The Jaguar hydrothermal nickel sulfide deposit: Evidence for a nickel-rich member of IOCG-type deposits in the Carajás Mineral Province, Brazil

Abstract

The Jaguar Ni sulfide deposit (mineral reserves of 58.6 Mt at 0.95 wt% Ni) occurs along a regional fault zone in the Carajás Mineral Province in the Amazonian Craton, Brazil. This study presents the first detailed description of the Jaguar deposit and provides a basic framework to constrain the origin of the Ni sulfide mineralization. Jaguar nickel sulfide orebodies are associated with ductile-brittle hydrothermal alteration zones developed over felsic subvolcanic or granitic country rocks. Prominent features of the Jaguar deposit include: i. its location along regional scale deep fault systems, ii. extensive zones of biotite-chlorite alteration overprinted by magnetite-apatite-quartz alteration zones, iii. sulfide mineralization occurring as steeply dipping orebodies closely associated with magnetite-apatite rich bodies, iv. sulfides that are disseminated or form the matrix of breccias consisting of pyrite and millerite, with minor pentlandite, chalcopyrite and pyrrhotite, v. pyrite, magnetite and apatite occur mostly as euhedral to subhedral crystals enclosed in irregular aggregates of fine-grained anhedral millerite, vi. sulfide mineralization with high Ni (Ni/S ~ 0.15–0.30) and Co (Co/S ~ 0.005–0.015) contents, high Ni/Cu ratios (~5–25) and low Zn and PGE contents, vii. metal association consisting of LREE, Fe, U, P, Pb, Bi, Te, Ni, and Co, and viii. mineralized zones with high F contents and a positive correlation of F with S, Ni and P2O5. The geological setting and characteristics of the Jaguar deposit are similar to the iron-oxide-copper-gold (IOCG) deposits in the Carajás Mineral Province, indicating that they all belong to a regional hydrothermal system. The existence of nickel-rich members of IOCG type mineralizations in the Carajás Mineral Province was previously suggested for other deposits (e.g., GT34, Castanha) and interpreted as deeper portions of the IOCG mineral system. The close association of nickel sulfide mineralization in the Jaguar deposit with magnetite-apatite-rich breccias may be interpreted as an iron-oxide-apatite (IOA) member within the regional hydrothermal system. In contrast to most hydrothermal nickel deposits in the world, the Jaguar deposit is neither hosted by mafic-ultramafic rocks nor associated with black shales. Therefore, the Jaguar deposit is interpreted as an uncommon hydrothermal Ni deposit associated with the IOCG mineral system in the Carajás Mineral Province. Our results provide new insights for worldwide exploration for Ni sulfide deposits in geological environments different from those traditionally considered prospective.