GeoExplo Ltda. Airborne Geophysical Consulting

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NEW!! Link to PDAC presentation on helicopter surveys in the High Andes 2013

-- last update March, 2013 --

Airborne Geophysical Survey Workshop

This collection of papers is provided in the hope that those that take the opportunity to study them will learn something about the; practical aspects of performing Airborne Surveys, (including airborne magnetic surveys, airborne radiometric surveys and airborne electro-magnetic surveys), the realities of the processes that convert measured data, in the real world, to usable presentations and the methods of interpretation that transform data into usable exploration information. We welcome comments, criticism and contributions these can be sent to the above e-mail address. If you would like to add a paper please send it to us and we will edit and re-format it for inclusion in the list with proper credit and links to the author.

Papers and Links Size (Kb) Abstract Authors
General -- Magnetic Surveys 130 View Abstract Dr. W.E.S.(Ted) Urquhart
Electro-Magnetic (EM) Surveys 281 View Abstract Dr. W.E.S.(Ted) Urquhart
Radiometric (Gamma-Ray Spectrometry) Surveys 301 View Abstract Dr. W.E.S.(Ted) Urquhart
Frequency Domain Filtering 397 View Abstract Dr. W.E.S.(Ted) Urquhart
Magnetic Data Compilation and Interpretation 431 View Abstract Dr. W.E.S.(Ted) Urquhart
Quality Control (QC) 22 View Abstract Dr. W.E.S.(Ted) Urquhart
The Economics of Geophysical Applications. 42 View Abstract Frank P. Fritz
New -- Sept. 18,2003

Efficacy of the SRM/MBS Approach for Analyzing Intra-Sedimentary Magnetic Anomalies. Presented to the SBGf Symposium -- Brazil , September 17th, 2003

90 View Abstract Dr. W.E.S.(Ted) Urquhart
Airborne Magnetic Surveys - Past, Present and Future Presented March 8,2003    Slide Presentation (40 Slides) 1070 View Abstract Dr. W.E.S.(Ted) Urquhart
Tectonomagmatic controls on porphyry and epithermal mineralization in the Central Andes.    Slide Presentation (38 Slides) 1600 View Abstract Jeremy P. Richards
Links to other Geophysical Sites 27    


General -- Airborne Magnetic Surveys Link to General -- Magnetic Surveys

This article deals with general issues of airborne geophysical surveys with special emphasis on airborne magnetic surveys. Under the airborne magnetic surveys section we discus: Basic Principles, Instrumentation, Magnetometers (fluxgate, proton precession and optically pumped magnetometers), Survey Operations, Contract Specifications, Survey Design and Noise.

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Electro-Magnetic (EM) Surveys Link to Electro-Magnetic (EM) Surveys

This paper on airborne Electro-magnetic (AEM) techniques deals with a number of topics relating to airborne EM survey systems and methods. These AEM topics include: Basic Principles, Transient Airborne Electro-magnetics, Frequency Domain Airborne Electro-magnetics, Airborne VLF Electro-magnetics, Factors Affecting Detectability, Combined AEM/Magnetometer Surveys, Survey Data Presentation and Interpretation.

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Radiometric (Gamma-Ray Spectrometry) Surveys Link to Radiometric (Gamma-Ray Spectrometry) Surveys

Airborne Spectrometer surveys are an important exploration technique. A number of topics on radiometric surveying are discussed in this section, these Gamma-ray topics include: Basic Principles, Compton Scattering, Cosmic Rays, Atmospheric Radiation, Instrumentation, Detectors, Analyzers, Spectrometer Calibration and Data Corrections, Calibration, Dead time Correction, Background Correction, Compton Stripping, Altitude Compensation, Radioelement Abundance Calculations, Processing of Airborne Data, Radiometric Survey Design, Counting Statistics, Line Spacing, Detector Selection and Radiometric Survey Specifications, Interpretation, Natural Radioactivity of Rocks and Effects of Weathering and Metamorphism

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Frequency Domain Filtering Link to Frequency Domain Filtering

Frequency Domain Filtering has developed over the last decade with the advancement computing power to be one of the most commonly used and misused aid to interpreting 2 dimensional data presentations. The article on FFT filtering techniques deals with a number of subjects fundamental to the understanding and proper use of the frequency domain filtering process. these topics include: General Theory, Basic Principles and Filter Recipes including - Downward Continuation, First Vertical Derivative, Matched Regional/Residual Filter, Reduction to the Pole, Analytic Signal.

