Ulrich Petersen, 89

At a meeting of the Faculty of Arts and Sciences on Nov. 7, 2023, the following tribute to the life and service of the late Ulrich Petersen was spread upon the permanent records of the Faculty.

Ulrich Petersen was born in Negritos, Peru, to parents Georg Petersen, a petrogeologist, and Harriet Bluhme.  A lifelong love of science and the outdoors led him to become a geologist.

Petersen studied mining engineering at the Escuela de Ingenieros Civiles y de Minas (1954).  He spent three years (1949 to 1951) working for the Geological Institute of Peru (National Institute of Mining Research and Development) in the Office of the Collaborative Mission with the United States Geological Survey.  He was then chief geologist in charge of exploration and mines for the Cerro de Pasco Corporation between 1951 and 1963.  During this time, he was also a student at Harvard University in the Department of Geological Sciences and conducted combined geological and geochemical research projects at all the Cerro de Pasco mines.  Based on this work, he received Master of Arts (1955) and Ph.D. (1963) degrees from Harvard University.

In 1963 Harvard hired Petersen as a lecturer on geology, appointed him as Associate Professor of Mining Geology in 1966, and promoted him to Professor of Mining Geology in 1969.  He was named the Harry C. Dudley Professor of Economic Geology in 1981 and was a professor at Harvard for 30 years until his retirement in 1996.  He was also a visiting professor at Heidelberg University, Germany, and at the University of California, Berkeley.  Petersen worked as a private consultant to many mining companies and nongovernmental organizations in the Americas, Europe, Africa, and Australia, including the Buenaventura mining company in Peru.

Petersen, his doctoral students, and his colleagues co-authored numerous scientific publications on diverse types of ore deposits.  He firmly believed that understanding the origins of ore deposits is essential for developing the Earth’s metal resources.  Furthermore, such an understanding could not just be theoretical: it had to be rooted in studies of real rocks and ore deposits.  Using his imaginative scientific approach and his special interest in precious (gold and silver) and base (copper, lead, and zinc) metal mineralization, he developed methods with practical applications to predict the most likely places for economically viable ore deposits.

Petersen also coauthored two books: “Hydrothermal Uranium Deposits” with Robert A. Rich and Heinrich D. Holland in 1977 and “Living Dangerously: The Earth, its Resources, and the Environment” with Holland in 1995.  The first is the only book devoted entirely to hydrothermal uranium deposits.  The second deals with natural resources and the fate of humanity over the 21st century.  This work is based on a course that was co-taught by Holland and Petersen over many years.

Most of Petersen’s research was on ore deposits called hydrothermal ore deposits.  These are the most difficult deposits to understand because they form from hot waters circulating in Earth’s crust that leach various metals from common rock and result in metal-rich fluids that become supersaturated and then precipitate ore minerals.  The ultimate source rocks of the metals are often highly uncertain and need both detailed field and laboratory investigations to be understood.  He found that one sulfosalt mineral, tetrahedrite, a copper zinc antimony sulfide with substantial substitution of other elements (silver, iron, arsenic, and bismuth), often provides useful insight.  Ascending hydrothermal fluid precipitates tetrahedrites of progressively changing compositions in response to temperature, pressure, and hydrothermal chemical evolution.  He found that the pattern distribution and composition of this mineral can aid significantly in ore deposit exploration and development.  In these deposits, he also studied a group of hydrothermal deposits called high-sulfidation deposits, which are characterized by the relatively oxidized state of sulfur in the hydrothermal system and are rich in gold, copper, silver, bismuth, lead, and zinc.  He was able to characterize the ore fluid by combining sulfur, oxygen, and hydrogen isotope measurements.  These deposits represented valuable exploration targets that had been overlooked in the past.  Lead isotopes were used to constrain hydrothermal mineral deposits because the potentially different sources of lead have very different isotopic compositions.  In the case of some Peruvian ore deposits, it was shown that the lead was supplied by local magmatic rocks and not by the supracrustal host rocks enriched in ore metals or by meteorically derived waters.

Uranium is necessary for nuclear energy.  Petersen’s concern about the sufficiency of uranium ores that can be mined cost-effectively led him to consider hydrothermal uranium deposits because the majority of uranium ore deposits are typified by significant hydrothermal fluid activity occurring at temperatures ranging from 150 to 400°C.  Fluids leach uranium from moderately uranium-enriched source rocks, such as granites and granitic gneisses.  His and other works on this subject have led to the understanding that there is sufficient uranium to meet our energy needs for millions of years into the future.  His book with Holland makes a clear case that the only problem is how the human population decides to manage its wealth of essentially inexhaustible resources.

Petersen was a fellow of the Mineralogical Society of America and an active member of the Society of Economic Geologists.  He served as president of the Society of Economic Geologists in 1988.  He was the International Exchange Lecturer of the Society of Economic Geologists in 1996.  He was the Thayer Lindsley Visiting Lecturer of the Society of Economic Geologists in 1973–74.  He received Germany’s Humboldt Research Award.  The Order of the Sun of Peru in the rank of Commander was awarded to Petersen in 1968 by the Peruvian Government for his important and innovative work on the geology and ore deposits of Peru.

Petersen was predeceased by his first wife, Edith Martensen, and son Armin Petersen.  He is survived by his wife of 35 years, Eileen; brother, C. Richard Petersen, and his children, Marco and Daphne; son, Erich U. Petersen, and his children, Alexander and Mark Petersen; daughter, Heidi Petersen Loh, and her children, Thomas, Francis, and Sebastian Loh; and Eileen’s children.  Beyond research, he was loved by his family and admired by students and colleagues alike.

Respectfully submitted,

Charles W. Burnham †
Roger R. Fu
Andrew H. Knoll
Erich U. Petersen (University of Utah)
Stein B. Jacobsen, Chair