| Abstract | dc.description.abstract | Although studies have proposed that iron oxide-apatite (IOA) deposits may represent the deeper
roots of some Andean iron oxide copper-gold (IOCG) systems, their genetic links remain obscure
and controversial. A key question when considering an integrated genetic model is whether a
magmatic-hydrothermal fluid that precipitates massive magnetite will continue transporting
significant amounts of dissolved Fe, Cu, and Au after IOA precipitation. Here we provide new
geochemical data for accessory pyrite from the Los Colorados IOA deposit in the Chilean iron belt
that confirm the role of this sulfide as a relevant repository for economic metals in IOA deposits.
Pyrite occurs at Los Colorados as disseminated grains and as veinlets associated with magnetite
and actinolite that postdate the main igneous magnetite stage. Electron probe microanalysis
(EPMA) data for pyrite show anomalously high Co and Ni concentrations (up similar to 3.9 and
similar to 1.5 wt %, respectively) and relatively high As contents (100s of ppm to a maximum of
similar to 2,000 ppm). When combined with results from secondary ion mass spectrometry (SIMS)
spot analyses, pyrite data show significant amounts of Cu that range from sub-ppm values (similar
to 100 ppb) up to 1,000s of ppm, plus nonnegligiblc concentrations of Zn, Ph, Cd, Sb, Se, and Te
(up to 100 ppm). The highest contents of Cu measured (wt % level) most likely record the presence
of Cu-bearing submicron-sized mineral inclusions. Contents of Au and Ag are up to 1 and 10 ppm,
respectively, with maximum concentrations that can rise up to 800 ppm Au and 300 ppm Ag due to
the presence of submicron-sized inclusions. The high Co/Ni ratios of pyrite from Los Colorados are
consistent with a magmatic-hydrothermal origin associated with a greater mafic affinity, compared
to pyrite from porphyry Cu deposits. Furthermore, the geochemical signature of Los Colorados
pyrite shares important similarities of composition and microtexture with the few published data for
pyrite from IOCG deposits (e.g., Ernest Henry, Australia, and Manto Verde, Chile). These findings, combined with recent geochemical and isotopic studies that support an igneous origin for the dikeshaped
magnetite orebodies at Los Colorados, point to a magmatic source of mafic to intermediate
composition for the contained metals, and support the hypothesis that IOA systems can source Fe-
Cu-Au-rich fluids. Based on experimental studies, these IOA-derived fluids may continue
transporting significant amounts of metals to from IOCG mineralization at shallower levels in the
crust. | es_ES |
