Collaborative Research: Content and Behavior of Sulfur in Silicic Magma and Links to Generation of Sulfur-rich Ore-forming Fluids of Porphyry Cu-Mo-Au Deposits

Portland State University, Portland OR

Investigators

Abstract

This project will determine how silica-rich magmas release massive amounts of sulfur during volcanic eruptions or in hydrothermal fluids that produce ore deposits. These magmas should have low sulfur-carrying capacity. We will test the hypotheses that they store sulfur in anhydrite (calcium-sulfate) phenocrysts and vapor bubbles or merely transmit sulfur in aqueous bubbles derived from deeper, silica-poor magmas. Magmas and ore deposits from several ancient volcanic-dominated to plutonic-dominated systems will be studied including: San Luis Caldera, Colorado; Yanacocha Volcanics, Peru, and related gold deposits; and the Yerington batholith, Nevada, and its porphyry copper deposits. The water, sulfur, chlorine and trace-metal contents of minerals such as apatite (calcium-phosphate) and glass inclusions ("frozen" melt) will be determined by secondary ion mass spectrometry and laser ablation-inductively coupled plasma mass spectrometry and other methods. Isotopic ratios of sulfur and hydrogen will also be measured. These data will allow estimation of the volatile and trace metal contents of silicate melts, and show how these chemical components were acquired and lost. The project will engage up to four graduate students in thesis studies and up to four undergraduate students in field and laboratory research. The societal relevance of the research includes understanding how large silicic magmas contribute stratospheric sulfur with global climatic impact and understanding how some copper and other mineral resources are produced.