Gravity and magnetic methods are an essential part of oil exploration. They do not replace seismic. Rather, they add to it. Despite being comparatively low-resolution, they have some very big advantages.
These geophysical methods passively measure natural variations in the earth’s gravity and magnetic fields over a map area and then try to relate these variations to geologic features in the subsurface. Lacking a controlled source, such surveys are usually environmentally unobjectionable.
CLASSIFICATION OF 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”.
rly under seated
ore minerals
such
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.
Gravity and magnetic methods are an essential part of oil exploration. They do not replace seismic. Rather, they add to it. Despite being comparatively low-resolution, they have some very big advantages.
These geophysical methods passively measure natural variations in the earth’s gravity and magnetic fields over a map area and then try to relate these variations to geologic features in the subsurface. Lacking a controlled source, such surveys are usually environmentally unobjectionable.
CLASSIFICATION OF 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”.
rly under seated
ore minerals
such
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.
It covers seismic method, gravity method, electromagnetic method, magnetic method and radiometric method. all these methods help in mineral exploration
Introduction
Petrophysic of the rocks
It is the study of the physical and chemical properties of the rocks related to the pores and fluid distribution
Porosity, is ratio between volume of void to the total voids of the rock.
Permeability, is ability of a porous material to allow fluids to pass through it.
Electric, most of the sedimentary rocks don’t have conductivity.
Radiation, clay rocks have 40K, radiate alpha ray.
Hardness, it depends on the cementing material and thickness of the sediments.
WELL LOGGING
The systematic recording of rock properties and it’s fluid contents in wells being drilled or produced to obtain various petrophysical parameters and characteristics of down hole sequences (G.E Archie 1950).
The measurement versus depth or time, or both, of one or more physical properties in a well.
These methods are particularly good when surface outcrops are not available, but a direct sample of the rock is needed to be sure of the lithology.
A wide range of physical parameters can be measured.
In some cases, the measurements are not direct, it require interpretation by analogy or by correlating values between two or more logs run in the same hole.
Provide information on lithology, boundaries of formations and stratigraphic correlation.
Determine Porosity, Permeability, water, oil and gas saturation.
Reservoir modeling and Structural studies… etc.
Types of Well Logging
Logs can be classified into several types under different category
Permeability and lithology Logs
Gamma Ray log
Self Potential [SP] log
Caliber log
Porosity Logs
Density log
Sonic log
Neutron log
Electrical Logs
Resistivity Log
For contact : omerupto3@gmail.com
The presentation comprises the Gravity Method, It's anomaly, reduction, and its applications. The Gravity method is commonly used in Geology specifically in Geophysics.
Gravity anomaly across reagional structuresAmit K. Mishra
Gravity Anomaly across continents and ocean, gravity anomaly across mid-oceanic ridges, gravity anomaly across orogenic belts, and gravity anomaly across subduction zones.
Definition
Geophysics is the application of method of physics to the
study of the earth.
On the other sense, it is a subject of natural science
concerned with the physical processes and the physical
properties of the earth and its surrounding space
environment and the use of co-ordinate methods for the
analysis.
It involves the application of physical theories and
measurements to discover the properties and processes of the
earth.
It covers seismic method, gravity method, electromagnetic method, magnetic method and radiometric method. all these methods help in mineral exploration
Introduction
Petrophysic of the rocks
It is the study of the physical and chemical properties of the rocks related to the pores and fluid distribution
Porosity, is ratio between volume of void to the total voids of the rock.
Permeability, is ability of a porous material to allow fluids to pass through it.
Electric, most of the sedimentary rocks don’t have conductivity.
Radiation, clay rocks have 40K, radiate alpha ray.
Hardness, it depends on the cementing material and thickness of the sediments.
WELL LOGGING
The systematic recording of rock properties and it’s fluid contents in wells being drilled or produced to obtain various petrophysical parameters and characteristics of down hole sequences (G.E Archie 1950).
The measurement versus depth or time, or both, of one or more physical properties in a well.
These methods are particularly good when surface outcrops are not available, but a direct sample of the rock is needed to be sure of the lithology.
A wide range of physical parameters can be measured.
In some cases, the measurements are not direct, it require interpretation by analogy or by correlating values between two or more logs run in the same hole.
Provide information on lithology, boundaries of formations and stratigraphic correlation.
Determine Porosity, Permeability, water, oil and gas saturation.
Reservoir modeling and Structural studies… etc.
