BCGS Technical Talk – June 2021

Speaker: Mehrdad Darijani, PhD. CEO & Founder, Geotexera Inc.

Title: Independent, joint and constrained inversions using unstructured meshes

Date: Thursday, June 10, 2021

Time: 4:30pm – 5:30pm PDT

Location: Webinar video conference via Zoom.

Bio:

Mehrdad Darijani is CEO and founder of Geotexera Inc., a company that provides geophysical modelling and inversion services and products (software). Mehrdad holds a PhD in geophysics from Memorial University of Newfoundland, completed under the supervision of Dr. Colin Farquharson. He has over 10 years of experience with the modelling and inversion of geophysical data.

Abstract:

Independent, joint and constrained inversions using unstructured meshes

At Geotexera, we collaborate with academia not only to use the most advanced tools and methods for improving the quality of results, but also to always keep them up to date. We have the support and aid of Dr. Colin Farquharson (professor in the Department of Earth Sciences at Memorial University of Newfoundland) and Dr. Peter Lelièvre (assistant professor in the Mathematics and Computer Science Department at Mount Allison University) as our advisors. We use the software MAGNUM, which they developed in cooperation with their research groups.

The software MAGNUM has been used in many projects so far. It has been developed to be the most fully functional forward modelling and inversion software that provides many tools and methods for the inversion of different types of geophysical data using only a single platform. It is capable of doing independent, joint (using linear, correlation, fuzzy c-mean, cross-gradient, and Gaussian methods), constrained (using bounds and reference models), clustering, and MVI (for remanent-affected magnetic data using Cartesian and spherical formulations) inversions or any combination of them such as constrained joint, constrained clustering and so on. It also works with mesh-based, surface geometry, and lithological approaches. At this point, the software inverts magnetic (TMI, amplitude, and vector-components), gravity, gravity gradiometry, seismic refraction (first arrival travel-times), and muography data. In the near future, IP/DC and EM methods will be added to the software.

Geotexera is the first company that uses unstructured (triangular and tetrahedral) meshes in all its geophysical modelling and inversion services and products. The unstructured meshes enable us to easily and accurately add high-resolution topography, borehole information, geological contacts, and surfaces (e.g., those generated by Leapfrog) to our models to obtain reliable results. They can be extremely helpful when we are working with constrained inversions.

Webinar:

A recording of this webinar is available on our Youtube channel.

BCGS Technical Talk – February , 2021

Please note that this talk will be held at 12:00 PM PST.

Speaker: Andrea Certo and Greta Tresoldi, LSI LASTEM S.r.i., Milan Italy

Title: A Remote Resistivity Sensing System to Monitor Tailings Dams Structural Integrity

Date/Time: Thursday February 25, 2021 @ 12:00pm – 1:00pm PST

Location: Online webinar. The webinar link will be sent out via our mailing list in advance of the talk.

Bio:

Andrea Certo, Instrumentation Engineer.  Andrea will describe the development and implementation of the GRETA resistivity monitoring System

Andrea is CEO and owner of LSI-LASTEM S.r.i. which provides environmental monitoring systems for hydrological, meteorological, industrial and geophysical applications.

Dr. Greta Tresoldi, Environmental Engineer / Geophysicist. Greta will describe the geophysical implementation of resistivity monitoring and software integration for noise reduction, elimination of spurious effects, automatic inversion, translation of results to percent water saturation, integration with piezometer and other dam monitoring systems and integration with minesite monitoring networks.

Greta is a Ph.D. Environmental Engineer and Geophysicist. After three years as a university Researcher at Politecnico di Milano in the field of applied geophysics for hydrogeological risk reduction, she is now Product Manager at LSI Lastem. An earlier contributor to the G.Re.T.A. system, as she has been working on the project from its very beginning.

Abstract:

G.Re.T.A.” A Remote Resistivity Sensing System to Monitor Tailings Dams Structural Integrity

By Andrea Certo and Greta Tresoldi, LSI LASTEM S.r.i., Milan Italy

The increasing number of tailings dams’ failures in the recent decades highly demand to set up reliable systems to monitor the stability of these structures. Appropriate design, efficient operation and continuous monitoring are key solutions to guarantee the stability of earthen embankments including tailings dams.

Electrical resistivity tomography (ERT) is widely used in the mining industry for mineral exploration, groundwater studies, characterizing mine wastes and monitoring acid mine drainage. We present the capability of an Italian geo-electrical monitoring system (developed by LSI Lastem with the scientific support of Politecnico di Milano) for permanent monitoring of tailings dams.

G.Re.T.A. (Geo Resistivimeter for Time-lapse Analysis) is an autonomous ERT system including a remotely controlled resistivity-meter with two cables connected to 48 stainless steel electrodes. The protected cables can be buried in shallow trenches along the embankments. The system can be powered by solar panels or power grid. Datasets of resistivity sections and acquisition parameters are available on a cloud platform. Site-specific algorithms for time-lapse data analysis and visualization of resistivity differences for any desired measurement period are available online to monitor the subsoil in real-time. An automatic control algorithm can detect if changes have approached pre-set thresholds while sending alarms about anomalous changes to the customer.

