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Anisotropy Effects in Geophysical Data
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist S E G eoscience and Ex ploration
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Presented at BC Geophysical Society. Thursday February 18th, 2016
Objective of this Talk- Create awareness among mineral explorers.
- Start a discussion group.
- Answer following questions:
- (1) How can we integrate anisotropy in inversion calculations?
- (2) How can we use those effects to discover, delineate, and characterize ore deposits?
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
What is Anisotropy?
- let’s google !!!
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Wikipedia:- Anisotropy is the property of being directionally dependent,
as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties (absorbance, refractive index, conductivity, tensile strength, etc). An example of anisotropy is the light coming through a polarizer. Another is wood, which is easier to split along its grain than against it.
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Encyclopaedia Britannica:
- Anisotropy, in physics, the quality of exhibiting properties with different values when measured along axes in different directions. Anisotropy is most easily observed in single crystals of solid elements or compounds, in which atoms, ions, or molecules are arranged in regular lattices. In contrast, the random distribution of particles in liquids, and especially in gases, causes them rarely, if ever, to be anisotropic.
…
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Encyclopaedia Britannica:
- … A familiar example of anisotropy is the difference in the speed of light along different axes of crystals of the mineral calcite. Another example is the electrical resistivity of selenium, which is high in one direction but low in the other; when an alternating current is applied to this material, it is transmitted in only one direction (rectified), thus becoming a direct current.
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Motivation for this Talk
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
- let’s rewind a bit !!!
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Freiberg (Germany)
- 1988: B.Sc. in Applied Geophysics in Engineering * material sciences: concepts of homogeneity and isotropy
- 1989: M.Sc. in Geothermal * thermal flow in different directions
- 1992: Ph.D. in Hydro-fracs and Micro-seismicity * using S-wave splitting, quantification of anisotropic degree of rock mass after hydraulic fracturing event
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Berlin and Potsdam (Germany)
- 1993-1995: Postdoc and research in Seismology and Earthquake Hazards
* velocity anisotropies in the Andes
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Examples of Anisotropy:
- In daily life !!!
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
thinking about …
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Our thoughts are most of the time
anisotropic
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
going to the PDAC?
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
or going to the beach?
thinking about …
thinking about …
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
thinking about …
thinking about electric currents and
other flows
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
or thinking about Radiometrics?
thinking about electric currents and
other flows
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
different speed when walking in different
directions
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
different speed when walking in different
directions
Examples of Anisotropy in the natural world:
- In Mathematics !!!
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Scalars …
- are real numbers defined by a point in space (or in time)
e.g. temperature Talso: mass density Rho-m
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Vectors …
- are defined by two points in space (or in time)
e.g. velocity v = ( v1v2
)or any other vector field
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
- those two points define magnitude and direction
Tensors …
- are defined by at least two vectors in space
e.g. material property P = ( P11P21
P12P22
)
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
- or more commonly by three vectors in space
P = (P11 P12
)P13
P21 P22 P23P31 P32P33
- a tensor is anisotropic when all nine elements have different values
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Tensors …
- (furthermore)… describe relations between scalars (tensors 0th order), vectors (tensors 1th order), and other tensors (2nd order and more).
excitation
resp
onse
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
- can describe e.g. relations between excitations and responses
Tensors …
- In Physics !!!
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Examples of Anisotropy in the natural world:
Thermodynamics:
- q = - k * grad T
- T: temperature
- q: heat flow
- k: thermal conductivity coefficient
- Law of Fourier
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Continuum Mechanics:
- S = - k * d
- d: displacement
- S: applied stress
- k: elasticity coefficient
- Law of Hook
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Magnetics (Maxwell):
- M = - k * H
- H: magnetizing vector field
- M: magnetized vector field
- k: magnetic susceptibility
- Law of Magnetization
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Electrical (Maxwell):
- j = - k * E
- E: Electric vector field
- j: Current density vector field
- k: electric conductivity
- Law of Ohm
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Physical property of materials…- the tensor K might be thermal conductivity coefficient, elasticity
coefficient, magnetic susceptibility, electric conductivity… whatever it is, it is a material property, it is a rock property, it is a physical rock property
K = (k11 k12
)k13
k21 k22 k23k31 k32 k33
- in this example of a tensor of 2nd order, a material is anisotropic when all 9 elements have different values
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Scale-invariance of Anisotropy:
- In Astrophysics - In Regional Geology - In Mineralogy and Microscopy - In the Exploration of Oil / Gas - Why not in Geophysical Exploration of Ore Deposits?
