Abstract This study presents the first highly siderophile element (HSE: Re, Os, Ir, Ru, Rh, Pt, Pd, Au) abundance and Re–Os isotopic data for primary Pt–Fe minerals and Os-rich alloys from the Kondyor zoned-type ultramafic massif located in the southeastern part of the Siberian Craton, Russia. The Kondyor massif is composed of three zones: (A) the oldest dunite core with associated chromitites, with an age of emplacement of ~250 Ma, (B) a younger rim represented by metadunite, wehrlite, clinopyroxenite, and melanocratic gabbro that has transitional contacts with the dunite core, and (C) the youngest apatite-phlogopite-magnetite-rich clinopyroxenite stockwork exposed in the southwestern part of the massif. It has intrusive contacts with the dunite core and formed at ~125 Ma. Chromitites from zone (A) and clinopyroxenites from zone (C) analyzed in this study are characterized by distinct platinum-group mineral (PGM) assemblages dominated by Pt–Fe alloys in the former and cooperite with sperrylite and Pt–Fe alloys in the latter, with subordinate amounts of Os–Ir alloys present in both assemblages. The Re–Os isotope results identify a narrow range of initial 187Os/188Os values for Os–Ir alloys from the zone A chromitites (0.1249–0.1254) and the chromitites themselves (0.12466 ± 0.00005). Such chondritic initial 187Os/188Os values (γ187Os(T =250 Ma) ranging between −0.5 and + 0.1) indicate that the HSE budget of the chromitites and PGM from zone (A) was largely controlled by that of the mantle domain that evolved with long-term near-chondritic Re/Os, a notion that is also supported by the recent data of Luguet et al. (2019). In contrast, Os alloys from the zone C clinopyroxenites have initial 187Os/188Os values ranging between 0.1302 and 0.1308 (initial γ187Os(T =125 Ma) = +3.2 to +3.7), indicative of a suprachondritic time-integrated Re/Os in the source of these rocks. The mineralogical and isotope-geochemical data point to a high-temperature origin of the studied PGM and at least two distinct sources of HSE in the ultramafic rocks of the Kondyor massif.

中文翻译：

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对比 Kondyor 地块（俄罗斯）的铂族矿物组合：对分区型超镁铁质地块中 HSE 来源的影响

摘要 本研究展示了来自 Kondyor 分区的原生 Pt-Fe 矿物和富 Os 合金的第一个高度亲铁元素（HSE：Re、Os、Ir、Ru、Rh、Pt、Pd、Au）丰度和 Re-Os 同位素数据。型超镁铁质地块，位于俄罗斯西伯利亚克拉通东南部。Kondyor 地块由三个区域组成：(A) 最古老的单晶岩核与伴生铬铁矿，侵位年龄约 250 Ma，(B) 以变白云岩、纬长岩、斜辉石和具有过渡性的黑质辉长岩为代表的年轻边缘与纯晶岩核接触，以及 (C) 出露在地块西南部的最年轻的富含磷灰石-金云母-磁铁矿的单斜辉石岩网。它与纯晶岩核有侵入接触，形成于~125 Ma。本研究中分析的区域 (A) 中的铬铁矿和区域 (C) 中的单斜辉石岩的特征在于不同的铂族矿物 (PGM) 组合，前者以 Pt-Fe 合金为主，后者以钴磷矿为主，两种组合中都存在少量的 Os-Ir 合金。Re-Os 同位素结果确定了来自 A 区铬铁矿 (0.1249–0.1254) 和铬铁矿本身 (0.12466 ± 0.00005) 的 Os-Ir 合金的初始 187Os/188Os 值范围很窄。这种球粒陨石初始 187Os/188Os 值（γ187Os（T = 250 Ma）范围在 -0.5 和 + 0.1 之间）表明来自 (A) 区的铬铁矿和 PGM 的 HSE 收支很大程度上受地幔域的收支控制。长期近球粒状 Re/Os，这一概念也得到 Luguet 等人最近数据的支持。(2019)。相比之下，来自 C 区单斜辉石岩的 Os 合金的初始 187Os/188Os 值在 0.1302 和 0.1308 之间（初始 γ187Os（T =125 Ma）= +3.2 到 +3.7），表明在这些岩石的来源。矿物学和同位素地球化学数据表明所研究 PGM 的高温起源和 Kondyor 地块超基性岩中至少两个不同的 HSE 来源。