Transcript U5-T 1.1-Economic Minerals and Mineral Depositsx

Earth Systems 3209
Unit: 5
Earth’s Resources
Reference:
Chapters 21; Appendix A & B
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Unit 5:
Topic 1.1
Economic Minerals and Mineral Deposits
Focus on . . .
 defining economic mineral and ore.
 identifying factors which determine if a mineral is of
economic value
 identifying and describing the different types of
mineral deposits.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Terminology Associated with Economic Minerals
 Economic Minerals
 minerals that can be extracted, processed, and
marketed at a profit.
 Factors:
 interest in the mineral
 size of the deposit
 mineral concentration
 mineral depth below the surface
 market value.
Text Reference:
Pages 583
 An Ore is a natural material with a high concentration
of economically valuable minerals that can be mined
for a profit.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Origin of Mineral Deposits
 A mineral deposit is a volume of rock enriched in one or more
minerals. In this sense a mineral refers to a useful material, a
definition that is different from the way we defined a mineral
earlier in this course.
 Mineral deposits can be classified on the basis of the mechanism
responsible for concentrating the valuable substance.
Examples Include:
1) Magmatic Mineral Deposits
2) Hydrothermal Mineral Deposits
3) Sedimentary Mineral Deposits
Text Reference:
Pages 583 - 596
4) Placer Mineral Deposits
5) Metamorphic Deposits
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Metallic Mineral Deposits
1) Magmatic Deposits
 Accumulations of metals associated with magma that
forms igneous rocks
 Certain metals are enriched in certain magmas and
further concentrated during cooling of the magma
 As minerals crystallize from a
magma body, heavy minerals
may sink to the bottom of the
magma chamber and others
may form on the sides of the
magma chamber.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Magma
Chamber
Crystal
Settling
Metallic Mineral Deposits
1) Magmatic Deposits
a) Layered
 Gravitational Settling - heavy minerals that crystallize
early, settle and concentrate on the bottom of the
magma chamber this results in a layered deposit.
High-density minerals sink to the
bottom of the magma chamber.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Metallic Mineral Deposits
1) Magmatic Deposits
b) Disseminated
 A mineral deposit in which the metal is evenly
distributed in generally low concentrations
throughout large masses of igneous rock.
 Ex: porphyry copper deposit
 Ex: Nickel deposits.
Sudbury, Ontario and Voisey’s Bay,
Newfoundland Labrador
A sample of nickel-bearing
rock from Sudbury.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Metallic Mineral Deposits
2) Hydrothermal Mineral Deposits
 Minerals are concentrated by hot fluids flowing through
fractures and pore spaces in rocks.
 Hydrothermal deposits are produced when groundwater
circulates down to depths and heats up, either by
coming near a hot igneous body or by circulating to
great depths which naturally heat the water.
 Such hot water can dissolve valuable minerals as it
passes through a large volume of rock.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Metallic Mineral Deposits
2) Hydrothermal Mineral Deposits
 As the hot water moves into cooler
areas of the crust, the dissolved
minerals are precipitated and deposited
from the hot water solution.
Ore minerals
depositing in veins
 If the cooling takes place rapidly in open
fractures or upon reaching cool surface
waters, then precipitation will take place
over a limited area, resulting in a higher
concentration of minerals than was
originally present in the rocks.
 Example: Vein deposits
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Cooler water
moving toward
surface
Hot water
moving at
depths
Metallic Mineral Deposits
2) Hydrothermal Mineral Deposits
 Black Smokers
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Metallic Mineral Deposits
2) Hydrothermal Mineral Deposits
Note:
In the diagram to the
right both vein deposits
and disseminated
deposits are seen
surrounding the
magma chamber.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Metallic Mineral Deposits
3) Placer Deposits
 Formed when heavy metals are mechanically
concentrated by flowing surface waters depositing high
density minerals either in streams or along coastlines.
 When the velocity of the water slows, minerals with a
higher density are deposited. Heavy minerals like gold,
diamond, and magnetite will be concentrated in areas
where water current velocity is low. The lighter minerals
(quartz) are carried away.
