Crystalline Placer Gold from the Rio Neuquen,Argentina: Implications for the Gold Budget in Placer Gold Formation

McCready, A. J.; Parnell, John; Castro, Liliana Norma

doi:10.2113/gsecongeo.98.3.623

Cited by 15 publications

(15 citation statements)

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“…Based on their morphology a microbial origin has been proposed ( Fig. DR1A in the GSA Data Repository 1 ) (Mossman et al, 1999;Watterson, 1992), which is consistent with evidence of Au addition during growth of secondary Au (McCready et al, 2003). However, Au nanocrystals and bacterioform morphologies have also been produced abiogenically, leading to the rejection of the biogeochemical aggregation model in favor of an abiogenic, detrital model (Watterson, 1994;Hough et al, 2007).…”

Section: Introductionmentioning

confidence: 73%

“…The Au locked in nanoparticles present on the surface of the biofi lms may originate from dissolution of the underlying Au grain, but may also represent capture of soluble Au from solutions by metallophilic bacteria (McCready et al, 2003). To elucidate this we used FIB-SEM to obtain the fi rst comprehensive insight into the internal structure and composition of the polymorphic layer.…”

Section: Results and Disussionmentioning

confidence: 99%

“…Since biofi lms are subject to cycles of formation and destruction via desiccation or grazing by soil fauna, nanoparticulate Au will be periodically released and dispersed in the environment via transport in soil solutions and groundwater. This continuous release of nanoparticulate Au can explain the high mobility of Au in many nearsurface environments, which leads to the formation of secondary Au deposits (McCready et al, 2003) and the development of geochemical halos around buried mineralization even in transported cover (Reith et al, 2007;Hough et al, 2008). This process can also serve as a natural analogue to understand the toxicology of manufactured Au nanoparticles released into the environment (Diegoli et al, 2008), and must be taken into account for estimating mobility of other rare, poorly soluble metals such as platinum group elements.…”

Section: Discussionmentioning

confidence: 99%

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Nanoparticle factories: Biofilms hold the key to gold dispersion and nugget formation

Reith

Fairbrother

Nolze

et al. 2010

Geology

142

109

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Biofi lms living on gold (Au) grains play a key role in the biogeochemical cycle of Au by promoting the dispersion of Au via the formation of Au nanoparticles as well as the formation of secondary biomorphic Au. Gold grains from Queensland, Australia, are covered by a polymorphic, organic-inorganic layer that is up to 40 µm thick. It consists of a bacterial biofi lm containing Au nanoparticles associated with extracellular polymeric substances as well as bacterioform Au. Focused ion beam (FIB) sectioning through the biofi lm revealed that aggregates of nanoparticulate Au line open spaces beneath the active biofi lm layer. These aggregates (bacterioform Au type 1) resulted from the reprecipitation of dissolved Au, and their internal growth structures provide direct evidence for coarsening of the Au grains. At the contact between the polymorphic layer and the primary Au, bacterioform Au type 2 is present. It consists of solid rounded forms into which crystal boundaries of underlying primary Au extend, and is the result of dealloying and Ag dissolution from the primary Au. This study demonstrates that (1) microbially driven dissolution, precipitation, and aggregation lead to the formation of bacterioform Au and contribute to the growth of Au grains under supergene conditions, and (2) the microbially driven mobilization of coarse Au into nanoparticles plays a key role in mediating the mobility of Au in surface environments, because the release of nanoparticulate Au upon biofi lm disintegration greatly enhances environmental mobility compared to Au complexes only.

