Mining and Ore deposits

Question 1

What is a Natural Resource? Give a definition and examples.

Answer 1

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.

Question 2

What are the requirements for a resource to enter cumulative production?

Answer 2

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.

Question 3

What is the natural resource concept?

Answer 3

The relation of price, value, demand, supply and substitution. These are determined by how easy it is to extract a resource.

Question 4

What might you do if the price of a resource is too high?

Answer 4

Substitute it for a different material, the original material will then go down in demand and then price.

Question 5

Demand is determined by:

Answer 5

A resources usefulness

Question 6

Supply is determined by:

Answer 6

Ease of extraction and distribution. Supply is responsive to demand

Question 7

Lack of supply can lead to:

Answer 7

Substitution

Question 8

What is an industrial mineral:

Answer 8

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.

Question 9

Give examples of Building stone substitution and why it might occur.

Answer 9

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)

Question 10

Give examples of local building stone used:

Answer 10

Aberdeen: Granite
Sailsbury Cathedral: Chilmark stone (limestone)
Raglan Castle: Sandstone

Question 11

Name 3 industrial minerals that can be found in this country that aren’t building materials

Answer 11

• Potash
• Rock Salt
• China Clay

Question 12

What is Kaolinite and how is it mined?

Answer 12

Feldspar rich clay, (china clay) and its sprayed with high pressure water, held in suspension.

Question 13

Whats the definition of an Orebody:

Answer 13

An accumulation of minerals distinct from its host rock that is rich enough in metal to be worth economic exploitation, i.e. Profitable.

Question 14

What are gemstones?

Answer 14

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

Question 15

What is an Energy mineral?

Answer 15

In its natural state or after refinement it can be used to generate energy

Question 16

Define sustainable development:

Answer 16

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.

Question 17

Define Mining Legislation:

Answer 17

Robust conditions in which the mining company must show environmental awareness ad proactivity.

Question 18

How much gold has ever been mined?

Answer 18

161,000 tons

- barely enough to fill 2 Olympic sized swimming pools

Question 19

Disadvantages of current large open pit gold mines:

Answer 19

• Large visual impact
• 1-2g of gold per ton of rock (very wasteful)
• geography restricted
• 250t = 1 wedding ring

Question 20

Disadvantages of artisanal gold mines:

Answer 20

• minor due to local nature of mining but environmental rehab isn’t assessed.
• more destructive
• pollution from mercury and cyanide extraction.

Question 21

Define a metalliferous ore:

Answer 21

A rock that can be worked economically for a metal or group of metals that it contains.

Question 22

What are Native Ores:

Answer 22

Ore that contains a metal in its elemental free state.

- Gold, silver, mercury, copper, platinum

Question 23

What is a troy Oz equivalent to in grams?

Answer 23

31g

Question 24

What are Sulphide Ores:

Answer 24

Contain a metal or group of metals in combination of Sulphur

• Common
• Iron (pyrite), Lead (Galena), Zinc, Copper, Nickel

Question 25

What are Oxide Ores:

Answer 25

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

Question 26

What are Carbonate + Sulphate Ores:

Answer 26

Contains metal/group in combination with oxygen and carbon OR oxygen and sulphur. - Barium sulphate, Iron carbonate, Copper Carbonate (Malachite)

Question 27

Advantage and disadvantage of carbonate + sulphate ores:

Answer 27

- Good signal for presence of primary ores. | - Usually form due to weathering/interaction with primary ores (not helpful for extraction of metals)

