Elsevier Encyclopedia of Geology

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Bishop Richard of Durham would have been

saddened to see his word ‘Geologia’ fall into desue-

tude after 700 years.

Further Reading

Ernst WGF (ed.) (2000) Earth Systems: Processes and

Issues. Cambridge: Cambridge University Press.

Hamblin K (2002) The Earth’s Dynamic Systems:

A Textbook in Physical Geology. New York: Prentice

Hall.

Jacobson MC, Charlson RJ, Rodhe H, and Orians H (2000)

Earth System Science. San Diego: Academic Press.

Kump LR, Keating JF, Crane RG, and Kasting JF (2003)

The Earth System: An Introduction to Earth Systems

Science. New York: Prentice Hall.

Lovelock J (2000) The Ages of Gaia: A Biography of Our

Living Earth. Oxford: Oxford University Press.

Nisbet E (2002) The influence of life on the face of the

Earth. In: Fowler CMR, Ebinger CJ, and Hawkesworth

CJ (eds.) The Early Earth: Physical, Chemical and Bio-

logical Development, pp. 275–307. Special Publication

199. London: Geological Society.

EARTHQUAKES

See ENGINEERING GEOLOGY: Aspects of Earthquakes; TECTONICS: Earthquakes

ECONOMIC GEOLOGY

G R Davis, Imperial College London, London, UK

Introduction

If you visit the strangely dimpled landscape known

from Saxon times as Grimes Graves in Norfolk,

England, you will see not an ancient burial ground,

but hundreds of backfilled shafts in the white

Cretaceous Chalk. Here Neolithic man discovered

and exploited a thin subsurface layer of dark flint

(Figure 1) so extensive and of such superior quality

that, after due process of mining and treatment,

the finished product could profitably be traded and

fashioned into the finest flint tools and weapons at

the cutting edge of technology. If you visit the flat

forested landscape known as Weipa in the Yorke

Peninsula, Australia, you will see where twentieth

century man discovered and now exploits a surface

layer of red bauxite (Figure 2) so extensive and of

such superior quality that, after due process of

mining and treatment, the finished product can prof-

itably be traded and fashioned into the finest alumin-

ium utensils and machines at the cutting edge of

technology.

In his long march from hunter-gatherer to moon-

walker, Homo has used his sapiens to exploit the

Earth’s bountiful mineral resources that, apart from

food and clothing, have provided the materials for his

advancement. At about 2000 bc flint from Grimes

Graves and many other flint workings in the Cret-

aceous Chalk of Europe was an economic industrial

mineral because insufficient copper and bronze was

available to meet demand. The occurrence in nature

of native copper and gold had already led to their use

Figure 1 A sketch to illustrate how high-quality flint was mined

in the chalk of Britain about 4000 years ago.

434 ECONOMIC GEOLOGY

for over 2000 years as tools, ornaments and weapons.

Supplies of metal increased when smelting was

discovered to reduce the natural ores of Cu, Pb, Sn

and later Fe into metal. The ownership of valuable

metals and other minerals, such as salt, begat wealth

and power. The rise and fall of ancient civilizations

is intimately bound up with the riches derived

from control of mineral resources, and the historical

theme continues to this day. For example the shift

of power and control of trade routes from the

Persians to the Greeks was greatly influenced by

wealth from the newly discovered Laurium Ag-Pb

deposits near Athens, and then gold in Macedonia.

Finance was available to build a powerful navy

that enabled Themistocles to conquer Xerxes at the

decisive battle of Salamis in 480 bc. The Greeks

enjoyed a golden age of philosophy and art; the

mining revenues assisted Philip of Macedonia to

establish his dominance, and for his son Alexander

the Great to finance the first campaign in his great

Middle Eastern conquests about 330 bc. In that same

region, the 20th century has witnessed the global

economic and political impact of the discovery and

development of major oilfields upon the countries of

the Middle East.

