High-grade massive sulphide boulders were discovered by Merrill Palmer at the base of a stranded glacier at the Mt. Henry Clay (MHC) prospect in 1983. The average grade of several types of boulders, as sampled by the United States Bureau of Mines (‘USBM”; Still 1984), are as follows:
26 Barite-sulphide (zinc-rich) boulders: 1% Cu, 0.4% Pb, 19.3% Zn, 38.2 g/t Ag, 0.22 g/t Au, and 20.6% Ba. A 6.0 ft (1.83 m) chip of the largest boulder barite-sphalerite boulder assayed 33% Zn, 2.5% Cu, and 5% Ba.
4 Boulders of massive pyrite and chalcopyrite: 5.18% Cu, 0.03% Pb, 1.00% Zn, 44.1 g/t Ag, tr. Au, and 0.12% Ba.
6 Boulders of mineralized volcanic host rocks (lacking barite): 2.83% Cu, 0.02 % Pb, 3.90% Zn, tr Au, 9.8 g/t Ag, and 0.41% Ba.
The mean grade of all the boulders sampled by the USBM: 18.5% Zn, 0.87% Cu, 1.3 oz/ton Ag, 0.02 oz/ton Au, and 5.9% Ba.
Thirteen holes, for a total of 2957 m, have been drilled at the MHC prospect in an attempt to find the source of the high-grade float. Seven holes were drilled by Kennecott Exploration, four holes were drilled by Granges Exploration Ltd, and two holes were drilled by Rubicon. The drilling identified two mineralized horizons beneath the Mt. Henry Clay glacier, but did not intersect mineralization with grades equivalent to those in the boulders. Several of the holes did intersect lower-grade mineralization within broad pyrite-sericite alteration zones, including 49.1 m of 0.19% Cu in hole K85-3, 10.7 m of 0.44% Cu in hole K84-2, and 36.6 m of 0.29% Cu in hole G89-9. Retreating ice led to the discovery of an intensely foliated chlorite-sericite alteration zone containing pyrite-chalcopyrite stockwork veins which was then mapped by Rubicon. It is speculated that this zone may represent footwall feeder mineralization and alteration to the horizon from which the high-grade boulders were sourced. An untested source for the high grade MHC float has been suggested to lie to the south-southeast and on trend with the alteration zone discussed above.
MOUNT HENRY CLAY (MHC) PROSPECT
