Some facts on diamonds worth remembering

Investors around the globe are holding their breath in anticipation of bulk sample results from the Lac de Gras diamond play in the Northwest Territories.

The sample is a follow-up to a recent discovery made by Dia Met Minerals (VSE) and BHP-Utah Mines, which yielded 81 small diamonds, some of gem quality and all less than two millimetres in diameter, from a 465-ft. core sample of kimberlite. The purpose of the bulk sample is to search for larger stones within the kimberlite pipe.

Because Dia Met is a public company subject to strict disclosure requirements, it is likely that much of this information gleaned from the sample will find its way into the public domain. BHP officials say results should be available by the end of May, at the latest.

Meanwhile, here are some diamond facts to remember:

— Diamonds are found in two types of volcanic rock-kimberlite and lamproite. — In order for diamonds to remain intact (without converting to graphite or carbon dioxide), they must be brought to surface from depths of 100 miles or more at great speed. Estimates range from 5-20 miles per hour at the beginning of the trip to several hundred miles per hour as the kimberlite/lamproite magma reaches surface.

— The volcanic host rocks, or “pipes,” are shaped like carrots and extend to depths of up to 1.5-2 miles.

— Diamondiferous kimberlites occur only on ancient cratons (stable, continental areas).

— Kimberlites usually occur in clusters of 10-40, over an area of 40 square miles or more.

— Due to their high iron content, kimberlites usually respond well to geophysics.

— Indicator minerals such as garnet, illmenite and chrome diopside are always associated with diamondiferous pipes but almost never with barren pipes.

— There are more than 3,000 known kimberlite bodies in the world, but less than 1,000 carry any diamonds. Only 50-60 have ever been economic. — Only a handful of the rarer lamproite bodies are economic. One of these is Australia’s Argyle mine, the world’s largest diamond producer. — There are several diamond occurrences in North America but only one, the Crater of Diamonds State Park in Arkansas, ever reached production. — Most of the well-known producing pipes have an area of 12-75 acres. — Diamonds are classified into one of more than 3,000 categories based on size, shape, color and quality. Industrial diamonds, the most common and the least valuable, sell for a couple of dollars per carat. Gem quality diamonds, at the top of the range, can fetch thousands of dollars.

— A macrodiamond (as opposed to a microdiamond) is any diamond greater than 0.45 mm in diameter. Microdiamonds are far more prolific than macrodiamonds. — Clear diamonds with a blue or pink tinge are the most valuable. Inclusions can reduce the value of the stone dramatically.

— The Central Selling Organization, controlled by De Beers Consolidated, markets at least 80% of the world’s rough gem diamonds.