Classification of Ore Deposits | Economic Geology

CLASSIFICATION OF ORE DEPOSITS
M.Hisan Mehdi
Dr Abdul Shakoor Mastoi
Prepared by
M.Hisan Mehdi 47/GLG/2K18
Submitted to
Abdul Shakoor Mastoi

CONTENT
 Magmatic ore deposits.
o Early magmatic deposits
 Dissemination deposits
 Segregation deposits
o Late magmatic deposits
 Sublimation ore deposits.
o Hypothermal deposit
o Mesothermal deposit
o Epithermal deposit
 Cavity Filling Deposits
 Fissure vein
 Shear zone deposits
 Saddle reefs
 Ladder Vein
 Replacement Deposits
 Pegmatitic ore deposits.
 Contact metasomatic ore deposits.
 Hydrothermal ore deposits
 Cavity filling deposits.
 Replacement deposits.
 Sedimentation ore deposits.
 Evaporation ore deposits.
 Residual Deposits
 mechanical concentration deposits
o Eluvial placers
o Stream Placers
o Beach placers
o Eolian placers
o
 Metamorphic ore deposits.

The Mixture of ore minerals are gangue minerals form an Ore deposit. The ore
deposits are generally found enclosed within the country rocks. The ore deposits
are formed in many different ways. Depending upon the process that may
operate to produce them, the ore deposits may be classified as follow:
 Magmatic ore deposits.
 Sublimation ore deposits.
 Pegmatitic ore deposits.
 Contact metasomatic ore deposits.
 Hydrothermal ore deposits
 Cavity filling deposits.
 Replacement deposits.
 Sedimentation ore deposits.
 Evaporation ore deposits.
 Residual and mechanical concentration deposits
 Metamorphic ore deposits.
MAGMATIC ORE DEPOSITS:
The magmatic ore deposits are the magmatic products which crystallize from
magmas. The magmatic ore deposits are classified as follows:
o Early magmatic deposits
o Late magmatic deposits

Early magmatic deposits:
Early magmatic deposits are formed during the
early stage of the magmatic period. In this case the
ore minerals crystallize earlier than the rock
silicates. The Minerals of Nickel, Chromium, and
Platinum are usually found as early magmatic
deposits. The early magmatic deposits can be sub
divided into two groups:
o Dissemination deposits
o Segregation deposits
Dissemination deposits:
When magma crystallizes
conditions, a granular igneous rock is formed. In
such a rock early formed crystals of
may occur in dissemination.
Segregation deposits:
Magmatic segregation deposits are
formed as a result of gravitative
crystallization differentiation. In
case, the ore mineral which crystallize
early, get ocean-trated on a particular
part of igneous part. The ore deposits
thus formed are known as “Segregation
deposits”.
Early magmatic deposits are formed during the
early stage of the magmatic period. In this case the
ore minerals crystallize earlier than the rock
Nickel, Chromium, and
are usually found as early magmatic
rly magmatic deposits can be sub
Dissemination deposits
Segregation deposits
crystallizes under seated
conditions, a granular igneous rock is formed. In
such a rock early formed crystals of ore minerals
Magmatic segregation deposits are
formed as a result of gravitative
crystallization differentiation. In such
case, the ore mineral which crystallize
trated on a particular
part of igneous part. The ore deposits
thus formed are known as “Segregation

