Abstract
The Eagle–Telbel gold deposit, located within the Archean Abitibi greenstone belt of Canada, represents an unusual gold system characterized by stratiform, pyrite-rich mineralization hosted in carbonate-altered volcano-sedimentary horizons. Despite decades of study, its genetic origin has remained controversial, with proposed models ranging from syngenetic and diagenetic to epigenetic and orogenic. To constrain the metallogenic evolution of the deposit, trace-element analyses of pyrite were conducted using LA-ICP-MS on 240 grains from 24 samples ranging from high-grade (40.8 ppm Au) to barren, and from various host rocks. Samples display various pyrite morphologies: (1) porous–amorphous, (2) porous–subeuhedral, (3) subeuhedral, (4) euhedral, and (5) pyritohedral. The latter is dominant in high-grade gold-bearing samples but lacking in low-grade and barren samples. Trace-element signatures reveal remarkable compositional similarity among all pyrite types, including barren nodular pyrites from overlying black shales, indicating formation within a common hydrothermal system. Gold enrichment is systematically associated with elevated As, Te, and W concentrations and is most pronounced in pyritohedral pyrite, with enrichment of 10,000X, although all pyrite types carry gold. Element mapping and time-resolved LA-ICP-MS signals demonstrate that Au occurs predominantly in solid solution or as micro-inclusions within pyrite and was introduced during successive stages of pyrite growth rather than by late remobilization. Comparison with established pyrite signatures from orogenic, intrusion-associated, and volcanogenic massive sulfide deposits shows that Eagle–Telbel pyrites are distinct and instead closely resemble Archean sedimentary pyrite. These results support a model involving a low-temperature and low-depth submarine hydrothermal system that generated pyrite and pervasive carbonate alterations at or near the seafloor, while episodic inputs of magmatic fluids supplied Au, As, Te, and W. The Eagle–Telbel deposit is therefore interpreted as a syngenetic, sub-seafloor gold system combining sedimentary–hydrothermal pyrite formation with intrusion-related metal contributions, representing the first documented Archean example of this hybrid style of gold mineralization.