Mineral Resources Mapping

Mineral
• A mineral is defined as an element or chemical compound
that is normally crystalline and has formed as a result of
geologic processes.
• Remote sensing data, by virtue of its synoptic overview,
multispectral and multi-temporal coverage, can help in rapidly
delineating the metallogenic province/belts/sites thereby
cutting down the cost.
• Remote sensing enables mapping the location of altered areas
and regions of hydrothermal upwelling and outflow zones
related to mineralization.
 How Minerals Form?
• 1. crystallization of magma (cools inside the crust) or lava
(cools & hardens on the surface)
• 2. crystallization of materials dissolved in water.
• Magma heats the water underground. The elements &
compounds dissolve in hot water to form solution. the
solutions follow cracks within the rock. elements &
compounds leave the solution during cooling and crystallize as
minerals. these minerals form a narrow channel or slab in the
rock called a vein.
 How to explore mineral ?
• The hydrothermal fluid creates the ore deposit and also
hydrothermal alteration is developed in the host rocks
surrounding the ore deposit, and thus the alteration zone is
an important feature for mineral exploration.
• Different characteristics of the hydrothermal fluid such as
temperature, fluid/rock ratio and also the chemical difference
of the host rock produce diverse alteration minerals. This
causes the development of alteration zoning and provides
important information on the hydrothermal fluid and for
exploration.
• The location of the ore deposit and ore deposit type can be
estimated from the alteration mineralogy and by the mode of
occurrence of the alteration zoning.
 Hydrothermal alteration zones
• Hydrothermal vents are commonly found near volcanically active
places, areas where tectonic plates are moving apart at
spreading centers, ocean basins, and hotspots.
• Hydrothermal alteration is defined as the reflection of response
of pre-existing, rock-forming minerals to physical and chemical
conditions different than those under which they originally
formed, especially by the action of hydrothermal fluids with
possible temperature of 500˚C to 50˚C.
• The fluid resulting as an end product of magmatic
differentiation, constitutes hydrothermal solution which carries
metals originally present in the magma to the site of deposition.
• The process is responsible for formation of epigenetic mineral
deposits i.e. those formed later than the rocks that enclose
them.
• The hydrothermal solution in its journey through the rocks loses
heat and metal content with increased distance.
Hydrothermal Alternation Zones
Methods for utilization of Remote Sensing data for Mineral Exploration

• Primary rock-forming minerals as well as many secondary

weathering and alteration minerals exhibit wavelength
dependent (spectral) absorption features throughout the
visible and infrared wavelength ranges of the electromagnetic
spectrum.
• These features result from the selective absorption of
photons with discrete energy levels and are dependent on the
elemental composition, crystal structure, and chemical
bonding characteristics of a mineral, and are therefore
diagnostic of mineralogy.
• The steps involved in mineral exploration include area
selection, target definition, resource evaluation, reserve
definition and extraction.
Methods for utilization of Remote Sensing data for Mineral Exploration

• Spaceborne multispectral sensors/ hyperspectral sensors can detect

the spectral signatures characteristic to the alternation zone
associated with a mineral deposit.
• These features can easily be detected specially in airborne hyper
spectral scanner. The detection of alteration zone, favorable
geological structures prospective for mineral deposits or suitable
host rock of any particular mineral helps in area selection and target
delineation phase of the mineral exploration.
• Other collateral data, namely geological map, geochemical data,
and geophysical data is required along with remote sensing data to
model the reserve potential.
• Alteration minerals that create alteration zoning have characteristic
absorption patterns, especially in the short wave infrared (SWIR)
region (2.0 to 2.5 μ). Remote sensing used in mineral exploration of
hydrothermal ore deposits often use the spectral features of the
alteration minerals at wavelength of 2.0 to 2.5 μ to find alteration
zones and identify alteration minerals.
Spectral Signature of Rocks Cations/Anions Absorbtion peaks (mm )
Normal - Visible and near Infrared (VNIR ) Region

• The spectral signatures of Ferric ion * 0.40, 0.50, 0.70 and 0.87
Ferrous ion* 0.43, 0.45, 0.57, 0.55, 1.00
rocks depend mainly on the and 1.80 – 2.00
spectral characteristics of Manganese 0.34, 0.37, 0.41, 0.45 and 0.55
Copper 0.80
constituent cations, anions Nickel 0.40, 0.74 and 1.25
and internal molecular Chromium 0.35, 0.45 and 0.55
structure. Normal - Short Wavelength Infrared (SWIR)
Region

•
Hydroxyl ions 1.44 and 2.74 – 2.77
Spectral features in visible and AI – OH 2.20
NIR(0.4 – 1.0 µm)are dominated by Mg – OH 2.30
transition metals, such as Fe, Mn, Water 1.40 and 1.90
molecules
Cu, Ni,Cr etc. and in SWIR (1.0- Carbonates 1.90, 2.00, 2.16, 2.35 and 2.55
3.0µm) are dominated by hydroxyl Thermal Infrared (TIR) Region
ions, carbonates and water Silicates 9.00 – 11.50 (depending
molecules. upon the crystal structure)
Carbonates 7 (not used in remote
• The abundant rock forming minerals sensing ) and 11.30
like silicates, oxides, nitrates, nitrites Sulphates 9 and 16
and phosphates etc. has Phosphates 9.25 and 10.30
characteristic reflectance in TIR (3 – Nitrates 7.20
14µm). Nitrites 8 and 11.8
Hydroxides 11
 Spectral Reflectance of Major Minerals
• Alunite and kaolinite, which
are alteration minerals
present in advanced argillic
alteration, have absorptions
at 2.16μ and 2.2μ that are by
the aluminum hydroxyl (Al-
OH) bond.
• Chlorite, epidote and calcite,
which are present in
propylitic alteration, have an
absorption at 2.35μ that is
created by the magnesium
hydroxyl (Mg-OH) bond and
the carbonic (CO3) bond.
• Iron oxide and hydroxide
minerals such as limonite,
jarosite and hematite tend to
have spectral absorption
features in the visible to
middle infrared from 0.4 to
1.1μm of the EMS.
 Flow Chart to map
Minerals using GIS and
RS technology
 A case study of Tamilnadu

Satellite Imagery Lithology Map

A case study of Tamilnadu

Lineament Map
Hydrothermal Alteration Zone