Flagstaff GeoConsultants Training Courses
EM and IP METHODS FOR GEOLOGISTS EM METHODS FOR GEOLOGISTS / GEOPHYSICISTS

EM and IP METHODS FOR GEOLOGISTS

This course on electrical and induced polarisation methods of geophysics is targetted for geologists in industry, and for geophysicists who need an update in current practice.

The course presenter is Dr Michael Asten (Flagstaff Geo-Consultants and Monash University). He has presented this popular course thirty times over the last decade, to exploration Companies and university MSc students on four continents.

Dr Asten was formerly a Principal Geophysicist and Snr Principal Research Scientist with BHP, who pioneered many innovations in electrical methods into BHPs mineral exploration practice.
 

Course Duration: 2 days or 3 days (depending on Client requirements).

Outline:
The course is a two-day workshop-style course aiming to introduce geologists/ processors/technicians to current geophysical exploration methodologies in ground, borehole and airborne electromagnetic exploration, induced polarization and Controlled-Source Audio-magneto-telluric (CSAMT) methods.  This last method also has significant applications in basin studies and  petroleum exploration.

Issues covered include fixed-loop, moving-loop and sounding methods for reconnaissance and detail surveys, borehole surveys for target location and/or definition of geometry, and considerations where conductive overburden is present.  Emphasis is on time-domain EM methods, but VLF and ground FEM (Max-Min) methods can be included.  The course incorporates ground and airborne (GEOTEM) case histories from vms, sedex, copper-gold and porphyry-copper prospects, plus examples where electrical methods have complemented seismic methods in basin studies.  Participants have an opportunity to perform basic interpretations on ground, borehole and airborne data.

Where available, local exploration geophysicists contribute case-history material relevant to participants' projects.

All course participants receive a comprehensive Course Manual.  Click here to view Contents.

Michael Asten
Flagstaff GeoConsultants,
ph  61 3 8420 6200   fax  61 3 8420 6299
email  michaelasten@flagstaff-geoconsultants.com.au

COURSE CONTENTS

CHAPTER 1.
Introduction to transient EM and induction

Why are we here – a few examples.
Rocks as conductors

• define resistivity, conductivity, conductance
• effect of weathering, saline water, clay, metallic minerals, graphite
• effect of mineral texture: py vs po/cpy
• The Electromagnetic spectrum
• radar RIM TEM Res/IP
• an elementary EM system and response
• real and imaginary
• in-phase and quadrature
• decay constants
• Time-domain EM and "smoke rings"
• induction (vortex) currents
• channelled (galvanic) currents

CHAPTER 2
Fixed and moving-transmitter loop surveys
Fixed transmitter-loop surveys (FL)

• roving receiver
• why z-component
• profile shapes
•             target pick, interpretation rules
• coupling diagrams
•             blind spots, pairs of loops
• typical loop sizes and profile spacing
• example
• current channelling example

• coincident-loop receiver
• separated loop receiver (why)
• in-loop receiver
• profile shapes
• target pick, interpretation rules
• example
• when twin peaks generate; into one peak (the usual!)

• FL – Thalanga, Eloise
• ML - Mt Bulga, Teutonic Bore

• horizontal loop EM systems – Max-Min
• field set-up
• presentation of HLEM data
• HLEM interpretation

CHAPTER 3
WORKSHOP 1

• ML over conductor
• pick conductor, design follow-up survey
• WORKSHOP 2
• FL follow up over conductor
• pick conductor
• site drill hole

CHAPTER 4

• Effect of conductive overburden on profiles
• FL vs ML (Time Domain) & HLEM
• Different EM instruments
• Sirotem, Protem,  Crone, UTEM
• transmitter power and loop size- comparison
• Time Domain vs Frequency Domain systems
• Logistics
• gridding requirements – FL vs ML
• cost per station or line km
• production rate
• Reconnaissance vs Detail surveys

• Uniformity of illumination
• Relative coupling with horizontal and vertical targets
• Case History – Hellyer (UTEM)
• Case History – HLEM
• Discrimination between targets
• thin/thick
• shallow/deep
• mineralogical assemblage

TEM on a layered earth

• apparent conductance
• apparent conductivity
• conductance-depth parasection
• conductivity-depth parasection
• alternative algorithms available

