Exploration Of Minerals Flashcards
What is an ore?
The rock containing valuable metal(s) that is economic to mine
E.g. we mine bauxite for aluminium
What is a resource?
A useful and valuable natural material.
Not always economically viable
What is a reserve?
The amount of the resource that can be extracted at a profit using existing technology.
Economically viable
Resource>reserve.
What is a gangue mineral?
A low-value waste mineral.
E.g. what’s left of bauxite after extraction
What is a cutoff grade?
The grade below which it is uneconomical to mine
What is the concentration factor?
The amount by which the metal is concentrated to make an ore deposit
How is concentration factor calculated?
Grade % / Average crust abundance %
Grade = concentration of metal in ore
What is the main ore mineral for the metal copper?
Chalcopyrite. CuFeS2. Copper-iron sulphide (all same)
What is secondary enrichment?
Occurs when metals are leached from within surface rocks and precipitated just below the water table
What is chemical weathering?
In situ breakdown of rocks at the Earth’s surface due to chemical reactions
How does chalcopyrite form?
Associated with igneous intrusions. Often found in medium-high hydrothermal veins. ultramafic melt. Magmatic segregation
Why might we not extract copper from chalcopyrite?
Concentration factor not high enough, or hasn’t met cut off grade.
May be a resource but not a reserve.
Inaccessibility, depth
What supergene sulphide enrichment?
Happens near the surface. Copper-sulphide minerals (chalcopyrite) altered and concentrated by weathering and groundwater.
Original copper minerals can be leached by acidic, often rich in CO2 + other acids.
Copper transported by groundwater.
When conditions change (can be acidity and temps) the copper can precipitate out solution.
Leads to formation of enriched secondary copper minerals
How common is chalcopyrite?
Quite abundant. However concentration factor of copper not high enough.
What is secondary enrichment of copper?
The natural process that can occur which can concentrate the copper from chalcopyrite and deposit it elsewhere, making it economically viable to mine
How does secondary enrichment of copper happen?
Chalcopyrite = Copper iron sulphide.
Copper sulphides insoluble in water.
CuFeS2 exposed at surface - chemical weathering - oxidation.
Produces copper sulphates - soluble in water.
In water, copper sulphates percolate - reaches water table.
Below water table is anaerobic - copper sulphate gets rid of oxygen (reduction)
Copper deposition just below water table
What happens to the iron during the secondary enrichment of copper?
It doesn’t percolate, so it leaves a layer at the top of iron oxides (gossan)
What is a gossan?
An insoluble (didn’t percolate) cap of iron oxides at the surface of a mineral vein.
Why are gossans useful?
They are a useful marker for a copper deposit
What is a porphyry?
Large igneous intrusion with a porphyritic texture
How do porphyry deposits form?
As a result of hydrothermal processes associated with granite intrusion at convergent plate margins
In a porphyry copper, are copper deposits porphyritic?
No.
Which is the most important between porphyry deposits and secondary enrichment for copper deposition?
> 60% of the world’s copper comes from porphyry deposits
How do copper porphyry deposits form?
Convergent plate boundary - melting - granite intrusion - wet & silicic - Increased H2O.
Magma chamber cools - common silicic minerals form (quartz + feld).
Water & incompatible metals (Cu, Au) collect at top of chamber.
Some crystals take more space as a solid than a liquid (e.g. feld) - less space than expected - pressure builds.
Fracture surrounding country rock.
Hydrothermal fluid moves away from intrusion (cools) - metal deposited and come out solution along fractures - because metals deposit at different temps
Form mineral veins
What does incompatible mean?
Metals don’t fit into the structure of feldspar and quartz
What is another name for placer deposits?
Alluvial deposits
What are placer deposits best known for?
Panning for gold
What are placer deposits?
Surface deposits formed by sed. processes of weathering, erosion, transport and deposition.
Dense, physically and chemically resistant minerals including cassiterite, gold, and diamonds can be concentrated into small, but high grade ore deposits
How do placer deposits form?
