 5 5 i r 9 k 9 r 9 e d c a 9 1 1 K n a J .

.

Ž

Ž

. .

Ž Ž

, 3 1 9 9 9 1 9 1 r . e p l a i P t e d e n a d n r e o t s R e o d F .

.

Ž

Ž

f n o o g i t n i a z t t i e l s a e r r e l n i a m m r r e o h f t t d o c i e r l e f s p e r e g t g a n h e g u i o u y m r t

; d s n t y a r t a a a g s o a l n n h m b i o i f i t t o n o P s e i a a t u m i h z r a t l i s l a h z i f t i a l t h r o r r s a e p t e r r t n f o e a u i A h n a m . m i t n , y a m h t r . t e n e e i t o m t h w s m t e r 0 e e 0 l f t w a b o a , r n a 1 e k t i o e l c B s r l m r g o a n l e e i r o s o c b

? 0 9 6 2

3 4 6 2 – 0 9 6 2

t a e m o s , 0 0 2 3 0 5 8 ) 2 , , 0 6 0 0 0 0 5 1 7 2 3 2 – – , 7 0 0 3 4 0 0 0 6 3 3 2

n o i t u l o v e l a t s u r c d e t a d y l r o o p

, 0 0 6 6 3 6 2 2 – – 0 9 0 5 6 2 6 2

0 9 6 2 t u o b a

, 0 0 3 6 6 6 2 2 – – 0 0 9 6 5 6 2 2

– 0 4 6 2 , 5 3 6 6 8 5 2 2

, t 8 0 2 e 0 a r 4 6 2 G 2 , – e 0 0 k 0 7 6 4 y 2 2 D

, 3 7 1 1 6 2 6 2 – – 0 5 2 7 4 6 2 2

5 8 6 2 – 0 5 7 2

n a d e a n h a c r e A l d e d i t a M L

e t a L d n n a a e a y h l r r a c E A

n a d e a n h a c r e A l d e d i t a M L

? 0 0 4 2 t u o b a

, ? 0 5 2 6 6 2 5 – 2 , 0 4 2 0 6 6 2 2

0 6 6 2 – 0 7 6 2 t u o b a

, 9 5 6 2 ? , 0 7 0 1 6 2 4 2

, ? 4 0 7 6 0 4 2 2 – – 0 2 3 3 7 2 6 2

t l e 0 b 0 s 0 5 p n 4 n 7 a 8 o 6 2 i o 2 h s 0 t r t 3 r e h ) a e – b ; p e r c 0 t h 0 r a l t m u i 2 e 3 B b w o s M

, n o t a r c r a i a w d r n a h I . D S

, n o a t i l a r r c a t s n r u a A g l . i Y W

a , d n o a n t a a r c C , e T v a W l S N

, n o t a r c e e w b w b a a b b m i m i Z Z

a d a n a C , r c o e i n r i e v p u o r S P

, n o t a a r c c i r l f a a A v h p t a a u o K S

0 5 5 2 0 3 5 2 – 0 0 7 2

. Ž

. Ž

. Ž

Ž .

n i 0 0 2 n o 3 t – r e 0 b r t 0 6 a l e 3 B b

Ž

.

.

. Ž

. Ž

.

Ž

Ž

13

14


Fig. 1. Tectonic settings of gold-rich epigenetic mineral deposits. Epithermal veins and gold-rich porphyry and skarn deposits, form in the shallow ŽF 5 km. parts of both island and continental arcs in compressional through extensional regimes. The epithermal veins, as well as the sedimentary rock-hosted type Carlin ores, also are emplaced in shallow regions of back-arc crustal thinning and extension. In contrast, the so-called ‘mesothermal’ gold ores Žtermed orogenic gold on this diagram. are emplaced during compressional to transpressional regimes and throughout much of the upper crust, in deformed accretionary belts adjacent to continental magmatic arcs. Note that both the lateral and vertical scale of the arcs and accreted terranes have been exaggerated to allow the gold deposits to be shown in terms of both spatial position and relative depth of formation.

and begin to widely look at Archaean gold as a product of continental-margin deformational events. The concept of a general spatial association between the gold deposits and subduction-related thermal processes in accretionary orogens Žoceanic-continental plate interactions. became commonplace in the mid-1980’s. Fyfe and Kerrich Ž1985. presented a model at that time to explain the massive fluid volumes required for the numerous gold-bearing vein swarms adjacent to crustal-scale thrust zones of continental margins. They hypothesized that underplated hydrated rocks contained the required water and such water was released during thermal reequilibration as subduction ceased. Subsequent models for the Mesozoic and Cenozoic gold fields of westernmost North America relied heavily on correlating gold vein em placement with subduction-driven processes ŽBohlke and Kistler, 1986; Goldfarb et al., 1988 .. Landefeld Ž1988. , expanding on the ideas in Fyfe and Kerrich Ž1985., detailed how the seaward stepping of subduction accompanying terrane accretion could have been

crucial for the formation of the Sierra foothills gold districts Žincluding the Mother lode belt.. With an abundance of new geochronological data from western North America, recent models of gold genesis in accretionary orogens have been able to look closely at specific processes Že.g. changing plate motions, changing collisional velocities, ridge subduction, etc. . occurring during accretionrsubduction that tend to be most closely associated with veining Že.g. Goldfarb et al., 1991b; Elder and Cashman, 1992; Haeussler et al., 1995 .. Theoretically, as a subduction zone steps seaward, a series of gold systems and plutonic bodies should develop and young towards the trench-part of a so-called Turkic-type ŽSengor and Okurogullari, 1991. orogen. This type of scenario crudely characterizes Alaska, USA, a part of the North American margin almost entirely composed of accreted oceanic rock sequences ŽPlafker and Berg, 1994.. Collisional orogens Žcontinent–continent collision., including the Variscan, Appalachian and


Alpine, also are host environments for gold deposits. In fact, collisional Žor internal. and accretionary Žor peripheral. orogens may represent end-members of a continuous process. Any continent–continent collision will be preceded by closure of an ocean basin, and hence is nothing more than a final stage of a peripheral orogen. The gold systems that are associated with the Phanerozoic internal orogens are actually all spatially associated with marine rocks that have been caught up within the suture. In addition, within peripheral orogens, accretion of microcontinents such as Wrangellia along western North America ŽPlafker and Berg, 1994. or Avalonia along Laurentia ŽKeppie, 1993. may be viewed as a type of small-scale continent–continent collision. A key point in all examples is that hydrated marine sedimentary and volcanic rocks were added to continental margins and, at some time during this growth, the accreted rocks experienced relatively high geothermal gradients. Oligocene veins in the western European Alps ŽCurti, 1987. are the youngest recognized, economic examples of this deposit type. They also serve to point out that more than simple plate subduction is required for vein formation. The closure of an ocean basin between Europe and Adria Žperhaps a part of northern Africa. occurred during an 80-m.y.-long period of Early Cretaceous–early Tertiary oceanic crust subduction without any preserved evidence of gold veining or magmatism; blueschist metamorphic facies in the Alps now record the low thermal gradients. By the early Eocene, complete closure of the ocean had led to continent–continent collision and a partial subduction of the European continental margin between 55 and 45 Ma ŽBlanckenburg and Davies, 1995.. It was not until almost 100 m.y. subsequent to the onset of convergence, perhaps due to slab delamination resulting in the cessation of subduction at 45–40 Ma ŽBlanckenburg and Davies, 1995. , that magmatism and high temperature metamorphism impacted the obducted upper nappes of the western Alps near the collisional suture. Much of the Alpine gold veining occurred during the early Oligocene peak of magmatism ŽCurti, 1987.. The understanding of gold-forming processes and timing in older Phanerozoic orogens may be complicated by the hundreds of millions of years of additional geological time, but certainly such Palaeozoic

