Effect and significance of contamination-related compositional melt variations of the Tweerivier and Bulhoekkop carbonatites, South Africa, with special reference to their REE mineralization

南非 Tweerivier 和 Bulhoekkop 碳酸盐岩与污染相关的成分熔体变化的影响和意义，特别是其稀土矿化

• 批准号: 437542348
• 负责人: Privatdozent Dr. Benjamin Walter
• 金额: --
• 依托单位: Rhodes University
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/437542348?language=en
• 关键词: Effect; significance; contamination; related; compositional

Carbonatites represent important rare earth elements (REE) deposits, which is reflected by the fact that REE exploration projects worldwide are dominated by carbonatites and accompanying rock types. The extraordinary REE enrichment in carbonatitic melts is generally attributed to a combination of parameters, including low-degree partial melting of enriched mantle sources, crystal fractionation, separation of fluid phases and hydrothermal alteration. However, the effect of contamination by crustal and cogenetic rocks, as a potential first order process is only weakly constrained. Nevertheless, our recent study on Kaiserstuhl carbonatites clearly provided evidence that the interaction of carbonatite magma with silicate wall rocks can enable strong REE enrichment in apatite via the britholite substitution mechanism involving Si. Based on the results from the Kaiserstuhl, the role of variable contaminants needs to be tested in detail to show if this process is of general importance in carbonatitic systems.This project will investigate the impact of carbonatite-country rock interaction on REE enrichment in carbonatites. The study will be performed using field examples from the Tweerivier and Bulhoekkop carbonatites (South Africa) which are known to bear a large variability of crustal xenoliths (BIF, sedimentary dolomites, granites, anorthosites and gabbros) and contain variable amounts of silicate minerals (e.g., amphibole, clinopyroxene, mica, tremolite) that may indicate crustal contamination.To test this hypothesis, whole rock data (XRF and ICP-MS), textural, mineral chemical and isotopic data (microscopy, EMPA, C and O-isotope systematics) will be carried out for the different carbonatites samples to study the effect of contamination by Fe, Mg, Al and Si-rich lithologies. The expected results will allow for (1) the identification of the influence of contamination on the REE pattern of the residual melt, and (2) the identification of mineralogical and compositional variation of major mineral phases.

碳酸盐代表重要的稀土元素（REE）沉积物，这反映出，全球REE勘探项目以碳酸盐和伴随岩石类型为主。碳质熔体中的特殊REE富集通常归因于参数的组合，包括富集地幔源的低度局部融化，晶体分级，流体相和水热改变的分离。然而，作为潜在的一阶过程，地壳和造成岩石污染的影响仅受到薄弱的约束。然而，我们最近对Kaiserstuhl碳酸盐岩的研究清楚地提供了证据，表明碳岩岩浆与硅酸盐壁岩石的相互作用可以通过涉及SI的Britholite替代机制在Apatite中富集强烈的REE。根据KaiserStuhl的结果，需要详细测试可变污染物的作用，以证明此过程是否在碳质体系中至关重要。该项目将研究碳酸盐岩岩石相互作用对碳酸盐中REE富集的影响。 The study will be performed using field examples from the Tweerivier and Bulhoekkop carbonatites (South Africa) which are known to bear a large variability of crustal xenoliths (BIF, sedimentary dolomites, granites, anorthosites and gabbros) and contain variable amounts of silicate minerals (e.g., amphibole, clinopyroxene, mica, tremolite) that may indicate crustal为了检验该假设，将针对不同的碳酸盐矿样品进行该假设，全岩数据（XRF和ICP-MS），纹理，矿物质化学和同位素数据（显微镜，EMPA，C和O-同位素系统），以研究FE，MG，MG，Al和SI-RICH-RICHLITHOLOGIES的污染作用。预期的结果将允许（1）鉴定污染对残留熔体REE模式的影响，以及（2）鉴定主要矿物相的矿物学和组成变化。