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Section: Introductionmentioning

confidence: 73%

Section: Results and Disussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Nanoparticle factories: Biofilms hold the key to gold dispersion and nugget formation

Reith

Fairbrother

Nolze

et al. 2010

Geology

142

109

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“…The fine-grained gold cannot break the surface tension of the water, clings to the lower surface of the water, and is washed out of the gold pan (West, 1974: 21;Oyler, 1997). Background mercury content can be inferred from microprobe analyses of placer gold which show that the cores of placer gold do not contain mercury even though there is an amalgam rim of contaminant mercury released from placer mining (McCready et al, 2003). On table 3 are compiled data on the mercury and elemental content of three samples of pre-contact gold foils from northern Perú and four samples of precontact gold foils from Colombia.…”

Section: Analytical Techniquesmentioning

confidence: 99%

“…The mercury content of the Chimú artifact, <100 ppm, analyzed by Petersen (1970: 57) is also far below the contaminant range established by Gordus & Shimada (1995). Microprobe analyses of placer gold indicate that the native mercury released during small-scale mining in 18 th century Argentina is not pervasive and is limited to the rim of the placer gold grain (McCready et al, 2003). This indicates that any tomb-related cinnabar contamination would have been similarly limited to the surface of the gold artifact and would have been removed during cleaning at the respective museums.…”

Section: Contaminationmentioning

confidence: 99%

Amalgamation and small-scale gold mining in the ancient Andes

Brooks¹,

Schwörbel²,

Castillo³

2011

bifea

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In 1532, the volume of gold provided by Atahualpa, the Inka king, as ransom for his release from the Spanish was hard evidence for the efficient small-scale gold mining that took place before European contact and the number of gold occurrences in the Andes. At Huancavelica, Perú, mercury occurs as a native metal and as cinnabar [HgS], which was used for pigments, funeral preparations, and retorted to obtain mercury. Using Inductively Coupled Plasma analysis (ICP), an average of 15 ppm (parts per million) mercury was found in the gold after the gold-mercury amalgam, with more than 300 000 ppm mercury, was burned to volatilize (rogado) the mercury. From 12,3 to 13,9 ppm mercury was found in worked gold foils from Huaca la Ventana, a Middle Sicán (A. D. 900-1200) site at Lambayeque, Perú and low levels of mercury were found in pre-contact gold foils from Colombia (1-12 ppm). Similarly low levels of mercury in the analyses of modern refogado gold and pre-contact gold foils are consistent with a comparable, ancient small-scale mining technology that would have used mercury to amalgamate the fine-grained gold; and then, as now, burning the amalgam to volatilize the mercury and beautify and recover the gold.

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Chemical and physical heterogeneity within native gold: implications for the design of gold particle studies

et al. 2021

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Studies of populations of gold particles are becoming increasingly common; however, interpretation of compositional data may not be straightforward. Natural gold is rarely homogenous. Alloy heterogeneity is present as microfabrics formed either during primary mineralization or by modification of pre-existing alloys by chemical and physical drivers during subsequent residence in either hypogene or surficial environments. In electron-probe-microanalysis (EPMA)-based studies, the combination of Cu, Hg, and Pd values and mineral inclusion suites may be diagnostic for source style of mineralization, but Ag alone is rarely sufficient. Gold characterization studies by laser-ablation-ICP mass spectrometry linked to both quadrupole and Time-of-Flight (ToF-MS) systems show that only Ag, Cu, and Hg form homogenous alloys with Au sufficiently often to act as generic discriminants. Where present, other elements are commonly distributed highly heterogeneously at the micron or submicron scale, either as mineral inclusions or in highly localized, but low concentrations. Drawing upon our own data derived from individual inspection and analyses of approximately 40,000 gold particles from 526 placer and in situ localities worldwide, we show that adequate characterization of gold from a specific locality normally requires study of a minimum of 150 particles via a two-stage approach comprising spatial characterization of compositional heterogeneity, plus crystallographic orientation mapping, that informs subsequent targeted acquisition of quantitative compositional data by EPMA and/or laser-ablation ICP-MS methods. Such data provide the platform to review current understanding of the genesis of gold particle characteristics, elevating future compositional studies from empirical descriptions to process-focused interpretations.

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Crystalline Placer Gold from the Rio Neuquen,Argentina: Implications for the Gold Budget in Placer Gold Formation

Cited by 15 publications

References 50 publications

Nanoparticle factories: Biofilms hold the key to gold dispersion and nugget formation

Nanoparticle factories: Biofilms hold the key to gold dispersion and nugget formation

Amalgamation and small-scale gold mining in the ancient Andes

Chemical and physical heterogeneity within native gold: implications for the design of gold particle studies

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