Alexander Prikhodko

Airborne Inductive Induced Polarization Chargeability Mapping of VTEM Data

Airborne inductive induced polarization (AIIP) effect has been widely recognized in airborne time domain EM system data. AIIP chargeability mapping opens new and exciting areas in mineral exploration for airborne time domain EM systems in the search for sulphides and clay minerals. An AIIP chargeability mapping tool based on CSIRO/AMIRA Airbeo is created for VTEM data, with examples from Mt Milligan, British Columbia, Canada and Tullah, Tasmania. Using the Cole-Cole frequency dependent resistivity, the tool examines the VTEM decay data spectrally and selects the decay associated with the lowest RMS error from a set of decays generated by varying chargeability m and time constant T within specific ranges, giving a constant frequency factor c, while the background resistivity is inverted. The parameter mo used to generate the decay is the AIIP apparent chargeability.

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

Magnetic and electromagnetic (EM) results from two helicopter EM surveys, a time-domain (VTEM) and AFMAG (ZTEM), are compared over the Nuqrah sedimentary exhalative (SEDEX) massive sulphide deposits in the Western Arabian Shield of the Kingdom of Saudi Arabia. The magnetic and EM data from both surveys map the major controlling structures that host the Nuqrah North and South deposits. Neither Nuqrah deposits stand out as distinctive aeromagnetic anomalies, but both EM surveys define the massive sulphide mineralised vent and bedded portions of the SEDEX orebodies. ZTEM is interpreted to be more capable in defining the larger, lower conductance and less mineralised distal portions of the SEDEX system. The modelled ZTEM also defines a down-dip extension of the Nuqrah South zone below a depth of 750 m. 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.

ZTEM and VTEM airborne EM and magnetic results over the Lalor copper‐gold volcanogenic massive sulfide deposit region, near Snow Lake, Manitoba

AbstractThe 14.4-Mt Lalor copper-zinc-gold deposit situated in the Flin Flon Greenstone Belt of north-central Manitoba is large (>900×700  m) but deeply buried (>550−1200  m) and was discovered using deep penetrating ground fixed-loop time-domain electromagnetic (EM). Results from three different airborne EM surveys over a five-year span permit comparisons of the system responses over the Lalor volcanogenic massive sulfide deposit region, assisted using 1D-2D-3D inversions. In late March, 2007, soon after its drilling discovery, Hudson Bay Exploration contracted Geotech to fly helicopter versatile time-domain electromagnetic (VTEM) surveys over the region west of Snow Lake, Manitoba. The deposit was not detected due to its large depth of burial (>550  m) and the lack of magnetic response. In 2009, Geotech carried out a helicopter z‐axis tipper electromagnetic (ZTEM) passive EM test survey over the Lalor deposit, which was successful and led to a larger survey over the area. In 2012, a second VTEM survey t...

An Improved Early-Channel Vtem Helicopter System for Near-Surface Applications

The helicopter-borne Versatile Time Domain Electromagnetic System (VTEM) is a geophysical instrument which has been in continuous development, utilizing the most recent advances in digital electronics and signal processing for deeper penetration; higher spatial resolution; better resistivity discrimination; and increased detection of a broad variety of conductive targets. Since its inception in 2002, more than 1 300 000 line kilometers have been flown around the world, in a wide variety of geological environments, primarily involving mineral exploration, but also including near-surface groundwater applications. However, although the VTEM system has progressively achieved marked improvements in its deep penetration characteristics, at the same time its near-surface imaging capability has been limited by its early time data. This is significant because early time or high frequency airborne electromagnetic data (AEM) are desirable for shallow sounding or mapping of resistive areas. Yet many time-domain AEM system have problems obtaining quantitative early-time data due to a variety of issues, namely system bandwidth. Recently, workers and researchers in shallow electromagnetic sounding have confirmed the calibration accuracy of VTEM mid to late delay time data (>100μsec to 10msec) while at the same time highlighting the quantitative incompatibility issues with its early channel data and near-surface conductivity layering. Processing strategies, such as deconvolution, aimed at correcting system imperfections, such as bandwidth, have been proposed with promising results but are still not routinely implemented. in an effort to address this issue, Geotech has embarked on a system design strategy aimed at improving the early-channel VTEM data and achieving fully calibrated, quantitative measurements closer to the transmitter current turn-off. This development has led to new model of VTEM system designed specifically for near-surface, high resolution applications, while maintaining reasonably optimal deep penetration characteristics. Results have shown a significant improvement in quantitative VTEM data at earlier times than previously achieved, approaching 5μseconds after the current turn-off.