Types of Well Logging
Logs can be classified into several types under different category
Permeability and lithology Logs
Gamma Ray log
Self Potential [SP] log
Caliber log
Porosity Logs
Density log
Sonic log
Neutron log
Electrical Logs
Resistivity Log
For contact : omerupto3@gmail.com
The presentation comprises the Gravity Method, It's anomaly, reduction, and its applications. The Gravity method is commonly used in Geology specifically in Geophysics.
Gravity anomaly across reagional structuresAmit K. Mishra
Gravity Anomaly across continents and ocean, gravity anomaly across mid-oceanic ridges, gravity anomaly across orogenic belts, and gravity anomaly across subduction zones.
Definition
Geophysics is the application of method of physics to the
study of the earth.
On the other sense, it is a subject of natural science
concerned with the physical processes and the physical
properties of the earth and its surrounding space
environment and the use of co-ordinate methods for the
analysis.
It involves the application of physical theories and
measurements to discover the properties and processes of the
earth.
International Refereed Journal of Engineering and Science (IRJES)irjes
a leading international journal for publication of new ideas, the state of the art research results and fundamental advances in all aspects of Engineering and Science. IRJES is a open access, peer reviewed international journal with a primary objective to provide the academic community and industry for the submission of half of original research and applications.
Page 22 2.1 IntroductIonStudying the Earth’s interior .docxalfred4lewis58146
Page | 22
2.1 IntroductIon
Studying the Earth’s interior poses a significant challenge due to the lack of
direct access. Many processes observed at the Earth’s surface are driven by the
heat generated within the Earth, however, making an understanding of the interior
essential. Volcanism, earthquakes, and many of the Earth’s surface features are a
result of processes happening within the Earth.
Much of what we know regarding the Earth’s interior is through indirect means,
such as using seismic data to determine Earth’s internal structure. Scientists dis-
covered in the early 1900’s that seismic waves generated by earthquakes could
be used to help distinguish the properties of the Earth’s internal layers. The veloc-
ity of these waves (called primary and secondary waves, or P and S waves) changes
based on the density of the materials they travel through. As a result, seismic waves
do not travel through the Earth in straight lines, but rather get reflected and re-
fracted, which indicates that the Earth is not homogeneous throughout.
The Earth’s interior consists of an inner and outer core, the mantle, and the
crust. Located in the center of the Earth is the inner core, which is very dense
and under incredible pressure, and is thought to be composed of an iron and nick-
el alloy. It is solid, and surrounded by a region of liquid iron and nickel called the
outer core. The outer core is thought to be responsible for the generation of the
Earth’s magnetic field. A very large portion of the Earth’s volume is in the man-
tle, which surrounds the core. This layer is less dense than the core, and consists
of a solid that can behave in a plastic (deformable) manner. The thin outer layer
of the Earth is the crust. The two types, continental and oceanic crust, vary from
each other in thickness, composition, and density.
2.1.1 Learning outcomes
After completing this chapter, you should be able to:
• Determine the different layers of the Earth and the distinguishing
properties of each layer
2earth’s InteriorRanda Harris and Bradley Deline
Page | 23
Introductory GeoloGy earth’s InterIor
• Understand how seismic waves behave within the different layers of the
Earth
• Understand how seismic tomography has been used to gain a better
understanding of the Earth’s interior
• Understand the Earth’s magnetic field and how it changes over time
• Learn how to use the program Google Earth for geological applications
2.1.2 Key terms
2.2 InterIor oF the eArth
The study of seismic waves and how they travel through the Earth has been
very useful in helping to determine the changes in density and composition within
the Earth and in locating the boundaries be-
tween the inner core, outer core, mantle, and
crust. Seismic waves are energy waves
generated during earthquakes; two types
known as P and S waves propagate through
the Earth as wave fronts from their place of
origin. P-waves are compressional waves
that move back and f.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.
Magnetic Survey
1. MAGNETIC SURVEY
Date : May 21, 2020
Time : 12 : 30 P.M.
APPLIED GEOPHYSICS
ENGINEERING GEOLOGY
Presenter :
Sudhan Kumar Subedi
Meeting ID : 725 0504 4902
Meeting Password : 5qxJwu
Interested can Join Zoom Meeting
https://us04web.zoom.us/j/6755682948?pwd=YW5xVkZ4MzQxcWVuRjA0SmN4Z3d1QT09
2.
3.
4. Magnetic Survey Method
May 21, 2020
Magnetic Susceptibility
Magnetic susceptibility is the ratio of intensity of magnetization (I) and magnetic intensity of substance (H).
