Mining and Ore deposits Flashcards
What is a Natural Resource? Give a definition and examples.
Naturally forming substances that are considered valuable in their relatively unmodified, natural form e.g. Metals, industrial rocks and minerals, energy minerals, gemstones, wood, wind, water and fish.
What are the requirements for a resource to enter cumulative production?
With increasing certainty, a resource becomes identified and has demonstrated and measured reserves. With increasing concentration it becomes more economic. If all factors are present.
What is the natural resource concept?
The relation of price, value, demand, supply and substitution. These are determined by how easy it is to extract a resource.
What might you do if the price of a resource is too high?
Substitute it for a different material, the original material will then go down in demand and then price.
Demand is determined by:
A resources usefulness
Supply is determined by:
Ease of extraction and distribution. Supply is responsive to demand
Lack of supply can lead to:
Substitution
What is an industrial mineral:
Any earth material of economic importance, excluding metal ores and fuels. It has value due to its nature/properties/strengths used in its mineral form without extracting any metal. E.g. Building stone, china clay, Barite, Fluorite and ‘industrial’ diamonds.
Give examples of Building stone substitution and why it might occur.
If there is no better option from local resources then some must be imported. E.g. Millstone Grit, N.Wales Slate, Larvikite (Syenite from Larvik Norway)
Give examples of local building stone used:
Aberdeen: Granite
Sailsbury Cathedral: Chilmark stone (limestone)
Raglan Castle: Sandstone
Name 3 industrial minerals that can be found in this country that aren’t building materials
- Potash
- Rock Salt
- China Clay
What is Kaolinite and how is it mined?
Feldspar rich clay, (china clay) and its sprayed with high pressure water, held in suspension.
Whats the definition of an Orebody:
An accumulation of minerals distinct from its host rock that is rich enough in metal to be worth economic exploitation, i.e. Profitable.
What are gemstones?
Artificially polished, faceted and shaped for decorative purposes.
- They are controlled by marketing, rarity, imperfections
- Precious stones: Diamonds, Rubies, Emeralds
- Semi-precious: Topaz, Garnet, Zircon
What is an Energy mineral?
In its natural state or after refinement it can be used to generate energy
Define sustainable development:
A pattern of resource use that aims to meet human needs while preserving the environment so the the needs can be met in the indefinite future.
Define Mining Legislation:
Robust conditions in which the mining company must show environmental awareness ad proactivity.
How much gold has ever been mined?
161,000 tons
- barely enough to fill 2 Olympic sized swimming pools
Disadvantages of current large open pit gold mines:
- Large visual impact
- 1-2g of gold per ton of rock (very wasteful)
- geography restricted
- 250t = 1 wedding ring
Disadvantages of artisanal gold mines:
- minor due to local nature of mining but environmental rehab isn’t assessed.
- more destructive
- pollution from mercury and cyanide extraction.
Define a metalliferous ore:
A rock that can be worked economically for a metal or group of metals that it contains.
What are Native Ores:
Ore that contains a metal in its elemental free state.
- Gold, silver, mercury, copper, platinum
What is a troy Oz equivalent to in grams?
31g
What are Sulphide Ores:
Contain a metal or group of metals in combination of Sulphur
- Common
- Iron (pyrite), Lead (Galena), Zinc, Copper, Nickel
What are Oxide Ores:
Contain a metal or group of metals in combination of oxygen.
- Non ferrous to ferrous metals commonly found here and economically important for these metals
- Iron, Tin, Chromium, Titanium
What are Carbonate + Sulphate Ores:
Contains metal/group in combination with oxygen and carbon OR oxygen and sulphur.
- Barium sulphate, Iron carbonate, Copper Carbonate (Malachite)
Advantage and disadvantage of carbonate + sulphate ores:
- Good signal for presence of primary ores.
- Usually form due to weathering/interaction with primary ores (not helpful for extraction of metals)
Name the crustal abundance from Oxygen to Gold
Oxygen : 47 Silicon: 27 Aluminium: 8 Iron: 5 Chromium: 0.01 Copper: 0.005 Gold: 4 parts per billion
What concentration factor is needed to get a normal crustal abundance of Au up to to Ore levels?
