April 2015 Technical Talk

BCGS April Technical Talk – Wednesday April 15, 2015

SPEAKER: Doug McConnell, P.Eng, P.Geoph, DMT Geosciences Ltd.

TITLE: Geophysicists are from Earth, Engineers are from Mars and other controversial theories: Risks related to misconceptions and limitations of engineering and environmental geophysics

DATE/TIME: Wednesday April 15, 2015 @ 4:30pm

LOCATION: Room 451, 409 Granville St (UK Building at Granville and Hastings), Vancouver


DMT has been specializing in geotechnical engineering, environmental and hydrogeological geophysics for 25 years. Geophysics is best presented to the engineer as a risk management tool to identify targets for drilling or other follow up investigation and not a silver bullet solution. Except in a few cases where geophysical results can be used directly in engineering formulas, there is often the need to make assumptions and provide guidance to deal with equivalence in geophysical results.

Working for engineers presents a unique set of communication, economic and technical challenges to the Geophysicist. One of the most significant is integration of geophysical results into geotechnical and other engineering projects. Of course we are not alone in this, the Geotechnical Engineer has similar problems communicating with the Civil Engineer, but that’s another story.

This presentation includes case histories to illustrate some of the challenges, pitfalls, and misconceptions of that work and how they can be overcome. The case histories present examples of multi-method geophysics studies integrating other geoscience data to minimize risk in directional drilling for pipelines, water inundation in surface mines, RQD determination and hazards from karst in construction projects.

March 2015 Technical Talk

BCGS March Technical Talk – Wednesday March 18, 2015

SPEAKER: Peter Fullagar, Fullagar Geophysics

TITLE: Fast 3D inversion of TEM resistive limit data

DATE/TIME: Wednesday March 18, 2015 @ 4:30pm

LOCATION: Room 451, 409 Granville St (UK Building at Granville and Hastings), Vancouver


Rapid interpretation transient electromagnetic (TEM) data sets is highly desirable for timely decision-making in exploration. However, full solution 3D inversion of TEM data sets is often still not feasible on current day PCs. Therefore, a fast 3D TEM inversion scheme has been developed for time-integrated (resistive limit) data. The resistive limits are amenable to linear 3D magnetic inversion, which is up to 100 times faster than “rigorous” 3D TEM inversion. The evolution of the decay lost during time integration can be recovered in large part by constructing a starting model based on conductivity-depth images (CDIs) or 1D inversion, by applying depth weights, and by imposing geological constraints if available.

Incorporation of geological constraints reduces the non-uniqueness of any 3D TEM inversion. Integrated interpretation is facilitated here by performing inversion on a geological model, i.e. one attributed with lithology as well as conductivity. Geological models also offer a number of practical advantages over pure property models during inversion. In particular, they permit adjustment of geological boundaries. In addition, optimal conductivities can be determined for homogeneous units.

The resistive limit inversion scheme has been successfully tested on both synthetic and real airborne, ground, and downhole TEM. It is illustrated here via application to a Spectrem data set from Brazil, a SQUID data set from Manitoba, and a downhole data set from a North American nickel prospect.

February 2015 Technical Talk

BCGS February Technical Talk – Wednesday February 25, 2015

SPEAKER: Sergio Espinosa,

TITLE: Anisotropy Effects in the Geophysical Exploration of Ore Deposits

DATE/TIME: Wednesday February 25, 2015 @ 4:30pm

LOCATION: Room 451, 409 Granville St (UK Building at Granville and Hastings), Vancouver

Please see the following link to Sergio’s blog.


January 2015 Technical Talk

BCGS January Technical Talk – Wednesday January 21, 2015

SPEAKER: Joel Jansen, Teck

TITLE: Results of a muon geotomography survey from the Pend Oreille Zn-Pb mine

DATE/TIME: Wednesday January 21, 2015 @ 4:30pm

LOCATION: Room 451, 409 Granville St (UK Building at Granville and Hastings), Vancouver


Muon geotomography is a new imaging technology that creates 3D images of subsurface density distributions. Similar in concept to computed tomography scanning, muon geotomography uses naturally occurring cosmic radiation that gets attenuated when traversing matter. Cosmic ray muon data were acquired in the Pend Oreille Zn-Pb mine in Metaline Falls, Washington State, USA without prior knowledge of the presence or absence of ore bodies.  The resulting 3D density distribution of the overburden indicated a substantial volume of rock with higher density than the host stratigraphy above the survey site. Subsequently, a model of existing ore shells based on drill core data was provided and a simulation of the expected muon tomography data was found to be consistent with the muon geotomography measurements. This is the first blind test demonstration of muon geotomography applied to mineral exploration.