Metals, minerals, mining and (some of)
A short series of lectures prepared for the London Mining Network
24 April 2009
I acknowledge gratefully the extent to which I have leant on the work
contained in several good text books:
Mine Wastes: Characterization, Treatment and Environmental
Impacts, 2nd Edition, by Bernd Lottermoser, 2007. Springer, Berlin
Mining and the Environment: From Ore to Metal, by Karlheinz Spitz
and John Trudinger, 2009. CRC Press, Leiden.
Introductory Mining Engineering, 2nd Edition, Howard Hartman and
Jan Mutmansky, 2002. Wiley, New Jersey.
Thank you also to CAFOD, London, for suggesting and organising the
workshop, and for covering my travelling expenses to London for the
Outline of lectures:
Topic 1: Ore mineralogy and orebodies
Topic 2: Mining
Topic 3: Ore processing and metal recovery
Topic 4: Mine wastes
Topic 5: Environmental and social concerns
Specific mining problems examined in some detail:
• Surface subsidence above underground longwall-mining panels
• Rockbursts in deep underground mines
• Tailings dam failures
• Riverine and submarine tailings disposal
• Cyanidation wastes and their attenuation (destruction)
• Radioactive uranium wastes and water contamination
• Sulphide wastes and acidification of waters
Topic 1: Ore mineralogy and orebodies
From a series of 5 lectures on
Metals, minerals, mining and (some of) its problems
prepared for London Mining Network
24 April 2009
Outline of Topic 1:
• Elements and metals
• Types of minerals
• Radioactive elements, minerals and radioactive decay
• The process of oxidation
• Acids and alkalis
• Types of rocks and orebodies
• Examples of typical orebodies
Elements – minerals – rocks (orebodies)
Elements are the building blocks of minerals EXTRACTION
e.g., iron, zinc, sulphur and oxygen are elements. Recover target metal from
Minerals are the building blocks of rocks PROCESSING
e.g., silicon-oxide (silica), iron-sulphide (pyrite) and tin-oxide Liberate target minerals from
(cassiterite) are minerals. rock and concentrate them
Metal-bearing minerals are the target of mining.
Non metal-bearing minerals are referred to as gangue minerals.
Rocks are aggregates of minerals MINING
e.g., granite, limestone, sandstone and gneiss are rocks. Recover orebody from host
“Orebodies” are rocks containing an enhanced percentage of
metal-bearing minerals, high enough to be economic (i.e.,
mined at a profit), and a lower percentage of gangue minerals.
Metals enrichment factors
Metals require significant enrichment
above their normal background levels in
the Earth’s crust to form a mineable
Minerals are enriched to form orebodies
through a wide range of different
The enrichment factor required to make a
mine viable (i.e., profitable – within today’s
economic framework for minerals exploitation)
will vary from time to time, depending on
commodity prices, and the ease of
extraction of both the orebody from the
ground and the target metal from the
Figure from Spitz and Trudinger, 2009.
World production of non-fuel mineral commodities in 1999.
Table from Lottermoser, 2007.
Elements are made up of atoms which consist of protons, neutrons and
electrons. The number of protons (the “atomic number”) defines the
For example oxygen (O) has 8 protons, Uranium (U) has 92 protons.
In a well ordered fashion through the periodic table, the number of
protons, neutrons and electrons increases, and the atoms (elements)
become heavier and larger in diameter.
Electron 1 “valence” 3 Electrons
Negative electrical charge electron in the 3 Protons
No mass outer electron - 4 Neutrons
- “shell” -
Positive electrical charge
Hydrogen (H) atom Lithium (Li) atom
Periodic Table of Elements
Some definitions regarding metals:
• Metals are elements that are malleable, ductile, and conduct heat and
electricity well – gold (Au), silver (Ag), copper (Cu), platinum (Pt) etc.
• Metalloids (or “semi-metals”) are elements with both metallic and
non-metallic properties, and have a lower ability to conduct heat and
electricity – boron (B), arsenic (As), antimony (Sb), bismuth (Bi),
selenium (Se) and tellurium (Te).
• Heavy metals are those metals with a density greater than 6 g/cm3:
Fe, Cu, Pb, Zn, Sn, Ni, Co, Mo, W, Hg, Cd, In, Tl. (Gold ~18 g/cm3)
• Base metals are those metals that tend to be used in industry by
themselves, rather than alloyed with other metals – Cu, Pb, Zn, Sn.
Making minerals from elements:
The sharing of electrons by different elements forms the basis of the
creation of compounds.
Minerals are compounds – combinations of elements held together by
the forces established through the sharing of electrons.
Gold (Au) is stable and unreactive, and forms no compounds in nature.
