BHP Billiton comes up empty at Royce

Using its proprietary Falcon airborne gravity system to pinpoint potential kimberlite targets on the Royce Group of claims in the Northwest Territories, BHP Billiton (BHP-N) failed to intersect kimberlite in a spring drilling program that tested four high-priority anomalies.

The claims are wholly owned by GMD Resource (GMD-V) and comprise three blocks of claims, 120 km northwest of Yellowknife. Last September, GMD struck a deal with BHP to fly a 3,500-line-km airborne gravity survey at 100-metre line spacings over a portion of the property that contained five distinct indicator mineral trains at an agreed cost to GMD. BHP had the option of drilling, at its own cost, targets generated from the Falcon survey, in conjunction with previously flown magnetic and electromagnetic (EM) geophysical surveys. BHP would have earned an initial 35% interest in the Royce Group claims upon intersecting kimberlite.

The BHP deal came several months after De Beers Canada Exploration terminated an option agreement with GMD following two years of field work. De Beers had the right to earn a 51% interest by spending $16 million before April 30, 2004.

In the summer of 1999, De Beers initially collected 1,148 glacial till samples from across the claim blocks, following up on previous sampling by GMD. Helicopter-borne magnetic and EM surveys were flown at 150-metre line spacings over a large block of previously unsurveyed ground, and surveys were done at 50-metre line spacings over seven smaller areas of interest. De Beers drill-tested eight priority targets in early 2000 but encountered no kimberlite.

In the summer of 2000, De Beers collected a further 1,509 till samples, focusing on the southeastern portion of the property, where previous sampling returned anomalous indicator mineral counts in the Wheeler Lake area. GMD received all of the microprobe analysis from till sampling carried out in 2000, after De Beers dropped out of the joint venture.

GMD says the sampling results show five distinct mineral trains, four of which occur in the Wheeler Lake area, with the fifth lying 20 km to the north near Bessonette Lake. The Bessonette train can be traced for 6 km to an area covered by glacio-fluvial sediments where till sampling is restricted. This subtle indicator train is characterized by indicator mineral counts of up to 11 grains per sample and an ilmenite-to-garnet ratio of 2-to-1.

Recovered mineral grains include G10 garnets, two chromites greater than 63.5% Cr2O3, chrome diopsides as high as 3.42% Cr2O3 and ilmenites displaying diamond preservation chemistries. Further sampling 3 km up-ice yielded background mineral counts of zero to one grain per sample, suggesting the kimberlite source lies beneath the area covered by the glacio-fluvial material.

Two of the four Wheeler Lake trains lie parallel to one another on the west side of the lake, whereas the other two occur 5 and 10 km northeast of the lake. All four trains contain G10 garnets and favourable ilmenite chemistries. Mineral counts are as high as 71 grains per sample. Each train exhibits a distinctive mineral chemistry, suggesting multiple sources.

Last fall, GMD collected 106 till samples to define the potential source area of four of the trains. The fifth train terminates in Wheeler Lake.

BHP had no success drilling two strong coinciding EM targets in the Wheeler Lake area or two adjacent targets in the northern Bessonette area, 4 km up-ice from the head of the previously defined indicator mineral train. Three of the Falcon-generated gravity anomalies were found to be caused by deep water and deep overburden, resulting in gravity density contrasts. The fourth target, a magnetic high and moderate gravity anomaly, was explained by the intercept of magnetite-bearing granite and thick overburden.