How the Earth works Lecture 10: Earth resources Flashcards
What are the two categories are mineral resources split into
Metallic and Non metallic
List the Metallic mineral resources
Gold
Silver
Copper
Lead
Zinc
Iron
List the non metallic mineral resources
Sand and gravel
Gypsum
Halite
Dimension stone
Define a metal/metallic mineral resource
Metals are opaque, shiny, smooth solids that conduct electricity.
These properties derive from metallic chemical bonds with delocalized electrons that move.
Define native metals
Native metals (gold, silver, copper, iron) occur naturally in a pure form.
Native metals are uncommon and valuable.
Copper is an example.
Define an Ore
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
Define smelting
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
Define an Ore deposit
ORE DEPOSIT - an economically significant accumulation of minerals within a host rock.
Define a mineral resource
MINERAL RESOURCE is a mineral deposit occurring in high enough concentration to be economically viable.
List the various methods/environments in which ore can form
Magmatic activity
Hydrothermal alteration
Secondary enrichment
Groundwater transport (MVT)
Sedimentary processes
Residual weathering
Hydraulic sorting
Source of metals
->
Transportation
->
Concentration
Describe and explain metal transport mechanisms
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.
Define a Ligand
Any atom or molecule attached to a central atom, usually a metallic element.
Can act as helper to transport metals in fluids.
What is the relationship between ore deposits and tectonic boundaries
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.
Describe the distribution of Porphyry deposits
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.
Describe the environment of a porphyry deposit
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.
Describe the classic porphyry model/structure
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.
What are Carbonatites
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.
What is the worlds largest REE deposit
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
Describe the African copper belt and its copper deposits
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)
What are banded iron formation
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.
What is weathering and leaching in ore deposits
Intense chemical weathering strips almost everything out of soil except the most insoluble elements, leaving behind a residual ore.
What is Bauxite
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.
