The relationship between placer gold particle shape, rimming, and distance of fluvial transport as exemplified by gold from the Klondike District, Yukon Territory, Canada

Knight, J.; Morison, S R; Mortensen, James K.

doi:10.2113/gsecongeo.94.5.635

Cited by 100 publications

(73 citation statements)

References 17 publications

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“…The gold-rich rims on grains and nuggets from the white placers are typical of the rims observed for deeply chemically-weathered placer gold in alluvial environments [4,36,52]. Given the smooth outer surfaces produced by mechanical weathering in the steep streams of the Devils Nest, and the difficulties this would pose for the establishment of gold-tolerant microbial communities, it is possible that the gold-rich rims are a result of abiological differential chemical weathering of silver and copper.…”

Section: Rim Enrichments and Elemental Abundancesmentioning

confidence: 85%

“…Surface textures varied from deformation, which likely resulted from physical weathering, to a wide range of putative (bio)geochemical forms. Gold from the white placer unit (stratigraphic middle unit) was largely restricted to physical weathering forms, with an appearance similar to water-worn nuggets from the rivers of some Canadian, California and Alaskan placer districts [4,36]. Gold from the red placers showed impact striations and angular surface forms with deep pockets, which contain mat-like structures with a strong morphological resemblance to bacterial mats [16] (Figure 6).…”

Section: Resultsmentioning

confidence: 99%

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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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Section: Rim Enrichments and Elemental Abundancesmentioning

confidence: 85%

Section: Resultsmentioning

confidence: 99%

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

et al. 2018

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“…The placer gold inventory derived from this study led to the identification of the characteristics of populations of placer grains contributing to economically important placers. Knight et al [42] studied the relationship between distance travelled in fluvial systems and gold grain shape and rimming. The roundness and flatness of gold grains increased rapidly over the first five kilometers of transport from the source.…”

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

confidence: 99%

“…The roundness and flatness of gold grains increased rapidly over the first five kilometers of transport from the source. This, coupled with the observed development of gold-rich rims, allowed for the separation of gold grains into the classification of proximal and distal relative to a likely source [42]. However, Hough et al [13] noted that the morphology of grains, and in particular those found in stream sediments, is not diagnostic for origin or distance, but rather provides a record of the supergene transformations the grains have undergone.…”

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

confidence: 99%

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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“…Sev eral ex am ples of such study of trans port of de tri tal gold grains have been de scribed (e.g., Boyle, 1979;Tishchenko, 1981;Giusti, 1986;DiLabio, 1990;Hérail et al, 1990;Knight et al, 1999;Youngson and Craw 1999;Wierchowiec, 2002).…”

Section: Introductionmentioning

confidence: 99%

Placer scheelite and gold from alluvial sediments as indicators of primary mineralization – examples from SW Poland

Mikulski¹,

Wierchowiec

2013

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De tailed mor pho log i cal stud ies of de tri tal schee lite and gold grains from clastic Ce no zoic de pos its (al lu vial and eluvial-colluvial) in two se lected ar eas of Lower Silesia al lowed de scrip tion of their spe cific fea tures (size, round ness, lus tre, and lack or rem nants of pri mary inter growths with other min er als, and for gold also of the flat ness in dex). This al lows es ti mation of the length of hy dro dy namic trans port and dis tance from the source area. Such fea tures are also an im por tant tool in de ter min ing the source of ore min er ali sa tion and of es tab lish ing the par ent area for de tri tal ac cu mu la tions. More over, electron microprobe (EMPA) in ves ti ga tion of de tri tal gold and schee lite al lowed rec og ni tion of the in ter nal struc ture and chem i cal com po si tion of these min er als. The gold grains com monly re vealed zonal struc tures due to chem i cal supergene gold mo bil ity rec og nized in nearly all pan-con cen trate sam ples stud ied.

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The relationship between placer gold particle shape, rimming, and distance of fluvial transport as exemplified by gold from the Klondike District, Yukon Territory, Canada

Cited by 100 publications

References 17 publications

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

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

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

Placer scheelite and gold from alluvial sediments as indicators of primary mineralization – examples from SW Poland

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