We extract minerals from ores• Metal = an element that is lustrous, opaque, and

malleable and can conduct heat and electricity

• Ore = a mineral or grouping of minerals from which we extract metals

• Economically valuable metals include copper, iron, lead, gold, aluminum

Tantalite ore is mined, processed into tantalum, and used in electronic devices

This lecture will help you understand:

• Mineral resources and their contributions to society

• Mining methods

• Social and environmental impacts of mining

• Sustainable use of mineral resources

Mineral Resources and Mining

Mineral Resources and Mining

• Ore, Ore Mineral, Gangue, Resource < Reserve• Reserves are profitable and also technically & legally extractable

• Is it profitable, i.e. “economic”? Consider futures price, costs of energy,

infrastructure, labor, processing and environmental protection & cleanup. To do that we consider grade, type of deposit and type of processes feasible, special environmental problems, etc.

Some definitions:

An ore deposit is a well-defined mineral deposit that has been tested

and found to be of sufficient size, grade, and accessibility to be

extracted (i.e. mined) and processed at a profit at a specific time. Thus,

the size and grade of an ore deposit changes as the economic conditions

change. Ore refers to industrial minerals as well as metals.

• “Without a market, an industrial mineral deposit is merely a geological curiosity”

• Demand feeds back from the end-use market, to the end product, to the intermediate end product, and finally back to the mineral supplier.

• Customer specifications include physical and chemical and other criteria

Stages of Mining

• Exploration (discovery)

• Feasibility study

• Mine development

• Extraction/production

• Processing/beneficiation/milling

• Marketing

• Closure/post-mining use

EXPLORATION

Exploration• identification of areas with potential for

discovery of an economic mineral deposit

• geology governs the quest

• surveys

• sampling

• geophysics

• drilling

• pits

• shafts, adits

• base-line/pre-existing conditions

Generation of new project ideas/targets

• Corporate objectives

• Previous experience or knowledge

• Old mining districts

• Recent information

• Literature, including unpublished reports, theses, news releases

• New developments by other companies

Steps in obtaining mineral resources

1. Prospecting: finding places where ores occur.

2. Mine exploration and development: learn whether ore

can be extracted economically.

3. Mining: extract ore from ground.

4. Beneficiation: separate ore minerals from other mined

rock. (Mill)

5. Refining: extract pure commodity from the

ore mineral. (Refinery)

6. Transporation: carry commodity to market.

7. Marketing and Sales: Find buyers and sell the

commodity.

Mining is an economic activity.

The decision to mine (or not to mine) a particular ore

deposit depends upon:

an analysis of costs, benefits and risks

These considerations are both:

• tangible (i.e. dollar profit)

and

• intangible (i.e. hopes of stimulating the economy,

fears of environmental damage)

Prospecting: finding where ores occur

Important Factors:

• Applying knowledge of association of ores with specific

geological settings.

• using remote sensing techniques such as satellite imagery, seismic reflection

profiles, magnetic field intensity, strength of gravity to detect geological

structures.

• photos useful in finding faults.

• small basaltic intrusions have prominent magnetic anomalies.

• dense ore bodies can have prominent gravity anomaly.

• developing detailed maps of rock types and geological structures (faults, folds,

intrusions).

• developing 3-d picture of geological structures containing ore.

• obtaining samples of ore for chemical analysis.

•WHERE DO WE LOOK?

A review from your Geology 1200 Course

Recall that several processes can producemagmas. All are initially basaltic in composition. Basalts contain minor amountsof precious metals.

Hydrothermal MOR

Late Fractionation Pegmatites

Magmas can form near subduction zones when water causes partial melting of nearby mantle. Granitic magmas form by fractionation of basaltic magmas and by assimilation. Once the granite has frozen, silica-rich late fractionation waters with dissolved metals are left to intrude nearby rock.

