Archive for category Airborne

New airborne electromagnetic data interpretation record release in Australia

Posted by on Monday, 8 February, 2016
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“The Southern Thomson Orogen VTEMplus® AEM Survey: Using airborne electromagnetics as an UNCOVER application, Geoscience Australia Record 2015/29 discusses the acquisition, processing and interpretation of data from the Southern Thomson Orogen VTEMplus® AEM Survey and highlights the use of regional AEM surveying for geological and depth to basement mapping in this greenfields area. Data acquisition, processing and interpretation methods are presented, followed by a series of case studies demonstrating the effectiveness of the technique for identifying and mapping depth to resistive basement, for characterizing cover sequences, for mapping weathering products and for mapping post-depositional structures.”

australiaVTEM

See more…


The newly-released airborne magnetic survey results in BC

Posted by on Saturday, 30 January, 2016

The Northern MinerRead the article about the newly-released airborne magnetic survey results. The survey is considered the largest ever done by Geoscience BC.

Geoscience BC revealed the survey results at a press conference Jan. 26 at the Mineral Exploration Roundup convention in Vancouver.

by Lesley Stokes:

Roundup 2016: Geoscience BC’s much-needed new survey results for explorers in BC

SEG Best Paper award in M&G, New Orleans, 2015

Posted by on Wednesday, 6 January, 2016

SEGbestpaper

The paper from Geotech Ltd. has been awarded as the Best Paper in the Mining and Geothermal sessions at the 2015 SEG annual meeting in New Orleans: “Airborne Inductively Induced Polarization effects in and their removal from the VTEM data from Mirny, Russia”.

As the Committee Chair says: “Out of all the papers presented, it was voted as highest ranking by the session participants”.

The paper is about airborne inductively induced polarization (AIIPTM) effects, which is expressed in the form of numerous negative transients, and observed in the VTEM helicopter time-domain EM (TDEM) data from Mirny, Russia. VTEM data reflect mainly two physical phenomena in the earth: i) electromagnetic induction and ii) airborne inductively induced polarization (AIIP) related to the relaxation of polarized charges in the ground. Typical AIIP effects in the VTEM data from Mirny corrupt only the early to mid-time channels, from 55 microsec to 400 microsec. Moreover, the earliest few time channels, from 18 microsec to 48 microsec, are not affected by AIIP, because the IP effect takes a finite time to build up. Cole-Cole analysis of the AIIP affected VTEM data showed that the frequency factor and the time constant are close to 0.8 and 0.0001s, respectively. Since the earliest time channel data are not affected by AIIP, the resistivity of the shallow ground can still be precisely determined. As a result, the purely inductive VTEM decay can be accurately modelled and used to remove the AIIP effect from later time-channels.

rdis

Read More: http://library.seg.org/doi/abs/10.1190/segam2015-5845297.1


Airborne geophysics in Kazakhstan

Posted by on Tuesday, 4 August, 2015

gbr-logo“Global Business Reports” (GBR), who provides information about all aspects of the hydrocarbon, Pharmaceuticals, Chemical, Energy, Minerals, Mining and the Metallurgical industries around the world, has published an interview with the director of an airborne geophysics Kazakhstan-Canada joint venture as part of GBR research on the mining industry in Kazakhstan, which will be published in Engineering and Mining Journal in September 2015.

10 questions and 10 comprehensive answers about KazGeotech, its achievements and plans.

details..

KazGeotech survey for Rio Tinto (rus):


Pioneer completes its first Commercial Multicopter UAV-MAG™ Survey

Posted by on Saturday, 11 July, 2015

by Michael Burns, President, Pioneer Exploration Consultants Ltd. on July,11, 2015

Pioneer Exploration Consultants Ltd. is a Canadian based geological consulting company that is quickly emerging as a leader in mining and exploration related UAV-based survey technology. Starting in 2014, they designed and built in-house a multicopter UAV-MAG™ survey system, and flew the first ever 590 line km multicopter-based survey.