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Magnetic Data Compilation and Interpretation Magnetic Data Compilation and Interpretation

Compilation and interpretation of airborne magnetic data are dealt with in the article. The Compilation topics such as: Database, Flight Path Plotting, Leveling and Mapping the Total Magnetic Intensity. The paper also looks at various topics in the interpretation of airborne magnetic survey data including: Interpretation, Interpreting Magnetic Data and Quantitative Interpretation

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Quality Control (QC) Quality Control (QC)

Quality Control is one of the most important parts of the survey operations. This QC paper deals with the what should be expected of a Quality Control officer and discusses the following topics: Basic Principals, QC Mandate, Client Representative, QC Officer Responsibilities, Survey Specifications and Typical Tests Required for a Magnetic Survey

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The Economics of Geophysical Applications The Economics of Geophysical Applications

Geophysical methods are an integral part of any exploration program and can be related to the cost of the only way to find new economic mineralization, the drill hole. For the same amount of dollars as one drill hole, the equivalent cost geophysical survey can collect data over 1 to 160 sq. km., depending on the method. If a reasonable physical property contrast can be expected for a particular target, an effective survey can be designed. Although any interpretation is only one of an infinite series, the addition of geological data and reasonable inferences can reduce infinite to an "optimistic" single interpretation. Attention to Survey Design, Survey Supervision, and Data interpretation for Regional, Local, or Detailed survey areas will assist in determining the best location for expensive drill holes.

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Efficacy of the SRM/MBS Approach for Analyzing Intra-Sedimentary Magnetic Anomalies -- Presented to the SBGf Symposium -- Brazil , September 17th, 2003 Efficacy of the SRM/MBS Approach for Analyzing Intra-Sedimentary Magnetic Anomalies

Magnetic methods have long been used to assist in the analysis of a prospective sedimentary basins in terms of the overall size, shape and structure. Less frequently has magnetic data been used for "pin pointing" hydrocarbon concentrations. The SRM/MBS method, as developed by Robert Foote, provides a tool for reducing exploration risk by providing direct targeting information. The method's efficacy has been demonstrated by statistical methods; however, the scientific basis on which this method is based needs to be examined. The method depends on the magnetic properties of the rocks in the sedimentary section being changed by the presence of hydrocarbons at depth and that these changes will produce magnetic anomalies that are distinguishable from anomalies produced by the magnetic basement and other effects. These two criteria are met in the real world and thus the SRM/MBS method has potential. Using the SRM/MBS method, as part of an exploration program, has the potential of reducing risk by focusing on areas where there is a higher probability of hydrocarbon concentration.

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Airborne Magnetic Surveys - Past, Present and Future -- Presented to the KEGS 50th anniversary symposium , March 8th, 2003 Airborne Magnetic Surveys - Past, Present and Future

Magnetic measurements are part of every airborne geophysical survey flown. One might argue that this is because it is relatively straight forward and not to expensive to add a magnetometer to any geophysical pay load, however, the real reason is that the results are so useful.

In 1946, the Gulf Airborne Fluxgate Magnetometer, developed during World War II for anti-submarine warfare, became available for commercial use. The tool allowed the rapid inventory of mineral resources regardless of terrain and accessibility and caused a revolution in reconnaissance surveys, worldwide.

Since that time there has been a continual improvement in all aspects of instrumentation, data acquisition, presentation, interpretation and safety. In this presentation we will look at some of the important developments on the way to current technology and technique as well as speculate what might be coming down the road.

In the author's view there are three areas of technology where advances have impacted significantly on resolution and how we perform magnetic surveys today. Of coarse the improvements in computer technology have played a vital role particularly in the areas of data acquisition systems, processing and data presentation. Nevertheless we will concentrate on:

We will also look at new developments in:

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SEG International Exchange Lecture No. 1: Tectonomagmatic controls on porphyry and epithermal mineralization in the Central Andes. Tectonomagmatic controls.

