Building the Las Cruces Gossan (SW Spain), Part I – Establishing a Geomicrobiological Model System

The Las Cruces gossan (Seville, Iberian Pyrite Belt, Spain) hosts a large cementation zone with abundant copper sulfides. Previous studies proposed that microbial sulfate reduction in the subsurface may have contributed to the secondary formation of these minerals^[1,2]. Here, we experimentally evaluated this hypothesis by investigating the potential role of sulfate reducing bacteria (SRB) in copper sulfide mineralization processes under conditions relevant to the Las Cruces gossan. More specifically, we established a geomicrobiological model system emulating the Las Cruces gossan subsurface environment. First, we exposed microbial enrichment cultures from sites characterized by moderate environmental conditions to 12.7 mg/L Cu at 40 °C for four weeks. Subsequent 16S rRNA sequencing revealed an increased relative abundance of several SRB (e.g. Desulfosporosinus, Desulfovibrio & Desulfitobacterium), which are also present in the Las Cruces gossan today^[2]. In further enrichments, different incubation temperatures and Cu concentrations were tested (see also abstract by Stoll et al.). We found that the SRB tolerated Cu concentrations of up to 38 mg/L at 40 °C. Subsequent SEM-EDS analysis revealed mineral-encrusted cell-like structures, together with colocalizations of Cu and S at or near these structures, potentially suggesting microbially mediated copper sulfide formation during the experiments. Although the observed mineralization could not be attributed to specific SRB, the results of our study lend support to the hypothesized microbial origin of copper sulfides in the Las Cruces gossan.

References

[1] Tornos et al. (2014) Nat. Commun. 5: 4600.

[2] Tornos et al. (2018) Geology 47 (2): 143-146.