15

continental margins were favorable environments for veining. Geochronological study of the gold deposits in the Meguma terrane of Nova Scotia, Canada, indicates veining between 380 and 362 Ma ŽKontak et al., 1990 ., during the late part of Acadian deformation of the Appalachian orogen. The Meguma was the final terrane accreted to the Atlantic margin during the poorly-understood late Palaeozoic Laurentia–Gondwanaland collision. Keppie and Dallmeyer Ž1995., noting that magmatism and high-temperature metamorphism were restricted to a narrow time range of about 380–370 Ma, rather than the prolonged 100 m.y. of Meguma collision, suggest a distinct episode of lower lithospheric delamination for the thermal perturbation. This brief thermal event, occurring at the same time as gold veining, is also likely to be important to the ore-forming process. Whereas little is certain about the subduction-related tectonics of the northern Appalachians, mesothermal-type gold ores such as the Hammer Down in northwestern Newfoundland ŽGaboury et al., 1996. indicate that a broad belt of gold systems accompanied continental growth. Palaeozoic gold veins of the Tasman orogenic system in eastern Australia make it clear that the ore-forming process need not require a ‘Cordilleranstyle’ of terrane accretion. Unlike the collage of small terranes that formed the accreted margin of western North America, eastern Australia is mainly composed of a single lithotectonic assemblage Žthe Lachlan ‘terrane’. that represents a 2,000-km-wide Palaeozoic turbidite fan sequence developed adjacent to the Gondwanan craton ŽConey, 1992.. Such an environment lacks deep-crustal terrane-bounding faults located between accreted material and the active margin, which, where present in the North American Cordillera, expose a variety of crustal levels and often serve as the focus of hydrothermal fluid flow. Compression-related deformation is solely intraplate rather than concentrated along sutures between terranes. The fact that such a large percentage of gold has been concentrated in the Bendigo–Ballarat area of Victoria ŽPhillips and Hughes, 1996; Ramsay, 1998 - this issue . indicates some significant and still poorly-understood, local control on vein emplacement in the orogenic system. Nonetheless, similar to the North American Cordillera, the Tasman orogenic system is characterized by significant


16

growth of the eastern Australian margin Žaddition of the Lachlan ‘terrane’. and a subduction zone east of the Lachlan assemblage throughout much of the Palaeozoic ŽSolomon and Groves, 1994.. The abundance of geological similarities between the gold ores of the Phanerozoic orogens and those in Archaean greenstone belts began to be interpreted by the late 1980’s as evidence of a similar tectonic setting for ore formation. Wyman and Kerrich Ž1988. hypothesized that gold mineralization in the Superior Province of Canada was ‘‘related to convergent plate margin-style tectonics’’. At roughly the same time, Barley et al. Ž1989. independently reached the same conclusion to explain the development of gold lodes in Western Australia. Subduction of oceanic rocks into the zone of partial melting appeared to be significant in the development of these gold ores within orogens of all ages ŽHodgson and Hamilton, 1989.. Major fault zones spatially associated with auriferous belts in the Archaean terranes were now recognized by several researchers as ancient terrane boundaries. Kerrich and Wyman Ž1990 . pointed out that, as observed in present-day convergent margins, Archaean ore-forming fluids were products of deeper crustal thermotectonic events which occurred subsequent to magmatism and metamorphism in ore-hosting supracrustal rocks. Detailed geochronological studies now recognize such lower- to mid-crustal, late deformational regimes in Archaean terranes ŽJackson and Cruden, 1995; Kent et al., 1996 .. Gold deposits in any given Archaean province may all be a part of the same supercontinent cycle Žcf. Barley and Groves, 1992., but can show a wide variation in age ŽTable 1 ., reflecting a variety of thermal events during many tens of millions of years of accretion and subduction. 2.3. Crustal en Õironment of ‘mesothermal’ gold de position

The majority of deposits of this ore style are sited in ductile to brittle structures, have proximal alteration assemblages of Fe sulfide–carbonate–sericite " albite Žin rocks of appropriate composition to stabilise the assemblage. and were deposited at 300 " 50 C and 1–3 kbar, as indicated by fluid inclusion and other geothermobarometric studies ŽGroves and Foster, 1991; Nesbitt, 1991. . They are consistently 8

syn- to post-peak-metamorphic and were emplaced at temperatures generally within 100 C of peak metamorphic temperatures experienced by the surrounding host rocks. However, recent studies in mainly Archaean greenstone belts have extended the ranges of temperature and pressure, and hence extended the inferred crustal range of formation of the deposits into higher- and lower-grade metamorphic rocks Že.g. the crustal continuum model of Groves, 1993.. The evidence for formation of these gold deposits over P – T ranges of about 180–700 C and - 1–5 kbar ŽGroves, 1993; Hagemann and Brown, 1996; Ridley et al., 1996. implies vertically extensive hydrothermal systems that contrast sharply with other continental-margin gold systems that are apparently restricted to the upper 5 km or so of crust ŽFig. 2.. Studies in the early 1990’s, summarized in McCuaig et al. Ž1993., identified higher P – T examples of these gold ores in amphibolite facies terranes of Western Australia, the Superior and Slave Provinces in Canada, India and Brazil. Most such mineralization occurred between 450–600 C and 3–5 kbar. A few examples in granulite terranes formed at even higher P – T regimes ŽBarnicoat et al., 1991; La pointe and Chown, 1993.. The gold ores were still precipitated from the same low salinity, CO 2- and 18 O-rich fluids, but, because of the higher temperatures and different mineral stabilities, there is a scarcity of carbonate phases and an abundance of calc-silicate minerals characterizing alteration haloes ŽMikucki and Ridley, 1993.. Such assemblages are similar to those typifying skarn systems ŽMueller and Groves, 1991.. It is somewhat problematic as to why a similar continuum of gold deposits has not been widely recognized in higher metamorphic-grade portions of Phanerozoic orogenic belts. Was there something inherently different between the tectonics of Archaean and Phanerozoic continental growth? Or do such gold deposits occur in high-grade terrains of the Phanerozoic and they have just been classified differently? Perhaps a re-evaluation of the classification of some of the gold-bearing ‘skarns’ or contactmetamorphosed deposits in younger orogenic belts might help to solve this problem. Ore fluid salinity might be a key discriminator in the case of the skarns, with relatively high ore-fluid salinities being 8

8

8


17

Fig. 2. Schematic representation of crustal environments of hydrothermal gold deposits in terms of depth of formation and structural setting within a convergent plate margin. This figure is by necessity stylised to show the deposit styles within a depth framework. There is no implication that all deposit types or depths of formation will be represented in a single ore system. Adapted from Groves Ž1993 ., Gebre-Mariam et al. Ž1995. and Poulsen Ž1996..

associated with typical gold skarn deposits that are more directly linked to intrusive sources ŽMeinert, 1993.. The late Palaeozoic Muruntau deposit in Uzbekistan is apparently one example of a postArchaean, higher metamorphic grade ‘mesothermaltype’ deposit. The abundance of thin quartz layering, fluid inclusion data suggesting trapping temperatures in excess of 400 C ŽBerger et al., 1994. and a skarn-like, calc-silicate assemblage ŽMarakushev and Khokhlov, 1992. from deeper parts of the ore system all suggest that the deposit may represent a deeper part of the crustal continuum. Ore formation at temperatures of 200–250 C and at crustal depths of only a few kilometers is not uncharacteristic of these ores where hydrothermal fluids have migrated to shallower crustal levels. However, a few anomalies from shallow gold systems in the Yilgarn block of Western Australia are 8

8

notable. Comb, cockade, crustiform and colloform textures at the Racetrack deposit, deposited from CO 2-poor fluids in lower greenschist facies rocks at depths F 2.5 km, are more like those developed in classic epithermal vein deposits ŽGebre-Mariam et al., 1993.. Similar textures at the Wiluna gold de posits in subgreenschist facies rocks, as well as 18 d Oquartz measurements as light as 6–7 per ml, provide some of the strongest evidence of meteoric water involvement in some of the ‘mesothermal’ hydrothermal systems ŽHagemann et al., 1992, 1994.. Gold solubility relationships at temperatures below 200–250 C best explain the observation that the continuum of this type of gold deposit does not continue into the uppermost few kilometres of the crust. The moderately-reducing and only moderately sulphur-rich conditions likely to characterize ‘mesothermal’ gold ore-fluids at low temperature 8

