Fractionation of silver isotopes in native silver explained by redox reactions

Mathur, Ryan and Arribas Moreno, Antonio and Megaw, Peter and Wilson, Marc and Stroup, Steven and Meyer-Arrivillaga, Danilo and Arribas Rosado, Isabel Pilar (2018). Fractionation of silver isotopes in native silver explained by redox reactions. "Geochimica et cosmochimica acta", v. 224 ; pp. 313-326. ISSN 0016-7037. https://doi.org/10.1016/j.gca.2018.01.011.

Description

Title: Fractionation of silver isotopes in native silver explained by redox reactions
Author/s:
  • Mathur, Ryan
  • Arribas Moreno, Antonio
  • Megaw, Peter
  • Wilson, Marc
  • Stroup, Steven
  • Meyer-Arrivillaga, Danilo
  • Arribas Rosado, Isabel Pilar
Item Type: Article
Título de Revista/Publicación: Geochimica et cosmochimica acta
Date: 2018
ISSN: 0016-7037
Volume: 224
Subjects:
Freetext Keywords: Silver isotopes; Fractionation; Native silver; Ore deposits; MnO2; FeOOH
Faculty: E.T.S.I. de Minas y Energía (UPM)
Department: Ingeniería Geológica y Minera
Creative Commons Licenses: Recognition - No derivative works - Non commercial

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Abstract

Scant data exist on the silver isotope composition of native silver specimens because of the relative newness of the technique. This study increases the published dataset by an order of magnitude and presents 80 silver new isotope analyses from native silver originating from a diverse set of worldwide deposits (8 deposit types, 33 mining districts in five continents). The measured isotopic range (defined as d109Ag/107Ag in per mil units compared to NIST 978 Ag isotope standard) is +2.1 to 0.86‰ (2r errors less than 0.015); with no apparent systematic correlations to date with deposit type or even within districts. Importantly, the data centering on 0‰ all come from high temperature hypogene/primary deposits whereas flanking and overlapping data represent secondary supergene deposits. To investigate the causes for the more fractionated values, several laboratory experiments involving oxidation of silver from natural specimens of Ag-rich sulfides and precipitation and adsorption of silver onto reagent grade MnO2 and FeOOH were conducted. Simple leach experiments demonstrate little Ag isotope fractionation occurred through oxidation of Ag from native Ag (Dsolution-native 109 Ag = 0.12‰). In contrast, significant fractionation occurred through precipitation of native Ag onto MnO2 (up to Dsolution-MnO2 109 Ag = 0.68‰, or 0.3amu). Adsorption of silver onto the MnO2 and FeOOH did not produce as large fractionation as precipitation (mean value of Dsolution-MnO2 109Ag = 0.10‰). The most likely cause for the isotopic variations seen relates to redox effects such as the reduction of silver from Ag (I) to Ag that occurs during precipitation onto the mineral surface. Since many Ag deposits have halos dominated by MnO2 and FeOOH phases, potential may exist for the silver isotope composition of ores and surrounding geochemical haloes to be used to better understand ore genesis and potential exploration applications. Aside from the Mn oxides, surface fluid silver isotope compositions might provide information about geochemical reactions relevant to both environmental and hydrometallurgical applications.

More information

Item ID: 54543
DC Identifier: http://oa.upm.es/54543/
OAI Identifier: oai:oa.upm.es:54543
DOI: 10.1016/j.gca.2018.01.011
Official URL: https://www.sciencedirect.com/science/article/pii/S0016703718300140?via%3Dihub
Deposited by: Memoria Investigacion
Deposited on: 09 Apr 2019 08:31
Last Modified: 24 Apr 2019 08:44
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