Most searches near continental volcanic arcse.g. Andes (Inca Gold) , Sierra Nevada (1849 gold rush)

MOTHER LODE

Au, Ag

Two mechanisms for metals emplacement near granitic intrusions (both occur)

Au, AgMetal-rich waters may originate from the magma or groundwater

Heated groundwater dissolves metals

Metal ores precipitate near surface

Popular term “Mother Lode” initial placementOre Body

Gold Ore Ore mineral Gold Au

Gangue Mineral Quartz

Black Smokers

Circulation of hot water in cracks at mid-ocean ridge dissolves metals in Basalt, (Copper, Iron, Zinc, Lead,

Barium) which are re-precipitated as various ores, often Sulfides. Accumulate in ocean sediments.

http://collections.ic.gc.ca/geoscience

Island of Cyprus made of Ophiolites with black smokers.Source of copper that started bronze age

Example: Sterling Hill

Placers: concentrated as a detrital sediment

enrichment in Laterites

Responsibilities of the geologist• Exploration--discovery

• Feasibility study--ore body evaluation, reserves

• Mine development--mine design and planning

• Extraction/production--grade control

• Processing/beneficiation/milling

• Marketing--develop a market

• Closure/post-mining use--environmental geology

Geologic methods

• Robust thermodynamic and kinetic geochemical data and models

• New ore deposit models, especially for deposits with minimal impact on the environment

• More sophisticated 3-dimensional geological and ore reserve models

• Better geohydrologic models relating to mineral deposits, including industrial minerals deposits

• Geologic maps of mineralized areas

• Databases of mineral deposits and mineralized areas

Geochemical and geophysical

methods• Hand-held and down-hole analytical instruments

• Improved cross-bore hole correlation methods and characterization

• Better understanding of element mobility in soils and water

• Drones (unmanned aircraft) for airborne geophysical methods

• Low-cost, seismic methods

• Better interpretation of remote sensing and hyperspectral data (Livo and Knepper, 2004)

• More sophisticated 3-dimensional geochemical, hydrological, and geophysical models

Mine exploration and development: learn

whether ore can be extracted economically

• Define size, shape and grade of ore body.

Grade, G: mass of commodity per mass of ore.

Gold: 5 grams of Au per metric ton (106 grams of ore)

Grade = 5 x 10-6.

Aluminum: 400 kg of Al per metric ton of ore, G=0.4

• Drill cores, though expensive, can be used to determine

underground extent of ore

Estimate the mass of the commodity:= volume of ore body x density of ore body x grade).

1 metric ton = “tonne” is 1000 kilograms

Slide 4Slide 4Slide 4Slide 4Slide 4Slide 4Slide 4Slide 4Slide 4Slide 4Slide 4Slide 4Slide 4Slide 4

Open Pit Mine Figure 15-4 (1)

Page 341

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Dredging Figure 15-4 (2)

Page 341

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Area Strip Mining Figure 15-4 (3)

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Contour Strip Mining

Figure 15-4 (4)

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Types of Surface Mining

open pit mining:

• funnel shaped hole in

ground, with ramp spiraling

down along sides, allows

moderately deep ore to be

reached.

Surface mining: two types

Initial mining for zinc at Franklinand Ogdensburg, New Jersey.

• Strip-mining: Blast, scoop off rock overburden, and then scoop out ore material. Fairly shallow.• Economics of strip mining depend on stripping ratio• Large land area can be involved, especially for coal and bauxite.

Strip mining.

Example: Alcoa’sSierra de BahorucoAluminum miningin D.R. Southern Peninsula until 1985

Types of Subsurface Mining

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Underground Coal Mine Figure 15-5(1)

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Longwall Mining of Coal Figure 15-5 (3)

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When do we mine underground?

• The ore deposit is deep

• Ore body is steep

• Grade is high enough to exceed costs

Modern safety standards mean that most modern mines, at least those constructed by large corporations, are engineering marvels. They are expensive, and are not constructed unless the commodity sought is known to be present in profitable quantities and is recoverable.