 Examples: Gold, Platinum, Diamonds
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Metallic Mineral Deposits
3) Placer Deposits
Placer deposits occur in any area where current velocity is low, such as;
1) between ripple marks
Stream Direction
2) behind rock bars
Placer
Deposit
3) on the inside of meandering streams
Placer
Deposit
Stream Direction
Placer Deposit
4) in holes on the bottom of a stream
Stream Direction
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Placer
Deposit
Metallic Mineral Deposits
3) Placer Deposits
Placer deposits occur in any area where current velocity is low, such as;
 formed when heavy metals are
mechanically concentrated by
currents
Examples:
Gold, Platinum, Diamonds
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Metallic Mineral Deposits
4) Secondary Enrichment (Sedimentation)
 These deposits often form as a result of chemical weathering in
warm tropical climates that receive high temperatures and high
amounts of rainfall which produces highly leached soils rich in
both iron and aluminium. Chemical weathering tends to remove
the soluble materials, leaving the less soluble residues.
 Two common mineral deposits formed in this way
are iron-rich Limonite and aluminium-rich Bauxite.
Bauxite is the world’s primary source of aluminium.
It forms in rainy tropical climates from chemical
weathering.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Metallic Mineral Deposits
4) Secondary enrichment (Sedimentation)
 In addition, an existing mineral deposit can be turned
in to a more highly concentrated mineral deposit by
weathering in a process called secondary enrichment.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Metallic Mineral Deposits
5) Metamorphic Deposits
 Many of the most important metamorphic ore
deposits are produced by contact metamorphism.
Skarns are metal-rich
deposits in Carbonate
rocks that has
undergone contact
metamorphism.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Non-Metallic Resources
 Diamonds
 Most diamonds are found in unique ultramafic
igneous rocks called kimberlites.
 Magma generated by partial melting of
asthenosphere below 150 kilometres and
then rises quickly to the surface, picking up
diamonds from solid lithospheric mantle.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Non-Metallic Resources
 Kimberlite Pipes and Diamonds
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Example 1:
Which letter represents a location in the river where
a placer deposit would most likely form. Explain two
reasons to support your choice.
C
A
D
B
Answer:
Letter “C” represents the only location along the river where a placer deposit would
most likely form. In a meandering river, current velocities differ from inside of turns
to outside of turns. The current velocity of water, at location “C”, is slower on the
inside of turns and faster on the outside of turns, location “B”. Placer deposits
usually involve high density and/or heavy materials, for example, gold. Because it
takes energy and/or high velocity (fast-moving) water to transport gold, then it is
only appropriate to look for gold along areas of a river (e.g. location C) where the
energy and/or current velocity is low.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Example 2:
Which process produces copper mineralization in veins
around granitic intrusions?
(A) Hydrothermal
(B) Layered magmatic
(C) Metamorphism
(D) Placer
Based on the statement below,
Beneath a circular lake is a carrot-shaped
deposit of ultramafic composition.
Which is the correct match between mineral and rock type?
Mineral
Rock Type
(A)
diamond
gabbro
(B)
diamond
kimberlite
(C)
gold
gabbro
(D)
gold
kimberlite
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Your Turn . . .
Take the time and complete the following questions . . .
(Solutions to follow)
Questions:
Indicate the type of mineral deposit which could form at
location A and explain the process.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Solutions . . .
Questions:
Indicate the type of mineral deposit which could
form at location A and explain the process.
Answer:
Hydrothermal (or vein) is the type of mineral deposit that could form at location
A. Pressure from the magma intrusion causes fractures or cracks to form in the
overlying sedimentary rock layers. Ground water in the overlying sedimentary
rock layers is warmed by the heat that is radiating out from the magma intrusion.
Warm water can dissolve large quantities of elements. As the warm water, which
is enriched in elements, flows toward Earth’s surface (away from the magma
intrusion) through fractures or cracks, it begins to cool. Since cold water cannot
dissolve elements as readily as warm water, minerals begin to precipitate out of
the solution. These minerals are found in the fractures or cracks forming
hydrothermal vein deposits.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador
Summary . . .
Overview of Points covered:
 Economic Mineral - minerals that can be extracted, processed, and
marketed at a profit.
 Ore - natural material with a high concentration of economically
valuable minerals that can be mined for a profit.
5 Types of Mineral Deposits Include:
1) Magmatic Mineral Deposits
4) Placer Mineral Deposits
2) Hydrothermal Mineral Deposits
5) Metamorphic Deposits
3) Sedimentary Mineral Deposits
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador