GEOMICROBIOLOGY APPLIED TO MINERAL EXPLORATION IN MEXICO

This paper presents the main results of a study that validates the use of a geomicrobiological method in the search for polymetallic, and, p articularly, Au mineralizations. Six different types of mineralization were selected in Mexico. The spatial occurrence of Bacillus cereus an d anomalous metal concentrations in the soils suggest to us that the B . cereus content is selectively related to mineralization and may be t o some extent proportional to the total content of chalcophile element s in subsurface mineralization. A spatial interval or ''offset'' betwe en elevated B. cereus contents and high metal contents in mineralized soils was observed. A possible explanation for this spatial interval i s a local toxic effect that exceeds the capacity of the soil microflor a to adapt; and/or (conversely) a reduced bioavailability mainly cause d, among other factors, by the dominance of chalcophile metals in Fe-M n oxides/hydroxides. The reproducibility of the method was acceptable if tests were done on the same day. Generally, B. cereus counts were o bserved to decrease with length of storage throughout the study period . Although B. cereus distributions do not appear to be an adequate sub stitute for geochemical analysis, the qualitative data were sufficient ly significant to suggest that the method be further investigated. At present, B. cereus appears to be more useful as a complementary techni que for exploration; although some results suggest the potential of th e bacterial method to search for blind polymetallic mineralizations.