Beneficiation

Means of separation of ore mineral from waste material (gangue minerals)

A great deal of bench testing using planned treatment processes avoids nasty surprises later

Loading Ore in the Pit

Crushing

Grinding

Ball Mill

Floatation

Dewatering and Impoundment

Refining

Smelting

Removes the metal from the ore mineral by heating the ore with a flux, reducing the metal ion to its elemental form

Leaching

Removes metal from the ore by reaction with a solution, often using cyanide CN- ion

smelting reactions:

coke + oxygen = carbon monoxide.

hematite + carbon monoxide = iron (melt) + carbon dioxide.

quartz + calcium carbonate = calcium silicate (melt) + carbon

dioxide.

• iron melt and silicate melt are immiscible, with the iron being

denser.

• The iron is drawn off from the bottom of the furnace.

• The silicate melt is drawn off the top ("slag").

Environmental problems particular to smelting.

• Production of huge piles of slag.

• Emission of CO2, a greenhouse gas, into the

atmosphere.

• Sulfur dioxide emissions from the refining of sulfide

ores are a major source of air pollution. The sulfur

dioxide combines with water to produce sulfuric acid,

H2SO4

• Release of heavy metals (As, Cd, Hg), present in

trace quantities in sulfide ores, into the environment.

Smelting:

Refining : Leaching

• In this process, typically done for Au, the ore is crushed

and piled on a liner.

• Weak solutions of sodium cyanide NaCN (0.05%) percolate through the material, leaching out the desired metals.

• The solutions are collected and the metals are precipitatedLa Herradura owned by Newmont Mining

• During the extraction phase, the gold ions form complex ions with the cyanide:

Au+(s) + 2CN- (aq) --> Au(CN)2- (aq)

• Recuperation of the gold is readily achieved with an oxidation-reduction reaction:

2Au(CN)2- (aq) +Zn(s) --> Zn(CN)4

- (aq) +2Au(s)

DANGEROUS if cyanide is not carefully recovered.

Discussion: Pete Feigley and Coeur D’ Alene

Acidified water

• Acid Mine Drainage

–Sulfide deposits react with groundwater to make acid

–Acidic streams can pick up heavy elements and transport them. POISON

Discussion: Lake Baikal Galena PbS and Sphalerite ZnS

Tailings pond: problems and solutions

• From concentrating usually have high pH (alkaline = basic)

• So modern Fix:

– At Bingham acid waters mixed with alkalinetailings water to neutralize

• Different metals have different problems

Tailings Pond: any collection of wastewater separated out during the processing

of mineral ores.

Cost of production.

• Costs that scale with grade of ore. The lower the grade,

• the more ore must be mined.

• the more ore must be shipped to the mill.

• the more ore must be milled.

• the more tailings must be disposed of.

• Fixed costs.

• building a transportation infrastructure.

• refining ore minerals, once it has been milled.

Cost trends in the future

The price of mineral commodities passes through three

stages that depend on changes in costs:

1st: Technical improvements in mining and/or metallurgy

2nd: These improvements become balanced by effects of

decreasing ore grades

3rd: cost rises because improvements in technology can

not keep up with increasing scarcity.

When reserves are too costly to exploit, an “Economic

Barrier” exists and production is stopped.

10. Mine Safety

Heath problems experienced by miners.

• collapse of mine.

• fire (methane, coal dust, etc.).

• asphyxiation (methane, carbon monoxide, etc.).

• pneumoconiosis (from inhaling coal dust).

• asbestosis (from inhaling asbestos fibers).

• silicosis (from inhaling silicate dust).

• heavy metal poisoning (e.g. mercury).

• radiation exposure (in uranium mining).

Strategic Elements

Strategic minerals are a diverse set of elements which are limiting factors in high-demand commodities in the global economy. In particular, these elements are vital to energy, technology, and agricultural industries. These elements, while varied and diverse in their uses, properties, and locations, can be categorized into five main groups: Rare Earth Elements, Fission Elements, Rare Metals, Platinum Group Elements, and Phosphorus.

