Download Supercontinent cycles and the distribution of metal

Supercontinent cycles and the distribution of metal
deposits through time
M. E. Barley, D. I. Groves
K e y C e n t r e for Strategic Mineral Deposits, D e p a r t m e n t of G e o l o g y , University of W e s t e r n A u s t r a l i a
N e d l a n d s 6009, Australia
ABSTRACT
Systematic temporal variations in the distribution of several important groups of metal deposits reflect the cyclic aggregation and
breakup of large continents. In particular, metal deposits that form in
continental basins or are associated with anorogenic magmatism were
extraordinarily abundant in the Middle Proterozoic (2.0 to 1.4 Ga),
corresponding to the assembly of the first large continents. It is important to note that peaks in the abundance of continental metal deposits
also coincide with a postulated Late Proterozoic supercontinent (1.0
to 0.8 Ga) and the near maximum extent of Pangea. In contrast, metal
deposits that form, or are preserved, in convergent-margin orogens
were most abundant in the late Archean (2.9 to 2.6 Ga), corresponding
to a period of high global heat flow and rapid stabilization of continental crust, and the past 200 m.y., which corresponds to the present
tectonic cycle. Similar mineralization was also present, albeit less
abundant, in Early Proterozoic orogens, as well as in Late Proterozoic
and Phanerozoic orogens. Future metals exploration may benefit from
the application of sequence stratigraphy, as used by the oil industry, to
recognize such cycles, particularly in the Precambrian rock record.
INTRODUCTION
In two important papers summarizing the distribution of mineralization through time, Meyer (1981,1988) clearly demonstrated that there are
characteristic peaks in the abundance of specific styles of metallic mineralization (Fig. 1). This uneven temporal distribution of different styles of
metal deposit is related to three major factors: (1) the evolution of the
hydrosphere-atmosphere, (2) a secular decrease in global heat flow, and
(3) long-term tectonic trends. The first of these has been extensively discussed (e.g., Holland, 1984) and has resulted in the restricted distribution
of deposit styles for which transport of metal is strongly dependent on
oxidation-reduction conditions (e.g., banded iron formations in the Precambrian; Fig. 1A). These deposit styles, therefore, are not discussed
further in this paper. Similarly, secular decrease in global heat flow is
thought to be responsible for the restriction of Kambalda-type, komatiiteassociated nickel deposits to the Archean and Early Proterozoic (Fig. 1 A).
However, the relation between the abundance of specific metal deposit styles and long-term tectonic trends is less clear cut. For example,
major peaks in the abundance of metal deposits that form, or are preserved, in convergent-margin orogenic belts (such as mesothermal lode
gold and volcanogenic massive-sulfide mineralization; Fig. IB) in the late
Archean (2.9 to 2.6 Ga), and metal deposits associated with either anorogenic magmatism or continental sedimentation (such as Olympic Damtype U-Cu-Au mineralization, Ni, Cr, platinum-group elements [PGE],
and Fe-Ti-V mineralization in layered intrusions, and sediment-hosted
Pb-Zn and Cu mineralization; Fig. 1C) in the Proterozoic are difficult to
reconcile with the now generally accepted idea that plate tectonic processes have operated since the late Archean. This metallogenic problem has
been explained in terms of an evolutionary trend in global tectonics from
an Archean permobile regime, through a stable cratomc Proterozoic, to the
operation of plate tectonics in the Phanerozoic (e.g., Meyer, 1988; WindGEOLOGY, v. 20, p. 291-294, April 1992
ley, 1984; Veizer et al., 1989). In contrast, Sawkins (1976) suggested that
the abundance of sediment-hosted Cu deposits (Fig. 1C) was related to the
breakup of supercontinents in the Middle Proterozoic, Late Proterozoic,
and Phanerozoic. Our purpose is to show how such tectonic cyclicity
resulting from the interaction between large continents, such as Pangea,
and mantle convection (Anderson, 1982; Gurnis, 1988; Worsley et al.,
1985), combined with decreasing global heat flow, provides a relatively
simple but coherent explanation for the uneven temporal distribution of a
wide range of metal deposit styles.
