A combined Re-Os and Pt-Os isotope and HSE abundance study of Ru-Os-Ir alloys from the Kunar and Unga placer deposits, the Taimyr Peninsula, Polar Siberia

• Published in: Minerals
• Main Authors: Malitch, Kreshimir N., Puchtel, Igor S., Belousova, Elena A., Badanina, Inna Yu
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2022
• Subjects: highly siderophile elements; mantle; ophiolite; Polar Siberia; Re-Os and Pt-Os isotopic systems; Ru-Os-Ir alloys; the Kunar and Unga placer deposits; the Taimyr Peninsula; Kunar; Taimyr; Siberia
• Online Access: https://researchers.mq.edu.au/en/publications/a3644ba7-d4a7-47cb-9cfd-40c26d45909c; https://doi.org/10.3390/min12111463; https://research-management.mq.edu.au/ws/files/233439369/230699307.pdf; http://www.scopus.com/inward/record.url?scp=85149580060&partnerID=8YFLogxK

In order to provide further insights into the origin of Ru-Os-Ir alloys, this study presents new highly siderophile element (HSE: Re, Os, Ir, Ru, Pt, and Pd) abundance and 187 Re- 187 Os and 190 Pt- 186 Os isotope data for detrital grains of native Ru-Os-Ir alloys in placer deposits of the Kunar and Unga Rivers, which display a close spatial association with the Kunar dunite–harzburgite complex in the northern part of the Taimyr Peninsula in the Polar Siberia. The study utilized electron microprobe analysis, negative thermal ionization mass-spectrometry (N-TIMS) and laser ablation multiple-collector inductively coupled plasma mass-spectrometry (LA MC-ICP-MS). The primary nature of the Ru-Os-Ir alloys is supported by the occurrence of euhedral inclusions of high-Mg olivine (Fo 92–93 ) that fall within the compositional range of mantle olivine. The LA MC-ICP-MS data show similar average initial 187 Os/ 188 Os and γ 187 Os(740 Ma) values for PGM assemblages from the Kunar and Unga deposits of 0.1218 ± 0.0010, −0.18 ± 0.85, and 0.1222 ± 0.0025, +0.10 ± 2.1, respectively. These values are identical, within their respective uncertainties, to the initial 187 Os/ 188 Os value of the Ru-Os-Ir alloy grain measured by N-TIMS (0.1218463 ± 0.0000015, γ 187 Os(740 Ma) = −0.1500 ± 0.0012). The combined 187 Re- 187 Os isotopic data for all studied grains (γ 187 Os(740 Ma) = −0.02 ± 1.6) indicate evolution of the Kunar and Unga mantle sources with a long-term chondritic 187 Re/ 188 Os ratio of 0.401 ± 0.030. In contrast to the 187 Os/ 188 Os data, the initial 186 Os/ 188 Os value of 0.1198409 ± 0.0000012 (µ 186 Os(740 Ma) = +34 ± 10) obtained for the same Ru-Os-Ir alloy grain by N-TIMS is suprachondritic and implies evolution of the Kunar and Unga mantle source(s) with a long-term suprachondritic 190 Pt/ 188 Os ratio of 0.00247 ± 0.00021. This value is ~40% higher than the average chondritic 190 Pt/ 188 Os ratio of 0.00180 and indicates long-term enrichment of the Kunar source in Pt over Os. Establishing the source of this ...