MET 05105 ORE AND WASTE PRODUCTION CONTROL
(09 credits)
Lect 1
Ore forming processes
Instructor: Eng Promiseana Komba
JEMA Institute of Technology, JIT
Introduction
Ore is a rock body that is enriched in one or more minerals.
There about five ore forming processes these include;
Magmatic process
Hydrothermal process
Sedimentary process
Weathering process
Metamorphic process
MAGMATIC PROCESS
Magmatic process
Magmatic process
Magmatic is when liquid magma cools and solidifies to form igneous rock, it
forms ore of metals, gems and other precious minerals.
As magma solidifies (plutonic) its temperature gradually decreases.
Minerals crystalize first in the liquid magma. Some crystals are denser than
the magma which will settle down and is concentrated at the bottom which
is also called crystal settling.
In the mafic magma crystallization usually starts from the bottom so early
forming minerals are concentrated at the base.
Magmatic process
Fractional crystallization: separates ore and non-ore minerals
according to their crystallization temperature. These crystals
may settle onto the bottom of the intrusion, concentrating ore
minerals there. Chromite and magnetite are ore minerals that
form in this way.
Liquid immiscibility: As a magma changes, parts of it may
separate from the main body of magma. In magmas, sulfides
may separate and sink below the silicate-rich part of the
intrusion or be injected into the rock surrounding it. These
deposits are found in mafic and ultramafic rocks.
Magmatic process….
Magmatic segregation.
Magmatic segregation is a process by which one or more
minerals become locally concentrated (segregated) during the
cooling and crystallization of a magma. Rocks formed because
of magmatic segregation are called magmatic cumulates.
While a magma may start as a homogeneous liquid, magmatic
segregation during crystallization can produce an assemblage
of cumulates with widely differing compositions.
HYDROTHERMAL PROCESS
Hydrothermal process
Hydrothermal process is the most common ore forming process.
Water is heated by the magma chamber and this water dissolves metals.
Metals are dissolved in the water and this solution seeps through cracks,
fractures and through permeable rocks until they are precipitated and form a
deposit.
Sources of hydrothermal solutions include seawater, meteoric water circulating
through fractured rock, formational brines (water trapped within sediments at
deposition), and metamorphic fluids created by dehydration of hydrous minerals
during metamorphism.
Hydrothermal process
As of the fact that salty water increases the solubility of the water which
is further enhanced by the heating.
Hot salty water is a powerful agent in dissolving and transporting
metals.
Hydrothermal process
There are several types of hydrothermal mineralization
Hydrothermal vein deposits are formed when these hydrothermal
solutions enter a country rock along cracks and fractures. It precipitates
in the parent rock in a vein like structure.
The hydrothermal solution in vein deposits can also soak through the
country rock which for disseminated ore deposits. This is less
concentrated but as formed with the vein together they form economical
deposit.
Hydrothermal process
Disseminated copper deposits are associated with porphyry copper
deposits.
SEDIMENTARY PROCESS
Sedimentary process
• These deposits owe their origin to the weathering of preexisting rock,
which facilitates the segregation of the ore into an anomalously high
concentration.
• Sedimentary mineral deposits may be classified as
(1) placer deposits,
(2) residual concentrations
(3) supergene enrichments
(4) primary chemical precipitates.
Sedimentary…………
• Placer deposit
Are mineral deposits in which certain heavy minerals have been
concentrated by the selective sorting and transportation action of
currents and waves. The ore material is chemically and physically
resistant and has a higher density than associated sedimentary
materials.
• Residual placer
Are concentrations of weathering-resistant ore minerals that are due to
supergene abstraction of non-ore material.
Assignment, to be collected on next session
• Explain about supergene enrichment and primary chemical
precipitate.