Mineral veins exposed - weathered mechanically or chemically.
Ore & gangue separated.
Weathered material transported (sorted)
How are most placer deposits concentrated?
Action of moving water in rivers and the sea
Most minerals in placer deposits are hard, with little to no cleavage. Gold is not, what is gold instead?
Soft but malleable.
It rolls into nuggets
Why is it useful placer deposits are chemically unreactive?
They’re not dissolved and taken into solutions
Where can placer deposits be found? (5)
Meander bends, plunge pools, upstream of projections, downstream of confluences, on beaches
Why are placer minerals found at meander bends?
When river around bend, current swings around outside - velocity highest around outside & slowest inside.
Erosion on the outside, deposition on the inside. Forms a point bar.
Placers deposited inside bends
Why are placer minerals found at plunge pools?
River flows from hard rock to less resistant - erodes downward to form waterfall.
Turbulent water + boulders at the bottom of waterfall scour the deep bottom (plunge pool).
Denser placer minerals become trapped in the sediment in the plunge pool
Why are placer minerals found upstream from projections?
Projections (things sticking up) from riverbeds trap dense placer minerals on upstream side.
This may be where hard rock, such as dykes project upwards
Why are placer minerals found downstream of confluences?
Where fast flowing tributary channels join slower river - current velocity drops.
Dense placer deposited. Forms a mid channel sandbar
Why are placer minerals found on the beach?
Rivers transport sediments into the sea - move along by LSD.
Strong swash, weaker backwash - dense placers deposited as energy too weak in backwash.
What are geophysical techniques?
Remote sensing. Done without digging. Surveys
What are geochemical techniques?
Not remote. Samples.
What are the 4 geophysical techniques used to find minerals (usually metals)?
Gravity surveys, magnetic surveys, electromagnetic surveys, electrical resistivity surveys
How are gravity surveys used to find metals?
Gravity is directly related to mass and density. The greater the mass/density = the greater the gravity. - Positive gravity anomaly.
Can also be used to find porphyry deposits if a negative anomaly
Why might positive gravity anomalies not always show metal deposits?
Any increase in mass causes positive anomalies, e.g. presence of mafic rock.
For low readings, gas also shows low gravity anomalies
How are magnetic surveys used to find metals?
If readings are positive, metals are present.
Magnetic anomalies.
Rich in iron specifically (mafic/ultramafic) or minerals such as haematite and magnetite
How can electromagnetic surveys be used to find metals?
Sends electromagnetic waves (currents) down, conductive material is able to re-emit or conduct it back.
Metallic material will be conductive
How can electrical resistivity surveys be used to find metals?
two probes in the ground. Pass electricity through the ground. Measures resistivity.
If rock is a good conductor = low resistivity.
We look for low resistivity materials.
This has been used for gold extraction
What are the 4 types of geochemical techniques that can be used to find metals?
Stream sediment sampling, soil sampling, water sampling, vegetation sampling
How can stream sediment sampling be used to find metals?
Take sediments from streams and look for anomalies (placers).
1-2 kg of sediment analysed for metals.
Sediments up from the source have normal metal values. Sediments down from the source have positive anomalies (metal values).
Catastrophic dilution
How can soil sampling be used to find metals?
hand held tools used to collect samples of soil and subsoil. Usually collected on systemic grid pattern.
Interpretation depends on:
Soil samples on top and downslope of source will have +ve anomalies (metal).
Soil samples upslope of the source will have normal metal values
How can water sampling be used to find metals?
Samples taken at regular intervals along river course.
Metal values in rivers are a few parts per billion, so sensitive analytic techniques needed and seasonal variations taken into account.
Increase in metal content of water to a few parts per million - presence of metallic mineral deposits nearby
Colour may also be an indicator
How can vegetation sampling be used to find metals?
Metals can be taken into plants through roots. Sampling of leaves, twigs, or seeds from chosen plant.
Elevated metal content may indicate presence of underlying metal deposits. Plants may also be burned to find metals.
