Developing a Genetic Model for Puerto Rico’s Tibes Iron Deposit through Field Observations and Geochemical Analyses

Abstract

Understanding the formation of iron deposits is key for locating new resources and upholding our pledge to transition to renewable energy as iron is required to make steel, a critical component of all green energy technologies. Puerto Rico’s dynamic geologic history produced a wealth of ore deposits, including the Tibes iron skarn near Ponce. Linear massive magnetite bodies have sharp contacts with the host rock and orientations similar to local faulting, indicating lithologic and/or structural control(s) on ore deposition. The whole rock mineralogy and trace element (Ca, Al, Mn, Ti, V) concentrations of Tibes magnetite are consistent with the limited existing data from iron skarns. Variations in the concentrations of these elements correlate with the proximity of each ore body to the Tibes diorite. Isotope analyses of Tibes magnetite reveal 56Fe values between 0.13-0.39‰ and 18O values between 2.83-5.02‰, indicating a magmatic source of the ore fluid with minimal meteoric input or post-depositional alteration. Compositional zonation and silicate micro-inclusions in the magnetite record multiple ore-forming events and fluctuating ore-fluid conditions. The proposed genetic model is a major step in understanding the Tibes deposit as a resource and these data provide a new framework for studying similar deposits worldwide.