A SOIL GEOCHEMISTRY ORIENTATION STUDY OVER THE GIANT PEBBLE CU-AU-MO PORPHYRY DEPOSIT, ALASKA
Soil samples were collected along three traverses across the West and East zones of the Pebble deposit and were analyzed by the following commonly-used and proprietary geoanalytical methods: (1) de-ionized water leach; (2) BioLeach; (3) Enzyme Leach; (4) TerraSol leach; (5) Ionic Leach; (6) Mobile Metal Ion (MMI) extraction; (7) cold hydroxylamine hydrochloride leach; (8) sodium pyrophosphate leach; (9) aqua regia partial digestion; (10) 4-acid near-total digestion; (11) sodium peroxide sinter total digestion; plus (12) soil gas hydrocarbon analyses.
The interpretation of this complex multi-element dataset derived from multiple analytical techniques is challenging and ongoing. All of the analytical methods used show anomalous single-element distribution patterns in some soils over the near-surface Pebble West zone and most methods also show possible indications of the deeply buried Pebble East zone. The most significant patterns were seen in Ag, As, Au, Cu, Mo, Re, Sb, Tl, U, and V concentrations; although some of these elements may be related more to the cover rocks than to buried mineralization. The mechanisms for migrating elements from depth into the soil profile are yet to be determined although there is some evidence for ‘leakage’ along fault zones.