Cyclicity in orogenic and anorogenic activity has important implications for eustasy, seawater chemistry, and biotic evolution (Worsley et al.,
1985), as well as the generation and distribution of continental crust, and
is, therefore, likely to affect both the spatial and temporal distribution of
metal deposits. Numerical modeling of mantle convection and plate motion by Gurnis (1988) confirms the conjectures of Anderson (1982) and
Worsley et al. (1985) that fragments of continental crust move off upwelling domes and aggregate above convective downwellings to form supercontinents. Such large continents inhibit subduction and mantle cooling,
which results in buildup of heat, large-scale convective upwelling (including hotspots), uplift of the continental lithosphere, injection of mantle
melts into the crust, extensive crustal melting, and eventually breakup and
divergence of continental lithosphere. The resulting continental fragments
may then be swept toward convective downwellings, where they reaggregate, initiating another cycle. Estimates of the time between assembled
supercontinents are in the range from a few hundred to 2000 m.y. (Gurnis,
1988). Worsley et al. (1985) recognized an - 5 0 0 m.y. tectonoeustatic
cyclicity for the post Archean. Vail et al. (1977) recognized first-order
cycles (or megacycles) of 210 to 325 m.y. for the Phanerozoic, and
Hoffman (1989) and Krapez and Horwitz (1992) interpreted megacycles
of similar length for the North American Proterozoic and Australian Archean, respectively.
In this scenario, metal deposits that are related to anorogenic magmatism, or are preserved in intracontinental basins (anorogenic and continental deposits), would be most abundant toward the end of a period of
aggregation and during the initial stages of the breakup of a large continent. Deposits that are related to convergent tectonics or preserved in
orogenic belts (orogenic deposits) would be most abundant during periods
of rapid plate movement and supercontinent aggregation.
METAL DEPOSITS, TECTONICS, AND TIME
Phanerozoic
The Phanerozoic was dominated by the breakup of a Late Proterozoic supercontinent, its reassembly as Pangea at - 3 0 0 Ma, and its
subsequent breakup. This provides the basis for interpreting evidence of
earlier supercontinent cycles in the Precambrian rock record. The near
maximum assembly of Pangea (400 to 200 Ma) corresponded with a
period of widespread cratonic subsidence and the development of extensive intracontinental sedimentary basins (Kominz and Bond, 1991). At this
time there were important peaks in the abundance of sediment-hosted
Pb-Zn and Cu mineralization (Fig. 1C). This mineralization is interpreted
to have formed in either epicontinental or foreland settings to the
291
Ore type
3000 Ma
2000
1000
Banded iron-formations
1 III 1l l l l l l
Kambalda-type nickel
|
i.
1
.
• 1
1
A. Precambrian metal deposits
Ore type
3000 Ma
2000
1000
Volcanic-hosted sulfide
Cyprus-type
•.I
Abitibi-type
I .
{ i . L.
•
J
Kuroko
Gold veins
• 1
• illi
i
Gold and uranium
Porphyry deposits
conglomerates
11
1
1
Porphyry coppers
•
• -
iJ
•
.1
Porphyry molys
B. Orogenic metal deposits
Ore type
3000 Ma
Anorogenic
intrusions
Uranium in
weathered profile
Kiruna-type
Olympic Dam-type
llmenite-anorthosite
Sediment-hosted sulfide
ii
Lead-zinc in clastic
sediments
2000
i
1000
F
©
1
I.
J.
..h
t ,
,1®
1
Lead-zinc in carbonates
Mississippi Valley type
L
(D
Copper in clastic
sediments
, 1i J
C. Androgenic a n d continental basin metal deposits
292
Caledonian-Appalachian orogen (e.g., Duane and deWit, 1988) or during
periods of active rifting (e.g., Sawkins, 1976). Layered intrusions that
contain Ni sulfides and PGE mineralization, such as Norilsk (in Siberia)
and Insizwa (in Transkei) also formed during the early stages of the
breakup of Pangea (Sawkins, 1990). Because they developed on thick,
relatively stable continental crust, these deposit styles are highly likely to
have been preserved.