Figure 3 (with logarithmic scale on the vertical

axis) illustrates how world demand for mineral prod-

ucts over the last 150 years of the industrial age has

been met by production growth rates that exceed even

the ‘explosive’ growth rate of world population.

Annual production rates for the basic industrial ma-

terials iron and petroleum have grown dramatically,

and the production rate of copper, a primary base

metal, has increased a hundredfold. During the

twentieth century newer metals such as nickel became

industrially important, and aluminium, once rare and

precious, reached production rates exceeding that of

copper, and at a lower cost per tonne. Many other

‘new’ elements continue to emerge in response to the

growth of modern high-technology industry. For in-

stance, demand is now growing rapidly for indium

(mine production about 340 tonnes in 2002), which is

needed for making flat-panel electronic displays as

used in mobile telephones and plasma-screen televi-

sions. World population is increasing, and the average

per capita demand for mineral products, while heav-

ily skewed by industrialized Western world usage, is

also increasing. Economic geology plays an integral

part in meeting this challenge to the mineral resource

base of the world.

Figure 2 The cliffs facing the Gulf of Carpentaria in Queensland, Australia, and a working face in the vast expanse of pisolitic

bauxite. Scale shown by white penknife near the centre. Photos: GR Davis.

Figure 3 Over the past 150 years, world demand for mineral

products has exceeded the ‘explosive’ growth in population,

shown on a logarithmic scale.

ECONOMIC GEOLOGY 435

Characteristics of Economic

Mineral Deposits

The AGI Glossary of Geology defines economic

geology as... ‘‘the application of geologic knowledge

and theory to the search for and the understanding of

mineral deposits; study and analysis of geologic

bodies and materials that can be utilized profitably

by man, including fuels, metals, non-metallic min-

erals, and water’’. In this work (Encyclopedia) water

and hydrocarbon fuels are treated separately in view

of their major industrial and economic importance.

The solid mineral resources also fall into specialist

groups, as indicated in the definition quoted above.

Collectively, they comprise the non-renewable re-

source base of the extractive industries. To qualify

for ‘‘profitable utilisation by man’’ they must all dem-

onstrate certain characteristics that are, appropriately,

both economic and geological.

Geological Attributes of Economic Deposits

The size (tonnage) must be sufficient to sustain

exploitation for a period long enough (mine life)

to justify development.

The valuable content (grade) must be high enough

to repay all costs. Taken together, the tonnage and

average grade express the comparative geological

potential of the deposit.

The shape, attitude, depth and physical properties

of the deposit must be amenable to extraction by

existing mining technology.

The valuable constituent(s) must be amenable to

separation from the unwanted portions (waste),

and beneficiation to marketable product by

existing technologies.

Economic Attributes of Economic Deposits

The price received for the product(s) must cover all

production costs and assure competitive advan-

tage.

The geographical situation must be amenable to

mine development, including water and power sup-

plies; and within economic transport distance to

market, especially for bulky products.

Socio-political conditions must be favourable.

These include planning permission and mineral

rights, various taxes and royalties, labour and

safety laws and conditions, regulations for waste

disposal, and rehabilitation when the mine is

worked out.

A new mining development is typically capital in-

tensive with a lead-time of years between discovery

and profitable production. Brief consideration of

the seven attributes listed reveals that the risk of

financial failure is shared between measurable geo-

logical, engineering and logistical natural factors on

the one hand and indefinite state-imposed constraints

or incentives on the other. Economic geologists need

a sound appreciation of mineral economics, mining

engineering and mineral processing technology, but

their core expertise rests upon their knowledge of

mineral deposits.

Figure 4 illustrates the hierarchical progression

from mineral occurrence to mineral prospect to min-

eral deposit, and then through mineral resources and

proved mineral reserves to profitable mining. This

progression rests for its success, above all else, on the

quality of geological observation and interpretation,

and its application in industry.