χ =
I
H
For Ferromagnetic material, χ >> +1
For Paramagnetic material, χ > +1
For Diamagnetic material, χ < 0, i.e. –ve
χ
T
Tc (curie
Temperature)
Ferromagnetic Paramagnetic
Diamagnetic
5. Magnetic Survey Method
May 21, 2020
Magnetic Susceptibility of rocks
Magnetic Susceptibility of rocks is in principle, controlled by the type and amount of the magnetic minerals
contained in rock.
Dominantly Controlled by
Paramagnetic minerals i.e.
mafic silicates such as
- Olivine
- Pyroxenes
- Amphiboles
- Micas
- Tourmaline
- Garnets
Often controlled by
ferromagnetic minerals
(iron oxides or sulphides :
- Magnetite
- Pyrrhotite
Much less frequently
controlled by diamagnetic
minerals :
- Calcite
- Quartz
6. Magnetic Survey Method
May 21, 2020
Magnetic Susceptibility of rocks and their ranges
Source : Reynolds, J. M. (2011)
7. Magnetic Survey Method
May 21, 2020
Magnetic Susceptibility of rocks and their ranges
Source : Telford, W. M., Geldart, L. P., & Sheriff, R. E. (2010)
8. Magnetic Survey Method
May 21, 2020
Magnetic Susceptibility of rocks and their ranges
Metamorphic rocks are dependent upon their parent material and thus, metapsammites are likely to have
different susceptibilities as compared with metapelites.
9. Magnetic Survey Method
May 21, 2020
Magnetic Susceptibility of rocks and their ranges
In addition to mineral composition, Susceptibility depends on the alignment and shape of the magnetic
grains dispersed throughout the rock.
Magnetic fabric analysis provides a very sensitive indication as to the physical composition of rock or
sediment, which in turn can be important in interpreting the physical processes affecting the rock.
If there is a marked orientation of particles, such as in sedimentary or metamorphic rocks, a strong
physical anisotropy may exist. The variation of magnetic property as a function of orientation and shape of
the mineral grain is known as ‘Magnetic Fabric’.
For example, it is possible to
correlate the magnetic fabric
variation in estuarine sediments
with sonograph image of estuary
floor.
11. Magnetic Survey Method
May 21, 2020
Magnetic Susceptibility of rocks and their ranges
• For Magnetic ore bodies with extremely high susceptibilities (k >> 10 6 SI) , the measured susceptibility
(i.e. apparent susceptibility can be reduced substantially by a shape demagnetization effect.
• This involves a demagnetization factor Nɑ ,
which depends on direction ɑ .
Ka = K / ( 1 + Nɑ K)
For Sphere,
Nɑ = 1/3 in all directions
For thin-sheet like body ,
Nɑ ≈ 1 in transverse directions
Nɑ ≈ 0 in longitudinal directions
13. Magnetic Survey Method
May 21, 2020
Elements of Earth Magnetic Field
How did the Earth become differentiated to have different layers ???
• Earth is such a distance away from the sun that water can exist in all the three forms of solid , liquid
and gas.
• Density of water is 1 g/cc.
• Density of the most of the rocks available at the Earth’s surface is ≤ 3 g/cc.
• Overall density of the Earth is about 5.5 g/cc.
• clearly indicates that Earth’s interior consists of layers of increasing densities.
• Dense layers at the depth and higher ones at the surface and most dense at the center of the earth.
• Gravity is the driving force for such a wide sedimentation of different layers over the area.
14. Magnetic Survey Method
May 21, 2020
Elements of Earth Magnetic Field
Crust
Can be divided into two – The Continental crust and the Oceanic Crust
The Continental Crust
• Much thicker (up to 75 km) and is composed of less dense granitic rocks (2.7 g/cc) and is strongly
deformed.
• Composed of planet’s oldest rocks (billions of years in age)
The Oceanic Crust
• Relatively thinner (about 8 km thick) and is composed of basaltic rocks of volcanic origin heavier
than continental (3 gm/cc).
• Comparatively undeformed and geologically younger (200 millions of year of age)
15. Magnetic Survey Method
May 21, 2020
Elements of Earth Magnetic Field
Mantle
Also include iron and magnesium in abundance
2900 km thick and constitute 82 % of Earth’s volume and 68 % of Earth’s mass.
Composed of rocks (made from compounds of silicates and oxygen)
Covers the core
Fragments of mantle are brought during volcanic eruption.
Because of pressure of overlying rocks, its density increase with depth (3.2 g/cc in the upper
part to 5.0 g/cc near the core )
State of Mantle
• It is in semi-molten state and exhibit the convection current to the plate tectonics to occur.
