Aula 11 Exploração de Minerais MINAS Mineralogia

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Mining Geology and Exploration
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Mining Geology 
and 
Exploration
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Plate Tectonics and mineral deposition.
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How much metal is available?
What is a mineral? What is ore?
How do ore deposits form?
Mining exploration methods
Role of exploration in mining
Case histories
 Mining Geology and Exploration
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Note for comparison:
Silicon 28%
Oxygen 46%
Economically Important Metal 
Concentrations in Earth’s Crust
Metal
Concentration
(% by weight)
Aluminum
8.0
Iron
5.8
Copper
0.0058
Nickel
0.0072
Zinc
0.0082
Uranium
0.00016
Lead
0.001
Silver
0.000008
Gold
0.0000002
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A solid naturally-occurring compound having a definite chemical composition
Examples:
	quartz - SiO2 (an oxide)
	hematite - Fe2O3 (another oxide)
	chalcopyrite - CuFeS (a sulphide)
What is a mineral?
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What is ore grade?
Weight percentage (base metals) 
Grams/tonne or oz/ton (precious metals)
Ore grade is the concentration of economic mineral or metal in an ore deposit.
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 Economically Important Metals 
 Typical Ore Deposit Average Grades
Metal
Typical Grade
(% by weight)
Aluminum
30
Iron
53
Copper
0.5-4
Nickel
1
Zinc
4
Uranium
0.3
Lead
5
Silver
0.01
Gold
0.0001-0.001
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As magma cools, more abundant metals (silicon, aluminum) deposit first 
Solidification of magma releases water - a hydrothermal solution
Minerals precipitate from hydrothermal solution and deposit in cracks or veins in rock
Hydrothermal Ore Deposits
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Concentration of minerals caused by high temperatures and pressures near intrusions
Examples:
Lead-zinc deposits in southeast B.C.
Diamonds
Garnets
Metamorphic Ore Deposits
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Hydrothermal and Metamorphic Ore Deposits
zoning
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Deposition of dense, resistant minerals in streams, lakes etc (Alluvial Deposits), e.g. Placer gold
Precipitation of minerals from lakes-oceans (Evaporite Deposits), e.g. Potash and Salt Deposits 
Accumulation, burial and petrification of vegetation, e.g. Coal Deposits. 
Sedimentary Ore Deposits
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Exploration Methods
Remote sensing 
Geological mapping
Geophysical surveys
Geochemical surveys
Bulk sampling 
Drilling (core or destructive)
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Airborne Geophysics
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GEOPHYSICAL
METHODS
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Geochemical Anomalies
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Próxima aula MINAS SUBTERRÂNEAS
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Crust is the outer 20 km of earth
Underlain by mantle - about 3000 km thick
Underlain by core - about 3400 km thick
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A rock is an assemblage of minerals
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Define base metals and precious metals
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Magma - molten rock beneath surface of earth
Lava - molten rock above surface that could ruin your day 
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Should say that intrusions not necessary for metamorphism
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Hydrothermal deposits are probably being formed as we speak in Yellowstone National Park
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The most interesting mineral crystal structures form in sedimentary environments.
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These are roughly in increasing order of cost per square km
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Birds capable of measuring numerous physical responses
Passive methods - simply measure a physical field, e.g., magnetic field
Active methods - emit a signal and measure the response, e.g., electromagnetic field
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Define base metals and precious metals
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Anomaly: something different from the normal or expected.
From a mineral deposit point of view, the earth is generally boring and barren - sometimes it produces anomalies
Concentrations of metals in soils, water and trees is measured in parts per million and sometimes parts per billion
The closer an orebody is to the surface, the more likely there will be a geochemical anomaly - remember this for later this morning