Geochemical soil survey over the K4B kimberlite, Buffalo Head Hills, northern Alberta

The K4B kimberlite, one of three kimberlites forming the K4 kimberlite complex, is located in the southeastern Buffalo Head Hills of northern Alberta. The K4B kimberlite is covered by as little as 7 m of overburden composed largely of till. During the summer of 2001, an organic soil and mineral soil (B- and C-horizons) sampling program was completed over and west of the K4B kimberlite. A total of 122 routine soil samples and 22 field site duplicate samples were collected from 42 sites. Multi-element chemical results were obtained for all samples by inductively coupled plasma atomic emission spectroscopy/mass spectrometry (ICP-AES/MS) analyses following aqua regia digestion. Additional results were obtained on the B- and C-horizon soil samples by a) four-acid digestion ICP-AES, b) four-acid digestion ICP-MS, c) instrumental neutron activation analysis (INAA) and d) cold vapour atomic absorption (CVAA).

Aqua regia extractable results for most elements are lower in the organic soil samples than in the C-horizon soil samples. Exceptions are K, Ca, Co, Zn, Sr, Nb, Mo and Ba, for which the median values are similar, and B, P, S, Mn, Se, Ag, Cd and Hg, for which the median organic soil values exceed the median C-horizon values.

Total and near-total results, determined by four-acid ICP-AES/MS and INAA, indicate B-horizon depletion of Mg, P, S, Ca, Mn, Co, Br, Sr and Cd, coupled with B-horizon enrichment of Cr, Rb, Y, Zr, Ag and Sn. Aqua regia extractable results indicate B, Na, Mg, P, Ca, Mn, Co, Sr, Ag, Cd and Ba values are generally lower and Li, Be, Al, Sc, Ti, V, Cr, Fe, Ga, Se, Rb, Y, Nb, In, Sn, Te, Th, U and rare-earth element values are generally higher in B-horizon soil relative to C-horizon soil. Variability in Mg, P, Cr and Nb concentrations in mineral soil related to depth have implications for the use of soil geochemistry in diamond exploration as they may serve as kimberlite pathfinder elements.

Evidence of anomalous soil geochemistry related to kimberlite is found in the results of the organic soil survey for which elevated Mg/Fe, Ni/V and B values are spatially associated with the K4B kimberlite.