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

泡云岩是一种地幔成因的强烈不饱和的深成堆积岩。与橄榄岩有关的具有经济意义的HFSE矿床的研究一般很少，但对格陵兰岛东部的Gardiner杂岩和俄罗斯的Kovdor杂岩进行了较详细的研究。这两个杂岩的不同岩性被认为来自梅拉-肾病母岩浆。在这两个杂岩中都有一套橄榄岩(纯橄榄岩和斜方辉石岩)、熔岩到牛耳岩、橄榄岩(黄橄榄岩)和碳酸盐岩。尽管Kovdor杂岩和Gardiner杂岩的母岩浆成分是黑色的，但这两个杂岩的黄长岩和碳酸盐岩的矿物学成分有明显的差异：Gardiner杂岩的黄长岩在堆积体中显示出矿石级钙钛矿的富集物，而Kovdor的黄长岩只含有副钙钛矿。相比之下，Kovdor碳酸盐岩是HFSE矿化的，但在Gardiner，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杂岩，并破译导致Gardiner早期堆积物中HFSE富集和Kovdor碳酸盐岩中晚期HFSE富集的过程。拟议的研究将以以下两个工作假设为指导：(I)Gardiner和Kovdor杂岩中橄榄岩(少量铬铁矿与少量钛磁铁矿)和黄长岩(存在或不存在大量钙钛矿堆积体)之间的矿物学差异与其母岩浆成分的不同有关，这影响了钙钛矿饱和的时间；(Ii)Gardiner(低)和Kovdor(富)碳酸岩中HFSe的浓度与先前钙钛矿分离的强度有关。为了验证这些假设，将收集并彻底比较这两个复合体不同岩石类型的详细岩石学、矿物化学和岩石学数据。将特别关注稀土+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，以帮助在一个杂岩中寻找不同的浓缩类型(早期堆积与晚期岩浆或热液叠加)。

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).