• Decay of radioactive material in the lower mantle used to generate lots of heat during Archean age (3800-
2500 Mya. Presently, the rate of decay is less to drive the Plates through convection. Thus, Presently Mantle
is considered as in solid state and not of causing convection current ( Tackley, 2000; Koranaga, 2006)
16. Magnetic Survey Method
May 21, 2020
Elements of Earth Magnetic Field
Core
Constitute 16 % of Earth’s volume
Density increases with depth
Average density of 10.8 g/cc
Extending in a diameter of 7000 km
32 % of Earth’s mass
Mainly consist of Iron and Nickel
17. Magnetic Survey Method
May 21, 2020
Elements of Earth Magnetic Field
Core
Outer Core is extending between 2900 km to 5100 km. Alloy of iron and nickel having temperature range
from 4000°C to 5000°C in liquid form and causing the convection current.
- It causes the Earth’s magnetic field due to its high density and constant motion and metallic properties.
- Causes shift in the magnetic poles
- Leaves record of the rocks in terms of Paleomagnetic value. Useful to understand the movement of
continents over the past
Divided into Outer Core and Inner Core :
Inner Core is extending between 5100 km to 6400 km. Mostly composed of iron having temperature of
5000°C to 7000°C as high as the surface of the sun.
- Even though the temperature is so high, the overburden pressure is so high that the Iron cannot melt
and thus inner core is in solid state unlike outer core.
18. Magnetic Survey Method
May 21, 2020
Elements of Earth Magnetic Field
Considering the presence of iron, at a high temperature in solid core and as a result of convection
current generated due to the temperature variation in outer core, drives the inner core.
As a result of this, the inner core rotates resulting in generation of electric current.
Further, magnetic field comes into picture
For magnetic force to exist, there should be dipole, very much similar to magnet.
Presence of inclination of axis joining the poles is about 11° with respect to true north.
19. Magnetic Survey Method
May 21, 2020
Elements of Earth Magnetic Field
The present configuration of magnetic poles, keep changing.
Period in which such change occurs is defined as Chrons.
While Normal Polarity indicates pole configuration matching with present North Pole and South Pole.
Reverse polarity indicates a situation in which present North pole becomes South pole and present
South pole becomes North pole.
So far, 183 reversals in magnetic poles has happened in last 83 million years ( Leonardo et. al.,
2014)
Change in Polarity (Geomagnetic Reversal)
As per Byrd (2018), reversal lasts for almost 200 years.
A complete reversal known as Laschamp event, occurred about 41000 years ago.
20. Magnetic Survey Method
May 21, 2020
Elements of Earth Magnetic Field
Change in Polarity (Geomagnetic Reversal)
21. Magnetic Survey Method
May 21, 2020
Elements of Earth Magnetic Field
In early part of 20th century, geologists reported to have volcanic deposit showing reverse orientation
on magnetic depositions.
Change in Polarity (Geomagnetic Reversal)
While some rocks indicated magnetic depositions matching with present pole configuration, other
showing complete reverse field.
Based on dating method, it was found that rock which were showing reverse magnetic field belonged
to the Pleistocene age (2.5 million years – 0.12 million years).
22. Magnetic Survey Method
May 21, 2020
Elements of Earth Magnetic Field
At plate boundaries, mainly divergent boundary, new material from mantle comes to the surface and
gets deposit.
Important Observations
This way new surface is formed.
Molten material which is coming to the surface, having magnetic minerals. These minerals will orient
themselves as per the magnetic pole configuration during the time of deposition and cooling.
This way, magnetic rocks preserve the characteristics of pole configuration to the point.
23. Magnetic Survey Method
May 21, 2020
Elements of Earth Magnetic Field
At divergent boundary, deposition of material is a continuous process, which means that just at the
boundary the deposition characteristics will be matching with present configuration.
Important Observations
However, away from the boundary, depending upon the rate of deposition and configuration of poles
when material was deposited, its mineral orientation will be different and may be closer or far
distance from the boundary.
Based on age of deposition and mineral orientation, the configuration of magnetic polarities in the
geological time scale can be assessed.
24. Magnetic Survey Method
May 21, 2020
Elements of Earth Magnetic Field
Depending upon the characteristics of divergent plate boundary, the mineral deposited in a region
should be indicative of average magnetic properties to be constant throughout.
Magnetic Anomaly
In case of small magnetic when comes in contact with Earth’s magnetic field, exerts addition force.
Similar way, presence of material such as ore deposits, unconformity, buried objects, voids etc. which
can cause change in magnetic characteristics in comparison to average characteristics.
Such a change, if detected, based on field measurement, is known as MAGNETIC ANOMALY.
25. Magnetic Survey Method
May 21, 2020
Survey Can be done :
On Ground
In Air
Based on Satellite Data
Offshore Vessels
26. Magnetic Survey Method
May 21, 2020
Instruments : Magnetometer
Magnetometers are used for measurement of strength of field.
