ugrc 140 (earth resources)

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MINERAL AND ROCK RESOURCES

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Page 1: Ugrc 140 (earth resources)

MINERAL AND ROCK RESOURCES

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OVERVIEW Purpose and Objectives of lesson Introduction Elements as building blocks What are minerals? Types of mineral deposits Minerals extraction Economic factors in mining Environmental consequence of mining Conclusion

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Purpose and Objectives

This lesson is to enable you understand what minerals/ores are, the various ore deposits and extraction

It is expected that by the end of the lesson you should be able to …..

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Purpose and Objectives State the characteristics of minerals Identify the various formations of minerals State and explain the types of mineral

deposits Differentiate between metallic and non-

metallic minerals State the mineral extraction methods Develop the understanding of the

environmental problems associated with minerals extraction

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Introduction

There is the understanding of the existence of minerals

More detailed knowledge is required to understand the various categories of minerals/deposits and the environmental impact of mining

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Elements and the Periodic Table

Elements are the basic building blocks of minerals

Over 100 elements are known

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The Periodic Table

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What are Minerals

1. Naturally occurring2. Solid substance3. Orderly crystalline structure4. Definite chemical composition5. Generally considered inorganic

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How many minerals are there?

About 4000 minerals are listed but relatively few are popular due to their pleasing appearance

Generally composed of more than one element or compound

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Native Elements

Minerals made up of only one element

E.g. copper, gold, mercury, silver

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Formation of mineralsCrystallization from magma

Precipitation from solution

Recrystallization as a result of high pressure and temperature

Crystallization from hydrothermal solutions

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Minerals formed as a result of Crystallization of Magma

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Metallic and non-metallic minerals

Metallic If the surface of the mineral reflects light

e.g. Copper, Gold, Pyrite, Iron, Aluminum Non-metallic

If the surface of the mineral does not reflect light

e.g. Sulfur, Halite (rock salt),Feldspar, quartz, calcite

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Pyrite (Fool’s Gold) is Metallic

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Native Copper

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RocksThey consist of many individual

mineral grains firmly held together in a solid mass

Types of RocksIgneousSedimentarymetamorphic

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Ore DepositsAn ore is a rock in which a valuable mineral

or metal occurs at the concentration sufficiently high, relative to average rocks, to make it economically worth mining

The value of a mineral or metal extracted and its concentration in a particular deposit are the major factors determining the profitability of mining a specific deposit

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Definition of a mineral or rock resource

Mineral or rock resources are any material of value that are derived from rocks or minerals

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Definition of a mineral or rock resource

The resources can be separated into three groups

Metallic

E.g. gold, platinum, silver, copper, iron, aluminum, tin, lead, uranium)

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Definition of a mineral or rock resource

Non-metallic

E.g. diamonds and other precious stones, salt, gypsum, potash

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Definition of a mineral or rock resource

Rocks

E.g. marble, cut granite, crushed stone, sand and gravel

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Mineral ResourcesNon-metallic Minerals

Sulfur, Gypsum, Coal, Barite, Salt, Clay, Feldspar, Gem Minerals, Abrasives, Borax, Lime, Magnesia, Potash, Phosphates, Silica, Fluorite, Asbestos, Mica

Metallic MineralsFerrous: Iron and Steel, Cobalt, Nickel Non – ferrous: Copper, Zinc, Tin, Lead,

Aluminum, Titanium, Manganese, Magnesium, Mercury, Vanadium, Molybdenum, Tungsten, Silver, Gold, Platinum

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Types of Mineral Deposits

Igneous rocks and magmatic depositsHydrothermal oresMetamorphic depositsSedimentary deposits

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Types of Mineral DepositsWeathering-leaching away of unwanted

minerals leaving a residue enriched in some valuable metal

Placer -ores concentrated by stream or wave action on the basis of mineral densities or resistance to weathering

All require a concentration mechanism

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Igneous rocks and magmatic deposits

Gravity causes early-crystallizing dense minerals to sink to bottom of magma chamber

Minerals may also float to the top if they are less dense than magma

Chromite, magnetite, and platinum-group mineral deposits often formed in this way

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Magmatic segregation

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Diamonds Diamonds are formed at very high pressures

Usually require 100-200 km depth

Brought rapidly to the surface by Kimberlite

magmas.

These are gas-rich magmas that explode on their

way to the surface. May erupt at very high

velocities.

Only need a few diamonds per ton of rock to make

the rock an ore.

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Hydrothermal deposits Hot waters percolating through the rocks

surrounding an intrusion leach elements from them

Later deposits these elements in minerals that crystallize when the fluids cool as they approach the surface.

Often this process forms veins rich in sulfide minerals that contain metals such as Cu, Pb, Zn, Au, Ag, Pt, and U

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Mineral-Rich Hot Water Seeps into Rock Fractures

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Metamorphic deposits

Increasing pressure and temperature creates new minerals, sometimes in great abundance if the composition is right

Generally, metamorphism produces concentrations of useful minerals, rather than a concentration of a specific element.

