Eco. Lec. No.1 & 2 , 2011

8/13/2019 Eco. Lec. No.1 & 2 , 2011

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Economic Geology

Lec. No. 1 & 2

Introduction to Economic Geology

!Introduction and aims

! What is economic geology?

! Brief history of Economic geology

! A simple classification scheme for mineral deposits

! Magmatic Ore Deposits

! What make a viable mineral deposit?

! Terminology

! Some relevant compilations: [Periodic table of the elements, Table

of the main ore and gangue minerals]

Topics

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Introduction and Objectives:

Given the unprecedented growth of human population over the past

century, as well as the related increase in demand for and production of

natural resource, it is evident that understanding the nature, origin, and

distribution of the world's mineral deposits remains a strategic topic.

The discipline of economic geology which covers all aspects pertaining

to description and understanding of mineral resource is therefore, one

which traditionally has been and should remain a core component of the

University earth science curriculum.

This lecture intended to provide a comprehensive glossary term used

in economic geology and brief history of economic geology as well as

classification scheme for ore deposits.

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What is economic geology?

Economic geology involves the study of mineral resources and their

geological environments. You will learn about the geological

processes that lead to the formation of ore deposits, and how we

explore for new deposits using geochemistry and geophysics.

Economic geology is concerned with earth materials that can be used

for economic and/or industrial purposes. These materials include1- precious and base metals,2- nonmetallic minerals, construction-

grade stone,3- petroleum, coal, and 4- water.

The term commonly refers to metallic mineral deposits and mineral

resources.

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Brief history of Economic geology

These Ages refer to different periods in human cultural development

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A classification scheme for ore deposits

There are many different way of categorizing ore deposits, and the

best classification schemes are probably those that remain asindependent of genetic linkage as possible these are:

Igneous, Metamorphic, and Sedimentary ore deposits (Fig 1, a, b)

Einaudi, (2000), stated that all mineral deposits can be classified

into three types based on process, namely

magmatic deposits, hydrothermal deposits, and surfacial deposits

formed by surface and groundwater.

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Fig 1 classification of the principle rock types (a) and an analogous, but

much simplified, classification of ore deposit types (b) photograph show

interplay between ore forming processes

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Magmatic Ore Deposits

Magmatic ore deposits are those which are formed during

crystallization of a magma, deep underground. The host rock forthe mineralization can range from ultramafic to felsic. The deposit

can consist of massive ores in some cases, and disseminations of rare

minerals in others. In the case of more massive ores, there are three

primary means of concentrating minerals of value during the

formation of these deposits (Fig. 3.38):

• gravitational settling

• differentiation

• immiscible separations

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immiscible separations

Oil and water don’t mix …

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High T

Desirable element preferentially concentrated into low-volume melt

Low T

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• Types of Immiscible Melts

•Oxide melts can be rich in Fe (Fe2O3, hematite) and Ti(FeTiO3, ilmanite).

• Sulfide melts can be rich in Ni, Cu, and the platinum-group elements, in addition to iron sulfur (FeS,

pyrrhotite).

• Carbonate melts can be rich in niobium, tantalum, rareearths, copper, thorium, and phosphorous.

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What make a viable mineral deposit?

Table 1 average crustal abundance for selected metal and typical concentration

factors that need to be achieved in order to produce a viable ore deposits

(From Evan, A.M, 1993) Note: 1 ppm is the same as 1 gt -1

* 12505 gt -14 ppbAu

* 1000

* 2500

* 700

* 130

* 180

* 10* 4

Approximate

concentration

factor

5 gt -15 ppbPt

0.5 %2 ppmSn

5 %70 ppmZn

1 %75 ppmNi

1 %55 ppmCu

50 %5.60%Fe30 %8.20%Al

Typical exploitable

grade or \

(Av.minimum exploitable

grade)

Average Crutal

abundance

Elements

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Terminology:

Ore: any naturally occurring material from which a mineral or

aggregate of value can be extracted at profit.

To be ore must be ,1-Payable, 2- Involve economic consideration, 3- involving geologic

consideration.

Economic Consideration:

• Mineral exploration

• Economic evaluation

• Mine development• Mine extraction

• Ore dressing

• Smelting

• Refining

• Marketing

• Power supplies• 10-Eqipments cost

• 11-water supplies

• 12-Transport metal cost

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Gangue minerals: Usually worthless, non metallic minerals of adeposit that may be:

Introduced minerals, b- The inclosing rocks c- are discarded inthe treatment of the ore

Economic minerals: Are natural resources which, once extracted

and used, are not renewable.

Grade: The concentration of an element in a mineral deposit is termed

grade usually expressed as % or in ppm

Cut-off grade: The lowest percentage at which deposits can beeconomically worked is termed cut-off grade.