Commonly used magnetometers are :
- Proton Precession Magnetometer
- Alkali-vapor/Optical Pumping Magnetometer
- Flux-gate Magnetometer
27. Magnetic Survey Method
May 21, 2020
Instruments : Magnetometer
Proton Precession Magnetometer
• Proton Precession Magnetometer operates on the principle that protons in all atoms are spinning on an axis
aligned with the magnetic field, according to Larmor equation.
• Ordinarily, proton tends to line up with the earth’s magnetic
field.
• When subjected to an artificially-induced magnetic field,
the protons will align themselves with the new field. When
this new field ceases, the protons return to their original
alignment with the earth's magnetic field.
28. Magnetic Survey Method
May 21, 2020
Instruments : Magnetometer
Proton Precession Magnetometer
In a proton precession magnetometer, a container of fluid
rich in hydrogen atoms, usually a hydrocarbon, is
surrounded by a coil of wire which can be energized by a
direct current to produce a strong magnetic field, forcing all
protons to align in a certain direction.
The current is then shut off, letting the protons to precess
back to their original direction.
The precession induces a very weak signal into the same coil, which is measured by a frequency
counter to give a direct readout of the magnetic field strength.
As they change their alignment, the spinning protons precess, or wobble, like a gyroscope. The
frequency at which the protons precess is directly proportional to the strength of the earth's magnetic
field.
30. Magnetic Survey Method
May 21, 2020
Instruments : Magnetometer
Alkali-vapor/Optically Pumped Magnetometer
• Alkali vapor optically pumped magnetometers use alkali metals including Cesium, Potassium or
Rubidium. The cell containing the metal must be continuously heated to approximately 45 to 55 degrees
Celsius to render the metal in gaseous form.
31. Magnetic Survey Method
May 21, 2020
Instruments : Magnetometer
Alkali-vapor/Optically Pumped Magnetometer
• A glass vapour cell containing gaseous metal is exposed (or pumped) by light of very specific wavelength
– an effect called light polarization.
• Electrons at level 3 are not stable, and they spontaneously decay to both energy levels 1 and 2.
Eventually, the level 1 is fully populated (i.e. level 2 is depleted).
• When this happens, the absorption of
polarizing light stops and the vapour
cell becomes more transparent.
• The frequency of light is specifically selected and circularly polarized for each element (i.e. the D1
spectral line) to shift electrons from the ground level 2 to the excited metastable state 3
32. Magnetic Survey Method
May 21, 2020
Instruments : Magnetometer
Alkali-vapor/Optically Pumped Magnetometer
• This is when RF depolarization comes into play. RF power corresponding to the energy difference between
levels 1 and 2 is applied to the cell to move electrons from level 1 back to level 2 (and the cell becomes
opaque again).
• Depolarization by a circular magnetic field at the Larmor frequency will rebalance populations of the two
ground levels and the vapour cell will start absorbing more of the polarizing light.
• The effect of polarization and depolarization is that light intensity becomes modulated by the RF
frequency. By detecting light modulation and measuring the frequency, we can obtain a value of the
magnetic field.
• The frequency of the RF field required to repopulate level 2 varies with the ambient magnetic field and is
called Larmor frequency.
33. Magnetic Survey Method
May 21, 2020
Instruments : Magnetometer
Flux-gate Magnetometer
• The fluxgate magnetometer is a magnetic field sensor for vector magnetic field. Its normal range is
suitable for measuring earth’s field and it is capable of resolving well below one 10,000th of that.
• Fluxgate magnetometer designs fall into broadly two styles, those employing rod cores and those using
ring cores-
• The name fluxgate clearly derives from the action of the core gating flux in and out of the sense coil
• All fluxgates use a highly permeable
core which serves to concentrate the
magnetic field to be measured.
34. Magnetic Survey Method
May 21, 2020
Applications
• Can be used to locate:
- Drums, pipes,
- metallic objects,
- buried military objects such as shells,
- underground coal burns,
- mine shafts
• For Mapping :
- Archaeological remains such as cemeteries,
- Landfills
- Dikes, faults
- underground coal burns,
- Steep Geological features
35. Magnetic Survey Method
May 21, 2020
Advantages
- Quick method of Exploration
- Field observations are less expensive and easy
- Even possible from small vessel in offshore environment
- Presence of scarp metal and electric cable might alter field observations and thus are
not suitable in urban areas,
- Material with magnetic characteristics can be detected in form of anomaly
- Resolution decreases with depth
Limitations