Examples include graphite, asbestos, and garnet (abrasive).

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Sedimentary Deposits

Processes associated with the formation of sedimentary rocks can also produce economic mineral deposits

E.g. Banded iron oresIron-rich layers alternating with

silicate - or carbonate-rich layers

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Sedimentary DepositsBanded iron ores

Mode of formationIn early earth's history, atmosphere was

reducing (oxygen poor).

In reducing environments iron is soluble in water

However, world's oceans contained more oxygen due to the action of one-celled plants, such as algae

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Sedimentary DepositsBanded iron ores

Mode of formationTherefore, the oceans were oxidizing

In oxidizing environments iron precipitates out of solution

So as iron-rich waters entered the oceans the iron precipitated out forming layers of iron-rich sediment and eventually forming rocks

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Sedimentary deposits

E,g. Evaporites: As seawater evaporates in hot, dry

climates dissolved minerals, such as calcite, gypsum and halite, crystallize

Form sediment layers (and rocks) rich in these minerals

Occurs naturally and also in man-made evaporation ponds

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Weathering

  Intense chemical weathering leaches out

most elements

Material left behind is enriched in Al and Fe

Forms bauxite (the ore for aluminum) in lateritic soils

 

 

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Placer deposits

Dense, heavy minerals fall out of suspension when water velocity decreases

This can concentrate a specific mineral in a confined area, and often occurs in streams or in coastal environments

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Placer deposits

The minerals formed in a particular area are transported, sorted, and concentrated by the water, to form a placer deposit

Many gold, tin, and diamond deposits are formed in this way

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Placer deposit

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Metallic ResourcesAbundant Metals

Iron, aluminum, manganese, titanium, silicon, magnesium

Produced by variety of geologic processes

Supplies for future is adequateNot distributed uniformly

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Metallic ResourcesScarce Metals

Comprise less than 0.1% of Earth’s crust (rare conditions concentrate them) (e.g. copper, lead, zinc, gold, and silver)

Fewer deposits, so supplies are more precarious

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End of Lecture 3

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MINERAL AND ROCK RESOURCES

Cont………….

Lecture 4

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Can be classified based on their composition

Classification of Minerals

1. SilicatesSilicon and oxygen combine to form a

structure called the silicon-oxygen tetrahedron. This silicon-oxygen tetrahedron provides the framework of every silicate mineral.

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Classification of Minerals

2. CarbonatesMinerals that contain the

elements carbon, oxygen, and one or more other metallic elements

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Classification of Minerals

3. Oxides Minerals that contain oxygen and

one or more other elements, which are usually metals

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Classification of Minerals

4. Sulfates and Sulfides Minerals that contain the element

sulfur

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Classification of Minerals

5. Halides Minerals that contain a halogen

ion plus one or more other elements

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Classification of Minerals

6. Native elements Minerals that exist in relatively

pure form

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Sulfides

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Native Copper

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Properties of Minerals

StreakThe color of a mineral

in its powdered form

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Properties of Minerals

LusterUsed to describe how

light is reflected from the surface of a mineral

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Pyrite (Fool’s Gold) Displays Metallic Luster.

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Properties of Minerals

Crystal formThe visible expression

of a mineral’s internal arrangement of atoms

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Quartz Often Exhibits Good Crystal Form.

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Properties of Minerals

HardnessIs a measure of the

resistance of a mineral to being scratched

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Properties of Minerals

Mohs scaleConsists of 10

minerals arranged from 10 (hardest) to 1 (softest)

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Mohs Scale of Hardness

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Properties of Minerals

CleavageThe tendency of a

mineral to cleave, or break, along flat, even surfaces

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Mica Has Cleavage in One Direction

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Properties of MineralsFractureMinerals that do not

show cleavage when broken are said to fracture

Fracture is the uneven breakage of a mineral

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Conchoidal Fracture

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Properties of Minerals

DensityIs a property of all

matter and it is the ratio of an object’s mass to its volume

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Prospecting, Exploration and Mining

Prospecting

The act of looking for a spot where there is

valuable ore in order to mine there

Very low impact work

involved

Mining

The extraction of the ore from such a place

Great impact work also involved

Exploration

Involves many different methods in looking for spot of mineralization

Great impact work involved. Drilling,

trenching, etc.

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Prospecting and Exploration

Satellite and Aerial Photography

Remote Sensing Geological Mapping Magnetic Mapping Gravity Mapping Radioactivity Mapping

Geochemical Sampling

Electrical Sounding

Ground-Penetrating Radar

Seismic Methods

o Reflection : Detailed but expensive

o Refraction : Cheap but not Detailed

Core Sampling and Well Logging

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Mineral extractionMineral resources are typically extracted from rocks using a variety of techniques: • Strip mining• Quarrying• tunnel mining • heap-leaching • Flotation • Crushing - treatment by chemicals to extract

metal from rock "flour" • Smelting

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Economic Factors in Mining

Richness of OreQuantity of OreCost of Initial DevelopmentEquipment, Excavation, Purchase of RightsOperating Costs: Wages, Taxes,

Maintenance, Utilities, RegulationPrice of the ProductWill Price Go up or down?

