Enrichment and transport of Cr in magmatic systems in the mantle and crust

铬是一种对欧盟经济具有高度重要性的关键金属，其可持续供应风险很高。从四种不同的存款类型中开采铬：层状、豆荚状、砂矿和以铬铁矿矿物形式存在的红土矿床，但只有层状和豆荚状铬铁矿矿床代表最重要的类型。目前在欧盟只有豆荚状铬矿床，与镁铁质-超镁铁质岩石密切相关。铬矿床与地幔岩的密切关系决定了铬铁矿形成过程中铬的来源必须在地球上地幔中寻找。铬的浓度非常低，需要饱和的铬铁矿岩浆表明，似乎有限的提取过程中地幔熔融和岩浆结晶过程中似乎是足够的豆荚状铬铁矿矿床。然而，尽管有大量的研究和各种各样的建议机制，导致铬富集，有一个特定的模式，可以充分解释豆荚状铬铁矿deposit.In我们的研究，我们的目标是了解的过程中，导致铬富集的岩浆系统从地幔到矿石存款缺乏普遍的共识。为了实现这一目标，我们提出了一个实验研究相结合的建模方法，重点放在三个阶段的铬富集：1）地幔熔融; 2）熔体演化;和3）熔体运动，固态变形和流体流动。在这个项目中，我们将专注于前两个步骤，并进行实验研究，揭示和量化不同的物理化学参数在地幔和地壳条件下的贡献：源岩的化学成分，地幔熔融的程度，在熔融和随后的结晶过程中不同的地幔和岩浆相（橄榄石，斜方辉石，单斜辉石和尖晶石）中铬的特定分布。特别注意水的作用和氧化还原条件有关的超俯冲构造环境的蛇绿杂岩托管豆荚状铬矿床。所获得的实验结果将被用来校准热力学代码，并制定一个一般模型的铬铁矿富集在自然系统中。

Chromium is a critical metal with a high importance to the economy of the EU and high rick of sustainable supply. Chromium has been mined from four different deposit types: stratiform, podiform, placer, and laterite deposits in the form of chromite mineral but only stratiform and podiform chromite deposits represent the most significant types. Only podiform Cr deposits, intimately associated with mafic-ultramafic rocks, are present and currently mined in the EU. The close association of Cr deposits with mantle rocks dictates that the source of chromium in the formation of chromite deposits must be sought in the Earth’s upper mantle. The very low concentrations of Cr needed to saturate magmas with chromite indicate that seemingly limited extraction processes both during mantle melting and during magma crystallization appear to be sufficient to generate podiform chromite deposits. However, despite numerous studies and a variety of proposed mechanisms leading to Cr enrichment, there is a lack of general consensus on a particular model which can fully explain the formation of podiform chromite deposits.In our research we aim at understanding the processes leading to the Cr enrichment in magmatic systems from the mantle to the ore deposit. To achieve this goal we propose an experimental investigation combined with a modelling approach focusing on three stages of Cr-enrichment: 1) Mantle melting; 2) Melt evolution; and 3) Melt movement, solid-state deformation and fluid mobilization. In this project we will focus on the two first steps and conduct experimental study unrevealing and quantifying the contributions of different physico-chemical parameters at mantle and crustal conditions: the chemistry of the source rocks, the degree of mantle melting, the particular distribution of chromium among the different mantle and magmatic phases (olivine, orthopyroxene, clinopyroxene and spinel) during melting and consequent crystallization. Particular attention will be paid to the role of water and redox conditions relevant for the supra-subduction tectonic environment of the ophiolitic complexes hosting podiform Cr ore deposits. The obtained experimental results will be used to calibrate thermodynamic codes and to develop a general model of chromite enrichment in natural systems.