Magnetite-Apatite and IOCG deposits formed by magmatic-hydrothermal evolution of complex calcalkaline melts

AUTHORS: Fernando Tornos

ABSTRACT: The geology and geochemistry of the coeval magnetite-apatite and IOCG deposits of the Central Andes are consistent with the ores being produced by evolving magmatic-hydrothermal systems associated with arc-related calc-alkaline magmatism. The magnetiteapatite deposits derive from the crystallization of waterand volatile-rich iron oxide melts that separated from intermediate composition silicate magmas. They show a vertical continuum from deep seated large plugs to pegmatite-like and extrusive bodies and lack evidence of fractional crystallization processes; it is unlikely that the magnetite-apatite systems represent the roots of the Cu-Au deposits. IOCG deposits formed during the magmatichydrothermal evolution of similar crystallizing silicate melts, and they also show vertical zoning. Late hydrothermal remobilization of IOCG ores by basinal brines produced the shallower hematite-Cu-Au mineralization. Both ore systems formed from contaminated magmas, being the variable incorporation of Fe-P-Si-rich crustal rocks the ultimate cause of the generation of immiscible iron oxide melts.The geology and geochemistry of the coeval magnetite-apatite and IOCG deposits of the Central Andes are consistent with the ores being produced by evolving magmatic-hydrothermal systems associated with arc-related calc-alkaline magmatism. The magnetiteapatite deposits derive from the crystallization of waterand volatile-rich iron oxide melts that separated from intermediate composition silicate magmas. They show a vertical continuum from deep seated large plugs to pegmatite-like and extrusive bodies and lack evidence of fractional crystallization processes; it is unlikely that the magnetite- patite systems represent the roots of the Cu-Au deposits. IOCG deposits formed during the magmatichydrothermal evolution of similar crystallizing silicate melts, and they also show vertical zoning. Late hydrothermal remobilization of IOCG ores by basinal brines produced the shallower hematite-Cu-Au mineralization. Both ore systems formed from contaminated magmas, being the variable incorporation of Fe-P-Si-rich crustal rocks the ultimate cause of the generation of immiscible iron oxide melts.

KEYWORDS: IOCG, magnetite-apatite, isotope geochemistry, melt inclusions, fluid inclusions

EAN: SGA_2011_A009
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