An ion is an atom or molecule (compound) which has lost or gained one or
more electrons, giving it a positive or negative electrical charge.
Anions a negative charge (e.g., CN-).
Cations have a positive charge (e.g., H+)
H+ cation lies at the root of acid mine drainage
CN- (cyanide) anion is the basis of cyanidation waste problems.
A mineral is often crystalline in form.
The crystal lattices of minerals hold metal elements very tightly.
Aggressive chemical means, or large amounts of thermal or electrical
energy, are therefore required to liberate the metals from their host
The mineral pyrite Model of the crystal
(FeS2) in its form of the titanium
characteristic oxide mineral rutile
cubic crystal form (TiO2)
“Classes” or groups of minerals:
Significant metal-hosting minerals
- Native metals: pure metals or metal alloys
- Oxides: compounds with oxygen (O)
- Sulphides: compounds with sulphur (S)
Minerals primarily of “industrial” interest
- Silicates: Si-O
- Carbonates: CO3
- Halides (salts): Cl
Minerals hosting interesting metals (and with some industrial interest)
- Sulphates: SO4
- Phosphates: PO4
- Borates: B-O
A native metal is a metal found in its metallic form in nature.
Only gold, silver, copper and platinum metals occur in nature in
All mined gold is native metal, alloyed with up to 15% silver.
There are no common naturally occurring gold oxides, sulphides or other
Prospector B. O. Holtermann
with 286 kg solid gold nugget
Native silver (Ag). Source: US Native copper (Cu) about 4 cm in found in 1872 at Hill End,
Government. size. Credit: Jonathan Zander. NSW, Australia. From Spitz
and Trudinger, 2009.
Are simple compounds with the element oxygen (O). Metals are relatively
easily extracted from oxide minerals. Examples include:
Hematite: Fe2O3 Ilmenite: FeTiO3
Rutile: TiO2 Cassiterite: SnO2
Coltan (Columbite-Tantalite): (Fe,Mn)(Nb,Ta)2O6
“kidney ore” from
yellow is the
reflection of a lamp
Cassiterite (SnO2). Source: US used for lighting.
Are simple compounds with the element sulphur (S). Metals are less
easily extracted from sulphide minerals, and are often oxidised first, as the
initial stage in metal recovery. Examples include:
Chalcocite: Cu2S Sphalerite: ZnS Galena: PbS
Cinnabar (HgS), Buckskin Mnts., Aggregate of Sphalerite (ZnS) Galena (PbS) crystal.
Nevada. Credit: Chris Ralph. crystals. Credit: Andreas Früh
Are compounds with silicon-oxygen (Si-O) and occur in many different
Silicates all contain metallic elements, but it is currently not possible
to extract the metals from them, so interest in silicate minerals lies in their
industrial uses. Examples include:
Quartz (silica): SiO2 Beryl (emerald): Be3Al2(SiO3)6
Muscovite (mica): KAl2(AlSi3O10)(F,OH)2
Beryl Be3Al2(SiO3)6 Crocidolite (blue) asbestos
variety emerald Na2Fe2+3Fe3+2Si8O22(OH)2
from the now closed mine at
Wittenoom, Western Australia.
Credit: John Hayman.
Other minerals of interest:
Formed with sulphur-oxygen (SO4).
Gypsum: CaSO4∙2H2O - used in cement
Formed with boron-oxygen (B-O) and are exploited for the metalloid
element boron (B).
Formed with carbon-oxygen (CO3). They are easily dissolved in acids,
and are able to neutralise acids.
Calcite, limestone: CaCO3 - limestone is the main component of cement
Other minerals of interest:
Formed with phosphorous-oxygen (PO4).
Phosphates exploited for Rare Earth Element (REE) metals and thorium (Th):
Monazite: (Ce,La,Pr,Nd,Th,Y)PO4 - radioactive, due to thorium,
and the most common ore of
Apatite: (Ca,Sr,Ce,La)5(PO4)3(F,Cl,OH) - a non-radioactive source of
Phosphates are also mined to http://en.wikipedia.org/wiki/File:Apatite09.jpg
obtain phosphorus for use in
agriculture and industry:
Apatite, variety fluorapatite (Ca5(PO4)3F
from Mexico. Credit: Chris Ralph
Other minerals of interest:
Salts are “evaporite” minerals formed with chlorine (Cl).
They are easily dissolved in water and are often mined in-situ using
Halite (rock salt): NaCl
Sylvite: KCl - fertiliser industry
Sylvite (KCl). Credit: Luis Miguel Bugallo
Oxidation is a reaction with oxygen that results in the breakdown of
Metallic sulphide minerals (e.g., pyrite) oxidise in the presence of
water and oxygen to:
• produce acids and
• release dissolved metals into water.
