Speaker: Peter Fullagar, Fullagar Geophysics Pty Ltd.

Title: Beyond Plates – fast TEM inversion using conductive ellipsoides

Date: Thursday, May 25, 2023

Time: 4:30pm to 5:30pm PDT

Location: Room 111 – 409 Granville Street, Vancouver, BC, V6C 1T2

Abstract:

Interpreting TEM anomalies in terms of conductive rectangular plates is effective in many situations. However, not all conductors are thin and planar. Triaxial ellipsoid conductors represent an attractive alternative: geometrically simple (corner-free), mathematically tractable at early and late time limits, and able to encompass shapes ranging from poddy to tabular to lensoidal to elongate. Accordingly a fast  magnetostatics-based algorithm has been developed to compute ellipsoidal conductor responses in both resistive and inductive limits. Focusing on TEM data close to the resistive or inductive limit is attractive not only because it simplifies both the physics and the computations, but also because in many cases the late time or early time response is of particular interest in mineral exploration. Inversion of measured data entails adjustment of selected ellipsoid parameters, subject to user-imposed upper and lower bounds. The methodology is suitable for downhole, ground, or airborne TEM, either impulse or step response. In this presentation the conductive ellipsoid forward and inverse algorithms are briefly described and illustrated via application to TEM field data.

Bio:

Peter Fullagar holds a PhD in geophysics from UBC. He has over 40 years experience in base metal and precious metal exploration, and in metalliferous and coal mining geophysics. He worked for a total of 14 years with Western Mining Corporation (WMC) and Rio Tinto in Australia. Peter has also held academic and research positions, at Ecole Polytechnique in Montreal and with CSIRO Exploration & Mining in Brisbane. Since his tenure as Chief Geophysicist for WMC in the early 1990s he has promoted utilisation of geophysics in operating mines. He established Fullagar Geophysics Pty Ltd in Brisbane in 1998 and has consulted privately for the past 25 years. During that time he has developed geophysical modeling and inversion software, mostly for EM, potential fields and borehole logging, with a focus on integrated interpretation of geophysics and geology. He has also supervised several MSc and PhD students, and has taught undergraduate courses in potential fields, and electrical and EM methods, at the University of Queensland. He is currently based in Noosa, Queensland.

Webinar:

Speaker: Heather Schijns, Global Principal Geophysicist, Seismic Geophysics, BHP

Title: 3D Seismic Feasibility Study of Olympic Dam

Date: Wed, May 10, 2023

Time: 4:30pm to 5:30pm PDT

Location: Room 111 – 409 Granville Street, Vancouver, BC, V6C 1T2

Abstract:

Olympic Dam is a world-class IOCG (iron-oxide copper gold) deposit located in Southern Australia, and is the flagship deposit for the IOCG deposit-style. It is one of the largest known copper deposits and single largest uranium deposit in the world. Mineralisation at Olympic Dam is disseminated in nature, and is hosted in hydrothermal breccia within Roxby Downs Granite. Between the gradational nature of the contacts between the iron-oxide rich breccia and the altered granite, and the small-scale heterogeneity of the breccia itself, few apparent opportunities exist to generate coherent seismic reflectivity. The feasibility of hard rock reflection seismic to effectively image IOCGs, and more broadly, deposits with disseminated mineralisation, has been unclear to date, with few examples in the literature. In 2021, BHP undertook an in depth 3D seismic feasibility study of Olympic Dam. Utilising a physical property model that included representative 3D geometry and geological variability, the feasibility study allowed detailed examination of the impact of various seismic acquisition and processing decisions on successfully imaging this complex geology. Here we present the feasibility study process and results.

Bio:

Heather Schijns joined BHP in 2017 and works out of Vancouver, Canada as Global Principal Geoscientist, Seismic Geophysics.  In this role Heather provides technical guidance and strategy for application of seismic methods and R&D across global copper, nickel, coal, iron ore and potash assets for purposes ranging from resource exploration/targeting to geotechnical characterisation. 
Prior to joining BHP, Heather worked in exploration-focused roles at companies including MMG, Aurora Geosciences and TerraNotes using a broad range of geophysical methods. Work took her across 5 continents and offshore, including major projects in arctic Canada, Brazil and Tanzania.  Heather is a graduate of the University of Alberta, where she completed an MSc and a PhD in geophysics with a focus on seismic rock physics of metamorphic rocks.