Geobotanical surveys can also be used
What is a geobotanical survey?
Plant species may be adapted to withstand high metals. Mapping and plant identification used to find metal
Phytomining
Once geophysical and geochemical surveys are completed, what further exploration is required?
Potential areas now mapped. Geophysical techniques show where ore body is, composition and likely grade (purity). Finding the highest grade requires the use of GIS - produces red spots in high areas, yellow spots in low chance.
May use boreholes to narrow down more.
May drill between red spots in case of syncline, showing deeper metal deposits.
What is the purpose of exploration drilling?
Boreholes.
It is the most accurate, but most expensive info we can get.
Also, downhole logging is able to happen.
It helps to determine what useful ores are present, how much gangue material is in the ore body, how much ore is present, depth (accessibility)
What type of drills can be used for boreholes?
Rotary, percussion or diamond drills
What is downhole logging?
The hole is wide enough to drop equipment down and complete further surveys
Why is estimating a reserve important?
Helps to make an evaluation of the deposit. Allowances for waste rock which may ‘dilute’ ore mineral and accounts for unavoidable losses during mining
What is the kriging method?
Used in mining to determine size and location of valuable reserves.
Requires computer programme that uses stats and probability.
Feed known data to computer - learns from previous exploration.
This produces a 3D blocked image showing location and grades.
Uses geostatistics.
The more data fed into it, the more accurate
How is a block model of an ore body (kriging) useful?
Show where is better to mine first as it shows highest grade ore. Instead of spending lots of money mining the whole area
What are the other three main types of considerations when determining the viability of resource extraction?
Geological, operational, economic
What are the geological considerations that should be taken into account when determining the viability of resource extraction?
Whether there are areas of very high grade.
Styles and zones of minerals.
Whether minerals have sharp or gradual boundaries.
How easy the rock is to work.
The presence of toxic elements, such as arsenic
(toxicity, setting, grade, rock)
What are the operational considerations that should be taken into account when determining the viability of resource extraction?
Type of mine and its stability, open pit or underground mining.
Methods and rates of extraction and processes.
Pollution management and acid mine drainage.
Dilution by waste rock mixed with ore.
Water control, drainage and pumping.
(market, stability, water issues, pollution, closure, cut off grade)
What are the economic considerations that should be taken into account when determining the viability of resource extraction?
Set-up costs (include assembling plant).
Level at which cut off grade is set.
Long term projections for the metal prices for the ore (will mining be worth it?).
Closure and reclamation plans, as laid out in the planning consent
What are some other factors that affect the accuracy of the estimation of reserves? (6)
Detail of the survey,.
Variation in grade of the mineral and size of body.
Unexpected geological conditions, such as faulting.
Unrecorded earlier workings, especially underground.
Variations in the economic climate and in demand.
Improvements in extraction technology
How many stages are there in the life cycle of a mine?
5
What is stage 1 of the life cycle of a mine?
Design and planning.
Assumes surveys have already been done
What is stage 2 of the life cycle of a mine?
Construction.
Getting ready to mine extraction and processing facilities, roads, environmental management systems, housing and other facilities
What is stage 3 of the life cycle of a mine?
Production (actual mining).
May be open pit or by underground mining depending on depth, shape, and size of target body and the limits imposed by health and safety (HSE), technology, environmental and economic concerns
What is stage 4 of the life cycle of a mine?
Processing.
Mixed minerals sent through huge crushers or mills to separate commercially valuable ores from the gangue and waste rock, so that transport to a smelter is more economical
What is stage 5 of the life cycle of a mine?
Rehabilitation and reclamation.
Once mine has been exhausted. Land is returned to the original state.
Ensures public health and safety., minimise environmental effects, remove waste ad hazardous materials, preserve water quality, stabilise land, establish new vegetation and landforms
What are the three types of mine?
Open cast/open pit
Stope mining
Longwall retreat
What is open cast (open pit) mining used?