It is important also to appreciate that the mines of

today are exploiting only those selected deposits that

have met all the criteria for current economic devel-

opment. They represent only the tip of the iceberg of

the Earth’s mineral resources. Large deposits of many

mineral commodities, currently identified but sub-

economic, may in future become payable because of

improvements in mining or mineral extraction tech-

nology, commodity demands and prices, and similar

conditions. Those deposits may one day join the stock

of future discoveries that will provide the economic

deposits and mines of tomorrow.

Figure 4 The progression from a mineral prospect to mineral

extraction. Expenses increase as work becomes more detailed.

Mine development requires capital expenditure before cash flow

starts from mineral product sales. The categories of resources

and reserves, and the technical terms proved, probable, meas-

ured, and indicated are strictly defined in codes of practice for-

mulated by professional mining institutions in some leading

mining countries (Australia, Canada, South Africa, UK/Europe,

and USA) and accepted by financial organizations such as stock

exchanges.

436 ECONOMIC GEOLOGY

Variety and Use of Mineral Deposits

The range of ‘geologic bodies and materials’ that

is utilized by man has grown in scope and volume

over the course of history, but falls into a few

practical groups.

Construction Materials

These include building stones, sand, aggregates,

clay, and cement raw materials. The high cost of

transporting these bulk products requires source

rocks to be as close as possible to the place of utiliza-

tion, but typically the costs of extraction and treat-

ment are low. A long history of use (the stone walls of

Jericho were packed with a clay mortar circa 8000

bc) has built a body of experience concerning desir-

able source materials and their properties. In de-

veloped countries today, geological knowledge is

applied to not only ensure that technical specifica-

tions are met, but also to discover and delineate

those particular sources that best suit land develop-

ment planning and minimize environmental prob-

lems. Some industrial rock products are valuable

enough for export, such as clays for ceramics and

ornamental stone for decorative use in buildings.

Fuel or Energy Mineral Deposits

These include hydrocarbon fluids, coal and uranium.

Coal is a sedimentary rock derived from plant

remains, the fossil fuel on which modern industrial

development was built. Together with petroleum, this

versatile material supplies most of the worlds’ energy

needs. It is also a major industrial raw material for the

manufacture of chemicals, and coke for iron and steel

production. Economic deposits of uranium-bearing

minerals, the base on which the atomic age is built,

occur at a scale of magnitude nowhere near that of

coal and oilfields.

Industrial Minerals

Sometimes termed non-metallic minerals, these are

valued for their chemical and/or physical properties

and the fact that they are not of widespread occur-

rence. In general, prices are sensitive to market

demand and product specifications (with premium

prices for premium grade products), and quality is

a major factor in the economic geological evaluation

of mineral reserves and productive life of industrial

mineral deposits. A vast range of industrial minerals is

produced in an equally impressive range of tonnages.

Minerals with valuable chemical properties, used

mainly in the chemical and fertilizer industries, in-

clude rock phosphate, potash and mixed chloride

salts, sulphur, nitrates and borates. Fluorspar and

limestone are prominent as fluxes in the metallurgical

industry and ceramics, and other process industries

consume silica sand, feldspars, and kyanite. Physical

attributes useful in filler and extender applications

make talc, limestone and kaolin competitive in

paints, paper and plastics. Other minerals with useful

physical properties include asbestos, barytes, diatom-

aceous earth, and the lightweight aggregates per-

lite, pumice and vermiculite. Hardness is utilized in

abrasives such as corundum, garnet and industrial

diamond. The extensive list of industrially useful

minerals makes it clear that a wide range of geological

knowledge finds application in the search for indus-

trial minerals and in ensuring products that conform

to specifications set by the industrial user.

Metallic Mineral Deposits

The metallic ore minerals are commonly metal com-

pounds such as sulphides and oxides in which the

metal content is high compared with rock-forming

minerals. Natural concentrations of ore minerals

form discrete ore bodies that may typically contain

only a few percent of the valuable metal. Unlike

many industrial minerals that find direct use after

mining and limited beneficiation, the ore minerals,

in general, must be reduced to metal by complex

processing. Modern mining and mineral extraction

procedures are tending towards greater use of

chemical and bacterial leaching methods for suitable

ores, such as in-situ extraction of some uranium de-

posits, and heap leaching of some gold ores. The great

bulk of metalliferous ore, however, is mined by

surface or underground rock-breaking methods.

