The role of early cumulate formation for HFSE enrichment in foidolitic systems

深成堆晶岩是幔源的、SiO2强烈欠饱和的深成堆晶岩。对与foidolitic岩石有关的具有经济意义的HFSE矿床的研究通常很少，但对格陵兰东部的加德纳杂岩和俄罗斯的科夫多尔杂岩进行了详细研究。这两个复杂的各种岩性被认为是来自一个黑霞石母岩浆。在这两个复杂的一套橄榄岩（纯橄榄岩和单斜辉石岩），熔融到urtitic岩石，foidolitic岩石（黄长石）和碳酸盐岩发生。尽管Kovdor和加德纳杂岩的母岩浆成分为黑闪石岩，但这两个杂岩的黄长石岩和碳酸岩的矿物学成分显示出明显的差异：加德纳杂岩的黄长石岩在堆积物中显示出矿石级的钙钛矿富集，而Kovdor的黄长石岩仅含副钙钛矿。相比之下，科夫多尔碳酸盐岩是HFSE矿化的，但在加德纳，这些岩石在HFSE中是贫瘠的。该项目旨在详细比较这两个类似的复合体，并解释导致加德纳早期堆积物中HFSE富集和科夫多尔碳酸盐岩晚期HFSE富集的过程。拟议的研究将遵循以下两个工作假设： 橄榄岩与橄榄岩之间的矿物学差异（少量铬铁矿与少量钛磁铁矿）和黄长石（存在或不存在大量钙钛矿累积）在加德纳和科夫多尔复合物涉及其母岩浆组成的差异，这影响了钙钛矿饱和的时间;（ii）加德纳（低）和科夫多尔（富集）碳酸岩中HFSE的浓度与先前钙钛矿分馏的强度有关。为了验证这些假设，将收集并彻底比较两个复合体不同岩石类型的详细岩相学、矿物化学和岩石学数据。特别关注REE + HFSE（Zr，Hf，Nb，Ta）在磷灰石，单斜辉石，橄榄石，钙钛矿和黄长石之间的分布。该项目还旨在制定勘探指标，以帮助寻找复合体内不同的富集类型（早期累积相对于晚期岩浆相对于热液叠加）。

Foidolites are mantle-derived and strongly SiO2-undersaturated plutonic cumulate rocks. Studies on economically interesting HFSE deposits associated with foidolitic rocks are generally rare, but the Gardiner Complex in E-Greenland and the Kovdor Complex in Russia were studied in some detail. The various lithologies of both complexes are believed to derive from a mela-nephelinitic parental magma. In both complexes a suite of peridotitic rocks (dunite & clinopyroxenite), melteigitic to urtitic rocks, foidolitic rocks (melilitolite) and carbonatite occur. Although the parental magma compositions are melanephelinitic for the Kovdor and Gardiner complexes, the mineralogical composition of melilitolite and carbonatite of these two complexes show clear differences: Melilitolite of the Gardiner Complex shows ore grade enrichment of perovskite in cumulates, whereas melilitolite at Kovdor contains only accessory perovskite. In contrast, Kovdor carbonatite is HFSE-mineralized, but at Gardiner these rocks are barren in HFSE. This project aims at comparing these two similar complexes in detail and to decipher the processes leading to the HFSE-enrichment in early cumulates at Gardiner and the late-stage HFSE-enrichment in the Kovdor carbonatite. The proposed study will be guided by the following two working hypotheses: (i) the mineralogical differences between the peridotitic rocks (minor chromite versus minor Ti-magnetite) and melilitolite (presence or absence of massive perovskite cumulates) at the Gardiner and Kovdor complexes relate to differences in their parental magma composition, which influenced the timing of perovskite saturation; (ii) the concentration of HFSE in carbonatite of Gardiner (low) and Kovdor (enriched) relate to the intensity of previous perovskite fractionation. To test these hypotheses, detailed petrographic, mineral chemical and petrological data for the different rock types of the two complexes will be gathered and thoroughly compared. Special focus will be given to the distribution of REE + HFSE (Zr, Hf, Nb, Ta) between apatite, clinopyroxene, olivine, perovskite, and melilitite. The project further aims at developing exploration indicators that will help to search for the different enrichment types within a complex (early cumulate versus late stage magmatic versus hydrothermal overprint).