18


ŽMikucki, 1998 - this issue., would favor low gold solubilities at these low temperatures Že.g. Shen berger and Barnes, 1989 .. However, hydrothermal fluids that have been depositing ‘mesothermal’ gold along crustal-scale fault zones at depth, must still advect along these faults to the surface. Such is probably the case in the westernmost part of North America where CO 2-rich, isotopically-heavy fluids migrated to near-surface environments of very low P – T in the Cordilleran orogen. Cinnabar " stibnite bearing epithermal, silica– carbonate veins, which were deposited within the upper few kilometres of crust, define such flow ŽNesbitt and Muehlenbachs, 1989.. Examples include the Hg–Sb deposits of the Kuskokwim basin in SW Alaska, the Pinchi belt of British Columbia and the coast ranges of northern California. In fact, it has been recognized now for thirty years that many of the thermal springs within the accreted margin of western North America have a unique chemical character ŽWhite, 1967. and could be the surface expression of deeper ‘mesothermal’ 18 gold deposits. d Oquartz values for Hg-rich veins emplaced in the near surface are as heavy as q30 per ml because of greater quartz –water fractionation, as temperatures of ore fluids cooled to as low 150 C. Such heavy oxygen values are very distinct from 18 d Oquartz values of other types of vein systems deposited in classical epithermal environments, such as those of the Nevada Basin and Range ŽGoldfarb et al., 1990.. The identification of this type of Hg–Sb epithermal system in a continental margin terrane with limited erosion may be a valuable guide to the down-dip existence of a so-called ‘mesothermal’ gold occurrence. 8

2.4. Comparisons with other lode-gold deposit types

Most deposit types that contain ore-grade gold ŽTable 2., whether with gold as the principal metal or together with copper, are sited along convergent plate margins ŽSawkins, 1990.. There are notable exceptions, such as gold-rich volcanogenic massive sulfide deposits developed along spreading ocean ridges Že.g. Bousquet. and other deposit styles associated with possible anorogenic hot spots Že.g. Olympic Dam. . However, as a rule, many of the Phanerozoic gold-bearing epithermal vein, Carlin-

type sedimentary rock-hosted and porphyry rskarn deposits developed within the same active continental margins as the so-called ‘mesothermal’ deposits ŽFig. 1.. Notable distinctions, however, can be made that relate to local changes in tectonism within a developing orogen and to crustal depth range Ža reflection of regional geothermal gradient. of the auriferous hydrothermal systems. As shown schematically in Fig. 1, a significant proportion of epithermal and porphyry deposits are distinct in that they form above subduction zones distal to continental margins or within continental margins, but during post-collisional extension. Many other gold-rich epithermal and porphyry systems develop in oceanic regimes within the top few kilometres of crust of volcano-plutonic island arcs located above intermediate- to steeply-dipping subduction zones Že.g. Sawkins, 1990; Sillitoe, 1991., with a vertical transition from porphyry-style to classic epithermal vein-style mineralization Že.g. White and Hedenquist, 1995.. Other epithermal lodes, including some of the world-class deposits ŽMuller and Groves, 1997., are associated with alkalic, mantle-related rocks that reflect extensional episodes in a convergent orogen in either a near-arc region Že.g. Porgera: Richards et al., 1990. or far inland of the accretionary wedge Že.g. Cripple Creek: Kelley et al., 1996. . Certainly, many of the well-studied Tertiary epithermal ores associated with volcanic rocks throughout Nevada are products of post-orogenic Basin and Range extension. Geochronological evidence is beginning to favour a similar temporal setting for Carlin-type mineralization ŽHofstra, 1995; Emsboo et al., 1996.. The gold-bearing epithermal vein and porphyry systems that are, however, associated with collisional, subduction-related tectonics ŽSillitoe, 1993. are typically located in different crustal regimes in the orogen than the so-called ‘mesothermal’ gold systems. Whether in an island arc, compressional orogen, or a zone of back-arc rifting, the porphyryskarn-epithermal vein continuum normally is telescoped into the upper 2– 5 km of crust ŽFigs. 1 and 2; Poulsen, 1996.. Magmatism Žgenerally I-type. and high temperatures impose a very steep geothermal gradient on the upper crust, often locally far in excess of 100 Crkm. An abundance of subvolcanic to volcanic rocks necessitates that much of the gold 8


20

ore is hosted in lithologies of roughly equivalent age. The shallow level of the hydrothermal activity restricts much of the lode-gold emplacement to rocks that are unmetamorphosed to only slightly regionally metamorphosed. In contrast, the so-called ‘mesothermal’ ore de posit type is deposited over a very broad range of the upper crust ŽGroves, 1993; Poulsen, 1996 .. Rather than bringing a concentrated heat source to the near surface, the fluids, granitic magmas and heat are carried to higher crustal levels along major fault zones that may have been suture zones between accreted terranes. Crustal geotherms of perhaps G 30 Crkm are elevated, but not to the levels of the more telescoped group of ore deposit types. Where hydrothermal fluids reach the near-surface environment, their relatively low temperature hinders significant gold transport; however, bisulphide complexes still may carry significant Sb and Hg into the upper few kilometres of crust ŽFig. 2 .. Where such fluids migrate into the realm of the typical porphyryskarn-epithermal continuum, complex overlapping of deposit styles may develop. Such a situation may characterize southwestern Alaska, where epithermal Hg–Sb ores that suggest so-called ‘mesothermal’ gold deposits at depth ŽGray et al., 1997. are spatially associated with volcano-plutonic-related gold deposits ŽBundtzen and Miller, 1997 ., or northern California where the McLaughlin gold deposit sits among a series of Hg-rich hot springs ŽSherlock and Logan, 1995.. 8

research interest in gold genesis studies. In fact, in the 75th Anniversary Volume of Economic Geology Ž1981., there is notably no chapter that is devoted to this economically important ore deposit type. Economic geologists had begun to notice the basic association of the Phanerozoic deposits with subduction zones and convergent margins during the growth of plate tectonic theories. However, books on tectonics and ore deposits barely mentioned these gold systems Že.g. Mitchell and Garson, 1981. . As the price of gold increased dramatically in the late 1970’s, so did interest in the understanding of these gold deposits. ‘Mesothermal’ lode-gold de posits began to receive extensive study by ore geologists, and were subsequently described by a variety of terms during the last fifteen years as workers began recognizing them as a single mineral deposit type. The abundance of terms that define these ores reflects both the great expansion of knowledge about these systems accumulated during the 1980’s Že.g. Robert et al., 1991. and the efforts by various groups to establish ore deposit model volumes that classify deposits by type Že.g. Cox and Singer, 1986.. One consequence of so many terms for the same deposits is the resulting confusion for those not extremely familiar with the gold literature. Certainly, a single deposit type title would be helpful for all workers. The paper by Nesbitt et al. Ž1986. on lode-gold deposits of the Canadian Cordillera seemed to initiate popularity of the phrase mesothermal. They define a group of Canadian ‘mesothermal’ gold de posits that formed between 200– 350 C within a series of accreted terranes. Prior to this paper, the broad class of ‘mesothermal’ gold deposits did not exist. Major gold volumes such as ‘Gold ’82’ ŽFoster, 1984., ‘Turbidite-hosted Gold Deposits’ ŽKeppie et al., 1986. and ‘Gold ’86’ ŽMacdonald, 1986. lacked any mention of such a deposit type. However, since the Nesbitt et al. Ž 1986. paper, the ‘mesothermal’ terminology has become well-entrenched in the literature. This may be a response, in part, to the need to easily contrast this group of gold deposits with the generally more shallowly-deposited types of gold ores that had already been classified as ‘epithermal’ for many years previous. Because of this widespread acceptance of the mesothermal label, subsequent comprehensive descriptions of these gold deposits have tended to group them under such a 8

3. Problem of nomeclature

Prior to 1980, the so called ‘mesothermal’ group of Archaean through Tertiary deposits was not widely recognized as a single special type of gold ore. Most classifications scattered the deposits among the mesothermal and hypothermal regimes of Lindgren Ž1933.. Others, such as Bateman Ž1950., divided these deposits into groups within a very broad ‘cavity filling’ type of epigenetic ore deposit. Hence, many Archaean lodes were classified as fissure filling type deposits, Otago was a shear zone deposit type, Bendigo was a saddle reef deposit type, Treadwell, Alaska was a stockwork type deposit, etc. The relatively low price of gold correlated with a limited


