March 2018 – Technical Talk

BCGS Technical Talk – March 15, 2018

Speaker: Obone Sepato, Anglo American

Title: Density and magnetic susceptibility data of the Bushveld Complex, South Africa

Date/Time: Wednesday, March 15, 2018 @ 4:30pm PST

Location: 4th Floor Conference Room, Room 451, 409 Granville St. (UK Building at Granville and Hastings), Vancouver


The Bushveld Complex (BC) is the largest known layered intrusion. This suite of rock crop out in northern South Africa to form the Western, Eastern and Northern Limbs. Most research carried out focuses on the mineralized horizons in the Rustenburg Layered Suite (RLS) of the BC. This study presents a large database of wireline geophysical logs across a substantive part of the stratigraphy of the RLS of the West- and Eastern Limbs. These consist of density and magnetic susceptibility datasets sampled at 1 cm. The major lithologies of the RLS intersected in the boreholes presented are gabbro, gabbronorite, pyroxenite, norite and anorthosite whose density histograms reveal that they are predominantly normally distributed, with density averages of 2.86-3.2 g/cm3. The magnetic susceptibility for these lithologies has a large variation from 10-7 to 13.2 SI with distributions that are multi-modal and asymmetric, which is typical of large layered mafic intrusions. Cross-correlation plots between density and magnetic susceptibility for several boreholes show that the above-mentioned lithologies form clusters (circular to elliptical), which typically overlap. This has been further investigated using k-means classification, to automatically detect these to create a semi-automatic lithology logging system, which has been particularly successful in boreholes from the Eastern Limb.

The final analysis carried out was using wavelet analysis across individual locations in the BC. This has revealed multi-scale cyclicity in all of the boreholes studied, which is attributed to subtle layering created by variations in modal proportions between plagioclase and pyroxene. In addition to this, since layering is generally ubiquitous across layered intrusions, this cyclicity can be assumed to be present across the entire BC. This technique may become increasingly important should the cyclicity in physical property data correlate with reversals in fractionation (demonstrated in the Northern Limb thus far) trends since this may suggest zones of magma addition, challenging the current perspective of four major magma additions as opposed to smaller periodic influxes of magma for the creation of this intrusion.

February 2018 – Technical Talk

BCGS Technical Talk – February 28, 2018

Speaker: Mike Dentith, Centre for Exploration Targeting, The University of Western Australia

Title: The Implications of the Mineral Systems Concept for Geophysical Exploration: A Perspective

Date/Time: Wednesday, February 28, 2018 @ 5:00pm PST

Location: 4th Floor Conference Room, Room 451, 409 Granville St. (UK Building at Granville and Hastings), Vancouver

About the Author:

Prof Mike Dentith is Professor of Geophysics at The University of Western Australia and a research theme leader in the Centre for Exploration Targeting (CET).  He has 25 years experience researching, teaching and consulting in mineral exploration geophysics.  He is editor of two case study ‘geophysical signatures’ publications on Australian mineral deposits and co-author of the textbook ‘Mineral Exploration Geophysics for Geoscientists’ published by Cambridge University Press.


The Implications of the Mineral Systems Concept for Geophysical Exploration: A Perspective

Mike Dentith, Centre for Exploration Targeting, The University of Western Australia

A mineral system is defined as “… all geological factors that control the generation and preservation of mineral deposits”. Most authors describe a mineral system as comprising a source of metals and/or ligands, a pathway along which fluids transport the metals to a location where they are concentrated (physical trap) and precipitated (chemical trap).

The mineral system concept has two main implications for geophysical exploration practices: the definition of additional types of targets at the district and larger scale (metal source region, fluid flow path, fluid reservoir), and the need to provide information over the full extent of the mineral system, i.e. larger areas and in particular to greater depths than is currently normal exploration practice.  At the same time the mineral system concept draws attention to the need for a better understanding of the petrophysical consequences of fluid-related alteration.

