between Earth's Evolutionary History and
Evolutionary Trends in Ore Deposits
molecular clouds, from one of which the Earth and all other planets of the
solar system formed, are made up of widely dispersed microscopic dust particles
containing just about a dozen refractory minerals. These represent the
starting point of planetary mineral evolution. Gravitational compression and
consequent heating produced the primary refractory constituents of chondritic meteorites, including chondrules
and calcium-aluminum inclusions, with about 60 different mineral phases.
Subsequent aqueous and thermal alteration of chondrites,
asteroidal accretion, differentiation, and
consequent formation of achondrites resulted in a
mineralogical assemblage of about 250 different minerals species found in unweathered meteorite samples.
of this material into planetary masses led to further physical and chemical
processes. Mineralogy of the Earth has largely evolved as a consequence of
physical, chemical, and biological processes following planetary accretion
initial mineral evolution of Earth’s crust was most likely governed by
processes that produced the first continents with their associated granitoids and pegmatites,
metamorphic terrains hydrothermal deposits, evaporates and zones of surface
weathering which resulted in an estimated 1500 different mineral species.
These geochemical and petrologic processes included:
1) Volcanism and degassing,
and contact metamorphism,
7) Associated large-scale ﬂuid-rock
processes began to affect Earth’s surface mineralogy by the Eoarchean Era (~3.85–3.6 Ga). The
Paleoproterozoic “Great Oxidation Event" (2.2
to 2.0 Ga), witnessed changes in the atmospheric
and ocean chemistry and the formation of large-scale mineral deposits,
including banded iron formations, when atmospheric oxygen may have risen to
>1% of modern levels. The Neoproterozoic
increase in atmospheric oxygen, which followed several major glaciation
events, ultimately gave rise to multicellular life and skeletal biomineralization and irreversibly transformed Earth’s
surface mineralogy. Biochemical processes may be responsible, directly or
indirectly, for most of Earth’s 4500 known mineral species. Thus, different
stages of mineral evolution arise from three primary mechanisms:
separation and concentration of the elements from their original relatively
uniform distribution in the pre-solar nebula;
increase in range of intensive variables such as pressure, temperature, and
the activities of H2O, CO2, and O2; and
generation of inequilibrium conditions by living
sequential evolution of Earth's mineralogy from chondritic
simplicity to Phanerozoic complexity introduces a temporal dimension to
mineralogy. It provides a dynamic alternate approach to understanding the
evolutionary trends of ore deposits. The mineralogical diversity now found at
or near Earth’s surface at crustal depths less than about 3 km was not
present for much of the planet’s history. Indeed, both the variety and
relative abundances of near-surface minerals have changed dramatically over
more than 4.5 billion years of Earth history through a variety of physical,
chemical, and biological processes. The main objective here is to explore the
diversity and distribution of ore deposits in juxtaposition with significant
episodes of evolutionary change in the Earth's crust.
It is neither possible nor desirable here to consider
crustal evolution in detail for the purpose in question. The continents are
widely believed to have developed by accretion -- each has developed from a
volcanic nucleus or nuclei, being joined and added to by peripheral volcanic
nuclei. The process is aided by the accumulation of volcanic matter
(pyroclastic material) and products of erosion. The pattern is complicated by
later fractures and relative movement of various crustal segments. This
evolutionary pattern seems to form a plausible framework for the succession
of geologic environments which is parallelled by a
similar pattern of evolution of ore types.
For the sake of simplicity, the process of crustal
evolution is considered in six successive stages.
STAGE I: THE EARLY VOLCANIC STAGE
The beginning of crustal evolution is marked by the formation of
broad swells on the basaltic ocean floor. These represent the early stages in
the development of volcanic islands. Development of these swells leads to
block faulting, extrusion of lavas, and their protrusion above the sea level
to form volcanic islands (Eg Solomon Is in SW
Pacific). The islands are composed of pillow lavas (
basalts poor in olivine with spilites and keratophyres). Pyroclastic material is absent, but
products of erosion have started forming.
