A drilling program at the ATW Mackay Lake diamond property, south of Lac de Gras in the Northwest Territories, is testing three geophysical targets. The effort is designed to locate the source of a prominent kimberlite indicator mineral train.
Situated mid-way between the Diavik and Snap Lake projects, ATW Mackay Lake covers 65 sq. km. It is held 75% by ATW Resources, 15% by
Kennecott Canada Exploration relinquished its interest in the property in May 2001. However, should a diamondiferous kimberlite be found, the
Kennecott first optioned the ATW property in 1992, whereupon it carried out till sampling and geophysical surveying. The effort led to discovery of the barren TR107 kimberlite pipe in 1994. Since its chemistry did not match the indicator minerals being recovered a few kilometres to the north, Kennecott concentrated its efforts on further defining that train, which was traced over a distance of 20 km to the shores of Mackay Lake.
In February 1998, Kennecott used a reverse-circulation rig to sample the till beneath the lake. A series of holes were drilled perpendicular to the glacial ice-flow. The last two lines were drilled 5 km apart on the lake. The most westerly line of the two had four holes 100 metres apart, with elevated counts of pyrope garnets in the basal till. Three of the holes yielded elevated counts of olivine, with one hole returning more than 50 grains.
About 5 km to the east, up-ice, the last-drilled holes were essentially blank, indicating that the potential source of the indicator minerals lies somewhere between the two lines. A microprobe analysis performed on the indicator minerals by Mineral Services International indicated that the assemblage is derived from a kimberlite source that is at least moderately diamond-bearing. The indicator mineral assemblage included 74 olivine grains, 18 orthopyroxenes, 127 clinopyroxenes and 198 garnets, but no kimberlitic ilmenite or chromite. G10 garnets comprise 16-20% of the various samples, with moderate Cr2O3 G10s well-represented.
After re-acquiring Kennecott’s interest, ATW Resources subjected the area of interest to airborne geophysics and outlined two circular targets, plus one long linear resistivity low closely associated with one of the pipe-like features. Follow-up ground geophysics further defined the three targets.
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