Biogeochemistry as an aid to exploration for gold, platinum and palladium in the northern forests of Saskatchewan, Canada

Abstract

Twigs of shrub alders ( Alnus crispa and Alnus rugosa) tend to contain more gold than other common species in the northern forests of Saskatchewan. Alders are not cyanogenic, hence samples can be ashed to preconcentrate gold without loss of the metal as the volatile gold cyanide. Samples from mineralized zones commonly have over 50 ppb Au in the ash of the outermost 50 cm of alder twig. Background values are about 10 ppb Au. In the absence of alder from a given locality, other species may provide useful information on gold in the substrate. Examples are given of surveys using balsam fir ( Abies balsamea), white spruce ( Picea glauca) and black spruce ( Picea mariana). A reconnaissance scale survey in which alder twigs were collected at 2-km intervals has outlined an area, coincident with a major lithostructural domain, within which ashed twigs contained from 20 to 130 ppb Au ( x = 45 ppb Au ). In sharp contrast, alders in a neighbouring area contained less than 10 ppb Au. It appears that this regional approach to biogeochemical sampling in glaciated terrains may provide a quick appraisal of the gold potential of underlying bedrock. Platinum and palladium show a tendency to concentrate in twigs and trunk of black spruce ( Picea mariana) and jack pine ( Pinus banksiana), and in stems of labrador tea ( Ledum groenlandicum). Spruce was sampled close to a worked out nickel-copper deposit that contained 3000 ppb Pt and 6000 ppb Pd. The ashed twigs yielded up to 880 ppb Pt and 1350 ppb Pd, compared to background levels of below 10 ppb Pt and 2 ppb Pd.