In contrast, metal deposits that form or are preserved at modern
convergent-plate margins were particularly abundant during the past 200
m.y. (Fig. IB), following the breakup of Pangea. These deposit types are
most abundant in island arcs and basins along the margins of the Pacific
and include most types of gold deposits, volcanic-hosted massive sulfide
deposits, podiform chromite in ophiolites, and porphyry-style Cu and Mo
mineralization (e.g., Sawkins, 1990; Sillitoe, 1989). The scarcity of
porphyry-style Cu and epithermal Au deposits older than - 2 0 0 m.y. is
generally thought to have resulted from their low preservation potential in
rapidly exhumed magmatic arcs and collisional mountain belts (e.g., Laznicka, 1973; Veizer et al., 1989).
During the aggregation of a supercontinent, the likelihood of preservation of metal deposits partly depends on whether they become part of
peripheral or interior orogens. Peripheral orogens, as defined by Murphy
and Nance (1991), form adjacent to an ocean external to the continent
(such as the Pacific during most of the Phanerozoic). Consequently
they do not undergo major continental collisions and generally preserve
some richly mineralized, low-metamorphic-grade island-arc and marginalbasin terranes. In contrast, internal orogens (such as the Himalayas) form
as a result of ocean closure during continental aggregation and undergo
extensive crustal thickening, with uplift and exposure of medium- to highmetamorphic-grade rocks following continental collision. The chance of
preservation of metal deposits that form in the upper crust is even lower in
internal orogens than in peripheral orogens. However, deposits that form
in continental magmatic arcs (such as granite-associated and mesothermal
Au-Cu mineralization) are locally preserved, as are deposits that form at
lower crustal levels (e.g., Fe-Ti-V in layered intrusions). Deposits that
form inboard of the orogen (e.g., sediment-hosted Pb-Zn) may also
become incorporated within it and become metamorphosed during
collision.
Despite this low preservation potential, important gold and volcanichosted massive sulfide mineralization is found in Phanerozoic orogens such
as the Caledonian-Appalachian and Hercynian orogenic belts in northern
America and Europe (e.g., Sawkins, 1990) and the Tasman fold belt in
Australia, which were active convergent margins during the aggregation of
Pangea.
Late Archean
In terms of global tectonics, the extraordinary abundance of Au,
volcanic-hosted massive sulfide (Fig. IB), and Kambalda-type, komatiiteassociated Ni (Fig. 1A) mineralization in late Archean greenstone belts
Figure 1. Distribution through geologic time of styles of metal deposits
discussed in text. Width of each vertical bar represents interval of - 5 0
m.y. Length of each bar is geological estimate of quantity of ore formed
during that 50 m.y. as compared with total estimated tonnage for that
style of deposit through geologic time. Data have been taken from
Meyer (1988); ages of Archean gold mineralization are corrected to
reflect new geochronological data from Witwatersrand basin and Archean greenstone belts (e.g., Woodall, 1988). Peaks in abundance of
anorogenic and continental basin metal deposits correspond to:
1—extensive Middle Proterozoic continents?); 2—Late Proterozoic
supercontinent; 3—Pangea.
GEOLOGY, April 1992
and sedimentary basins is most likely the result of rapid growth and
stabilization of continental crust combined with high global heat flow. The
greenstone and metasedimentary assemblages that compose Archean eratons and sedimentary basins are similar in many respects to terranes in the
convergent margins of the Pacific basin (e.g., Tarney et al., 1976), which
host most modern gold and volcanic-hosted massive-sulfide mineralization.
Cyclic, progressive accretion of volcanic-arc, marginal-basin, and related
assemblages to protocratonic nucleii during the late Archean resulted in
the diachronous formation of numerous cratons, abundant mineralization
being a direct result of this tectonic regime (Barley et al., 1989; Kerrich
and Wyman, 1990; Krapez and Horwitz, 1992). In this scenario, the
gold-rich Witwatersrand basin is thought to have formed as a foreland
basin during the collision of two late Archean cratons (Burke et al., 1986).
