Archive for category Publications

Fault reconstructions in Northwest Territories using aeromagnetic data

Posted by on Tuesday, 5 May, 2015
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Canadian Journal of Earth Sciences has published an article “Fault reconstructions using aeromagnetic data in the Great Bear magmatic zone, Northwest Territories, Canada” written by Nathan Hayward, Louise Corriveau from Geoligical Survey of Canada

The authors have chosen for the investigation the Great Bear magmatic zone (interpreted as a Paleoproterozoic magmatic arc)  which includes economically important mineralization of vein-type silver, radium, and uranium deposits, polymetallic iron oxide copper–gold and iron oxide ± apatite.

 

 

 

 

 

 

 

 

 

 

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Geological development of the Great Bear magmatic zone is described in details in the paper including magmatism, tectonic (folding and faulting) events. A model of conjugate transcurrent faulting with the principal shortening direction and the boundary of the system has been presented.

The aeromagnetic data used for the study has been compiled and integrated from different sources including public archival aeromagnetic data and data from private sector. In the result of the integration, nearly complete high-resolution coverage of the Great Bear magmatic zone was obtained.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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The magnetic data interpretation process included regional magnetic interpretation and detection of magnetic lineaments related to faults and dykes.

In the result of this work authors made structural reconstruction of the Great Bear magmatic zone, analysed horizontal offsets on fault zones and developed Vertical Offset Rotation Model and Maximum Offset Model. In the conclusion the authors made an analysis of mineralization distribution in connection with the structural units.

The full paper with tables and all pictures is here..


IP or not IP? (notes about IP in transient EM)

Posted by on Tuesday, 28 April, 2015

by Alexander Prikhodko

During the last few years the topic about IP effect (induced polarization) in the EM (electromagnetic) transient method (mostly in airborne time-domain) has been actively raised by many authors through geophysical magazines, conferences and meetings.

Here we will look into the topic without formulas and deep theory for a better understanding of the IP effect by general users of electro-prospecting  methods.

The nature of the IP phenomenon is universal regardless of an electric field source inducing (causing) the phenomenon or a measurement way of the appearance. First of all, the IP theory is out of Maxwell equations solutions because the process is accompanied by mass transfer and connected with EM field transformations. In contrast to IP theory Maxwell’s equations deal with electromagnetic induction which the time-domain (transient) method is built from.

In the case of IP the term “induced” means “caused” and does not relate to the concept of EM induction.

The concept of Induced Polarization (a substance ability to separate opposite charges) incorporates different phenomenons but related processes that occur:

1) in heterogeneous fluids or in pores filled with fluids;

2) due to electrochemical processes.

These two phenomenons – electrokinetic (1) and electrochemical (2), is a key to understanding how IP is used in applied geophysics.

Electrokinetic processes occur on contacts between ionic conductive fluids and a solid phase.

Electrochemical processes occur on contacts, or surfaces, between phases with electronic (metallic) and ionic (non-metallic) conduction. This is fundamental when IP method used when exploring for sulfide mineralization, especially if the sulfides are disseminated as the IP effect will be stronger than for massive sulfides of the same volume because its surface area is less.

Historically electrochemical nature of IP phenomenon first investigated and used in geophysics by Conrad Schlumberger (published in 1920). Later, during further electronic industry development and equipment sensitivity and bandwidth increasing, IP effect began to be observed all over the geologic environment due to the possibility of measurement of rapid and comparatively weak IP signal of the electrokinetic nature.

Generally, the IP effect of both natures potentially may affect data obtained with any electro-prospecting method including inductive time-domain method, regardless that the strongest IP effect occurs in the geologic environment at galvanic (grounded) way of the current inducing and the voltage measuring.

So, the IP component in transient or time-domain data is a parasitic effect which is not under Maxwell’s EM theory. (By the way, in the widely employed original DC-IP method, the inductive component is considered as a source of noise.) There are some technical requirements to sensitivity, bandwidth and geometry of a time-domain system to get better the parasitic signal superimposed on the inductive, native to the method, component.

