2. Placer deposits
Placer minerals are important economic mineral
deposits with high specific gravity and formed by the
process of mechanical concentration due to weathering,
transportation and deposition in suitable location. These
deposits are known as Placer Deposits and minerals that
accumulated in the deposits are called as Placer Minerals.
The placer minerals are formed by natural gravity
separations.
These placer deposits consists mostly in heavy
minerals.
Placer materials must be both dense and resistant
to weathering processes.
3. To accumulate in placers, mineral particles must be
significantly denser than quartz (whose specific gravity is
2.65), as quartz is usually the largest component of sand
or gravel.
Placer environments typically contain black sand, a
conspicuous shiny black mixture of iron oxides,
mostly magnetite with variable amounts
of ilmenite and hematite.
Valuable mineral components often occurring with
black sands
are monazite, rutile, zircon, chromite, wolframite,
and cassiterite.
4. Heavy minerals are minerals with a density greater
than 2.8…2.9 g/cm3.
Heavy minerals are of great value in studying the
provenance, transportation and weathering history of the
sediments and in correlation purposes.
They include economically important minerals rich in
titanium, zirconium and rare earths.
most of heavy minerals are in dark and bright colour.
Which is easy to identify.
Heavy Minerals
5.
6. Heavy minerals are classified into types for the
convenience of density of the useable.
i). Heavy heavy minerals with a density of
6.8 – 21 g/cm3.
( mainly gold, platinum, cassiterite).
ii). The light heavy minerals with a density of
4.2 – 6.7 g/cm3.
( mainly ilemenite, rutile, zircon, monazite, magnetite,
chromite)
iii). Gemstones with a density of 2.9 – 4.1 g/cm3.
( mainly gold).
7. Seperation Methods
The heavy mineral deposits are beneficiated through
a combination of unit operations such as gravity
concentration, magnetic separation, and electrostatic
separation techniques.
All these physical separation processes exploit the
difference in specific gravity, electrostatic, and magnetic
properties of heavy mineral species .
Low-intensity magnetic separation is used to remove
ferromagnetic minerals such as ilmenite and high-
intensity magnetic separation is used to separate minerals
like monazite from other heavies.
8. Magnetic separation is initially done to recover the
Fe-bearing magnetic minerals like ilmenite, followed by
electrostatic separation for recovering the conductors
such as rutile from the nonconductors such as zircon,
quartz, and monazite.
Due to the relatively high specific gravity, gravity
separation can be used to concentrate heavy minerals by
eliminating low specific gravity gangue minerals such as
quartz and other light minerals,
9. Representative raw placer samples of 20 kg
each collected up to a depth of about 1 m from A and
B coastal stretches were processed to separate and
estimate heavy minerals from the bulk beach sand.
The raw sand samples were subjected to a
series of mineral separation techniques which include
magnetic, electrostatic, and gravity methods..
10. Magnetic separation is used to separate minerals
with different magnetic properties. It separates magnetic
minerals from those of nonmagnetic or less magnetic
nature. Minerals are classified as ferromagnetic,
paramagnetic, and diamagnetic based on their magnetic
properties.
Ferromagnetic and paramagnetic mineral particles
will both be attracted, whereas a diamagnetic mineral
particle will be repelled by a magnetic field.
The applications of high-intensity dry magnetic
separators are well accepted to selectively separate
paramagnetic minerals such as ilmenite.
Magnetic separation
12. Electrostatic separation is used to separate
minerals with different electrical properties. It separates
conducting minerals from those of nonconducting or less
conducting nature.
When the minerals are passed through an intense
electrical field, each particle acquires a charge depending
upon their composition and becomes separated into
conducting and nonconducting.
When a high potential difference is applied,
titanium-bearing minerals like ilmenite, rutile, and
leucoxene behave as conducting, whereas garnet, monazite,
sillimanite, and zircon behave as nonconducting material.
Electrostatic separation
13. Gravity separation methods such as centrifugal
separation using spiral concentrators are used to separate
the heavy minerals based on the differences in their
specific gravity .
Short spiral concentrator is used for the separation
of garnet, rutile, ilmenite, zircon, and other heavies from
low-density minerals such as quartz, clay
Gravity separation
15. These minerals occur in very low concentrations in a
variety of igneous and metamorphic rocks, but being
chemically and physically resistant to weathering, and having
comparatively high specific gravity, they tend to accumulate
in placer deposits in river channels or along coastal
shoreline
Beach sands contain the most important accumulations
of these minerals; wave action deposits sand on the beach,
and the heavy minerals are concentrated when backwash
carries some of the lighter minerals such as quartz back
into the sea.
Onshore winds which preferentially blow lighter grains
inland can lead to higher concentrations of heavy minerals
at the front of coastal dune
Occurrence
16. Heavy minerals are often used as indicators of sediment
provenance and flow dynamics in various types of sediments,
including in tsunami deposits.
Heavy minerals described in tsunami deposits are likely
concentrated in pockets or laminae, but their distribution
within the deposits sometimes shows no vertical trend
Heavy minerals such as iron oxides (ilmenite, magnetite),
diamonds, and some silicates (zircon, garnet, and olivine) are
characterized by high coefficients of X-ray attenuation,
and they are easily distinguished from other minerals on X-
ray imagery.
Distribution of heavy minerals
