Silicate liquid immiscibility and the formation of Fe (±Ti ±P ±F ±REE) ore deposits

两种硅酸盐熔体（铁玄武岩-流纹岩）之间的不相容性在分异和成矿过程中的作用几十年来一直存在争议。在自然系统中，两种硅酸盐熔体分离的明确证据很少在岩石中记录，因为在冷却和凝固过程中，不相容性是短暂的。因此，实验方法是至关重要的，以测试的重要性，熔体不可渗透性的岩浆和相关的成矿过程。在这项研究中，我们建议使用一个双重的方法来了解硅酸盐液体的不溶性在铁的形成中的作用，（±Ti ±P ±F ±REE）矿床：（1）我们将研究几个主要铁矿床磷灰石中的熔融包裹体，这将直接限制平衡液体成分;我们将进行一个详细的实验方法，以了解不相容性开始的条件（岩浆成分，温度，压力，氧逸度和流体含量），以及主要元素在成对熔体之间的分配。熔体不可渗透性的作用将被测试为三个著名的自然的例子，都含有富铁和富磷协会，并涵盖了广泛的组成范围：拉斑玄武岩系统（布什维尔德复杂），铁苦橄岩/高钛玄武岩系统（峨眉山大火成岩省），和Kiruna型系统（Vergenoeg存款）。在选定的实验中，我们还将研究微量元素分馏之间的富铁和贫铁硅酸盐熔体的不可渗透性的效果。研究结果将为定量讨论熔体不渗透性在玄武岩系统分异过程中的作用、重要铁矿床的形成以及微量元素（特别是稀土元素）的富集机制提供重要的数据。

The role of immiscibility between two silicate melts (ferrobasalt-rhyolite) on differentiation and ore-forming processes is under debate since decades. Clear evidence for the separation of two silicate melts in natural systems is rarely recorded in rocks because of the transient nature of immiscibility during cooling and solidification. Thus, experimental approaches are crucial to test the importance of melt immiscibility in magmatic and associated ore-forming processes. In this study, we propose to use a twofold approach to understand the role of silicate liquid immiscibility in the formation of Fe (±Ti ±P ±F ±REE) ore deposits: (1) we will study melt inclusions trapped in apatite of some major iron deposits which will give us direct constraints on the equilibrium liquid compositions and (2) we will perform a detailed experimental approach to understand the conditions for the onset of immiscibility (magma compositions, temperature, pressure, oxygen fugacity and fluid content), and the partitioning of major elements between paired melts. The role of melt immiscibility will be tested for three well known natural examples, all containing Fe- and P-rich associations and covering a broad compositional range: tholeiitic basaltic system (Bushveld complex), ferropicritic/high-Ti basaltic system (Emeishan large igneous province), and Kiruna-type systems (Vergenoeg deposit). In selected experiments, we will also study the effect of immiscibility on trace elements fractionation between Fe-rich and Fe-poor silicate melts. The results will provide crucial data allowing us to discuss quantitatively the role of melt immiscibility on differentiation processes in basaltic systems, on the formation of some economically important Fe ore deposits and on enrichment mechanisms of trace elements (especially REE).