Connoisseur's Choice: Wire Silver, Kongsberg, Norway &amp; Wire Gold, Ground Hog Mine, Gilman, Colorado

Anderson, Calvin J.; Rakovan, John

doi:10.1080/00357529.2017.1308793

Cited by 3 publications

(1 citation statement)

References 11 publications

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“…To investigate the possibility of SSIC in natural systems, we chose to study the mineral acanthite (Ag 2 S) for several reasons: (1) its hightemperature polymorph argentite possesses the highest ionic conductivity of any known material (Hull, 2004;Kato et al, 2016), (2) it is an important and relatively common ore mineral (commonly found as paramorphs after argentite) (Ercker, 1951;Fontboté et al, 2017), and (3) it is sometimes intimately associated with an unusual and poorly understood habit of native silver, commonly called "wire silver" (see Fig. DR1 in the GSA Data Repository 1 ; Anderson and Rakovan, 2017;Böllinghaus et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Natural solid-state ion conduction induces metal isotope fractionation

Anderson

Mathur

Rakovan

et al. 2019

Geology

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Solid-state ion conduction (SSIC) occurs in the formation of natural and synthetic wire silver and causes consistent isotope fractionation of the mobile ion, favoring the heavy isotope. Textural analysis of natural and synthetic samples revealed that wire silver is a mosaic-like polycrystalline aggregate with superimposed striations, consistent with very rapid basal addition of Ag atoms constrained within a lateral growth footprint at the Ag-Ag 2 S interface. Growth experiments demonstrate that this process is fundamentally dependent not on the chemical environment, but only on the SSIC ability of the substrate, readily provided in this case by argentite (Ag 2 S), a superionic-conducting material. Stable Ag isotope analysis of wire silvers provides a means to observe the geochemical effects of SSIC in Ag 2 S. Natural samples were found to be enriched in the heavy isotope with a median (interquartile range) of +0.283‰ (+0.145‰ to +0.453‰). Furthermore, 109 Ag enrichment was amplified by an order of magnitude in synthetic samples grown at high temperature (>450 °C), which had a median δ 109 Ag of +2.788‰ (+1.829‰ to +3.689‰). Known isotope fractionation mechanisms would indicate that SSIC products should have negative δ isotope values because normal reaction kinetics are more likely to mobilize the lighter isotope. This indicates a previously unrecognized isotope fractionation mechanism associated with SSIC in nature, and has important implications for the geochemistry of ore deposits where SSIC phases are present.

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