‘mesothermal heading’ ŽGroves et al., 1989; Kerrich, 1991; Hodgson, 1993.. Whereas ‘mesothermal’ has become the most common term used in referring to this type of de posit during the last ten years, Poulsen Ž1996 . has recently shown how it is very inconsistent with the meaning originally proposed by Lindgren Ž1907, 1933.. Lindgren’s description of such a deposit type is for that which formed at depths of about 1,200– 3,600 m and at temperatures of 200–300 C. Because of the restrictive temperature range, high-temperature alteration phases, including tourmaline, biotite, horn blende, pyroxene and garnet, were stated as being absent in and surrounding mesothermal type ores. Gold districts such as those of the California foothills belt, the Meguma domain of Nova Scotia, central Victoria, and Charters Tower in Queensland were classified by Lindgren Ž1933. as mesothermal. Many other gold districts, however, that are routinely classified as ‘mesothermal’ today were actually termed ‘hypothermal’ by Lindgren Ž1933.. These deposits were described as having formed at 300– 500 C, thus exhibiting higher temperature alteration assemblages, and at depths below 3,600 m. Most of the world’s Archaean gold deposits were clearly stated as being hypothermal deposits. In addition, some Phanerozoic lodes, including those of the Bohemian Massif and Juneau, Alaska, were included in the class. The groupings into the mesothermal and hypothermal temperature ranges by Lindgren are remarkably accurate in light of many modern fluid inclusion studies. But the key point is that many of the deposits that are now termed ‘mesothermal’ did not fit in the mesothermal category in the early 20th century and still do not fit in the category today. If one such Lindgren-type term was used to define the broad observed range for P – T conditions of these deposits, it probably is ‘xenothermal’. The term, coined by Buddington Ž1935. , covers the P – T conditions from lepothermal Ža vague P – T regime between epithermal and mesothermal. to hypothermal. As such, it would include the broad range of ore forming pressures and temperatures that is welldocumented in the Yilgarn block of Western Australia, as summarised by Groves Ž1993 .. However, other factors, such as structural control, wall rock type and fluid chemistry play a major role in the localization of a gold deposit and definition of a gold 8

8

21

deposit type solely on P – T environment is not advisable ŽBateman, 1950.. The contrasting tectonic setting between the sites of most ‘epithermal’ gold deposits and the sites of all so-called ‘mesothermal’ deposits presents another basic problem with usage of the Lindgren model. As envisioned by Lindgren Ž1907, 1933 ., the epithermal, mesothermal and hypothermal terms were intended to define a continuum among deposits. However, as implied in Fig. 2, the term ‘epithermal’ is now entrenched in the literature as a specific mineral-deposit type that most commonly describes high-level veining and alteration broadly associated with volcanism or subvolcanic magmatism Že.g. Berger and Bethke, 1985.. As discussed above, such epithermal gold deposits may form in oceanic arcs long before continental margin orogenesis or, as in the Basin and Range of the USA, during post-orogenic extension, as shown schematically in Fig. 1. Hence, there are typically neither consistent spatial nor temporal relations between the two gold deposit types. Many other terms relating to host rocks, vein mineralogy or ore-fluid chemistry are equally unacceptable in the overall description of these deposits. Commonly used terms, such as ‘greenstone gold’, ‘slate belt gold’, or ‘turbidite-hosted gold’, disguise the fact that the deposits have many similarities despite their different hosting sequences Žthe theme of this special Ore Geology ReÕiews issue. and should be used, if at all, to describe subgroups of the major deposit type, and not the deposit type itself. The use of ‘Archaean’ or ‘Mother lode-type’ gold deposits is also unacceptable, clearly reflecting a specific temporal or spatial preference, respectively. ‘Metamorphic gold’ implies an understanding of the ore-forming process which is, however, still strongly under debate. The fact that these deposits contain only a few percent sulfide minerals, in most cases, has led to classifications referring to them as ‘low sulfide’ ŽBerger, 1986., and the fact that gold is enriched by orders of magnitudes over base metals and Au:Ag ratios are generally ) 1 has led to their classification as ‘gold only’ ŽHodgson and MacGeehan, 1982; Phillips and Powell, 1993. deposits. However, many other types of gold deposits, including the sedimentary rock-hosted ores at Carlin and elsewhere in Nevada, show the same low sulfide

22


content. Similarly, ‘lode-gold’ ŽMcCuaig and Kerrich, 1994. may be interpreted to contain a variety of gold deposit types. A critical feature of all these deposits seems to be their common tectonic setting, as described in detail above. These deposits were classified as ‘pre-orogenic’ by Bache Ž1980, 1987 ., who recognized their association with the world’s orogenic belts. However, at the same time, the classification assumed a syngenetic exhalative origin for the auriferous lodes, an assumption clearly in conflict with modern geochronological data. Goldfarb et al. Ž1991a, 1998 this issue. have often preferred the term ‘synorogenic’, given the clear overlap of gold-forming events in the North American Cordillera with a broad, 120-m.y.-long period of continental margin growth. The term ‘post-orogenic’ has been used by other workers ŽGebre-Mariam et al., 1993; Groves, 1996. who emphasize that deformation and metamorphism of ore host rocks commonly predate hydrothermal vein emplacement ŽGroves et al., 1984; Colvine, 1989; Hodgson and Hamilton, 1989..

4. Proposed classification

These gold deposits, throughout the world’s collisional orogenic belts, can actually be viewed as both syn- and post-orogenic in origin. Whereas host rocks for ore may already be undergoing uplift and cooling Žthus ‘post-orogenic’., the ore-forming fluids may be generated or set in motion by simultaneous thermal processes at depth Žthus ‘syn-orogenic’ . as described by Stuwe et al. Ž1993.. For example, Kent et al. Ž1996. show that the main episode of gold mineralization in the Yilgarn craton postdates thermal events in the ore-hosting upper crust, but temporally correlates with melting and magmatism of lower-middle Archaean crust. Because of this, it is suggested that the gold ores simply be classified as ‘ orogenic’ lode types, as was originally suggested by Bohlke Ž1982.. A remaining problem is whether to classify many ‘intrusion-related gold deposits’ within this group of orogenic gold deposits. Sillitoe Ž1991. places de posits such as Muruntau and Charters Tower in such an intrusion-related deposit type. McCoy et al. Ž1997. distinguish ‘plutonic-related mesothermal gold de posits’ of interior Alaska, such as Fort Knox, as

those where ore fluids are derived from evolving magmas. The Proterozoic gold lodes of northern Australia and the Mesozoic deposits of the north China craton and Korea are also commonly suggested to be genetically associated with igneous processes. Are such deposits, with ore fluid chemistries essentially identical to those of typical orogenic gold deposits, a different deposit type? Sillitoe Ž1991. indicated that the intrusion-related gold deposits also form in Phanerozoic convergent plate margins above zones of active subduction, although regional extension is stressed as an important characteristic and thus indicates some difference from the orogenic class defined here. Sillitoe Ž1991. does stress that the apparent overlap between orogenic and intrusion-related gold systems requires further attention. We would certainly agree. A convenient terminology that both retains the prefixes ‘epi’, ‘meso’, and ‘hypo’ used by Lindgren Ž1907, 1933., and subdivides the orogenic gold de posit type, is introduced by Hagemann and Ridley Ž1993. and then further modified by Gebre-Mariam et al. Ž1995.. Its continued usage is recommended. In such a scenario, epizonal deposits form within 6 km of the surface at temperatures of 150–300 C, meso zonal deposits form at depths of 6–12 km and at temperatures of 300–475 C and hypozonal deposits form below 12 km and at temperatures exceeding 475 C. It is critical to note that this terminology has been defined solely as a subdivision for orogenic gold deposits based on many modern geothermo barometric studies. Because of this, the depth zones for these orogenic subclasses do not correspond to those in Lindgren’s epithermal, mesothermal, and hypothermal regimes. 8

8

8

Acknowledgements

The authors acknowledge the input of past and present staff and students at the Key Centre at UWA, particularly Mark Barley, Kevin Cassidy and John Ridley. The research was funded largely by mining companies and supported by Key Centre Corporate Members, DEETYA, AMIRA, MERIWA and UWA. The paper was inspired as a result of a course given by F. Robert in Perth in February, 1996, and conferences on mesothermal gold deposits in Ballarat and


Perth in July, 1996. The encouragement of Ross Ramsay is greatly appreciated. This manuscript was much improved through the exceptionally insightful comments of Kevin Cassidy, Rob Kerrich, Howard Poulsen, Ed Mikucki and one anonymous journal reviewer.

