Copper and Gold in Sulfur-rich Magmatic-hydrothermal Systems

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Magmatic-hydrothermal ore deposits are important sources of copper and gold, however, there are many outstanding questions on how these deposits form. The results of this research can provide direct economic benefits by improving existing metal exploration models associated with magmatic-hydrothermal ore deposits. Funds from this project will be used to support and train both graduate and undergraduate students in economic geology, experimental geology, thermodynamics, and data interpretation. The graduate students will also mentor the junior members involved in this project. Each student will be expected to present their portion of the project at a national scientific meeting. Furthermore, recognizing the importance of science education and the dissemination of knowledge, the PI has and will continue to participate in numerous mentoring activities and outreach programs focused on the importance of geology and mineral resources in society.The proposed study will conduct experiments to determine the concentrations of copper and gold in various fluids and minerals as a function of temperature and pressure to address these questions. The data obtained will increase our understanding on the transportation of metals in hydrothermal fluids and the process of precipitation responsible for the formation of select ore deposits. Experiments will be conducted from 500-700 degrees Celsius and pressures from 50-100 MPa. This temperature and pressure range that bridges the magmatic to hydrothermal transition where many deposits are thought to form but where few consistent data are currently available. This pressure-temperature region has added importance because it represents portions of natural systems where a supercritical fluid may cool and undergo phase separation into a vapor + brine pair. The sulfur and oxygen fugacity will be buffered by sulfide and oxide minerals commonly found in ore deposits. The importance of sulfur in hydrothermal fluids on ore metal concentrations and speciation will be evaluated. This study will also examine the extent to which gold is incorporated into sulfide minerals during their formation and how it is impacted by changes in sulfur, temperature, and pressure. An internally consistent thermodynamic model will be generated by using the data obtained in this study.