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

该项目将确定富含二氧化硅的岩浆在火山喷发期间或在产生矿藏的热液中如何释放大量硫。这些岩浆的载硫量应该很低。我们将检验这样的假设，即它们将硫储存在硬石膏(硫酸钙)斑晶和蒸汽泡中，或者只是在来自更深的、缺乏二氧化硅的岩浆的水泡中传输硫。将研究几个古老的火山为主到深成为主的系统的岩浆和矿藏，包括：科罗拉多州的圣路易斯火山口；秘鲁的亚纳科查火山和相关的金矿；以及内华达州的耶灵顿岩基和它的斑岩铜矿。用二次离子质谱仪和激光烧蚀-电感耦合等离子体质谱等方法测定磷灰石(钙磷)、玻璃包裹体(“冻结”熔体)等矿物的水、硫、氯和微量金属含量。硫和氢的同位素比率也将被测量。这些数据将有助于估计硅酸盐熔体的挥发性和微量金属含量，并显示这些化学成分是如何获得和丢失的。该项目将吸引最多四名研究生进行论文研究，最多四名本科生进行实地和实验室研究。这项研究的社会意义包括了解大型硅质岩浆如何贡献平流层硫对全球气候的影响，以及了解一些铜和其他矿产资源是如何产生的。

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.