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depends upon such factors as total
amount of heat present and the
amount of overlying,
insulating
rocks present. Depending on their
temperatures of formation in the
magma solution, minerals begin to
crystallize out and rise or sink
depending on their specific gravities.
By this method of differential
crystallization, high temperature
minerals, such as magnetite and
chromite are formed. They separate
into localized concentrations and
upon solidification
of the magma,
become ore deposits. As cooling
continues minerals continue to
crystallize out of the magma solution,
the remaining liquid becomes
increasingly rich in
low temperature
minerals, such as quartz, and volatile
minerals, such as water. The great
bulk of metallic ore minerals are
concentrated in this late-stage
residual solution.
Metamorphic deposits result from
rearrangement
of minerals already
existing in a rock, from heat and
pressure. No outside minerals are
added. Graphite, asbestos, talc,
garnet, jade are examples of minerals
which form economic deposits of this
type.
(**The above information was adapted from
Leo Mark Anthony and Michael Mark
Anthony, Introductory Prospecting and
Mining, pp. 69-93. Mining and Petroleum
Training Service, University of Alaska,
Soldotna, AK, 1997.)
2. Match the headings to the paragraphs 1-3.
Paragraph 1 ……..
Paragraph 2 ……..
Paragraph 3………
a. Magma – the major source.
b. Different formations of ore minerals.
c. Formation of ore deposits.
3. Put steps in the correct order to show the formation of ore deposits in
paragraph 1.