title: Formation of recent Pb-Ag-Au mineralization by potential sub-surface microbial activity.
abstract: Las Cruces is a base-metal deposit in the Iberian Pyrite Belt, one of the world's best-known ore provinces. Here we report the occurrence of major Pb-Ag-Au mineralization resulting from recent sub-surface replacement of supergene oxyhydroxides by carbonate and sulphide minerals. This is probably the largest documented occurrence of recent microbial activity producing an ore assemblage previously unknown in supergene mineralizing environments. The presence of microbial features in the sulphides suggests that these may be the first-described natural bacteriomorphs of galena. The low δ(13)C values of the carbonate minerals indicate formation by deep anaerobic microbial processes. Sulphur isotope values of sulphides are interpreted here as reflecting microbial reduction in a system impoverished in sulphate. We suggest that biogenic activity has produced around 3.1 × 10(9) moles of reduced sulphur and 10(10) moles of CO2, promoting the formation of ca. 1.19 Mt of carbonates, 114,000 t of galena, 638 t of silver sulphides and 6.5 t of gold.
authors.affiliation: Centro de Astrobiología. Ctra Ajalvir km. 4.5, Torrejon de Ardoz, 28850 Madrid, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: Tornos
authors.affiliation: Dpto. Mineralogía y Petrología, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU, 48080 Bilbao, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Velasco
authors.affiliation: Centro de Astrobiología. Ctra Ajalvir km. 4.5, Torrejon de Ardoz, 28850 Madrid, Spain.
authors.forename: César
authors.initials: C
authors.lastname: Menor-Salván
authors.affiliation: Laboratorio de Biogeoquímica de Isótopos Estables, Instituto Andaluz de Ciencias de la Tierra IACT (CSIC-UGR). Avda. de las Palmeras, 4, 18100 Armilla, Granada, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Delgado
authors.affiliation: U.S. Geological Survey, National Center, MS 954, Reston, Virginia 20192, USA.
authors.forename: John F
authors.initials: JF
authors.lastname: Slack
authors.affiliation: Cobre Las Cruces S.A., Gerena, 41860 Seville, Spain.
authors.forename: Juan Manuel
authors.initials: JM
authors.lastname: Escobar
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D002245:Carbon Dioxide / Q000737:chemistry; D002247:Carbon Isotopes / Q000737:chemistry*; D002254:Carbonates / Q000737:chemistry; D004783:Environmental Microbiology; D005843:Geography; D006046:Gold / Q000737:chemistry*; D060587:Groundwater; D007854:Lead / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D010103:Oxygen Isotopes / Q000737:chemistry; D012834:Silver / Q000737:chemistry*; D018030:Silver Compounds / Q000737:chemistry; D013053:Spectrophotometry; D013431:Sulfates / Q000737:chemistry; D013440:Sulfides / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature
chemical_list: D002247:Carbon Isotopes; D002254:Carbonates; D010103:Oxygen Isotopes; D018030:Silver Compounds; D013431:Sulfates; D013440:Sulfides; D002245:Carbon Dioxide; D007854:Lead; D012834:Silver; D006046:Gold; C013251:silver sulfide