Run of mine ore is first crushed and milled to a fine

pulp, from which the desired ore minerals are sep-

arated from the gangue minerals by various methods

to produce a concentrate. Metal is then extracted

from the mineral concentrate by further treatment,

which may include smelting or various chemical

methods such as solvent extraction and electrowin-

ning, followed by refining to market standards. The

expensive multi-stage process of extraction results in

complex engineering works at the site of large ore

bodies, often in remote locations. The commonly

used metals are sometimes grouped for convenience

by their geochemical or industrial affinities. Base

metals include Pb, Zn, Sn and Cu. Iron and ferro-

alloy metals include Cr, Co, Ni, Mn and V. Light

metals include Al, Ti, Mg, Li and Be. The precious

metals comprise Ag, Au and PGM (platinum group

metals) (Table 1, Figure 5).

The attached statistical data illustrate some world

production rates and the relative importance of

the broad mineral groups in the world economy. It

should be noted that most metal production ton-

nages are less by one or two orders of magnitude

ECONOMIC GEOLOGY 437

than the tonnages of rock mined to produce them.

The relative value of metallic mineral and industrial

mineral production varies considerably from one

country to another. For instance, for the mean of the

years 2001 and 2002, industrial minerals accounted

for 78% of the total value of non-fuel minerals in the

USA whereas in neighbouring Canada the metallic

minerals accounted for 57% of the non-fuel group.

(Compiled from various sources).

World Distribution of Economic

Mineral Deposits

Like all other geological bodies, mineral resources are

unevenly distributed in the Earth’s crust. Many

nations owe a major part of their wealth to discovery

and development of economic mineral deposits, while

others may be either very poorly endowed by nature,

or ignorant of their undiscovered mineral resources.

The people of Nauru are richly blessed because their

small Pacific island homeland contains 40 million

tonnes of high grade phosphate rock. In developed

countries even with a large mining industry, the lack

of domestic sources of certain vital commodities leads

to the concept of ‘strategic minerals’ and defensive

stockpiling against national emergencies. Before

entry into World War II the USA included Cr, Mn

and Sn in a list of 14 strategic commodities. Statistics

of world mineral production illustrate the imbalances

that cause geopolitical concern about national vulner-

ability to imported supplies (Figure 6), or to dam-

aging price changes in key commodities. For

example South Africa, a country about twice the

size of France, dominates Pt production, supplies

almost half the worlds Cr and major amounts of Au,

Mn and V, but has inadequate domestic resources of

Mo and Al, oil and gas, potash, sulphur and kaolin.

China, a large country with a rapidly expanding econ-

omy, dominates world production of the rare earth

elements (REE), produces over 80% of world Sb, over

one-third of world V, Sn and W, and is a key nation in

world minerals trade.

The observed major world patterns of distribution

of economic mineral deposits become less arbitrary

and more understandable when viewed in the light

of metallogenic and geological maps. Relationships

appear between mineral resources and the geological

environments and rock systems in which they occur.

For instance, oilfields and coalfields are associated

with large sedimentary basins of upper Phanerozoic

age, and one would not search hopefully for these

Figure 5 The importance of industrial minerals in the modern

world is not always appreciated. The relative values of the four

commodity groups is a better measure than tonnages, because

the amount of rock mined to produce metals and precious metals

from their ores is at least an order of magnitude higher. Compiled

from data quoted in Evans (1995), after Noetstaller.

