Partners
Drilling at the project, situated in Nunavut, has indicated substantial new mineralization at three gold deposits. But the program has also prompted Miramar and Hope Bay to tighten up the resource estimates to reflect some of the geological controls that have come to light.
Two of the property’s three defined gold deposits emerged with resource estimates substantially smaller than those calculated by the previous owner,
The biggest of the deposits, Boston, which lies near the southern end of the belt, about 60 km south of tidewater, has 1.3 million measured and indicated tonnes with a grade of 15.2 grams gold per tonne. A further 2.6 million tonnes grading 10.9 grams is in the inferred category.
At Doris North, near the northern end of the belt, the partners have outlined measured and indicated resources of 710,000 tonnes grading an average of 21.2 grams per tonne, and inferred resources of 957,000 tonnes grading 16.9 grams. In the Doris Central deposit, 418,000 tonnes grading 14.9 grams per tonne are measured and indicated, and 114,000 tonnes grading 16 grams are inferred.
The Doris mineralization lies below Doris Lake, and, accordingly, the partners have also broken out a separate resource — classified as inferred — in a 30-metre sill pillar below the lake. That pillar holds 207,000 tonnes grading 22.4 grams per tonne.
At the Madrid deposit, about 8 km south of Doris, the measured and indicated resource is estimated at 328,000 tonnes grading 7.3 grams, with additional inferred resources of 744,000 tonnes running 9.3 grams.
The estimated resource at Boston has shrunk considerably from the one calculated by BHP, which showed 5.7 million tonnes grading 13.1 grams gold. The new resource — 3.9 million tonnes grading 12.3 grams in all categories — reflects more conservative assumptions, including a cutoff grade of 5 grams per tonne and a practice of capping high assays at grades between 50 and 175 grams.
Similarly, where BHP had calculated a large, low-grade resource of 5 million tonnes grading 4.3 grams per tonne at Madrid, the partners have imposed a 5-gram cutoff grade and a 30-to-40-gram cap on gold assays, leaving a much smaller resource of 1.1 million tonnes grading 8.7 grams.
The drilling campaign of the past field season poked holes in some theories as well as in the shear zone; the partners’ knowledge of the structural behaviour of the Boston host structures has led them to make more conservative projections about how continuous the mineralization in that deposit is.
Some deeper resources included in BHP’s resource estimate on Boston were also dropped out of the new calculation, because sketchy survey data for the holes put the true depth of the intersections in doubt.
The geological picture of Boston that is now emerging is of subvertical “shoot” zones in three nearly vertical, north-striking shears: B2, B3 and B4. The main zone, B2, carries much the greater part of the mineralization, and most of the balance is in B3, a parallel shear 20-50 metres east of B2.
The B4 shear, 50 metres east of B3, which carries only an inferred resource of 283,000 tonnes grading 11.4 grams per tonne, saw no drilling in the past field season. But structural re-interpretations of B2 and B3 have led the partners to postulate that the B4 zone may open toward the south.
The increased Doris resource (2.4 million tonnes grading 18.3 grams, against a BHP-calculated resource of 2.1 million tonnes at 17.8 grams) includes substantial new mineralization drilled off in 2000 and sets aside a sill pillar beneath Doris Lake.
The two companies also announced they had drilled mineralized intersections north and south of the Boston deposit, though these are not included in the recent resource estimates. Of seven holes drilled on the northern extension of the B2 shear zone, six intersected gold-mineralized zones ranging from 0.5 to 1.8 metres in width, with grades of between 5.1 and 16 grams per tonne, and a high-grade intersection of 0.6 metres grading 283 grams.
To the south, six holes encountered mineralization in the B2 shear, mainly over true widths of 0.3-1.1 metres but frequently in multiple zones. Grades were highly variable, from 5 to 157 grams per tonne, but clustered in the 10-to-30-gram range.
Two “bonanza” intersections — a 0.4-metre section grading 157 grams, and a 1.1-metre width grading 153 grams — also came out of this round of drilling. These and other high-grade intersections at the southern end, including a 4.2-metre core length grading 88.8 grams per tonne, are leading the partners to believe that there may be additional high-grade “shoots” along the shear zone south of the known mineralization, either near-vertical or plunging steeply to the south.
One of the southern holes also intersected the parallel B3 mineralized shear, finding 13.7 grams over 2 metres, 84.7 grams over 1.2 metres, and 39.1 grams over 2.5 metres. The intersections represented true widths of 0.8-1.7 metres.
About 200 metres north of the deposit, an exploration hole intersected a series of mineralized zones the partners have correlated with the B3 shear. Grades ranged from 5.9 to 7.9 grams gold, over true widths of 0.5-1.9 metres.
Surface drilling on the Domani showing, a carbonate-facies iron formation about 3 km south of the main Boston deposit, tested part of a shear zone underlying an area where earlier bedrock and soil sampling had revealed high concentrations of gold.
Grades encountered in the shear ranged from 1.4 to 4.5 grams per tonne, over core lengths of 0.5-1.3 metres; the zone is thought to have a horizontal width of 0.3-0.8 metre. The gold grades in the core did not match some of the higher-grade rock samples, and the partners are planning further drilling to see whether there are higher-grade mineralized zones in the structure.
The Hope Bay property is 650 km northeast of Yellowknife, N.W.T.
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