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.

BCGS 2014 Fall Symposium: Hudbay Lalor Case Study – Registration is Now Open!

The BC Geophysical Society is pleased to announce that registration is officially open for the 2014 Fall Symposium.

Exploration for Deep VMS Ore Bodies: The Hudbay Lalor Case Study

When: October 16 and 17, 2014

Where: BCIT Downtown Campus, Rooms 280, 282, 284, Vancouver, BC,

Cost: Industry $150 / Students $50

Please register in advance by completing and submitting the registration form below. Adobe Reader is required to electronically submit the form by email.

Registration Form BCGS 2014 Symposium_distributed

Payment will be accepted through PayPal. Click on the ‘Buy Now’ button below.

Registration Options:

BCGS Fall Symposium: Oct 16 & 17, 2014

The BC Geophysical Society, in cooperation with Hudbay, is proud to present a two-day symposium on the discovery of the Lalor Deposit. The amount and variety of geophysical work undertaken, coupled with the geological understanding and insight provided by the owner of this prominent deposit, is sure to make this an extremely interesting session.

Additional details including the full speaker schedule will be available this summer. Registration is scheduled to open August 2014.

Exploration for Deep VMS Ore Bodies: The Hudbay Lalor Case Study

When: October 16 and 17, 2014

Where: BCIT Downtown Campus, Vancouver, BC

Cost: Industry $150 / Students $50

Please see the following link to the symposium abstract for additional details.

BCGS Symposium – Deep VMS Exploration- Lalor Case Study



KEGS Foundation Scholarship Deadline – April 30, 2014

Every year the BCGS proudly supports the KEGS Foundation Scholarship program by donating revenue from the yearly symposium.

The deadline for the 2014/2015 scholarship program is April 30, 2014. We encourage students (particularly undergraduates) to apply before the upcoming deadline. Please see the attached poster for additional information.

KEGSF14c9.Schol Announcement Poster 2014-2

April Technical Talk

BCGS April Technical Talk – Thursday April 17th, 2014

Speaker: Peter Fullagar, Fullagar Geophysics

Title: 3D magnetic modelling and inversion incorporating self-demagnetisation and interactions

Date/Time: Thursday April 17th, 2014 at 4:30pm.

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


Self-demagnetisation can significantly reduce the amplitude and modify the shape of the response from highly magnetic bodies. The direction of magnetisation rotates in a manner determined by the shape and orientation of the body. Furthermore, when highly magnetic bodies are in close proximity, the magnetisation induced in one body is affected by the magnetisations in all the others. When modelling highly magnetised bodies, it is important to take both self-demagnetisation and interactions into account. Inverting for magnetisation vector has become popular recently. However, this is not a substitute for physically valid magnetic modelling. Magnetisation inversion is highly nonunique, with the result that any particular solution must be interpreted with care. An inverted magnetisation rotated from the ambient field is not necessarily indicative of remanence. Moreover, relating an inverted in situ magnetisation to rock properties is often problematic. In this respect, magnetisation inversion complicates ground truthing. Potential field modelling and inversion software “VPmg” has been upgraded to account for self-demagnetisation within, and interaction between, 3D magnetic bodies. Remanence can be taken into account. The algorithm computes H-field perturbations at the model cell centres in two stages: initialisation and optimisation. During initialisation, a first estimate for the H-field perturbation is derived from the demagnetisation tensor computed for each cell.

During optimisation, the H-field perturbation is refined iteratively via an inversion procedure. The algorithm has been validated for homogeneous spheres, spheroids, slabs, and cylinders. It has also reproduced magnetic interactions between two horizontal cylinders, published by Hjelt (1973). Explicit verification for complex heterogeneous bodies requires a suitable independent algorithm for benchmarking. The application to inversion in highly magnetic environments is illustrated on field data examples.