Magnetite-(apatite) ore deposits are interpreted as being formed by the crystallization of iron-rich ultrabasic melts, dominantly generated by the interaction of silicate melts with oxidized P-F-SO₄-bearing sedimentary rocks. This hypothesis is supported by geologic evidence, experimental studies, numerical modeling, stable and radiogenic isotope geochemistry, mineralogy, and melt- and mineral-inclusion data. Assimilation of crustal rocks during ascent promotes separation from a silicate magma of Fe-rich, Si-Al-poor melts with low solidus temperatures and viscosities, allowing coalescence, migration, and emplacement at deep to subaerial crustal environments. When the iron-rich melt attains neutral buoyancy, fractional crystallization leads to melt immiscibility similar to that observed in industrial blast furnaces, which promotes separation of massive magnetite ore overlain by different types of “slag” containing actinolite or diopside ± phosphates ± magnetite ± feldspar ± anhydrite ± scapolite, commonly enriched in high field strength elements. The mineralogy and morphology of this iron-depleted cap strongly depend on the depth of emplacement and composition of the iron-rich magma. Most of these systems exhibit high oxygen fugacity, which inhibits the precipitation of significant sulfide mineralization. The initially high fO₂ of these systems also promotes the formation of low-Ti (< 1 wt%) magnetite: Ti acts as an incompatible component and is enriched in the iron-poor caps and in the hydrothermal aureole. High fluid-phase pressures produced during massive crystallization of magnetite from the melt further facilitate the exsolution of magmatic-hydrothermal fluids responsible for the formation of aureoles of alkali-calcic-iron alteration with hydrothermal replacement-style iron mineralization. On the whole, these systems are dramatically different from the magmatic-hydrothermal systems related to intermediate to felsic igneous rocks; they are more akin to carbonatite and other ultramafic rocks.

_{磁铁矿（磷灰石）矿床被解释为由富铁超基性熔体结晶形成，主要由硅酸盐熔体与氧化 PF-SO 4}相互作用产生-含沉积岩。这一假设得到了地质证据、实验研究、数值模拟、稳定和放射性同位素地球化学、矿物学以及熔体和矿物包裹体数据的支持。上升过程中地壳岩石的同化促进了与低固相线温度和粘度的富铁、贫硅铝熔体的硅酸盐岩浆的分离，从而允许在深部到地下地壳环境中的聚结、迁移和就位。当富铁熔体达到中性浮力时，分步结晶导致熔体不混溶，类似于在工业高炉中观察到的情况，这促进了块状磁铁矿石的分离，其上覆盖着含有阳起石或透辉石的不同类型“炉渣”±磷酸盐±磁铁矿±长石± 硬石膏 ± 方柱石，通常富含高场强元素。这种贫铁盖的矿物学和形态很大程度上取决于富铁岩浆的侵位深度和成分。这些系统中的大多数表现出高氧逸度，这抑制了显着硫化物矿化的沉淀。最初的高这些系统的f O ₂还促进低Ti（< 1 wt%）磁铁矿的形成：Ti作为不相容组分并且在贫铁帽和热液光环中富集。磁铁矿从熔体中大量结晶过程中产生的高流体相压力进一步促进了岩浆热液的溶出，从而导致了热液置换型铁矿化的碱钙铁蚀变光环的形成。总体而言，这些系统与中长英质火成岩相关的岩浆热液系统有很大不同。它们更类似于碳酸岩和其他超镁铁质岩石。