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8/18/2019 Chris Fleming Pp t

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1Lakefield Research

GOLD EXTRACTION

TECHNOLOGY DEVELOPMENTSAND THEIR IMPLICATION TO

PROFITABILITY AND SUSTAINABILITY

By: C. A. Fleming

SGS LAKEFIELD RESEARCH


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2Lakefield Research

CUMULATIVE WORLD GOLD

PRODUCTION (TONS)

Total World

120,000

100,000

80,000

60,000

40,000

20,000

0

1850 1875 19501900 1925 1975 2000

1900-1970

60,000 tons

800 t/y

1490 - 1900

15,000 tons

35 t/y

Production110,000 tons

1970-1992

35,000 tons

1,600 t/y

Cumulative

WorldProduction

(tons)

YEAR


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3Lakefield Research

HISTORY OF THE

CYANIDATION PROCESS

Cyanidation process patented in 1887

First used:

−Crown Mine, New Zealand 1889

− Robinson Deep, S.Africa 1890

−Consolidated Mercur, USA 1891

− El Oro, Mexico 1900

−

La Belliere, France 1904


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HISTORY OF THECYANIDATION PROCESS

Increased gold recovery from 90%

Vital for the development of theSouth African gold industry, whichhad low gold grades, very finely

disseminated in silica rock (gravityrecovery ~20%, cyanidation >95%)



FLOWSHEET OF A MERRILL CROWE

GOLD PLANT (pre 1980)Leaching

(16-48 Hours)MillingCrushingOre Stock Pile

Cyanide

Solid/LiquidSeparation

(CCD or Filter)

Cementation

ZincPowder

Tailings

Smelting

Filtration

Dore

VacuumDeaeration

Calcining

AirAirPregnant

Leach Liquor

ClarificationWash



CUMULATIVE WORLD GOLD

PRODUCTION (TONS)

Total World

120,000

100,000

80,000

60,000

40,000

20,000

0

1850 1875 19501900 1925 1975 2000

1900-1970

60,000 tons

800 t/y

1490 - 1900

15,000 tons

35 t/y

Production110,000 tons

1970-1992

35,000 tons

1,600 t/y

Cumulative

WorldProduction

(tons)

YEAR



THE LAST THIRTY YEARSKey changes

Gold extraction technology

Characteristics of gold ore bodies

The demographics of goldproduction

The price of gold

Gold’s role in the market place



ERA OF MAJOR TECHNICAL

DEVELOPMENT-1970-1990

Heap leaching

Activated carbon processes

Improved refractory ore

treatment processes:

Fluid bed roasting

Whole ore roasting

Pressure leaching

Biological oxidation


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9Lakefield Research

HEAP LEACHING

• Originally developed for leaching low-gradeuranium and base metal (copper) deposits.

• Adapted for treatment of low-grade gold ores by

USBM in the 1970’s.

• Lime/cement agglomeration process developedby USBM allowed crusher fines and high clay

ores to be treated.


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HEAP LEACHING

• First large-scale gold heap leach at Carlin, Nevada, in1970.

• Integrated heap leach/carbon adsorption circuits

developed in the 1980’s.• Gold recoveries generally only in the 50-80% range,

but cut-off grades lowered to


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HEAP LEACHING

Higher grade (2-3 g/t) operations produce goldfor $50-100/oz.

Gold leached by cyanidation

Accounts for ~400 t (~16%) of mine production

Not suited to hard, impervious or refractory ores


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TYPICAL HEAP

LEACH OPERATION


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ACTIVATED CARBON

PROCESSES

CIP/CIL/CIC


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FLOWSHEET OF A MODERN

CIP GOLD PLANT (post 1980)Leaching

(16-48 Hours)

MillingCrushingOre Stock Pile

Cyanide

Carbon

Advance

4-8 CIP

Adsorption

Stages

Carbon

Elution

Carbon

Reactivation

Tailings

+-

SmeltingElectrowinningDore

GoldEluate

CarbonAcidWash

CarbonFines

SpecialTreatment

PulpAdvance


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ADVANTAGES OF CIP/CIL

versus MERRILL-CROWE

• No solid-liquid separation step-lower capex, opex -better gold recovery

• Insensitive to most impurities• Insensitive to cyanidation conditions• Mechanically robust process

• Insensitive to process upsets• Versatile/able to treat most feed stocks


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HISTORICAL DEVELOPMENT

EARLY 1980’s

At least 20 CIP plants built in South Africa, ranging incapacity from 5000 to 2,000,000 tons per month, with feedmaterial ranging from whole ore to concentrates totailings.