 

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Rather than waiting for a turn-key UAV based magnetometer system to hit the market, Pioneer came up with the idea of designing and building their own…

“Starting in the summer of 2014, we combined a proven UAV platform with a potassium vapor GSMP-35A magnetometer, resulting in a system with excellent performance specifications and survey capabilities. The UAV is a multicopter flight platform, chosen based on its payload capacity and flight time of about 30 min. The GSMP-35A potassium vapor sensor package is a proven airborne magnetometer with 0.0001 nT resolution, 0.3 pT sensitivity and 10 Hz sampling. The sensor package includes an ultra-light weight laser altimeter, GPS, and an IMU (inertial measurement unit) to record the sensor’s velocity, orientation and XYZ movement. The result was our UAV-MAG™ system which can fly up to 70 line km per day at an all in cost to the client of less than $100 per line km. Mobilization costs are the same as getting a person on site with 100 pounds of gear, due to the light weight and compact size of the UAV-MAG™, so rather than being a major cost addition to the survey, it’s becomes an insignificant expense.

To our knowledge, our survey costs are at least $40.00/ line km lower than anyone else on the market. This becomes a significant advantage for our clients, letting them put more resources into ground, and that’s huge for them.

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Example of first vertical derivative results from two sample surveys, line spacing 50m, height 45m.

Our initial design focused on achieving three main goals:

1) To reduce magnetic interference of the flight platform in order to collect high quality magnetic data.

2) Create a system that is both reliable and flexible enough to fly a mag survey and collect aerial photos for orthoimagery and digital elevation models in the same day.

3) Create a highly portable system with the ability to fly a survey safely and simply in any terrain and under challenging weather conditions.

We achieved the first goal by employing a “towed bird” sensor configuration. The sensor is slung below the craft by a special designed light weight mount system, allowing sufficient craft-sensor separation and achieving low drag and no noticeable reduction in flight time. The remaining requirements pushed us away from fixed wing platforms and into multicopters for a number of reasons. With the UAV-MAG system, we can launch from the middle of a survey grid in heavily forested, steep terrain and not worry about takeoff and landing. Once in the air, the UAV-MAG™ takes care of the rest by flying the survey autonomously and returning home for landing. We found this invaluable for remote surveys. The small size of the platform, compared to a fixed wing system allows fast flight launching and easy transport. We can carry our fully flight-ready system by hand, ATV or vehicle, and launch within minutes. No complicated launching platforms, or landing fields required. What we have created is a truly versatile survey platform for multiple sensor packages, essentially a Swiss Army knife UAV, and our clients so far have been extremely pleased with the results and reduced survey costs.”

-Michael Burns, President, Pioneer Exploration Consultants Ltd.

For more information about our UAV-MAG™ Surveys, or to request a quote, please contact Michael Burns at: Michael.burns@pioneerexploration.ca

 


2015 Astana Mining and Metallurgy Congress

Posted by on Friday, 26 June, 2015

The Astana International Mining and Metallurgy Congress (AMM) (17-18 June) jointed political, business, financial and scientific leaders of the mining and metallurgical industry from many countries. The main goals of the congress was development of partnerships, introduction of technological innovations, attraction of investments and development of the country’s mining act.

The congress was held in the Palace of Independence. The world leader in airborne geophysics Geotech Ltd. together with the JV KazGeotech participated in the exhibition, in the “GEOLOGY SESSION” and in the bilateral business-meeting with Albert Rau, Vice Minister, Ministry of Investment and Development (Republic of Kazakhstan) presenting Geotech airborne geophysical technologies and Geotech-KazGeotech potential for geological exploration of Kazakhstan and the Middle Asia region.

