Abstract
Trace element concentrations in magnetite, hematite, pyrite and apatite, Fe and O stable isotope abundances of magnetite and hematite, and H isotopes of magnetite and actinolite from IOA and IOCG deposits in the Chilean Iron Belt are used to develop a new genetic model that explains IOA and IOCG deposits as a continuum produced by a combination of magmatic and magmatic-hydrothermal processes. Together, the data are consistent with a model where 1) magnetite and apatite crystallize as near-liquidus phases from silicate melt; 2) magnetite and apatite crystals serve as nucleation sites for gas bubbles and promote volatile saturation of the melt; 3) the volatile phase coalesces and encapsules magnetite and apatite, and scavenges metals, S and P from the melt; 4) the magnetite-apatite-fluid suspension ascends from the host magma during regional extension; 5) as the suspension ascends, magnetite and apatite grow from the fluid and record an evolving magmatic-hydrothermal composition; 6) during ascent, magnetite and apatite are deposited to form IOA deposits; 7) the further ascending fluid transports Fe, Cu, Au, S where hematite, magnetite and sulfides precipitate to form IOCG deposits. The model explains the globally observed temporal and spatial relationship between magmatism and IOA and IOCG deposits.