- Native copper and
associated sulfides as orthomagmatic
disseminations and vesicular fillings Eg
- Nickel and associated
sulfides in volcanic sills Eg Kambalda, W Australia, Manitoba. iii)
Precious metals viz. tellurides Eg Fiji.
- Minor chemical
sedimentation viz. manganese and iron with jasper. NOTE: Manganese in
the more important at this stage and the only important iron ore
deposits are of Lake Superior-Ontario-Quebec.
NOTE: Manganese in more important at this stage and the
only important iron ore deposits are of Lake Superior-Ontario-Quebec.
STAGE II: EARLY ALPINE TYPE ULTRAMAFIC
Vulcanism continues, but changes to
basaltic andesite, gradually progressing to andesites,
dacites and rhyolites. Pyroclastic activity becomes
conspicuous with the onset of the andesitic stage and increases with the
increase in the felsic nature of vulcanism. By this
time the island is quite large ( 150 Km in length)
and new swells are developing either in a linear or arcuate
arrangement with respect to the earlier swells. The older swells are
undergoing extensive erosion and much sedimentation. The sedimeents
become folded, faulted and deformed due to near vertical block faulting and
- Alpine type chromite deposits in intrusives
Eg Paleozoic to Tertiary "Serpentine
- Nickel sulfide concentrations.
NOTE: Some of the nickel sulfide
deposits associated with stage I may actually belong to this stage.
- Nickel also occurs as Ni-rich olivine which may be
concentrated to ore by later weathering.
STAGE III: DEVELOPING EUGEOSYNCLINAL STAGE
islands are by now well established and are enlarged by bodily uplift,
volcanic accretion and sedimentation. Volcanic products are becoming more
felsic and pyroclastic material is becoming prominent. Earliest plutonic
rocks of granitoid texture and dioritic-
granodioritic composition appear (in pipe or stock
form). These are of shallow subvolcanic nature.
These may be products of magmatic differentiation or transformation of the
deeply buried pyroclastic rocks.
- Banded Iron Formations
developed as volcanic chemical sediments as a result of sea-floor
exhalative activity. Deposition of these took place in troughs (eugeosynclines) in inter-island regions of arcs.
- Considerable jasper and
some manganese Eg Guyana.
- Modern analogues of these
processes are operative in the Kuriles and the
- Stratiforn Sulfide Deposits of marine and marine-volcanic
affiliation. These include chemical sedimentation, sulfide pyroclastic
concentrations and some lavas. All these are
essentially sea floor volcanic accumulations. A few of these are
- associated with basaltic and more mafic lavas Eg
Cyprus and Japan, whereas a vast majority are associated with andesitic
and dacitic rocks. Eg
Base metals of Ontario, Mount Isa and McArthur River (Precambrian);
Bathurst, New Brunswick and E. Australia (Paleozoic) and Japan
- Some Banded Iron
Formations and minor manganese concentrations and barite are associated
with the Stratiform Sulfide Deposits.
- Most of these deposits are formed near the continental
margins and biological activity (2500 y ago) is always indicated.
to these are the sulfide bearing subvolcanic intrusives,
breccia plugs and related shallow igneous bodies of andesitic-rhyolitic composition -- these are the
STAGE IV: ADVANCED EUGEOSYNCLINAL
& MIOGEOSYNCLINAL STAGE
oldest swells have become quite large (Java & Sumatra) with smaller
intervening swells beginning to coalesce (Aleutian-Malaysian). Volcanic
festoons isolated from continents, or extending outwards from these are
characterized by igneous sedimentation (with formation of reefs in
appropriate climates). There is a mixing of volcanic material with products
of continental erosion around volcanic festoons bordering continents. There
is, therefore, a hybrid sedimentation on the
continental side of the arc (the miogeosyncline)
while volcanic sedimentation progresses in the outward seaward trough (the eugeosyncline). Vulcanism at
this stage becomes more felsic.
