Kimberlites

Natural diamonds are found in kimberlite of ancient volcanic "pipes," found in South Africa, Arkansas, and elsewhere. Diamonds are now also being recovered from the ocean floor off the Cape of Good Hope. About 30% of all industrial diamonds used in the U.S. are now made synthetically. 

Diamonds are found in ancient volcanic pipes embedded in a relatively soft, dark coloured basic rock called blue ground or kimberlite , from the South African town of Kimberley where such pipes were first discovered in 1870. Diamonds... 

A. Dissemination Disseminated crystallisation without concentration Most diamond bearing kimberlite pipes... 

Plouffe, A., Paulen, R.C., Smith, I.R. Kjarsgaard, I.M. 2007. Chemistry of kimberlite indicator minerals and sphalerite derived from glacial sediments of northwest Alberta. Geological Survey of Canada, Open File 5545 and Alberta Geological Survey, Special Report 87. 

Keywords diamond, kimberlite, soil geochemistry, imaging, volatile... 

A second location approximately 5 km south of the Honerat kimberlite was also studied (named Unknown) (Fig. 1). 

Fig. 1. The Honerat kimberlite and the Unknown Site are located in western Quebec, Canada. The labeled points represent sample collection sites along transects at Honerat and Unknown.

Although no kimberlite is known of in this second area, kimberlite boulders and elevated kimberlite indicator mineral counts in glacial sediments have been... 

Soil samples were collected along a traverse over the Honerat kimberlite and extended off the kimberlite approximately 75 m SE and 225 m NW from the pipe s centre (Fig. 1). Although it is common practice to collect samples from upper B-horizon soil (Levinson 1980 Bajc 1998 Mann et al. 2005) our samples were collected from C-horizon soil because GAGI samplers were placed at a depth of 60 cm (well below the B horizon). Within 8 hours of sampling, a portion of each soil sample was mixed with Milli-Q water (1 1) to create a slurry. The values of pH and oxidation-reduction potential (ORP) were determined in each slurry. Ammonia acetate leach of the soil samples were performed at Acme Analytical Laboratories, Vancouver, where 20 ml of ammonium acetate was mixed with 1 g soil sample and elements were determined by inductively coupled plasma-mass spectrometry. The GAGI samplers installed at Unknown were placed in piezometers and submerged in water at a depth of approximately 1 m below ground surface. 

Soil slurry ORP values are lower over the Honerat kimberlite (near 0 mV) compared to other locations along the sampling traverse (up to 100 mV). Over this kimberlite there is also a marked depletion... 

The partial leach results from soil samples identify the location of the buried Honerat kimberlite. The depletion of Ni, Mg, Co, K, and total REEs in C-horizon soils over the Honorat kimberlite suggests that numerous kimberlite pathfinder elements are not adsorbed on to soil particles. Instead, they are remaining in the dissolved phase in solution due to the more reducing environment inside... 

Fig. 2. Low relative ORP values correlate with low Ni values in soils over the Honerat kimberlite (depicted as the grey zone).

Kimberlite bodies can be identified at ground surface using soil geochemistry where 90 m of glacial sediment overlies a kimberlite. This is based on variations in element concentrations of pathfinder elements such as Ni, Mg, Co, K, and total REEs over versus off a kimberlite. 

The Gore Amplified Geochemical lmagingSM technique, like soil geochemistry, shows anomalous concentrations of sulfides and hydrocarbons in soils over the kimberlite. 

Values of 813C-DIC correlate with some hydrocarbons at the Unknown Site and suggest that Amplified Geochemical lmagingSM responses could be the result of surficial bacterial communities that thrive over kimberlites. 

McClenaghan, M.B., Hamilton, S.M., Hall, G.E.M., Burt, A.K., Kjarsgaard, B.A. 2006. Selective Leach Geochemistry of Soils Overlying the 95-2, B30, and A4 Kimberlites, Northeastern Ontario. Geological Survey of Canada, Open File 5069. 

Indicator minerals recovered for morphological and mineralogical analyses include those from kimberlite and... 

Lee, H.A. 1968. An Ontario kimberlite occurrence discovered by application of the glaciofocus method to a study of the Munro Esker. Geological Survey of Canada, Paper 68-7. 

Thorleifson, L.H., Garrett, R.G. Matile, G.L.D. 1994. Prairie kimberlite study -indicator mineral geochemistry. Geological Survey of Canada, Open File 2875. 

KEYWORDS kimberlite, exploration, geochemistry, groundwater, peat... 

In many northern regions, peat bogs are widespread. Our study shows that peat groundwater can have geochemical responses consistent with its interaction with kimberlite rocks (Sader et al. 2007). The geochemical responses can be different from those in mineral soil. Therefore, exploration in peat bog terrains requires specific sampling methods. 

The kimberlites in this study are located in the James Bay Lowlands and are in close proximity to the DeBeers Victor Mine. The kimberlites are mid Jurassic ( 170 Ma) in age and have been emplaced into... 

Paleozoic limestone (Webb et al. 2004). These kimberlites all have similar groundmass mineralogies consisting mainly of carbonate, spinel, and serpentine with lesser monticellite, mica, apatite, and perovskite (Kong et al. 1999) and they are all of volcaniclastic facies near ground surface. Varying thicknesses of clay and fine marine sediments of the Tyrell Sea ( 4000 - 12000 years BP) and 1 to 4 m of peat overlie kimberlites (Fraser et al. 2005). Bioherms composed of coral and skeletal remains of other marine organisms sometimes outcrop. 

Fieldwork was conducted at Attawapiskat kimberlites (Yankee, Zulu, Alpha-1, Bravo-1, and X-ray), and at the Control location August 14-23, 2007 and October 14-18, 2007. Shallow piezometers were used to collect peat groundwater. At the Yankee and Zulu kimberlites piezometers were installed along transects between 25 to 50 m apart. Between 3 and 5 piezometers were installed at Alpha-1, Bravo-1, and X-ray. Piezometers were typically pushed into the peat 1.1 m with a loosely fitting plastic champagne cork at the end to prevent peat entering the pipe while it was... 

Our results indicate that peat groundwater can be an effective medium for surficial geochemical exploration. The dilute, acidic peat groundwaters contrast well with groundwaters that have interacted with kimberlite. 

---