References Abraham, A.P.G., Spooner, E.T.C., 1995. Late Archean regional deformation and structural controls on gold–quartz vein mineralization in the northwestern Slave province, N.W.T., Canada. Can. J. Earth Sci. 32, 1132–1154. Ansdell, K.M., Kyser, T.K., 1992. Mesothermal gold mineralization in a Proterozoic greenstone belt, Western Flin Flon domain, Saskatchewan, Canada. Econ. Geol. 87, 1496–1524. Arne, D.C., Bierlein, F.P., McNaughton, N.J., Wilson, C.J.L., Morard, V.J., Ramsay, W.R.H., 1996. Timing of felsic magmatism in Victoria and its relationship to gold mineralization. In: Hughes, M.J., Ho, S.E., Hughes, C.E. ŽEds.., Recent Developments in Victorian Geology and Mineralisation. Aust. Inst. Geosci. Bull. 20, 43–48. 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., 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. Bache, J.J., 1980. Essai de typologie quantitative des gisements mondiaux d’or. BRGM Note SGNrGMXrGIT, No. 622. 9 pp. Bache, J.J., 1987. World Gold Deposits: A Quantitative Classification. North Oxford Academic, London, 179 pp. Balakrishnan, S., Hanson, G.N., Rajamani, V., 1990. Pb and Nd isotope constraints on the origin of high Mg and tholeiitic amphibolites, Kolar Schist Belt, South India. Contrib. Mineral. Petrol. 107, 279–292. Barley, M.E., Groves, D.I., 1992. Supercontinent cycles and the distribution of metal deposits through time. Geology 20, 291– 294. 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. Barnicot, A.C., Fare, R.J., Groves, D.I., McNaughton, N.J., 1991. Synmetamorphic lode-gold deposits in high-grade Archean settings. Geology 19, 921–924. Bateman, A.M., 1950. Economic Mineral Deposits, 2nd ed. Wiley, New York, 916 pp. Berger, B.R., 1986. Descriptive model of low-sulphide Au–quartz veins. In: Cox, D.P., Singer, D.A. ŽEds.. . Mineral Deposit Models. U.S. Geol. Surv. Bull. 1693, 183–186.

23

Berger, B.R., Bethke, P.M. ŽEds.., 1985. Geology and geochemistry of epithermal deposits. Rev. Econ. Geol. 2, 298 pp. Berger, B.R., Drew, L.D., Goldfarb, R.J., Snee, L.W., 1994. An epoch of gold riches: The Late Paleozoic in Uzbekistan, central Asia. Soc. Econ. Geol. Newslett. 16 Ž1 ., 7–11. Von Blanckenburg, F., Davies, J.H., 1995. Slab breakoff: A model for syncollisional magmatism and tectonics in the Alps. Tectonics 14, 120–131. Bohlke, J.K., 1982. Orogenic Žmetamorphic-hosted. gold–quartz veins. U.S. Geol. Surv., Open-file Rep. 795, 70–76. 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. Bouchot, V., Gros, Y., Bonnemaison, M., 1989. Structural controls on the auriferous shear zones of the Saint Yrieix district, Massif central, France. Evidence from the Le Bourneix and Laurieras gold deposits. Econ. Geol. 84, 1315–1327. Buddington, A.F., 1935. High temperature mineral associations at shallow to moderate depths. Econ. Geol. 30, 205–222. Bundtzen, T.K., Miller, M.L., 1997. Precious metals associated with Late Cretaceous–Early Tertiary igneous rocks of southwestern Alaska. In: Goldfarb, R.J., Miller, L.D. ŽEds.., Mineral Deposits of Alaska. . Econ. Geol. Monogr. 9, 242–286. Cathelineau, M., Boiron, M.C., Hollinger, P., Poty, B., 1990. Metallogenesis of the French part of the Variscan orogen. Part II: Time–space relationships between U, Au and Sn–W ore deposition and geodynamic events. Mineralogical and U –Pb data. Tectonophysics 177, 59–79. Colvine, A.C., 1989. An empirical model for the formation of Archean gold deposits. Products of final cratonization of the Superior Province, Canada. In: Keays, R.R., Ramsay, W.R.H., Groves, D.I. ŽEds.., The Geology of Gold Deposits: The Perspective in 1988. Econ. Geol. Monogr., 6, 37–53. Colvine, A.C., Andrews, A.J., Cherry, M.E., Durocher, M.E., Fyon, J.A., Lavigne, M.J., Macdonald, A.J., Marmont, S., Poulsen, K.H., Springer, J.S., Troop, D.G., 1984. An integrated model for the origin of Archean lode-gold deposits. Ont. Geol. Surv. Open-File Rep. 5524, 98 pp. Coney, P.J., 1992. The Lachlan belt of eastern Australia and Circum-Pacific tectonic evolution. Tectonophysics 214, 1–25. Conners, K.A., 1996. Unraveling the boundary between turbidites of the Kisseynew belt and volcano-plutonic rocks of the Flin Flon belt, Trans-Hudson Orogen, Canada. Can. J. Earth Sci. 33, 811–829. Cox, D.P., Singer, D.A. ŽEds.., 1986. Mineral Deposit Models. U.S. Geol. Surv. Bull. 1693, 379 pp. Curti, E., 1987. Lead and oxygen isotope evidence for the origin of the Monte Rosa gold lode deposits ŽWestern Alps, Italy .: A comparison with Archean lode deposits. Econ. Geol. 82, 2115–2140. Darbyshire, D.P.F., Pitfield, P.E.J., Campbell, S.D.G., 1996. Late Archean and Early Proterozoic gold–tungsten mineralization in the Zimbabwe Archean craton: Rb–Sr and Sm–Nd isotope constraints. Geology 24, 19–22. deRonde, C.E.J., Hall, C.M., York, D., Spooner, E.T.C., 1991.


24 40

39

Laser step heating Ar r Ar age spectra from early Archean Barberton greenstone belt sediments: A technique for detecting cryptic tectono-thermal events. Geochim. Cosmochim. Acta 55, 1933–1951. Drew, L.J., Berger, B.R., Kurbanov, N.K., 1996. Geology and structural evolution of the Muruntau gold deposit, Kyzylkum desert, Uzbekistan. Ore Geol. Rev. 11, 175–196. Economic Geology, 1981. 75th Anniversary Volume. Econ. Geol. Publ. Co., Littleton, CO, 964 pp. Elder, D., Cashman, S.M., 1992. Tectonic control and fluid evolution in the Quartz Hill, California, lode-gold deposits. Econ. Geol. 87, 1795–1812. Emsboo, P., Hofstra, A.H., Park, D., Zimmerman, J.M., Snee, L., 1996. A mid-Tertiary age constraint on alteration and mineralization in igneous dikes on the Goldstrike property, Carlin Trend, Nevada. Geol. Soc. Am. Abstr. Prog. 28 Ž7., 476. Fayek, M., Kyser, T.K., 1995. Characteristics of auriferous and barren fluids associated with the Proterozoic Contact Lake lode-gold deposit, Saskatchewan, Canada. Econ. Geol. 90, 385–406. 40 39 Ford, R.C., Snee, L.W., 1996. Ar r Ar 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. Foster, D.A., Kwak, T.A.P., Gray, D.R., 1996. Timing of gold mineralisation and relationship to metamorphism, thrusting, and plutonism in Victoria. In: Hughes, M.J., Ho, S.E., Hughes, C.E. ŽEds.. , Recent Developments in Victorian Geology and Mineralisation. Aust. Inst. Geosci. Bull. 20, 49–53. Foster, R.P. ŽEd.. , 1984. Gold ’82: The Geology, Geochemistry and Genesis of Gold Deposits. A.A. Balkema, Rotterdam, 753 pp. Foster, R.P. ŽEd.. , 1991. Gold Metallogeny and Exploration. Blackie and Son, Glasgow, 432 pp. Foster, R.P., Piper, D.P., 1993. Archaean lode-gold deposits in Africa: Crustal setting, metallogenesis and cratonization. Ore Geol. Rev. 8, 303–347. Fyfe, W.S., Kerrich, R., 1985. Fluids and thrusting. Chem. Geol. 49, 353–362. Gaboury, D., Dube, B., Lafleche, M.R., Lauziere, K., 1996. Geology of the Hammer Down mesothermal gold deposit, Newfoundland Appalachians, Canada. Can. J. Earth Sci. 33, 335–350. Gebre-Mariam, M., Groves, D.I., McNaughton, N.J., Mikucki, E.J., Vearncombe, J.R., 1993. Archaean Au– Ag mineralisation at Racetrack, near Kalgoorlie, Western Australia: A high crustal-level expression of the Archaean composite lode-gold system. Miner. Deposita 28, 375–387. Gebre-Mariam, M., Hagemann, S.G., Groves, D.I., 1995. A classification scheme for epigenetic Archaean lode-gold deposits. Miner. Deposita 30, 408–410. Goldfarb, R.J., Leach, D.L., Pickthorn, W.J., Paterson, C.J., 1988. Origin of lode-gold deposits of the Juneau gold belt, southeastern Alaska. Geology 16, 440–443. Goldfarb, R.J., Gray, J.E., Pickthorn, W.J., Gent, C.A., Cieutat, B.A., 1990. Stable isotope systematics of epithermal mercury–antimony mineralization, southwestern Alaska. In:

