Soil geochemical survey over concealed kimberlites in the Attawapiskat area in northern Canada

Abstract

A soil geochemical survey was conducted over kimberlites in a discontinuous permafrost zone in the James Bay Lowlands, southeastern Hudson Bay Lowlands. The kimberlites are concealed by 10 to 30 m of tills and Tyrell Sea clay sediments. Samples of humus and B-horizon soil were collected at 25-50-m intervals over traverses with the total lengths of 562 m over the Whiskey kimberlite and 740 m over the Yankee kimberlite pipe. B-horizon soil samples, sieved to <80 mesh and dried at 60 C, have high carbonate contents above the margins of the kimberlite pipes. Ammonium acetate leach at pH 5 (AA5) dissolves most of these carbonates, and shows anomalies of REE, Y and Ni above the margins instead of the centres of kimberlites. Since the leach dissolves not only carbonates but also amorphous Al-O-OH originating from the clastic component, the ratios of metals to Al are effective to display geochemical anomalies associated with kimberlites. The concentrations of high field strength elements, such as Nb and Ta, are low in AA5 relative to their detection limits, whereas these elements show anomalies in the Enzyme leach. The ratios of these metals to Mn in the Enzyme leach are useful to display the anomalies associated with kimberlites because soil samples over kimberlites contain high contents of these metals and low contents of Mn. Our data suggest that a soil geochemical survey may be used to assist in discriminating kimberlites from other targets during diamond exploration in sub-Arctic settings.

Role of trace element Pedogeochemistry in Diamond Exploration- A first Report from Lattavaram Kimberlite Cluster, Wajrakarur Field, Eastern Dharwar Craton, southern India

“…They have noticed that elements like Ni, Co, Cu, Cr, Ti, V, Mg, Mn and Fe as 'the primary element associated' with kimberlites and Nb, Rb, Zr, Y, Sc, Th, U, Cs, REE, P, Al, K, Na, Ca, Ba, Sn, Mo, W, Cd, Zn, Pb, B, Hf, and Ga as 'the secondary element association'. Pedogeochemical surveys conducted over kimberlites in a discontinuous permafrost region in the James Bay Lowlands, southeastern Hudson Bay Lowlands have been successful in delineating REE, Y and Ni anomalies and ratios of these elements to low surface concentrations of Mn in discriminating kimberlites from other targets in sub-Arcitic regions (Hattori et al, 2009). Yet another example from African countries is discovery of concealed kimberlites with the successful utilization of soil geochemistry (e.g.…”

Application of weak leaches in kimberlite exploration

“…the flanks allowing mobile ions to travel more easily to the surface. Sader et al (2011) cite this as a reason for an upwelling of groundwater measured at the flanks of the Attawapiskat kimberlites that were also marked by surface soil flank REE anomalies (Hattori et al 2009). Figure 4 shows the chondrite normalized MMI REE data patterns for the Pacaud MMI survey line.…”

“…Using strong multiple ligands in the extracting solution avoids readsorption effects and keeps the analytes in solution. This is a key difference between MMI and other leaches such as ammonium acetate that have been used in kimberlite studies (McClenaghan et al 2006, Hattori et al 2009 It is important to note that a consequence of using a weak leach is that the mobile metal ion population in solution is in the sub ppb to low 10 th International Kimberlite Conference, Bangalore -2012 ppm range and the use of ICP-MS for analysis of the solution is essential. The advantages of ICP-MS for analysis of heavy elements notably the rare-earth elements (REE) has been evident since the technology became available in the mideighties (Caughlin 2010).…”