Table 1 Annual world production levels of selected metals and

industrial minerals

1982–

1983

2000–

2001 Main producing countries

Tonnes per

annum (millions)

Coal 4000 4500 China USA

Asbestos 4.1 2.0 Russia Canada

Bauxite 78 139 Australia Guinea

Chromite 8.2 13 South

Africa

Kazakhstan

Copper 8.0 13.6 Chile USA

Diatomite 1.9 1.7 USA China

Fluorspar 4.4 4.2 China Mexico

Iron ore 750 1150 China Brazil

Kaolin (21) 23 USA UK

Lead 3.5 3.0 Australia China

Manganese

ore

24 22 China South

Africa

Phosphates 130 130 USA China

Potash 25 27 Canada Belarus

Talc 7.4 8.4 China USA

Zinc 6.5 9.0 China Australia

Tonnes per

annum

(thousands)

Antimony ? 123 China Guatamala

Gold 1.4 2.5 South

Africa

USA

Mercury 6.0 1.8 Kyrgyzstan Spain

Platinum

group

metals

0.3 0.5 South

Africa

Russia

Silver 12 19 Mexico Peru

Tin 205 245 China Indonesia

Uranium 50 34 Canada Australia

Vermiculite 540 376 South

Africa

USA

Data compiled from World Mineral Statistics (2003) by permission

IPR/46–28cw.

438 ECONOMIC GEOLOGY

great energy resources in sedimentary basins within

ancient shield areas of Archaean rocks. The converse

applies for the great banded iron formations (BIF) in

Precambrian sedimentary basins that are host to most

of the world’s high-grade Fe ore deposits (see Sedi-

mentary Rocks: Banded Iron Formations). Similarly,

large and highly productive porphyry copper deposits

are strongly grouped in the mountain chains made up

of volcanic rocks and granitic intrusions along the

western margins of the Americas. This pattern has

been more readily understood over the past 40 years

in the light of geological mapping and plate tectonic

theory. Empirical associations between mineral de-

posits and their host rocks have long been noted and

put to use by miners, and the list is still growing as

geological knowledge of Earth’s physico-chemical

systems advances. Concepts have developed of min-

eral provinces and mineral epochs, and in recent

decades regional patterns of mineralization have

been related to the various kinds of tectonic plate

boundaries (Figure 7)(see Plate Tectonics).

Economic Geology and the Extractive

Minerals Industries

Every producing mineral deposit is a non-renewable

resource with a finite life. In order to continue to meet

world demand, the extractive industries are geared to

a life cycle of activities as shown in Table 2.

These four activities are very briefly outlined

below, and the reader is referred to specific topics

for more comprehensive information.

The State of Relevant Geological Knowledge

Economic geologists are widely employed in the

many specialized areas of the extractive industries.

All, however, rely on the quality and appropriate

application of their geological knowledge of mineral

deposits (see Mineral Deposits and Their Genesis).

Great advances have been made in the geological

understanding of the 4500 million year history of

the earth, and of the igneous, sedimentary and meta-

morphic processes in which the genesis of mineral

deposits is an integral part. Concentrations of valu-

able minerals into economic deposits are no longer

seen as special, isolated events, but as the result of

processes, often sequential and superimposed, that

operate in geological environments of every kind

and in every age from the Archaean to the present.

Advancing views on regional patterns of mineral de-

position related to space and time (i.e., in mineral

provinces and mineral epochs) were dramatically

boosted through definition of crustal tectonic regimes

by the theory of plate tectonics. The scientific over-

view of mineral deposits has moved away from

worthy attempts at genetic classification, notably

that of Lindgren, towards development of ‘mineral

Figure 6 This map, showing the sites of tin production, is an example of the uneven global distribution of several mineral

commodities. Modified from World Mineral Statistics (2003) by permission of the British Geological Survey. ß NERC. All rights

reserved. IPR/46–28CW.

ECONOMIC GEOLOGY 439

deposit models’. These models marshal all the pertin-

ent facts concerning related deposits that are seen as

‘types’. Modern advances in nearly all fields of geol-

ogy are of relevance and application to some aspect

of economic geology. For example structural geology

from the scale of electron microscopy in rock de-

formation studies to megastructures on satellite im-

agery; evolution and structure of sedimentary basins;

the geochemistry of sediments as source rocks for

hydrocarbons and metalliferous brines; the volcanic

realm and its diverse products; magma generation and

crystallization; metamorphic effects on rock struc-

tures and mineral chemistry; and even the profound

effects of major meteorite impacts on the Earth’s crust.