Goldfarb, R.J., Nash, J.T., Stoesser, J.W. ŽEds.., Geochemical Studies in Alaska by the U.S. Geological Survey, 1989. U.S. Geol. Surv. Bull., 1950, pp. E1–E9. Goldfarb, R.J., Leach, D.L., Pickthorn, W.J., 1991a. Source of synorogenic fluids of the northern Cordillera: Evidence from the Juneau Gold Belt, Alaska. In: Robert, F., Sheahan, P.A., Green, S.B. ŽEds.. , Greenstone Gold and Crustal Evolution. Geol. Assoc. Can., Mineral Deposits Div. Publ., pp. 160–161. Goldfarb, R.J., Snee, L.W., Miller, L.D., Newberry, R.J., 1991b. Rapid dewatering of the crust deduced from ages of mesothermal gold deposits. Nature 354, 296–298. Goldfarb, R.J., Phillips, G.N., Nokleberg, W.J., 1998. Tectonic setting of synorogenic gold deposits of the Pacific Rim. Ore Geol. Rev. 13, 185–218 Žthis issue.. Gray, J.D., Gent, C.A., Snee, L.W., Wilson, F.H., 1997. Epithermal mercury–antimony and gold-bearing vein lodes of southwestern Alaska. In: Goldfarb, R.J., Miller, L.D. ŽEds.., Mineral Deposits of Alaska. Econ. Geol. Monogr. 9, 287–305. Groves, D.I., 1993. The crustal continuum model for late-Archaean lode-gold deposits of the Yilgarn Block, Western Australia. Miner. Deposita 28, 366–374. Groves, D.I., 1996. Geological concepts in the exploration for large to giant late-orogenic Žmesothermal . gold deposits: The Archaean greenstone experience. In: Mesothermal Gold De posits: A Global Overview. Geol. Dept. ŽKey Centre. Univ. Ext., Univ. West. Aust. Publ. 27, 114–117. Groves, D.I., Foster, R.P., 1991. Archean lode-gold deposits. In: Foster, R.P. ŽEd.., Gold Metallogeny and Exploration. Blackie and Son, Glasgow, pp. 63–103. Groves, D.I., Phillips, G.N., Ho, S.E., Henderson, C.A., Clark, M.E., Woad, G.M., 1984. Controls on distribution of Archaean hydrothermal gold deposits in Western Australia. In: Foster, R.P. ŽEd.., Gold ’82: The Geology, Geochemistry and Genesis of Gold Deposits. A.A. Balkema, Rotterdam, pp. 689–712. Groves, D.I., Barley, M.E., Ho, S., 1989. Nature, genesis and tectonic setting of mesothermal gold mineralization in the Yilgarn Block, Western Australia. In: Keays, R.R., Ramsay, W.R.H., Groves, D.I. ŽEds.. , The Geology of Gold Deposits: The Perspective in 1988. Econ Geol. Monogr., 6, 71–85. Groves, D.I., Barley, M.E., Barnicoat, A.C., Cassidy, K.F., Fare, R.J., Hagemann, S.G., Ho, S.E., Hronsky, J.M.A., Mikucki, E.J., Mueller, A.G., McNaughton, N.J., Perring, C.S., Ridley, J.R., Vearncombe, J.R., 1992. Sub-greenschist to granulitehosted Archaean lode-gold deposits of the Yilgarn Craton: A depositional continuum from deep sourced hydrothermal fluids in crustal-scale plumbing systems. Geol. Dept. ŽKey Centre. Univ. Ext., Univ. West. Aust. Publ. 22, 325–338. Le Guen, M., Lescuyer, J.L., Marcoux, E., 1992. Lead-isotope evidence for a Hercynian origin of the Salsigne gold deposit ŽSouthern Massif Central France. . Miner. Deposita 27, 129– 136. Guild, P.W., 1971. Metallogeny: A key to exploration. Mining Eng. 23 Ž1., 69–72. 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.


Hagemann, S.G., Brown, P.E., 1996. Geobarometry in Archean lode-gold deposits. Eur. J. Mineral. 8, 937–960. Hagemann, S.G., Ridley, J.R., 1993. Hydrothermal fluids in epiand katazonal crustal levels in the Archaean–Implications for P – T – X – t evolution of lode-gold mineralisation. In: Williams, P.R., Haldane, J.A. ŽEds.., An international conference on crustal evolution, metallogeny and exploration of the Eastern Goldfields. Extended Abstr. Aust. Geol. Surv. Org., Record 54, pp. 123–130. Hagemann, S.G., Groves, D.I., Ridley, J.R., Vearncome, J.R., 1992. The Archaean lode-gold deposits at Wiluna, Western Australia. High level brittle-style mineralisation in a strike-slip regime. Econ. Geol. 87, 1022–1053. Hagemann, S.G., Gebre-Mariam, M., Groves, D.L., 1994. Surface-water influx in shallow-level Archean lode-gold deposits in Western Australia. Geology 22, 1067–1070. Hedenquist, J.W., Lowenstern, J.B., 1994. The role of magmas in the formation of hydrothermal ore deposits. Nature 370, 519– 527. Hirdes, W., Davis, D.W., Ludtke, G., Konan, G., 1996. Two generations of Birimian ŽPaleoproterozoic. volcanic belts in northeastern Cote d’Ivorie ŽWest Africa .: Consequences for the ‘Birimian controversy’. Precambrian Res. 80, 173–191. Hodgson, C.J., 1993. Mesothermal lode-gold deposits. In: Kirkham, R.V., Sinclair, W.D., Thorpe, R.I., Duke, J.M. ŽEds.. , Mineral Deposit Modeling. Geol. Assoc. Can., Spec. Pap., 40, 635–678. Hodgson, C.J., Hamilton, J.V., 1989. Gold mineralization in the Abitibi greenstone belt: End stage result of Archaean collisional tectonics? In: Keays, R.R., Ramsay, W.R.H., Groves, D.I. ŽEds.., The Geology of Gold Deposits: The Perspective in 1988. Econ. Geol. Monogr., 6, 86–100. Hodgson, C.J., MacGeehan, P.J., 1982. A review of the geological characteristics of ‘Gold Only’ deposits in the Superior Province of the Canadian Shield. In: Hodder, R.W., Petruks, W. ŽEds. ., Geology of Canadian Gold Deposits. Can. Inst. Min. Metall., Spec. Vol. 24, 211–229. Hofstra, A.H., 1995. Timing and duration of Carlin-type gold mineralization in Nevada and Utah: Relation to back-arc extension and magmatism. Geol. Soc. Am. Abstr. Progr. 27 Ž6 ., 329. Jackson, S.L., Cruden, A.R., 1995. Formation of the Abitibi greenstone belt by arc-trench migration. Geology 23, 471–474. Kelley, K.D., Romberger, S.B., Beaty, D.W., Snee, L.W., Stein, H.J., Thompson, R.B., 1996. Genetic model for the Cripple 40 39 Creek district: Constraints from Ar r Ar geochronology, major and trace element geochemistry and stable and radiogenic isotope data. In: Thompson, T.B. ŽEd.., Diamonds to Gold. I. State Line Kimberlite district, Colorado. II. Cresson mine, Cripple Creek district, Colorado. Soc. Econ. Geol., Guidebook Ser. 26, 65–83. Kent, A.J.R., Hagemann, S.G., 1996. Constraints on the timing of lode-gold mineralisation in the Wiluna greenstone belt, Yilgarn Craton, Western Australia. Aus. J. Earth Sci. 43, 573–588. Kent, A.J.R., McDougall, I., 1995. Constraints on the timing of gold mineralization in the Kalgoorlie goldfield, Western Aus 40 39 tralia, from Ar r Ar and U–Pb dating: Evidence for multiple mineralization episodes. Econ. Geol. 90, 845–859.