A concentration factor of 5 for Iron but 250 for gold
- the cut off for a gold deposit is >1ppm
How do hydrothermal ore deposits form?
Scavenge, Transport, Concentration and Deposition.
- Hydrothermal water flowing through area of ore deposit will pick up the gold etc and transport it within an economically efficient enough level even if normal extraction (mining) is 1%.
Where do the hot fluids in hydrothermal processes come from?
- Magmas (intrusion)
- Metamorphism
- Sea Water
- Anywhere the geothermal gradient is high enough to heat the water.
What causes precipitation of minerals from hydrothermal fluid?
- Change in temp (cooling)
- Change in pressure (entering veins and closer to the surface)
- Compositional change (chemistry)
- Fluid mixing (brine and magma)
Whats the definition of hydrothermal:
to do with hot fluids - usually related to magmatic activity
What happens upon cooling of hydrothermal fluid?
They precipitate out ore and gangue minerals
- they typically form veins, dissemminations and stockworks.
Describe a Porphry deposit:
A large high tonnage, low grade (<1%Cu) deposits associated with plutons of intermediate-acidic porphyritic igneous rock.
What are porphyries a major source of?
Copper, gold and molybdenum
Where does a porphyry typically form
In plutons above subduction zones
How does a porphyry form?
Sudden release of fluids near the surface, with a shattering of the enclosed rocks, forming ‘stockwork’ mineralisation.
What is the source of metals and heat to form a porphyry?
Magma, most likely if not always an intrusion
Explain how mineral veins form:
sudden release of volotiles causes rocks to crack and change in pressure so minerals/metals precipitate out to fill the gap.
What mineral structures do porphyrys typically produce
veins, disseminations and stockworks with chalcopyrites
A porphyry is an example of what?
A hydrothermal ore deposit
What is an Epithermal deposit?
A low tonnage but high grade deposit that telescopes up from depth, usually form within 1km of the surface.
What temperature do epithermal deposits reach the surface at?
100-200 degrees C as hot springs
Name typical minerals found in epithermal deposits
Gold, Silver, Mercury and Antimony
How do Epithermal deposits form?
Heat source at depth causes fluid mixing as well as groundwater as source water.
- metals sourced from magma
- found in hot spring veins
- boiling as well as change in pressure, temp, etc can cause precipitation (mixture of processes that cause precipitation)
Whats different about the cornish vein deposits?
From a granite pluton, the change in temperature radiating outwards causes zoning of different minerals.
Metamorphism produces fluids which may carry gold what geological structure aids the golds deposition and what name is given to this deposit
Major transcrustal faults (e.g. San Andreas) acts like an outlet for this fluid depositing gold on cooling and decompression forming an Orogenic gold deposit.
Advantage of Orogenic gold deposit
Largest source of gold
- quartz
- pyrite
Whats another name for hydrothermal deposits that form at mid ocean ridges?
VMS - Volcanogenic Massive Sulphides
How do VMS form?
During submarine volcanic activity at the sites of black smokers. Crust is at its thinnest and sea water percolation into the crust is heated to about 275-350
What are black smokers made from?
Mainly sulphides as well as Anhydrite mixed in. Cones become more porous upward.
Name the main elements found at black smokers
Copper and Zinc. Sometimes Lead, Silver and Gold
What is a Placer Deposit?
Mineral deposits that have been concentrated by mechanical action, typically fluvial processes
Name common placer deposit minerals:
Gold, magnetite, ilmenite, chromite and diamonds
What was found in Witwatersrand basin in S.Africa?
Lithified palaeo placer deposits of conglomerate.
- 1886 George Harrison found the largest gold deposit on the planet
- Gold Rush
- it now contributes to 1/4 of Africa’s GDP
What is a Laterite deposit
When chemical weathering removes soluble elements from a rock, leaving insoluble residual deposits which may be enriched metals.
- Typically tropical
Give an example of a metal typically found in a laterite deposit?