Specialist fields of knowledge are required for each

phase of the industrial cycle of activity (Table 2)in

each branch of the extractive industries, and eco-

nomic geologists have formed several specialist

groups such as petroleum geologists, mining geolo-

gists and exploration geologists.

Discovery of New Deposits

To maintain a stable extractive industry long

term, the huge tonnages of minerals extracted each

year must be replaced, on average, by discovery and/

or development of an equivalent amount of new

materials. The difficulty imposed by this high

demand is compounded by the fact that new mineral

fields and individual deposits become progressively

harder to discover as the easier finds are made. Scien-

tifically based mineral exploration has developed into

a sub-industry, in which the participants include gov-

ernment agencies, mineral resource companies of

all sizes, and specialist groups offering contract and

consulting services.

Exploration objectives are targeted on either cer-

tain commodities or certain regions of interest. The

search area for bulk materials such as aggregates or

low-grade coal is restricted by transportation costs

and environmental factors; some mines concentrate

their search close to existing infrastructure; and state

organizations are of course interested in their own

territories. Most mineral commodities are inter-

nationally traded, and exploration money and effort

tend to favour countries that offer the most attractive

combination of geology, political stability, mining

taxation and operational infrastructure. Commodity-

targeted exploration is based solidly on favourable

Table 2 Life cycle of extractive industry activities

Activity Applied geology input

Discovery of new

deposits

Dominant role

Feasibility studies and

mine development

Major role in defining reserves and

critical technical parameters

Mineral extraction Essential engineering role in

operational efficiency

End of life of deposit Long-term environmental

assessment

Figure 7 Development of the theory of plate tectonics in the 1960s led rapidly to a new view of the genesis of some ore deposits as

shown on this early diagram in 1972. Reproduced with permission from Evans AM (1995) Introduction to Mineral Exploration. Oxford:

Blackwell, p. 40 (modified from Sillitoe 1972).

440 ECONOMIC GEOLOGY

geological environments, the oil and gas sector being

a prime example. Views on the factors that have

controlled or generated mineral deposits (e.g., where

in the world to look for kimberlite pipes?) are of

paramount importance to cost-effective exploration.

Many small specialized groups undertake exploration

on this basis. Their successes may be sold to large

companies, which have the policy options of either

buying their future mineral resources or organizing

their own exploration teams on a long-term basis.

Exploration programmes generally follow phases

of target definition, reconnaissance, selective follow-

up, and detailed exploration of prospects. A great and

growing number of exploration technologies, includ-

ing heavy mineral, geochemical and geophysical

surveys, are available to supplement the essential art

and science of sound geological mapping based on

wide-awake observation. At the detailed stage of ex-

ploration, physical methods are used, such as pitting,

trenching and especially the various types of drillholes

now available.

Mineral exploration is a high-risk enterprise justi-

fied by potentially high reward, but a historically low

success rate overall. Organizations with a relatively

high success rate tend to be well managed, exploring

in carefully researched and targeted areas, employing

teams of well-qualified and motivated people to use

the most cost-effective sequence of search technolo-

gies, with financial backing stable enough to ensure

long-term effort. The constant application of sound

geological judgement to ensure that exploration data

at all stages make geological sense, and especially

when deciding whether to abandon a prospect or

press on at higher cost and effort, makes discip-

lined mineral exploration a professionally rewarding

activity (Figure 8).

Feasibility Studies and Mine Development

At some point enough is known about a prospect

through physical exploration to either abandon it or

proceed to further detailed exploration work. A deci-

sion must then be made whether the prospect is worth

the high cost risk of development into an operating

mine. This is the period of feasibility study, when

a multidisciplinary team will rigorously test the pro-

spect against all the criteria for full economic status.

