Mining Geology and Exploration

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Transcript Mining Geology and Exploration

MMPE 290
Introduction to Mining & Mineral Process
Engineering
Mining Geology and Exploration
Mining Geology and Exploration
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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
Economically Important Metal
Concentrations in Earth’s Crust
Metal
Aluminum
Iron
Copper
Nickel
Zinc
Uranium
Lead
Silver
Gold
Concentration
(% by weight)
8.0
5.8
0.0058
0.0072
0.0082
0.00016
0.001
0.000008
0.0000002
Note for comparison:
Silicon 28%
Oxygen 46%
What is a mineral?
A solid naturally-occurring compound
having a definite chemical composition
Examples:
quartz - SiO2 (an oxide)
hematite - Fe2O3 (another oxide)
covelite - CuS (a sulphide)
What is an ore deposit?
An occurrence of minerals or metals
in sufficiently high concentration to
be profitable to mine and process
using current technology and under
current economic conditions.
What is ore grade?
Ore grade is the concentration of
economic mineral or metal in an ore
deposit.
· Weight percentage (base metals)
· Grams/tonne or oz/ton (precious
metals)
Economically Important Metals
Typical Grades of Ore Deposits
Metal
Aluminum
Iron
Copper
Nickel
Zinc
Uranium
Lead
Silver
Gold
Typical Grade
(% by weight)
30
53
0.5-4
1
4
0.3
5
0.01
0.0001-0.001
What does it take to be an ore
deposit?
2
10
Iron
Aluminum
Typical Orebody Concentration
1
10
Lead Zinc
Copper
Nickel
0
10
Uranium
y=x
-1
10
-2
Silver
10
-3
10
Gold
-4
10
-7
10
-5
10
-3
10
-1
10
Crustal Concentration
1
10
3
10
Hydrothermal Ore Deposits
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
Metamorphic Ore Deposits
Concentration of minerals caused by high
temperatures and pressures near intrusions
Examples:
Lead-zinc deposits in southeast B.C.
Diamonds
Garnets
Hydrothermal and
Metamorphic Ore Deposits
Geyser or hot spring
zoning
Hydrothermal solutions
entering veins in rocks
Ore deposit
Alteration of rocks by
heat and pressure
Intrusion
Sedimentary Ore Deposits
Deposition of dense, resistant minerals in
streams, lakes etc (Alluvial Deposits),
e.g. Placer gold
Precipitation of minerals from ancient
oceans (Evaporite Deposits), e.g. Potash
and salt deposits
Accumulation, burial and petrification of
vegetation, e.g. Coal Deposits.
Exploration Methods
· Remote sensing
· Geological mapping
· Geophysical surveys
· Geochemical surveys
· Bulk sampling
· Drilling (core or destructive)
Airborne Geophysics
Helicopter
Bush
Cable
“Bird”
GEOPHYSICAL
METHODS
Geochemical Anomalies
DIAMOND DRILL
DIAMOND DRILL
HOLE SIZES
SURFACE SET
DIAMOND DRILL
CORE BIT AND
REAMING SHELL
Senior Mining Company Exploration
Expenditures - 1997
Total: $817.7M
US
14.0%
Canada
27.0%
Other
48.2%
Chile
6.7%
Mexico
4.1%
Junior Mining Company Exploration
Expenditures - 1997
US
10.5%
Other
18.4%
Total: $262.2M
Canada
33.9%
Mexico
17.7%
Chile
19.6%
Role of Exploration
Each ton of ore mined must be replaced
with another ton to continue business.
The alternative to exploration is
acquisition of mining properties.
Exploration has a high failure rate, but
this should not affect a diversified mining
company.
Exploration costs are tax-deductible.
Diamonds in Canada?
Diamonds are formed at high pressure
deep in the earth and transported to
surface in kimberlite pipes
Other minerals also formed if pressures
high enough - indicator minerals
Indicator minerals are mobile and easily
transported by erosion.
An eroded kimberlite pipe
Direction of glacier flow
Indicator minerals
Kimberlite pipe
Lac de Gras
The Ekati Mine
Recommended Reading
Fire into Ice
Charles Fipke and the
Great Diamond Hunt
by Vernon Frolick
Raincoast Press
Nevada Gold
Formed 30-50 million years ago by
hydrothermal activity in sedimentary rocks
Part of a large mineralized zone extending
into Mexico and Central America
Carlin, Bootstrap, Cortez, Gold Acres
Some deposits low grade but can now be
processed using heap leach technology
South American Ore Deposits
Volcanic and igneous activity in Andes
produces a variety of rich mineral deposits
Minerals are exposed at or very near the
surface - leads to oxidation requiring
different kinds of mineral processing
Transport of mineral products, power and
water supply a concern in high Andes