Question 28

Name the crustal abundance from Oxygen to Gold

Answer 28

``` Oxygen : 47 Silicon: 27 Aluminium: 8 Iron: 5 Chromium: 0.01 Copper: 0.005 Gold: 4 parts per billion ```

Question 29

What concentration factor is needed to get a normal crustal abundance of Au up to to Ore levels?

Answer 29

A concentration factor of 5 for Iron but 250 for gold | - the cut off for a gold deposit is >1ppm

Question 30

How do hydrothermal ore deposits form?

Answer 30

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%.

Question 31

Where do the hot fluids in hydrothermal processes come from?

Answer 31

- Magmas (intrusion) - Metamorphism - Sea Water - Anywhere the geothermal gradient is high enough to heat the water.

Question 32

What causes precipitation of minerals from hydrothermal fluid?

Answer 32

- Change in temp (cooling) - Change in pressure (entering veins and closer to the surface) - Compositional change (chemistry) - Fluid mixing (brine and magma)

Question 33

Whats the definition of hydrothermal:

Answer 33

to do with hot fluids - usually related to magmatic activity

Question 34

What happens upon cooling of hydrothermal fluid?

Answer 34

They precipitate out ore and gangue minerals | - they typically form veins, dissemminations and stockworks.

Question 35

Describe a Porphry deposit:

Answer 35

A large high tonnage, low grade (<1%Cu) deposits associated with plutons of intermediate-acidic porphyritic igneous rock.

Question 36

What are porphyries a major source of?

Answer 36

Copper, gold and molybdenum

Question 37

Where does a porphyry typically form

Answer 37

In plutons above subduction zones

Question 38

How does a porphyry form?

Answer 38

Sudden release of fluids near the surface, with a shattering of the enclosed rocks, forming 'stockwork' mineralisation.

Question 39

What is the source of metals and heat to form a porphyry?

Answer 39

Magma, most likely if not always an intrusion

Question 40

Explain how mineral veins form:

Answer 40

sudden release of volotiles causes rocks to crack and change in pressure so minerals/metals precipitate out to fill the gap.

Question 41

What mineral structures do porphyrys typically produce

Answer 41

veins, disseminations and stockworks with chalcopyrites

Question 42

A porphyry is an example of what?

Answer 42

A hydrothermal ore deposit

Question 43

What is an Epithermal deposit?

Answer 43

A low tonnage but high grade deposit that telescopes up from depth, usually form within 1km of the surface.

Question 44

What temperature do epithermal deposits reach the surface at?

Answer 44

100-200 degrees C as hot springs

Question 45

Name typical minerals found in epithermal deposits

Answer 45

Gold, Silver, Mercury and Antimony

Question 46

How do Epithermal deposits form?

Answer 46

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)

Question 47

Whats different about the cornish vein deposits?

Answer 47

From a granite pluton, the change in temperature radiating outwards causes zoning of different minerals.

Question 48

Metamorphism produces fluids which may carry gold what geological structure aids the golds deposition and what name is given to this deposit

Answer 48

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.

Question 49

Advantage of Orogenic gold deposit

Answer 49

Largest source of gold - quartz - pyrite

Question 50

Whats another name for hydrothermal deposits that form at mid ocean ridges?

Answer 50

VMS - Volcanogenic Massive Sulphides

Question 51

How do VMS form?

Answer 51

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

Question 52

What are black smokers made from?

Answer 52

Mainly sulphides as well as Anhydrite mixed in. Cones become more porous upward.

Question 53

Name the main elements found at black smokers

Answer 53

Copper and Zinc. Sometimes Lead, Silver and Gold

Question 54

What is a Placer Deposit?

Answer 54

Mineral deposits that have been concentrated by mechanical action, typically fluvial processes

Question 55

Name common placer deposit minerals:

Answer 55

Gold, magnetite, ilmenite, chromite and diamonds

Question 56

What was found in Witwatersrand basin in S.Africa?

Answer 56

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

Question 57

What is a Laterite deposit

Answer 57

When chemical weathering removes soluble elements from a rock, leaving insoluble residual deposits which may be enriched metals. - Typically tropical

Question 58

Give an example of a metal typically found in a laterite deposit?

Answer 58

Nickel

Question 59

Where is Nickel sourced from?

Answer 59

Ultra basic rocks form nickel laterites

Question 60

Describe the sequence of beds that form a laterite deposit:

Answer 60

- 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)

Question 61

What is Bauxite?

Answer 61

A mixyure of 3 hydrates. Its a rock type not an ore mineral from broken down clays forming alumina-gibbsites

Question 62

Name the key identification properties of native copper

Answer 62

- Element - Streak = Dark Brown - Very Dense = 8.96 - Pipes and wires

Question 63

Name the key identification properties of Sphalerite

Answer 63

- ZnS - Greasy Lustre - Rhombic crystal form - Jewellery

Question 64

Name the key identification properties of Galena

Answer 64

- PbS - Dense = 7.4 - Making lead acid batteries

Question 65

Name the key identification properties of Chalcopyrite

Answer 65

- CuFeS2 - Brass/Yellow - Amorphous crystal form - Magnetic when heated - Finding copper

Question 66

Name the key identification properties of Pyrite

Answer 66

- FeS2 - Gold/Brass - Hardness = 6 - Cubic - Used to make sparks with flint

Question 67

Name the key identification properties of Magnetite

Answer 67

- FeO - Octohedral crystal form - Magnetic - Gravity separation

Question 68

Name the key identification properties of Haematite

Answer 68

- Fe2O3 - Hardness = 6 - Cherry red streak - Reniform crystal form - Ballast in ships

Question 69

Name the key identification properties of Malachite

Answer 69

- Cu2CO3(OH)2 - Teal green - Silky lustre - massive, botryiodal, stalactitic crystal form - Pigment in Jewellery

Question 70

Name the key identification properties of Siderite

Answer 70

- FeCO3 - White streak - Tabular crystal form - Steel production

Question 71

Name the key identification properties of Barite

Answer 71

- BaSO4 - White - Pearly lustre - Fibrous, Nodular, Massive crystal form - Weighting filler in rubber

Question 72

What are magmatic ore deposits?

Answer 72

Forming at high temperature that occur during the cooling of magma.

Question 73

Which elements are found in magmatic sulphides?

Answer 73

Platinum, palladium, rhodium are most economical but you can find all PGE - Cu and Ni

Question 74

What are PGE (Platinum Group Elements) used for?

Answer 74

- autocatalysts (e-tech) - in jewellery - anti cancer drugs

Question 75

Where can you find magmatic sulphides?

Answer 75

- Great dyke (Zimbabwe) - Bushveld Complex (S.Africa) - Sudbury (Canada) - Ni dominant but PGE are a bi-product.

Question 76

Where does 75% of PGE come from?

Answer 76

S.Africa

Question 77

How do magmatic sulphide deposits form?

Answer 77

- 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)

Question 78

What mineral ores is found in the magmatic sulphide deposits?

Answer 78

- pyrrhotite - pentlandite - chalcopyrite

Question 79

Name some early forming magmatic oxide minerals

Answer 79

- Chromite - ilmenite - magnetite

Question 80

How do magmatic oxide deposits form?

Answer 80

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.

Question 81

Whats is the composition of a magmatic oxide deposit?

Answer 81

- Chromite, Ilmenite and Magnetite. (45% Cr2O3) | - Fe and Ti can also form (18% TiO2)

Question 82

What is a Pegmatite?

Answer 82

An igneous rock with very coarse grain/crystal size, crystals >1cm.

Question 83

How do pegmatites form?

Answer 83

- 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.