Special Issue "Geomicrobiology and Biogeochemistry of Precious Metals"

A special issue of Minerals (ISSN 2075-163X).

Deadline for manuscript submissions: closed (31 January 2018)

Special Issue Editors

Guest Editor
Dr. Frank Reith

ARC Future Fellow, School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
Website1 | Website2 | E-Mail
Interests: geomicrobiology; biogeochemistry; microbial ecology; OMICS; forensics; modelling; biomineralisation; gold; platinum-group-elements; uranium; synchrotron applications; bacterial metal resistance
Guest Editor
Dr. Jeremiah Shuster

School of Biological Sciences, University of Adelaide, Adelaide, South Australia 5005, Australia
Website | E-Mail
Interests: geomicrobiology; biogeochemistry; gold; metal cycling; microbe–mineral interactions; electron microscopy; biomineralisation; microfossils

Special Issue Information

Dear Colleagues,

Precious metals continue to have economic and sociocultural importance as their usage evolves and diversifies over time. Since antiquity, gold, silver and later platinum-group-elements have been valued as currencies and stored-investment commodities. Today, the industrial application of precious metals is increasing with developing scientific and technological innovations. For example, the discovery of microbial resistance mechanisms to highly toxic mobile precious metals can be used in biosensors and bioindicators for gold, silver and platinum, thereby expanding biotechnology into mineral exploration and hydrometallurgy. From a geochemical perspective, the in situ cycling and transformation of precious metals is a dynamic balance between dissolution-, transport- and re-precitation processes that are catalysed by the biosphere. Microbial weathering mobilises precious metals by releasing metals ‘trapped’ within minerals and by solubilising these metals via oxidation-promoting complexation. Higher organisms such as plants mitigate precious metal mobility within soils as well as within hydrological regimes. The cycling of precious metals is completed as microbes destabilise soluble metal complexes through bioprecipitation and biomineralisation forming secondary colloids, crystalline microparticles, as well as macroscopic grains and even nuggets.

This Special Issue aims to bring together studies in the areas of geomicrobiology and biogeochemistry of precious metals. Contributions that demonstrate or enhance the fundamental understanding of how biogenic process affect precious metal cycling of or how organisms are effected by mobile precious metals are invited. We especially encourage studies highlighting biological applications for precious metal exploration, mineral/ore processing and bioremediation to encourage sustainable use of resources.

Dr. Frank Reith
Dr. Jeremiah Shuster
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1200 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Geomicrobiology
  • Biogeochemistry
  • Precious metals
  • Gold, silver, platinum-group-elements
  • Prokaryotes
  • Fungi
  • Plants
  • Biomineralisation
  • Metal-resistance
  • Exploration
  • Metallurgy
  • Bioremediation

Published Papers (4 papers)

