Ugrc 140 (earth resources)

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
2

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
…..

3

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
4

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

5

Elements and the Periodic Table

 Elements are the basic building
blocks of minerals
 Over 100 elements are known

What are Minerals

1. Naturally occurring
2. Solid substance
3. Orderly crystalline structure
4. Definite chemical composition
5. Generally considered inorganic

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

Native Elements

Minerals made up of only one
element
E.g. copper, gold, mercury, silver

Formation of minerals
Crystallization from magma
Precipitation from solution
Recrystallization as a result of
high pressure and temperature
Crystallization from
hydrothermal solutions

Minerals formed as a result of Crystallization
of Magma

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

Pyrite (Fool’s Gold) is
Metallic

Rocks
They consist of many individual
mineral grains firmly held together
in a solid mass
Types of Rocks
Igneous
Sedimentary
metamorphic

Ore Deposits
 An 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

Definition of a mineral or rock
resource
Mineral or rock resources
are any material of value
that are derived from rocks
or minerals

resource
The resources can be separated into three
groups

Metallic
E.g.
gold, platinum, silver, copper,
iron, aluminum, tin, lead, uran

resource

Non-metallic
E.g. diamonds and other
precious
stones, salt, gypsum, potash

resource

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

Mineral Resources
 Non-metallic Minerals
Sulfur, Gypsum, Coal, Barite, Salt, Clay, Feld
spar, Gem
Minerals, Abrasives, Borax, Lime, Magnesia
, Potash, Phosphates, Silica, Fluorite, Asbest
os, Mica
 Metallic Minerals
Ferrous: Iron and Steel, Cobalt, Nickel
Non – ferrous:
Copper, Zinc, Tin, Lead, Aluminum, Titaniu
m, Manganese, Magnesium, Mercury, Vana
dium, Molybdenum, Tungsten, Silver, Gold,
Platinum

Types of Mineral Deposits

Igneous rocksand magmatic deposits
Hydrothermal ores
Metamorphic deposits
Sedimentary deposits

Types of Mineral Deposits
 Weathering-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

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

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.

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

Mineral-Rich Hot Water Seeps
into Rock Fractures

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).

Sedimentary Deposits
 Processesassociated with the
formation of sedimentary rocks can
also produce economic mineral
deposits
 E.g. Banded iron ores
 Iron-rich layers alternating with
silicate - or carbonate-rich layers

Banded iron ores

Mode of formation
In 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

Banded iron ores

Mode of formation
Therefore, 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

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

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

Placer deposits
 Dense,heavy minerals fall out of
suspension when water velocity
decreases
 Thiscan concentrate a specific
mineral in a confined area, and
often occurs in streams or in coastal
environments

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

Metallic Resources
Abundant Metals
Iron, aluminum, manganese,
titanium, silicon, magnesium
Produced by variety of geologic
processes
Supplies for future is adequate
Not distributed uniformly

Metallic Resources
Scarce 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

Lecture 4

Cont………….

Classification of Minerals
Can be classified based on their
composition
1. Silicates
Silicon and oxygen combine to form a
structure called the silicon-oxygen
tetrahedron. This silicon-oxygen
tetrahedron provides the framework of
every silicate mineral.


2. Carbonates
Minerals that contain the
elements carbon, oxygen, and one
or more other metallic elements


3. Oxides
 Minerals that contain oxygen and
one or more other
elements, which are usually
metals


4. Sulfates and Sulfides
 Minerals that contain the element
sulfur


5. Halides
 Minerals that contain a halogen
ion plus one or more other
elements


6. Native elements
 Minerals that exist in relatively
pure form

Properties of Minerals

Streak
The color of a mineral
in its powdered form


Luster
Used to describe how
light is reflected from
the surface of a mineral

Pyrite (Fool’s Gold) Displays
Metallic Luster.


Crystal form
The visible expression
of a mineral’s internal
arrangement of atoms

Quartz Often Exhibits
Good Crystal Form.


Hardness
Is a measure of the
resistance of a mineral
to being scratched

Mohs scale
Consists of 10
minerals arranged from
10 (hardest) to 1
(softest)

Cleavage
The tendency of a
mineral to cleave, or
break, along flat, even
surfaces

Mica Has Cleavage in One Direction

Fracture
Minerals that do not
show cleavage when
broken are said to fracture
Fracture is the uneven
breakage of a mineral

Density
Is a property of all
matter and it is the ratio
of an object’s mass to its
volume

Prospecting, Exploration and
Mining
Prospecting Exploration Mining

The act of looking for a Involves many different
spot where there is methods in looking for
spot of mineralization The extraction of the ore
valuable ore in order to
from such a place
mine there

Great impact work
Very low impact work involved.
involved Drilling, trenching, etc.
Great impact work also

Prospecting and Exploration
 Satellite and Aerial  Geochemical Sampling
Photography  Electrical Sounding
 Remote Sensing
 Ground-Penetrating
 Geological Mapping Radar
 Magnetic Mapping
 Seismic Methods
 Gravity Mapping
o Reflection : Detailed
 Radioactivity Mapping
but expensive
o Refraction : Cheap
but not Detailed
 Core Sampling and Well
Logging

Mineral extraction
Mineral 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

Economic Factors in Mining
 Richness of Ore
 Quantity of Ore
 Cost of Initial Development
 Equipment, Excavation, Purchase of Rights
 Operating Costs: Wages, Taxes,
Maintenance, Utilities, Regulation
 Price of the Product
 Will Price Go up or down?

Life Cycle of a Mine
Exploration
Development
Active Mining
o Excavation
o Crushing, Milling, Flotation, Chemical
Separation
o Smelting and Refining

o Disposal of Waste (Tailings)

Shut-down

Issues in Mineral Exploitation
Who 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.

Problems of Mining
Safety Environmental
 Mine Wastes Problems
 Pollution  Exploration
 Dust  Construction and
 Noise Operation
Sulfur Economic Impact
 Acid Rain  "Boom and Bust"
 Acid Runoff Cycles
 Dissolved Metals
(Fe, Cu, Zn, As...)

POSITIVE IMPACT
• Creation of Employment
• Provide raw materials for the
construction Industries
• Encourage cottage Industries
• Generate income
• Earn revenue for the government

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

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.

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.

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

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

Environment

 Produces dust
 Lowers the water tables
 Destroys wildlife habitat.
 The additional vehicular traffic around a
mine site brings noise and increases wear
on the roads.

ACID MINE DRAINAGE
 Mining 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

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.

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

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.

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.

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

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.

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 drainage
 An understanding of natural processes to detect and
predict where and when acid mine drainage might
occur.

Ugrc 140 (earth resources)

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