The work should enable Ashton and its joint-venture partners,
The K252 was discovered in March 2000 and so far has yielded encouraging results. An initial, 1,280-kg sample of volcaniclastic kimberlite yielded a 0.85-carat parcel of diamonds larger than 0.8 mm, for a preliminary grade of 0.662 carat per tonne, or 66.2 carats per 100 tonnes. The largest recovered stone was a colourless composite crystal weighing 0.36 carat.
K252 is covered by up to 77 metres of overburden and comprises 2 ha. It consists of two main phases: fine-to-medium-grained volcaniclastic kimberlite and volcaniclastic kimberlite breccia. The volcaniclastic kimberlite unit contains abundant olivine macrocrysts and, to a lesser extent, juvenile lapilli. The altered, fine-to-medium-grained olivine macrocrysts and irregular magmaclasts are set in a fine-grained serpentized matrix, with variable carbonate content. Mantle xenoliths are rare and appear to belong mainly to the peridotite family.
By contrast, the breccia phase is coarse-grained, with olivine macrocrysts and juvenile lapilli ranging in size from 10 to 50 mm. Xenoliths of both mantle and crustal rock are abundant, comprising up to 15% of the rock. Mantle xenoliths are ovoid-to-elongate and quite altered, and most appear peridotitic.
The 20-tonne mini-bulk sample comprises equal amounts of volcaniclastic kimberlite and kimberlite breccia. The sample will be processed using Ashton’s dense media separation plant in North Vancouver. Macrodiamond results are expected in four to six weeks.
Ashton has so far discovered 36 kimberlite bodies in the Buffalo Hills region, 350 km north of Edmonton. Twenty-three of the kimberlites are diamondiferous, albeit low-grade, with six having grades of greater than 3 carats per 100 tonnes, based on the testing of at least 1 tonne of kimberlite. Microdiamond results from kimberlite K281, discovered in March of this year, 15 km southeast K252, are also expected in four to six weeks.
The kimberlites range from 1 to 47 ha and are covered by 0-127 metres of overburden.
The Buffalo Hills region is underlain by Precambrian basement rocks, known as the Buffalo Head terrain, together with sediments of the Western Canadian Sedimentary Basin. The Buffalo Head terrain is composed of rocks up to 2.3 billion years old. Paleozoic- and Mesozoic-age sedimentary bedrock, up to 5,000 metres thick, overlies the basement. The entire region was glaciated during the Laurentide ice advance, and its retreat deposited a blanket of till, lake sediment and glaciofluvial sediment up to 200 metres thick. Kimberlite magmatism in northern Alberta is thought to be controlled by the Peace River Arch.
The first 34 kimberlites were discovered by the Ashton joint venture using aeromagnetic surveys. The kimberlites display a marked magnetic susceptibility, in contrast to the sedimentary rocks. The K252 kimberlite, however, is virtually non-magnetic and was discovered using an electromagnetic survey. The conductive, clay-rich bedrock contrasts with the resistive kimberlitic rocks. Gravity and seismic surveys have also proved effective geophysical tools for identifying kimberlite bodies.
Ashton says infrastructure in northern Alberta is conducive to the development of a mine, thanks to the roads and facilities built to accommodate the oil and gas industry. The economic threshold for kimberlites found in Alberta is therefore lower than those in the Northwest Territories and Nunavut.
Ashton and Alberta Energy each hold a 45% interest in the Buffalo Hills project. Pure Gold holds the remainder.
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