MEG Luncheon November 10, 2011 and AGM

Basics of Gravity and Magnetic Methods in Exploration

These passive geophysical methods aim to detect map-scale variations in the earth’s gravity and magnetic fields that are related to lateral variations in rock composition. Data recording can be done on the ground and in the air, on local and regional scales. Useful regional data coverage in North America is available free from government sources.

Rock density and total magnetization – as opposed to lithology – are the rock properties whose lateral variations cause gravity and magnetic anomalies.  They are a function of the rocks’ entire history and present state.

The gravity field is essentially vertical and unipolar, and rock density is a simple scalar.  The magnetic field is very much more complex, usually inclined and (at least) dipolar.  Besides, rock magnetization depends on the presence of only a few specific minerals, and it is a vector quantity composed of a mindboggling array of remanent and induced constituent magnetizations.

Gravity and magnetic surveys are best designed for the sparsest – hence cheapest – coverage that would resolve all diagnostic anomaly wavelengths and dimensions expected from the exploration target.  Field quality control and careful crafting of the contract are essential.

Processing and display of the data should not rely on any stock set of methods and parameters.  Rather, it should be designed to highlight those anomalies that are expected to be of geological interest.  Because the optimal methods and parameters may be hard to know in advance, processing normally involves a great deal of experimentation.

Exploration examples will be presented.  My summary tutorial article is available here.

Presenter's Biography: Dr. Henry Lyatsky, P.Geoph., P.Geol.

Henry Lyatsky is a Calgary-based geophysical and geological consultant who has worked across Canada, northern and western U.S., and internationally in oil and mineral exploration.

He was born in St. Petersburg, Russia and moved to Calgary as a teenager.  He holds a B.Sc. in geology and geophysics (1985, University of Calgary), an M.Sc. in geophysics (1988, University of Calgary) and a Ph.D. in geology (1992, University of British Columbia).  He is the first or sole author of three books (Springer-Verlag) on the regional geology and geophysics of western Canada, two gravity and magnetic atlases of the Alberta Basin (Alberta Geological Survey) and many papers.  He is a member of CSEG, MEG, AGU and APEGGA.
Henry is a past president of the MEG.  To avoid the downtown rat-race and congestion, he works from home, enjoys the free space of the Alberta outdoors, and loves nothing better than in-depth history books and good hikes in the mountains.