Deposition continues from the
Developing Eugeosynclinal Stage (III) resulting in
the formation of:
- Stratiform or non-stratiform marine
volcanic sulfide ores.
- Banded Iron Formations in
the eugeosynclines (for some reason major iron
formations are not associated with basemetal
- Volcanic basemetals are contributed to the reef and off-reef
environments on both sides of the arc (particularly on the miogeosynclinal side). These are eventually
concentrated by sedimentary, diagenetic and
later processes to form Limestone-Lead-Zinc Deposits.
- Some manganese deposits (Usinsk Type) also develop in the eugeosynclines
STAGE V: EARLY CONTINENTAL AND INTRUSIVE STAGE
The volcanic islands are by now welded to each other and
also to the continental margins. Intense fault movement, compressional
folding, more felsic plutonic intrusions, waning of vulcanism
and rapid erosion are characteristic of this stage of crustal evolution.
Plutonic rocks are granitic and pegmatitic in
- Cassiterite deposits as disseminations in granites, contact
metamorphic deposits and pegmatitic deposits.
- Quartz-gold veins.
- Stibnite and stibnite-scheelite-gold veins.
- Basemetal sulfide veins with arsenopyrite
and increasing proportions of Pb & Zn as
compared to Cu. NOTE: Some basemetal veins may result
from the remobilization (destruction) of earlier eugeosynclinal
stratiform ores (Stages III & IV).
- Plutonic type anorthositic iron-titanium oxides.
- In the more mafic parts of
these intrusions chromite is segregated. Eg Bushveld Complex.
- Sometimes ilmenite, magnetite and minor Fe-Ti-O.
- Major nickel-copper
sulfides (Eg Sudbury) are also identified with
this stage (?).
- Chromite deposits formed
in ultramafic rocks during the Alpine Type Ultramafic Stage (II) are
well serpentinized by this time and move along
large fault systems (along which they formed) and take up new lithological
and structural positions in the evolving crust.
STAGE VI: SHELF AND SHIELD STAGE
folding, faulting and varying degrees of metamorphism leads to the formation
of a "Continental Shield". This stage is marked by outpouring of
flood basalts and stabilization of the crustal segment. Erosion and peneplanation lead to the development of broad flat areas
susceptible to inundation during sea-level rises resulting in extensive
deposits of detrital sediments, reefs (carbonate), evaporites
and chemical sediments. Movement of the shoreline in response to sea-level
fluctuations leads to the interfingering of shallow
water marine and fluviatile sediments, particularly
in the lower reaches of braided streams, deltas and outwash fans. Mineral
deposits forming at this stage include a variety of igneous and sedimentary
ores, and deposits formed during the earlier stages undergo substantial
- There are few mineral
deposits associated with flood basalts. Exceptions are the copper
bearing lavas of the Keweenaw Peninsula,
deposits often associated with oil bearing strata and evaporites, Eg Pine Point,
- Non-volcanic sedimentary
manganese deposits (orthoquartzite-glauconite-clay association), Eg
Nikopol, USSR, and Morocco.
- Ironstones of the Clinton,
Lorraine and English type associated with near-shore, estuarine or lagoonal sedimentation.
- "Sandstone Type"
Cu-U-V ores formed in coarse sediments of outwash fans, near-shore braided
streams and deltas, Eg Colorado.
- Gold-uranium deposits of
Witwatersrand-Bhind River- Jacobina
Type in coarse conglomerates and grits of braided stream channels.
- Basemetal sulfide deposits of non-volcanic association occurring
with evaporites, Eg Kupferschiefer Marl Slate of Europe and England and
the Copperbelt of Zambia. viii) A very minor
category of iron ores -- the bog or marsh iron ores such as those of the
present northern hemisphere.