Douglas Pitcher, Managing Partner and VP, Geotech with Gary Hodgkinson, General Manager Exploration, Rio Tinto - Central Asia

Douglas Pitcher, Managing Partner and VP, Geotech with Gary Hodgkinson, General Manager Exploration, Rio Tinto – Central Asia

 

 

 

 

 

 

 

 

 

 

 

Bazarbay Nurabayev - The chairman of Commitee of geology and subsoil use is reporting about strategic partners in the mineral exploration sector

Bazarbay Nurabayev – The chairman of Commitee of geology and subsoil use is reporting about strategic partners in the mineral exploration sector

 

 

 

 

 

 

 

 

 

 

 

 

 

Galym Nurjanov, Head of JSC “NATIONAL COMPANY KAZGEOLOGIA” - about  strategic directions of the company development

Galym Nurjanov, Head of JSC “NATIONAL COMPANY KAZGEOLOGIA” – about strategic directions of the company development

 

 

 

 

 

 

 

 

 

 

 

 

 

Douglas Pitcher, Managing Partner and VP, Geotech  - presenting Geotech airborne geophysics technologies and accelerating discoveries using Airborne Geophysics.

Douglas Pitcher, Managing Partner and VP, Geotech – presenting Geotech airborne geophysics technologies and accelerating discoveries using Airborne Geophysics.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

D Pitcher-Geotech_AMM Kazakhsatan 2015-eng-rus

KazGeotech-Globus_RUS

Other posts “Geotech in Kazakhstan”…

 

Photo: A.Prikhodko


Newly discovered historical gravity data pushes exploration activity

Posted by on Thursday, 28 May, 2015

The Aston Bay‘s Storm Project in Nunavut is focused on exploring high-grade sedimentary hosted copper mineralization.

The company recently has undertaken a review of the project data to gain further insight into the untested anomalies identified in the 2011 Versatile Time Domain Electromagnetic (VTEM) survey conducted by Geotech Ltd.

The results of the survey confirmed that the mineralized zones of the Storm deposit can be accurately mapped and modeled with electromagnetic techniques and the data suggests there remain portions of multiple zones that have not been adequately drill-tested along strike and beneath existing known mineralization.

One of the drill-ready VTEM anomalies is oval in shape and called SE anomaly with approximate dimensions of 4.0km x 1.5km. The anomaly is coincident with elevated levels of copper in the rocks and soils at surface and located along the structural system that hosts mineralization identified in previous drilling.

In 2013 Aston Bay acquired the ground gravity survey data collected in 1999 by Quantec IP Incorporated.  APEX Geoscience Ltd. confirmed the quality and veracity of the data and analysis of the data shows a coincident gravity high over the southern third of the SE Anomaly (see picture below).

 

 

 

 

 

 

 

 

 

 

 

 

 

SE Anomaly Comparison (VTEM vs Gravity) – Coincident Anomalies Suggestive of Large Prospective Target

“The combination of geochem data, gravity data, electromagnetic data and historic drilling encountering high-grade copper sulphides, reinforces the potential for a large sedimentary-hosted copper target at the Storm Project. The discovery of a compelling gravity anomaly also underscores the value of our on-going investigation and evaluation of the extensive historical database that the Company acquired from Teck. This also makes a stronger case for a larger gravity survey on the property to identify other potential targets within this basin scale system”, commented Benjamin Cox, President and CEO of Aston Bay.

Read in detail..


GEOMODEL – online time-domain EM data inversion

Posted by on Tuesday, 19 May, 2015

Significant improvements have been made since the last presentation of the webapp on ExplorationGeophysics.Info pages. Now the shareware TDEM data inversion web application (ww.geomodel.info) has easy and comfy Eng-Rus interface, the input supports six different file formats (airborne and ground systems), sounding stations position can be represented on the scalable Google Map, data is showed in a sheet, TEM off-time decay chart and calculated apparent resistivity with time or depth.

 

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The software can be used with data from WalkTEM, TerraTEM, ProTEM, Geotech airborne VTEM, TEM-FAST 48HPC, Tsikl and other TEM systems. A user can suggest any new data format and provide GEOMODEL developers with corresponded information.

The inversion process is interactive (forward modeling with thickness and/or resistivity changing) or iterative (automatic iterations to get correspondence between calculated and measured decay curve).

The inversion is based on 1D algorithm with support of CSIRO Division of Exploration and Mining and Australian Mineral Institute Research Association (AMIRA), P223F project.

