A COMPARISON OF LITHOGEOCHEMICAL AND BIOGEOCHEMICAL PATTERNS ASSOCIATED WITH GOLD MINERALIZATION IN MOUNTAINOUS TERRAIN OF SOUTHERN BRITISH-COLUMBIA

Analyses of rock and tree tissue samples collected from an area surrou nding gold mineralization at tile inactive Carolin mine show geochemic al distribution patterns with some striking similarities and significa nt differences. Lithogeochemical sampling outlines a zone, several hun dred meters across, in which hydrothermally altered rocks are enriched in Na and depleted in K and Ba. Within this zone lies a 40 m wide are a where the rocks are enriched sporadically in Au and As. The Au, As, and Na biogeochemical halos outlined by twigs and needles of the most common tree in the survey area, Pacific silver fir (Abies amabilis), a re significantly larger in areal extent than the respective lithogeoch emical halos of these elements. This is a result of physical and chemi cal downslope dispersion of these elements in tile colluvium and groun d water. Differences in the biogeochemical and lithogeochemical patter ns of Ba and Cr are attributed to the availability of these elements t o the plant roots: in the hydrothermally altered rocks, Ba and Cr are more readily released from the crystal structure of such minerals as s ericite and fuchsite than in the nonaltered rocks where these elements are roost likely contained in K feldspar and chromite. This comparati ve study indicates that the biogeochemical method is a valuable approa ch to gold exploration in the mountainous terrain of British Columbia, because trees can integrate and amplify the geochemical signatures of rocks, surficial deposits, and ground water and give rise to large an d intense anomalies derived from narrow zones of mineralization. Sampl ing and analysis of tree tissues is a cost-efficient method to identif y areas of metal enrichment. At the Carolin mine, reconnaissance-levee sampling at a density of a few trees per square kilometer would have been sufficient to identify the area of anomalously high Au, As, and N a concentrations. Reconnaissance biogeochemical surveys at this sample density in rugged terrain may assist in identifying valleys hosting m ineralization that subcrops beneath a veneer of surficial deposits, an d thereby, provide a focus for followup prospecting by lithogeochemica l or other methods of exploration.