Where metal-bearing fluids are sourced in the lower crust or mantle it is possible that the processes that create the fluids, or the preferential removal of certain components of the rocks, cause changes to the physical properties of the rocks.    For example, depleted mantle may be different from primitive mantle, as may be mantle that has been re-fertilised via metasomatism.  Targeting the fluid flow path(s) is also a possibility, but may critically depend on the nature of the fluid flow.  If fluid flow is concentrated along a relatively small number of major faults then these comprise very difficult targets given they are expected to be relatively narrow and at significant depths.  Since they are expected to be shallower, the fluid flow pathways post-deposition of metals are a potential target.  If fluid flow is distributed (which may equate to focussed flow at a scale that cannot be resolved) in the lower crust then the associated alteration is another possible target.  However, the most attractive target which emerges from the mineral systems concept, as described by McCuaig and Hronsky (2014), is the postulated reservoir that contains high pressure metal-bearing fluid which is subsequently rapidly emptied causing concentrated fluid flow and metal deposition.  With dimensions measured in kilometres at depths of a few kilometres these are much more attractive targets than fluid flow paths.  Such reservoirs are potential targets at a camp/district scale that are needed to fill the ‘gap’ between prospect-scale targets (mineralisation, alteration) and regional/terrane-scale targets (major linears, suture zones).

Successful identification of the kinds of targets described above requires the petrophysical properties of alteration to be understood.  As noted by Witherly (2014) there is little known about this.  An exception is serpentinisation.  The available data, nearly all collected as part of academic studies of ophiolites and ocean crust, demonstrates how important a process this is.  The difference in density and magnetic properties between fresh mafic/ultramafic rocks and fully serpentinised equivalents encompasses the entire range of the common rock types.  Serpentinisation also affects electrical properties, albeit probably to a lesser degree, and potentially also electrical polarisation (due to the creation of magnetite) and dielectric properties due to the involvement of water in serpentinisation reactions.  The petrophysical consequences of other forms of common deposit-related alteration are virtually unstudied in a systematic fashion, although it is intuitively obvious that processes such as silicification will significantly affect electrical properties and talc-carbonate alteration will significantly affect density.

The large size and depth extent of most proposed mineral systems, compared to that of a mineral deposit, requires deep penetrating geophysical methods to detect features of exploration significance.  This has led to increased numbers of deep penetrating geophysical surveys such as magnetotelluric (MT) and passive seismic surveys, often funded by Government’s seeking to encourage exploration within their jurisdictions.  Deep seismic reflection surveys are too expensive to be widely used in this way.  MT surveys have the great advantage of being comparatively cheap  and with the widespread availability of 3D inversion codes and the super computers required to run them the resulting sub-surface conductivity distributions are much more ‘interpretable’ due to reduction in artefacts and more accurate representation of actual source geometries.  The weakness of the method remains its poor resolution and the very limited understanding of causes of conductivity variations in the deep crust and to a lesser extent the mantle.  Passive seismic methods, i.e. those that use natural sources of seismic energy, are also comparatively cheap but require deployment of equipment for periods of months to a few years.  Ambient noise and teleseismic body-wave tomography can map major crustal and mantle boundaries.  The final product is a data volume, usually of seismic wave speed, and these can make a useful contribution to minerals system analysis at the largest scales.  Another potentially significant development in passive seismic techniques is in receiver-function based methods.  Traditionally used to determine crustal thickness and Moho character (sharp, diffuse) the development of common-conversion-point based processing has allowed closely spaced (few kms) recordings to be combined with the resulting product resembling a low-resolution seismic reflection section.

Deep seismic and MT surveys can in principle, detect broad zones of alteration associated with metal-bearing fluid sources, pathways and reservoirs indicative of the presence of a mineral system.  A programme of trial surveys, comprising MT, receiver function and wide-angle seismic surveys across selected deposit camps/mineralised terrains and also unmineralised areas in Western Australia is on-going.  A parallel line of research aims to better understand the petrophysical consequences of fluid-related alteration processes and hence predict the geophysical responses of the various components of a mineral system.

KEGS/BCGS Roundup Breakfast 2018

KEGS/BCGS Roundup Breakfast – Tuesday, January 23, 2017

Speaker: Dr. Jaymie Matthews, UBC Astronomy Professor

Title: Asteroseismology: Stealing the geophysicists’ rule book and launching it into space

Date/Time: 2018-01-23 @ 7:30am – 9:00am

Location: Princess Louisa Room, The Fairmont Waterfront Hotel
900 Canada Place, Vancouver, BC V6C 3L5

Registration: Online at (Deadline Jan 22, 2017)


Astronomers have been updating the biography of the Sun for decades, at the same time trying to confirm models of its internal structure. Like the Earth – of which we can sample directly less than 0.2% of its total depth – most of the interior of the Sun is hidden from direct view. Except for neutrinos from the solar core, we receive direct information only from a surface layer of gas whose depth is only 0.05% of the radius of the Sun.

