Russians say telltale gases in rock may point to diamond deposits

Rough diamond. Picture courtesy USGS

The method was recently developed by the All-Russian Research Institute of Geological, Geophysical and Geochemical Systems [link] in Moscow in conjunction with Moscow State University and the Russian state-owned diamond-mining company ZAO Alrosa, which produces about 20 per cent of the world's diamonds.

Using a gas chromatograph, researchers compared the composition of adsorbed gases in rock from diamond-bearing areas in Russia's Yakutia and Arkhangelsk territories with that in rock from areas of the country where diamonds have never been found. To do this, crushed rock was heated to about 200 degrees centigrade.

"'Look guys, a very interesting thing is happening here!' we said," related Lev Kondratov, chief researcher at the geological institute in Moscow. "There were characteristic compositions and concentrations of gases. This could be used in exploration."

It turned out there was usually a much higher proportion of heavy carbohydrates in rock from diamondiferous regions, whose gas "fingerprint" also differed from that of rock overlying oil and natural gas deposits.

"Gases are present in rock in various forms," Kondratov said. "We were the first to learn how to analyse the adsorbed form."

Kondratov said the gas-analysis method was less labor-intensive than traditional diamond-prospecting since it required taking samples of rock lying just a half-meter or so below ground.

Prospectors typically search for "indicator minerals" - such as garnet, chromite, ilmenite, clinopyroxene, olivine and zircon - which, normally rare near the Earth’s surface, are a sign of a kimberlite pipe, the primary source of diamonds.

Kimberlite, named after the South African city of Kimberley, where a rich source of diamonds was discovered in the second half of 19th century, is soft, easily eroded rock found in subterranean volcanic pipes - or vents - created by the explosive escape of magmatic gases.

The eruptions propelled diamonds, crystalline carbon formed 1-3 billion years ago under intense heat and pressure at depths of about 150 kilometers, toward the surface.

The results of the Russian researchers' studies have been published in the Proceedings of the Russian Academy of Sciences [link]. Kondratov said the gas-analysis method of diamond exploration had not yet been patented and that investors were needed.