Demonstrated that the process could be applied to almostany feed, with lower capital and operating costs andhigher gold recovery than Merrill -Crowe.

Developed engineering know-how and new technology forlarge-scale CIP.

Developed fundamental knowledge of adsorption, elution

and regeneration processes.


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HISTORICAL DEVELOPMENT

1980’s, 1990’s

Process spread rapidly through every gold producing

country in the world accounting for practically everynew gold plant in the last 25 years. More than 60% ofworld gold production (~1800 tpa) is now by

CIP/CIL/CIC.


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CHANGING TRENDS IN WORLD

GOLD PRODUCTION (1970-1990)

0

20

40

60

80

Percentage

of World

Gold

Production

(%)

Merrill Crowe Refractory Heap Leach CIP/CIL/CIC

1970

(1300 tons total)

1990

(2200 tons total)


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MARKET FORCES

Gold price “fixed”, 1934-1968

Declining profitability and production, 1955-1970

Release of gold price from gold “standard” in 1968

“Boom” times in the industry, 1970-1985

Fantastic growth in USA, Canada, and Australiaversus declining production in RSA and USSR


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CHANGING LOCATION OF

WORLD GOLD PRODUCTION


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MARKET FORCES

To a greater extent than at any time sincethe 1960s, the price of gold today is afunction of supply and demand marketforces.

The volume of gold traded each year is

orders of magnitude greater than new mineproduction.


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MARKET FORCES

The price of gold is fairly insensitive to globalpolitical and economic factors such as:

Political crises

The threat of war

Natural catastrophes

The price of oil/energy

The fear of inflation


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MARKET FORCES

Negative Influences on the

Gold Price in the 1990’s

Political/economic stability in the first world

Central bank sales creating “unnatural” supply

Gold never truly “disappears”. Scrap recyclingcontributes ~20% of supply

Gold mine production increased ~5% pa in the1990’s. It is now stable.

Hedging


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MARKET FORCES

Positive Influences on the

Gold Price in the 1990s

Developing countries (particularly India and China)

are becoming wealthier.

Gold production in South Africa and Russiadeclining rapidly (1200t in 1970, ~600t in 2000)

Fabrication demand (jewelry, electronics) exceedsproduction from gold mines by ~1000t per annum.


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THE NEGATIVE FORCES

ARE WINNING!

The gold price has trendedsteadily downward

through the 1990’s


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CONCLUSIONS

GLOBAL METALLURGICAL TRENDS

The primary gold production industry is in a crisis due to:

Declining gold prices (in local currencies)

Declining gold reserves in the ground

Increasing production cost

The cost of gold production will increase due to:

The need for deeper mining

Lower gold grades More refractory mineralization

More stringent environmental, social and political

responsibilities


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CONCLUSIONS

GLOBAL METALLURGICAL TRENDS

New technology will make a limited impact in theareas of:

Cyanide recovery

Alternative leaching chemistries

(thiosulphate, platsol)

In situ mining/processing

But will not arrest the trend of declining production.

Cyanide leaching and carbon adsorption will continueas “processes of choice” in the 21st century.


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CONCLUSIONS

GLOBAL ENVIRONMENTAL/SOCIAL TRENDS

Despite its extreme toxicity, cyanide can be handledvery safely in operating plants and destroyed veryefficiently in tailings.

Despite this, the anti-cyanide lobby will gainmomentum around the world, and more countries willban its use in the years ahead.

Alternatives to cyanide exist, but they are not asefficient as cyanide and also have many as yetunanswered environmental issues to deal with.


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CONCLUSIONS

GLOBAL MARKET TRENDS

Gold production from primary sources has peaked at2500-2800 tpa and will decline through the 21st century.

There will be further consolidation in the gold mining

industry, as mining companies seek to address themetallurgical and environmental problems, while trying tomeet shareholder expectations.

Increasing proportions of gold supply will come fromrecycling and central bank reserves (mining currentlysupplies ~70% of demand).


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CONCLUSIONS

GLOBAL MARKET TRENDS

The price will increase in real terms as a result, butwill ultimately be dictated by people’s appetite forgold jewelry, which takes 80-90% of supply.

This scenario could be upset by a collapse of theUS$ and a global flight from paper currencies to gold- in which case the price of gold could increasedramatically.

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