CHAPTER 6
Examples of parasections and EM response maps

• parasections over vertical orebody
• stripping
• transforms
• images

CHAPTER 7
Down-hole EM

• positioning of loops (primary field)
• elementary profile shapes
• current elements and EM signatures
• graphical interpretation procedures
• intersected plates

WORKSHOP 3
Plot conductor off hole and site new drill hole

WORKSHOP 4
Assess whether follow-up hole intersected best mineralisation

Conductor beyond end of hole
Migration of currents in thick conductor - Hellyer example
Case histories on

• plot vertical extent of intersected conductor
• dip of a conductor
• strike extent of conductor
• 3 component borehole TEM

Computer demonstration eg. Filament

Graphical interpretation tools

• Exercise-Field data

CHAPTER 8
Other borehole EM methods
MMR (magnetometric method)
 Anomaly shapes in boreholes
Examples –
 Pinnacles Lead MVT, Thalanga VMS, Broken Hill  BHT

RIM (radio imaging method)
 borehole to borehole
 Eloise eg

CHAPTER 9
Airborne EM

Helicopter AEM–  eg Dighem

• Geometry
• Anomaly shapes
• parasections
• Examples – Bathurst mining camp,

Fixed wing – Geotem, Questem

• transmitter waveform
• anomaly signatures

• mapping of the regolith

Data integration – mag & conductivity
AEM mapping

• example Lady Loretta
• lag effects – example Bushman
• AEM depth penetration

AEM image enhancement

• time constants
• principal components
• horizontal derivatives
• discrimination between classes of conductors

CHAPTER 10
Transient EM Surroundings
 

• diffusion of EM current in layered earth ("smoke rings")
• apparent resistivity curves
• field procedure (in/out of loop readings)

CHAPTER 11
Induced polarization method,
CSAMT and ISR
Electrode arrays
Pseudo-sections thick and thin conductors
Cause of IP effect

• frequency and time domain, chargeability and  and phase anomalies

•  Century,  MacArthur River

-   Mt Milligan
-   Obuasi

Introduction to CSAMT and ISR

• case histories in gold exploration
  (Ohui, Temora)

CHAPTER 12
Open discussion

• What "extra" information should a geologist supply to a geophysicist to maximize usefulness of geophysical surveys

 
EM METHODS FOR GEOLOGISTS / GEOPHYSICISTS
Course Notes for Industry Short Courses

Michael Asten
Flagstaff Geo-Consultants and Monash University

The courses cover air, ground and borehole electromagnetic methods in exploration geophysics.
Courses for geologists use a descriptive approach, plus discussion of case histories.  Courses for geophysicists draw on more detailed material in the Manual, plus specialist material as required.
All overhead transparencies and data used in discussions will be supplied to participants as a set of paper copies.  Simple interpretation exercises are designed to illustrate principles, and can be accomplished with pencil and graph paper.

Participants should provide colour highlighting pens (red green blue), a calculator, A4/quarto or metric graph paper, pencil, ruler, and protractor.

These course notes are copyright © Michael Asten 1999.  Reproduction of any part of these notes is not permitted without permission of the author.
 
 

ALSO AT

Department of Earth Sciences
Monash University
Clayton  Vic  3169  Australia
masten@mail.earth.monash.edu.au
 
 

The Presenter

Dr Michael Asten is a consulting geophysicist and Partner with Flagstaff Geo-Consultants in Melbourne, Australia, and  also holds a part-time academic position as Principal Research Fellow at Monash University. He majored in Physics, Geology and Geophysics  at the University of Tasmania before entering post-graduate study at Macquarie University in 1972.  After excursions into magneto-tellurics and DC electrical methods he gained a PhD in geophysics on the topic of  using micro-seismic waves as a tool for studying sedimentary basins.  In 1977 he took up a two-year appointment lecturing and coordinating an MSc (geophysics) programme at Ahmadu Bello University in Nigeria. He then  joined BHP Minerals in 1979 and worked in coal and  base-metal exploration in Australia, East Africa and North America, with particular emphasis on geophysical research issues. He has been active in EM research for a decade,  initiated the airborne gravity gradiometer project in BHP, and has conducted numerous short Industry courses on EM Methods at various levels, for Geologists and Geophysicists on four continents.  He is a past Vice-President of the ASEG, an Associate Editor for the SEG, and was Co-Chairman of the ASEG Conference 1998.