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 ElementsMinerals made up of only one elementE.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-metallicminerals 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
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 rockresourceMineral or rock resources are any material of value that are derived from rocks or minerals
Definition of a mineral or rockresourceThe resources can be separated into threegroups Metallic E.g. gold, platinum, silver, copper, iron, aluminum, tin, lead, uran
Definition of a mineral or rockresourceNon-metallicE.g. diamonds and otherpreciousstones, salt, gypsum, potash
Definition of a mineral or rockresourceRocksE.g. marble, cutgranite, crushed stone, sandand gravel
Types of Mineral DepositsIgneous rocksand magmatic depositsHydrothermal oresMetamorphic depositsSedimentary 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 weatheringAll 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
Sedimentary Deposits Banded iron ores Mode of formation In early earths history, atmosphere was reducing (oxygen poor). In reducing environments iron is soluble in water However, worlds oceans contained more oxygen due to the action of one-celled plants, such as algae
Sedimentary Deposits 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 ResourcesAbundant Metals Iron, aluminum, manganese, titanium, silicon, magnesium Produced by variety of geologic processes Supplies for future is adequate Not 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
Classification of MineralsCan 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.
Classification of Minerals 2. Carbonates Minerals 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
Properties of MineralsDensityIs a property of all matter and it is the ratio of an object’s mass to its volume
Prospecting, Exploration and Mining Prospecting Exploration MiningThe act of looking for a Involves many different spot where there is methods in looking for spot of mineralization The extraction of the orevaluable 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 extractionMineral resources are typically extractedfrom 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 MineExplorationDevelopmentActive 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, GovernmentUnclaimed Areas: Sea Floor, AntarcticaWho 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.
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 theEnvironment 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 theEnvironment 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 theEnvironment 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 theEnvironment 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.