Proterozoic
Hoffman (1988,1989,1991) described the Early to Middle Proterozoic evolution of Laurentica-Baltica-Siberia as comparable to that of
Pangea during the Phanerozoic. This involved an initial period of intense
orogenic activity during the aggregation of cratons to form a large continent (2.0 to 1.8 Ga). Sediment-hosted Cu mineralization occurred at Udokan (in Siberia) within this postulated continent at ~2.0 Ga (Fig. 1C).
However, orogeny and related mineralization occurred along a continental
margin that may have extended from southern California to Scandinavia
until 1,6 Ga (see also Gaal and Gorbatchev, 1987). Mineralization in this
major Early Proterozoic peripheral orogen includes Archean-style mesothermal Au (e.g., Homestake), volcanic-hosted massive sulfide (e.g., Crandon, Flin Flon, and Scandinavian deposits), and komatiite-associated Ni
deposits (e.g., Thompson belt), as well as some porphyry Cu deposits
(Scandinavia). Between 1.8 and 1.6 Ga, high sea levels resulted in the
preservation of large marine platforms and intracontinental basins (such as
the Athabasca basin, which hosts important U mineralization), and anorogenic magmatism occurred within the continent. The next stage was dominated by continued and extensive anorogenic magmatism (-1.6 to 1.3
Ga) that preceded and accompanied fragmentation. This included the
emplacement of anorthosite bodies that host Fe-Ti-V mineralization and
the intrusion of large ion lithophile element (LILE)-enriched granitoids
(Hoffman, 1988; Sawkins, 1989). Low sea levels at this time meant that
most sedimentary sequences deposited outside rifts on continental crust
were nonmarine. The important Sullivan sediment-hosted Pb-Zn deposit
probably formed near the edge of one of these rifts.
A return to intense orogenic activity accompanied a period of continental reaggregation between 1.3 and 1.0 Ga (the Grenville orogeny).
Metal deposits that formed at this time are copper deposits (e.g., White
Pine, Coppermine) associated with sedimentation and basaltic volcanism
in intracontinental rifts (Sawkins, 1976). Sediment-hosted Pb-Zn deposits
(e.g., Balmat-Edwards) were metamorphosed and incorporated into the
orogen, which also contained relatively minor late-tectonic mesothermal
gold mineralization (Sangster and Bourne, 1982). There is now increasing
evidence for the assembly, during this period, of a Late Proterozoic supercontinent that included Laurentia, most of the Gondwana continents, Baltica, and Siberia (Hoffman, 1991; Moores, 1991).
In Australia there was a similar pattern of Proterozoic crustal evolution and metallogeny, which may reflect amalgamation of northern Australia with Laurentia during the Early Proterozoic (Hoffman, 1991). Gold
mineralization in the Capricorn orogen and Pine Creek and Tennant
Creek inliers accompanied Early Proterozoic orogeny (up to 1.8 Ga;
e.g., Etheridge et al., 1987). This was followed by a prolonged period of
episodic extension and compression, intracontinental sedimentation, and
anorogenic magmatism (1.8 to 1.3 Ga). The world-class sediment-hosted
Pb-Zn deposits of Mount Isa, McArthur River, and Broken Hill formed in
~1.7 to 1.6 Ga intracontinental basins (Gustafson and Williams, 1981)
during this period. LILE-enriched anorogenic magmas probably provided
GEOLOGY, April 1992
the ultimate source of metals in these deposits (Sawkins, 1989), as well as
in unconformity-related U deposits such as the Alligator Rivers area. The
huge Olympic Dam U-Cu-Au deposit is hosted by granitoid breccias that
belong to an - 1 . 6 Ga LILE-enriched magmatic suite in the Gawler craton
(Reeve et al., 1990). As in Laurentia, there was a return to orogeny
between 1.3 and 1.0 Ga, but there is relatively little known associated
mineralization. However, most Late Proterozoic gold mineralization is
from the - 6 9 0 Ma Telfer deposits (Goelnicht et al., 1989) in the Paterson
orogen in Western Australia.