Late Magmatic Deposits:
The ore deposits which are formed to
called late magmatic deposits. The late magmatic deposits contain those ore
minerals which have crystallized at rather low temperature from the residual
magma. The magma which is left after crystallization of early for
is called residual magma. This magma frequently contains many ore minerals. The
late magmatic deposits include most of the magmatic deposits of iron and
titanium ores, these deposits are almost always associated with mafic igneous
rocks.
SUBLIMATION DEPOSITS:
Sublimation is a very minor process of formation of ore deposits. Sublimation
deposits contain only those minerals which have been volatilized by hear and
subsequently redeposit in the same form at low temperature and pressure. The
sublimation deposits are found associated with Volcanoes and Fumaroles. Sulfur
of this origin has been mined in Japan, Italy, and Mexico.
PEGMATITIC DEPOSITS:
The late residual magma which is left in the last stage of crystallization, commonly
contains silica, alkalis, water, carbon dioxide and concentration of rare elements
and metals. Pegmatites are formed when this residual magma gets injected into
the enclosing rocks. Many such pegmatite form valuable mineral deposits. The
economic minerals which comm
gemstone, and feldspar. Deposits are tantalum, niobium, tin,
molybdenum and uranium are also found in some pegmatites.
economic importance are mostly found associated with felsic igneous ro
are quartz dioritic rocks.
CONTACT METASOMATIC DEPOSITS:
When certain igneous rocks invade carbonate
rocks, such as limestone, ore deposits are formed
near the contain by the reaction of the magmatic
vapors on the host rock. These reactio
place under condition of high temperature and
pressure. The new minerals that develop may be
composed of partly or wholly of constituents
added from the magma. All the magma do not
The ore deposits which are formed toward the close of magmatic period are
magma. The magma which is left after crystallization of early formed rock silicates
of this origin has been mined in Japan, Italy, and Mexico.
ilica, alkalis, water, carbon dioxide and concentration of rare elements
formed when this residual magma gets injected into
economic minerals which commonly occur in pegmatite are mica, corundum,
gemstone, and feldspar. Deposits are tantalum, niobium, tin, tungsten,
molybdenum and uranium are also found in some pegmatites. Pegmatite`s
economic importance are mostly found associated with felsic igneous ro
CONTACT METASOMATIC DEPOSITS:
When certain igneous rocks invade carbonate
rocks, such as limestone, ore deposits are formed
near the contain by the reaction of the magmatic
vapors on the host rock. These reaction take
place under condition of high temperature and
pressure. The new minerals that develop may be
composed of partly or wholly of constituents
added from the magma. All the magma do not
ward the close of magmatic period are
med rock silicates
ilica, alkalis, water, carbon dioxide and concentration of rare elements
formed when this residual magma gets injected into
only occur in pegmatite are mica, corundum,
tungsten,
Pegmatite`s
economic importance are mostly found associated with felsic igneous rocks such

give rise to contact metasomatic deposits. Mostly felsic intrusive of intermediate
composition, such as monzonites and granodiorites yield Ore deposits. Contact
metasomatic
deposits usually carry ores of copper, iron, zinc and more rarely gold, silver and
lead. The characteristic gangue minerals which are found associated with these
ore deposits are high temperature silicates, such as garnet, diopside, tremolite,
wollastonite, and phlogopite. The contact metasomatic deposits are generally
discontinuous and irregular in shape. They are in general of comparatively small
size.
HYDROTHERMAL DEPOSITS:
The epigenetic ore deposits formed by hydrothermal solution are called
hydrothermal ore deposits.
Hydrothermal Solution:
The fluid left during the later stage of crystallization of intrusive magma when the
main rock forming minerals have already been precipitated, is called “Residual
fluid”. Metals originally present in the magma, concentrate in this fluid. This fluid
which is a hot watery solution containing mineralized liquids derived from an
intrusive magma is called “hydrothermal Solution”
The hydrothermal solution move through cracks and opening present in the
cracks and deposit their dissolved minerals there.
Classification:
On the basis of temperature of deposition, “Lindgren” has classified the
hydrothermal deposits into three groups:
o Hypothermal deposit
o Mesothermal deposit
o Epithermal deposit
Hypothermal Deposit:
These are the high temperature deposits
which are formed closed to the intrusive
body. Here the temperature ranges between
300° to 500 °C. The chief ore mineral which
are commonly found in hypothermal
deposits are arsenopyrite, wolframite, native gold and chalcopyrite

Mesotherma Deposits:
These are the intermediate temperature
deposits which are formed at some
distance outward from the intrusive
igneous mass. Here temperature ranges
between 200° to 300°C. The chief ore
minerals of Mesothermal deposits are native gold, bornite, sphalerite galena and
argentite.
Epitharmal deposits:
These are low temperature deposits formed very much away from intrusive body.
Their temperature of formation ranges between 50° to 200° the commonly accor
minerals are, Ruby, Silver, Stibnite and Cinnabar.
On the basis of mode of formation, the hydrothermal deposits have been
classified into two groups;
o Cavity Filling Deposits
o Replacement Deposits
Cavity Filling Deposits:
These deposits are formed when hydrothermal solution deposit their dissolve
minerals in the various types of openings present in the rocks. Here precipitation
of minerals is chiefly caused by change in temperature, pressure and chemical
character of the mineralizing solutions. The characteristic features of cavity filling
deposits are as follow:
Crustification:
The mineral which precipitates first lines the walls of the cavity. Its crystals grow
inward and point toward the centre. Generally successive layers of different
minerals are deposited upon the first one. This process is repeated until the filling
is complete. A filling of this type is called crustification.

