Geo-Note 2003-41

Geo-Note 2003-41

GEO 2003-41

Magnetic susceptibility measurements on kimberlite and sedimentary rocks in Alberta

Author(s) Eccles, D.R. Sutton, R. Date 2004-10-01

This report includes magnetic susceptibility measurements on Alberta ultramafic and Devonian to Late Cretaceous sedimentary rocks to allow for a comparison between Alberta kimberlite and their potential hostrocks.

The magnetic susceptibilities of kimberlitic rocks in Alberta yielded measurements between 0.19 x 10-3 SI units and 52.7 x 10-3 SI units. In contrast, the magnetic susceptibilities of middle to Late Cretaceous sedimentary rock, which includes shale interlayered with kimberlite, are generally less than 0.15 SI x 10-3 SI units. Therefore, the results show the contrast in magnetic properties between the kimberlitic pipes and the host sedimentary rocks is sufficient to produce a geophysical target.

Variations in magmatic differentiation between primitive and evolved kimberlite alter the mineralogy of the resulting kimberlite magma, and thus, offer a plausible explanation for variable degrees of magnetic susceptibility in the kimberlite. In addition, distinct trends of magnetic susceptibility versus kimberlite emplacement age suggest that relatively weakly magnetic northern Alberta kimberlite should be emplaced between 78 and 86 Ma. This may be an important observation for future diamond exploration in northern Alberta, particularly because pipe K252, which has the best diamond results to date, is low magnetic susceptibility kimberlite.

The magnetic susceptibility data presented in this study can be considered during the planning and interpretation of future ground-based and airborne magnetic surveys associated with diamond exploration work in Alberta. Finally, magnetic susceptibility can be used as a complementary tool in drillcore logging, particularly in sections of complicated intercalated kimberlite and sedimentary rock.

Eccles, D.R. and Sutton, R. (2004): Magnetic susceptibility measurements on kimberlite and sedimentary rocks in Alberta; Alberta Energy and Utilities Board, EUB/AGS Geo-Note 2003-41, 109 p.