Tenor: The grade or amount of commodity actually present

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Factors controlling cut-off grade limit:

A-Geological factor, B-Geochemical factors, C-Other factors

The point B and C depend on the following factors:

1-By product2-Undesirable substance

3-Mineralogical form

4-Grain size and shape

5-Size and shape of ore body

6-Mineral charactersThe other factors controlling the classification of Cut-off grade are:

• 1-Commodity price

• 2-Cost of capital

• 3-Location

• 4-Environmental consideration

• 5-Taxation

• 6-Political factors

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Syngenetic: refers to ore deposits that form at the same time as their hostrocks.

Epigenetic: refers to ore deposits that form after their host rocks.

Hypogene: refers to mineralization caused by ascending hydrothermalsolution.

Supergene: refers to mineralization caused by descending solutions.

Generally refers to the enrichment process accompanying the

weathering and oxidation of sulfide and oxide ores at or near the

surface.

Metallogeny: the study of genesis of mineral deposits, with emphasis

on their relationship in space and time to geological features of the

Earths crust.

Metallotect:any geological, tectonic, lithological, or geochemicalfeature that has played a role in the concentration of one or more

elements in the Earths crust.

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Metallogeneic Epoch: a unit of geologic time favorable fordeposition of ores or characterized by a particular assemblage of

deposit types.Metallogenic Province: a region characterized by a particular

assemblage of mineral deposit type.

Epithermal: hydrothermal ore deposits formed at shallow depth (lessthan 1500 m) and fairly low temperature (50-200 !C)

Mesothermal: hydrothermal ore deposits formed at intermediatedepth (1500 – 4500 m) and temperature 200 - 400!C)

Hypothermal: hydrothermal ore deposits formed at substantial depth

(grater than 4500 m) and elevated temperature (400-600 !C)

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Periodic table of the elements:

Fig 2 Periodic table showing the 92 geologically relevant elements classified on

the basis of their rock and mineral associations ( From Robb, 2005)

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Common Ore and Gangue mineral

1- Native element

Metals Non-Metals

Gold - Au Sulfur –

S

Silver - Ag Diamond – C

Platinum - Pt Graphite - C

Palladium - Pd

Copper - Cu

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2- Halides

•

Halite –

NaCl• Sylvite – Kcl

• Chloragyrite – AgCl

• Fluorite - CaF2• Atacmite Cu2 Cl(OH)3

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4- Oxides:

Oxides

Cuprite- Cu2OHematite – Fe2O3

Illminite – FeTiO3

Hercynite – FeAl2O4

Gahnite – ZnAl2O4

Magnetite – Fe3O4

Chromite –

FeCr2O4

Rutile – TiO2

Anatase – TiO2

Pyrlucite – MnO2

Casseterite – SnO2

Uraninite –

UO2Thorianite – ThO2

Hydroxide (or Oxyhydroxide)

Geothite FeO(OH)

Gibbsite – Al(OH)3

Boehemite – MnO(OH)

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Salts-Oxy- 5

Azurite Cu3(OH)2(CO3)2

Cerussite PbCO3

Simthonite ZnCo3

Epsomite

MgSO4.7H2O

Rhodochrosite MnCO3

Malachite Cu2(OH)2 CO3

Gypsum

CASO4.2H2O

Siderite FeCO3

Apatite

Ca5(PO4)3(F,Cl,OH)

Alunite

KAl3(OH)6

(SO4)2

Ankerite CaFe(CO3)2

Monazite

(Ce,La,Th)PO4

Anhydrite CaSO4Wolformite

(Fe,Mn)WO4

Dolomite CaMg(CO3

Carnotite

K2(UO2)(VO4)2.3H2O

Xenotime YPO4Barytes BaSO4Scheelite

CaWO4

Calcite CaCo3

Vanadates PhosphatesSalfatesTungestatesCarbonates

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6- Silicate

Spodumene,

Wollastonite

Biotite, ChloriteEpidoteTourmalineGarnet,

Sillimanite

Albite,Orthoclase

ChrysocollaTremoliteKaolinite,

Montmorilionite,

Illite,Talc

LawsoniteBerylZirconOuartz

Unknown

structure

Ino (Chain) Phyllo(Sheet)Soro (Di)Cyclo

(Ring)

Neso (Ortho)Tekto (Framework)

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References:

! Evans, A.M., 1993, Ore Geology and Industrial Minerals

An Introduction, Third Edition, Blackwell Publishing,

PP.84-95

! Jensen, M. L and Batman, A. M., 1979, Economic mineral

deposits 3rd edition, New York, 593p.

!Robb, L., Introduction to ore-forming process, (2005)Blackwell Publishing, 373p.

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End of the Lecture

Good Luck

Instructor

Dr. Tola A. Mirza

Assistant Professor

[email protected]

Eco. Lec. No.1 & 2 , 2011

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Transcript of Eco. Lec. No.1 & 2 , 2011