Authigenic realgar and gold in dynamic redox gradients developed on historic mine wastes, New Zealand

Kerr, Gemma; Craw, Dave; Trumm, D.; Pope, James Gray

doi:10.1016/j.apgeochem.2018.08.009

Cited by 17 publications

(25 citation statements)

References 52 publications

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“…Potential Au reducing agents to precipitate spherical AuNPs are manifold ( 3 , 17 , 40 , 41 ). This process is enabled because Au 3+ is a strong oxidant so that it can be reduced by almost any other metal or metal ion ( 3 , 42 , 43 ).…”

Section: Discussionmentioning

confidence: 99%

Natural corrosion-induced gold nanoparticles yield purple color of Alhambra palaces decoration

Cardell

Guerra-Tschuschke

2022

Sci. Adv.

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Despite its fame as a chemically inert noble metal, gold (alloys) may suffer degradation under specific scenarios. Here, we show evidence of electrochemically corroded gilded tin plasterwork in the Alhambra (Granada, Spain) driving spontaneously made gold nanospheres with the optimal size (ca. 70 nm) to impart purple color at the surface. Purple gold on damaged artworks is found sparsely, and its formation is not fully explained yet. We prove that our decayed gold/silver-tin ornament is due to sequential/coexisting galvanic corrosion, differential aeration corrosion, and dealloying of nonperfectly bonded and defect-based metals. Damage is enhanced by exposure to a chloride-rich atmosphere. A white gypsum coat applied during the 19th century to overlap the unaesthetic gilding assists observation of the gold-based purple color. Our work demonstrates gold dissolution, millimetric migration, physical translocation, and deposition as secondary pure gold nanospheres over a centurial time scale under natural environmental conditions.

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Section: Discussionmentioning

confidence: 99%

Natural corrosion-induced gold nanoparticles yield purple color of Alhambra palaces decoration

Cardell

Guerra-Tschuschke

2022

Sci. Adv.

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“…Dissolution of scorodite causes localised acidification, while incursion of oxygenated rainwater during frequent major rain events in the area can change pH and Eh (Fig. 13a; Davies et al , 2011; Kerr et al , 2018).…”

Section: Discussionmentioning

confidence: 99%

“…More detailed textural and geochemical observations were made using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) on polished thin sections and freshlybroken surfaces. Details regarding SEM instrument parameters and settings are given in Kerr et al, (2018) and Henne et al, (2019aHenne et al, ( , 2020. Synchrotron X-ray fluorescence microscopy was used on selected samples to obtain relative element-distribution maps of transition metals, with detection limits of ∼100 ppm.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…These tailings were deposited in a shallow (~10 m) depression that has been water-saturated for >80 years and subjected to regular heavy rain events in a wet climate (rainfall >2000 mm/year). The deposit hosts abundant organic matter, including mosses, algae, and bacteria, and some woody material from the surrounding rainforest (Kerr et al, 2018). The most chemically-reduced cementing mineral, realgar, occurred principally on decomposing wood fragments within the tailings (Fig.…”

Section: Laminated Precipitates In Historic Mine Wastesmentioning

confidence: 99%

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Biogeochemical formation of metalliferous laminations in surficial environments

Henne

Craw

Hamilton

et al. 2021

MinMag

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Finely laminated (cm–μm scale) metalliferous precipitates are widespread in the surficial environment, especially around mineral deposits and reflect biogeochemical processes that can pervade near-surface environments on a larger scale. Examples in this paper involve precipitates of the transition metals Fe, Cu and Mn with minor Co, Ni, V and Zn; the metalloids As and Sb; and authigenic Au. Mobility and re-precipitation are driven primarily by geochemical disequilibrium, especially with respect to pH and redox states, that arises from complex interactions between biological processes, geological processes, and variations in the surrounding environment. Different degrees of chemical disequilibrium arise on small spatial scales on time scales of days to millennia. Interactions between biota, waters and rocks in these small near-surface settings affect the biogeochemical environments. Sulfur- and iron-oxidising bacteria are common biogeochemical agents associated with sulfide-bearing lithologies, but localised reductive environments can also develop, leading to gradients in pH and redox state and differential metal mobility. In general, there is commonly a spatial separation of Fe-rich precipitates from those with Cu and Mn, and other transition metals also follow Cu and Mn rather than Fe. Metalloids As and Sb have a strong affinity for Fe under oxidising conditions, but not under more reducing conditions. However, complex biogeochemical parageneses of laminated metalliferous deposits preclude prediction of finer formation details. The textures, mineral species, and metal associations within these deposits are likely to be encountered in all facets of mineral deposit development: initial exploration activity of near-surface locations, mining of shallow portions of orebodies, especially supergene zones, and downstream environmental management with respect to discharging metalliferous waters.

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Realgar (As4S4) bioprecipitation in microcosm fed by a natural groundwater and organic matter

Falteisek

Duchoslav

Drahota

2019

Environ Sci Pollut Res

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Authigenic realgar and gold in dynamic redox gradients developed on historic mine wastes, New Zealand

Cited by 17 publications

References 52 publications

Natural corrosion-induced gold nanoparticles yield purple color of Alhambra palaces decoration

Natural corrosion-induced gold nanoparticles yield purple color of Alhambra palaces decoration

Biogeochemical formation of metalliferous laminations in surficial environments

Realgar (As4S4) bioprecipitation in microcosm fed by a natural groundwater and organic matter

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