When ore is relatively close to the surface. When it is more economic to strip away the overburden by quarrying
What is open cast mining?
Mined down in steps to protect equipment and workers from slope instability as rocks would collapse into steps
What are the advantages of open cast mining?
Cheaper set-up and work costs (still a lot).
Very efficient + high rates of production.
Only small workforce needed.
Ventilation not required.
Safer
What are the disadvantages of open cast mining?
Massively environmentally damaging
What is stope mining?
These may use explosives.
Drill shafts vertically down, then drive horizontally across the ore body.
Slope may be backfilled/
Specific methods depend on the dip + width of the deposit, grade, hardness, strength of bedrock.
Waste material taken by remote dumpster trucks
What are the advantages of stope mining?
Less habitat disruption
What are the disadvantages of stope mining?
More expensive
More technology needed
Risk of subsidence
What is longwall retreat mining?
2 horizontal roadways.
Up to 400m long.
Extracting machine (shearer) moves along face.
Roof held up by closely spaced, mobile hydraulic steel.
Once mined in one area, the area is allowed to collapse.
What are the advantages of longwall retreat?
Doesn’t require much labour.
Production rates similar to open pit.
Shouldn’t collapse in future
What are the disadvantages of longwall retreat?
Causes subsidence (however this is controlled. avoids future collapse).
Expensive
What are the three methods of mineral recovery and processing?
Leaching, froth floatation, smelting
What are the two types of leaching used for mineral recovery and processing?
In situ leaching at depth.
Heap leaching at the surface
What is leaching?
Uses chemical solutions to dissolve ore from rock, dissolving the target mineral (transported as a liquid)
What is in situ leaching?
Bore holes are drilled, explosives used to fracture rocks.
Leaching solution is pumped down.
Once the solution contains the dissolved ore, it is pumped back to the surface (separate bore hole).
Evaporites dissolve in warm saline water, e.g. salt (like Cheshire).
Leaching solution can be reused
How much of the world’s uranium production comes from in situ leaching?
21%
How is uranium produced using in situ leaching?
Uses acids
What are the advantages of using in situ leaching?
No waste,
Cheaper,
Little disturbance
What are the disadvantages of using in situ leaching?
Potential chemicals
What is heap leaching?
Similar to in situ leaching, but material is brought to the surface.
Crushed and heaped onto impermeable barrier (clay/plastic) to prevent percolation.
Leaching solution applied, and solution with dissolved material is accumulated in a pond, then taken for further processing.
They re-use the leaching solution
What are the advantages of using heap leaching?
Cheap
What are the disadvantages of using heap leaching?
Only gives 60-70% of the ore,
Takes a long time, 2 months-2 years
What does hydrophilic mean?
Loves water
How is the world’s copper produced (%s)?
70% froth floatation,
30% in situ leaching
What is froth floatation?
Separates hydrophobic and hydrophilic minerals.
The ore is crushed with water = slurry.
They add chemicals to make the target material hydrophobic.
Aerate the slurry. Hydrophobic particles attach to the bubbles - rise to the surface.
The froth from the top is collected rich in the target material
What are problems caused by the crushings and tailings (gangue) after froth floatation?
Crushing produces fine grained waste.
Contain toxic metals + harmful chemicals.
Radioactive uranium tailings.
Spoil heaps of waste rock can be unstable too.
How are target material smelted for production?
Reduction of the ore.
Separation using heat and the reactivity series (blast furnace).
Used for extraction of iron oxides e.g. haematite.
Carbon (coal) is more reactive than iron.
Iron steals oxygen (reduction).
Displacement reaction and reduction reactions.
What are the problems with minewater?
Acid mine drainage
Many mined minerals are sulphide ores.
Empty mines contain many fractured rocks.
Empty mine exposed to h2o and O2.
Oxidation reactions with ore produces sulphuric acid.
What are the 4 treatment methods for Acid Mine Drainage?
Source control,
Migration control,
Active treatment,
Passive treatment
How is source control used for acid mine drainage?
