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MINERAL AND ROCK 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
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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
The Periodic Table
What are Minerals
1. Naturally occurring2. Solid substance3. Orderly crystalline structure4. Definite chemical composition5. 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 mineralsCrystallization 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
Native Copper
RocksThey consist of many individual
mineral grains firmly held together in a solid mass
Types of RocksIgneousSedimentarymetamorphic
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
Definition of a mineral or rock resource
Mineral or rock resources are any material of value that are derived from rocks or minerals
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)
Definition of a mineral or rock resource
Non-metallic
E.g. diamonds and other precious stones, salt, gypsum, potash
Definition of a mineral or rock resource
Rocks
E.g. marble, cut granite, crushed stone, sand and gravel
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
Types of Mineral Deposits
Igneous rocks and magmatic depositsHydrothermal oresMetamorphic depositsSedimentary deposits
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
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
Magmatic segregation
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
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
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
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
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
This can 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
Placer deposit
Metallic ResourcesAbundant Metals
Iron, aluminum, manganese, titanium, silicon, magnesium
Produced by variety of geologic processes
Supplies for future is adequateNot distributed uniformly
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
End of Lecture 3
MINERAL AND ROCK RESOURCES
Cont………….
Lecture 4
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.
Classification of Minerals
2. CarbonatesMinerals that contain the
elements carbon, oxygen, and one or more other metallic elements
Classification of Minerals
3. Oxides Minerals that contain oxygen and
one or more other elements, which are usually metals
Classification of Minerals
4. Sulfates and Sulfides Minerals that contain the element
sulfur
Classification of Minerals
5. Halides Minerals that contain a halogen
ion plus one or more other elements
Classification of Minerals
6. Native elements Minerals that exist in relatively
pure form
Sulfides
Native Copper
Properties of Minerals
StreakThe color of a mineral
in its powdered form
Properties of Minerals
LusterUsed to describe how
light is reflected from the surface of a mineral
Pyrite (Fool’s Gold) Displays Metallic Luster.
Properties of Minerals
Crystal formThe visible expression
of a mineral’s internal arrangement of atoms
Quartz Often Exhibits Good Crystal Form.
Properties of Minerals
HardnessIs a measure of the
resistance of a mineral to being scratched
Properties of Minerals
Mohs scaleConsists of 10
minerals arranged from 10 (hardest) to 1 (softest)
Mohs Scale of Hardness
Properties of Minerals
CleavageThe tendency of a
mineral to cleave, or break, along flat, even surfaces
Mica Has Cleavage in One Direction
Properties of MineralsFractureMinerals that do not
show cleavage when broken are said to fracture
Fracture is the uneven breakage of a mineral
Conchoidal Fracture
Properties of Minerals
DensityIs a property of all
matter and it is the ratio of an object’s mass to its volume
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.
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
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
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?
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
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.
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
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.
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
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
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.
ENVIRONMENTAL CONSEQUENCE OF
MINING
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
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 drainageAn understanding of natural processes to detect and
predict where and when acid mine drainage might occur.