Lindsey Heagy
Nov 3, 2018 · 10 min read

Nov 16–17

Following DISC Lab day in Buenos Aires, we hopped on a plane and landed in Santiago, Chile late on Tuesday night. By the time we arrived at our airbnb in the heart of Santiago, it was Wednesday. It was a bit eerie arriving so late in an unfamiliar city, seeing stray dogs running around, and not being entirely sure where our accommodation was. However, when we woke up the next morning, we looked out the window, saw the view captured in the above image, and were please to be situated in a bustling part of the city.

coffee with Daniel

On Wednesday afternoon, we met up with Daniel Diaz, our local host to see the venue at the University of Chile and chat about the local applications of interest. Mining is perhaps the most prevalent industry application; one of the case histories we planned to present, Santa Cecilia, incorporates 4 types of electrical and electromagnetic data sets (DC, IP, CSAMT and MT) to characterize a porphyry deposit in Chile. This case history was first presented in Toronto, and we were excited to include it for to the home-crowd.

On the academic side, there is much work being done to understand volcanism in Chile. One of the projects Daniel is involved in is an MT survey over Laguna del Maule, a region of volcanic activity in Chile that is uplifting at a rate of ~25 cm/year!

We wrapped up our chat getting a few tips from Daniel on what to do for our couple free days after the course.

Day 1: DISC Course

Participants at the DISC in Santiago (left & right), Doug using the DC resistivity app to show where the charges are in a DC survey for a tunnel (centre)

The course started at 9am, and nearly 40 participants attended, among them included some well-informed professionals in the mining industry. Having well-informed participants engage in the course elevates it for everyone (including us!); discussions promote looking at a concept from multiple angles, and new applications or challenges are brought to light when people are willing to share their experiences. In Adelaide, we encountered this as participants who were involved with data collection and interpretation at Mt Isa (the case history we use to book-end the course) shared some of the current unanswered questions about the site. Here in Santiago, Héctor Verdejo shared aspects of the state of the art for processing DC resistivity and IP data (more coming in the DISC Lab section of the blog). We are grateful to Daniel for his efforts to promote attendance and to Mike Webb and Terry Ritchie for bringing participants from BHP and GRS. Having leaders within a company support initiatives like the DISC makes a significant impact.

participant of DISC 2017 in Chile

We have ~21 case histories (and some tutorial material on advanced topics such as EM decoupling) prepared for the presentation. Depending on audience interest in each of the applications or methods, we choose a subset of these at each location. For Santiago, we presented a significant number of these. We reached the end of Natural Sources as we wrapped up day 1, and planned to cover the remaining material on day 2.

Day 2: DISC Lab

Day 2: DISC Lab

We picked up on day 2 with Ground Penetrating Radar, Induced Polarization and finished the “course” portion of the DISC with a summary and discussion of the future. From there, we turned the floor over to the participants to discuss the applications they are currently working on.

Héctor Verdejo

Héctor Verdejo (slides) — There is often a big difference between simulated, theoretical data and measurements taken in the field. Hector, who works for GRS, showed an example of DC/IP data collected in a routine survey. The data were contaminated with telluric noise which had to be removed before standard processing techniques could be applied. Magnetotelluric transfer functions were used to estimate the telluric noise which was subsequently subtracted from the data. There are often many types of noise that need to be accounted for to obtain high quality data suitable for inversion. Delineating those noise types and providing software and tutorials to show how the observations can be cleaned up is a long term goal for us. We are pleased that Hector has volunteered to show us how his processing works and we look forward to developing a tutorial about this.

In the second part of his talk, Hector showed an example of the use of their telluric cancellation at Olympic Dam where both MT and CSEM data were collected. The orebody shows up as a conductive and chargeable target. However, EM coupling can affect the chargeability data and this invites further investigation.

Eduardo Alarcón Guerra

Eduardo Alarcón (slides) — The concept of capturing surface water in containment ponds and having that recharge an underlying aquifer is something that is being worked on at many locations. Eduardo, who works for Aguaex, is involved in carrying out a time-lapse DC resistivity survey to image subsurface flow when water is injected at the surface. Some of the field challenges were that there were multiple locations at which water was injected and multiple lines of data needed to be acquired rapidly. Preliminary analysis identified locations where water permeated more rapidly.

Daniel Díaz

Daniel Díaz (slides) — Chile has considerable geothermal potential, particularly in the northern part where it shares a border with Bolivia and Argentina. Daniel, a professor a Universidad de Chile, has been carrying out Magnetotelluric (MT) surveys in that area for many years. Investigating geothermal areas and also the volcanoes themselves to get an understanding of their composition and dynamics are interesting and important problems and Daniel has a number of students working on projects. The remoteness of the region and the ruggedness of the topography (elevation changes of 2km over a 15 km transect, make acquisition difficult and station spacing is sparse. He presented the results from two areas. The first is an area where Chile’s first geothermal plant has just started. The inversion of the MT data was challenging because of the effects of topography and the size of the model. Nevertheless, first results were obtained along with a geologic interpretation.

The second area is the El Tatio geyser field in northern Chile. Of special interest was a large dacite dome which was only about 20,000 years old. MT data have been collected and preliminary inversions have been obtained. The MT data will be complemented by the acquisition of Time domain EM data.

David Maldonado

David Maldonado (slides) — Magnetic data are modelled with Maxwell’s equations at zero frequency and so a talk about inverting total field data to find a 3D model of magnetization fits within our EM framework. David presented a synopsis of his approach to solve this problem.

We concluded day 2 by showing the resources available within, the numerical tools in SimPEG, and tutorials, including a tutorial on Magnetotellurics, for getting up and running with the software.

