Platinum enrichment processes in ultramafic massifs of the Uralian Platinum belt, Russia - evidence for mineralization at the magmatic to hydrothermal transition

俄罗斯乌拉尔铂矿带超镁铁质地块中的铂富集过程——岩浆到热液转变过程中矿化的证据

基本信息

批准号：
325281966
负责人：
Professor Dr. Christian Gerhard Ballhaus
金额：
--
依托单位：
Abteilung Geochemie/Petrologie
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2017
资助国家：
德国
起止时间：
2016-12-31 至 2020-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/325281966?language=en
关键词：
Platinum enrichment processes ultramafic massifs

项目摘要

Chromite and native Pt are usually considered to be early high temperature phases of primitive basaltic melts. Consequently, when chromite and Pt-Fe alloy are found enriched within primitive magmatic cumulates, it is assumed that these phases were enriched at magmatic temperature.The chromite-Pt enclaves in the massifs of the Uralian Platinum belt show many features that argue against a purely magmatic origin. Compared with the respective liquidus phases in basaltic melts, chromite and Pt-Fe alloys in the Uralian massifs can be orders of magnitude more coarse-grained. Hydrous silicates are commonplace, and chromite carries many generations of late hydrous phases within euhedral cavities that follow the crystal symmetry of chromite. The question is whether the fluid phases were derived directly from the parental melts of the cumulates or whether they reflect a random overprint. Primitive island arc melts - the potential parents to the ultramafic Uralian massifs - contain ~ 4 wt.% H2O. That H2O concentration is sufficient to render derivative melts and their cumulates saturated with a hydrous fluid phase. The working hypothesis is whether and to what extent magmatic chromite and Pt-Fe microliths can be mobilized and concentrated by intercumulus melts and fluids segregating from the crystallizing plutonic roots of island arc ankaramites.An important aspect to understand the enrichment processes is to date the mineralization. All platiniferous ultramafic massifs of the Uralian Platinum Belt are aligned parallel to the old suture marking the former Silurian convergent plate margin in the Ural mountains. Hence, if they outline a fossil volcanic arc, they should all return similar emplacements ages. The dating method of choice is the 190Pt-186Os decay scheme, tested here on Pt-Fe alloys from the Kondyor massif. If all platiniferous intrusions of the UPB return Pt mineralization ages identical within error, a genetic link must have existed between emplacement and cooling histories of the Uralian massifs and their Pt mineralization.

铬铁矿和天然Pt通常被认为是原始玄武岩熔体的早期高温阶段。因此，当发现在原始岩浆累积的铬铁矿和pt-fe合金中富集时，假设这些相在岩浆温度下富集。岩浆起源。与玄武岩熔体中各自的液体相相比，乌拉拉利亚地块中的铬铁矿和PT-FE合金可以是更粗粒的数量级。含水硅酸盐很常见，铬铁矿在遵循铬铁矿的晶体对称性的euhedral腔内携带了许多世代的后期水相。问题是流体相是直接源自累积的父母熔体还是反映随机覆盖的。原始岛屿弧融化 - 超镁质Uralian massifs的潜在父母 - 含有〜4 wt。％H2O。 H2O浓度足以使衍生物熔体融化，并用液压液相饱和。有效的假设是，岩浆铬铁矿和pt-fe微石是否可以通过与岛弧形植物的结晶岩石根分离的融化和液体进行动员和浓缩。。乌拉拉利亚白金带的所有铂二含量超镁铁质地块都与旧缝合线平行，标记了乌拉尔山脉的前志留纪聚合板缘。因此，如果他们概述了化石火山弧，则应返回类似的恢复年龄。选择的约会方法是190PT-186OS衰减方案，该方案在此处测试了昆托尔地块的PT-FE合金。如果UPB返回PT矿化年龄在误差范围内相同的所有铂金属侵入，则在乌拉利亚地块的迁移和冷却史之间必须存在遗传联系及其PT矿化。