Mollys - Exploration and Mining

what is the crustal abundance?

the amount of metal in the average continental crust

what is the concentration factor?

the amount by which the metal is concentrated to make an ore deposit

what is a gangue mineral?

A low value waste mineral

what is an example of a gangue mineral?

quartz, calcite

what is an ore?

the rock containing valuable metals that is economic to mine

how do you calculate the % composition?

e.g copper in chalcopyrite
Mr of copper 64/184 x 100
divided by the total Mr of the compound

what is the equation for concentration factor?

cut off grade average/ abundance of metal in the continental crust

what is the cut off grade?

The grade below which it is uneconomical to mine.

what is the cut off grade determined by?

- value of the metal
- demand
- abundance of the metal
- size of an ore deposit
- cost of mining

how does the value of the metal affect the cut off grade?

more valuable the lower the cut off grade

how does the demand of a metal affect the cut off grade?

higher demand the more valuable the metal so the cut off grade is lower

how does the abundance of the metal affect the cut off grade?

if the metal is scarce and useful it will have a lower cut off grade

how does the size of an ore deposit affect the cut off grade?

larger deposits are economic to mine at lower grades than smaller deposits

how does the cost of mining and extraction affect the cut off grade?

if it is costly to mine and extract then the metal cut off grade is higher

What is the "grade" of an ore?

the concentration of useful metal in an ore

how is the grade of an ore calculated?

mass of extractable metal/ mass of the rock x 100

what is an ore mineral of lead?

galena (PbS)

what is an ore mineral of copper?

malachite, chalcopyrite (CuFeS2)

what is an ore mineral of iron?

magnetite (Fe3O4)
haematite (Fe2O3)

what is an ore mineral of aluminium?

bauxite (Al2O3)

what is an ore mineral of tin?

cassiterite (SnO2)

what is an ore mineral of zinc?

Sphalerite (ZnS)

how do placer deposits form?

when a current slows down an energy is lost, the heaviest particles are deposited, then there is a concentration of dense metallic minerals in the river and seas in areas of decreasing energy

why are placer deposits easy to work?

the metals are usually in the form of loose sand or gravel

what metals are found in placer deposits?

gold, platinum and cassiterite

what characteristics do minerals have for placer deposits?

- not affected by the oxidising environment of surface weathering (not corroded or dissolved)
- dense
- little or no cleavage

why are placer deposit minerals dense?

so that they are preferentially deposited

why do placer deposit minerals have little/no cleavage?

so that they do not break up during transportation

why is there a placer deposit when a fast flowing stream joins a slow river?

as the energy level decreases, the sediment load coarsest and dense metals are deposited

why is there a placer deposit at a plunge pool?

the river flow slows in velocity causing the deposition of the sediment in the plunge pool below the waterfall and nearby potholes

why is there a placer deposit with projections in the stream bed?

they form in areas of calm water on each side enabling the build up of sediment either side

why are there placer deposits on the inside of meander bends of a river?

current velocity is greatest on the outside bend, this causes the deposition of sediment on the inside bend forming a point bar as the velocity of the river is slower and the dense mineral is deposited

why are there placer deposits on the beach?

when the energy of water is reduced on the backwash with sediment thrown up the beach on the swash.

what is placer mining?

open cast at the surface using bulldozers on the river or beach sediments and running water to separate the heavy minerals e.g gold and tin from the sand and gravel

what is the advantages of placer deposit mining?

cheap, safe, produces little pollution, requires little machinery or technology

what are the disadvantages of placer deposit mining?

it has an environmental impact as the surface is scarred but only in the short term as it grows back. water can become muddy as machinery stirs up the water

what is secondary enrichment?

the ore concentrating process that naturally occurs

what happens in secondary enrichment above the water table?

rainwater percolates down through the pore spaces of the rocks. in the upper oxidation zone, insoluble copper sulphides are converted to soluble copper sulphates. they are then dissolved and carried downwards by rainwater. a leached zone is left behind

what happens below the water table in secondary enrichment?

the copper is carried in solution down through permeable rocks, the conditions are reducing and chemical reactions convert soluble copper sulphates to insoluble copper sulphides that then deposit. higher grade copper content minerals form as an enriched deposit

what happens at the lowest part of the mineral vein during secondary enrichment?

it is unweathered copper ore of lower grade as it is less concentrated

what are the conditions like above the water table?

oxidising.

what are the conditions like below the water table?

reducing.

what is the gossan?

at the surface leached zone covered in insoluble iron oxide which is useful to indicate ores present

what happens to the metal values further from an ore deposit?

they have lower metal content

what is the halozone?

zone of weathered ores with higher metal content so they are a geochemical anomaly

what is a geochemical anomaly?