Supply and Demand

A large part of the strategic element crisis stems from the disparity between supply and demand: global demand for strategic elements is rising rapidly and supply is not growing quickly enough to match the increasing demand. Many nations, particularly those with developing economies, do not have reliable access to strategic elements. In addition, inefficiencies in the supply chain, from mining and refinement to distribution and usage, make the availability of strategic minerals unpredictable.

Distribution

The unequal geographic distribution of strategic mineral deposits has led to individual nations dominating certain industries. China possesses a near-monopoly on the majority of REEs and has recently decided to decrease their export quotas in an attempt to regulate their industry and conserve their supplies. Morocco holds 70 percent of the world's phosphorus reserves. South Africa and Russia control nearly all of the world's platinum reserves. 64 percent of the world's coltan, plus 40% of its cobalt, is buried under the Democratic Republic of the Congo. Given the defensive and industrial advantages afforded by strategic minerals, such drastic inequality of these resources has caused much economic and political tension, a conflict that will surely escalate as these materials become scarcer.

Secondary Mining – Example: Recovery of strategic elements from mining residue deposits from selected locations in Chile, combined with a subsequently more environmentally friendly deposition of the remainders.

Chile is one of the biggest producers of natural resources and is well known for its great open pits from copper mining. Most of these copper deposits are associated to porphyries mined in open pits. For decades million tons of rock have been mined and discharged after processing creating huge piles, which can still contain minable amounts of valuable ore. Next to copper also gold, molybdenum, rhenium, selenium and rare earth elements get more and more into the focus. Nevertheless, mining residues can be a problem for the environment due to contaminant transport by wind or acid rock drainage (ARD) from sulphide weathering. Also the stability of tailing impoundments is an important issue in the seismically active Chile.

Central Case: Mining for … cell phones?

• Cell phones and other high-tech products contain tantalum

- Coltan = columbite + tantalum

• The Democratic Republic of the Congo was at war

- Since 1998, 5 million died and millions more fled

• Soldiers controlled mining operations and forced farmers and others to work, while taking most of the ore

- People entered national parks, killing wildlife and clearing rainforests

- Profits from coltan sales financed the war

• Most tantalum from the Congo goes to China

La columbite-tantalite o columbo-tantalite (abbreviata anche come coltan) è una miscela complessa di columbite (Fe, Mn)Nb2O6 e tantalite (Fe, Mn)Ta2O6, due minerali della classe degli ossidi che si trovano molto raramente come termini puri.Il termine "coltan" (contrazione di "columbo-tantalite") è usato colloquialmente in Africa per riferirsi ad una columbite-tantalite a relativamente alto tenore di tantalio. La miscela estratta in diversi paesi africani è spesso scambiata con armi e altri beni da organizzazioni paramilitari e guerriglieri africani, in particolare nella regione del fiume Congo.

Columbite e tantalite costituiscono una serie isomorfa a causa della mutua vicarianza fra tantalio e niobio nel reticolo cristallino. I termini della serie non sono equamente diffusi in natura, ma vedono prevalente un tenore medio-elevato di niobio a causa della maggior rarità del tantalio.

Il niobio si usa nell'industria metallurgica per lapreparazione di leghe metalliche con elevato punto difusione, per aumentare la resistenza alla corrosione inalcuni tipi di acciai inossidabili e, infine, nellapreparazione di superconduttori elettromagnetici.Il tantalio si usa sotto forma di polvere metallicanell'industria elettronica e dei semiconduttori per lacostruzione di condensatori ad alta capacità edimensioni ridotte che sono largamente usati intelefoni cellulari e computer.

General petrogenetic/metallogenetic model for rare-metal mineralization in the Central African metal province.

We process metals after mining ore

• Most minerals must be processed after mining

• After mining the ore, rock is crushed and the metals are isolated by chemical or physical means– The material is processed to purify the metal

• Alloy = a metal is mixed, melted, or fused with another metal or nonmetal substance– Steel is an alloy of iron and carbon

• Smelting = heating ore beyond its melting point then combining it with other metals or chemicals

Processing minerals has costs

• Processing minerals has environmental costs– Most methods are water- and energy-intensive

• Chemical reactions and heating to extract metals from ores emit air pollution

• Tailings = ore left over after metals have been extracted– Pollutes soil and water

– They may contain heavy metals or acids (cyanide, sulfuric acid)

– Water evaporates from tailings ponds, which may leach pollutants into the environment

Rare earth

Sono elementi che hanno in natura un comportamento geochimico coerente.