Inversions

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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The next procedures can be done with TDEM Geomodel webapp:

-Import-export TEM data and inversions from a large number of industrial formats, including USF;

-Viewing and analysis of transient field decay curves;

-Editing individual decays or tens of decays together in a fast and easy way;

-Runing 1D inversion and compiling resistivity sections;

-Saving results in ASCII format for further processing and presentation in third-party software (Surfer, Autocad, Geosoft Oasis Montaj, etc.).

-Saving inversion results as resistivity sections and maps in different image file formats.

The next example shows  Geotech airborne VTEM  data inversion (Alberta, Canada):

 

The development team welcomes user’s comments and suggestions.


The next UAV magnetic system

Posted by on Wednesday, 29 April, 2015

Abitibi Geophysics together with GEM Systems announced about creation of  the partnership AeroVision™ for using UAV magnetic system which explores two potassium sensors. The system is going to be available since June, 1.  Sampling interval is promised 2 meters and resolution of .0001 nT, absolute accuracy  +- 0.05 nT. Laser-altimeter, GPS and auto-pilot are included.

The UAV mag surveys cost is going to be over 50% of the present ground geophysics pricing.


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.


Foreign investments in mineral exploration in Kazakhstan

Posted by on Monday, 27 April, 2015

Galym Nurjanov (a head of JSC “National exploration company “Kazgeology”) has held a press conference at RSU “Central Communications Service for the President of the Republic of Kazakhstan” and reported about success in investments attraction in the mineral exploration sector of Kazakhstan economy.

Over the past two years the four major foreign investors came to Kazakhstan – the Australian-British concern “Rio Tinto”, a South Korean corporation “KORES”, the Australian company “Iluka Resources” and the German investment fund “ULMUS FUND”. These companies are willing to invest into the mineral exploration sector over $ 5.5 billion tenge.  Airborne geophysical surveys are going to be started soon in connection with Rio Tinto and Iluka Resources projects. The advanced airborne geophysical technologies including VTEM and ZTEM which are used right now in Kazakhstan, have been brought by Canadian company Geotech Ltd.


Factors of Modern Discoveries

Posted by on Wednesday, 8 April, 2015

“INTEGRATING NEW TECHNOLOGY WITH HISTORICAL DATA, GEOLOGICAL INTUITION AND A LITTLE LUCK, COMPANIES ARE FINDING SUCCESS WHERE OTHERS HAVE NOT”

E&MJ News

Mineral Exploration Strategies

E&MJ News published an article by Steve Fiscor where some factors of new mineral deposits discoveries have been outlined – these factors include applying modern geophysical technologies. The author provides some examples – airborne EM (VTEM, ZTEM), airborne gravity gradiometer, and airborne radiometric surveys which played key role in discoveries of mineral deposits.

“All of the discoveries were in the zone of other major discoveries, but most of them had been overlooked for one reason or another. The motivation could only be attributed to a geologically motivated hunch. New technology in the form of deep-penetrating airborne surveys allowed ground-based geophysical surveys to target undiscovered anomalies. Combining the new information with what they knew historically, exploration geologists were able to improve the drilling programs to quickly determine a resource.”

The next discoveries made with airborne geophysical technologies:

Albany Ultra-pure Graphite – VTEM survey

The Balboa Discovery at Cobre Panama – ZTEM survey

Kennady North Kimberlite Discoveries – airborne gravity gradiometer survey

PLS High Grade, High Techand Contrarian – airborne radiometric survey

Details..

 


Novel technologies for greenfield exploration – GEOLOGICAL SURVEY OF FINLAND 2015

Posted by on Wednesday, 1 April, 2015

The Geological Survey of Finland (GTK) reports about new mineral exploration and mapping methods which were developed in the project ‘Novel technologies for greenfield exploration’ (NovTecEx) carried out in 2012–2014. The project was a part of the Green Mining Programme funded by Tekes. The research partners of the project were the Geological Survey of Finland and the University of Oulu. The main study areas were in the SavukoskiPelkosenniemi area and in the Lätäseno area in Finnish Lapland.

The methods include a tool for Audiomagnetotelluric (AMT) measurements, GUI developing for 2D MODELLING AND INVERSION SOFTWARE FOR AIRBORNE TIME-DOMAIN EM DATA, and description  THE EQUIVALENT SOURCE METHOD for CALCULATION OF THE DERIVED BOUGUER ANOMALY.