“Oxidised” sulphide minerals are not the same as “primary” oxide
A primary oxide of iron is hematite: Fe2O3
Oxidation of pyrite (FeS2) produces iron-hydroxide: Fe(OH)3
Acids and alkalis and pH:
Anything that reacts with an “acid” is called an “alkali”.
pH is a measure of the acidity or alkalinity of a solution.
Acidic pH less than 7 (lemon juice = 2, battery acid = 0)
Neutral pH equal to 7 (distilled water)
Alkaline pH greater than 7 (household ammonia = 11)
They neutralise each other through the following reaction:
H+ + OH- H 2O
Acid Alkali Water
Figure from: http://en.wikipedia.org/wiki/File:PH_scale.png. Credit Stephen Lower
Rocks and orebodies:
Rocks and orebodies are aggregates of different minerals.
Orebodies have high concentrations of metal bearing minerals and are
hosted in barren “country” rock.
Mined country rock is referred to as gangue or waste.
Volcanic, sedimentary and metamorphic processes form rocks and
Hydrothermal fluids associated with volcanic and metamorphic processes
contain high concentrations of dissolved metals and also form ores
Igneous rocks are formed when
molten magma cools and
crystallises either on the surface
or at depth in the crust.
Examples: granite, basalt,
An outcrop of orbicular granite.
Locality: Orbicular Granite Nature
Sanctuary, near Caldera, Chile.
Photo credit: Herman Luyken
Sedimentary rocks are formed by
• clastic sediments derived from
the erosion of other rocks (mud,
gravel, sands) http://en.wikipedia.org/wiki/File:Conglomeratereyes.jpg
• organic matter
• chemical precipitates (evaporites)
followed by burial and compaction
of the material.
conglomerate, limestone, coal,
An outcrop of conglomerate
Locality: Point Reyes, Marin County,
Metamorphic rocks are formed
when any rock type is subjected to
high temperature and pressure.
Examples: marble (from limestone
precursor), quartzite (from
sandstone precursor), gneiss (from
Banded gneiss, formed by high
pressure compression that aligned
minerals, forming a layered fabric.
Locality: Skagit Gneiss Complex, North
Cascades Range, Washington, USA.
Credit: US Geological Survey
Enrichment of metal-bearing minerals occurs in specific geo-tectonic
settings in response to specific geological processes.
These geological settings and processes produce different types of
orebodies, with “classic” mineral assemblages/combinations, e.g.:
Placer (alluvial) gold
Massive copper sulphide + gold
Massive lead-zinc sulphide
Layered igneous intrusions: platinum, palladium, chromium
Nickel laterite and bauxite
Massive sulphide lead-zinc deposit, Black Angel Mine, Greenland (1973 – 1991)
Black Angel Mine exploited a SIMPLIFIED CROSS-SECTION THROUGH BLACK ANGEL MINE
massive sulphide lead-zinc
deposit (sphalerite, galena and Massive
pyrite) hosted in marble and sulphide
metasediments. Ore-grades of
12.5% Zn, 4.1% Pb, 30 ppm
(g/ton) Ag were reported (Asmund
et al., 1994). The massive sulphide 600 m
orebodies are developed sub-
parallel to metamorphic banding in
the country rock, and were mined
using a room-and-pillar method. Approx. 9 km
Massive sulphide ore (dark band) showing
in a support pillar left remnant after
cessation of mining in 1990. (From: Black http://www.angusandross.com/AR-NEW/pages/proj-black-angel.htm
Angel News, 2005).
Kimberlite diamond deposits
Kimberlite volcanic pipes are the hosts of Diagram showing
“primary” diamond deposits. the structure of a
Both the volcanic magmas and the contained pipe.
diamonds originate at depths of about 170 to
200 km below the Earth’s surface, and are
brought to surface during a very rapid and
explosive eruption events.
Kimberlite pipes are subsequently eroded
through geologic time, exposing deeper parts
of the pipe, and developing “secondary”
deposits of alluvial diamonds that are found
in river beds, flood plains, and offshore as
Figure from McCarthy and Rubidge (2005)
Diamond grades in kimberlite pipes are highly
variable, and some pipes are completely
barren (for good geological reasons). Some Udachnaya Pipe,
reported grades lie in the range 0.28 – 7.5 Russia, in the
carats per ton (Roberts, 2007, pg 68). summer of 2004.