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Life Cycle of a Mine

ExplorationDevelopmentActive Mining

o Excavation o Crushing, Milling, Flotation, Chemical

Separation o Smelting and Refining o Disposal of Waste (Tailings)

Shut-down

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Issues in Mineral ExploitationWho Owns (or should own) minerals?

Landowner, Discoverer, Government

Unclaimed Areas: Sea Floor, Antarctica

Who Controls access for Exploration?o Nobody is obligated to let someone onto their

property to prospect. However, they must allow access if someone owns the subsurface rights.

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Safety Mine Wastes Pollution Dust Noise Sulfur Acid Rain Acid Runoff Dissolved Metals

(Fe, Cu, Zn, As...)

Environmental Problems

Exploration Construction and

Operation

Economic Impact "Boom and Bust"

Cycles

Problems of Mining

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POSITIVE IMPACT

• Creation of Employment

• Provide raw materials for the construction Industries

• Encourage cottage Industries

• Generate income

• Earn revenue for the government

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Environmental impacts of mineral and rock exploitation

Mining is any activity that involves excavating the earth surface for the purpose of exploiting and processing the mineral wealth for economic and industrial development

both for local and export markets. This process normally has a negative impact on the

environment.

There are two main methods of mining; Underground mining Open cast mining

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Underground Mining This refers to any sub-surface vertical or

horizontal excavations that are made for the extraction of minerals.

This method has little effect on the vegetation and the ecosystem in general.

Open-casting Mining This refers to uncovered excavations made on

the ground for the purpose of mineral or rock exploitation such as the open quarries, pits, trenches, etc.

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Impact of Mining on the Environment

Any mining operation draws ores and other raw materials from the earth

This has a direct impact on the biological and physical environment

The nature and degree of impacts vary widely depending on the location and type of operation.

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Impact of Mining on the Environment

However, mining operations will generally affect the hydrological functions and hence water quality.

This is because mining interferes with the ground water table by lowering it and introducing pollutants to the aquifer

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Impact of Mining on the Environment

Effects can either be physically or chemically influenced depending on the mining activities

Disturbs land by removing surface vegetation and changing topography

Affects hydrological functions and water quality, causes soil erosion and stream sedimentation that cause death of trees along river banks

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Impact of Mining on the Environment

Produces dustLowers the water tables Destroys wildlife habitat. The additional vehicular traffic around a

mine site brings noise and increases wear on the roads.

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ENVIRONMENTAL CONSEQUENCE OF

MINING

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ACID MINE DRAINAGEMining activity occurs in areas that have

high concentrations of economically important materials, such as gold, silver, copper, cobalt, iron, lead, and zinc

These areas may also contain high concentrations of noneconomic elements such as arsenic, selenium, mercury, and sulphur, whose presence is closely tied to the formation of the heavy metals

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ACID MINE DRAINAGE

Many of these economic and noneconomic elements can be hazardous if released into the environment

Even without mining, mineralized areas can naturally adversely affect the environment.

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ACID MINE DRAINAGE A common process that results in

dispersion of elements from a mineralized site is acid rock drainage.

When acid drainage results from mining activity, it is more specifically called acid mine drainage.

As the name implies, acid mine drainage is the formation and movement of highly acidic water rich in heavy metals

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ACID MINE DRAINAGE This acidic water is formed principally

through chemical reaction of surface water (rainwater, pond water) and shallow subsurface water with rocks that contain sulphur-bearing minerals (e.g., pyrite), resulting in sulphuric acid.

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ACID MINE DRAINAGE Heavy metals can be leached from rocks

that come in contact with the acid, a process that may be substantially enhanced by bacterial action.

The resulting fluids may be highly toxic and when mixed with groundwater, surface water, and soil may have harmful effects on humans, animals and plants.

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ACID MINE DRAINAGE Mining accentuates and accelerates natural

processes. The development of underground

workings, open pits, ore piles, mill tailings, and spoil heaps and the extractive processing of ores enhance the likelihood of releasing chemical elements to the surrounding area in large amounts and at increased rates relative to unmined areas

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ACID MINE DRAINAGE

Studies describing both the extent and effect of acid drainage both in unmined mineralized areas and in areas containing inactive and abandoned mines are required if the environmental impact of heavy metals is to be understood.

Studies in unmined mineralized areas describe the natural, baseline chemical characteristics and variations of the mineralized areas.

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ACID MINE DRAINAGE

By combining these baseline studies with information from areas containing inactive and abandoned mines, it is possible to provide:An assessment of the intensity and extent of

environmental impact due to acid mine drainageAn understanding of natural processes to detect and

predict where and when acid mine drainage might occur.