March 2014 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 2014 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 2014 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.

KEGS/BCGS Roundup Breakfast

KEGS/BCGS Roundup Breakfast – Tuesday, January 27, 2015

SPEAKER: Greg Hodges, CGG

TITLE: Mad Scientists and Other Salesmen

DATE/TIME: Tuesday, January 27th, 2015 @ 7:30am

LOCATION: Fairmont Waterfront Hotel, Princess Louisa Room, Vancouver

REGISTRATION: Online at (Registration opening soon)


Pseudo-geophysical exploration tools have been available from over-zealous salesmen, misguided scientists, and blatant scam artists for longer than real geophysics has been available. From the middle ages (described by Agricola) to the early days of oil exploration (Blau in Geophysics, vol 1, pg 1) to today: when a current database of dubious geophysics includes almost 70 systems, of which more than 40 are still active. While they might seem like amusing distractions that no sensible geophysicist would use, in fact a conservative estimate suggests ten million dollars a year may be wasted on non-effective geophysics. That is money that will not be spent on geophysics that works, will not find a mine, but will definitely tarnish the reputation of geophysics and geophysicists everywhere.

Governments and large exploration companies attract the majority of bad geophysics, nearly always targeted at senior management with an impressive sales pitch. It is up to geophysicists to understand the nature of these voodoo geophysical methods, and educate their managers and clientele to at least recognize the warning signs and get some unbiased expertise in the evaluation.

For non-geophysicists, common sense and instinct are often all that is needed to raise a red flag that something needs to be checked: for example if a system offers incredible accuracy with uncommon simplicity. Everyone knows: “there’s no free lunch”. Uncommon resolution requires extensive effort. If a unique system is offered with no known history of development or theoretical background, it should be checked carefully before any investment is made. (Voodoo systems are often sold as an investment rather than a service.) And of course, shrouding the “geophysics” in secrecy is a loud warning that cannot be allowed.

Geophysicists need to have the confidence in their own basic science to recognize that if a technical description seems incomprehensible, it is probably not because of the advanced science, but rather because of the lack of real science – replaced by techno-babble and obfuscation. Geophysicists often need to set aside professional courtesy and trust, and challenge the science offered and the claims made.

As scientists in a young field still advancing rapidly, we geophysicists need to keep an open mind to new ideas, but be prepared to evaluate them with a healthy dose of skepticism using good science and common sense.

December 2014 Technical Talk

BCGS December Technical Talk – Wednesday December 10, 2014

SPEAKER: Ken Witherly, Condor Consulting

TITLE: Application of Airborne Magnetics, EM and Gravity to the Ring of Fire Intrusive Complex, Ontario

DATE/TIME: Wednesday December 10th, 2014 at 4:30pm. LOCATION: Room 451, 409 Granville St (UK Building at Granville and Hastings), Vancouver


The Ring of Fire is an intrusive complex composed of mafic and ultramafic rocks hosted in the Archean age McFaulds greenstone belt located in James Bay lowlands of northern Ontario. Due to low topographic relief and an extensive cover of Paleozoic platform carbonate rocks, the area remained largely under explored until kimberlites were found in 1988. This lead to the development of the Victor diamond mine in 2006. Subsequent exploration for kimberlites resulted in the serendipitous discovery of the McFaulds VMS deposits in 2002 (ref Mugall 2010). With this discovery came the recognition that there was a greenstone belt present in the area and it could host economic deposits. A semi-regional Geotem survey was flown in 2003. Exploration in the area was complicated as a number of junior companies had positions in the area and while they would share the costs of expensive surveys, they were competing for what was deemed the best land positions. Ground surveys were conducted based on the Geotem results, with the targeting model being either kimberlite or VMS. This work eventuated in the discovery of a major deposit of chromite and a number of significant nickel sulfide deposits in 2007-2008. During this time, numerous airborne and ground surveys were carried out including a regional Falcon AGG and mag survey in early 2011. While various technical and commercial presentations have been made on the Ring of Fire geophysical work, due to the complicated claim ownership most of these have tended to focus on the results controlled by one group. This review is intended to look at the overall area which hosts at three significant deposit styles; VMS, magmatic nickel and chromite.