The source magmas for porphyry Cu and related epithermal deposits show no obvious geochemical differences to other voluminous and widespread calc-alkaline arc magmas, making it unlikely that petrogenetic processes in the sub-arc asthenospheric mantle wedge control the relative fertility of these magmas. Instead, a cumulative sequence of processes occurring in the overlying lithosphere appears to dictate the chances of forming a magmatic-hydrothermal ore deposit from magmas with a uniform latent potential. The continental lithosphere offers a significant physical obstacle to the ascent of mantle-derived magmas, and in fact primitive magmas rarely erupt in mature continental volcanic arcs because they are negatively buoyant relative to felsic crust. Where mafic magmas do erupt they are usually confined to back arc regions of rifting, where extensional trans-lithospheric fractures permit rapid ascent of mafic melts driven by hydrostatic pressure. In the main arc, primary asthenospheric melts are trapped at the base of the crust due to their density. Here, they interact with, heat, and ultimately melt the lithosphere, resulting in the generation of hybrid, intermediate composition magmas of lower density (the MASH process of Hildreth & Moorbath, 1988). Depending on the state of stress in the lithosphere and its kinematic response, these hybrid magmas may either pool in large partial melt zones at the base of the crust, or may periodically rise to shallower levels in the crust; a small proportion (probably <10% of total magma volume) may erupt at the surface. Geological records in arc terrains show that upper crustal plutonism and volcanism are episodic, and appear to be broadly related to periods of crustal deformation. The correlation is offset, however, such that major magmatic episodes usually follow but are not coeval with periods of contractional deformation. Furthermore, porphyry Cu-forming plutons tend to occur towards the end of these magmatic cycles. The majority of plutons in these settings show no evidence of syn-emplacement strain, suggesting that they were intruded during periods of relatively low differential horizontal stress. It is suggested that periods of elevated compressional stress are not conducive to the ascent of magmas from the base of the crust, because potential magma conduits are held closed. Such contractional events are often related to periods of rapid subduction with augmented magma and heat flux to the base of the lithosphere, resulting in the build-up of voluminous lower crustal MASH zones. Upon relaxation of compressive stress at the end of a tectonic cycle, evolved magmas with positive buoyancy will begin to rise through the crust, and may pool to form mid-crustal batholith complexes. Magma ascent may be channeled by deep-seated structures, and dilational zones formed at jogs in major strike-slip faults provide conduits of maximum permeability that may focus plutonism and batholith construction. Porphyry Cu deposits and associated epithermal systems form at late stages in the evolution of these batholiths, from hydrothermal fluids exsolved from residual melts after extensive crystallization and fractionation. The fate of these late magmatic fluids, whether to be vented to surface or constrained to interact with host rocks and groundwaters thereby potentially forming ore deposits, also depends on the state of stress in the upper crust. Differential stresses that would lead to shear fracturing of the brittle carapace above the magma chamber will likely cause venting or volcanic eruption, short-circuiting the ore-forming process. In contrast, conditions of low horizontal differential stress appear to be optimal for containing subvolcanic hydrothermal activity and ore formation.

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About GeoExplo Ltda.

GeoExplo Ltda. is a geophysical consulting company servicing the Oil, Gas and Mining industry world wide. We offer a full spectrum of geophysical services focusing on: Acquisition, Interpretation, Management, Planning, Processing, Quality Control and Safety with respect to Airborne Geophysical Surveys of all types.

Dr. W.E.S.(Ted) Urquhart is the owner and principle employee of GeoExplo. His more than 35 years of experience in exploration geophysics and "bottom to top" knowledge of the Airborne Survey business can help to ensure that your Airborne Survey and Exploration program are a success.

If you have need our services please contact us at the address below.

Also please let us know if you found these papers helpful by sending us a note at the address below.

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GeoExplo Ltda.
Santiago, Chile
Phone(56-2) 326-5116