Rare earth element deposits

The rare earth elements (REE) occur in a number of environments within the Earth's crust. They may be found in igneous, sedimentary, or metamorphic rocks of a wide range of different ages. However, enrichments in the REE can typically be divided into two classes: primary types, generally formed by igneous or hydrothermal processes, and secondary types, in which the REE have been further concentrated from a primary enrichment through sedimentary processes or weathering. Primary types are typically veins, layers or zones of REE enrichment within the bedrock; secondary types may include weathered horizons such as laterites, placers, and sea-floor sediments

Primary REE enrichmentThe most significant primary types of REE enrichment are those associated with alkaline silicate igneous rocks and carbonatites. REE enrichments can also be found associated with hydrothermal veins, breccias and metasomatic zones in a variety of sedimentary and metamorphic environments. The world's main source of REE, Bayan Obo in China, appears to have formed by hydrothermal replacement associated with carbonatite magmatism.Alkaline silicate igneous rocks and carbonatites (igneous rocks dominated by carbonate rather than silicate minerals) are most commonly found in extensional rift settings like the present day East African Rift, or the Precambrian Gardar Province in south west Greenland. They are also emplaced during the post-collisional stage in orogenic belts; an example is the Cenozoic Mianning-Dechang REE belt in China. Within these igneous rocks, the REE can be concentrated by magmatic processes, such as fractional crystallisation and the development of igneous layering, or they can be concentrated by hydrothermal activity during and after emplacement of the magmas.

Secondary REE enrichment

Primary enrichments in the REE may then be upgraded further by secondary processes. Tropical weathering of alkaline silicate igneous rocks and carbonatites may form laterites or ion-adsorption clays, and concentrate the heavy minerals that contain the REE, such as in the Mount Weld REE deposit in Australia. River and beach sedimentary processes may also concentrate those heavy minerals into placer deposits.

REE-bearing minerals

The REE are found in a wide range of minerals, including silicates, carbonates, oxides and phosphates. Around 270 minerals are known to contain the REE as an essential part of their crystal structure, but only a small number are ever likely to have commercial significance. The majority of historical production has come from a small number of minerals, most importantly bastnäsite, monazite. Many REE enrichments are associated with other minerals such as apatite, allanite and eudialyte, and research on the processing of these minerals continues.

Bastnasite (Ce, La, Nd)(CO3)F

Monazite (Ce,La,Nd,Th)PO4

Allanite (Ce, La, Nd, Ca)2(Al,Fe)3(SiO4)3(OH)

EudialyteNa4(Ca,Ce)2(Fe,Mn,Y)ZrSi8O22(OH,Cl)2

Very large Rare Earth elements (REE)-Fe-Nb deposit (Bayan-Obo type), discovered as an iron deposit in 1927. REE minerals were discovered in 1936, and niobium-bearing ores in the late 1950s. Reserves are estimated at more than 40 million tons of REE minerals grading at 3-5.4% REE (70% of world's known REE reserves), 1 million tons of Nb2O5 and 470 million tons of iron. The deposit also contains an estimated 130 million tons of fluorite.

Bayon Obo is the world's largest known REE deposit. The fluorite content of the ores also makes it the world's largest fluorite deposit.

The deposit occurs in an east-west trending Mesoproterozoic rift zone along the northern margin of the Sino-Korean Craton. Host strata are quartzite, slate, limestone, and dolomite. Dolomite is the main host rock. The orebodies are stratiform and lenticular, with masses, bands, layers, veins, and disseminations. Besides clear features of hydrothermal mineralization, the deposit also exhibits Mg, Fe, Na and F metasomatism.

Baotou Mine (Mongolia)

As demand for high-tech devices grows, so does interest in recycling the esoteric metals that make them run.