Secondary alluvial diamond deposits may be Stepanov.
significantly enriched in diamonds as the
process of erosion “concentrates” heavy,
Palaeo-placer gold deposit - Witwatersrand Basin, South Africa
The Witwatersrand Basin in an ancient (2.8
billion years old) palaeo-placer deposit,
consisting of multiple stacked and alternating
shale, sandstone and thin conglomerate
The gold mineralisation is found in the
conglomerate bands (called “reefs”), typically
between 5 to 100 cm thick. The gold was
either introduced at the time the sediments
were deposited, or was introduced later by
gold-bearing hydrothermal fluids (or both). Geological cross-section through the Welkom
Goldfield. Figure from McCarthy, 2006
The sedimentary basin subsequently suffered Carbon
extensive deformation, producing folds and
faults that disrupt the deposit. Faults impact Pyrite
significantly on safe (and efficient) mining.
Underground mines operate up to a maximum
depth of about 4,000 meters. Mineable
grades in a deep goldmine operations are
of the order of 10 – 20 g/ton. 1 cm
Many of the reefs contain accessory Gold and carbon nodules with “buckshot” pyrite
in conglomerate reef from the Witwatersrand
uranium, which is processed as by-product on
Basin, South Africa. Figure from McCarthy and
several mines. Rubidge, 2005. Photo credit: Goldfields.
Nickel laterite deposits
Nickel laterite ore deposits are the surficial, deeply
weathered residues formed on top of ultramafic rocks h_New_Caledonia.JPG.JPG
that are exposed at surface in tropical climates. They
are found widely in New Caledonia, Cuba, Australia,
Papua New Guinea, the Philippines, and Indonesia,
and are estimated to comprise about 73% of the Limonite zone
world continental nickel resource.
Two kinds of lateritic nickel ore can be distinguished:
limonite (oxide) types and saprolite (silicate) types.
Deep downward Near surface upward
penetration of water evaporation of water
producing weathering precipitates Fe, Ni oxide
LIMONITE A Creek in southern New-Caledonia.
ZONE Red colours reveal the richness of the
1- 2% Ni ground in iron oxides, and nickel.
ZONE (hydrated silicate)
1.5 - 2.5% Ni
The process of oxidation and
Olivine and weathering depletes the original
Mg RICH “ULTRAMAFIC”
pyroxene mafic rock of Mg and Si, and
(silicate minerals) concentrates Fe and Ni in the
In radioactive elements, the configuration of the nucleus is unstable, and
breaks down, emitting radioactive “decay” products:
alpha, beta and gamma radiation.
Isotopes of an element have nuclei with the same number of protons but
different numbers of neutrons.
Some isotopes are stable, and others subject to radioactive decay.
Alpha radiation is readily
stopped by a sheet of paper.
Beta radiation is halted by an
Electron Gamma radiation is eventually
absorbed as it penetrates a
dense material. Lead, being
dense, is good at absorbing
gamma radiation – several
centimeters of thickness is
Modified from http://en.wikipedia.org/wiki/Alpha_particle
A parent nuclide is an element that undergoes radioactive decay, producing
a daughter nuclide, that may be a different element.
U-238 decays to form Th-234 by releasing an alpha particle.
92 protons 90 protons
146 neutrons 144 neutrons
The daughter nuclide may itself be stable or unstable (i.e., radioactive).
The half-life is the time taken for half the radionuclide's atoms to
decay. Half-lives vary between more than 1019 years, for very nearly
stable nuclides, to 10−23 seconds for highly unstable ones.
Uranium radioactive decay series – and half-lives
Uranium-238 Series starts with
(92 protons, 146 neutrons)
Series ends with
stable lead isotope
The SI unit of radioactive decay is the Becquerel (Bq).
One Bq is defined as one decay per second.
Table from Lottermoser, 2007, and references therein.
Radioactive uranium minerals:
The main “primary” ore in uranium deposits is
Other important “primary” uranium ore minerals are:
Brannerite: (U,Ca,Y,Ce)(Ti,Fe)2O6 – a mixed uranium, iron, titanium
Coffinite: USiO4∙nH2O – a hydrated uranium silicate
Pitchblende – an amorphous, poorly crystalline mix of uranium oxides
often including triuranium octoxide: U3O8.
“Daughter” nuclides are trapped in uranium minerals or escape
At the time the
formed in orebody 1 Billion years later
Uraninite: UO2 Uraninite: UO2
100% uranium 75% uranium has decayed
to daughter radionuclides.
Some daughters will remain
trapped in the mineral, or they
migrate elsewhere in the orebody
to form other minerals
The “primary” uranium minerals weather and break down very easily when
exposed to water and oxygen, to produce numerous “secondary”
(oxidised) minerals, for example carnotite and autunite, which are
often mined, but in significantly lower quantities that uraninite.
Uranium is also found in small amounts in other minerals:
allanite, xenotime, monazite, zircon, apatite and sphene.
An important “secondary”
bearing mineral, from
Happy Jack Mine, White
Canyon District, Utah,
USA. Credit: Andrew
Uraninite (pitchblende) UO2 Silver.