25

Kent, A.J.R., Cassidy, K.F., Fanning, C.M., 1996. Archean gold mineralization synchronous with the final stages of cratonization, Yilgarn Craton, Western Australia. Geology 24, 879–882. Keppie, J.D., 1993. Synthesis of Palaeozoic deformation events and terrane accretion in the Canadian Appalachians. Geol. Rundsch. 82, 381–431. Keppie, J.D., Dallmeyer, R.D., 1995. Late Paleozoic collision, delamination, short-lived magmatism and rapid denudation in the Meguma Terrane ŽNova Scotia, Canada .: Constraints from 40 39 Ar r Ar isotopic data. Can. J. Earth Sci. 32, 644–659. Keppie, J.D., Boyle, R.W., Haynes, S.J. ŽEds.., 1986. TurbiditeHosted Gold Deposits. Geol. Assoc. Can., Spec. Pap. 32, 186 pp. Kerrich, R., 1991. Mesothermal gold deposits - A critique of genetic hypotheses. In: Robert, F., Sheahan, P.A., Green, S.B. ŽEds.. , Greenstone Gold and Crustal Evolution. Geol. Assoc. Can., Mineral Deposits Div. Publ., pp. 13–31. Kerrich, R., 1993. Perspectives on genetic models for lode-gold deposits. Miner. Deposita 28, 362–365. Kerrich, R., 1994. Dating Archaean auriferous quartz vein de40 39 posits in the Abitibi greenstone belt, Canada: Ar r Ar evidence for a 70–100 m.y.-time gap between plutonism–metamorphism and mineralisation. A discussion. Econ. Geol. 89, 679–686. Kerrich, R., Cassidy, K.F., 1994. Temporal relationships of lodegold mineralization to accretion, magmatism, metamorphism and deformation, Archean to present: A review. Ore Geol. Rev. 9, 263–310. Kerrich, R., Wyman, D.A., 1990. The geodynamic setting of mesothermal gold deposits: An association with accretionary tectonic regimes. Geology 18, 882–885. Kirkham, R.V., Sinclair, W.D., Thorpe, R.I., Duke, J.M. ŽEds.., 1993. Mineral Deposit Modeling. Geol. Assoc. Can., Spec. Pap. 40, 798 pp. Kontak, D.J., Smith, P.F., Reynolds, P., Taylor, K., 1990. Geolog40 39 ical and Ar r Ar geochronological constraints on the timing of quartz vein formation in Meguma Group lode-gold deposits, Nova Scotia. Atl. Geol. 26, 201–227. Krogstad, E.J., Balakrishnan, S., Mukhopadhyay, D.K., Rajamani, V., Hanson, G.N., 1989. Plate tectonics 2.5 billion years age: Evidence at Kolar, south India. Science 243, 1337–1340. Landefeld, L.A., 1988. The geology of the Mother Lode-gold belt, Sierra Nevada Foothills metamorphic belt, California. In: Bicentennial Gold 88, Extended Abstracts, Oral Programme. Geol. Soc. Aust. Abstr. 22, pp. 167–172. Lapointe, B., Chown, E.H., 1993. Gold-bearing iron-formation in a granulite terrane of the Canadian Shield: A possible deeplevel expression of an Archean gold-mineralizing system. Miner. Deposita 28, 191–197. Leitch, C.H.B., Van der Hayden, P., Godwin, C.I., Armstrong, R.L., Harakal, J.E., 1991. Geochronometry of the Bridge River camp, southwestern British Columbia. Can. J. Earth Sci. 28, 195–208. Lindgren, W., 1907. The relation of ore deposition to physical conditions. Econ. Geol. 2, 105–127. Lindgren, W., 1933. Mineral Deposits, 4th ed. McGraw Hill, New York and London, 930 pp. Macdonald, A.J. ŽEd.., 1986. Proceedings of Gold ’86. An Inter-

26


national Symposium on the Geology of Gold Deposits. Toronto, 517 pp. MacLachlan, K., Helmstaedt, H., 1995. Geology and geochemistry of an Archean mafic dike complex in the Chan Formation: Basis for a revised plate-tectonic model of the Yellowknife greenstone belt. Can. J. Earth Sci. 32, 614–630. 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. In: Keays, R.R., Ramsay, W.R.H., Groves, D.I. ŽEds.. , The Geology of Gold Deposits: The Perspective in 1988. Econ. Geol. Monogr. 6, 242–251. Marakushev, A.A., Khokhlov, V.A., 1992. A petrological model for the genesis of the Muruntau gold deposit. Int. Geol. Rev. 34 Ž1. , 59–76. 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. McCuaig, T.C., Kerrich, R., 1994. P – T – t -deformation-fluid characteristics of lode-gold deposits: Evidence from alteration systematics. In: Lentz, D.R. ŽEd.., Alteration and Alteration Processes Associated with Ore-forming Systems. Geol. Assoc. Can., Short Course Notes, 11, 339–379. McCuaig, T.C., Kerrich, R., Groves, D.I., Archer, N., 1993. The nature and dimensions of regional and local gold-related hydrothermal alteration in tholeiitic metabasalts in the Norseman goldfields: The missing link in a crustal continuum of gold deposits?. Miner. Deposita 28, 420–435. McKeag, S.A., Craw, D., 1989. Contrasting fluids in gold-bearing quartz vein systems formed progressively in a rising metamor phic belt: Otago Schist, New Zealand. Econ. Geol. 84, 22–33. Meinert, L.D., 1993. Igneous petrogenesis and skarn deposits. In: Kirkham, R.V., Sinclair, W.D., Thorpe, R.I., Duke, J.M. ŽEds.. , Mineral Deposit Modeling. Geol. Assoc. Can., Spec. Pap. 40, 569–583. Mikucki, E.J., 1998. Hydrothermal transport and depositional processes in Archaean lode-gold systems: A review. Ore Geol. Rev. 13, 307–321. Mikucki, E.J., Ridley, J.R., 1993. The hydrothermal fluid of Archaean lode-gold deposits: Constraints on its composition inferred from ore and wallrock alteration assemblages over a spectrum of metamorphic grades. Miner. Deposita 28, 469– 481. 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. Mitchell, A.H.G., Garson, M.S., 1981. Mineral Deposits and Global Tectonic Settings. Academic Press, London, 405 pp. Moravek, P. ŽEd.., 1995. Gold deposits of the central and SW part of the Bohemian Massif. In: Excursion Guide, Third Biennial SGA Meeting. Mineral deposits: From their origin to their environmental impacts. Prague, August 28–31, 104 pp. Mueller, A.G., Groves, D.I., 1991. The classification of Western Australian greenstone-hosted gold deposits according to wallrock-alteration assemblages. Ore Geol. Rev. 6, 291–332.

