Bob Middleton
Our Geophysical Advisor, Bob Middleton will be giving a talk at the NW Ontario Prospectors association meeting. The Abstract follows..
NWOPA2020 February 16, 2020
ABSTRACT
GEOPHYSICS FOR MAPPING SHEAR AND FAULT CONTROLS OF GOLD MINERALIZATION
By R. S. Middleton, P.Eng. MSc. BSc. And J. Laarman, P.Geo, MSc., PhD
The majority of gold deposits in the Canadian Shield are associated directly or indirectly with shear zones and major faults or “Breaks” that provide the plumbing for gold bearing fluids to travel into favourable host rocks or settings where gold can be precipitated and attach to preferred minerals or structures.
Conventional magnetic surveys can define shears by locating folds and identify offsets and deflections of other geological units by the presence of a shear or fault. Alteration zones along a fault or shear are often defined by magnetic depletion zones. Shears are also weakly conductive because of the development of chlorite, sericite and clay minerals and are porous and often contain ground water near surface and fluids at depth. Therefore these structures can be followed by various EM (electromagnetic) methods or resistivity surveys. Shears and faults also become deeply weathered in tropical terrains and contain conductive clay and become indicators of epithermal gold veins along the walls of these veins. VLF EM can trace these conductive clays and therefore indicate the presence of adjoining veins.
Mineralized shears can also be traced by IP-resistivity as moderate resistivity zones with correlating chargeability indicating sulphide grains.
Deep mantle tapping listiric faults have been defined in the Red Lake Camp by seismic methods that are associated with the main mine trend at the Cochenour, Campbell and Red Lake Mine (Dickenson mine), and a number of other faults have been identified associated with the LP shear on the Dixie Lake property (Great Bear) and on the Kwai property (Golden Goliath), and SLF property to the south. Deep seismic work is presently being carried out in the Abitibi greenstone belt to look for similar features.
This paper will present examples of shears and geophysics used to map these structures in the Timmins (Porcupine Camp), Wawa area (Eagle Mine), Hemlo, and Red Lake Camps.