Preventing the h2o and o2 from entering the mine.
Pump waters out, but expensive.
Sealing and filling the mine with concrete or clay
How is migration control used for acid mine drainage?
Directing AMD acid to a safe storage area/pond for further treatment or neutralisation
How is active treatment used for acid mine drainage?
Neutralising the acid.
Adding a base/alkali the acid.
Expensive
How is passive treatment used for acid mine drainage?
Using nature base system (alkali) - Lime (contains limestone). e.g. wetlands and tricklebeds.
Trickling AMD through limestone and gravel, natural neutralisation.
Micro organisms can consume the metals.
Best solution but difficult
What kind of waste can be stored underground? (8)
Chemical waste, heavy metal, municipal sewage, agricultural, solid waste (landfill), nuclear, radioactive, gas sometimes
What type of waste is solid waste?
Landfill waste.
Domestic and business waste.
Cardboard, food, municipal, green waste, paper
How is nuclear waste stored underground?
Different levels of nuclear waste (equipment least bad).
They have to be treated and stored differently
What are the 5 advantages or using underground storage for waste?
Reduces surface impact, containment, space efficiency, quick easy and cheap, long term storage
How is reducing surface impact an advantage for underground waste storage?
Minimised visual and environmental impact on the surface. Preserves natural landscapes and habitats
How is containment an advantage for underground waste storage?
Contains hazardous materials, preventing soil contamination and water sources
How is space efficiency an advantage for underground waste storage?
Allows more efficient land use, especially urban areas where surface space limited
How is long term storage an advantage for underground waste storage?
Underground facilities can be designed for long term storage, ensuring waste is managed safely
What are the disadvantages of underground waste storage (6)?
Public opposition, environmental risks, technical challenges, limited access, produce methane, may be prone to subsidence
How is public opposition a disadvantage of underground waste storage?
Communities may oppose it due to fears of contaminated or other environmental impacts, leading to social and political challenges
How are environmental risks a disadvantage of underground waste storage?
Potential risks of groundwater contamination if not stored or managed properly (toxic leaching)
How are technical challenges a disadvantage of undergound waste storage?
Ensuring integrity can be difficult, with leaks or structural failures over time.
How is limited access a disadvantage of underground waste storage?
Difficult to monitor and manage, making challenges accessing the condition of the waste
How is methane production a disadvantage of underground waste storage?
Anaerobic breakdown of organic waste. 25x more harmful than CO2 in atmosphere
What is a leachate?
As rainwater percolates through waste - dissolves soluble chemicals and collects microbial contaminants. This produces a liquid called leachate
What are the 3 types/stages of nuclear waste?
Low level,
Intermediate level,
High level
What is low level nuclear waste and how is it stored?
90% of all radioactive waste.
e.g. equipment, clothing used.
Usually compacted into steel cannisters and stored in concrete vaults underground.
Ensures no radiation reaches surface.
What is intermediate level nuclear waste and how is it stored?
7% of all radioactive waster.
Deep geological disposal. The rock and soil acts as a barrier to radiation.
Contains long lived unstable radionuclides in concentrations that require isolation and containment for longer than 100s years, or irradiated reactor core components
What is high level nuclear waste and how is it stored?
3% of all radioactive waste. 95% all radioactivity in waste.
Vitrification to store it. This is done before deep geological burial.
Produced as a by product of the reactions that occur in the nuclear reactor, e.g. used reactor fuel
What is vitrification?
Incorporating nuclear waste into glass and stored up to 50 years to allow the heat to dissipate.
Ground into fine powder, added to glass granules then melted
What features must be present for underground nuclear waste to be disposed?
Suitable geology (hard, competent).
Low seismicity.
Low water table.
Few faults and joints
How can CO2 be prevented from entering the atmosphere?
Carbon capture or carbon sequestration - permanently storing underground
What is the difference between carbon capture and carbon sequestration?
Carbon capture - man made
Carbon sequestration - natural or man made