when the value for metal content is higher than the background values

how is geochemical surveying done?

soil sampling and stream sediment sampling and vegetation sampling

how are soil sampling done for geochemical surveying?

in a grid pattern soil samples taken for analysis. results plotted to show anomalies

what does a high anomaly of soil sampling suggest?

that there is an ore body present, it could be of high grade or shallow and low grade

how does stream sediment sampling occur for geochemical surveying?

weathered material from ore bodies ends up in the stream. ore upstream of the anomalies. downstream the anomalies become more lower as the solution is more dilute with less metal ore in the solution. metals leach out into river if soluble

how does vegetation sampling for geochemical surveying occur?

plants take up soluble elements and may concentrate in leaves. it can be measured from samples by leave samples or satellite imaging as plant metals increase, biochemical changes occur and light reflection changes. or plants can die forming barren areas seen from air or ground

what are the types of geophysical surveying?

- electromagnetic
- magnetic
- gravity
- electrical resistivity

what is electromagnetic surveying?

from a helicopter, electromagnetic waves generate a current in the ore body. the ore then generates its own magnetic waves. these are recorded by the coil. for metal sulphides

what is electrical resistivity surveying?

ore bodies have a relatively high metal content and are good conductors. by measuring the current flowing through the rocks. sulphides have a low resistivity and allows current to flow easily (this can be measured)

what is magnetic surveying?

magnetometer measures variation in the Earth's magnetic field strength.
minerals rich in iron produce positive magnetic anomalies suggesting either magnetite mineral or a mafic/ultramafic rock with cumulate ores

what are gravity surveys?

variation in the gravity of the Earths gravitational field strength

what does a positive gravity survey suggest?

that a high density mafic or ultramafic intrusion which may contain cumulate ore deposits or the presence of dense metallic ore minerals due to high iron content they have high densities (other minerals too)

what does a negative gravity anomaly suggest?

a low density silicic intrusion is present

what is an ore reserve?

the amount of the resource that can be extracted for a profit using existing technology

what is reserve estimation?

quantification of economic mineral present in the ore body

what are the three phases of developing metal deposits?

target selection, exploration drilling, reserve estimation

what is target selection?

is it worth spending more time and further investigations and areas not to do so
- surface mapping rock and mineral sampling
- geophysical and geochemical analysis to indicate where an ore body is
- radiometric dating, x-ray, and metallurgical to indicate the position of an ore and composition
- geographical information system (GIS) used when data entered so that geophysical maps, charts and table relationships can be identified

what is exploration drilling?

determining what useful ores are present, how much ore by grade and tonnage, how much gangue minerals, depth and extent of an ore body, how it could be accessed for mining
- accurate information by costly
- core samples taken from boreholes for extra geophysical data

what is reserve estimation in determining a metal deposit?

estimating the value of an ore body and determining whether it is a metal ore body or another mineral deposit

How can waste rock affect the grade of an ore?

it can cause the grade to be lower as it dilutes the ore. or a company might choose to leave some behind so that it is of a higher grade

what are the 4 groups of factors that affect how easily done an ore extraction is?

operational, geological, economic and reserve estimates

what are the operational factors that affect ore deposit feasability?

- type of mine and its stability
- methods and rate of extraction and processing
- pollution management and acid mine drainage
- dilution of ore mixed with waste rock

what are the geological factors that affect ore deposit feasability?

- geological setting
- whether there are areas of higher grade
- the styles and zonation of mineralisation
- whether mineralisation is sharp or gradual boundary
- how easy the rock is to work
- any presence of toxic elements e.g arsenic

what are the economic factors that affect ore deposit feasabiliity?

- set-up costs like assembling machinery
- level of cut off grade
- long term projections for metal prices
- closure and reclamation plans

what are reserve estimate factors that affect ore deposit feasability?

- detail of the survey
- variation in mineral grade and size of ore body
- unexpected faulting or earlier mining unrecorded
- improvements in extraction technology

what are the stages of a mine?

1) exploration and design
2) construction
3) production
4) processing
5) rehabilitation and reclamation

what are the advantages of open cast mining?

- very efficient and high rate of production
- set up costs are low in comparison to underground mining
- no ventilation equipment needed
- thinner low grade can be mined for profit
- safer for workers (smaller crew too)
- easy and cheap to shut down
- easy damage of water

what problems can be caused by open cast mining?

environmental and slope stability with soil heaps from excavated overburden cause problems

what is strip mining?

surface mining that displaces overburden from the front of mining to the behind of it so that active mining can move along a coal layer. it is good for coal as it is in thin layers that can be mined in strips

what is stope mining?

extracting desired ore or other mineral from an underground mine leaving a space called the stope
used when country rock is sufficiently strong enough not to collapse into the stope but there can be support too

what is longwall mining?

underground method of excavating coal from tabular deposits
large rectangle defined then extracted by one operation. each coal panel has tunnels around it that head deep connected to the main mine roads. they join the longwall face. as coal is cut there are hydraulic supports for the longwall face
- it is a safe environment for working as the roof is supported but a ventilation system is needed for the mine workers

is mining bad?

