『Abstract
Metallogenic studies that try to identify the geochemical fluxes
of metals in the lithosphere leading to ore formation have a higher
sensitivity when the traditional mining data, based on grades
and tonnages, are normalized to crustal element abundances, and
derivative units such as clarke of concentration and tonnage accumulation
index are used. This technique has been applied to the world-class
deposits of all industrial metals, i.e., to 34 metals plus the
rare earth elements and platinoid groups. The lower magnitude
limits for inclusion in the giant and supergiant categories (ore
metal content in a deposit/metal clake > 1×10^11 metric tons
(t) and 10^12 t of average crustal material, respectively) have
been established for each metal. There are, presently, 486 giant
and 61 supergiant metal accumulations of the various metals in
446 deposits and districts. A single deposit and/or district,
such as the Olympic Dam Cu-U-Au-REE-Fe deposit, could be the site
of a giant accumulation of more than one metal. Cu with 103 giant
accumulations followed by Au (99), Pb (55), Mo (41), Sb (24),
and Sn (22) are the most superaccumulated metals, whereas 11 metals
entirely lack giant deposits. Although this is partly influenced
by economic factors, such as low demand and price, the main cause
is the geochemical behavior of metals, especially the trace metals
compatibilities at the various of crustal evolution.
Porphyry Cu-Mo deposits have the greatest number of giant accumulations
among the popular ore deposit types (90), followed by sedimentary
exhalative Zn-Pb-Ag (23), volcanogenic massive sulfides (22),
stockwork Mo (17), epithermal Au-Ag veins (13), and Broken Hill-type
Pb-Zn-Ag (12). In terms of origin, the greatest number of giant
deposits is among the mesothermal Cu deposits (67), which reflect
the porphyry Cu-Mo preeminence, followed by mesothermal Au (61),
mesothermal Mo (39), mesothermal Sb (22), mesothermal Pb (19),
and sediment-hosted Cu deposits at redox interfaces (19). As a
class, the mesothermal epigenetic deposits account for 271 giant
metal accumulations, which represents 52 percent of the entire
database. Hydrothermal deposits including exhalative and epithermal
deposits possess 333 giant representatives, or 63.5 percent. Other
genetic families of ore deposits, including precipitates from
less than 150℃ hot hydrous fluids (59 giant deposits), orthomagmatic
deposits (40), sedimentary deposits (39), and weathering-generated
deposits (14), are less significant. An astonishing 446 giant
metal accumulations (92.5％) thus relied on water as the principal
agent of formation.
Of the giant deposits genetically associated with magmatism, the
metaluminous granodiorite-quartz monzonite suite at subductive
margins is related to most giant deposits (98, or 19％). Second
in importance is the high potassium granite suite (23 giant deposits).
Carbonatites, with only about 350 occurrences known world-wide,
are the most striking rare magmatic hosts to giant deposits. Five
carbonatites host giant or supergiant deposits and an additional
11 carbonatites host large deposits (i.e., tonnage accumulation
index > 1×10^10 t), so there is a 4.5 percent chance that any
newly discovered carbonatite will host a large or giant deposit.
The major period of preserved giant deposit accumulation occurred
during lower-middle Tertiary (103 giant deposits or 20％ of the
total), followed by middle-upper Tertiary (59 giant deposit),
Jurassic (39 giant deposits), Carboniferous (37 giant deposits),
and Paleoproterozoic (33 giant deposits). The predominantly young
age of mineralization indicates that shallow crustal depths or
subsiding subaqueous and subaerial depositories provide the most
favorable milieu for superaccumulation of many metals but, on
the other hand, are vulnerable to removal by erosion.』
Introduction
The database
Ore deposit data in geochemical context
The giant metal accumulations
Giant metal deposits quantified by origin
Giant metal accumulations in geologic time
Conclusions
Acknowledgments
References