How the Earth works Lecture 10: Earth resources

Question 1

What are the two categories are mineral resources split into

Answer 1

Metallic and Non metallic

Question 2

List the Metallic mineral resources

Answer 2

Gold
Silver
Copper
Lead
Zinc
Iron

Question 3

List the non metallic mineral resources

Answer 3

Sand and gravel
Gypsum
Halite
Dimension stone

Question 4

Define a metal/metallic mineral resource

Answer 4

Metals are opaque, shiny, smooth solids that conduct electricity.

These properties derive from metallic chemical bonds with delocalized electrons that move.

Question 5

Define native metals

Answer 5

Native metals (gold, silver, copper, iron) occur naturally in a pure form.

Native metals are uncommon and valuable.

Copper is an example.

Question 6

Define an Ore

Answer 6

ORE – a rock or sediment containing concentrated metal-rich minerals.

The difference between an ore and other rock is that metals are concentrated in the ore

Question 7

Define smelting

Answer 7

Smelting is a process that releases metals from ore minerals.

Different minerals require different smelting techniques at different temperatures.

Blending metals creates alloys. The properties of alloys are often superior to those of the constituent metals

Question 8

Define an Ore deposit

Answer 8

ORE DEPOSIT - an economically significant accumulation of minerals within a host rock.

Question 9

Define a mineral resource

Answer 9

MINERAL RESOURCE is a mineral deposit occurring in high enough concentration to be economically viable.

Question 10

List the various methods/environments in which ore can form

Answer 10

Magmatic activity
Hydrothermal alteration
Secondary enrichment
Groundwater transport (MVT)
Sedimentary processes
Residual weathering
Hydraulic sorting

Source of metals
->
Transportation
->
Concentration

Question 11

Describe and explain metal transport mechanisms

Answer 11

Metal can be extracted from the mantle or the crust during partial melting or fluid interactions.

Ligands (such as fluorine, chlorine, phosphorous) control how soluble metals are in fluids and can act as a ‘helper’ to transport metals in fluids.

Fluid temperature, pH, oxidation state, salinity are also important for how likely metals are to be transported in the crust.

Changes in these variables are important for controlling whether metals are dumped out of solution into an ore deposit.

Question 12

Define a Ligand

Answer 12

Any atom or molecule attached to a central atom, usually a metallic element.

Can act as helper to transport metals in fluids.

Question 13

What is the relationship between ore deposits and tectonic boundaries

Answer 13

Plate tectonics are the most important control on the location and style of mineralisation in mineral deposits.

For example there is a strong relationship between Subduction zones and Porphyry copper deposits.

Question 14

Describe the distribution of Porphyry deposits

Answer 14

Porphyry deposits typically form above subduction zones, where metals are enriched in the crust through melting of the down-going slab, melting of the upper mantle/ lower crust and emplacement of metal enriched melts beneath volcanic systems.

Question 15

Describe the environment of a porphyry deposit

Answer 15

In a porphyry deposit mineralisation there is a dynamic environment of faulting, brecciation and fluid interaction caused by both magmatic and meteoric waters being put under pressure

causing explosive fracturing and fluid flow events, mixing fluids and causing mineralisation.

Question 16

Describe the classic porphyry model/structure

Answer 16

The classic porphyry alteration model is shown where;

mineralisation occurs in a series of shells that surround a causative intrusion.

Potassic alteration is the hottest and most proximal (closest), propylitic and chloritic are lower temperature.

Question 17

What are Carbonatites

Answer 17

Carbonatites are rare carbonate-bearing igneous rocks associated with alkaline igneous complexes.

Carbonatites are found associated with volcanoes in continental settings, associated with Archean cratons.

These rocks are enriched in REE which commonly found in accessory minerals such monazite and apatite.

Question 18

What is the worlds largest REE deposit

Answer 18

The world’s largest REE deposit is Bayon Obo in northern China/ Mongolia

In 2015 it was responsible for 45% of global production of REE.

In carbonatites metasomatism and fluid flow is important for enriching the rocks in REE-bearing minerals

Question 19

Describe the African copper belt and its copper deposits

Answer 19

The African Copper Belt is a sediment-hosted stratiform Cu-Co deposit that has produced ~20% of the world’s copper and is said to host ~40% of the world’s cobalt.

Salt-rich sedimentary rocks (ca. 880 Ma) host the mineralisation, where brines are through to be critical for causing mineralisation.

The sedimentary basin was inverted during the Pan-African orogeny (ca. 545-530 Ma)

Question 20

What are banded iron formation

Answer 20

Banded iron formations (BIFs) consist of alternating layers of gray hematite (Fe2O3) and iron-rich red chert (jasper). BIFs formed from 2.5–1.8 Ga and record the onset of oxygen buildup in Earth’s atmosphere.

Question 21

What is weathering and leaching in ore deposits

Answer 21

Intense chemical weathering strips almost everything out of soil except the most insoluble elements, leaving behind a residual ore.

Question 22

What is Bauxite

Answer 22

Bauxite is an aluminium-rich sedimentary rock.

Chemical weathering of feldspar forms an Al-rich clay kaolinite, in very hot climates along the tropics, this kaolinite further concentrating the aluminium.

In tropical climates other non-useful elements such as silica can dissolve, leaving the Al as bauxite behind.