Comb Structure:
If a mineral vein prominent crystals projects
inward from the walls. It is said to ha
structure.
Vugs:
When a vein is not filled completely with the
mineral matter open spaces are left in the
centre. Such unfilled spaces are called vugus.
Types of Cavity Filling Deposits:
Depending upon the nature of opening the cavity filling opening deposits occur in
a variety of shape and size. The common types of cavity filling deposits are:
o Fissure vein
o Shear zone deposits
o Saddle reefs
o Ladder Vein
Fissure Vein:
A fissure filled with ore is called fissure Vein. It
is a tabular ore body which occupies one or
more fissure within in a rock. Fissure vein
deposits are the most important of all the
cavity filling deposits. They are the chief source
of most of the metals like gold, silver, copper,
lead, zinc and mercury.
Shear zone Deposits:
The shear zones are the zone of thin and
closely spaced and parallel fractures. Here as
the opening are minute, the open space
deposition is minor. However the large
specific surface of the opening makes the
Shear zones very susceptible to
replacement. Hence many large and
valuable ore deposits are foun
If a mineral vein prominent crystals projects
om the walls. It is said to have a comb
lled completely with the
mineral matter open spaces are left in the
centre. Such unfilled spaces are called vugus.
Types of Cavity Filling Deposits:
size. The common types of cavity filling deposits are:
A fissure filled with ore is called fissure Vein. It
is a tabular ore body which occupies one or
rock. Fissure vein
deposits are the most important of all the
cavity filling deposits. They are the chief source
of most of the metals like gold, silver, copper,
The shear zones are the zone of thin and
spaced and parallel fractures. Here as
the opening are minute, the open space
deposition is minor. However the large
specific surface of the opening makes the
Shear zones very susceptible to
replacement. Hence many large and
valuable ore deposits are found in the shear zones.
size. The common types of cavity filling deposits are:

Ladder Veins:
Ladder veins are commonly found in dykes they
are the short, transverse, roughly parallel
fracture that are filled with the ore. Because
they appear like a ladder they are called ladder
veins.
REPLACEMENT DEPOSITS:
Replacement is one of the important process in the formation of epigenetic
mineral deposits. The chief epigenetic mineral deposits are contact metasomatic
deposits, supergene mineral deposits and hydrothermal replacement deposits.
The replacement deposits commonly contain ores of iron, lead, zinc, copper,
silver and many non-metallic minerals the process of replacement may be
summarized is follow:
1. Replacement is the chemical process of simultaneous capillary solution
and deposition. process new minerals are
substituted for earlier minerals and rocks.
2. placement occur through the action of hot
vapours or hydrothermal solutions. The new
minerals are carried in solution and the
replaced substances are carried away in
solution it is an open circuit not a closed one.
3. The replacement takes place molecule by
molecule. consequently the shape, size,
structure and texture of the rocks are
faithfully preserved
4. post any Rock may be replaced by or but the
rapidly soluble carbonate rocks are the most susceptible. certain
structural features such as fissure may also localised replacement.

SEDIMANTATION DEPOSITS:
Sedimentation deposits are the syngenetic ore deposits which are formed at the
same time as the enclosing rock. They occur as beds in the sedimentary rocks.
Some of the important sedimentation deposits are iron ore, manganese ore,
copper ore, phosphates, limestone, Coal and clays these deposits are formed by
the process of sedimentation. This process may be summarized as follows:
1. During weathering the materials are released from the source Rock. In this
process the valuable mineral constituents are taken into solution the chief
solvents are carbonated water organic acids and sulfate solutions.
2. Most of the valuable substances are transported either in suspension or in
solution by means of river water to the sea.
3. In the sea, the valuable material is deposited mechanically, chemically or
biochemical the chemical precipitation of materials in solution is controlled
largely by the pH and Eh of the environment. The pH is responsible for the
acidic are alkaline conditions and the Eh for the oxidation-reduction
potential.
Features of Sedimentation deposits:
The sedimentation mineral deposits show many of the characteristics of normal
sedimentary rocks.
a. They commonly show bedding planes, ripple marks, and other
sedimentary features.
b. They normally occur as a bedded sedimentary rock interstratified
c. They are often a deposit of great geographical Extent.

