Lakefield lab makes honest mistake

The recent announcement by Aber Resources (TSE) and its partners Commonwealth Gold (VSE) and SouthernEra Resources (TSE) that the yellow microdiamonds recovered from a kimberlite on their Lac de Gras area property originated from the drill bit has put Lakefield Research at the centre of controversy.

Lakefield, a division of Falconbridge, was responsible for processing and visually evaluating the microdiamonds found in the Aber kimberlite samples. The samples were processed at the Lakefield facility near Peterborough, Ont., using a caustic fusion technique (T.N.M., Nov. 2/92). According to Russ Calow, Lakefield’s manager of analytical services, the company’s mineralogist genuinely felt that the stones were natural. The mineralogist was concerned by their yellow color, but the stones were not degraded or broken up and lacked inclusion trains that are typical of most synthetic microdiamonds. Calow says problems like this can arise when relying on visual as opposed to quantitative analyses.

The Aber core samples were collected using an impregnated diamond drill bit. The microdiamonds used in this type of bit are synthetic. About 95% of all drill bits used in core drilling today are of this type. Although synthetic microdiamonds cost the same as industrial-grade diamonds, they are more consistent in their physical properties, making them better for use in abrasive or cutting products. All synthetic microdiamonds used in drill bits are yellow to olive green in color.

According to a Longyear Canada spokesman, an NQ-sized drill bit which produces drill core about 4.8 cm in diameter can contain more than 10,000 synthetic microdiamonds in the size range of 0.3-1 mm.

Ideally, impregnated diamond drill bits are designed in such a way that all the microdiamonds are consumed in the hole. However, with the Aber samples this does not appear to have been the case, as some of the synthetic stones found their way into the drill core.

After SouthernEra representatives expressed concern over the colored stones, Lakefield examined one of the drill bits used in the program and carried out further tests on some of the synthetic stones. The microdiamonds in the bit were green-yellow in color, but once put through the caustic fusion process, they lost their green color.

Calow says that the change in color appears to be caused by a change in the oxidation state of iron in the synthetic microdiamonds. Additional research is being conducted on the color change process. One of the deciding factors in determining that the colored stones were synthetic was that they had the same crystal structure as those in the drill bit.

In future, Lakefield is requesting that all kimberlite samples sent for analysis be accompanied by a reference drill bit.

As all the furor over the contamination incident subsides, Calow says it is important to stress that the three other microdiamonds in the samples are genuine and this in itself is a significant finding.