The professional contribution from economic geol-

ogy is the foundation stone upon which the entire

edifice will be built, and confidence in the reliability

of all geological data is essential. The main geological

information will include the following:

Knowledge of the general characteristics of the type

of deposit involved.

Complete mineralogical and chemical information,

including grain size and distribution, and useful

by-products or deleterious constituents, that affect

amenability of the deposit to processing.

The three-dimensional geometry and depth of the

deposit, the physical condition of the ore and its

wall rocks, and other factors affecting amenability

to mining methods.

A set of clear records including reports, geological

and other survey maps, drillhole data and logs, and

assay data.

Mineral resource and reserve estimates, including

estimates of the degree of error attached to such

basic data as sampling methods, sample prepar-

ation and assays, bulk density of ore and gangue

types, the range and distribution of values within

the deposit, and the continuity of mineralization

between drillholes or other exposures.

The process is illustrated by some geological

aspects of the case history of the Lihir gold mine,

situated in a volcanic caldera on the island of Lihir,

Papua New Guinea (Figure 9). After 3 years of

encouraging physical exploration, in 1985, the

epithermal pyritic gold ore failed the test of amenabil-

ity to conventional processing. Tests on an alternative

advanced technology worked well, but meant that

Figure 8 McArthur River, Queensland, Australia. A large stratiform pyritic Zn–Pb sulphide deposit. (A) The gossanous discovery

outcrop, broken open to reveal white secondary Pb and Zn minerals. (B) Polished surface (about 20 mm across) of very fine-grained

stratiform sulphide ore. The 2–5 micron grain size of the base metal sulphides in this large and easily mined deposit made it too

difficult and expensive to process by conventional technology. Photographs: GR Davis.

ECONOMIC GEOLOGY 441

only large-scale mining would provide an economic

return. A further detailed drilling campaign was

followed in 1992 by a feasibility study. This was

based on a data bank that included 56 000 samples

from 83 000 m of core from 343 drillholes, and 4479

specific gravity tests on the 12 ore types recognized.

Four adjacent and partly overlapping ore zones amen-

able to open-pit mining were defined within an area

of 2.0 km by 1.5 km. Using three computerized geos-

tatistical methods to optimize confidence in ore con-

tinuity and distribution of gold values, an overall

mineral resource of 478 million tonnes was estimated.

Mining engineers then designed an open pit to mine

445 million tonnes in 15 years. Of this total, 341 mil-

lion tonnes will be waste rock, 42 million tonnes will

be high-grade ore reserves averaging 6.9 g/t Au to be

processed through the plant, and the remaining

62 million tonnes will be stockpiled as low-grade ore

averaging 2.9g/t Au to be processed during years 15

to 36. Gold production commenced in 1998, some 16

years after initial work on the discovery. As usual in

a new mining area, exploration will continue, with a

view to extending the life of the mining infrastructure

beyond the presently planned project.

Mineral Extraction

Geological services are now widely employed in all

forms of mineral extraction operations, the mainstay

of the minerals industries. The proven usefulness

of applied geology lies in its contribution towards

optimizing the efficiency of the overall production

engineering process, and the geologist is an integral

member of the engineering team and its objectives.

The nature of the work extends the quantitative

aspects of exploration at the feasibility study stage

into an even more detailed and practical realm where

geological predictions are at once put to the test.

Geological services fulfill the following main func-

tions, differing only in detail across the spectrum

from bulk material quarries through industrial min-

erals to metalliferous mines.

Maintaining mineral reserves A new mine is

brought into production with only enough proved

reserve to provide reasonable assurance that the

invested capital will be returned. The greater part of

the detailed exploration of the deposit must continue

over the whole life of the operation. The planning

Figure 9 The open pit gold mine at Lihir Island, Papua New Guinea, under development in 1998, twenty months after inception of

mining operations. The two pits, then about 40 m deep, and centred on ore bodies 1.5 km apart, will merge into a pit about 2 km across,

with a planned depth of 300 m. The background and foreground hills are the walls of the volcanic caldera in which the epithermal gold-

pyrite mineralization occurs. Photograph by courtesy of Rio Tinto PLC. Reproduced with permission from Evans AM (1995) Introduction

to Mineral Exploration. Oxford: Blackwell p. 34.