The report pdf


Current Issue of “Exploration Geophysics” – Airborne Electromagnetics AEM 2013

Posted by on Monday, 30 March, 2015

Exploration Geophysics
Volume 46 Number 1 2015
6th International Conference in Airborne Electromagnetics (AEM 2013)

This special issue of Exploration Geophysics comprises papers from the 6th International Conference in Airborne Electromagnetics (AEM 2013) held in South Africa, and showcases the latest ideas and advancements in the discipline of airborne electromagnetic geophysics.

Developing an efficient modelling and data presentation strategy for ATDEM system comparison and survey design
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Magdel Combrinck
pp. 3-11

A proposal to simplify the display of ATDEM responses through the concept of a three-dimensional signal:noise nomo-volume is presented. It contains the signal:noise values of all system time channels and components for various target depths and conductances integrated into a single interactive three-dimensional image.

3D-spectral CDIs: a fast alternative to 3D inversion?
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James Macnae
pp. 12-18

Spectral 3D approximations of the EM response can efficiently model vortex induction and current gathering for simple geological target geometries. This paper presents results of a spectral model fitting algorithm to automatically pick, locate and define a sulphide target from VTEM data at the Forrestania test range, Western Australia.

The analysis of ZTEM data across the Humble magnetic anomaly, Alaska
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Daniel Sattel and Ken Witherly
pp. 19-26

ZTEM data acquired across a magnetic anomaly of almost 30 000 nT were analysed for the presence of a magnetic gradient response and the effects from elevated magnetic susceptibilities. Modelling results indicate distortions in the conductivity structure recovered by 3D inversion when elevated magnetic susceptibility values are ignored during the inversion.

Regional TEMPEST survey in north-east Namibia
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Geoffrey Peters , Gregory Street , Ivor Kahimise and David Hutchins
pp. 27-35

A regional scale low-cost TEMPEST208 survey in north-east Namibia has provided a geo-electric map of the area, including an indication of Kalahari cover thickness. While there are limitations in terms of detail and depth penetration, the results will assist explorers in selecting areas of shallow cover to reduce costs.

Helicopter EM (ZTEM–VTEM) survey results over the Nuqrah copper–lead–zinc–gold SEDEX massive sulphide deposit in the Western Arabian Shield, Kingdom of Saudi Arabia
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Jean M. Legault , Carlos Izarra , Alexander Prikhodko , Shengkai Zhao and Emad M. Saadawi
pp. 36-48

Magnetic and electromagnetic (EM) results from both time-domain (VTEM and AFMAG (ZTEM) helicopter EM surveys are compared over the Nuqrah sedimentary exhalative (SEDEX) massive sulphide deposit in Saudi Arabia. The magnetic and EM data map major controlling structures but only the EM surveys are able to define the Nuqrah deposits.

MULTIPULSE – high resolution and high power in one TDEM system
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Tianyou Chen , Greg Hodges and Philip Miles
pp. 49-57

The MULTIPULSE technology airborne TEM system transmits a high power pulse and low power pulse(s) (trapezoid or square) within a half-cycle. The high power pulse ensures good depth of exploration and the low power pulse allows higher near-surface resolution and better sensitivity to weak conductors as confirmed by field results.

Geobandwidth: comparing time domain electromagnetic waveforms with a wire loop model
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Greg Hodges and Tianyou Chen
pp. 58-63

The effect of time domain EM waveform, power and receiver sampling times are effectively compared for a wide range of time constants using a wire loop conductor model. Peak time constant and equivalent frequency can be determined analytically or numerically. Arbitrary waveforms can be modelled as a sum of simple short ramps.

Not extinct yet: innovations in frequency domain HEM triggered by sea ice studies
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Andreas A. Pfaffhuber and Stefan Hendricks
pp. 64-73

Operational use of frequency domain HEM for sea ice thickness mapping was the driving force for developing new purpose-designed systems. We present improvements in decreasing noise levels by one to two orders of magnitude, and implemented control signals to eliminate system drift. Ground tests and airborne field data confirmed the achievement of these goals.

