A GEOMICROBIOLOGICAL STUDY OF SOILS COLLECTED FROM AURIFEROUS AREAS OF ARGENTINA

Geomicrobial and geochemical studies were carried out in Argentina (Pa tagonia, Chubut Province) on four Au and polymetallic sulfide vein-typ e deposits. A horizon soils were analyzed for Bacillus reacting to lec ithin [Bacillus L.(+)], Au and 12 additional elements. In two of the f our sampling sites, exhibiting known and relatively simple mineralized structures, Bacillus L.(+) populations are clearly related to Au, As, Pb, Zn, Cu-sulfide mineralization. In areas containing more complex m ineralized structures, the spatial relationship between Bacillus L.(+) and metals in the A horizon is more difficult to interpret. Results o f a factor analysis performed on all analytical data (n = 130) suggest a partial relationship between Bacillus L.(+) and Au-As-Y pedochemica l associations located above known Au mineralization. Bacillus L.(+) w as first analyzed in Argentina in December 1994 and re-analyzed in Bel gium five to seven months later. Most of the Bacillus contents (85%) o f the Belgian tests are higher than those determined in Argentina. The present results and data of a previous study in Mexico (Melchior et a l., 1994a; Melchior et al., 1994b) suggest that this may be the result of temperature variations during sample storage between periods of mi crobial analysis. From a strictly analytical point of view, the geomic robial method is not an accurate, reproducible technique. However, Bac illus L.(+) can be used as a microbiological indicator of Au and polym etallic mineralization at a reconnaissance-level regional survey. At a local scale, this microbiological tool should be combined with classi cal exploration techniques such as soil geochemistry. It is recommende d that the collection of all A horizon samples (for microbial study) s hould be accompanied by B or C horizon soils (for potential geochemica l study, after prioritizing targets) so that a second field sampling p rogram does not have to be undertaken.