Giovannetti Nazario, David A.

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Insights into Fe-Skarn mineralization processes through garnet geochemistry and geochronology in Tibes, Puerto Rico
(2022-12-12) Giovannetti Nazario, David A.; Hudgins, Thomas R.; College of Arts and Sciences - Sciences; Hughes, K. Stephen; Bilenker, Laura D.; Department of Geology; Arroyo Caraballo, José R.
The Tibes Skarn is a calcic-iron skarn in southern Puerto Rico containing abundant magnetite and garnet mineralization, the latter of which are significant geochemical tracers of magmatic-hydrothermal activity. These garnets are a grossular-andradite solid solution ranging from 70.85% grossular to 98.79% andradite. Constraints on the fluid chemistry of Tibes are reported, with rare earth element (REEs) concentrations showing light-REE depletion and heavy-REE enrichment, with varying Eu anomalies. These patterns, along with La(n)/Lu(n) < 1, are indicative of nearly neutral to slightly basic pH conditions in a magmatic-hydrothermal system. Concentrations of Zr supports this observation and are also suggestive of relatively high saline fluid conditions. Tibes garnet ages range from 60.28±0.56 Ma and 55.11±0.70 Ma, where the older age represents the timing of ore mineralization. Hence, the Tibes Skarn formed coevally with the Tibes diorite stock and culminated at a time coinciding with the Eocene collision between the NE Caribbean Plate and the Bahamas Platform.