Airborne electromagnetic modelling options and their consequences in target definition
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Alan Yusen Ley-Cooper , Andrea Viezzoli , Julien Guillemoteau , Giulio Vignoli , James Macnae , Leif Cox and Tim Munday
pp. 74-84

Given the range of geological conditions under which airborne EM surveys are conducted, there is an expectation that 2D and 3D methods used to extract models of geological significance would be favoured over 1D inversion and transforms. We analyse data from the Musgrave province, South Australia, used for mineral and for hydro-geological prospecting.

Modelling an arbitrarily oriented magnetic dipole over a homogeneous half-space for a rapid topographic correction of airborne EM data
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Julien Guillemoteau , Pascal Sailhac and Mickael Behaegel
pp. 85-96

In mountainous areas, the airborne electromagnetic system can be at an angle with regard to the ground. We analyse how the data and the eddy current are affected in such a context. We also suggest a simple correction for the data and for the sensitivity function that reduces topography effects.

New developments in AEM discrete conductor modelling and inversion
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Marc A. Vallée
pp. 97-111

In the last 20 years, sphere and plate models have been integrated in parametric inversion programs which are used today for interactive interpretation of airborne electromagnetic surveys on powerful workstations. Different problems encountered in the implementation and application of these models are discussed and a case history from Abitibi, Canada, is presented.

Rapid approximate inversion of airborne TEM
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Peter K. Fullagar , Glenn A. Pears , James E. Reid and Ralf Schaa
pp. 112-117

Two algorithms have been developed to perform rapid approximate 3D inversion of airborne TEM. VPem1D performs 1D inversion at each data location above a 3D model. Interpretation of cover thickness is a natural application. VPem3D performs 3D inversion of resistive limit data. Conversion to resistive limits delivers a massive increase in speed. Both programs can operate on geological models to foster integrated interpretation.

Modelling the superparamagnetic response of AEM data
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Daniel Sattel and Paul Mutton
pp. 118-129

VTEM data flown at different system elevations across a known sulphide body and surface cover with elevated superparamagnetic (SPM) properties were analysed. The results indicate that SPM responses can be distinguished from deep conductor responses if the vertical AEM gradient is measured, with EM sensors being offset vertically by 2–40 m.

Using the in-line component for fixed-wing EM 1D inversion
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Adam Smiarowski
pp. 130-135

In conductive areas, the in-line component of an offset transmitter–receiver EM system can be more sensitive to the near-surface than the vertical component. Using estimated noise levels, this paper calculates the expected uncertainty on the inverted parameters of a bathymetry model and compares this to inversion results from field data.

Extending the range of time constants recorded by the SPECTREM AEM system
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Peter B. Leggatt
pp. 136-139

The Spectrem AEM transmitter has no off-time; secondary signals are recorded at the same time as the transmitter primary. By assuming the secondaries have decayed away by the last window, the signal value is used as an estimate of the primary. The result is underestimation of the secondary amplitudes if the target is highly conductive. This paper describes a method to compute a better estimate of the primary amplitude.


EM surveys over Green Giant graphite property in Madagascar

Posted by on Tuesday, 24 February, 2015

by Alexander Prikhodko, 24 Feb., 2015

Graphite mineralization has a high electrical conductivity, which makes it an excellent target for electromagnetic (EM) methods.

Energizer Resources Inc. and it’s predecessors have conducted several airborne and ground electromagnetic  surveys over different areas of Green Giant graphite property in Madagascar (province of Toliara). Different EM technologies have been used in accordance with their progress.

Geological position and characteristics of the property:

Regional position – Ampanihy Shear Zone, NS foliation of rocks;

-Vertical to sub-vertical nature;

-The area is underlain by supracrustal and plutonic rocks deformed with N-NE trending structures;

-Graphitic zones consist of multi-folded graphitic strata;

-Graphitic schist and gneiss with vanadium mineralization.

 Geologic map (magnetic field interpretation)

Green_Giant_quick_Mag

 

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AEM surveys covering with different technologies is in the picture above.

