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F E B R U A R Y / M A R C H 2 0 1 5 www.resourceworld.com 21 Russia is now the largest producer of dia- monds in volume and value. Examples of cratons are the Canadian shield, Brazilian shield, the African shield and the Siberian shield." Prior to 1991, De Beers was prospecting for diamonds in Ontario based on alluvial diamonds found in Michigan. Dr. Chuck Fipke, then president of Kelowna, BC-based Dia Met Minerals, theorized that diamond- bearing kimberlites should occur in the Northwest Territories because of its ancient, stable Precambrian shield. Under the guidance of Fipke and part- ner, Stu Blusson, extensive exploration programs were carried out in northern Canada that eventually led to the opening of the Ekati diamond mine in the Lac de Gras region of the Northwest Territories, followed by the Diavik and Snap Lake diamond mines. Ekati and Diavik are now partially owned by Dominion Diamond and are part of a large cluster of kimberlite pipes, not all of which are diamondiferous. These producing mines are textbook exam- ples of successful diamond exploration. "I think describing how Dia Met ratio- nalized how Lac de Gras was found, going from diamond indicator sampling along the Mackenzie River by De Beers to theorizing that indicator minerals probably came from a much distant source to the east, was based on the fact the Keewatin Ice pack/sheet sited over Keewatin District (a former territory now called Nunavut) extended westward to the Mackenzie Valley and carried the indi- cator minerals," said Schiller. Commonly occurring diamond indicator minerals can be considered to be "pathfinders" that can lead to the discovery of diamonds. "De Beers thought the indicator minerals they found along the Mackenzie River came from kimberlites nearby. In 1988/89, Fipke, then with pilot, Dave Mackenzie, did wide- spaced geochemical sampling over a huge area of what is now called the Northwest Territories south of the Arctic Ocean. It was like taking a sample every 500 plus square miles. With subsequent sampling on a more detailed grid, a concentration of indicator minerals appeared in the vicinity of Lac de Gras," said Schiller. "We then undertook very detailed till sampling and – bingo – we were drawn to Point Lake. Thanks to South Africa geologist, John Gurney, and his ana- lytical study of mineral chemistry of specific indicator minerals and unique geophysical anomalies over Point Lake, we drilled there and found kimberlite. Although proven uneconomic, it led to other kimberlites that were economic." Due to the glacial nature of mainland Canada's terraine, Fipke undertook an extensive and widespread sampling of glacial till in search for resistate (the abil- ity to resist weathering) indicator minerals common to kimberlites that would be pre- served in weathered glacial deposits. These minerals were garnet, chromite, ilmenite and chrome diopside and, due to their chemical make-up, were known to be con- tained in kimberlties of deep-seated origin in the mantle over 100 km from the sur- face. Studies completed by South African and Russian geologists established the link between these four common minerals and the presence of diamonds in kimberlites. John Gurney was a pioneer in this think- ing and, due to his input, was instrumental in advancing how diamonds were in the Northwest Territories. KIMBERLITE PIPES HIDDEN UNDER ROUND LAKES "In Arctic Canada, sampling of glacial till delineated indicator mineral trains that originated out from circular lakes that with magnetic and electromagnetic surveys targeted the kimberlite body," said Schiller. "Diamond drilling of the coincident indicator mineral/geophysical anomaly intersected kimberlite in most cases. Analyses of micro-diamond con- tents established the potential of a viable deposit. Prior to 1991, when Dia Met drilled the first diamond-bearing kim- berlite at Point Lake, no diamonds were ever found in the glacial deposits' sample program. Subsequent drilling of other anomalous targets by Dia Met and partner BHP Minerals discovered diamond-bearing kimberlites that proved to be economic." The round lake/indicator mineral train anomalies and subsequent kimberlite discovery was a remarkable Canadian suc- cess story. The movement of glacial ice had scoured out the circular outcropping kimberlite which was softer than the sur- rounding hard Precambrian rocks. When the glacier retreated, it left a circular void a few hundred metres in diameter which filled with water, forming a round lake. All this happened some 50,000 years plus ago. Not all diamonds survive the voyage towards the surface. Those that do are in what is called the diamond stability field. "The diamond stability field within a par- ticular kimberlite can only be established after a kimberlite sample has been obtained, generally through drilling after which certain minerals of the kimberlite are chem- ically analyzed and the data compared to theoretically derived information of mineral stability," said Schiller. He explained that kimberlite targets are drilled initially with a small diameter core drill a few centimetres in width. The core is analyzed for micro diamonds and, if popu- lation and size distribution is favourable, then a larger diameter core drill is used to obtain a mini-bulk sample of the kimberlite, amounting to a few tonnes. If the mini-bulk sample proves favourable, then additional drilling is done to obtain a bulk sample of larger weight to extract a sizeable number of diamonds, on the order of thousands of carats, which upon grading by diamond experts will establish the economic viability of the kimberlite. In addition to carat weight per tonne, value per carat is equally as important," said Schiller. "In general NWT diamond mines have carat grades in the order of 1 to 3 carats per tonne and carat values in the range of $100 to $300 per carat. Total ton- nages and mining costs are factored in to determine the deposits viability." Canadian kimberlites, mined by open pits, generally are a few hundred metres deep and can be converted to underground mines that could descend another 100 to 200 metres, depending on grade and carat value. With an early stage diamond exploration program, diamond stock investors like to see well-defined diamond indicator mineral trains that can be followed to their source, that is, a kimberlite pipe. If a pipe is found, of course it is encouraging to intersect