Minerals (Aug 2024)
LA-ICP-MS Analyses of Sulfides from Gold-Bearing Zones at the Perron Deposit, Abitibi Belt, Canada: Implications for Gold Remobilization through Metamorphism from Volcanogenic Mineralizations to Orogenic Quartz–Carbonate Veins
Abstract
The Perron deposit, located in the northern part of the Archean Abitibi belt, bears some of the highest gold-grade mineralization for orogenic-vein-type deposits worldwide (High-Grade Zone: HGZ). More than 13 gold-bearing zones with different sulfide assemblages, hydrothermal alterations, and gold grades have been recently outlined, and they range from volcanogenic to orogenic in origin. In addition, seven zones are hosted in a restricted volume of ~1 km3, which is called the Eastern Gold Zone. Pyrite, sphalerite, pyrrhotite, and chalcopyrite—each from a different gold-bearing zone—were analyzed with LA-ICP-MS to decipher their genetic links, mineralizing processes, and temperature of formation. The temperatures calculated with the sphalerite GGIMFis thermometer range from 348 to 398 °C. All gold-bearing zones recorded volcanogenic hydrothermal inputs at different intensities, manifested by pyrrhotite. Pyrite was late-metamorphic and related to the orogenic gold system induced by the contact metamorphism of amphibolite facies. The pyrrhotite grains had very homogeneous trace element signatures in all zones, which is a characteristic of metamorphic recrystallization, exhibiting a loss of mobile elements (Au, Te, Bi, Tl, Sn, W, In) but high concentrations of Ni, Co, and As. Conversely, the pyrite was systematically enriched with all elements depleted from pyrrhotite, bearing five specific signatures of element enrichments: W, Tl, Sn, In-Cd-Zn, and Bi-Te-Au. For gold-rich zones (e.g., the HGZ), gold was linked to the Bi-Te-Au signature of pyrite, with Bi enrichment occurring at up to 72,000 times the background level in Archean shale pyrite. It was concluded that gold was transported, at least in part, as Bi-Te melts in the previously documented non-aqueous orogenic fluids, hence accounting for the very-high-grade gold content of the HGZ. Genetically, the metamorphism of primary gold-bearing volcanogenic mineralizations was the main source of gold during the overprinting of amphibolite (600 °C) in a metamorphically induced orogenic mineralizing event. A strong volcanogenic pre-enrichment is considered the main factor accounting for the gold endowment of the Eastern Gold Zone.
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