Other important metallogenic events are recorded in the African
continent. In southern Africa, the Bushveld Complex, which dominates
world PGE production, and the Palabora carbonatite, which hosts the
giant Palabora Cu-Fe-P deposit, were emplaced at - 2.0 Ga within a piece
of continental crust that was stabilized by - 3 . 0 Ga and had been little
affected by orogenic activity since the late Archean. Africa also contains
1.3 to 1.0 Ga orogens, and important sedimentary-hosted Cu deposits
formed in the Zambian copper belt at - 1 . 0 Ga (Gustafson and Williams,
1981; Sawkins, 1976). Late tectonic mesothermal gold mineralization, as
well as older sediment-hosted Pb-Zn and Cu deposits, also occur in internal Pan-African (900 to 600 Ma) orogens that formed during the assembly
of Gondwana (e.g., Hoffman, 1991), and volcanogenic massive-sulfide
and mesothermal gold mineralization occur in ophiolite complexes and
island-arc terranes that were accreted to a peripheral Pan-African orogen
in the Arabian-Nubian shield (Al-Shanti, 1979).
DISCUSSION AND CONCLUSIONS
A well-documented temporal variation exists in the distribution of
mineral deposits. This can be explained partly by a progressive increase in
the O2 concentrations in an evolving atmosphere-hydrosphere system and
partly (mainly the greater abundance of many styles of magmatic or
hydrothermal metal deposit in the Precambrian) by a secular decrease in
global heat flow. However, a large part of the temporal variation can be
related to plate-tectonic cycles, rather than to progressive changes in tectonic processes, as previously supposed.
When the production from important mineral deposit styles formed
in intercontinental settings and convergent settings is plotted against the
geologic time scale (Fig. 1, B and C), cyclicity is apparent. This is most
simply illustrated by those deposit styles that formed in intracontinental
basins (e.g., sediment-hosted Pb-Zn and Cu), or that are directly or indirectly related to anorogenic magmatism (e.g., Olympic Dam-style U-CuAu) or layered intrusions (e.g., PGE, Fe-Ti-V). As first recognized by
Sawkins (1976), these deposits have major peaks that correspond with the
assembly of a large continent (or continents) in the Middle Proterozoic, a
Late Proterozoic supercontinent, and Pangea (Fig. 1C). The dominance of
intracratonic and anorogenic styles of mineralization in the Middle Proterozoic is most likely a result of hotter Precambrian mantle upwelling
beneath the first large continents. This resulted in more pronounced anorogenic magmatism than occurred within subsequent supercontinents,
with the emplacement of large mafic layered complexes and generation of
extensive LILE-enriched anorogenic granitoids.
In contrast, the distribution of those metal deposit styles characteristic
of convergent-margin or orogenic settings is more complex. Deposit styles
with relatively high preservation potential show dominant peaks in the late
Archean and Mesozoic-Holocene (e.g., mesothermal Au, volcanogenic
massive sulfide), whereas those with lower preservation potential (epithermal Au, porphyry-style Cu) have their peak in the MesozoicHolocene. The abundance of orogenic mineralization during the late
Archean corresponds with a period of high global heat flow and rapid
growth and stabilization of continental crust by accretion of island arcs and
related terranes (greenstones). The abundance of Mesozoic to Holocene
deposits reflects subduction around the margins of the Pacific basin during
the present tectonic cycle. During continental aggregation, metal deposits
293
in low-metamorphic-grade terranes (greenstones and slate belts) in such
peripheral orogens have a greater chance of preservation than those in
internal orogens that experience the collision of two large continents.
Despite low preservation potential, most orogenic deposit styles can b e
found in Proterozoic and Phanerozoic orogens.