442 ECONOMIC GEOLOGY

and execution of this vital work is the special re-

sponsibility of the geologist, as part of long-term

management planning. It calls for skills in detailed

geological mapping at scales up to 1/250, knowledge

of sampling theory and practice, and competence in

computerized data manipulation.

Services to the mining department Clean mining

and low production costs depend on physically de-

fining in the greatest detail the three kinds of

material in a deposit – waste that must be dumped,

payable ore or feed that goes to the processing

plant, and marginal material that may be stockpiled

for future processing. This daily task of the geo-

logist at the working faces finalizes the preliminary

outlines predicted from drillholes, sampling and

assaying, and contributes also to quality control at

the processing plant and towards planned pro-

duction targets. This definitive work is as important

to product quality and cost in a cement raw materials

quarry as it is in an underground vein gold mine.

Mining procedures rely also on information from

rock mechanics, a specialized subject in which

knowledge of the detailed structural geology of the

deposit is linked with engineering parameters. This

overlap with engineering geology occurs also in

hydrogeology, as control of groundwater is important

in nearly all mining operations.

Services to mineral processing plants Improvements

in mineral recovery and efficiency over the life of a

deposit may be brought about not only by processing

technology, but by awareness of changes in the

geological conditions to which the plant is tuned.

The geologist is in the best position to forecast and

make known changes in run-of-mine deliveries, such

as grade and mineral composition of the ore, or clay

content of the gangue, that are expected in long-life

operations, and which upset the routine best

performance of the processing plant.

Other engineering services Geological advice is

often called for, especially in remote mining locations,

in selecting sites for buildings, works, tailings dis-

posal, stockpiles, etc., to select the best foundation

conditions and especially to ensure that permanent

works are not built in places that would sterilize

future mineral resources. Geologists are also well

placed to advise concerning natural hazards such as

earthquakes, and landslides in mountainous terrain.

Even in so curtailed a summary, it must be men-

tioned that the overall usefulness of applied geology

rests heavily on effective communication by geolo-

gists with the working industrial community. Good

personal relationships at all levels are helpful, but

clearly written reports that can be readily understood

by non-geologists are essential.

End of Life of Deposit

In the environmentally conscious world of the

twenty-first century, few mineral deposits are de-

veloped to the stage of extraction without a searching

environmental impact investigation and statement.

Similarly, when mineral workings reach the inevitable

end of their productive lives, the impact of the closure

may be planned so as to reduce deleterious effects and

optimize beneficial effects upon the environment and

the community that has grown around the deposit.

For example, the Lihir gold mining project (men-

tioned in the feasibility study above) has from incep-

tion of operations provided finance and facilities for

periodic review and action on environmental and

community effects. Applied geology has entered the

new professional field of environmental science in an

age of positive and proactive approach.

Conclusion

From time to time ill-founded alarms have arisen that

world resources of some minerals will be insufficient

to meet mankind’s growing demands. An influential,

but ill-advised report of the Club of Rome in 1972, for

instance, concluded that the limiting factor to world

economic growth would be mineral resource deficien-

cies. Led by applied economic geology, exploration

within the minerals sector has in practice demon-

strated an abundant resource base open to ever-im-

proving mining and processing technologies. There is

no indication that future needs for traditional and new

materials will not be met. In a crowded world, the

concept of transition to sustainable development has

become a serious global issue that geological science is

well placed to appreciate. In the spirit of this new drive

forward, the world’s leading mining companies

have proactively organized the Global Mining Initia-

tive, a programme to ensure that the issues relevant

to the extractive industries are positively identified

and addressed. Both the theoretical and practical

aspects of economic geology are involved in this

broadening framework to its contribution in dis-

covering and extracting the precious non-renewable

mineral resources of our world.

Elsevier Encyclopedia of Geology - vol I A-E

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