Abstract

This article presents the ¹⁹⁰Pt–⁴He dating results of native platinum group minerals from a unique platinum-metals placer deposit in the basin of the Kondyor and Uorgalan rivers and dunite fragments from the Kondyor alkaline-ultramafic massif. The results of ¹⁹⁰Pt–⁴He dating of 75 samples determine the age of the minerals and also date the ore-forming processes. It confirms the previously developed model of polycyclic genesis of placer-forming formations of platinum group minerals (PGMs) and, thus, sheds light on the duration of the formation of the Kondyor alkaline-ultramafic massif. The following ¹⁹⁰Pt–⁴He age stages are distinguished: (a) 143 ± 7 Ma, the formation time of the massif itself and early formation stages of PGMs of magmatogenic platinum (Pt) and the magmatogenic–fluid–metasomatic Pt and Os–Pt (Pt > Os) types, as well as PGMs of fluid-metamorphogenic iridium–platinum (Pt > Ir) type; (b) 128 ± 6 Ma, the early formation stages of the magmatogenic–fluid–metasomatic Pd–Pt (Pt > Pd) type and the late stages of the Pt, Pt > Os, and Pt > Ir types; (c) 115 ± 6 Ma, the late formation stages of the Pt > Pd type. The good agreement of these dates with the geological and mineralogical data allows us to conclude that the formation of placer-forming PGMs and their formations in the Kondyor alkaline-ultramafic massif was a polycyclic process for about 30 Ma.

中文翻译：

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Kondyor 碱性-超镁铁质地块铂砂形成地层多环成因的新证据：190Pt-4He 测年结果

摘要

本文介绍了来自 Kondyor 和 Uorgalan 河流域独特铂金属砂矿床的天然铂族矿物和来自 Kondyor 碱性超镁铁质地块的纯晶碎片的¹⁹⁰ Pt- ⁴ He 定年结果。75 个样品的¹⁹⁰ Pt- ⁴ He 测年结果确定了矿物的年龄，并确定了成矿过程的年代。它证实了先前开发的铂族矿物 (PGM) 砂矿形成地层的多环成因模型，从而揭示了 Kondyor 碱性超镁铁质地块形成的持续时间。以下¹⁹⁰ Pt– ⁴He年龄阶段区分：（a）143±7 Ma，地块本身的形成时间和岩浆成因铂（Pt）和岩浆-流体-交代Pt和Os-Pt（Pt> Os）PGMs的早期形成阶段类型，以及流体变质铱-铂（Pt > Ir）类型的铂族金属；(b) 128±6 Ma，岩浆-流体-交代Pd-Pt(Pt>Pd)型形成早期和Pt、Pt>Os、Pt>Ir型晚期；(c) 115 ± 6 Ma，Pt > Pd 型的晚期形成阶段。这些日期与地质和矿物学数据的良好一致性使我们能够得出结论，形成砂矿的铂族金属及其在 Kondyor 碱性-超镁铁质地块中的形成是一个大约 30 Ma 的多环过程。