Mapping Buried Aquifers with HTEM in the Fort McMurray, Alberta RegionEadie et al.: Mapping Buried Aquifers with HTEM

ABSTRACT Heliborne time-domain electromagnetic systems (HTEM) have proven to be effective tools in mapping sub-surface resistivity. As these systems are able to measure increasingly earlier time channels after the waveforms turn-off, they improve their ability to resolve resistivity contrasts in near-surface geology. This is demonstrated with the VTEM system over the Aspen property, near Fort McMurray, Alberta. This area provides a useful setting in mapping near-surface resistivity variations, specifically the location and geometry of the Pemmican Valley aquifer. This begins with the a Tau constant analysis of the earliest time channels of the VTEM decay curve that laterally mapped the Pemmican Valley aquifer and the existence of a shallower, previously unmapped, east-west trending aquifer. This is confirmed through 1D inversions of the dataset. The 1D inversion models accurately resolve the main near-surface geo-electrical units within the Aspen property when compared to resistivity well logs and a grou...

Supervised Neural Network Targeting and Classification Analysis of Airborne EM, Magnetic and Gamma-ray Spectrometry Data for Mineral Exploration

The amount of multi-disciplinary (geology, geophysics, remote sensing, etc.) and multi-parameter geophysical (potential field, EM, gamma-ray spectrometry, etc.) data available for mineral exploration is ever increasing. The integration and analysis of the data require effective and efficient search engines or data mining tools. The search engines will take the signatures of known mineral deposits or interpreted mineralization targets (“key words”), search the data space and return potential new targets (“matches”), thus providing locations to the decision makers for follow-up. Two supervised feedforward multilayer neural network (NN) search algorithms will be presented and analysed. The utility of the NN search tools will be demonstrated with the integration and analysis of airborne electromagnetic (EM), magnetic and radiometric data for mineralization targets in Iullemmeden Basin, Niger.

VTEM airborne EM, aeromagnetic and gamma-ray spectrometric data over the Cerro Quema high sulphidation epithermal gold deposits, Panama*

In March 2012, a helicopter-borne versatile time-domain electromagnetic (VTEM), magnetic and radiometric survey was flown over the Cerro Quema high sulphidation (HS) epithermal gold deposits and the surrounding area. The Cerro Quema deposits are located in the Azuero Peninsula, Panama, approximately 8 km east of Güerita. The gold mineralisation is associated with clay-pyrite alterations topped by an acid-leached resistive cap, and the principal ores are pyrite-rich sulphides located within mineralised vuggy silica rocks. The geophysical data over the Cerro Quema deposits have been analysed. The electromagnetic (EM) responses over the deposits are characterised by resistivity highs and chargeability lows, surrounded by resistivity lows and chargeability highs. Radiometric Th/K ratio highs and magnetic susceptibility lows are observed over the deposits. These geophysical signatures over the Cerro Quema deposits are characteristic responses from HS epithermal gold deposits. The success of the VTEM survey points to the applicability of the regional helicopter electromagnetic, magnetic and gamma-ray spectrometry (EM-Mag-Spec) surveys for the exploration of similar HS epithermal gold deposits to depths < 500 m in weathered terrains. In March 2012, a helicopter-borne VTEM survey was flown over the Cerro Quema high sulphidation (HS) epithermal gold deposits. The geophysical data obtained were analysed for geophysical signatures characteristic of HS epithermal gold deposits. The success of this survey points to the applicability of EM-Mag-Spec surveys for the exploration of similar deposits.

THE IMPORTANCE OF A SINGLE TRANSMITTED WAVEFORM IN THE CHARACTERIZATION OF DISCRETE CONDUCTORS

Recently the idea of using dual transmitted waveform systems for airborne EM time-domain surveys has gained popularity with the opinion that such systems could provide the best of both worlds – strong dipole moment for deep penetration and early time gates for better definition of near surface features. Although at first glance the idea of dual waveform might seem to be attractive, more detailed analysis shows that the dual waveform has serious disadvantages, especially for mining applications where conductors are discrete and highly conductive in many cases. The single waveform system delivers better definition for the discrete conductors, the situation typical for mining applications.

Recent AEM Case Study Examples of a Full Waveform Time-Domain System for Near-Surface and Groundwater Applications

Early time or high frequency airborne electromagnetic data (AEM) are desirable for shallow sounding or mapping of resistive areas but this poses difficulties due to a variety of issues, such as system bandwidth, system calibration and parasitic loop capacitance. In an effort to address this issue, a continued system design strategy, aimed at improving its early-channel VTEM data, has achieved fully calibrated, quantitative measurements closer to the transmitter current turn-off, while maintaining reasonably optimal deep penetration characteristics. The new design implementation, known as “Full Waveform” VTEM was previously described by Legault et al. (2012). This paper presents some case-study examples of a Full Waveform helicopter time-domain EM system for near-surface applications