High-noble measurement of 107Ag/109Ag in native silver and gold by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS)

The MC-ICP-MS technique was used to study Ag isotope systematics in various silver and gold deposits. Owing to the correction of measured ¹⁰⁷Ag/¹⁰⁹Ag values in samples for the mass discrimination effect on the basis of the ¹⁰⁸Pd/¹⁰⁶Pd reference ratio, a precision of ±0.4ɛ (±2SD) was achieved. The ¹⁰⁷Ag/¹⁰⁹Ag ratio was determined in native silver and gold samples from ten well-known noble-metal deposits of varying age (from the Archean to Miocene) in Europe (Kongsberg, Banska Hodrusa, Kremnica, Maiskoe, and Karabash); northeastern, central, and southern Asia (Sukhoi Log, Dukat, Aktepe, and Kolar); and North America (Kidd Creek). The ¹⁰⁷Ag/¹⁰⁹Ag values of the samples studied range from +0.9 to −5.0 $\varepsilon _{107_{Ag} }$ . The observed range is similar to that (6.4 $\varepsilon _{107_{Ag} }$ ) reported previously (Hauri et al., 2000) for oceanic basalts and Ag ores. The ¹⁰⁷Ag/¹⁰⁹Ag ratio shows no correlation with the age of deposits and the composition of their ores and host rocks. The most probable reasons for the observed variations in Ag isotope composition are the isotope geochemical heterogeneity of Ag sources in mineral deposits and Ag isotope fractionation in ore-forming processes.