EVAPORATION DEPOSITS
Many non metallic mineral deposits are formed as a result of evaporation of
shallow and isolated bodies of saline water. the
evaporation deposits are common salt gypsum and other salts of K,
Mg. the process of evaporation may briefly be summarised as follows:
1) The main source of the evaporation
deposits in a sea water.
2) -When a body of seawater is cut off
during oscillations of land and sea its
water evaporates. This leads to the
concentration of soluble salts.
3) When supersaturation of a salt is
reached that salt is precipitated and
thus evaporation deposits are formed.
4) Evaporation deposits are mostly formed in warm climates where
evaporation proceeds very rapidly
RESIDUAL DEPOSITS:
Residual deposits are formed a result of weathering of rocks in enclosed mineral
deposits. the economic minerals which commonly occur is residual deposits
iron, manganese, bauxite, tin, kyanite etc.
During weathering the rock undergo chemical decay. in this process the
undesirable constituents are removed in solution leaving behind a concentration
of valuable minerals at the site of the original rock for
necessary for the formation of residual mineral deposits are as follows.
1. The Rock undergoing weathering must contain some valuable minerals.
2. The valuable minerals must be resistant to chemical weathering.
3. The outcrop surface
water cannot remove in soluble products of weathering.
4. There should be adequate when to carry away in solution the soluble
products of weathering. Hence residual deposits commonly developed
in tropical are subtropical climate.
any non metallic mineral deposits are formed as a result of evaporation of
shallow and isolated bodies of saline water. the chief minerals which occur is
evaporation deposits are common salt gypsum and other salts of K, NA, CA, and
g. the process of evaporation may briefly be summarised as follows:
he main source of the evaporation
eawater is cut off
during oscillations of land and sea its
water evaporates. This leads to the
concentration of soluble salts.
When supersaturation of a salt is
reached that salt is precipitated and
thus evaporation deposits are formed.
its are mostly formed in warm climates where
evaporation proceeds very rapidly.
are formed a result of weathering of rocks in enclosed mineral
deposits. the economic minerals which commonly occur is residual deposits
iron, manganese, bauxite, tin, kyanite etc.
undergo chemical decay. in this process the
of valuable minerals at the site of the original rock for the stop the conditions
The Rock undergoing weathering must contain some valuable minerals.
The valuable minerals must be resistant to chemical weathering.
The outcrop surface should have low relief so that gravity and running
water cannot remove in soluble products of weathering.
There should be adequate when to carry away in solution the soluble
e subtropical climate.
any non metallic mineral deposits are formed as a result of evaporation of
chief minerals which occur is
NA, CA, and
its are mostly formed in warm climates where
are formed a result of weathering of rocks in enclosed mineral
deposits. the economic minerals which commonly occur is residual deposits are
undergo chemical decay. in this process the
the stop the conditions
The Rock undergoing weathering must contain some valuable minerals.
The valuable minerals must be resistant to chemical weathering.
should have low relief so that gravity and running
There should be adequate when to carry away in solution the soluble

MECHANICAL CONCENTRATION DEPOSITS:
The natural separation of heavy minerals from light ones by means of moving
water, or gravity is called "mechanical concentration" the mineral deposits
formed by this process are called places. the minerals which commonly occur as
placer deposits are diamond, gold, Platinum tinstone, magnetite, chromites,
ilmenite and monazite. This process of mechanical concentration may be
summarised as follows. This process of mechanical concentration may be
summarised as follows.
1. The ore minerals are released from the rock by weathering and
disintegration.
2. The disintegrated materials are carried downslope by water, air etc
ultimately this material reaches the stream or seashore.
3. The moving water or air heavier placer minerals sink to bottom while the
lighter material is carried further. Thus the heavier minerals are separated
from the lighter ones.
4. In this way the heavy minerals Gate concentrated in the particular localities
to form placer deposits.
The condition necessary for the formation of placer deposits are:
a) They must be primary source such as in ore deposit dissemination deposit
or a low grade deposits which supplies or minerals.
b) It must be exposed to weathering on slope from where the disintegrated
material may be carried away by water, air, etc
c) The ore minerals in the deposit must be of such chemical composition that
it can be resist weathering.

Types of Placer Deposits:
1) Eluvial placers
2) Stream Placers
3) Beach placers
4) Eolian placers
Eluvial Placer:
The eluvial placer deposits occur along the hill
slopes here the mineral concentration is caused
by gravity. When the debris is produced due to
the weathering of rocks moves down slow, the
heavier particles move more slowly than lighter
ones. In this way heavy and minerals get
concentrated to form in eluvial placer deposits.
Stream Placer:
These occur at various places along the stream.
Here the mineral concentration is caused by
running water. The weathered Rock material
travel with stream water and the concentration
of heavier minerals occurs in those places where
the velocity of water slackens.
Beach Placer:
These deposits occur along sea shore. Where mineral concentration is caused by
wave action.
Eolian Placers:
These occur in arid regions where mineral concentration is caused by wind action.
Eolian processes are found in Australia.

METAMORPHIC DEPOSITS:
Deposits formed due to metamorphism may be divided into two groups:
1) Deposits formed due to metamorphism of pre-existing ore deposits
2) Deposits originated due to formation of new minerals during
metamorphism of certain rocks.
The End

Classification of Ore Deposits | Economic Geology

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