Fortunately the IP parasitic signal is opposite to the inductive secondary field component allowing to recognize it and separate out it in some cases from the measured total secondary field. The favorable condition to get IP component from time-domain data and investigate it is rapid decaying inductive secondary field, i.e. resistive environment in general is favorable, but there are cases  when a strong IP component is prominent in presence of long inductive decay.

Unfortunately the existing theories of the electrokinetic and electrochemical natures of the IP phenomenon are on a qualitative basis. It means there is no chance to get petrophysical or/and petrochemical parameters of the geologic environment and to classify the IP sources according to their nature. On practice, empirical approximations are used for the IP process description with limited controlled parameters (in particular, Cole-Cole formula and the corresponded parameters) despite the nature of the phenomenon. To our delight it enables creative and thoughtful geological interpretation of the IP data if we get it correctly.


Earth Explorer: About Insightful geophysics..

Posted by on Thursday, 2 April, 2015

by VIRGINIA HEFFERNAN on MARCH 30, 2015

The founders of Insight Geophysics have deep roots in the past, but their approach to Induced Polarization (IP) represents the future of mineral exploration: real time interpretation of data, integration of non-geophysical information with 3D inversions, and a dynamic style of surveying that allows for tweaks on a day to day basis depending on feedback from the exploration team.

See more

 


Online Geophysics Lectures and Videos

Posted by on Thursday, 23 January, 2014

Geophysics Lectures in University of South Alabama:

Introduction to Geophysics; Seismic Stratigraphy; Wave Theory Refraction and Reflection; Petroleum Generation and Migration; The porosity Logs; Gamma ray logs; Electric SP and Resistivity Logs and many other are on KHURRAM TANVIR Official Page

 


Geology Films

Posted by on Tuesday, 21 January, 2014

During mineral exploration programs using geophysical methods it is highly important to know exploration models and mineralization controlling factors for proper choice of geophysical interpretation methods and approaches.

Clive Willman, geologist and film-maker, has created a series of short films covering Orogenic Gold Deposits, their formation, fluids and faults, illustrating with examples such as the Morning Star and Stawell Gold Mines in Victoria (Australia); The Metamorphic Gold Model; Gold, Faults and Fluids.

Clive presents his subject by way of interviews with leading workers in the field. Clive has worked as a geologist in both Industry and for the Geological Survey of Victoria, and brings a degree of authority to his film-making in this discipline.

Geology Films youtube.com


Multi-image blending for geophysical data visualisation and interpretation

Posted by on Thursday, 9 January, 2014

Interactive multi-image blending for data visualisation and interpretation

P Kovesi, E-J Holden and J Wong

ASEG Extended Abstracts 2013(1) 1 – 5
Published: 2013

Abstract

The ability to integrate data from a range of different images is often a crucial requirement for successful interpretation. Interactive multi-image blending is presented as a tool for facilitating the interpretation of complex information from multiple data sources. Traditionally, image blending has only been considered for cross-dissolving effects between two images. However, it is common for there to be more than just two images of interest in an interpretation task. We have developed a family of different multi-image blending tools to fill this need. These have been designed to support a number of different interpretation tasks and image types. For image blending to be a useful tool for multiple image interpretation it is important that the association between features and individual input images remain identifiable and distinct within the blend. We argue that interactivity of the blend is an important component for achieving this. Blending can also be usefully employed to interactively explore parameter variations for enhancement techniques. Often the best parameter values to use cannot be known beforehand, and it is common for different regions of an image to require different parameter values for best enhancement. By preparing a set of images processed over a sequence of scales and parameter values, and then interactively blending between these images, the interpretation of a data set can be greatly facilitated.

Geophysics researchers win innovation award

A team of researchers at The University of Western Australia has been recognised for its work to develop the most innovative use of a geophysical technique.

Research Professor Peter Kovesi, Associate Professor Eun-Jung Holden and Assistant Professor Jason Wong, won the Laric Hawkins Memorial Innovation Award at the International Geophysics Conference and Exhibition 2013 in Melbourne for their paper “Interactive multi-image blending for data visualisation and interpretation”.

The award is given for the most innovative use of a geophysical technique from a paper presented at the conference. The paper was delivered by Peter Kovesi.

Geoscientific data interpretation aims to understand complex geology in Earth’s subsurface by using a range of information including different types of geophysical, geological and geochemical data.

