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Sophie Hopp ‘20 Examines Sodic-Calcic Alteration at the White Rock Pluton: Constraining Fluid Sources with Oxygen Isotopes

Sophia Hopp’s ’20 senior thesis research explored Sodic-Calcic alteration of the White Rock Pluton. Her thesis advisor was Jim Rougvie.

Metasomatism is a process that involves a change in the chemical composition. Sodic-Calcic alteration, or metasomatism, is a type of hydrothermal alteration in which sodium and calcium are added to a rock at the expense of other elements. This type of alteration is widespread in contact metamorphic aureoles and is commonly associated with iron oxide-copper-gold (IOCG) deposits. The altering fluids can mobilize and deposit these valuable elements. The composition of geothermal fluids vary with their setting, which can directly impact the capacity for metal transport and deposition. Understanding the fluid involved in sodic-calcic alteration is crucial to understanding element mobility and deposition in metasomatism processes.

Whiterock Pluton, located at the southwestern side of the Elk Mountain Range in Aspen, Colorado, has locally been affected by sodic-calcic metasomatism. There are many ideas about the source of the altering fluid, but it is yet unknown. The source was likely magmatic or meteoric due to the study area’s distance from the ocean during alteration. Sophia will be analyzing individual minerals from samples of the altered zones to decipher the source of the altering fluid. The minerals will be analyzed with a mass spectrometer to find the δ18O values, which can determine the fluid source and approximate the temperature at which the alteration took place.

June 02, 2020

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