MAGNETITE, APATITE, TITANITE, AND ACTINOLITE GEOCHRONOLOGY OF THE CANDELARIA IRON OXIDE - COPPER - GOLD (IOCG) DEPOSIT, CHILE

Iron oxide - copper - gold (IOCG) deposits are major sources of Fe (in magnetite), Cu and Au (in sulfides). They are also usually enriched in Ag, Mo, Co, As, U and Rare Earth Elements (REE), which are critical metals for developing renewable energy technologies. Constraining the timing of Fe and Cu mineralization in IOCG deposits is vital to understand the duration and processes that generate them and their relationship with other deposit types.

In Chile, the Candelaria IOCG deposit transitions with depth from a chalcopyrite-magnetite to a magnetite-actinolite mineralization. We characterized samples from a drill hole that traverses the system via scanning electron microscopy and identified magnetite, apatite and titanite grains for U-Pb isotope measurements via in situ laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). This technique allows to perform spot analyses for detailed geochronological studies.

Published Re-Os dates for molybdenite (114.2 ± 0.6 Ma and 115.2 ± 0.6 Ma) indicate the timing of Cu mineralization. Our results yield dates (± 2se) of 114.9 ± 1.1 Ma for titanite, 115.4 ± 0.7 Ma for apatite, and 126.3 ± 4.9 Ma for magnetite. We also obtained an Ar-Ar date of 121.2 ± 0.6 Ma for actinolite. Our data indicate that there were at least two events at Candelaria, an early magnetite-actinolite event and a later apatite-titanite event that is coeval with Cu mineralization.

The results of this project will contribute to understanding the timescales of Fe and Cu mineralization in IOCG deposits and will help identify the tectonic setting(s) propitious for their occurrence in the Andes and elsewhere, allowing for the refinement of geophysical and geochemical exploration techniques to find new prospects that will optimize the exploration process and maintain the supply of resources for future generations. Additionally, the development of magnetite as a geochronometer opens the door not only to directly date mineralization in other other deposit types, but also to date rock types that are commonly challenging to date using traditional techniques.