It is unlikely that the processes involved in the genesis of most important metal deposits and their relation to tectonics have changed significantly through geologic time. Rather, it appears that temporal variations in
metallogeny can be related to tectonic cycles with wavelengths of several
hundred million years, involving aggregation and breakup of supercontinents. If so, then mineral deposits may be one of the more sensitive
indicators of tectonic regime. In the Phanerozoic, sequence stratigraphy
(e.g., Sloss, 1988; Vail et al., 1977), as applied to basin analysis by the oil
exploration industry, provides the best means of recognizing tectonoeustatic cycles in the rock record. This approach should also become a tool
of the metals exploration geologist, as the basis for recognizing the effects
of tectonic cycles and their relation to metal deposits in terranes of all ages.
REFERENCES CITED
Al-Shanti, A.M., ed., 1979, Evolution and mineralization of the Arabian-Nubian
Shield: Oxford, England, Pergamon, 551 p.
Anderson, D.L., 1982, Hotspots, polar wander, Mesozoic convection and the geoid:
Nature, v. 297, p. 391-393.
Barley, M.E., Eisenlohr, B.N., Groves, D.I., Perring, C.S., and Vearncombe, J.R.,
1989, Late Archean convergent margin tectonics and gold mineralization: A
new look at the Norseman-Wiluna Belt: Geology, v. 17, p. 826-829.
Burke, K., Kidd, W.S.F., and Kusky, T.M., 1986, Archean foreland tectonics in the
Witwatersrand, South Africa: Tectonics, v. 5, p. 439-456.
Duane, M.J., and deWit, M.J.,1988, Pb-Zn ores of the northern Caledonides:
Products of continental-scale fluid mixing and tectonic expulsion during continental collision: Geology, v. 16, p. 999-1002.
Etheridge, M.A., Rutland, R.W.R., and Wyborn, L.A.I., 1987, Orogenesis and
tectonic process in the Early to Middle Proterozoic of northern Australia, in
Kroner, A., ed., Proterozoic lithospheric evolution: American Geophysical
Union Geodynamics Series, v. 17, p. 131-147.
Gaal, G., and Gorbatchev, R., eds., 1987, Precambrian geology and evolution of the
central Baltic Shield: Precambrian Research, v. 35, p. 1-382.
Goelnicht, N.M., Groves, D.I., McNaughton, N.J., and Dimo, G., 1989, An
epigenetic origin for the Telfer gold deposit, Western Australia, in Keays, R.R.,
et al., eds., The geology of gold deposits: The perspective in 1988: Economic
Geology, Monograph 6, p. 151-167.
Gurnis, M., 1988, Large-scale mantle convection and the aggregation and dispersal
of supercontinents: Nature, v. 332, p. 695-699.
Gustafson, L.B., and Williams, N., 1981, Sediment-hosted stratiform deposits of
copper, lead and zinc: Economic Geology, 75th Anniversary Volume,
p. 139-178.
Hoffman, P.F., 1988, United plates of America, the birth of a craton: Early Proterozoic assembly and growth of Laurentia: Annual Review of Earth and
Planetary Sciences, v. 16, p. 543-603.
1989, Speculations on Laurentia's first gigayear (2.0 to 1.0 Ga): Geology, v. 17,
p. 135-138.
1991, Did the breakout of Laurentia turn Gondwanaland inside-out?: Science,
v. 252, p. 1409-1412.
Holland, H.D., 1984, Chemical evolution of the atmosphere and oceans: Princeton,
New Jersey, Princeton University Press, 582 p.
Kerrich, R., and Wyman, D., 1990, Geodynamic setting of mesothermal gold
deposits: An association with accretionary tectonic regimes: Geology, v. 18,
p. 882-885.
Kominz, M.A., and Bond, G.C., 1991, Unusually large subsidence and sea-level
events during middle Paleozoic time: New evidence supporting mantle convection models for supercontinent assembly: Geology, v. 19, p. 56-60.
294
Krapez, B., and Horwitz, R.C., 1992, Sequence stratigraphy for Archean supracrustal belts of the Pilbara Block: Precambrian Research (in press).
Laznicka, P., 1973, Developments of nonferrous metals in geological time: Canadian
Journal of Earth Sciences, v. 10, p. 18-25.
Meyer, C., 1981, Ore-forming processes in geologic history: Economic Geology,
75th Anniversary Volume, p. 6-41.