The ability to integrate a range of different sets of data is often a crucial requirement for successful interpretation, but this is a challenging task which often results in interpretations that are subjective and unreliable.

Nevertheless, these interpretations form the basis of significant economic, social and environmental decisions by resource industry and government agencies.

 


Exploration Geophysics Info on Flipboard

Posted by on Wednesday, 18 December, 2013

Magazine App for iOS and Andriod

Capture


Rio Tinto: “Geophysics playing an increasingly important role”

Posted by on Tuesday, 17 December, 2013

by VIRGINIA HEFFERNAN on DECEMBER 11, 2013 EXPERTISE

 

“Despite a steep appreciation in exploration spending over the past decade, the number of greenfield discoveries is falling every year. Narrowing this gap will require harnessing the power of big data and cloud computing, according to a presentation by Rio Tinto’s exploration chief Stephen McIntosh at the International Geophysical Conference in Melbourne.

“In a lot of cases, we have the data but we haven’t got the most out of it because of time constraints and our ability to find or “discover” this data,” Amanda Butt, McIntosh’s colleague and former manager of exploration and geophysics, said in a follow-up interview with Earth Explorer. “Now that we can do things more quickly, and efficiently we can get more effective information out of the data.”

Geophysics, in particular, has become an increasingly important exploration tool as the depth of the average discovery moves from close to surface in the 1950s to hundreds of metres deep. Indeed, geophysics contributed significantly to nine of the 16 greenfields discoveries Rio Tinto has made since 1996, including the Diavik diamond mine in Canada and more recently at the La Granja copper project in Peru.”

the original story


“Gravity and Magnetic Exploration Principles, Practices, and Applications”

Posted by on Thursday, 13 June, 2013

the new book

• End-of-chapter exercises, as well as overview and key concepts sections, help to engage students, encapsulate important concepts and consolidate the focus of study
• Online exercises utilising industry-standard software enable readers to develop practical experience
• Ancillary online case studies describe examples of gravity and magnetic methods in diverse successful applications, providing insight into their possibilities and limitations

“Near-Surface Applied Geophysics”

Posted by on Thursday, 13 June, 2013

the new book

• Presents emergent techniques and the newest developments in more traditional techniques, providing a fully up-to-date picture of the field

• Illustrated with insightful case studies selected from the current scientific literature, providing a powerful perspective on each technique’s capabilities
• Provides information on data analysis and inverse theory, essential to giving the reader full exposure to data acquisition, processing and interpretation

Advances in Airborne and Ground Geophysical Methods for Uranium Exploration

Posted by on Tuesday, 30 April, 2013

IAEA (International Atomic Energy Agency) has published a book “Advances in Airborne and Ground Geophysical Methods for Uranium Exploration”.

“Due to growing global energy demand, many countries have seen a rise in uranium exploration activities in the past few years, and newly designed geophysical instruments and their application in uranium exploration are contributing to an increased probability of successful discoveries. This publication highlights advances in airborne and ground geophysical techniques and methods for uranium exploration, succinctly describing modern geophysical methods and demonstrating their application with examples.”

Download..


New Geophysical Articles on Earth Explorer

Posted by on Monday, 11 March, 2013

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The new gravity books

Posted by on Sunday, 3 March, 2013

Acquisition and Analysis of Terrestrial Gravity Data

  • Leland Timothy Long, Georgia Institute of Technology
  • Ronald Douglas Kaufmann, Spotlight Geophysical Services

Gravity surveys have a huge range of applications, indicating density variations in the subsurface and identifying man-made structures, local changes of rock type or even deep-seated structures at the crust/mantle boundary. This important one-stop book combines an introductory manual of practical procedures with a full explanation of analysis techniques, enabling students, geophysicists, geologists and engineers to understand the methodology, applications and limitations of a gravity survey. Filled with examples from a wide variety of acquisition problems, the book instructs students in avoiding common mistakes and misconceptions. It explores the increasing near-surface geophysical applications being opened up by improvements in instrumentation and provides more advance-level material as a useful introduction to potential theory. This is a key text for graduate students of geophysics and for professionals using gravity surveys, from civil engineers and archaeologists to oil and mineral prospectors and geophysicists seeking to learn more about the Earth’s deep interior.