From the participants

coffee breaks (with delicious fruit skewers!)

“It was a great short course, with very good slides and supporting material [that took] into consideration several methods and applications. This is an exercise that has to repeat many times, especially in South America. I would like in the future if the SEG could do this same source format with inversion [of] geophysical data, use of the full waveform, and numerical modelling.” — Eduardo Alarcon, Geological Engineer

“The content of [the] course was very clear and illustrative. I like the simulations using SimPEG. I believe this [is] a good tool [for] modelling and better understanding some aspects of EM surveys” — Halis Benítez

“This course exceeded my expectations, and mine were very, very high! It meant a lot to me to get inspiration in the work we do everyday. You saved me! Thank you for all your effort and hard work in putting this together. I appreciate your approachability and kindness in addressing the lectures.” — Valentina Olmos Salvo, Geophysicist

“Long live the fundamentals! The course completely fulfilled my expectations. It was a great time to view concepts and understand those in a different or better way.” — Hector Verdeso, Geophysicist at GRS

“Really awesome. I could understand things I never could before. I loved how you showed [concepts] by images and videos [of] how the currents and magnetic fields are.” — Daniela Montecinos

“Very good, organized, well paced, appropriate level of detail. Great guidance towards other resources. Great interaction with the audience. Comfortable atmosphere.” — Brendan Purchase, Geophysicist

“Doug’s presentations were excellent, good exploration of complex ideas by breaking into simple terms and visualizations. Valuable refresher course for EM fundamentals.” — Andy Roberts, Geophysicist, Barrick

“Overall [it] was a great course, very well structured, that goes from the basics, through the concepts, moving from time domain to frequency domain, thinking logically about the physical processes occurring and taking it to the case studies where all the concepts get “proved.” — Camila Leyton Azocat

Participants in Chile

A few adventures

Sampling street food in Santiago.

Sampling street food has got to be one of the best way to get to know a city; Santiago did not disappoint! On our first evening in Santiago — the day before the DISC — we walked the streets near out accommodation and sampled burritos and an empanada for dinner.

Parque Forestal, National Museum of fine arts, display inside the museum

Following the DISC, we had 2 free days in Santiago. On our first day, we did a self-guided walking tour. We started off wandering along Parque Forestal, a picturesque urban park, towards the National Museum of Fine Arts. We stopped in at the museum and took in a range of displays from historic statues to modern, interactive displays.

La Vega Central market

From the museum, we walked to the La Vega Central fresh food market. The many rows of stalls were stocked with fresh peppers, large squash, and local fruit, including plenty of nisperos, a bright orange fruit native to Chile that is similar in shape and colour to an apricot. Seeing all of the fresh produce helped us build up an appetite, so we grabbed a pork arepa and a chicken taco for lunch in the market. Lunch was accomanied by a papelon & limon — a refreshing lemonade-style drink.

Cerro Santa Lucia

After lunch, walked through the central market, a large fish market and then made our way to Cerro Santa Lucia, an iconic hill in the centre of Santiago. The hill is lined with gardens, fountains, beautiful paths and viewpoints of the city. Charles Darwin visited the park in 1833 and was taken by its beauty — a plaque with his signature commemorates the occasion and one of the gardens has been named after him. We spent most of the afternoon walking around the parks and met a young group of scouts who were out for the day taking photos. We stopped for dinner at a nearby restaurant where we watched some street performers before making our way back to the airbnb.

Saturday evening in Santiago

As we walked back, we heard a violin fill the air. We encountered the performer and stopped to listen (conveniently, there was popcorn being sold nearby!). With that, our day was complete.

9 different fruits for breakfast!

Each morning in Santiago, we started off with a delicious spread of fruit for breakfast. Having been to the markets the day before, we had a quite the variety! Among them were a number of local fruits including: mangosteen, chirimoya, and nispero.

hike up San Cristobal

Our plan for the day was to hike up San Cristobal. It is famous for the statue of the Virgin on top, and was a viewpoint from our airbnb. It was close enough that we could walk to the base. The walk to the base took us through the Bellavista neighbourhood — a colourful neighbourhood lined with dramatic graffiti.

mote con huesillo

We started the hike late-morning and took our time (it was a hot day!). As a break along the way, we stopped at the half-way point for a mote con huesillo, a summertime drink / snack that combines dried peaches, a sweet tea, and cooked wheat. It was a popular stop with lots of families enjoying their Sunday afternoon together.

views and photos from the top of San Cristobal

We continued along to the top and were fortunate to have a clear day to take in the vistas of Santiago.

view of Santiago from San Cristobal

Sunday was election day in Chile, so many of the restaurants were closed, but we were fortunate to find a seafood place in the Bellavista area. We had ceviche and grilled fish for dinner before heading back to our airbnb to get packed and ready for our early flight out the Bolivia the next morning.

Thank you

Daniel Diaz and Doug Oldenburg

Daniel Diaz and Diana Comte were very proactive hosts and helped draw a strong group of participants in Chile — we thank them both for their efforts as well as the Advanced Mining Technology Center (AMTC) and the Geophysics Department (FCFM) for hosting us!

DISC 2017

Geophysical Electromagnetics: Fundamentals and Applications. A course taught by Doug Oldenburg, with Seogi Kang and Lindsey Heagy as co-instructors. The course is presented in ~30 locations worldwide and we are capturing the applications of EM geophysics at each location.

Lindsey Heagy

Written by

DISC 2017

DISC 2017

Geophysical Electromagnetics: Fundamentals and Applications. A course taught by Doug Oldenburg, with Seogi Kang and Lindsey Heagy as co-instructors. The course is presented in ~30 locations worldwide and we are capturing the applications of EM geophysics at each location.

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