- unsustainable- finite resources that take millions of years to concentrate minerals into resources
- air pollution (carbon dioxide, sulphur dioxide and dust) from smelting and burning fossil fuels
- water/soil pollution- heavy metals like lead and mercury into aquifers which poisons water supply. tailings destroys aquatic environments
- habitat destruction
- visual/traffic/noise pollution
- ethics- exploitation of workers/ indigenous communities as well as corruption

what is insitu leaching?

- leaching liquid pumped through drill holes into underground deposits.
- in rocks that are non-permeable. it dissolves the uranium in the ore deposit.
- the solution is then extracted and treated above the surface

what is heap leaching?

a process called "heap-leaching," whereby cyanide solutions percolate through the tailing piles to dissolve out the gold
the process can be repeated for higher gold extracted

what is smelting?

carbon in coal reacts with oxygen in iron oxide and combines with oxygen in the air to form carbon dioxide
sulphides form sulphur dioxide and without carbon

why is smelting bad for the environment?

it forms carbon dioxide which is a greenhouse gas
it also forms sulphur dioxide which when dissolved in water forms acid rain

why is electrolysis used for aluminium oxide?

elements high up the reactivity series (higher than carbon) cannot be displaced by carbon so it has to be extracted with electricity

what is froth floatation?

- separates hydrophobic and hydrophillic metals in ores
- ore crushed so that minerals are individual grains. mixed with water to form a slurry
- target mineral is made hydrophobic with the addition of chemicals
- slurry is taken to floatation cell where bubbles are formed. here the hydrophobic particles attach to bubbles which rise to the surface as froth. this concentrates the target mineral
- tailings do not attach to bubbles and will be left behind
- this process can be repeated with the tailings so that recovery is maximised

what are tailings?

fine waste rock fragments that do not attach to bubbles in froth floatation

what is the problem with tailings?

they can contain toxic metals and harmful chemicals used in extraction. stored in ponds or underground

how is acid mine drainage formed?

heavy metals e.g lead and mercury are more soluble in lower pH water. this dissolves in the acidic water formed from flooding of a mine (sulphur in exposed rock to oxygen and water forms sulphuric acid

what is the problem with acid mine drainage?

solution is then highly toxic and if in rivers or groundwater can have a harmful effect on humans, animals and plants

what is active treatment for acid mine drainage?

addition of a base e.g calcium carbonate or sodium hydroxide
to neutralise the AMD. a constant supply of chemicals needed which is expensive but it is reliable and effective.
heavy metals will precipitate out in a sludge as carbonates and hydroxides as their solubility is reduced

what is passive treatment for acid mine drainage?

from natural and constructed wetland ecosystems. expensive to set up and need more land. little maintenance and with little electricity or any hazardous chemicals. low acidity and low flow AMD
shallow ponds filled with limestone gravel, forms natural oxidation leading to precipitation of heavy metals

what is low level waste?

radioactively contaminated e.g clothes and reactor water treatment

what is medium level waste?

filters in purifying reactor water, reactor core components

How is low level waste stored?

secure landfill sites or concrete vaults

how is medium level waste stored?

deep underground in a geological repository

what is high level waste?

high radioactive minerals as by products of reactions in the nuclear reactor e.g control rods, piping and reactor components

how is high level waste stored?

deep underground in a geological repository. within steel barrels in concrete. it is mixed with glass so that it is inert

what is storage criteria for high level waste?

- isolation for 25000 years
- secure from accidental or deliberate entry
- safe from natural disasters e.g floods hurricanes and earthquakes
- no chance of leakage into surrounding environment

where geologically is high level nuclear waste stored?

- tectonically stable area away from plate boundaries (no earthquakes)
- dry impermeable rocks and a low water table (e.g igneous rocks as they are crystalline)
- no bedding planes
- no faulting

what ways is carbon dioxide sequestrated?

terrestrial, carbon dioxide from technology and geologically

what is carbon sequestration?

carbon dioxide is removed from the atmosphere and held in solid or liquid form permanently stored

how is carbon dioxide sequestrated?

carbon dioxide is separated from the flue gases produced
gas is then captured and compressed by electricity from nuclear power plant
transported by pipeline or road or ship