Author(s)/Editor(s):Thomas R. LaFehr and Misac N. Nabighian

Fundamentals of Gravity Exploration (Geophysical Monograph Series No. 17) covers a full range of gravity-exploration topics, including first principles, field instrumentation and operations, rock densities and density contrasts, data reduction, methods of interpretation, and geologic examples.  The subject matter includes inversion and an appendix on the Fourier transform.  This book will help students to efficiently gain knowledge and appreciation for the method, and it will provide experienced earth scientists with a valuable addition to their exploration libraries, both for reference and understanding of this important method.


Potential fields for basement investigations

Posted by on Wednesday, 30 January, 2013

Often not given its due in oil and gas geophysics, knowledge of basement geology can be critical to exploiting reservoirs including the unconventional.

by GRAHAM CHANDLER on JANUARY 24, 2013

There is an article in the last Earth Explorer issue:

New Approach to Basement Studies for Oil and Gas Explorers



The New Near-surface Resistivity Method

Posted by on Monday, 22 October, 2012

“The Leading Edge” has published in October 2012 issue the article of  Roy K. Warren, Warren Geophysical Service (Houston, TX), “Near-surface resistivity for hydrocarbon detection”. The article consists of many case studies which demonstrate the accuracy of the results.

Abstract

Roy K. Warren
Warren Geophysical Service
A new method called the “grid resistivity system” (GRS) is described which measures relative changes in subsurface resistivity using the low-frequency harmonics (either 50 or 60 Hz) generated by electric power lines. The electromagnetic waves emanate from the power grid, and some of this energy interacts with the air-Earth interface to be absorbed by the Earth. The lowest frequency penetrates to the greatest depth. The power from the grid causes current to flow in the rocks and soil. The Earth material with higher conductivity offers a path for the current to follow. The method can help locate geophysical signatures associated with the geochemical response of hydrocarbon chimney leakage. Data collection is fast and low cost. Processing results in cross sections of resistivity. Interpretation focuses on the identification of the larger conductors related to clay alteration caused by chimney leakage from a reservoir. ©2012 Society of Exploration Geophysicists

Environmental Geophysics: Everything you ever wanted to know

Posted by on Monday, 10 September, 2012


Bookshop Offer from EAGE

Environmental Geophysics: Everything you ever wanted (needed!) to know but were afraid to ask! (EET7)

Written by, Peter Styles

This is an outward facing book for people who need to understand Geophysics. It can solve the problems they regularly encounter and help them to deliver their optimal geotechnical solution, proved by the essential, but last to be applied, intrusive investigation.


Geoscience Australia: update on geophysical data

Posted by on Friday, 7 September, 2012

Update on geophysical data releases

Geoscience Australia will be managing the data acquisition program in New South Wales, Queensland, Western Australia and the Northern Territory.

The current status of Geoscience Australia’s geophysical survey data acquisition is available in a comprehensive table.

Minerals Alert Geophysical Surveys Table – survey boundary polygons in MapInfo TAB format.

Seismic and magnetotelluric data released for Youanmi Survey in Western Australia

The Youanmi deep crustal seismic survey was acquired in 2010 and extends nearly 700 kilometres over the Youanmi Terrane and Eastern Goldfields Superterrane of the Yilgarn Craton. This project was a collaboration between Geoscience Australia and the Geological Survey of Western Australia (GSWA). Funding was provided from the Western Australian Government’s Exploration Incentive Scheme, and Geoscience Australia’s Onshore Energy Security Program. The survey consists of three traverses with a total length of 695 kilometres. These seismic, magnetotelluric and gravity data aim to image the northern Yilgarn Craton from its north-western margin to the Ida Fault, near Leinster.

These data combined with the 2001 Northern Yilgarn and the 2010 Capricorn deep crustal reflection surveys result in a complete section across the northern Yilgarn Craton.

The processed SEG Y data, TIFF images, location information, magnetotelluric and gravity data are available and can be downloaded from the Seismic Acquisition and Processing project.

Interpretations of the seismic sections and magnetotelluric models undertaken by GSWA and Geoscience Australia geologists will be released in February 2013 at a public workshop in Perth.