An ore is a type of rock that contains sufficient
minerals with important elements including
metals that can be economically extracted
from the rock.
The ores are extracted through mining; these
are then refined to extract the valuable element(s).
The grade or concentration of an ore mineral,
or metal, as well as its form of occurrence,
will directly affect the costs associated
with mining the ore.
The cost of extraction must thus be weighed
against the metal value contained in the rock
to determine what ore can be processed and
what ore is of too low a grade to be worth
mining.
Metal ores are generally oxides, sulfides,
silicates, or "native" metals that are not
commonly concentrated in the Earth's crust,
or "noble" metals such as gold.
The ores must be processed to extract the
metals of interest from the waste rock and
from the ore minerals.
Ore bodies are formed by a variety of geological
processes.
The process of ore formation is called ore
genesis.
Ore deposits
An ore deposit is an accumulation of ore.
Now this is distinct from a mineral resource
as defined by the mineral resource classification
criteria.
An ore deposit is one occurrence of a particular
ore type.
Most ore deposits are named according to either
their location, or after a discoverer, or
after some whimsy, a historical figure, a
prominent person, something from mythology
or the code name of the resource company which
found it.
Classification
Ore deposits are classified according to various
criteria developed via the study of economic
geology, or ore genesis.
The classifications below are typical.
Hydrothermal epigenetic deposits
Mesothermal lode gold deposits, typified by
the Golden Mile, Kalgoorlie
Archaean conglomerate hosted gold-uranium
deposits, typified by Elliot Lake, Canada
and Witwatersrand, South Africa
Carlin–type gold deposits, including;
Epithermal stockwork vein deposits
Granite related hydrothermal
IOCG or iron oxide copper gold deposits, typified
by the supergiant Olympic Dam Cu-Au-U deposit
Porphyry copper +/- gold +/- molybdenum +/-
silver deposits
Intrusive-related copper-gold +/-, typified
by the Tombstone, Arizona deposits
Hydromagmatic magnetite iron ore deposits
and skarns
Skarn ore deposits of copper, lead, zinc,
tungsten, etcetera
Magmatic deposits
Magmatic nickel-copper-iron-PGE deposits including
Cumulate vanadiferous or platinum-bearing
magnetite or chromite
Cumulate hard-rock titanium deposits
Komatiite hosted Ni-Cu-PGE deposits
Subvolcanic feeder subtype, typified by Noril'sk-Talnakh
and the Thompson Belt, Canada
Intrusive-related Ni-Cu-PGE, typified by Voisey's
Bay, Canada and Jinchuan, China
Lateritic nickel ore deposits, examples include
Goro and Acoje, and Ravensthorpe, Western
Australia.
Volcanic-related deposits
Volcanic hosted massive sulfide Cu-Pb-Zn including;
Examples include Teutonic Bore and Golden
Grove, Western Australia
Besshi type
Kuroko type
Metamorphically reworked deposits
Podiform serpentinite-hosted paramagmatic
iron oxide-chromite deposits, typified by
Savage River, Tasmania iron ore, Coobina chromite
deposit
Broken Hill Type Pb-Zn-Ag, considered to be
a class of reworked SEDEX deposits
Carbonatite-alkaline igneous related
Phosphorus-tantalite-vermiculite
Rare earth elements - Mount Weld, Australia
and Bayan Obo, Mongolia
Diatreme hosted diamond in kimberlite, lamproite
or lamprophyre
Sedimentary deposits
Banded iron formation iron ore deposits, including
Channel-iron deposits or pisolite type iron
ore
Heavy mineral sands ore deposits and other
sand dune hosted deposits
Alluvial gold, diamond, tin, platinum or black
sand deposits
Alluvial oxide zinc deposit type: sole example
Skorpion Zinc
Sedimentary hydrothermal deposits
SEDEX
Lead-zinc-silver, typified by Red Dog, McArthur
River, Mount Isa, etc.
Stratiform arkose-hosted and shale-hosted
copper, typified by the Zambian copperbelt.
Stratiform tungsten, typified by the Erzgebirge
deposits, Czechoslovakia
Exhalative spilite-chert hosted gold deposits
Mississippi valley type zinc-lead deposits
Hematite iron ore deposits of altered banded
iron formation
Astrobleme-related ores
Sudbury Basin nickel and copper, Ontario,
Canada
Extraction
The basic extraction of ore deposits follows
these steps:
Prospecting or exploration to find and then
define the extent and value of ore where it
is located
Conduct resource estimation to mathematically
estimate the size and grade of the deposit
Conduct a pre-feasibility study to determine
the theoretical economics of the ore deposit.
This identifies, early on, whether further
investment in estimation and engineering studies
is warranted and identifies key risks and
areas for further work.
Conduct a feasibility study to evaluate the
financial viability, technical and financial
risks and robustness of the project and make
a decision as whether to develop or walk away
from a proposed mine project.
This includes mine planning to evaluate the
economically recoverable portion of the deposit,
the metallurgy and ore recoverability, marketability
and payability of the ore concentrates, engineering,
milling and infrastructure costs, finance
and equity requirements and a cradle to grave
analysis of the possible mine, from the initial
excavation all the way through to reclamation.
Development to create access to an ore body
and building of mine plant and equipment
The operation of the mine in an active sense
Reclamation to make land where a mine had
been suitable for future use
Trade
Ores are traded internationally and comprise
a sizeable portion of international trade
in raw materials both in value and volume.
This is because the worldwide distribution
of ores is unequal and dislocated from locations
of peak demand and from smelting infrastructure.
Most base metals are traded internationally
on the London Metal Exchange, with smaller
stockpiles and metals exchanges monitored
by the COMEX and NYMEX exchanges in the United
States and the Shanghai Futures Exchange in
China.
Iron ore is traded between customer and producer,
though various benchmark prices are set quarterly
between the major mining conglomerates and
the major consumers, and this sets the stage
for smaller participants.
Other, lesser, commodities do not have international
clearing houses and benchmark prices, with
most prices negotiated between suppliers and
customers one-on-one.
This generally makes determining the price
of ores of this nature opaque and difficult.
Such metals include lithium, niobium-tantalum,
bismuth, antimony and rare earths.
Most of these commodities are also dominated
by one or two major suppliers with >60% of
the world's reserves.
The London Metal Exchange aims to add uranium
to its list of metals on warrant.
The World Bank reports that China was the
top importer of ores and metals in 2005 followed
by the USA and Japan.
Important ore minerals
See also
Economic geology
Mineral resource classification
Ore genesis
Petrology
References
Further reading
DILL, H.G.
The “chessboard” classification scheme
of mineral deposits: Mineralogy and geology
from aluminum to zirconium, Earth-Science
Reviews, Volume 100, Issue 1-4, June 2010,
Pages 1-420