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
In Astrophysics and Cosmology:
- Cosmic microwave background radiation caused by primitive light of the early universe
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
In Regional Geology:
- Any topographic map is an example of anisotropy, since water will flow in preferred (or most probable) directions.
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
In Mineralogy:
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
In Mineralogy:
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
In Oil & Gas:- Although a lot of
times oil and gas reservoirs can be modelled in 1D (layered Earth), anisotropy effects play an important role in geophysical data.
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
In Ore Deposits:- Ore deposits are
geometrically very complex and are normally modelled in 3D. However, mineral / mining geophysicists do not normally talk about anisotropy of ore deposits.
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
In Ore Deposits:
- The Bingham Canyon Porphyry Cu-Mo-Au Deposit
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
In Ore Deposits:
- Porphyry stockwork veins in sericitized monzonite (Northparkes, Australia)
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
- visiting the core shack at Roundup 2016
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
- visiting the core shack at Roundup 2016
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
2/17/2016 Magnetic anisotropy and remanent magnetism in hemo-ilmenite from ore deposits at Allard Lake, Quebec - Hargraves - 1959 - Journal of Geophysical Researc…
http://onlinelibrary.wiley.com/doi/10.1029/JZ064i010p01565/abstract 1/3
Go to old article view
Journal of Geophysical Research Explore this journal >
Magnetic anisotropy and remanent magnetism in hemoilmenite fromore deposits at Allard Lake, Quebec
First published:
October 1959 Full publication history
DOI:
10.1029/JZ064i010p01565 View/save citation
Cited by:
54 articles Refresh Citing literature
Robert B. Hargraves
Abstract
The anisotropism of magnetic susceptibility of nearly pure hemoilmenite ore from deposits in the
Allard Lake area consists of a distinct plane of maximum susceptibility (defined by maximum and
intermediate axes along which the susceptibility is of similar magnitude) with a minmum susceptbility
axis at right angles. This plane coincides with a preferred crystallographic grainorientation indicated
by the parallelism of titanhematite lamellae which have exsolved on the basal plane of the
ferrianilmenite host grains. Measurement of the remanent magnetism (RM) shows a striking tendency
for the RM vectors to lie in or near this preferred plane. On the assumption that hematite (if not
ilmenite as well) is potentially ferromagnetic in the basal plane only (paramagnetic parallel to the caxis), it was inferred that the RM vectors could represent the resolved component of the magnetizing
field which tended to lie in the plane of maximum susceptibility. Under this hypothesis, it is possible to
resolve the broad spread shown by the RM vectors of samples from one deposit in terms of a single
Volume 64, Issue 10
October 1959
Pages 1565–1578
View issue TOC
- we are definitely not discovering the wheel !!!
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
- we are definitely not discovering the wheel !!!
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
- we are definitely not discovering the wheel !!!
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
- we are definitely not discovering the wheel !!!
- Do we see the reality (show) of geological anisotropy in our geophysical data?
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Questions:- (1) How can we integrate anisotropy in inversion
calculations?
- (2) Should we add anisotropy as a standard physical rock property?
- (3) How can we use those effects to discover, delineate, and characterize ore deposits?
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
What do we need?:- We need a geophysical flow (e.g. electrical, EM wave,
etc) illuminating the subsurface in all possible directions (we already do it).
- We need to measure responses in all possible directions (we also do it a lot of times).
- We need to think “out of the box”. Our physical rock properties are not scalars, they are tensors.
Proposal:
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
- Let’s start a brain storming group and let’s invite economic and structural geologists to these discussions.
Sergio Espinosa, Ph.D., P.Geo Principal Consulting Geophysicist; S E G eoscience and Ex ploration [email protected]
Thanks !!!