Coupled Lu-Hf and U-Pb apatite geochronology of Jatobá orebody supports ∼ 2.5 Ga metamorphism in deep shear zones from southern Copper Belt, Carajás Domain, Brazil

Abstract

A multi-isotopic geochronological study of apatite (U-Pb, Lu-Hf) in host basalts and mineralization from the Jatobá orebody, Southern Copper Belt, Carajás Domain, Brazil, constrains the age and setting of mineralization. Combined mineral textural relationships from cathodoluminiscence imaging, and compositional and isotopic data from EPMA and LA-ICP-MS, hint at initiation of an iron-oxide-copper–gold system at ca. 2.5 Ga during a deformation event linked to amphibolite facies metamorphism in deep (up to 20 km) shear zones. The ∼ 2.5 Ga Lu-Hf age is obtained from deformed, REE-rich cores of basalt-hosted apatite and is contemporaneous with metamorphism of a volcanic sequence deposited in a rift active during ca. 2.76–2.73 Ga. Some apatite grains retain a mafic, Cl-rich signature, testifying to a primary igneous origin. The Lu-Hf ages stretching from 2527 to 2384 Ma are obtained from apatite displaying textural diversity and geochemical heterogeneity, consistent with a prolonged event featuring dissolution-reprecipitation in response to fluid release during the retrograde cycle. The U-Pb system displays a younger ∼ 2 Ga U-Pb apatite age indicating later re-equilibration. This age corresponds to post-uplift mylonitization of the host sequences. The newly documented ∼ 2.5 Ga age for mineralization in a deposit from the southern Copper Belt is coeval with Cinzento Shear zone reactivation in the northern copper belt, and the ages of deposits like Salobo. Fluid flow along shears leached metals from the Mesoarchean basement, later deposited as sulphides intimately associated with the reworked apatite. We propose deep-rooted connections between mineralizing systems across the region.