Nickel
Where is Nickel sourced from?
Ultra basic rocks form nickel laterites
Describe the sequence of beds that form a laterite deposit:
- Fresh peridotite
- Altered and partially altered peridotite with garnierite concentration (Transition)
- Residual laterites
- Porous laterites (Yellow Limonite)
- Nodular iron oxides (Red Limonite)
- Iron oxide cap (Red Limonite)
What is Bauxite?
A mixyure of 3 hydrates. Its a rock type not an ore mineral from broken down clays forming alumina-gibbsites
Name the key identification properties of native copper
- Element
- Streak = Dark Brown
- Very Dense = 8.96
- Pipes and wires
Name the key identification properties of Sphalerite
- ZnS
- Greasy Lustre
- Rhombic crystal form
- Jewellery
Name the key identification properties of Galena
- PbS
- Dense = 7.4
- Making lead acid batteries
Name the key identification properties of Chalcopyrite
- CuFeS2
- Brass/Yellow
- Amorphous crystal form
- Magnetic when heated
- Finding copper
Name the key identification properties of Pyrite
- FeS2
- Gold/Brass
- Hardness = 6
- Cubic
- Used to make sparks with flint
Name the key identification properties of Magnetite
- FeO
- Octohedral crystal form
- Magnetic
- Gravity separation
Name the key identification properties of Haematite
- Fe2O3
- Hardness = 6
- Cherry red streak
- Reniform crystal form
- Ballast in ships
Name the key identification properties of Malachite
- Cu2CO3(OH)2
- Teal green
- Silky lustre
- massive, botryiodal, stalactitic crystal form
- Pigment in Jewellery
Name the key identification properties of Siderite
- FeCO3
- White streak
- Tabular crystal form
- Steel production
Name the key identification properties of Barite
- BaSO4
- White
- Pearly lustre
- Fibrous, Nodular, Massive crystal form
- Weighting filler in rubber
What are magmatic ore deposits?
Forming at high temperature that occur during the cooling of magma.
Which elements are found in magmatic sulphides?
Platinum, palladium, rhodium are most economical but you can find all PGE
- Cu and Ni
What are PGE (Platinum Group Elements) used for?
- autocatalysts (e-tech)
- in jewellery
- anti cancer drugs
Where can you find magmatic sulphides?
- Great dyke (Zimbabwe)
- Bushveld Complex (S.Africa)
- Sudbury (Canada) - Ni dominant but PGE are a bi-product.
Where does 75% of PGE come from?
S.Africa
How do magmatic sulphide deposits form?
- Mafic magma (gabbro)
- Magma reaches S saturation piont and can’t hold anymore sulphur in solution
- Sulphide liquid in magma is like oil in water forming droplets
- Saturation is caused by prolonged crystallisation and contamination from crustal S.
- PGE + Au, Ni, Cu are attracted to sulphide liquid => concentration.
- S liquid is denser than the magma now so sinks to the bottom to form a cumulative layer (4ppm)
What mineral ores is found in the magmatic sulphide deposits?
- pyrrhotite
- pentlandite
- chalcopyrite
Name some early forming magmatic oxide minerals
- Chromite
- ilmenite
- magnetite
How do magmatic oxide deposits form?
In ultramafic/mafic magma (gabbros and dunites). Magma starts to crystalize high temperature minerals (chromite, ilmenite, magnetite) which sink to form a layer/ ore deposit at the base of the reservoir.
Whats is the composition of a magmatic oxide deposit?
- Chromite, Ilmenite and Magnetite. (45% Cr2O3)
- Fe and Ti can also form (18% TiO2)
What is a Pegmatite?
An igneous rock with very coarse grain/crystal size, crystals >1cm.
How do pegmatites form?
- Felsic/acidic magma in the presence of volotiles (CO2, H2O) aids the growth of crystals such as Feldspar, quartz and mica.
- Incompatible elements concentrate in the magma that remains.
- The remaining magma crystallises and forms exotic minerals/rare earth minerals in the final stages.
- E.g. Li, Ur, Th, Zircon, Emeralds.
