The Macmillan Pass shale-hosted mineral district is located 400 km northeast of Whitehorse, Yukon Territory. On the Jason property, surface exploration based primarily on geological mapping and soil geochemistry has led to the discovery of three massive to laminated deposits rich in lead, zinc, silver, barium and iron. To date, diamond drilling has outlined geological reserves of 14.1 million tonnes grading 7.09% Pb, 6.57% Zn and 79.9 g/t Ag.
One of these deposits, known as the South Zone, exhibits classical zonation; a high-grade massive to thick-banded lead-rich facies is interpreted as being proximal to a vent source. A well-laminated facies consisting of layers of chert, barite and sulphides is more distal from the vent. Pb/(Pb+Zn) ratios decrease outward from the presumed vent area. A program of systematic sampling of selected drill cores from the wall rocks of the South Zone was instituted to identify geochemical halos which could be attributed to ore emplacement and which could be used as a predictive guide to new ore. Significant copper and arsenic concentrations are restricted to the footwall rocks in the immediate vicinity of the presumed vent. A manganese deficiency in hanging-wall rocks immediately above the sulphide-rich portion of the South Zone is noted. Barium concentrations well above the regional background occur in hanging-wall rocks in excess of 50 m above the distal or pooling facies of the South Zone. The shape of the barium diffusion curve into the hanging wall can be used as a guide to the source of the barium-rich solutions, and to the direction of the greatest brine pooling