The advancement of G.Re.T.A. is that it can be implemented as a long-term monitoring system to underline the internal heterogeneities or the tailings dams based on changes in resistivity values. The efficiency of the system has been proved in pilot sites for monitoring the internal conditions of river levees and through laboratory tests for shallow landslides. One G.Re.T.A. system was also installed in 2020 in a tailings dam in Chile to monitor underseepage. The system is capable of being used to monitor the inner properties of mine wastes, heap leaching facilities and tailings dams.

Webinar:

A recording of this webinar is available on our Youtube channel.

BCGS Technical Talk – January 20, 2021

Speaker: Doug Schouten, PhD. Ideon Technologies Inc.

Title: Advances in cosmic-ray muon tomography: a new approach to subsurface exploration

Date/Time: Wednesday, January 20, 2021 @ 4:30pm – 5:30pm PST

Location: Online Webinar

Bio:

Doug Schouten, PhD, Ideon Technologies

Doug Schouten is CTO and Co-founder of Ideon Technologies. He is a global leader in muon tomography and one of the few people in the world with the expertise to turn muon research into industrial problems solved.  Doug holds a BSc. (Hons) in physics and computer science from UBC, and a PhD in subatomic physics from SFU. Doug also has extensive expertise in computer simulation, data analysis and statistical inference – including machine learning methods and detector physics.

Abstract:

Advances in cosmic-ray muon tomography: a new approach to subsurface exploration

Canada’s Ideon Technologies Inc. is a world pioneer in the application of cosmic-ray muon tomography and has developed a discovery platform that provides x-ray-like visibility up to 1 km beneath the Earth’s surface.

Muons are naturally occurring sub-atomic particles that are produced by cosmic rays striking our atmosphere. They lose energy progressively as they pass through the Earth’s surface. As they encounter higher-density material, muons lose energy at an accelerated rate, which reduces their intensity. The intensity, and the density of the materials encountered, can be measured. Muon tomography maps the intensity of cosmic-ray muons underground, measuring the physical properties in a targeted search area. The images are then combined to produce a 3D model of any anomalies present.

A spin-off of TRIUMF (Canada’s national particle accelerator laboratory), Ideon Technologies grew from an idea that a curious Canadian geophysicist brought forward from industry. After securing seed funding in 2020, Ideon is now developing the world’s first compact muon detection instrument designed to be deployed down industry-standard boreholes – field trials are underway this spring. Proprietary algorithms and advanced inversion technologies now also allow for the combination of muon data with other data sources to enhance the characterization of subsurface geology.

Webinar:

A recording of the webinar is available on our Youtube channel.

Our 2020 annual general meeting (AGM) will be held:

at 4:30pm on Thursday, December 17, 2020
(via Zoom Webinar)

The main order of business will be to elect the Directors of the BCGS and review the past year’s activity.  Our bylaws allow for between 4 and 7 Directors. Five of the current directors are standing for re-election. Thomas Campagne will be stepping down as Secretary. The Executive would like to thank Thomas for his contributions to the society over the past 7 years.

We are inviting interested persons to nominate themselves for election to join the Board of the BCGS. The position of Membership Coordinator is currently open.  Please indicate your intent to do so by 23h59 on Sunday, December 13, 2020.  All names of prospective candidates will then be included on the AGM notice to be emailed out the following business day.

The BCGS directors standing for re-election are:

The following new individuals are standing for election:

Voting will occur virtually. Instructions will be provided in advance of the AGM.

We would like to remind you there are two classes of voting members in the BCGS:

1. General members. An annual fee of $20. Will be returned as a discount should they choose to enroll in our annual symposium; and
2. Student members. Free membership upon demonstration of enrollment in a post-secondary program at an accredited educational institution.

In order to participate in the vote, we ask that you pay your 2021 member dues online via Paypal below. These member dues will provide membership in the BCGS until December 31, 2021. Eligible students, as defined above, are entitled to vote. Please email the executive at info@bcgsonline.org to be added to the official member list.

The AGM is open to all members and non-members.

As no BCGS symposium was offered in 2020, the normally offered $20 discount offsetting the 2020 membership dues paid, will be allocated to the BCGS Scholarship program.