Muller, A.G., Groves, D.I., 1997. Potassic Igneous Rocks and Associated Gold–Copper Mineralization, 2nd ed. SpringerVerlag, Berlin, 238 pp. Nesbitt, B.E., 1991. Phanerozoic gold deposits in tectonically active continental margins. In: Foster, R.P. ŽEd. ., Gold Metallogeny and Exploration. Blackie and Son, Glasgow, pp. 104– 132. Nesbitt, B.E., Muehlenbachs, K., 1989. Geology, geochemistry and genesis of mesothermal gold deposits of the Canadian Cordillera: Evidence for ore formation from evolved meteoric water. In: Keays, R.R., Ramsay, W.R.H., Groves, D.I. ŽEds.., The Geology of Gold Deposits: The Perspective in 1988. Econ. Geol. Monogr. 6, 553–563. Nesbitt, B.E., Murowchick, J.B., Muehlenbachs, K., 1986. Dual origin of lode-gold deposits in the Canadian Cordillera. Geology 14, 506–509. Nie, F., 1997. An overview of gold resources in China. Int. Geol. Rev. In press. 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., Gry beck, 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. 513-A, 385 pp. Peters, S.G., Golding, S.D., 1989. Geologic, fluid inclusion, and stable isotope studies of granitoid-hosted gold-bearing quartz veins, Charters Towers, northeastern Australia. Econ. Geol. Monogr. 6, 260–273. 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. The Geology of North America, vol. G-1. Geol. Soc. Am., pp. 989–1021. Poulsen, K.H., 1996. Lode-gold. In: Eckstrand, O.R., Sinclair, W.D., Thorpe, R.I. ŽEds.., Geology of Canadian Mineral Deposit Types. The Geology of North America, vol. P-1. Geol. Soc. Am., pp. 323–328. Powell, W.G., Carmichael, D.M., Hodgson, C.J., 1995. Conditions and timing of metamorphism in the southern Abitibi greenstone belt, Quebec. Can. J. Earth Sci. 32, 787–805. Ramsay, W.R.H., 1998. A review of Victorian mesothermal gold, regional setting, styles, and genetic constraints. In: Keays, R.R., Ramsay, W.R.H., Groves, D.I. ŽEds.. , The Geology of Gold Deposits: The perspective in 1988. Richards, J.P., 1995. Alkalic-type epithermal gold deposits: A review. Turbidite - hosted gold deposits of Central Victoria, Australia: their regional setting, mineralisation styles and some genetic constraints. Ore Geol. Rev. 13, 131–151 Žthis issue. In: Thompson, J.F.H. ŽEd.. , Magmas, Fluids and Ore De posits. Min. Assoc. Can., Short Course Ser., 23, 367–400. Richards, J.P., Chappel, B.W., McCulloch, M.T., 1990.


Intraplate-type magmatism in a continent–island-arc collision zone-Porgera intrusive complex, Papua New Guinea. Geology 18, 958–961. Ridley, J., Mikucki, E.J., Groves, D.I., 1996. Archean lode-gold deposits: Fluid flow and chemical evolution in vertically extensive hydrothermal systems. Ore Geol. Rev. 10, 279–293. Robert, F., 1996. Quartz–carbonate vein gold. In: Eckstrand, O.R., Sinclair, W.D., Thorpe, R.I. ŽEds.. , Geology of Canadian Mineral Deposit Types. The Geology of North America, vol. P-1. Geol. Soc. Am., pp. 350–366. Robert, F., Brown, A.C., 1986. Archean gold-bearing quartz veins at the Sigma mine, Abitibi greenstone belt, Quebec. Part I. Geologic relations and formation of the vein systems. Econ. Geol. 81, 578–592. Robert, F., Sheahan, P.A., Green, S.B. ŽEds.. , 1991. Greenstone Gold and Crustal Evolution. Geol. Assoc. Can., Mineral De posits Div. Publ., 252 pp. 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. Sawkins, F.J., 1972. Sulfide ore deposits in relation to plate tectonics. J. Geol. 80, 377–397. Sawkins, F.J., 1990. Metal Deposits in Relation to Plate Tectonics, 2nd ed. Springer-Verlag, Berlin, 451 pp. Scheiber, E., 1996. Geology of New South Wales: Synthesis. Geol. Surv. N.S.W. Mem. Geol. 13 Ž1., 295 pp. Sengor, A.M.C., Okurogullari, A.H., 1991. The role of accretionary wedges in the growth of continents - Asiatic examples from Argand to plate tectonics. Eclogae Geol. Helv. 84 Ž3 ., 535–597. Shenberger, D.M., Barnes, H.L., 1989. Solubility of gold in aqueous sulfide solutions from 150 to 350 C. Geochim. Cosmochim. Acta 53, 269–278. Sherlock, R.L., Logan, M.A.V., 1995. Silica–carbonate alteration of serpentinite: Implications for the association of mercury and gold mineralization in northern California. Explor. Mining Geol. 4 Ž4., 395–409. Sibson, R.H., Robert, F., Poulsen, K.H., 1988. High-angle reverse faults, fluid pressure cycling, and mesothermal gold–quartz deposits. Geology 16, 551–555. Sillitoe, R.H., 1991. Intrusion-related gold deposits. In: Foster, R.P. ŽEd.., Gold Metallogeny and Exploration. Blackie and Son, Glasgow, pp. 165–209. Sillitoe, R.H., 1993. Gold-rich porphyry copper deposits: Geological model and exploration implications. In: Kirkham, R.V., 8

27

Sinclair, W.D., Thorpe, R.I., Duke, J.M. ŽEds.., Mineral De posit Modeling. Geol. Assoc. Can., Spec. Pap. 40, 465–478. Solomon, M., Groves, D.I., 1994. The Geology and Origin of Australia’s Mineral Deposits. Oxford Monogr. Geol. Geophys. 24, 951 pp. Stein, H.J., Markey, R.J., Morgan, J.W., Zak, K., Zachariad, J., Sundblad, K., 1996. Re–Os dating of Au deposits in shear zones using accessory molybdenite: Bohemian Massif, Carolina slate belt, and Fennoscandian Shield examples. Geol. Soc. Am. Abstr. Progr. 28 Ž7., 474. Stowell, H.H., Lesher, C.M., Green, N.L., Sha, P., Guthrie, G.M., Sinha, A.K., 1996. Metamorphism and gold mineralization in the Blue Ridge, southernmost Appalachians. Econ. Geol. 91, 1115–1144. Stuwe, K., Will, T.M., Zhou, S., 1993. On the timing relationship between fluid production and metamorphism in metamorphic piles: Some implications for the origin of post-metamorphic gold mineralization. Earth Planet. Sci. Lett. 114, 417–430. Thomas, D.J., Heaman, L.M., 1994. Geologic setting of the Jolu gold mine, Saskatchewan: U–Pb age constraints on plutonism, deformation, mineralization and metamorphism. Econ. Geol. 89, 1017–1030. Trumbull, R.B., Hua, L., Lehrberger, G., Satir, M., Wimbauer, T., Morteani, G., 1996. Granitoid - hosted gold deposits in the Anjiayingzi District of Inner Mongolia, People’s Republic of China. Econ. Geol. 91, 875–895. Vinyu, M.L., Frei, R., Jelsma, H.A., 1996. Timing between granitoid emplacement and associated gold mineralization: Examples from the ca. 2.7 Ga Harare-Shamva greenstone belt, northern Zimbabwe. Can. J. Earth Sci. 33, 981–992. 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 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. Geol. Dept. ŽKey Centre. Univ. Ext., Univ. West. Aust. Publ. 27, 34–38. White, D.E., 1967. Mercury and base-metal deposits with associated thermal and mineral waters. In: Barnes, H.L. ŽEd. ., Geochemistry of Hydrothermal Ore Deposits. Holt, Rinehart and Winston, New York, pp. 575–631. White, N.C., Hedenquist, J.W., 1995. Epithermal gold deposits: Styles, characteristics and exploration. Soc. Econ. Geol. Newslett. 23 Ž1., 9– 13. Wyman, D., Kerrich, R., 1988. Alkaline magmatism, major structures, and gold deposits: Implications for greenstone belt gold metallogeny. Econ. Geol. 83, 451–458.

Orogenic Gold Deposits_Groves

Recommend Documents