BACTERIA AS MEDIATORS OF COPPER SULFIDE ENRICHMENT DURING WEATHERING

Supergene chalcocite enrichment during weathering is an economically v ital natural process that may lead to severalfold increases in the cop per content of sulfide deposits. A scanning electron microscope study of chalcocite (Cu2S) from major enriched copper deposits in northern C hile revealed myriad bacterioform bodies in original growth positions near replacement interfaces with remnant hypogene sulfide grains. Thes e minute (0.03 to 0.2 micrometers) chalcocite bodies are interpreted a s fossilized and metallized nannobacteria that promoted the fixation o f mobilized copper ions. Bacterial activity may thus be a fundamental factor in supergene enrichment of copper deposits.