Supergene gold transformation: Biogenic secondary and nano-particulate gold from arid Australia

Fairbrother, Lintern; Brugger, Joël; Shapter, Joseph G.; Laird, J.S.; Southam, Gordon; Reith, Frank

doi:10.1016/j.chemgeo.2012.05.025

Cited by 84 publications

(39 citation statements)

References 43 publications

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“…Our studies in combination with works of other authors led to the understanding that the detrital and aggregation models for gold grain and nugget formation need to be combined into a unified formation model that covers all alluvial and lateritic gold ( Figure 5; e.g., [11,13,14,24,[32][33][34][35][36][37][38][39]. Hence, the more than 100 year lasting debate concerning the formation of gold grains and nuggets in surface environments was finally resolved.…”

Section: A Unified Model For Gold Grain Formation and Implications Fomentioning

confidence: 96%

“…This continuous release of nano-particulate gold can explain the high mobility of gold in many near surface environments, which leads to the formation of secondary gold deposits [40] and the development of geochemical halos around buried mineralization even in transported cover [11,14]. Model of processes responsible for the (trans)formation of gold grains in supergene environments; bright yellow is high fineness gold (>95 wt %), orange is gold-silver alloy, black is biofilm (after [35]). …”

Section: A Unified Model For Gold Grain Formation and Implications Fomentioning

confidence: 99%

“…To assess if geobiological processes play a role for the transformations of gold grains, grains were collected from eight arid sites in three Australian gold provinces, i.e., Lawlers (Yilgarn Craton, Western Australia), Tanami (Northern Territory), and Flinders Ranges (South Australia; [35]). Sites were chosen based on contrasting deposit styles, i.e., primary underground and epithermal deposits as well as secondary eluvial-, colluvial-and alluvial placers at increasing distances from primary mineralization.…”

Section: Arid Environmentsmentioning

confidence: 99%

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Geobiological Cycling of Gold: From Fundamental Process Understanding to Exploration Solutions

et al. 2013

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Microbial communities mediating gold cycling occur on gold grains from (sub)-tropical, (semi)-arid, temperate and subarctic environments. The majority of identified species comprising these biofilms are β-Proteobacteria. Some bacteria, e.g., Cupriavidus metallidurans, Delftia acidovorans and Salmonella typhimurium, have developed biochemical responses to deal with highly toxic gold complexes. These include gold specific sensing and efflux, co-utilization of resistance mechanisms for other metals, and excretion of gold-complex-reducing siderophores that ultimately catalyze the biomineralization of nano-particulate, spheroidal and/or bacteriomorphic gold. In turn, the toxicity of gold complexes fosters the development of specialized biofilms on gold grains, and hence the cycling of gold in surface environments. This was not reported on isoferroplatinum grains under most near-surface environments, due to the lower toxicity of mobile platinum complexes. The discovery of gold-specific microbial responses can now drive the development of geobiological exploration tools, e.g., gold bioindicators and biosensors. Bioindicators employ genetic markers from soils and groundwaters to provide information about gold mineralization processes, while biosensors will allow in-field analyses of gold concentrations in complex sampling media.

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Section: A Unified Model For Gold Grain Formation and Implications Fomentioning

confidence: 96%

Section: A Unified Model For Gold Grain Formation and Implications Fomentioning

confidence: 99%

Section: Arid Environmentsmentioning

confidence: 99%

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Geobiological Cycling of Gold: From Fundamental Process Understanding to Exploration Solutions

et al. 2013

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“…Other authors have rejected low-temperature or biogeochemical nugget growth and suggested an abiological, high-temperature origin within lode deposits [10]. The recent consensus of many workers is that the processes of both primary and secondary models likely play a role in placer gold formation, with the specific contribution of each end member varying from location to location [3,[11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Biological and Geochemical Development of Placer Gold Deposits at Rich Hill, Arizona, USA

et al. 2018

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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.

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“…The research involves the use of a synchrotron and transmission electron microscopy coupled with microarrays to detect the proteins that catalyse the reactions. Reith's team has also developed a method based on high-performance liquid chromatography and inductively coupled mass spectrometry to measure the complexed forms -such as gold chloride or gold thiosulphate -in which gold exists in aqueous solutions 3 . "This is important," Reith says, "because the type of ligand the gold is complexed with determines the mobility, as well as the environmental toxicity, of the complexes, which in turn is important for the biochemical reaction of the bacteria. "…”

Section: A Richer Harvestmentioning

confidence: 99%

Microbiology: There's gold in them there bugs

Gwynne¹

2013

Nature

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Supergene gold transformation: Biogenic secondary and nano-particulate gold from arid Australia

Cited by 84 publications

References 43 publications

Geobiological Cycling of Gold: From Fundamental Process Understanding to Exploration Solutions

Geobiological Cycling of Gold: From Fundamental Process Understanding to Exploration Solutions

Biological and Geochemical Development of Placer Gold Deposits at Rich Hill, Arizona, USA

Microbiology: There's gold in them there bugs

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