Astronomers, faced with the same challenge that geophysicists had tackled before us when they wanted probe the deep interior of the Earth, turned to the rule book of geoseismology. For the Sun, we could apply principles of global seismology and eventually local time-distance seismology, using the intrinsic vibrations of the Sun caused by sound waves propagating in the solar interior. Much of this was possible for the Sun with telescopes grounded on Earth, because of the extremely high signal-to-noise and surface spatial sampling possible for solar observations. But when it came to extending this technique to the distant stars, by asteroseismology, it was necessary not to toss out the rule book, but to toss it up, into space.

Canada’s first space telescope, called MOST, was one of the pioneers, later joined by the French CoRoT space mission and eventually NASA’s Kepler satellite. These are the most sophisticated stellar lightmeters ever built, and launching them into space launched a revolution in ultraprecise photometry of stars and exoplanets. That in turn launched a revolution in our ability to seismically probe distant stars, and to put our own Sun in better context by studying the interiors of other suns. Not just ‘middle-aged’ suns like our own, but senior suns, and teen suns, and baby suns, and even suns still in the womb.

Even for our own Sun, the seismic data are driving the physics, so we need to include what used to be considered third-order effects lost in the noise, if we’re to match models to observed frequencies to within their measured accuracies.

Join me on a voyage through space and time, where the guide book contains the principles of time series analysis and mathematical inversion, to see how far we have come in the last 15 years, and the exciting frontiers that are ahead of us.

January 2018 – Technical Talk

BCGS Technical Talk – January 18, 2018

Speaker: Doug Schouten, PhD, CRM GeoTomography Technologies Inc.

Title: Muon Tomography Applied to a Dense Uranium Deposit at the McArthur River Mine

Date/Time: Thursday, January 18, 2018

Location: 4th Floor Conference Room, Room 451, 409 Granville St. (UK Building at Granville and Hastings), Vancouver


Muon Tomography Applied to a Dense Uranium Deposit at the McArthur River Mine.
Doug Schouten, PhD, CRM GeoTomography Technologies Inc.

Muon radiography is a means of inferring density by measuring the attenuation of muon (a type of elementary particle naturally abundant from cosmic ray radiation) flux through matter. Muon tomography uses tomographic methods to derive 3D density maps from multiple muon flux measurements.

Measurements of the muon flux were first used by E. P. George (1955) to measure the overburden of a railway tunnel, and by Alvarez et al (1970) in searches for hidden chambers within pyramids. More recently, muon radiography has been used in volcanology, and has also been considered for industrial and security applications. CRM Geotomography Technologies, Inc. (CRM), a spin-off from TRIUMF, is bringing muon tomography technology to bear in mineral  exploration.

In this talk, I will report on the first application of muon tomography for imaging dense uranium deposits within the Athabasca Basin in Canada, performed by CRM at Cameco and Areva’s McArthur River mine in Northern Saskatchewan. I will demonstrate the applicability of muon tomographic imaging using data acquired at a depth of about six hundred meters underground. I will show that the statistical significance of the known uranium deposit signature in the muon data is very high (larger than five standard deviations), and I will report on the very good compatibility of the corresponding 3D density inversion with drill assay data from the deposit. I will also briefly recap other recent progress by CRM in various applications of muon tomography.

BCGS Christmas Party


Our first annual Christmas party will be held on Tuesday December 12th in conjunction with Doug Oldenburg’s 2017 SEG Distinguished Instructor Short Course on Geophysical Electromagnetics: Fundamentals and Applications.

We are pleased to invite you to mingle with fellow geophysicists around appetizers and drinks. There is no charge for this event but please let us know if you will be joining.

BCGC Christmas Party
18h30 on Tuesday, December 12th, 2017

at the Kingston Taphouse & Grille
755 Richards Street, Vancouver, BC