The roots and tops of magnetite-apatite mineralization: evolving magmatic-hydrothermal systems

Magnetite-apatite deposits form a well-defined type of mineralization characterized by the presence of a core of massive magnetite apatite with an extensive aureole of alkali-calcic alteration hosting a low grade mineralization. Geology and geochemistry suggest that these deposits are the product of the crystallization of oxidized water-bearing iron-rich melts that separated from a parental silicate magma. The temporal and vertical evolution of these systems is controlled by the timing and depth of separation of large amounts of aqueous fluids, a process that leads to the formation of complex magmatic-hydrothermal systems. These magnetite-apatite systems grade upwards into bodies of massive apatite or an extrusive magnetite-apatite mineralization. A key feature of this style of mineralization is the formation of large breccia pipes and diatremes that are related to melt degassing at shallow depths.