URANIUM

• Uranium Geology & Deposits

• Uranium Resources, Supply & Demand

• Uranium Exploration

• Uranium Mining

• Uranium Milling

• Associated Environmental Issues

Uranium• Uranium as an element

– The heaviest naturally occurring element(three main isotopes U-234, 235-0.71%, 238-99.28%)

– U+4 (reduced-insoluble) & U+6 (oxidized-soluble)

– Uranium minerals

• Oxides: uraninite (crystalline UO2-2.6), pitchblende(amorphous UO2-2.6)

• Silicates: coffinite (U(SiO4)1-x(OH)4x)

• Phosphates

• Organic complexes & other forms

Uranium Exploration• A complex process to find a uranium deposit – a

defined model needed

• Three main methods used:

– Geological methods (remote sensing, geologic mapping, drilling, trenching etc.)

– Geochemical methods (sampling, analyses, advanced methods-dating, isotope studies)

– Geophysical methods (radiometric, geomagnetic, geoelectric, gravimetric, seicmic etc. methods and borehole logging)

Field Uranium Exploration

Milling Process Scheme

The Mill

Yellow Cake

Uranium Production

• 2004 40 263 tonnes U

• 2003 35 492 tonnes U

2004 % share

Canada

Australia

Kazakhstan

Russia

Niger

Namibia

Uzbekistan

11 597

8 982

3 719

3 280

3 245

3 039

2 087

28.8

22.3

9.2

8.2

8.1

7.6

5.2

Uranium mining & processing

In US, conventional mining in open pit and underground, now mainly leach mining.

Uranium ore typically 0.05 to 0.3% uranium oxide (U3O8).

Ore milled (ground to uniform particle size) and U3O8 extracted yellowcake.

This is the common material Saddam Hussein was supposed to be trying to acquire prior to Iraq war.

U3O8 powder must be converted into uranium hexafluoride (UF6) before it can be enriched to make the uranium used by nuclear power plants or weapons.

UF6 still completely natural, not enriched.

However, enrichment starts with a gas, and UF6 can be easily turned into a gas.

Uranium mining & processing

In US, conventional mining in open pit and underground, now mainly leach mining.

Uranium ore typically 0.05 to 0.3% uranium oxide (U3O8).

Ore milled (ground to uniform particle size) and U3O8 extracted yellowcake.

This is the common material Saddam Hussein was supposed to be trying to acquire prior to Iraq war.

U3O8 powder must be converted into uranium hexafluoride (UF6) before it can be enriched to make the uranium used by nuclear power plants or weapons.

UF6 still completely natural, not enriched.

However, enrichment starts with a gas, and UF6 can be easily turned into a gas.

Light-water reactor fuel normally is enriched to 3.5% 235U by isotope separation.

Gas diffusion uses fact that lighter 235U travels slightly faster than heavier 238U atom, and diffuses more quickly through a semi-permeable membrane.

Source: Nucl.

Regulatory

Commission

Technique uses many cascading steps, used in Manhattan Project at Oak Ridge Natl. Lab.

Gas centrifuge process rotates UF in rapidly spinning cylinder, uses fact that heavier 238U moves to outside and can be concentrated. (Process used in Pakistan’s weapons

program.)

US gas centrifuge plant in Ohio.

Pictures from Wikipedia.

Enriched uranium hexafluoride converted into uranium dioxide (UO2) pellets and assembled into fuel rods.

Uranium ore Yellowcake UF6 Fuel rod

Used fuel rods must be removed periodically and replaced by fresh rods.

Hot fuel rods initially stored and cooled in water pools,

then removed to dry storage.

Nuclear Waste currently stored at 120 sites in 39 states

Source: US DOE

Yucca MountainUS Dept. of Energy national nuclear waste

disposal site

Proposed site 1500 ft underground, studied since 1978

Permanent storage site at Yucca Mountain, Nevada.Problems: local opposition, transport issues, fear of stability over geologic times.

Source: US DOE