We have planned a very exciting December talk, where a panel of four leading EM expects will discuss on-time and off-time EM systems. This talk is being organized and moderated by the BCGS and co-sponsored by MTNet. For additional information on MTNet, host of the EMinars series of EM webinars, please see their webpage. http://www.mtnet.info/

Speakers:

• Daryl Ball, Glencore Canada
• Andrew Duncan, Electromagnetic Imaging Technology (EMIT)
• Jim Macnae, RMIT University / CD3D Pty Ltd.
• Ben Polzer, Nova Mining Exploration Solutions

Title: Time-Domain Electromagnetics for High-Conductivity Mineral Exploration: On-Time Step Response and Low Frequency B-Field, Late Off-Time — A Discussion

Date/Time: Thursday, December 10, 2020 @ 4:30pm PST

Location: Online Webinar (Click on the below link to register!)

https://zoom.us/webinar/register/WN__f7v4XI-Qxe5PhchHW1pIg

Description: Time-Domain Electromagnetics for High-Conductivity Mineral Exploration: On-Time Step Response and Low Frequency B-Field, Late Off-Time — A Discussion

Panelists:

• Daryl Ball; Geophysicist, Raglan Mine, Glencore Canada
• Andrew Duncan; President, Electromagnetic Imaging Technology
• Jim Macnae; Professor, RMIT University, CD3D Pty Ltd
• Ben Polzer; President and Chief Scientist, Nova Mining Exploration Solutions

Organizer and Moderator: BC Geophysical Society

Co-Sponsor: MTNet

After development of the UTEM time-domain EM system at the University of Toronto by Gordon West and Yves Lamontagne in the early 70’s, there has been a debate among geophysicists who use TDEM to explore for high-conductivity ore bodies (e.g. magmatic Ni-Cu-PGE deposits), concerning the utility of off-time TDEM versus on-time readings. In principle, there will be no off-time TDEM response from a perfect conductive body (i.e. infinite conductivity), because the time-varying primary EM field cannot penetrate infinite conductivity, regardless of frequency. The EM skin depth of a conductor is inversely proportional to square-root of conductivity times frequency, and if conductivity is infinite, then skin depth must be zero. Hence, zero penetration by the primary EM field, and zero induced eddy currents penetrating into the conductor, and zero response after the primary field has been turned off.

There will be eddy currents induced on the surface of the infinite conductor, but they are entirely in-phase with the primary field and do not decay significantly within realistic time frames as they would in a moderate conductor. But the surface eddy currents do produced a secondary EM field, in-phase with the primary field. In close proximity to the conductor, the primary and secondary in-phase fields are equivalent and opposite, resulting in a near zero field. Time-domain measurement of the signal in-phase with a step waveform primary field is termed the ‘step response’. The primary and secondary fields can be separated if the primary field can be calculated theoretically, and this is the basis of the UTEM system’s approach to the problem of detecting a perfect conductor.

The early commercial application of TDEM for mineral exploration was based on the pioneering research in 1948-51 by James Wait and others at Newmont’s geophysical research facility in Jerome, Arizona (and contemporaneous research in the former Soviet Union), and by Tony Barringer with the development of his airborne INPUT TDEM system in the late 50’s. These systems all had in common the idea that the response from the ground can be measured more accurately and more sensitively in the absence of primary field. This is still a prevalent idea today. However, before about 2000, it was only practical to measure an EM field with an induction coil-based system, and the base frequency had to be high enough (i.e. above 5-10 Hz and routinely 25 or 30 Hz) to generate a high-fidelity reading above the noise level of the coil and electronics.

No conductors in nature have infinite conductivity. But some conductors (e.g. massive pyrrhotite in a nickel ore body) can be extremely conductive. So conductive at these relatively high frequencies, it was pointed out by the proponents of on-time step response TDEM, that there will be little to no measureable (i.e. above the noise level) off-time secondary response. One had to use step response to detect such extremely strong conductors. However, with the advent of small, sensitive fluxgate magnetometers and subsequently SQUID magnetometers for use in TDEM, in the late 90’s and into 2000, geophysicists were able to measure the B-field TDEM response (with ground and borehole systems at least) down to 1 Hz base frequency and lower.

Hence, the question of whether it is better to measure the on-time step response, or conversely a very low-frequency, late off-time secondary response, really comes down to a signal to noise discussion. In the first case, it is the noise inherent in calculating the free-space primary field to be subtracted from the measured primary field, versus the amplitude of the in-phase secondary field from the strong conductor, which depends on the conductivity and size of the conductor. In the second case, it is the B-field sensor noise, versus the amplitude of the off-time secondary field, which is dependent on the amplitude of the induced eddy currents, which is dependent on the conductivity of the conductor and the primary field generated by the transmitter.

And the final complication is the fact that almost all massive sulphide ore bodies have varying conductivity throughout the body. Hence, there is likely to be zones of lower conductivity, even with a massive pyrrhotite ore body, that will give rise to strong off-time secondary response, at a low enough frequency.

All of these factors will be discussed by leading TDEM geophysicists at this webinar. Each will have an opportunity to make a short (10 minute) presentation, followed by 20+ minutes of open discussion between presenters, with questions from the audience.

Webinar:

A recording of this webinar will be available on Youtube after the talk.