The basic AEM surveys results which demonstrate a potential of the territory and effectiveness of the applied methods are below.

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DIGHEM survey

Inverted (EMflow, Encom) DIGHEM data. Conductivity 3D voxel, sections and a map.

(conductors in red, resistors blue colors)

DIGHEMConVoxel

 

 

 

 

 

 

 

 

 

 

 

 

 

sections

 

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VTEM survey

Time-domain EM TAU parameter calculated with sliding window algorithm picks up the most conductive part of the geoelectrical section on each station-sounding.

TAU

 

 

 

 

 

 

 

 

 

 

 

 

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The resistivity-depth imaging (RDI) of EM time-domain data is a base of depth positioning of conductors potential for graphite mineralization and the first approximation of their geometry and dimensions.

rdisections

 

 

 

 

 

 

 

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3D apparent resistivity distribution with <1 Ohm-m clipping areas:

RDIvoxel

 


2014 issued patents by Assignee Geotech Airborne Limited

Posted by on Tuesday, 27 January, 2015
Patent number: 8878538
Abstract: An airborne geophysical surveying system comprising a receiver coil assembly for towing by an aircraft, the receiver assembly including a receiver coil for sensing changes in a magnetic field component of a magnetic field, and a receiver coil orientation sensing system for sensing orientation changes of the receiver coil. A controller receives signals representing the sensed changes in the magnetic field component from the receiver coil and the sensed orientation changes from the receiver coil orientation sensing system and corrects the sensed changes in the magnetic field component to provide a signal that is corrected for noise caused by changing orientation of the receiver coil in a static geomagnetic field.
Filed: November 26, 2010
Issued: November 4, 2014

Bucking coil and B-field measurement system and apparatus for time domain electromagnetic measurements

Patent number: 8786286
Abstract: According to one example embodiment is a time domain electromagnetic (TDEM) geophysical survey system for producing a B-field measurement, comprising: a transmitter coil; a bucking coil positioned in a substantially concentric and coplanar orientation relative to the transmitter coil; a receiver coil positioned in a substantially concentric and coplanar orientation relative to the bucking coil; an electrical current source connected to the transmitter coil and bucking coil for applying a periodic current thereto; and a data collection system configured to receive a magnetic field time-derivative signal dB/dt from the receiver coil and integrate the magnetic field time-derivative signal dB/dt to generate, a magnetic B-field measurement, the transmitter coil, bucking coil and receiver coil being positioned relative to each other such that, at the location of the receiver coil, a magnetic field generated by the bucking coil has a cancelling effect on a primary magnetic field generated by the transmitter coil.
Filed: August 28, 2009
Issued: July 22, 2014

Airborne time domain electromagnetic transmitter coil system and appratus

Patent number: 8766640
Abstract: A tow assembly for an airborne electromagnetic surveying system, including: a transmitter coil frame supporting a transmitter coil, the transmitter coil frame being formed from a plurality of serially connected frame sections forming a loop, the transmitter coil frame having rotating joints at a plurality of locations about a circumference thereof enabling the transmitter coil frame to at least partially bend at the rotating joints; and a suspension assembly for towing the transmitter coil frame behind an aircraft, the suspension assembly being attached to the circumference of the transmitter coil frame at spaced apart locations.
Filed: May 23, 2011
Issued: July 1, 2014

Airborne electromagnetic transmitter coil system

Patent number: 8674701
Abstract: A tow assembly for an airborne electromagnetic surveying system including a semi-rigid transmitter coil frame supporting a transmitter coil, the transmitter coil frame being formed from a plurality of serially connected frame sections forming a loop, the transmitter coil frame having articulating joints at a plurality of locations about a circumference thereof enabling the transmitter coil frame to at least partially bend at the articulating joints; and a suspension assembly for towing the transmitter coil frame behind an aircraft, the suspension assembly comprising a plurality of ropes and attached to the circumference of the transmitter coil frame at spaced apart locations.
Filed: February 25, 2009
Issued: March 18, 2014

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Posted by on Tuesday, 2 December, 2014

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