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Research

Open AccessArticle Biological and Geochemical Development of Placer Gold Deposits at Rich Hill, Arizona, USA
Minerals 2018, 8(2), 56; doi:10.3390/min8020056
Received: 18 January 2018 / Revised: 2 February 2018 / Accepted: 5 February 2018 / Published: 8 February 2018
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Abstract
Placer gold from the Devils Nest deposits at Rich Hill, Arizona, USA, was studied using a range of micro-analytical and microbiological techniques to assess if differences in (paleo)-environmental conditions of three stratigraphically-adjacent placer units are recorded by the gold particles themselves. High-angle basin
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Placer gold from the Devils Nest deposits at Rich Hill, Arizona, USA, was studied using a range of micro-analytical and microbiological techniques to assess if differences in (paleo)-environmental conditions of three stratigraphically-adjacent placer units are recorded by the gold particles themselves. High-angle basin and range faulting at 5–17 Ma produced a shallow basin that preserved three placer units. The stratigraphically-oldest unit is thin gold-rich gravel within bedrock gravity traps, hosting elongated and flattened placer gold particles coated with manganese-, iron-, barium- (Mn-Fe-Ba) oxide crusts. These crusts host abundant nano-particulate and microcrystalline secondary gold, as well as thick biomats. Gold surfaces display unusual plumate-dendritic structures of putative secondary gold. A new micro-aerophilic Betaproteobacterium, identified as a strain of Comamonas testosteroni, was isolated from these biomats. Significantly, this ‘black’ placer gold is the radiogenically youngest of the gold from the three placer units. The middle unit has well-rounded gold nuggets with deep chemical weathering rims, which likely recorded chemical weathering during a wetter period in Arizona’s history. Biomats, nano-particulate gold and secondary gold growths were not observed here. The uppermost unit is a pulse placer deposited by debris flows during a recent drier period. Deep cracks and pits in the rough and angular gold from this unit host biomats and nano-particulate gold. During this late arid period, and continuing to the present, microbial communities established within the wet, oxygen-poor bedrock traps of the lowermost placer unit, which resulted in biological modification of placer gold chemistry, and production of Mn-Fe-Ba oxide biomats, which have coated and cemented both gold and sediments. Similarly, deep cracks and pits in gold from the uppermost unit provided a moist and sheltered micro-environment for additional gold-tolerant biological communities. In conclusion, placer gold from the Devils Nest deposits at Rich Hill, Arizona, USA, preserves a detailed record of physical, chemical and biological modifications. Full article
(This article belongs to the Special Issue Geomicrobiology and Biogeochemistry of Precious Metals)
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Open AccessArticle Immobilisation of Platinum by Cupriavidus metallidurans
Minerals 2018, 8(1), 10; doi:10.3390/min8010010
Received: 1 December 2017 / Revised: 20 December 2017 / Accepted: 26 December 2017 / Published: 5 January 2018
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Abstract
The metal resistant bacterium Cupriavidus metallidurans CH34, challenged with aqueous platinous and platinic chloride, rapidly immobilized platinum. XANES/EXAFS analysis of these reaction systems demonstrated that platinum binding shifted from chloride to carboxyl functional groups within the bacteria. Pt(IV) was more toxic than Pt(II),
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The metal resistant bacterium Cupriavidus metallidurans CH34, challenged with aqueous platinous and platinic chloride, rapidly immobilized platinum. XANES/EXAFS analysis of these reaction systems demonstrated that platinum binding shifted from chloride to carboxyl functional groups within the bacteria. Pt(IV) was more toxic than Pt(II), presumably due to the oxidative stress imparted by the platinic form. Platinum immobilisation increased with time and with increasing concentrations of platinum. From a bacterial perspective, intracellular platinum concentrations were two to three orders of magnitude greater than the fluid phase, and became saturated at almost molar concentrations in both reaction systems. TEM revealed that C. metallidurans was also able to precipitate nm-scale colloidal platinum, primarily along the cell envelope where energy generation/electron transport occurs. Cells enriched in platinum shed outer membrane vesicles that were enriched in metallic, colloidal platinum, likely representing an important detoxification strategy. The formation of organo-platinum compounds and membrane encapsulated nanophase platinum, supports a role for bacteria in the formation and transport of platinum in natural systems, forming dispersion halos important to metal exploration. Full article
(This article belongs to the Special Issue Geomicrobiology and Biogeochemistry of Precious Metals)
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Open AccessArticle Biogeochemical Cycling of Silver in Acidic, Weathering Environments
Minerals 2017, 7(11), 218; doi:10.3390/min7110218
Received: 15 September 2017 / Revised: 1 November 2017 / Accepted: 6 November 2017 / Published: 10 November 2017
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Abstract
Under acidic, weathering conditions, silver (Ag) is considered to be highly mobile and can be dispersed within near-surface environments. In this study, a range of regolith materials were sampled from three abandoned open pit mines located in the Iberian Pyrite Belt, Spain. Samples
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Under acidic, weathering conditions, silver (Ag) is considered to be highly mobile and can be dispersed within near-surface environments. In this study, a range of regolith materials were sampled from three abandoned open pit mines located in the Iberian Pyrite Belt, Spain. Samples were analyzed for Ag mineralogy, content, and distribution using micro-analytical techniques and high-resolution electron microscopy. While Ag concentrations were variable within these materials, elevated Ag concentrations occurred in gossans. The detection of Ag within younger regolith materials, i.e., terrace iron formations and mine soils, indicated that Ag cycling was a continuous process. Microbial microfossils were observed within crevices of gossan and their presence highlights the preservation of mineralized cells and the potential for biogeochemical processes contributing to metal mobility in the rock record. An acidophilic, iron-oxidizing microbial consortium was enriched from terrace iron formations. When the microbial consortium was exposed to dissolved Ag, more than 90% of Ag precipitated out of solution as argentojarosite. In terms of biogeochemical Ag cycling, this demonstrates that Ag re-precipitation processes may occur rapidly in comparison to Ag dissolution processes. The kinetics of Ag mobility was estimated for each type of regolith material. Gossans represented 0.6–146.7 years of biogeochemical Ag cycling while terrace iron formation and mine soils represented 1.9–42.7 years and 0.7–1.6 years of Ag biogeochemical cycling, respectively. Biogeochemical processes were interpreted from the chemical and structural characterization of regolith material and demonstrated that Ag can be highly dispersed throughout an acidic, weathering environment. Full article
(This article belongs to the Special Issue Geomicrobiology and Biogeochemistry of Precious Metals)
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Open AccessArticle Mineralogy and Geochemistry of Biologically-Mediated Gold Mobilisation and Redeposition in a Semiarid Climate, Southern New Zealand
Minerals 2017, 7(8), 147; doi:10.3390/min7080147
Received: 21 July 2017 / Revised: 11 August 2017 / Accepted: 13 August 2017 / Published: 16 August 2017
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Abstract
Detrital gold in Late Pleistocene-Holocene placers has been chemically mobilised and redeposited at the micron scale by biologically-mediated reactions in groundwater. These processes have been occurring in a tectonically active semiarid rain shadow zone of southern New Zealand and are probably typical for
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Detrital gold in Late Pleistocene-Holocene placers has been chemically mobilised and redeposited at the micron scale by biologically-mediated reactions in groundwater. These processes have been occurring in a tectonically active semiarid rain shadow zone of southern New Zealand and are probably typical for this type of environment elsewhere in the world. The chemical system is dominated by sulfur, which has been derived from basement pyrite and marine aerosols in rain. Detrital and authigenic pyrite is common below the water table, and evaporative sulfate minerals are common above the fluctuating water table. Pyrite oxidation was common but any acid generated was neutralised on the large scale (tens of metres) by calcite, and pH remained circumneutral except on the small scale (centimetres) around pyritic material. Metastable thiosulfate ions were a temporary product of pyrite oxidation, enhanced by bacterial mediation, and similar bacterial mediation enhanced sulfate reduction to form authigenic pyrite below the water table. Deposition of mobilised gold resulted from localised variations in redox and/or pH, and this formed overgrowths on detrital gold of microparticulate and nanoparticulate gold that is locally crystalline. The redeposited gold is an incidental byproduct of the bacterially-enhanced sulfur reactions that have occurred near to the fluctuating sulfide-sulfate redox boundary. Full article
(This article belongs to the Special Issue Geomicrobiology and Biogeochemistry of Precious Metals)
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