1988, Ore deposits as guides to geologic history of the Earth: Annual Review
of Earth and Planetary Sciences, v. 16, p. 147-171.
Moores, E.M., 1991, Southwest U.S.-East Antarctica (SWEAT) connection: A
hypothesis: Geology, v. 19, p. 425-428.
Murphy, J.B., and Nance, R.D., 1991, Supercontinent model for the contrasting
character of Late Proterozoic orogenic belts: Geology, v. 19, p. 469-472.
Reeve, J.S., Cross, K.C., Smith, R.N., and Oreskes, N., 1990, Olympic Dam
copper-uranium-gold-silver deposit, in Hughes, F.E., ed., Geology of the mineral deposits of Australia and Papua New Guinea: Australasian Institute of
Mining and Metallurgy Monograph 14, p. 1009-1036.
Sangster, A.L., and Bourne, J., 1982, Geology of the Grenville Province and regional metallogenesis of the Grenville Supergroup, in Hutchinson, R.W., et al.,
eds., Precambrian sulphide deposits: Geological Association of Canada Special
Paper 25, p. 91-125.
Sawkins, F.J., 1976, Widespread continental rifting: Some considerations of timing
and mechanism: Geology, v. 4, p. 427-430.
1989, Anorogenic felsic magmatism, rift sedimentation, and giant Proterozoic
Pb-Zn deposits: Geology, v. 17, p. 657-660.
1990, Metal deposits in relation to plate tectonics (second edition): Berlin,
Springer-Verlag, 461 p.
Sillitoe, R.H., 1989, Gold deposits in western Pacific island arcs: The magmatic
connection, in Keays, R.R., et al., eds., The geology of gold deposits: The
perspective in 1988: Economic Geology Monograph 6, p. 274-291.
Sloss, L.L., 1988, Forty years of sequence stratigraphy: Geological Society of America Bulletin, v. 100, p. 1611-1655.
Tarney, J., Dalziel, I.W.D., and deWit, M.J., 1976, Marginal basin "rocas verdes"
complex from south Chile: A model for greenstone formation, in Windley,
B.F., ed., The early history of the Earth: New York, John Wiley & Sons,
p. 131-145.
Vail, P.R., Mitchum, R.M., and Thompson, S., 1977, Seismic stratigraphy and
global changes of sea level, Part four: Global cycles of relative changes of sea
level, in Payton, C.E., ed., Seismic stratigraphy; applications to hydrocarbon
exploration: American Association of Petroleum Geologists Memoir 26,
p. 83-98.
Veizer, J., Laznicka, P., and Jansen, S.L., 1989, Mineralization through geologic
time: The recycling perspective: American Journal of Science, v. 289,
p. 484-542.
Windley, B.F., 1984, The evolving continents (second edition): New York, John
Wiley & Sons, 399 p.
Woodall, R., 1988, Gold in 1988 (extended abstracts, oral programme, Bicentennial
Gold '88): Melbourne, Geological Society of Australia, p. 1-12.
Worsley, T.R., Moody, J.B., and Nance, R.D., 1985, Proterozoic to recent tectonic
tuning of biogeochemical cycles, in Sundquist, E.T., and Broecker, W.S., eds.,
The carbon cycle and atmospheric C 0 2 : Natural variations Archean to present:
American Geophysical Union Monograph 32, p. 561-572.
ACKNOWLEDGMENTS
We thank Gabor Gaal for discussions of the Proterozoic tectonics and mineral
deposits of the Northern Hemisphere, and Bryan Krapez, Nicki Netherway, and
Julian Vearncombe for reading earlier drafts of this manuscript and for helpful
comments. We also thank Thomas Worsley and Phillip Brown for reviews and
suggestions for improvements. Because of space limitations, we have endeavored to
cite the most up-to-date review papers and books rather than descriptions of all the
metal deposits listed. We apologize to the uncited.
Manuscript received September 3,1991
Revised manuscript received December 16, 1991
Manuscript accepted January 3,1992
Printed in U.S.A.
GEOLOGY, April 1992