Semester of Graduation

Spring 2024

Degree

Master of Science (MS)

Department

Geology & Geophysics

Document Type

Thesis

Abstract

The mineral tourmaline can be found in many geothermal systems around the world. Because tourmaline has the ability to partition elements from its host environment into its structure and record its host rock environment, tourmalines in geothermal systems contain a distinctive chemical signature. Studies have been done on tourmalines in energy-producing geothermal systems, however, a comprehensive overview of tourmaline’s occurrence in this specific environment is lacking. Additionally, tourmaline has been used as a single mineral thermometer that records temperatures in its host environment.

This research leverages tourmaline chemistry to achieve two objectives: (1) to characterize the chemistry of tourmalines in geothermal systems, and (2) to determine if a previously developed single-crystal tourmaline geothermometer (e.g., van Hinsberg & Schumacher, 2007) is suitable for determination of temperatures attained in geothermal systems.

To characterize geothermal tourmaline chemistry, tourmalines from two active geothermal systems, the Darajat Geothermal Field in Indonesia and the Geysers in California, USA, and one fossil hydrothermal system, Siglo, Bolivia, were obtained using the electron probe microanalyzer (EPMA). EPMA chemical data and images were supplemented with literature data from six active systems and four fossil systems. Data compilation of tourmalines from geothermal systems and plotting on Al-Mg-Fe discrimination diagrams demonstrated that tourmalines in these systems do not have a unique chemical signature but appear to reflect their host rock chemistry.

To evaluate the applicability of tourmaline as a geothermometer, a single sector-zoned tourmaline crystal was analyzed from a fossil geothermal system in Bolivia. Extrapolation of the element-partitioning tourmaline geothermometer (e.g., van Hinsberg & Schumacher, 2007) to lower temperatures was utilized. Using the Ti data from Bolivia tourmaline yielded a range of 290⁰C to 330⁰C for the Bolivian fossil geothermal system. The core-to-rim temperatures record a decreasing temperature interval, followed by increasing temperatures, then cooling to about 270oC at the rim of the crystal. These data suggest that single sector-zoned tourmaline temperatures are a viable option for estimating formation temperatures in geothermal systems

Date

4-1-2023

Committee Chair

Barbara Dutrow

Download

Available for download on Monday, January 20, 2031

Share

COinS