Development of Airborne Potassium Magnetometer

Dr. Ivan Hrvoic, Ph.D., P.Eng.President, GEM Advanced Magnetometers

Exploration 2007 & KEGS

Overview

Airborne Trends in Mineral Exploration

Why Develop Potassium?

Solutions and Examples

Fixed Wing

Helicopter

Helicopter and EM

UAV

Summary

Airborne Trends in Mineral Exploration

Last 5 years has seen a number of key trends that affect the implementation of any new airborne technology:

1. High Resolution Data

2. More Information from Data

3. Better Positioned Data

4. Safe Acquisition

5. Cost Effective Acquisition

Why Develop Potassium?

Reflects industry trends:

• High Resolution – Sensitivity, Sampling, Low Heading Error

• Good Gradient Measurements – Absolute Accuracy

• Positioning – Integrate with GPS

• Safety – Implement on Any Platform

• Cost Effective – Gradient Arrays

Potassium Principles -- Spectal Lines

4 Narrow Spectral Lines approximately 100 nT apart in 50,000 nT field

Narrow, symmetrical lines a key enabler of the technology

Affect sensitivity and gradient tolerance … GEM developed gradient optimization procedures (2002)

Sweep and “lock” on to first line

345 346 347

Frequency, KHz

Potassium Principles -- Polarization

1

2

Spontaneousdecay

RF Depolarization

3

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Potassium Principles -- Sensor

K-lamp

Filter

Circular Polarizer

Photo measurement

Potassium bulb

Solutions and Examples. Fixed Wing – Solutions

• Sensor (Single or Multiple)

• Electronics

• Pod and / or Stinger

• Data Acquisition Console (GEM or 3rd Party)

• Pilot Guidance (Optional 3rd Party)

• RS-232 Data Transfer (Optional)

• GPS

• Altimeter (Optional)

Fixed Wing -- Installation

Helicopter – Solutions

• Sensor (Single or Multiple)

• Electronics

• Towed Bird (Single or Multiple Sensors)

• Tow Cable

• Data Acquisition Console (GEM or 3rd Party)

• RS-232 Data Transfer (Optional)

• GPS

Helicopter – Magnetics Data

Silver exploration, Mexico

Gradiometers - Rationale

• Focusing on increased spatial resolution and detail; small anomalies on the flanks of large features can be clearly resolved

• Vertical gradient information used in vertical gradient maps, analytic signal maps and Euler products

• Longitudinal and horizontal gradient used to improve the accuracy and resolution of magnetic maps

• Detection of even the smallest source can be achieved with a line spacing of up to 2 times height above magnetic source (Scott Hogg, et al, 2004)

Tri-Directional Gradiometer – Bird

Fins are spaced at 120 degrees to allow for simplecalculation of gradients in all three directions:

• Average magnetic field of the two lower fins falls beneath the upper fin sensor to allow for vertical gradient calculation

• Average of all three sensors falls in the centre of the bird shell to allow for simple determination of along-track gradient

• Two lower fins used to calculate across-track gradient

Tri-Directional Gradiometer -- Bird

Tri-Directional Gradiometer Data

Improved Resolution of Small Targets

Raw Profiles – Vertical Gradient Data

Helicopter EM – Solutions

• Sensor (Magnetometer or Gradiometer)

• Support for 5V EM Trigger input (On in 50 ms, Off 20 ms)

• Data Acquisition (GEM Console or DAS)

• Continues operation close to Transmitter Coil (minimum distance 1.5m optimum 3m)

• RS-232 Data Transfer (Optional)

• GPS (20 Hz)

UAVs – Part of The Future

Unmanned Airborne Vehicles (UAV) offering new platforms for magnetic readings

Offer advantages of high resolution data, low level surveys over remote and offshore targets, reduced operator risk

UAV – Components

• Sensor (Single or Multiple)

• Electronics

• Data Acquisition Console (GEM or 3rd Party)

• RS-232 Data Transfer (Optional)

• GPS (20 Hz)

Base Stations – Capabilities

Overhauser or Potassium base stations available for effective elimination of diurnals:

• Precise time synchronization of airborne and base station units using a built-in GPS option

• Multiple modes of operation:

• Flexible (up to 30 periods)

• Daily (specify daily hours)

• Immediate (start instantly)

Potassium – Specifications

• Sensitivity: 4 pT / Hz @ 20 samples per second

• Resolution: 0.0001 nT

• Absolute Accuracy: +/- 0.1 nT

• Dynamic Range: 10,000 to 120,000 nT

• Gradient Tolerance: 30,000 nT /m

• Sensor Angle: Optimum angle 30 between sensor head axis and field vector

• Heading Error: <0.05 nT between 10 to 80 and 360 full rotation about axis

SUMMARY

• Airborne magnetics – Industry always seeking new technologies with additional benefits

• Potassium offers substantial improvements in sensitivity and in other parameters

• Results demonstrate the effectiveness of the system for high resolution magnetic and gradiometric mapping

Thank you for your attention ...